Abstract:
A material for protection against injurious ambient light composed of a binder mixed with non metallic reflective flakes is disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 09/504,051 filed Feb. 14, 2000 now as U.S. Pat. No. 6,535,268, which is a continuation in part of application Ser. No. 09/039,303 filed Mar. 14, 1998 now U.S. Pat. No. 6,661,486 entitled Reflective Films having Non-linear spacing of layers which is a continuation in part of application Ser. No. 08/805,603 entitled “Electro-optical glazing structures having total-reflection and transparent modes of operation for use in dynamical control of electromagnetic radiation” by Sadeg M. Faris and Le Li, filed Feb. 26, 1997, now U.S. Pat. No. 5,940,150,which is a continuation-in-part of: application Ser. No. 08/739,467 entitled “Super Broadband Reflective Circularly Polarizing Material And Method Of Fabricating And Using Same In Diverse Applications”, by Sadeg M. Faris and Le Li filed Oct. 29, 1996, now U.S. Pat. No. 6,034,753 which is a is a Continuation-in-Part of application Ser. No. 08/550,022 (Now U.S. Pat. No. 5,691,789) entitled “Single Layer Reflective Super Broadband Circular Polarizer and Method of Fabrication Therefor” by Sadeg M. Faris and Le Li filed Oct. 30, 1995. Each of the above identified Applications and patents are commonly assigned to the assignee of the present invention, and are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The field of the invention is the field of protective coatings for protecting surfaces from injurious ambient light. 
     BRIEF DESCRIPTION OF THE LITERATURE 
     Broadband reflecting polarizers were introduced in application Ser. No. 08/550,022 (now U.S. Pat. No. 5,691,789) entitled “Single Layer Reflective Super Broadband Circular Polarizer and Method of Fabrication Therefor” by Sadeg M. Faris and Le Li which was filed Oct. 30, 1995. Such broadband polarizers are made by producing a single layer having cholesteric liquid crystal order where the pitch of the liquid crystal order varies in a non linear fashion across the layer. 
     General references on polymer dispersed liquid crystals may be found in detail in “Polymer Dispersed Liquid crystal displays”, by J. W. Doane, a chapter in “Liquid Crystals”, Ed. B. Bahadur, World Scientific Publishing, Singapore, and “CLC/polymer dispersion for haze-free light shutters, by D. Yang et al. Appl. Phys. Lett. 60, 3102 (1992). 
     Since the early attempt of utilizing cholesteric film as optical filters and the effort on polymer encapsulated nematic liquid crystals for display, much attention has been focused on trying to bring polymeric liquid crystals and cholesteric liquid crystals together to make devices for light control application. (See, for example J. Adams, W. Hass, J. Dailey, Journal of Applied Physics, 1971, and J. L. Fergason, Society for Information Display Digest, 1985.). 
     The following applications are related to the present invention: application Ser. No. 09/093,017 filed Jun. 5, 1998; application Ser. No. 09/093,006 filed Jun. 5, 1998; application Ser. No. 09/039,303 filed Mar. 14, 1998; application Ser. No. 09/039,297 filed Mar. 14, 1998; application Ser. No. 08/891,877 filed Jul. 9, 1997 entitled “Reflective Film Material Having Symmetrical Reflection Characteristics and Method and Apparatus for Making the Same”, by Le Li and Sadeg Faris; application Ser. No. 08/739,467 filed Oct. 29, 1996 entitled “Circularly Polarizing Reflective Material Having Super Broad-Band Reflecting &amp; Transmission Characteristics &amp; Method of Fabricating &amp; Using Same in Diverse Applications” by Sadeg M. Faris, Le Li, and Yingqiu Jiang Jiang; application Ser. No. 08/890,320 filed Jul. 9, 1997 entitled “Coloring Media Having Improved Brightness and Color Characteristics” by Sadeg M. Faris and Le Li; The above identified US patents and other references are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Protection of surfaces from injurious effects of ambient light has heretofore generally used materials which absorbed the injurious light. Organic molecules used as sunscreens are chosen to have a very strong absorption in a particular band. For example, the absorption in the UVA band. Unfortunately, the absorption is usually not great in additional bands such as the UVB band. Unfortunately, the materials which absorb injurious light also tend to be “injured” by the light. For example, organic molecules applied to the skin as sunscreen tend to break down when subjected to strong ultraviolet light for a long time. In addition, such materials added to plastics and fabrics tend also to have limited life. Reflecting and scattering materials, such as zinc oxide used in sunscreens, tend to reflect and scatter visible light also, which leads to the faintly comical “white noses” familiar on lifeguards. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide a protective material which protects the surface of a material from injurious ambient light. It is a further object of the invention to provide a protective material which reflects the injurious ambient light. It is a further object of the invention to provide a protective material which is transparent in the visible spectral region. It is a further object of the invention to provide a protective material which reflects injurious ultraviolet light. It is a further object of the invention to provide a protective material which reflects both injurious ultraviolet light and infrared light. It is a further object of the invention to provide a protective material which acts as a sunscreen for human skin and which is not visible in visible light. 
     SUMMARY OF THE INVENTION 
     Non metallic, reflecting flakes of multilayer polymer, CLC, or inorganic material are used with a binder to form a protective coating on a material surface. The flakes reflect light in a spectral range where the light is injurious to the material surface, and transmit light in a spectral range where the light is not injurious to the material surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a sketch of the material of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a sketch of a layer  10  of the protective material of the invention covering a surface  11  of a material  15  which is to be protected from injurious ambient light. Layer  10  comprises non metallic reflecting flakes  12  imbedded in a binder material  13 . Light rays  14  of light in a spectral region which would be injurious to material  15  are shown reflecting from a non metallic reflecting flake  12 . In a preferred embodiment of the invention, flakes  12  are transparent in a spectral region for which light is not injurious to the material  15 , and such light rays  16  are shown passing through a flake  12  where they strike the surface  11  of the material and are reflected from the surface  11  of the material  15 . In particular, light rays  14  may be ultraviolet light, for example ultraviolet light in the UVA, UVB, or both UVA and UVB spectral ranges, and light rays  16  may be in the visible region. By convention, the UVA spectral range has wavelength in the range 320-400 nm, and the UVB spectral range is 280-320 nm. In addition, injurious light rays  14  may be in the infrared spectral range where the infrared light rays  14 , if they struck the surface  11  of the material  15  would be absorbed in the material  15  and heat the material  15  in an unacceptable manner. Each flake  12  may reflect all injurious light, or different flakes reflecting different spectral regions may be admixed in binder material  13  so that little or no injurious light may propagate to the surface  11 . The material  15  in one preferred embodiment is transparent to the non injurious light rays. One such light ray  17  is shown passing through the binder material  13 , non metallic reflecting flake  12 , the surface  11 , and the material  15 . In a preferred embodiment, transparent material  15  is used as a food covering, and the layer  10  keeps injurious ultraviolet light from the food surface. In an additional embodiment, layer  10  reflects infrared light and keeps the food product colder. In an additional embodiment, transparent material  15  is used for greenhouses to protect growing plants from harmful UV and IR light. 
     The binder material  13  in one preferred embodiment absorbs injurious light rays as indicated by light ray  18 . Such absorption is useful, in that very high absorptions may be obtained, for example in the UVA spectral region, while the flakes take care of the surface by reflecting the UVB spectral region. Alternatively, the flakes may reflect the UVA spectral region, while the binder material  13  absorbs light in the UVB spectral region. Alternatively, the binder material may absorb light in both the UVA and UVB spectral regions, while the flakes  12  reflect light in the IR spectral region. 
     The most preferred embodiment of the invention is the use of the material of the invention as a sunscreen for human skin and human fingernails. 
     In other preferred embodiments, the materials  15  to be protected are textile, polymer, leather, wood, metal, brick, stone, concrete, glass, paper, ice, rubber, paint, tar, or ink material. 
     Reflecting flakes  12  may be cholesteric liquid crystal (CLC) flakes, multilayer polymeric material flakes, or inorganic multilayer material flakes. Such flakes have high reflectivity in a particular spectral region because they are composed of many layers of alternating high and low index of refraction material. In order that the flakes may reflect light over a broad bandwidth, the thickness of the layers may be a non linear function of the distance from the layer to the surface of the flake as shown in great detail in the incorporated U.S. Pat. No. 5,691,789 and in incorporated application Ser. No. 09/039,303. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise then as specifically described.