Abstract:
Extruded material for forming blind slats has at least one textured surface with raised areas and adjacent lower areas. After extrusion and texturing processes, the slat material is passed through a spray painting process applying a substantially thicker coating of paint to the raised areas than to the adjacent lower areas.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 09/040,647, filed Mar. 17, 1998, now issued as U.S. Pat. No. 6,006,816. 
     This application is also related to a co-pending U.S. patent application Ser. No. 08/970,851, filed Nov. 14, 1997, now issued as U.S. Pat. No. 6,015,002, the disclosure of which is herein incorporated by reference. This co-pending application describes a multi-layer slat for venetian blinds which is translucent, allowing light to shine into a room during the day, together with a coextrusion process for making such a slat. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to textured and painted slats for both vertical and horizontal window or door blinds, and, more particularly, to a method for preferentially coating textured surfaces of such slats with paint, so that the peaks or ridges are coated more heavily than surrounding surfaces. 
     2. Background Information 
     A highly desirable feature of horizontal and vertical blind slats is a well-defined, highly-visible surface texture, which differentiates the slats from the plain, sterile appearance generally associated with plastic blind slats. A conventional method for obtaining such a surface texture is through the use of a fabric material. A narrow strip of fabric may itself be used as a vertical blind slat, with a metal weight sewn into the strip at its bottom end being used to provide a measure of stability for the slat, which would otherwise be much too light in weight to hang straight or to resist excessive movement in air currents. Altemately, a fabric strip may be applied to one or both sides of a thermoplastic slat material, such as an extruded PVC strip, which provides weight and rigidity. The fabric may present an ordinary textile appearance, or its appearance may be enhanced by weaving in fibers of larger diameter and differing colors. One problem associated with the use of fabric in these ways is a high maintenance requirement caused by dust and dirt lodging in the fibers of the porous fabric material, resulting in blinds which are particularly difficult to clean. This problem can also result in a shortened practical life of the horizontal or vertical blinds, which eventually become impossible to clean effectively. 
     What is needed is a way to produce a visual effect of a well-defined, highly-visible surface texture on the surface of an extruded plastic strip, without a necessity for using a porous fabric overlay. 
     Translucence is an optical property which is highly desirable in window coverings to afford admission of sunlight into a room during the day without compromising privacy at night. Popular examples of translucent window coverings are found in shades using translucent fabric materials, which may be rolled up on a single roll at the top of a window, or which may be raised into a pleated or accordion fold as Roman shades. While such shades can be lowered to cover a window or raised to reveal a clear view, they are limited to presenting a rectangular translucent area; they cannot be partially opened to reveal slots through which the outside world may be viewed. On the other hand, horizontal or vertical blinds are variable louvered structures, which may be fully closed, fully open and drawn back, or partly open to present a number of slots through which the outside world may be viewed. 
     However, blinds are not available with translucent slats. Part of the reason for this is caused by the fact that blinds are typically exposed to very harsh ultraviolet energy, both from exterior sunlight and from interior fluorescent lighting. Slats for horizontal and vertical blinds are often composed of thermoplastic materials, such as PVC (polyvinyl chloride), which are available in clear or translucent forms. However, such materials are subject to severe discoloration when they are exposed to ultraviolet light, unless they include UV stabilizers. These UV stabilizers additionally turn a transparent material into a translucent material. However, when otherwise transparent PVC is loaded with sufficient UV stabilizers to achieve an adequate lifetime in use as a blind slat, and when such material is formed into a slat having a thickness sufficient to provide the rigidity needed in a blind application, the resulting slat is essentially opaque, lacking an ability to provide indoor lighting by transmitting outdoor light during daytime. 
     Therefore, what is needed is a slat for vertical or horizontal blinds having a combination of sufficient thickness for rigidity, sufficient UV stabilizers to prevent discoloration, optical translucence, and a well defined surface texture, which is clearly visible both under conditions of backlighting (as viewed from inside during the day) and front lighting (as viewed from inside during the night). 
     SUMMARY OF THE INVENTION 
     It is a first objective of the present invention to provide a method for enhancing textural features in the surface of an opaque blind slat, with such enhancement providing a difference in shade or color from surrounding areas. 
     It is a second objective of the present invention to provide a method for enhancing textural features in the surface of a translucent blind slat, with such enhancement providing a difference in opacity or color from surrounding areas. 
     It is a third objective of the present invention to provide a method for enhancing textural features in the surface of a translucent blind slat, with such enhancement providing a difference in opacity as the slat is back lighted and in shade as the slat is front lighted. 
     It is a fourth objective of the present invention to provide an inexpensive means for painting a texture pattern on an extruded plastic slat. 
     It is a fifth objective of the present invention to provide a means for painting a textured pattern which is dried without an application of heat following the extrusion process. 
     In accordance with one aspect of the invention there is provided a slat for a blind assembly, with the slat including an elongated section of slat material having an inner surface with a texture pattern having raised areas and adjacent lower areas, and a partial coating of paint on the inner surface, with the partial coating of paint having a substantially greater thickness on the raised areas than on the lower areas. 
     In accordance with another aspect of the invention, there is provided apparatus for producing a visibly enhanced textured surface on slat material extruded to form a slat for a blind assembly. This apparatus includes a texturing station and a painting station. The texturing station has a texturing roll turning in contact with a first surface to the slat material and a back-up roll turning in contact with a second surface of the slat material, with the second surface being opposite the first surface. A peripheral surface of the texturing roll has a surface pattern forming, on the first surface of the slat material, a texture pattern with raised areas and adjacent lower areas. The painting station, through which the slat material is moved after being moved through the texturing station, includes a nozzle spraying a mixture of air and paint droplets onto the first side of the slat material in a painting process configured to apply a substantially thicker coating of paint to the raised areas than to the adjacent lower areas. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary transverse cross-sectional view of a translucent slat made in accordance with an embodiment of the present invention to include a selectively painted textured surface; 
     FIG. 2 is a schematic view of the internal transmission and reflection of light within an inside layer of the slat of FIG. 1; 
     FIG. 3 is a fragmentary longitudinal cross-sectional view of a die set used in the extrusion of material for the slat of FIG. 1; 
     FIG. 4 is a fragmentary end elevational view of the die set of FIG. 3, 
     FIG. 5 is a partially sectional side elevation of texturing and painting stations used to form the surface pattern of FIG. 1 on a surface of the material being extruded from the die set of FIG. 3; 
     FIG. 6 is a transverse cross sectional view of the painting station of FIG. 5, taken as indicated by section lines VI—VI therein; 
     FIG. 7 is an enlarged sectional view of the textured upper surface of the slat of FIG. 1, with this surface including a number of upstanding peaks; 
     FIG. 8 is an alternate enlarged sectional view of the textured upper surface of the slat of FIG. 1, with this surface including a number of upstanding ridges; 
     FIG. 9 is a partially sectional side elevation of an alternate painting station used to paint the surface pattern of FIG. 1 on a surface of the material being extruded from the die set of FIG. 3; 
     FIG. 10 is a fragmentary transverse cross-sectional view of a translucent slat made in accordance with a second embodiment of the present invention to include a selectively painted textured surface on each side; 
     FIG. 11 is a partially sectional side elevation of texturing and painting stations used to form the surface patterns of FIG. 8 on both surfaces of the material being extruded from the die set of FIG. 3; 
     FIG. 12 is a transverse cross-sectional view of the painting station of FIG. 9, taken as indicated by sections lines XII—XII therein; 
     FIG. 13 is a front elevation of a vertical blind assembly including a number of slats of a type shown in FIGS. 1 or  8 ; 
     FIG. 14 is a fragmentary cross-sectional plan view of the vertical blind assembly of FIG. 11, taken as indicated by sectional lines XII—XII therein; and 
     FIG. 15 is a cross-sectional end elevation of a horizontal blind assembly including a number of slats of the type shown in FIGS. 1 or  8 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a fragmentary transverse cross-sectional view of a slat  10 , made in accordance with a first embodiment of the present invention, to include a selectively painted inner surface  11  on an innermost layer  12  of a number of coextruded layers. The width of slat  10  extends in the direction of arrow  13 , with Its length, extending perpendicularly from the direction of arrow  13 , being much greater than its width. This slat  10  includes the inside layer  12 , which is preferably inwardly exposed (into a room) when the blind including the slat  10  are closed, and an outside layer  14 , which is preferably correspondingly outwardly exposed when the blind is closed. A first base layer  16  and a second base layer  18  lie between the inside layer  12  and the outside layer  14 . The inner surface  11  is textured to include a number of ridges or peaks  18   a , on which paint droplets  18   b  are deposited. The portions  18   c  of the inner surface  11  between ridges or peaks  18   a  have relatively little paint. 
     The inside layer  12 , which is 0.08-0.18 mm (0.003-0.007 inch) thick, is preferably composed of a UV stabilized PVC material having pearlescent pigmentation, such as the material sold by the Geon Company as GEON 87654. The outer layer  14 , which is 0.13-0.18 mm (0.005-0.007 inch) thick, is preferably composed of a semi-transparent UV stabilized PVC, such as GEON No. 1260. The first base layer  16 , which is 0.25-0.51 mm (0.010-0.020) inch thick, is preferably composed of a clear PVC material, such as GEON No. 87727-002. The second base layer  18 , which is 0.13-0.18 mm (0.005-0.007) inch thick, is composed, for example, of a UV stabilized PVC material having pearlescent pigmentation, such as GEON No. 87654. The UV stabilizing components serve to prevent transmission of ultra-violet rays through one layer into another. 
     In one version of the present invention, the inside layer  12  includes a P. 20  to P. 40  foaming agent, mixed with the PVC material at a ratio of 3 to 6 percent. This concentration of foaming agent, being insufficient to produce a structural foam product, produces a number of small gas pockets, some of which, being near the surface of the slat  10 , cause the appearance of a matte finish on this surface, in place of the glossy finish generally characterizing the surface of a molded or extruded plastic part. The type of foaming agent and its concentration are determined according to the surface roughness desired in the finished product. In the example of FIG. 1, the small gas pockets produced by the foaming agent also contribute to a cloudy, translucent appearance desired when the slat  10  is illuminated with transmitted outdoor light. 
     While FIG. 1 shows a portion of the slat  10  adjacent to a longitudinal edge  18   d  thereof, it is understood that the opposite longitudinal edge of the slat has features similar to those shown in FIG.  1 . In particular, the inside layer  12  and the outside layer  14  extend around the base layers  16 ,  18 , overlapping at the rounded edge  18   d . This configuration allows a relatively high concentration of pigments and UV stabilizers and in the layers  12 ,  14  to protect the base layers  16 ,  18  from discoloration which might otherwise occur if sunlight were allowed to enter these layers  12 ,  14  directly along the edge  18   d . This feature of the present invention provides a significant advantage over the prior-art multilayer extruded slats of U.S. Pat. Nos. 4,877,077 and 5,119,871, both of which show an inner layer exposed along the edges of a slat. This feature is particularly significant as a part of the present invention, as it facilitates the use of one or more base transparent base layers which cannot otherwise be sufficiently protected from discoloration with UV exposure over time. 
     FIG. 2 is a schematic cross-sectional view of the internal transmission and reflection of a light ray  19  in the inside layer  12 , which includes a number of pearlescent pigment particles  19   a . The light ray  19  enters the inside layer  12  from the second base layer  18 , having traveled through the semi-transparent outside layer  14  and the transparent first base layer  16  (both shown in FIG.  1 ). Each time the ray  19  strikes a surface of a pigment particle  19   a , a first portion of the ray is reflected, while a remaining second portion is refracted and transmitted. The transmitted portion eventually emerges as exiting ray  19   b.    
     This figure is admittedly a schematic oversimplification of the structure of inside layer  12 . In a preferred version of the present invention, this layer is 0.08 to 0.2 mm (0.003 to 0.007 in.) thick, being composed of a transparent PVC material filled with pearlescent pigment particles which, being configured particularly to produce a silvery-white appearance when viewed by reflected light, are composed of mica particles having a length of 5-25 μm and a thickness of 100-500 nm, coated with a layer to titanium oxide having a thickness of 40-60 nm. Thus, while the actual thickness of the pigment particles  19   a , compared to the thickness of the layer  12 , is much smaller than that shown in the figure, there are many more layers of pigment particles  19   a  within the layer  12  than shown in the figure. 
     Since the pearlescent pigment particles both transmit and reflect light, they are particularly desirable in the application of a layer of material being configured for overall translucence. With the alternative use of absorptive pigmentation, light rays striking pigment particles are simply absorbed. However, the layer of material including pearlescent pigmentation must be quite thin to provide a suitable level of translucence. 
     Referring again to FIG. 1, in its intended use, the slat  10  forms part of a horizontal or vertical blind for a window or door, being backlighted primarily by sunlight from outdoors during the day and being front lighted by artificial light from inside a room during the night. The textured inner surface  11  is directed into the room whenever the blind is closed. The artificial lighting is on the textured surface  11  is generally sufficiently non-uniform to produce shading of the textured features. Thus, in the absence of applied paint, under most conditions with front lighting, as at night, the textured pattern of inner surface  11  is readily apparent due to the shadows produced on the shaded sides of individual raised texture features  18   a  and on portions of the depressed surfaces  18   c  adjacent the shaded sides of individual raised texture features  18   a . However, in the absence of applied paint, with backlighting from outdoor sunlight, the textured pattern tends to disappear, This is because the differences in the overall thickness of the slat material  10  due to the textured pattern are not sufficient to cause significant changes in light transmission. In this regard, it is noted that, in FIG. 1, the texture features are greatly exaggerated for clarity. On the other hand, the application of paint droplets preferentially on peaks and ridges of the texture pattern, in the manner of the present invention, significantly enhances the visibility of the texture pattern as illuminated by backlight, as light passing through the painted surfaces is attenuated. Differences in the tone or shade between the applied paint and the unpainted portions of the inner surface  11  can also cause such an application of paint droplets to enhance the visibility of the texture pattern as illuminated by interior front light. 
     FIG. 3 is a longitudinal cross-sectional view of an extrusion die set  20  used in the production of the slat of FIG.  1 . The first base layer  16  is formed first, with thermoplastic material  20   a  being forced from a cavity  22  in the direction of arrow  24  through a channel  26  in a first die  28 . The first die  28  also includes an input channel  30  through which thermoplastic material  32  is inserted to form second base layer  18 . The input channel  30  is connected by a narrowed channel  34  to a trough  36  extending along a portion of the periphery of channel  26  corresponding to the peripheral contact between the second base layer  18  and the first base layer  16 . The shape of second layer  18  is determined by the shape of a channel surface  37  extending through a second die  38  and partially through a third die  40 . Second die  38  also includes an input channel  42  through which thermoplastic material  44  is inserted to form outside layer  14 . The input channel  42  is connected by a narrowed channel  46  to a trough  48  extending along a portion of the periphery of channel  26  corresponding to the peripheral contact between the first base layer  16  and the outside layer  14 . The shape of outside layer  14  is further determined by the shape of a channel surface  50  extending through third die  40  and through a fourth die  52 . The third die  40  also includes an input channel  54  through which thermoplastic material  56  is inserted to form inside layer  12 . The input channel  54  is connected by a narrowed channel  58  to a trough  60  extending along a portion of the periphery of the second base layer  18  corresponding to the extent of peripheral contact between the second base layer  18  and the inside layer  12 . The shape of inside layer  12  is further determined by a channel surface  62  extending through the fourth die  52 . 
     FIG. 4 is an end elevational view of the die set  20 , as viewed in a direction opposite that of arrow  24  in FIG.  3 . FIG. 4 shows an end of the die openings, within which a longitudinally extending rounded edge  18   d  of the slat  10  (shown in FIG. 1) is formed by coextrusion. 
     Referring to FIGS. 1 and 4, the channel surfaces  26 , which determine the shape of first base layer  16 , are formed in the shape of a slot with rounded ends  64 , around which the channel surface  50 , forming the shape of outside layer  14  partly extends. The trough  48 , through which material is supplied to form the outside layer  14 , also extends partly each slot end  64 . The channel surface  37 , which determines the shape of second base layer  18 , also wraps partly around the slot ends  64 . The channel surface  62 , which determines the shape of inside layer  12  wraps around the end  64  outside the surfaces  37 ,  50 . The trough  60 , through which material is supplied to form the inside layer  12 , also wraps around the end  64 . In this way, the outer layers  12 ,  14 , are formed to overlap and to encapsulate the inner layers  16 ,  18 . 
     FIG. 5 is a side elevation of a texturing station  66  used to impart a texture pattern on an inside surface  68  of slat material  70  being extruded from the die set  20 . This texturing station  66  includes a metal texturing roll  72  and a back-up roll  74  having a rubber coated peripheral surface  76 . The peripheral surface  78  of the texturing roll has a pattern which is the inverse of the pattern to formed in the inside surface  68 , with ridges in the peripheral surface  78  forming grooves in the slat material surface  68 . The rolls  72 ,  74  are allowed to rotate freely with the motion of the slat material  70  in the direction of arrow  24 , but are held in engagement with the slat material  70  by compression springs  79 . After passing between the rolls  72 ,  74 , the slat material  70  is pulled through an alignment fixture  79   a  having upstanding oblique surfaces at the edges of the slat material  70  for aligning this material  70 , a painting station  80  and a cooling station  82  onto a conveyer belt (not shown), and is cut to a suitable length by a powered knife (not shown) moving with the slat material  70  during the cutting process. Within the painting station  80 , heat from the extrusion process is used to dry the paint. Following the painting and drying, the slat material is cooled by cold water being pumped through the cooling station  82 . 
     Referring again to FIGS. 1 and 3, the second base layer  18 , which has been described above as being composed of a UV stabilized PVC material having pearlescent pigmentation, such as GEON No. 87654, is alternatively composed of a clear PVC material, such as GEON No. 87727-002. In this way, the second base layer  18  is used to provide a significant change in the percentage of light transmitted through the slat  10  without reformulating the plastic materials and without changing the die set  20 . Experiments have shown, for example, that the percentage of light transmitted through a slat of this type having the second base layer  18  composed of a PVC with pearlescent pigmentation is approximately six percent, while the percentage of light transmitted through an otherwise similar slat having the first base layer  16  composed of a clear PVC is approximately twelve percent. While the use of four layers provides this advantage of the present invention, it is understood that a version of the present invention includes only three layers—an inside layer, and outside layer, and a transparent base layer. 
     The layered construction of the present invention further allows the use of a relatively thick base layer, which is transparent to preserve the overall translucency of the slat, while achieving an overall thickness sufficient to retain stiffness and strength within the slat. 
     While the second base layer  18  is described above as being composed of a clear transparent PVC, this layer  18  is alternately composed of a pigmented transparent PVC material to provide transmitted light having the color of the pigmented material. A slat made in this way retains its silver-white appearance when it is illuminated from inside, with light reflected from the slat, but changes its effective color to a muted version of second layer. A particularly attractive slat has been made in this manner using a red pigment within the second base layer  18 . 
     FIG. 6 is a transverse cross-sectional view of painting station  80 , being taken as indicated by section lines VI—VI in FIG.  5 . 
     Referring to FIGS. 5 and 6, within painting station  80 , the slat material  70  is pulled along a longitudinally extending support channel  84  by the conveyer system (not shown), being moved through slots  86  in end covers  88 . The painting station  80  also includes side covers  90 , but is open at the top. A paint spray nozzle  92 , held in place by a paint support bracket  94  extending between the end covers  88 , is directed downward at the slat material  70  moving through the painting station  80 . Paint is supplied to the nozzle  92  through a hose  96  from a paint supply container  98 . To assure the proper flow of paint, the paint supply container  98  is preferably pressurized by means of a regulated air supply system (not shown). A second hose  100  carries compressed air to the paint spray nozzle  92 . Within the spray nozzle  92 , paint from hose  96  is atomized by air from hose  100 , so that a mixture of air and paint droplets is sprayed downward in a generally conical pattern  102 . 
     The painting station  80  is particularly configured to minimize variations in paint coverage along the top surface  104  of the slat material  70 , in the transverse direction of arrow  106 . Such variations, which are be caused by radial variations in the density of paint droplets within the conical pattern  102  and by the fact that the center of the top surface  104  passes under the conical pattern  102  for a longer time than the outer edges  108  of this surface  104 , are minimized by configuring the painting station  80  so that the conical pattern  102  overextends the width of the slat material  80 . Furthermore, a vertical renewable surface  110  is held adjacent to each edge of the causing the flow of air and paint to be deflected toward the top surface  104 , increasing the density of paint near each outer edge  108 , so that the painting process is more uniform in the transverse direction of arrow  106 . Each renewable surface  110  is held in place within a vertical support plate  112 , which is in turn held by a number of stand-offs  114  extending inward from the adjacent side cover  90 . Each renewable surface  110 , which may be composed of a sheet of cardboard, is inserted downward through a slot  116  formed by a lanced and formed strip  118  extending along the top edge of each vertical support plate  112 , to be held by a pair of hook tabs  120  extending at the bottom of the vertical support plate  112 . 
     The painting station  80  is also configured to prevent overspray paint damage to the undersurface  122  of the slat material  70 . The passage of air under the slat material  70  is prevented by the support channel  84 . Otherwise, air movement under the slat material  70  could carry paint droplets into contact with the undersurface  122 . 
     Furthermore, the painting station  80  is configured for the removal of paint in solid or liquid forms without allowing damage to occur to the slat material  70  from such paint. After an excessive amount of paint is deposited on the inner sides  124  of the renewable surfaces  110  by direct contact with the paint spray pattern  102 , these renewable surfaces  110  are removed and reversed to present new sides or replaced. During the painting process, paint runs or drips from the inner sides  124  of the renewable surfaces  110  into gutters  126  extending along the support channel  84 . The retaining hooks  120  do not interfere in this flow of paint since they are spread apart along each vertical support plate  112  far enough to lie on either side of the paint spray pattern  102 . The paint spray pattern  102  also extends downward through a slot  128  between each renewable surface  110  and the support channel  84 , causing the deposition of paint on the vertical surfaces  130  of support channel  84 . This paint drips downward into the gutters  126  extending below these vertical surfaces  130 . Paint accumulated in the gutters  126  flows away from the painting station  80  through drain hoses  132 . A spacing plate  134  holds the undersurface  122  of the slat material  70  in a spaced-apart relationship with the support channel  84  within the portion of the painting station  80  in which the paint spraying process occurs. In this way, the transfer of paint from the support channel  84  to the undersurface  122  is prevented. The slat material  70  overextends the spacing plate  134  so that the undersurface  122  does not contact any portion of the spacing plate  134  which is not covered by the slat  70 , either. A cul de sac is thus formed at either side of the spacing plate, with a mixture of air and paint droplets being pulled through the slot  128  instead of being driven against the exposed portion of the undersurface  122 . 
     A downward flow of air through the painting station  80  is maintained by means of an exhaust duct  135  pulling air away from the painting station  80  through a filter  136 , which minimizes the flow of paint into the duct  135 . 
     The preferential placement of paint droplets on peaks and ridges of the textured surface is an observed phenomenon that is believed to be caused by a combination of the principles described below in reference to FIGS. 7 and 8. Operation in accordance with these principles is understood not to be necessary for patentability. 
     FIG. 7 is an enlarged sectional view of the textured upper surface  104  having a number of upstanding peaks  142 . The air and paint mixture from the nozzle  92  (shown in FIG. 6) is directed downward, as indicated by arrow  144 . However, since the air cannot move through the upper surface  104 , it must flow horizontally outward, as indicated by arrow  146 . When paint entrained within the air flow comes into contact with the surface  104 , it generally is transferred to the surface  104 . This process occurs first at the tips of upstanding peaks  142 . The outward rate of airflow near flat or depressed portions  147  of the surface, as indicated by arrow  148 , is at much lower velocities than the airflow near the peaks, as indicted by arrow  146 . Since this airflow carries paint, the tips of peaks  148 , upon which more air impinges at a faster rate, are coated with much more paint. 
     FIG. 8 is an enlarged sectional view of the textured upper surface  104  having a number of upstanding ridges  150 . The air flows outward above the ridges, as indicated by arrow  152 , with generally stagnate air conditions being maintained in the regions  154  between ridges  150 . Thus, relatively little paint is deposited between the ridges  150 . 
     Furthermore, the electrostatic forces between paint droplets and the upper surface  104  may be responsible for preferential attraction of the paint droplets to the points and ridges of the texture pattern. In the process of mixing and atomization occurring within the spray nozzle  94 , triboelectric charging occurs between the paint droplets and the air in which they are carried, causing electrostatic charges to be placed on the droplets. Also, electrostatic charges are placed in the surfaces of the upper surface  104  during the processes of extrusion and of rolling to produce the desired texture. Since the upper surface  104  is not flat, the electrostatic field above it is not uniform. Fringing fields are directed toward the tips of raised features, causing the charged paint droplets to be placed preferentially on such tips. 
     Since such effects can be overcome by depositing enough paint that paint is deposited on all portions of the upper surface  104 , the deposition of paint must be controlled to achieve the particular visual result desired. A metallic clear water-based paint may be used, or the paint may have a matte or pearlizing pigment. Good results have been obtained using a high-volume, low-pressure nozzle with a 0.5 mm (0.02 in.) diameter orifice about 30 cm (12 in.) above the upper surface  104 , with a pressure measured at the nozzle tip of 3 to 6 psi. The painting process also is dependent on the temperature of the surface being painted. Good results have been obtained with the paint nozzle  92  being displaced horizontally, in the direction of arrow  24  from the texturing rollers  72 ,  74 , through a distance of about 76 cm (30 in.), with the temperature of the surface  104  being about 300 degrees F. 
     FIG. 9 is a partially sectional side elevation of an alternate painting station  160  used to paint the surface pattern of FIG. 1 on a surface of the slat material  70  following extrusion through the dies set  20  of FIG.  3  and texturing within the texturing station  66  of FIG.  5 . In comparison with the painting station  80 , described above in reference to FIG. 5, this alternate painting station  160  is elongated to include two spray painting nozzles  92 . Each nozzle  92  is connected to its own paint supply container  98  by a hose  96  and to an air supply (not shown) by means of a hose  100 . The two nozzles  92  are aligned longitudinally along the slat material  70  being painted. Other features of the alternate painting station  160  are generally as described above in reference to FIGS. 5 and 6. 
     This alternative painting station  160  is used to deposit a more even layer of paint on the surface of the slat material  70 , eliminating some of the splattered appearance of paint deposited through the use of the painting station  80  of FIG.  5 . Even with the alternative painting station  160 , paint is preferentially applied to peaks and ridges of the texture pattern, so that the effects described above are retained. Different visual effects can also be achieved by spraying different colors or types of paint through the two nozzles  92 . Experiments have shown that, in this painting station  160 , more paint is being applied, so that external heating is required to dry the paint as required for handling through the apparatus. Thus, a separate blowing heater  164  is added, being directed at the slat material  70  between the painting station  160  and the cooling station  82 . 
     FIG. 10 is a fragmentary transverse cross-sectional view of a slat  170 , made in accordance with a second embodiment of the present invention, to include a selectively painted inner surface  172  on an innermost layer  174  of a number of coextruded layers, and a selectively painted outer surface  176  on an outermost layer  178  of the coextruded layers. 
     FIG. 11 is a partially sectional side elevation of a texturing station  180  and a painting station  181  used to form the surface patterns of FIG. 10 on both surfaces of the slat material  70  being extruded from the die set  20  of FIG.  3 . The texturing station  180  includes a first texturing roll  72  and a first back-up roll  74 , used as described above in reference to FIG. 5, to place a textured image on the upper surface  104  of the slat material  70 , together with a second texturing roll  182  and a second back-up roll  184 . The second texturing roll  182  has a peripheral surface  185  forming the textured surface on the lower surface  122  of the slat material  70 . The textured pattern being placed on the lower surface  122  may be the same as, or different from, the textured pattern placed on the upper surface  104 . 
     FIG. 12 is a transverse cross-sectional view of the painting station  181 , taken as indicated by section lines XII—XII in FIG.  11 . 
     Referring to FIGS. 11 and 12, the painting station  181  includes an upper paint spray nozzle  186  directed downward at the upper surface  104  of the slat material  70  moving through this station  181  and a lower paint spray nozzle  187  directed upward at the lower surface  122  thereof. Each of these nozzles  186 ,  187  is attached within an inner structure  188  by means of a nozzle attachment bracket  189 . The inner structure  188  is closed at a front side  188   a , at a rear side  188   b , at a top side  188   c , and at a bottom side  188   d , being open at the ends. The inner structure  188  is fastened within an outer structure  189  by means of four angle brackets  190 , which extend between the end covers  191  of the outer structure  190 . The outer structure  190 , which also includes a front cover  192  and a rear cover  193  is open at the top and includes a filter  194  extending across the bottom, where an exhaust duct  196  keeps air moving downward through the outer structure  190 . Each nozzle  186 ,  187  is supplied with air under pressure through a hose  197  and with paint from a supply container  198  through a hose  199 . 
     In the general manner previously described in reference to painting station  80  of FIGS. 5 and 6, the spray patterns  200 ,  201  from nozzles  186 ,  187 , respectively, overextend the slat material  70 , with portions of the flow of air and paint being redirected by renewable surfaces  202 , in order to provide more uniform paint coverage across the width of the slat material  70 , in the transverse direction of arrow  203 . Most of the paint deposited on the renewable surfaces  202  runs downward, to the bottom side  188   d  of inner structure  188 . From this area, paint is carried outside the painting station  181  through a hose  204 . When an excessive build-up of paint occurs on the renewable surfaces  202 , they are removed and reversed or replaced, being removed and inserted through slots  203  in the upper side  188   c  of inner structure  188 . 
     The effect of overspray from upper nozzle  186  reaching lower surface  122  of slat material  70 , or of overspray from lower nozzle  187  reaching upper surface  104  thereof, is minimized by placing the nozzles  186 ,  187  in alignment with one another on opposite sides of the slat material  70 . Since air pressure is introduced from opposite sides of the slat material  70 , there is relatively little air flow around the ends of the slat material  70 , adjacent the renewable surfaces  202 . Nevertheless, this embodiment of the present invention is understood to include a paint spray station of this general type, having nozzles on opposite sides of the slat material  70 , which are displaced from one another in the longitudinal direction of arrow  24 . 
     The presence of surfaces contacting the slat material  70  within the paint spray station  181  is particularly avoided within the painting station  181 , since contact with such surfaces could otherwise smear the paint present on both sides of the slat material  70 . Thus, the slat material  70  travels unsupported between the alignment fixture  79   a  and the cooling station  82 , a distance of about 91 cm (36 in.). Tension is maintained within the slat material  70  by pulling this material with a conveyer belt (not shown) and rollers (not shown) engaging the slat material  70  beyond the cooling station  82 . 
     While pairs of paint spray nozzles have been described in detail as being located in a longitudinally displaced relationship on the same side of the slat material  70  and alternately in an opposed relationship on opposite sides of the slat material  70 , the present invention is understood to include the use of additional nozzles, such as a first pair of nozzles on a first side of the slat material  70  and a second pair of nozzles on a second side of the slat material, opposite the first side thereof. 
     FIG. 13 is a front elevation of a vertical blind assembly having a number of the slats  210  hanging from a track system  212 , which is of a conventional type well know to those skilled in the art of window and door coverings. Each slat  210  is of a type described above, either in reference to FIG. 1 or FIG. 10 Each slat  210  includes an aperture by which it is held on a slat holder (not shown) within the track system  212 . 
     FIG. 14 is a fragmentary plan view of the vertical blind assembly of FIG. 13, taken as indicated by section lines XIV—XIV in FIG. 13 to show three slats  210 . Each slat  210  has an inside surface  214 , which has, for example, a textured surface formed as described above in reference to FIG.  5 . The transverse sectional shape of the slat  210  is further characterized by a curvature of the inside surface  214 , such as a convex or “S”-shaped curvature, into which the slat material  70  (shown in FIG. 5) is formed following the extrusion process, while the material is still warm. 
     While FIG. 14 shows each slat having a textured surface on only one side, it is understood that the slats may also be of the type described above in reference to FIG. 10, having textured surfaces on both sides. 
     Referring to FIGS. 13 and 14, the track system  212  causes the slats  210  to rotate in unison about vertical axes between an open position in which the slats  210  are essentially parallel and a closed position, in which the slats  210  cooperate to cover the window or door (not shown) behind them. In this closed position, the slats  210  are preferably oriented so that their inside surfaces  214  face into the room in which the blind assembly is mounted. The track system  212  also causes the slats  210  to move toward one another and away from one another. 
     FIG. 15 is a cross-sectional end elevation of a horizontal blind assembly including a number of slats  216 . In the rotated-open position shown, each slat  216  rests, with its inside surface  218  facing upward, on a pair of transverse support cords  220  extending within a tilt cord loop  222 . The slats  216  are rotated in unison and lifted to form a stack from the bottom by means of a blind mechanism  223 , which is of a type well known to those skilled in the art of window coverings. The slats  216  are preferably rotated from the open position shown by moving an inside side  224  of the cord loop  222  downward while an outside side  226  of the cord loop is moved upward, so that the inside surfaces  218  of the slats  216  are exposed within the room in which the blind assembly is mounted. A lifting bar  228  is raised by means of two or more lifting cords  230  to raise the slats  216  in a stack formed from the bottom. 
     While the present invention has been described above in terms of the application of paint to translucent slat material, to achieve a particular advantage when the slat material is backlighted by sunshine during the day, it is understood that the processes described above are also applied to opaque slat material, forming a texture pattern which is more readily visible due to differences in color or shade between the paint and the opaque material of the slat. 
     While the invention has been described in its preferred form or embodiment with some degree of particularity, it is understood that this description has been given only by way of example and that numerous changes in the details of construction, fabrication and use, including the combination and arrangement of parts, may be made without departing from the spirit and scope of the invention.