Patent Publication Number: US-2018052263-A1

Title: Privacy filter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 62/127,360 filed on Mar. 3, 2015 the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Privacy filters, also known as light control films, are devices that can be placed between a viewer and an image plane to limit the viewing angle of the image plane. Privacy filters typically include a louver film made of alternating transmissive regions and absorptive regions. The louver film may be laminated, or otherwise attached, to a base substrate. Typically, the louver film is made of polyethylene terephthalate (PET) or polycarbonate (PC). Hard coatings may be applied to the louver film for protection, but hard coatings are easily scratched. 
     SUMMARY 
     Privacy filters suitable for use in touch panels or as screen protectors or in architectural applications are disclosed herein. The privacy filters are made out of durable materials and using methods that can enable mass production and short lead-time. 
     In one embodiment, a privacy filter includes a transparent substrate and a louver structured formed in a layer on the transparent substrate. The louver structure includes a plurality of first strip elements and a plurality of second strip elements in alternating arrangement on the transparent substrate. The first strip elements are made of a non-transparent thermally irreversible photochromic polymer, and the second strip elements are made of a transparent thermally irreversible photochromic polymer. 
     In another embodiment, a privacy filter includes a transparent substrate and a louver structure formed in a layer on the transparent substrate, where the louver structure includes a plurality of parallel, spaced-apart non-transparent strip elements, where each non-transparent strip element is made of cured ink. 
     In another embodiment, a privacy filter includes a photosensitive transparent substrate having a louver structure embedded therein. The louver structure is defined by an alternating arrangement of a plurality of non-transparent strip areas and a plurality of transparent strip areas of the photosensitive substrate. 
     It is to be understood that both the foregoing summary and the following detailed description are exemplary and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
         FIG. 1A  shows a privacy filter including a louver structure formed in an irreversible photochromic polymer layer on a surface of a transparent substrate. 
         FIG. 1B  shows the louver structure of  FIG. 1A  with louver elements having slanted side walls oriented in the same direction. 
         FIG. 1C  shows the louver structure of  FIG. 1A  with louver elements having slanted sides oriented in opposite directions. 
         FIG. 1D  shows viewing range and dimensions of a louver structure. 
         FIGS. 2A and 2B  illustrate a method of forming the privacy filter of  FIG. 1A  according to one embodiment. 
         FIG. 3  shows a privacy filter according to another embodiment. 
         FIGS. 4A and 4B  illustrate a method of forming the privacy filter of  FIG. 3 . 
         FIG. 5  shows a privacy filter according to yet another embodiment. 
         FIG. 6  illustrates a method of forming the privacy filter of  FIG. 5 . 
         FIG. 7  shows the privacy filter of  FIG. 5  with a mounting adhesive layer. 
         FIG. 8  shows a privacy filter with stacked micro-structures having orthogonally aligned louver elements. 
         FIG. 9A  shows a privacy filter as an add-on glass protector for a handheld device according to one embodiment. 
         FIG. 9B  shows a privacy filter integrated into a case for a handheld device according to another embodiment. 
         FIG. 9C  shows a handheld device with a privacy filter cover glass according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows a privacy filter  100  according to one embodiment. The privacy filter  100  includes a louver structure  104  formed as a layer on a surface  105  of a transparent substrate  106 . The transparent substrate  106  may be a planar substrate, with the surface  105  lying in the X-Y plane. In one embodiment, the transparent substrate  106  may have a thickness t G  in a range from about 0.1 mm to about 2 mm. In one embodiment, the louver structure  104  may have a layer thickness t L  in a range from about 20 μm to about 200 μm. The louver structure  104  includes a plurality of non-transparent strip elements  108  and a plurality of transparent strip elements  112  in parallel alternating arrangement. The strip elements  108 ,  112  extend across a dimension of the surface  105 , such as the dimension along the Y axis. In the parallel alternating arrangement, the non-transparent strip elements  108  and transparent strip elements  112  are parallel to each other, with a transparent strip element  112  being wedged between each adjacent pair of spaced-apart non-transparent strip elements  108 , or vice versa. It should be noted that the louver structure  104  will typically have many more strip elements  108 ,  112  than shown in  FIG. 1A , as many as are needed to form a privacy filter  100  of a desired dimension. 
     In the privacy filter  100  and other privacy filters that will be subsequently described herein, what is considered to be transparent or non-transparent may be defined in terms of some cutoff transmission T c . If a strip element or substrate has a transmission of at least T c , the strip element or substrate may be considered to be transparent. On the other hand, if the strip element or substrate has a transmission less than T c , the strip element or substrate may be considered to be non-transparent. Thus non-transparent can mean translucent or opaque. In one embodiment, the cutoff transmission T c  is 80% in a visible range of 390 to 700 nm. The material for transparent substrate  106  can include, but is not limited to, glass, fused silica, synthetic quartz, glass-ceramic, ceramic, or a crystalline material such as sapphire. In some embodiments, the transparent substrate  106  can be glass, and the glass can be chemically strengthened, for example by an ion exchange process in which ions in the surface layer of the glass are replaced by larger ions having the same valence or oxidation state. In one particular embodiment, the ions in the surface layer and the larger ions are monovalent alkali metal cations, such as Li +  (when present in the glass), Na + , K + , Rb + , and Cs + . Thus, for example, Na +  present in the glass may be replaced with the larger K +  ions. The ion-exchange process creates a compressive stress at the surfaces of the glass article or glass substrate sheet. These compressive stresses extend beneath the surface of the glass article or glass substrate sheet to a certain depth, referred to as the depth of layer (DOL). The compressive stresses are balanced by a layer of tensile stresses (referred to as central tension) such that the net stress in the glass article or glass substrate sheet is zero. The formation of compressive stresses at the surface of the shaped glass article makes the glass strong and resistant to mechanical damage and, as such, mitigates failure of the shaped glass article for flaws which do not extend through the depth of layer. 
     In  FIG. 1A , the interface walls  113 A,  113 B between each non-transparent strip element  108  and adjacent transparent strip elements  112  are straight.  FIG. 1B  shows an alternative structure where the interface walls  113 A,  113 B are slanted, relative to the transparent substrate surface  105 , in the same direction.  FIG. 1C  shows another example where the interface walls  113 A,  113 B are slanted, relative to the transparent substrate  105 , in opposite directions. The angles between the interface walls  113 A,  113 B and the transparent substrate surface  105  can be design variables. 
       FIG. 1D  shows that each non-transparent strip element  108  may have a width w NT  and a height h NT  and that each transparent strip element  112  may have a width w T  and height h T . If the interface walls  113 A,  113 B are slanted as shown in  FIG. 1B or 1C , the widths of the elements  108 ,  112  along the heights of the elements may vary. The combined width of a non-transparent strip element  108  and an adjacent transparent strip element  112  may be regarded as the pitch P of the louver structure  104 . Typically, the pitch P will be constant across the louver structure  104 . In some embodiments, the height h NT  of the non-transparent strip element  108  and the height h T  of the transparent strip element  112  may be the same. The height h NT  of the non-transparent strip element  108  and the height h T  of the transparent element  112  may be the same as the layer thickness t L  of the louver structure  104 , or in some cases may be smaller than the layer thickness of the louver structure. 
     The dimensions of the louver elements  108 ,  112 , as explained above, can be selected to achieve a desired viewing angle of the privacy filter  100 . The viewing angle is the angle within which an image on an image plane being viewed through the privacy filter is clear and undistorted.  FIG. 1D  illustrates a viewing angle of a degrees for a privacy filter. The viewing angle is measured relative to a normal viewing direction  118 , which is a direction normal to the transparent substrate surface  105 . A viewing angle of a degrees means that the image viewed through the privacy filter  100  should be clear and undistorted when viewed at a degrees or less from the normal viewing direction  118 . Outside of the viewing angle, the image will be blocked and unreadable because the viewing direction will land on the non-transparent strip elements  108  rather than within the transparent strip elements  112 . The viewing angle is a design variable and depends on the dimensions and material properties of the louver elements  108 ,  112 . One example of a viewing angle is 30°. 
     The aperture ratio A of the louver structure  104  can be determined from Equation (1) below, where W T  is the width of the transparent strip element  112  and w NT  is the width of the non-transparent strip element  108 . 
     
       
         
           
             
               
                 
                   A 
                   = 
                   
                     
                       w 
                       T 
                     
                     
                       
                         w 
                         T 
                       
                       + 
                       
                         w 
                         NT 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Aperture ratio can provide a measure of how much light is passing through the privacy filter since the light will be selectively blocked by the non-transparent areas of the privacy filter. In one embodiment, the aperture ratio of the louver structure  104  may be 50% or greater to prevent significant reduction in image resolution when an image plane is viewed through the privacy filter  100  within the viewing angle. In one embodiment, the non-transparent strip elements  108  in the louver structure  104  may each have a width in a range from about 1 μm to about 30 μm, and the transparent strip elements in the louver structure  104  may each have a width in a range from about 50 μm to about 150 μm. As an example, an aperture ratio of 80% may be achieved by selecting the width of each non-transparent strip element  108  as 10 μm and the width of each transparent strip element  112  as 40 μm (corresponding to a pitch P of 50 μm). 
     In one embodiment, the louver structure  104  is made from a thermally irreversible photochromic polymer that is selectively exposed to actinic radiation, such as UV light, to form the parallel alternating pattern of non-transparent strip elements  108  and transparent strip elements  112 . The term “thermally irreversible photochromic polymer” is intended to refer to a polymer that has thermally irreversible photochromic properties. When such a material is exposed to actinic radiation such as UV light, it will undergo an irreversible color change. If the starting material is a transparent thermally irreversible photochromic polymer, the areas of the material exposed to actinic radiation will experience irreversible color change and become irreversibly non-transparent. The unexposed areas of the material will remain transparent. As noted above, transparent substrate  106  may be made of any transparent materials having the desirable properties for the intended application of the privacy filter  100 . Also, as noted above, in some embodiments, the transparent substrate  106  may be made of a chemically-strengthened glass, resulting in a privacy filter  100  with sufficient toughness and scratch-resistance for use as screen protector. 
       FIGS. 2A and 2B  show a method of making the privacy filter  100  according to one embodiment. In  FIG. 2A , the method includes depositing a transparent thermally irreversible photochromic polymer layer  202  on a surface  205  of a transparent substrate  206  (corresponding to  106  in  FIG. 1A ). Examples of suitable thermally photochromic polymers are thermally irreversible spiropyrans, spirooxazines, diarylethene, azobenzene, phenoxy-naphthacenequinone, fulgimide, thioindigo, dithizonate, and dihydroindolizine photochromic compounds. The transparent thermally irreversible photochromic polymer may be deposited on the transparent substrate surface  205  by spraying, slitting, spinning, or other suitable film deposition processes to form the layer  202 . Alternatively, the transparent thermally irreversible photochromic polymer may be provided in the form of a film sheet that can be laminated to the transparent substrate surface  205  to form the layer  202 . 
     In  FIG. 2B , the method includes forming a louver structure in the transparent thermally irreversible photochromic material layer  202  by selective exposure of the transparent thermally irreversible photochromic material layer  202  to radiation from UV light sources  207  through a patterning mask  209 . The areas  208  of the transparent thermally irreversible photochromic layer exposed to the UV light will irreversibly change color and become irreversibly non-transparent, forming the non-transparent strip elements of the louver structure (corresponding to  108  in  FIG. 1A ). The areas  212  of the transparent thermally irreversible photochromic layer not exposed to the UV light will provide the transparent strip elements (corresponding to  112  in  FIG. 1A ) of the louver structure. 
       FIG. 3  shows a privacy filter  100 A according to another embodiment. The privacy filter  100 A includes a louver structure  104 A formed as a layer on a surface of a transparent substrate  106 A. The louver structure  104 A includes a plurality of non-transparent strip elements  108 A and a plurality of transparent channel elements (or spaces)  112 A in parallel alternating arrangement. The strip elements  108 A are spaced apart, by the transparent channel elements  112 A, and parallel to each other. The discussion above with respect to the louver structure  104  applies to the louver structure  104 A. The transparent channel elements  112 A, which are spaces, of the louver structure  104 A correspond to the transparent strip elements  112  of the louver structure  104  ( FIGS. 1A-1D ). The strip elements  108 A may in one embodiment have a height in a range from about 20 μm to 200 μm and a width in a range from 1 μm to 30 μm. The transparent channel elements (spaces)  112 A may have a width in a range from 50 μm to 150 μm. 
     The transparent substrate  106 A may have the same characteristics as described above for the transparent substrate  106 . In one embodiment, the non-transparent strip elements  108 A are made of cured ink, which will be non-transparent. The curable ink used in the non-transparent strip elements  108 A would generally include pigment(s) and resin(s) and may further include additives to formulate the ink with a desired rheology and stability. The curable ink may be selected from curable decorative and printing (inkjet or screen printing) inks. The pigment in the ink may be derived from various sources. For example, the pigment for curable black ink may be carbon black. 
       FIGS. 4A and 4B  show a method of making the privacy filter  100 A according to one embodiment. In  FIG. 4A , the method includes depositing an ink layer  302  on a surface  305  of a transparent substrate  306 . In one embodiment, the ink layer  302  is made of a thermally-curable ink. In one particular embodiment, the ink layer  302  is made of a thermally-curable black ink. The ink layer  302  may be deposited by a screen printing process, followed by curing of the ink. Other methods capable of depositing a uniform layer of ink on the substrate  306  may be used instead of screen printing. In  FIG. 4B , the method includes forming a louver structure in the cured ink layer  302  by selective exposure of the cured ink layer  302  to radiation from, for example, UV or Green light sources  307  through a patterning mask  309 . The areas of the cured ink layer  302  under openings  312  in the mask  309  will be etched away, forming the transparent channel elements or spaces (corresponding to  112 A in  FIG. 3 ) of the louver structure. The areas  308  of the cured ink layer  302  not exposed to the radiation will provide the non-transparent strip elements (corresponding to  108 A in  FIG. 3 ) of the louver structure  104 A. Selecting the ink to be thermally-curable allows the use of actinic radiation for etching of the cured ink layer. It may also be possible that the ink layer  302  may be made of an ink that can be cured with a first type of radiation (i.e., a radiation-curable ink layer), and that a second type of radiation may be used for the selective etching of the radiation-cured ink layer. 
       FIG. 5  shows a privacy filter  100 B according to another embodiment. The privacy filter  100 B includes a louver structure  104 B embedded in a photosensitive substrate  106 B. The louver structure  104 B includes a plurality of non-transparent strip elements  108 B and a plurality of transparent strip elements  112 B in parallel alternating arrangement. The non-transparent strip elements  108 B are provided by non-transparent (colored, translucent, or opaque) strip areas of the photosensitive substrate  106 B, and the transparent strip elements  112 B are provided by transparent (clear) strips areas of the photosensitive substrate  106 B. The thickness t G  of the photosensitive substrate  106 B may be in a range from about 0.1 mm to about 2.0 mm. The height of each strip element  108 B,  112 B will be limited by the thickness of the t G  of the photosensitive substrate  106 B. In one embodiment, the height of each strip element  108 B,  112 B will be the same as the thickness of the photosensitive substrate. As in the foregoing louver structures ( 104 ,  104 A), the width w NT  of each non-transparent strip element  108 B may be in a range from 1 μm to 30 μm, and the width W T  of each transparent strip element  112 B may be in a range from 50 μm to 150 μm. The thickness of the photosensitive substrate  106 B, the widths of the non-transparent strip elements  108 B and transparent strip elements  112 B, and the properties of the photosensitive substrate  106 B can be selected to achieve a desired viewing angle and aperture ratio of the privacy filter as described for the previous privacy filters. 
     In one embodiment, the photosensitive substrate  106 B is a photosensitive glass. A photosensitive glass is a glass that upon exposure to sufficient short wave radiation, such as ultraviolet radiation, develops coloration in the exposed areas while the unexposed areas remain unchanged. If the photosensitive glass starts out as a transparent glass, the areas with heat-developed coloration will be non-transparent, while the areas without heat-developed coloration will remain transparent U.S. Pat. No. 2,515,936 (Armistead, Jr., 1950) describes a photosensitive glass produced by incorporating silver chloride or silver halide into a silicate glass. This glass is capable of developing a yellow or amber color with UV light exposure. U.S. Pat. No. 3,208,860 (Armistead, Jr., 1965) discloses another example of a photosensitive glass produced by forming microcrystals of at least one silver halide selected from silver chloride, silver bromide, and silver iodide in a silicate glass. 
       FIG. 6  shows a method of making the privacy filter  100 B according to one embodiment. The method includes forming a louver structure in a photosensitive substrate  406  by selective exposure of the photosensitive substrate  406  to radiation from a UV light source  407  through a patterning mask  409 . The exposed areas  408  of the photosensitive substrate having heat developed coloration will provide the non-transparent strip elements (corresponding to  108 B in  FIG. 5 ) of the louver structure. The unexposed areas  412  of the photosensitive substrate not having heat developed coloration will provide the transparent strip elements (corresponding to  112 B in  FIG. 5 ) of the louver structure. 
     Any of the privacy filters  100 ,  100 A,  100 B described above can be provided with means for attaching it to a surface.  FIG. 7  shows one example where an optically-clear pressure-sensitive adhesive film  430  is attached to one side to the privacy filter  100 B. The adhesive film  430  can be used to mount the privacy filter  100 B on a screen, window, or other desired surface. Adhesive film can be similarly attached to the other filters  100 ,  100 A described above. 
     Two of any of the louver structures described above can be stacked, with their louver directions orthogonally aligned, to provide privacy filtering function in two orthogonal directions. This is illustrated in  FIG. 8 , where a second louver structure  120  is formed on the previous louver structure  104  on the transparent substrate  106 . The non-transparent strip elements  128  and transparent strip elements  132  of the louver structure  120  are oriented along the X-axis, while the non-transparent strip elements  108  and transparent strip elements  112  of the louver structure  104  are oriented along the Y axis. The viewing angle of the first louver structure  104  is illustrated by α x , and the viewing angle of the second louver structure  120  is illustrated by α y , where the meaning of viewing angle is as previously described. Another alternative is to locate the two louver structures on opposite sides of the transparent substrate, with the louver directions of the two louver structures being orthogonal to each other. 
     Privacy Filters as described above can be used in various applications, such as in screen protector for electronic devices, in touch panels, and in architectural material.  FIG. 9A  shows one application where the privacy filter  100  (or  100 A,  100 B) may be used as an add-on glass protector for a handheld device  502 . The privacy filter  100  (or  100 A,  100 B) may be attached to the front surface  504  of the handheld device by means of an optically clear adhesive.  FIG. 9B  shows another application where the privacy filter  100  (or  100 A,  100 B) is integrated into a case  512 , such as a leather case, for a handheld device  514 . When the case  512  is closed, the privacy filter  100  (or  100 A,  100 B) will cover the front surface  516  of the handheld device  514 . 
     Privacy filters as described above may also be used as cover glass for handheld devices.  FIG. 9C  shows a privacy filter cover glass  520 , which may incorporate any of the previously described privacy filters  100 ,  100 A,  100 B, for a handheld device  522 . The privacy filter cover glass  520  may be attached to the handheld device  522  using any suitable means known in the art, such as with a bezel  524 . A touch module (not shown) may be attached underneath the privacy filter cover glass  520  to enable touch functionality of the handheld device  522 . 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.