This invention relates to glazing and, more particularly, to chromogenic glazing for use in applications, such as automobiles and display filters, where it is desirable to reversibly alter the transmission or tinting of the glass.
Automobile windshields, movable and fixed side and rear windows, and divider panels between the front and the rear cabin, as well as sunroofs, employ various forms of glazing in a variety of colors and intensities. Typically, when tinted glazing is employed, the windshield and the front side windows are clear for safety reasons. Car glazing may provide for management of both ultra violet and infra-red solar energy penetration to enhance user comfort while reducing the power requirements for air-conditioning. Besides the need to carefully control tinting so that glass used in adjacent windows does not appear to be mismatched, it is important to consider the effect that glazing color can have on passengers""skin tones. For example, some colors, such as deep violet glazing may make the interior colors appear dull and/or strange and cause the skin tones of passengers to appear unnatural.
To adapt chromogenic glass, i.e., glass which has user-controllable transmissivity, for use in automobiles, it is important that the glass exhibit several characteristics:
1. Chromogenic glazing should be able to match its tint to the color of the car""s interior.
2. Chromogenic glazing should be available in xe2x80x9cwarmxe2x80x9d tones and in xe2x80x9cneutralxe2x80x9d tones.
3. Chromogenic glazing should not acquire an unacceptable color when it is changed from clearer to a darker state under user control.
4. Chromogenic glazing should maintain an acceptable color appearance from the outside, e.g., it is preferable that all of the windows should have similar color properties while permitting the depth of coloration of the windows (and of the sunroof) to vary.
5. Chromogenic glazing for use in a windshield may be colored or bleached to a different shade or color as compared to the other windows to maintain safe, non-glaring conditions during driving.
6. Chromogenic glazing should maintain a desired state of color without consuming too much battery power when the vehicle is parked for a long period of time.
Problems With Prior Art Chromogenic Glass
When a formulation for chromogenic glass is adopted, considerable thought is is given to selecting and processing the materials in order for the glass to meet a desired transmission range, durability and environmental resilience, i.e, performance over a range of temperature, typically between xe2x88x9240 to 100C, varying humidity, and solar radiation. Electrochromic (EC) devices used in automobile glazing should not drain the battery even when left parked in the darkened state. In automobile glazing the aesthetics of color choice play an important role. Automobile manufacturers currently prefer glazing colors which are xe2x80x9cneutralxe2x80x9d or xe2x80x9cwarmxe2x80x9d so that the flesh tones of the driver and passengers and the interior colors will not be cast in an unappealing light. Certain EC materials, such as those that derive their color principally from tungsten oxide, can typically color to a blue tint and maybe undesirable in some circumstances because their color change fails to meet the neutral/warm criteria. To meet the desired characteristics, such EC materials must be modified by doping so that they will color to a more neutral shade, but in doing so the coloration range may be compromised. Other compromises made in material selection may affect durability because of electrochemical changes in the material. In addition, glazing used in an automobile windshield may need to have different transmissivity and color characteristics as compared to the side or rear windows and sunroof While some chromogenic devices may be available that change to a more neutral color, they may not conform to the desired transmission range required for the various locations. The chemical modification of such materials to meet these diverse applications is a daunting task.
It is therefore an object of the present invention to accommodate the different xe2x80x9ctunabilityxe2x80x9d, xe2x80x9ctransmissivityxe2x80x9d and environmental attributes required of glazing destined for diverse applications, without entailing the time and expense required to formulate a new EC material having the desired characteristics.
The above noted problems of chromogenic glass for use in various glazing applications are solved in accordance with the principles of the present invention by providing a transparent chromogenic assembly in which color changes are selectively effectable over predefined areas of the assembly which comprises a pair of facing glass substrates separated by an electrolyte. A conductive transparent coating is deposed on facing surfaces of the substrates, the conductive coating of at least one of the surfaces being interrupted to define individual areas each of which is provided with as set of busbars, advantageously of silver frit. An electrochromic electrode layer overlies at least one of the conductive layers. An insulating adhesive sealant spaces apart the substrates and insulates the busbar sets from each other and from exposure to the electrolyte and the electrochromic layer, so that each busbar set may be individually energizeable to effect a color change through a respective one of the individual areas. Advantageously, the electrochromic layer may comprise a transition metal oxide or a mixture containing at least one transition metal oxide, preferably tungsten oxide, while a counterelectrode layer on the facing surface may comprise a mixture of at least three oxides, preferably two of which are transition metals and one of them is an alkali metal. A portion of each busbar advantageously extends from the facing surface to and over a respective edge of the substrate to form a connector for the terminal electrode that provides exceptional mechanical stability.
Further in accordance with the invention, it is important to select those attributes which allow chromogenic devices to exhibit low leakage currents, e.g., by employing inorganic EC and counterelectrodes that are selected principally from the transition metal oxides, such as tungsten oxide and vanadium oxide, respectively, and by using sulfolane or its derivatives in fall or part as the solvent and/or plasticizer in the electrolyte when a solid polymer matrix electrolyte is used. Further, the water content of the electrolyte is preferably lower than 2000 ppm, more preferably lower than 100 ppm and most preferably as low as 10 ppm.
According to another aspect of the invention, in one illustrative embodiment, a transparent chromogenic assembly is provided which comprises an active component layer and a passive component layer in which the active component layer is selected from the group consisting of electrochromic, liquid crystal, user-controllable-photochromic, polymer-dispersed-liquid crystal or suspended particle devices and the passive component layer is selected from the group consisting of substrates or covers for the active layer, the active and the passive layers being chosen so that the color and the transmissivity of the passive layer accommodates the range of color change and transmissivity of the active layer to maintain the transmitted color of the assembly in a warm or neutral shade, where warm colors correspond on the L*C*h color sphere scale to C having an approximate value between 15 and 45, preferably between 18 and 30; h having a value between 115 and 20, preferably between 40 and 100, and L having a value dictated by the desired degree of glass darkness or preferred degree of photopic transmission. A preferred counterelectrode composition consists of Li, Ni and Mn oxides to facilitate obtaining the desired color change as an intrinsic attribute of the EC device.