This invention relates to electro-optic devices for vehicles and, more particularly, to an enhanced vehicular rearview mirror or window glazing incorporating an electro-optic medium allowing variation in the transmission of light in response to application of an electric field to the electro-optic medium.
Specifically, in one aspect, the invention is a variable reflectance, electro-optic mirror including protection against laceration injuries and scattering of glass or other fragments if broken or damaged, against degradation from ultraviolet radiation, and against fogging and misting in high humidity conditions.
This invention also relates to glazing in vehicles and, more particularly, to an enhanced vehicular window, sun visor, shade band or sunroof incorporating an electrochromic medium allowing variation in the light transmitted by the glazing in response to application of an electric field to the electrochromic medium. Specifically, the invention is a variable transmission, electrochromic vehicular window including protection against laceration injuries and scattering of glass, other fragments, or chemicals if broken or damaged, against degradation from ultraviolet radiation, and including thin film means to reflect a substantial portion of incident, solar, near-infrared radiation. Optionally, and preferably, the electrochromic glazing assembly is blue or green in transmission, as viewed from the vehicle interior, so as to reduce glare from the sun and to optimize visibility and a true-to-nature blue view of the sky.
In a collision, the glass typically used as the substrate in vehicular rearview mirrors poses potential hazards to the driver or other vehicle occupants. Since glass easily shatters into sharp, irregular fragments, there is a high likelihood of facial or other injury, typically lacerative in nature, in any collision. For this reason, prior known interior and exterior vehicular rearview mirrors, which typically consist of a single glass piece coated with reflective material, are conventionally protected by applying a tape or a plastisol-type plastic adhesive to the back surface of the glass piece. Accordingly, if impacted or broken in an accident, and shattered, glass fragments are retained by the tape or plastisol-type plastic adhesive.
More recently, however, a new generation of electro-optical mirrors has emerged which are fabricated using two pieces of glass separated by a gap or space which contains an electro-optic medium allowing variation in the light reflected by the assembly. For example, in liquid crystal rearview mirrors, the space between the transparent front and reflective coated rear glass pieces is filled with a semi-viscous liquid crystal material. In electrochemichromic or electrochromic mirrors, the gap or space contains a liquid, thickened liquid, gel or semi-solid material.
In these types of electro-optic, laminated mirror assemblies, scatterproofing of the rear glass piece is relatively easy since tape or plastisol-type plastic adhesives can be applied to its rear surface behind the reflective coating in the conventionally known manner. However, scatterproofing the front piece of glass in such a laminated assembly is difficult since the material used to fill the space between the front and rear glass pieces is usually insufficiently viscous or adhering to retain fragments of the front glass should it shatter in a collision.
Another problem encountered with electro-optic rearview mirrors and windows or glazing assemblies is degradation due to exposure to ultraviolet radiation over the life of the mirror or glazing. Ultraviolet (UV) radiation from the sun which penetrates the earth's atmosphere has a wavelength in the range between 290 and 400 nanometers (nm) and can cause breakdown in the operational characteristics of the electro-optical medium including chain scission, cross-linking and stimulation of chemical changes in the chemicals used to formulate the electro-optical medium. This interferes with electronic conjugation in the aromatic conjugated materials typically used and thus the electro-optic activity of those materials is impaired. Moreover, the medium will often discolor taking on a yellowish tint visible in light reflected or passing therethrough and drastically affect the usefulness of the rearview mirror or window. Such degradation from UV solar radiation is particularly problematic in electro-optical automotive windows which are typically exposed to the full solar radiation, often when the electro-optical medium is in its colored state.
In order to overcome ultraviolet radiation degradation in such electro-optic rearview mirrors and glazings, it is possible to add UV radiation absorbing materials to the electro-optic medium. However, such UV absorbing additives, especially in higher concentrations and with broad UV absorbance, themselves impart a yellowish tint to the materials to which they are added. Such yellow tint is also visible in light reflected or transmitted therethrough. Yellow is aesthetically displeasing in many applications, and is particularly displeasing when used in rearview mirrors. Consumer acceptance of rearview mirrors having a yellowish tint or cast in the reflected light has been poor. Moreover, yellow mirrors are efficient reflectors of headlamp glare which itself is yellow. Consequently, prolonged exposure to sunlight and UV radiation, or reducing UV degradation in electro-optic mirrors with UV absorbing additives, can create negative consumer reaction and acceptance. Likewise, a yellow tint in, for example, an automotive sunroof is consumer displeasing as it detracts from the consumer's appreciation of, and natural view of, the blue sky.
Another objective in the use of rearview mirrors is the matching of human sight sensitivity in various light conditions during the use of such mirrors to the glare sources and ambient lighting present. It is known that the spectral sensitivity of the human eye depends on its light adaptation. Thus, daylight and night driving conditions create differing human eye sensitivities. Further, nearly all night driving is affected by the reflection of light from the headlights of the driver's own vehicle on the road. The electro-optic mirror assemblies of this invention should, therefore, optimally be constructed to correspond as much as possible with the eye sensitivities in both day and night driving conditions.
The electro-optic media commonly used in electro-optic mirrors and windows are often constituted of materials and chemicals of a potential toxic or otherwise hazardous nature. Should the mirror glass break in an accident, there is a possibility of automobile occupants contacting the electro-optic media, either directly or by contact with glass particles to which these potentially hazardous media are still adhering. Such contact presents a hazard to the occupants through toxic effects, and through skin irritation such as to eyes and facial areas. The anti-lacerative layers and laminate interlayers of this invention offer a barrier that ensures that contact with chemicals used within the mirror is minimized should the glass shatter in an accident.
Yet another problem is unwanted misting or fogging of the rearview mirror surface or the glazing surface when the vehicle encounters high humidity conditions. For example, in damp, cold conditions where the interior passenger compartment of a vehicle has a highly humid atmosphere, water droplets may tend to condense on the rearview mirror surface or window surface thereby obscuring vision in the mirror or through the window. Not only does such condensation prevent effective use of the mirror or window, but also requires frequent wiping by the vehicle driver which distracts his attention from driving.
Vehicular windows provide a field of view so that the driver can make safe driving decisions and allow occupants to comfortably view the surroundings. Glass vehicular sunroofs are luxury items that serve both aesthetic and functional needs. A transparent sunroof is primarily consumer-selected so that the occupants feel less claustrophobic and more linked to the outside environment. Sunroofs have a functional benefit in that, when opened, they can greatly increase cabin ventilation and so substitute somewhat for air-conditioning.
As reviewed in the publication SMART WINDOWS FOR AUTOMOBILES by Niall R. Lynam, SAE paper #900419, Society of Automotive Engineers, International Congress and Exposition, Detroit, Mich., Feb. 16-Mar. 2, 1990, the disclosure of which is hereby incorporated by reference, increases in the area of windows used in automobiles coupled with down-sizing of vehicular air-conditioners and environmental concerns associated with use of halocarbons in air-conditioners, have led to an increased need to use solar heat-load reducing glazing in vehicles. Since solar energy (for solar mass 2) is, on the average, 3% ultraviolet (UV), 48% visible radiation, and 49% near-infrared (NIR) radiation, nearly one-half of the solar energy can be eliminated without any loss in visibility.
Solar-energy reducing glazing is already in use on automobile windows and is based on two principles: modification of the glass composition to increase the infrared absorption; and deposition of single and multilayer coatings to reflect or absorb infrared radiation. In a vehicle, the glazing need not be concerned with heat insulative properties such as are required for solar efficient windows in buildings and homes. Building solar windows allow as much of the solar spectrum as is possible to transmit into the room but also trap this solar energy by acting as a heat mirror for energy radiated from walls, floors, furniture, etc.
With respect to a vehicle, heat built up when parked or driven in sunny climates is the principal concern. Thus, the solar glazing used in vehicles should, ideally, reflect away all of the incident near-IR solar radiation above around 800 nm since visible light is between about 400 and 800 nm. Even with such reflection, however, the approximate 50% of solar energy contained in the UV/visible spectral region, if transmitted, can contribute to heat buildup within the vehicular cabin.
Chromogenic materials have been suggested for providing electrically variable control over solar transmission in automobile windows. SAE paper #900419 discloses a variety of possible designs and constructions, among them being designs using liquid crystal or electrochromic materials. Liquid crystal designs, and particularly those that operate by scattering light rather than by absorbing/reflecting light, however, yield only moderate solar energy benefit when used in automobile glazing. Electrochromic windows, because they do not operate by a light scattering mechanism, are preferred for use in variable transmission solar-efficient automobile window glazing.
A wide variety of infrared attenuating means including those that operate principally by reflecting varying amounts of the near-IR region, or by absorption, also have been disclosed in the prior art. Some have been used in association with variable transmission liquid crystal panels. For example, U.S. Pat. No. 4,749,261 to McLaughlin et al. describes a liquid crystal material operable to modulate light transmitted through a panel such as a sunroof, window, or partition. The liquid crystal material selectively operates to transmit or to scatter light.
McLaughlin et al. describe an embodiment which includes an infrared light reflective material which may take the form of a stainless steel or tin oxide, optically transparent, infrared reflecting, and electrically conductive coating that preferentially reflects infrared light while allowing visible radiation to pass. McLaughlin et al., however, fail to explicitly distinguish to which portion of the infrared spectrum (i.e., near-IR between 800 nm and 2500 nm or IR above 2500 nm) their invention is directed, and fail to combine that revelation with an electrochromic medium. Other references have failed to distinguish the particular needs of vehicular variable transmission glazing from variable transmission glazing usable as building windows and the like.
Accordingly, a need is apparent for a laminate electro-optic vehicular rearview mirror and glazing assembly which can be effectively scatterproofed to retain glass fragments from both glass pieces in the assembly, protected against lacerative-type injuries, protected against ultraviolet radiation damage throughout its life, and protected against annoying fogging and misting of the interior cabin surface in high humidity conditions. In addition, there is a related need for electro-optic rearview mirror assemblies which provide reflected light of a commercially and consumer acceptable color or tint and which match human sight sensitivity in both day and night conditions to the glare sources and ambient lighting present.
In addition, a further need is apparent for a combination near-infrared attenuating/electrochromic window which maximizes solar attenuation performance while allowing maximum variability of visible light. There is also a related need for a vehicular window which combines an electrochromic medium which attenuates visible light by absorbance and/or reflection with an efficient near-infrared reflector and an ultraviolet reducing means. Further, there is a related need for a solar attenuating window which can be effectively scatterproofed to retain glass fragments from the glass pieces in the window, protected against lacerative-type injuries, protected against leakage of chemicals, protected against ultraviolet radiation damage throughout its life, and protected against annoying fogging and misting of its surface in high humidity conditions.