Anti-scatter ultraviolet protected, anti-misting, electro-optical rearview mirror

Abstract: A reduced ultraviolet radiation transmitting, electro-optic rearview mirror assembly (85) comprises first and second spaced, optically transparent elements (12, 16) mounted in a mirror case, said elements each having front and rear surfaces (13, 17) respectively and defining a space (18) between the rear surface (13) of said first element and the front surface (17) of said second element (16). An electro-optic medium (20) whose light transmittance is variable upon the application of an electric field thereto, is confined in the space (18) and means (22, 24) is provided for applying an electric field to said electro-optic medium to cause variation in the light transmittance of said medium (20). A reflective coating (26) is provided on one surface (25) of said second element (16) to reflect light incident thereon through said first element and said electro-optic medium. An ultraviolet radiation reducing means (12 d , 12 e ) is incorporated in said assembly (85) for reducing ultraviolet radiation degradation of said electro-optic medium (20) in said assembly.

Description: This invention relates to a rearview mirror for vehicles, in particular rearview mirrors of the kind incorporating an electro-optic medium. Electro-optical rearview mirrors are fabricated using two pieces of glass separated by a 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 space contains a liquid, thickened liquid, gel or semi-solid material. A problem encountered with electro-optical rearview mirrors is degradation due to exposure of the electro-optic medium to ultraviolet radiation over the life of the mirror. Ultraviolet (UV) radiation from the sun which penetrates the earth's atmosphere has a wavelength of between 290 and 400 nanometers (nm) and can cause breakdown in the operational characteristics of the electro-optic medium including chain scission, cross-linking and stimulation of chemical changes in the chemicals used to formulate the electro-optic 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 discolour, taking on a yellowish tint visible in light reflected therethrough and drastically affecting the usefulness of the rearview mirror. This is a particular problem for exterior rearview mirrors which have greatest exposure to UV radiation from the sun. Although some attempts have been made to provide UV protection for electro-optic mirrors by providing a UV absorbing material on the front face of the mirror, see for example GB-A-2,205,075 and EP-A-0,146,672 which correspond to the pre-characterising part of claim 1, these have been commercially unsuccessful. EP-A-0,240,226 describes a typical prior art electro-optic rearview mirror using an electrochemichromic medium as the electro-optic medium. However, this does not address the problem of UV degradation, and is not practical for use as an exterior mirror. It is therefore an object of the invention to provide an electro-optical rearview mirror with improved resistance to degradation by UV light. This object is achieved by the invention claimed in of claim 1. The invention is based upon the discovery that substantially improved resistance to degradation by UV can be obtained by using, as the electro-optic medium, a solution in an organic solvent of anodic and cathodic electrochemichromic compounds and an ultraviolet absorber, and that such a combination can be made stable to exposure to natural weathering, to enable the construction of a rearview mirror which may be successfully used on the outside of a vehicle. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a sectional side elevation of a scatter protected, anti-lacerative, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 2 is a sectional side elevation of a scatter protected, anti-lacerative and ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 3 is a graph showing percent transmission of electromagnetic radiation of wavelengths between 230 and 500 nanometers through a two millimeter glass sheet coated with indium tin oxide on one surface and having a sheet of polyvinylbutyral/polyester composite adhered to its opposite surface; Fig. 4 is a graph of the percent transmission of electromagnetic radiation of wavelengths between 230 and 500 nanometers through a two millimeter glass sheet coated only on one surface with indium tin oxide; Fig. 5 is a second embodiment of the scatter protected, anti-lacerative and ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 6 is a third embodiment of the scatter protected, anti-lacerative and ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 7 is a fourth embodiment of the scatter protected, anti-lacerative and ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 8 is an ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 9 is a second embodiment of an ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 10 is a scatter protected, anti-lacerative, anti-fogging, laminate, electro-optic rearview mirror assembly; Fig. 11 is a graph showing percent transmission of electromagnetic radiation through a one millimeter glass sheet coated with indium tin oxide on one surface and a coating of clear acrylic including Cyasorb™ UV radiation reducing compounds on its opposite surface; Fig. 12 is a graph showing percent transmission of electromagnetic radiation through a one millimeter glass sheet coated with indium tin oxide on one surface and a coating of clear acrylic on its opposite surface; Fig. 13 is a graph showing percent transmission of electromagnetic radiation through a one millimeter glass sheet coated with indium tin oxide on one surface and clear UV protecting lacquer on its opposite surface; Fig. 14 is a fifth embodiment of the scatter protected, anti-lacerative and ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 15 is a third embodiment of an ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 16 is a sixth embodiment of the scatter protected, anti-lacerative, ultraviolet radiation protected, laminate, electro-optic rearview mirror assembly of the present invention; Fig. 17 is a graph showing the solar spectrum in the ultraviolet region incident at a desert location such as Tucson, Arizona; Figs. 18a and 18b are graphs showing the percent light transmission of .063 inch thick, standard, clear, soda lime glass in the ultraviolet and visible regions of the spectrum, respectively; Fig. 19 is a graph showing the solar radiation in the ultraviolet region transmitted by 0.63 inch thick, standard, clear, soda lime glass; Fig. 20 is a graph showing the percent light transmission of specific solutions of four cathodic electrochemichromic compounds including methylviologen (MV), ethylviologen (EV), benzylviologen (BV) and heptylviologen (HV) in the ultraviolet region of the spectrum; Fig. 21 is a graph showing the percent light transmission of specific solutions of four anodic electrochemichromic compounds including dimethyldihydrophenazine (DMPA), diethyldihydrophenazine (DEPA), tetramethylphenylenediamine (TMPD), and tetratetramethylbenzidine (TMBZ) as well as thiafulvalene in the ultraviolet region of the spectrum; Figs. 22a and 22b are graphs showing the percent light transmission of Solextra 7010™ blue tinted specialized glass in the ultraviolet and visible regions of the spectrum, respectively; Figs. 23a and 23b are graphs showing the percent light transmission of Sunglas™ Blue blue tinted specialized glass in the ultraviolet and visible regions of the spectrum, respectively; Fig. 24 is a graph showing the relative spectral power of Standard Illuminant Sources A and C as well as the main color bands of the visible spectrum; Fig. 25 is a graph showing the dark/scotopic and bright/photopic sensitivity of the human eye superimposed on the spectral output of a tungsten lamp used as Standard Illuminant A; Figs. 26a and 26b are graphs showing the percent light transmission of Sunglas™ Green green tinted specialized glass in the ultraviolet and visible regions of the spectrum, respectively; Figs. 27a and 27b are graphs showing the percent light transmission of a pair of clear soda lime glass panels laminated together by Saflex™ SR#11 polyvinylbutyral sheeting in the ultraviolet and visible regions of the spectrum, respectively; Figs. 28a and 28b are graphs showing the percent light transmission of Butacite™ Cobalt Blue polymeric interlayer sheeting laminated between two clear soda lime glass panels in the ultraviolet and visible regions of the spectrum, respectively; Figs. 29a and 29b are graphs showing the percent light transmission of a pair of clear soda lime glass panels laminated by Saflex™ Blue Green 377300 polyvinylbutyral sheeting in the ultraviolet and visible regions of the spectrum, respectively; Fig. 30 shows the percent light transmission of conventional clear soda lime glass coated with UV absorbing PC-60 lacquer; Fig. 31 is a graph showing the percent light transmission of clear soda lime glass having a UV absorbing coating of ZLI-2456 lacquer; Fig. 32 is a graph showing the percent light transmission of clear soda lime glass coated with a sheet of Scotchtint™ SH2CLX clear polymeric film; Fig. 33 is a graph showing the percent light transmission of a 35 micron thickness coating of Norland 65 ultraviolet cured epoxy adhesive on clear soda lime glass; Fig. 34 is a graph showing the percent light transmission of a 500 microns thick coating of a cured mixture of 15% EPON 828™, 35% Heloxy MK107™ and 50% Capcure 3-800™ on clear soda lime glass; and Figs. 35a and 35b are graphs showing the percent light transmission of a pair of clear soda lime glass panels laminated together by Butacite™ 14 NC-10 polyvinylbutyral sheeting in the ultraviolet and visible regions of the spectrum, respectively. Referring now to the drawings in greater detail, Fig. 1 illustrates a laminate, electro-optic rearview mirror assembly 10 having a front element 12 which is scatter and anti-lacerative protected with a resinous, polymeric or other coated or applied layer 14 on its first or front surface 11. Element 12 is preferably formed from a generally planar sheet of conventional soda lime window glass as is second glass element 16 which is spaced slightly rearwardly from front glass piece 12 to define a gap or space 18 for receiving an electro-optic medium 20 as explained below. As explained hereinafter, elements 12, 16 may also be resinous, polymeric sheets to further prevent fragment scattering and lacerative injuries if broken and to reduce weight. Space 18 is formed between the generally parallel rear surface 13 of front glass element 12 and forward facing surface 17 of rear glass element 16. Preferably, each of the front and rear surfaces 13, 17 is coated with a layer of indium tin oxide (ITO) which is substantially transparent to incident visible light yet is sufficiently electrically conductive to enable application of an electric field or voltage across space 18 between ITO layers 13a, 17a. Electrical energy is provided by wire leads 22, 24 secured in conventional manner to the upper portions of ITO coatings 13a, 17a as shown in Fig. 1. The rear surface 25 of rear glass element 16 is coated with a reflective layer 26 preferably of metallic material such as aluminum, or a combination of silver and copper as is conventionally known. Such layer provides a highly specular surface which reflects approximately 80-90% of the light incident thereon through layer 14, front and rear glass elements 12, 16 and electro-optic medium 20 in space 18. In order to prevent scattering of glass fragments from the rear glass element 16 in the event of breakage or damage during a collision in the vehicle, a layer 28 of tape or a plastisol-type plastic adhesive, typically about 0.1 millimeters thick, is applied to the rear surface of reflective coating 26. Anti-scattering layer 28 may be opaque, translucent or transparent since it is behind reflective coating 26 and need not transmit or reflect any light. In order to confine and retain the electro-optic medium in gap 18, a peripheral seal 29, formed from an epoxy material which adheres well to the ITO coatings 13a, 17a on glass surfaces 13, 17 is applied adjacent the periphery of glass elements 12, 16. A suitable epoxy sealing material is EPON 828™ from Shell Chemical Company of Houston, Texas cured by polyamide based curing agents such as V-40™ from Miller Stephenson Company of Danbury, Connecticut. The epoxy is preferably silk screened onto the inner surface of the front glass element 12 or the back glass element 16 or onto both glass elements. The corresponding glass element is then placed face to face with the still tacky epoxy. Seal 29 is then fully cured, typically by placing the assembly into an oven at 110 C. for three hours. Gap 18 can then be filled by a variety of means such as simple injection of electro-optically active material using a syringe or by vacuum backfilling using a technique well established for manufacture of liquid crystal devices. Assembly 10 is preferably incorporated in a molded thermoplastic or other mirror case 30 of conventional form. Typically, glass elements 12, 16 will each be two millimeters in thickness while ITO coatings 13a, 17a will have a typical thickness of 1,500 angstroms. Reflective coating 26 may have a thickness within the range of between about 500 and 1,000 angstroms. For electrochemichromic mirrors, the gap 18 contains a liquid, thickened liquid, gel or semi-solid material such as formulations described in U.S. Patent No. 3,806,229 to Schoot. The gap or space 18 is typically 50 to 100 microns. Application of an electric field will cause the medium 20 to color to successively darker colors or shades as larger voltages are applied. When voltage is turned off or reversed, the coloring is bleached allowing full transmittance of light and, hence, full reflectivity from reflective layer 26. Because the electro-optic media 20 such as those described above are typically of relatively low viscosity and have little or no capability of retaining or holding solid elements thereto, the scatter and anti-lacerative protection conventionally available through the use of tape or plastisol layers such as those at 28 on rear glass element 16 has been unavailable for use with the front glass element 12 because transmission of light through the glass element must be unimpeded. The present embodiment overcomes that problem by providing scatterproofing, anti-lacerative layer 14 which retains fragments should glass element 12 be shattered. Layer 14 also provides enhanced anti-lacerative protection since it remains intact upon collision, is tear and perforation resistant and thus reduces or avoids laceration injury to the skin of any person contacting the shattered or broken mirror. A specific example of a material found useful for layer 14 is reticulated polyurethane having a thickness within the range of about 0.01 to about 0.25 inches and marketed under the trade name SECURIFLEX™ by Saint-Gobain Vitrage of Paris, France. When used as layer 14, SECURIFLEX™ has excellent adhesion to glass surface 11 for retaining glass fragments during and after shattering in a collision. It also has high deformation capacity to resist tearing while continuing to form a protective screen which protects the skin of any person impacting the mirror and preventing contact with broken, jagged edges of the glass. It also has excellent optical quality, clarity and transparency so as not to detract from the rear vision capability of the rearview mirror. Further, it is abrasion and scratch resistant so that high quality clear images can be obtained in the mirror throughout its life. It is also relatively inert and resistant to environmental variation such as high and low temperatures, high and low humidity conditions. Use of an anti-lacerative layer 14 also affords another advantage. It is known that several electro-optic mirror devices developed in recent years have generally poor ultraviolet radiation stability. When exposed to prolonged ultraviolet radiation from sunlight, such electro-optic assemblies may suffer substantial degradation of their electro-optic media resulting in poor electrical coloration responsiveness including increased response time and/or failure to properly bleach when electric voltage is switched off. Permanent discoloration of the medium may also occur. This can cause substantial vision problems. An example of the ultraviolet region of the solar spectrum incident at a desert location such as Tucson, Arizona is shown in Fig. 17. Such solar spectrum must typically pass through a glass front panel of an electro-optic rearview mirror assembly to irradiate the electro-optic solution in an electro-optic rearview mirror assembly such as that shown in Fig. 1 or the other assemblies shown herein. Fig. 17 shows that there is little or no incoming solar radiation below about 295 nm. The light transmission of a 1.6 mm thick panel of standard, clear, soda lime glass is shown in Figs. 18a and 18b while the solar energy spectrum transmitted into any electro-optic medium behind such a front glass piece is the combination of the graphs in Figs. 17 and 18 as shown in Fig. 19. The 0.063 inch (1.6 mm) soda lime glass panel passes about 63% of the incoming UV solar energy in the 250-350 nm region and about 90% in the 350-400 nm region. Overall, a 1.6 mm soda lime glass sheet passes about 83% of the incident solar energy in the 250-400 nm region. Thus, a substantial portion of the incoming solar UV radiation is unattenuated by the glass front panel. When such solar radiation passes into the electro-optic medium therebehind it irradiates the electro-optic species. Electrochemichromic (ECC) materials, especially organic species, are particularly susceptible to degradation by UV radiation. This is caused by their absorption of UV radiation with consequent disruption of electronic states. As shown in the graph of Fig. 20, the cathodically coloring ECC species most commonly used in prior art literature such as methylviologen (MV), ethylviologen (EV), benzylviologen (BV), and heptylviologen (HV), have an absorption peak below 295 nm and, thus, are largely nonabsorbing to the solar UV radiation transmitted into an ECC cell. However, as shown in Fig. 21, anodic compounds, such as dimethyldihydrophenazine (DMPA), diethyldihydrophenazine (DEPA), tetramethylphenylenediamine (TMPD), and tetratetramethylbenzidine (TMBZ) as well as thiafulvalene have substantial UV radiation absorbance in the 250-400 nm region. For example, DMPA in 0.0002M solution in acetonitrile (AN) and in a 1 mm pathlength quartz cell absorbs about 22% of the UV solar energy spectrum in the 250-350 nm region. Therefore, it is desirable to shield the ECC compounds from UV irradiation in this region. Also, because some absorption continues up to about 400 nm or so, and since the solar energy transmitted into the cell as shown in Fig. 19 is also substantial in the 350-400 nm region, it is beneficial to protect the ECC compounds from irradiation in this region as well. The use of ultraviolet radiation absorbing, blocking or screening materials, either incorporated in the anti-lacerative layer or in layers in addition to such layer, will reduce ultraviolet radiation impinging on the mirror assembly and the electro-optic media and significantly prolong its lifetime. It is also recognized that substantial reduction in the amount of UV radiation transmitted into the electro-optic medium of the assembly may be accomplished by using specialized glasses, paints/lacquers, and laminate interlayers, coatings and/or films while simultaneously and synergistically protecting a vehicle driver against laceration or injury due to scattering or breaking of glass fragments should the protected mirror assembly be struck in an accident. As shown in Fig. 2, an enhanced, laminate, electro-optic rearview mirror assembly 35 with increased ultraviolet radiation resistance and stabilization is shown. As with subsequent embodiments of the invention explained below, assembly 35 is similar to the mirror assembly 10 of Fig. 1 but includes a different scatter protecting, anti-lacerative, UV radiation reducing layer 36 on the front surface of glass element 12. Layer 36 is preferably of two-ply construction comprising a laminate of polyvinylbutyral and polyester commercially available from E. I. DuPont de Nemours and Company under Product No. DuPont BE1028D and also has the same qualities as described for polyurethane layer 14. The outer ply or layer 40 is abrasion resistant, weather resistant, polyester while the inner ply or layer 38 is resilient, tear resistant polyvinylbutyral. Composite layer 36 has a thickness preferably between about 0.005 and 0.25 inches, and provides a solution to two problems found during commercialization of prior known laminate electro-optic, and especially electrochromic mirrors, i.e., difficulty in scatter protecting the front glass element 12 and protection against degradation of the electrochromic media 20 in space 18 throughout the lifetime of the assembly due to inherent ultraviolet radiation instability and sensitivity. The polyester/polyvinylbutyral composite layer 36 is a particularly good filter for ultraviolet radiation as shown in Figs. 3 and 4. Fig. 3 is a graph of the percent transmission of electromagnetic radiation through a two millimeter thick element of conventional soda lime window glass coated with a layer of indium tin oxide (ITO) on one surface and a layer of DuPont BE1028D polyvinylbutyral/polyester composite on the opposite surface. The graph shows the transmission over the wavelength spectrum between 230 and 500 nanometers (nm) and illustrates that below about 350-360 nm, wavelength transmission is cut off or stopped. Ultraviolet radiation which penetrates the earth's atmosphere from the sun typically ranges in wavelength over a wide band of between about 290 and 400 nanometers (nm). In contrast, light sensitive to the human eye ranges from about 400 nm to about 700 nm. Hence, the composite polyvinylbutyral/ polyester layer 36 substantially eliminates ultraviolet radiation below about 350 nm while simultaneously scatter protecting and protecting against laceration when applied to the mirror glass surface. Compare the graph in Fig. 3 to that in Fig. 4 which illustrates a two millimeter glass element coated only on one surface with indium tin oxide and not including a polyvinylbutyral/polyester layer. Such ITO coated glass transmits light in the visible wavelength spectrum above about 400 nanometers but also allows transmission of ultraviolet wavelengths down to about 295 nm which is substantially farther into the UV region than with the coated glass having the two-ply composite layer 36 thereon as shown in Fig. 3. Hence, reduction of UV radiation intensity passing through front glass 12 of such laminate mirrors as in assembly 35 substantially increases the useful lifetime of the mirror assembly. A specific example of an assembly such as that shown at 35 comprising a laminate electrochromic mirror and providing the anti-lacerative, anti-scatter, UV radiation reducing advantages of the present invention was fabricated consisting of two plates of ITO coated, conventional soda lime window glass separated by a gap of 50 microns. The space between the two glass elements was filled with an electrochromic solution consisting of N,N,N′,N′ tetramethyl-1,4-phenylenediamine 0.025M, 1,1′-diheptyl-4,4′-bipyridinium dibromide 0.025M and tetrabutylammonium fluoroborate 0.5M dissolved in propylene carbonate. The nonmirrored front glass piece was anti-lacerative protected with a DuPont BE1028D two-ply, anti-lacerative layer consisting of an outer abrasion resistant layer of polyester and an inner layer of polyvinylbutyral as described above in connection with Fig. 2. Reflective coated, rear glass plate 16 was scatter protected on its rear surface using conventional tape. The assembly was shattered by dropping a one kg weight over a distance of one meter to impinge on the front nonmirrored glass element, the anti-lacerative layer retained glass fragments from the front glass and remained unperforated such that it would have provided anti-lacerative protection if struck by a person in an accident. Moreover, when this laminate electrochemichromic mirror assembly was placed under UV lamps in a sunlight simulator, electrochemichromic activity and general mirror performance was maintained for a period of some five (5) times longer than that obtained using a control sample which was similarly tested with UV radiation but was not anti-laceratively protected with a polyester/polyvinylbutyral layer. Although the anti-scattering, anti-lacerative layer 14 of assembly 10 in Fig. 1 provides some ultraviolet radiation reduction protection, and is itself ultraviolet radiation stable, the polyvinylbutyral/polyester composite is preferred since the polyvinylbutyral ply or layer has significantly higher UV radiation reduction capability as well as inherent UV stability than does polyurethane. Longer lifetimes for laminate electro-optic rearview mirror assemblies can be achieved by using ultraviolet radiation absorbing, blocking or screening materials added to or incorporated with the anti-scatter, anti-lacerative layers 14, 36 as shown in Figs. 1 and 2. Most commercial polymers absorb ultraviolet radiation because they possess chromophoric groups either as regular constituents or as impurities. Only those chromophores which absorb electromagnetic radiation of a wavelenght below about 400 nanometers are, therefore, effective screens against UV radiation. Polycarbonate, polyester and aromatic polyurethanes contain such chromophores as a major part of their structures. However, polyolefins contain only relatively insignificant amounts of these chromophores as impurities. Yet, these above materials do not absorb UV radiation uniformly over the entire UV range. The chromophores which do absorb UV radiation can be conjugated structures, carbonyl groups, aromatic repeat units and heterocyclic repeat units. In addition, if polymers are used as UV screeners, they themselves must be stabilized against UV radiation since UV absorption generates free radicals which lead to chain scission and cross-linking and creation of other structures in these polymers. Thus, UV radiation itself degrades the polymer material which is intended to provide a UV absorber, block or screen by making the polymer brittle and even imparting color in the visible region. The addition of UV absorbing, blocking or screening additives to polymers such as the polyurethane and/or polyvinylbutyral/polyester composite layers 14, 36 makes these materials more efficient UV screeners and preserves their properties over a longer period of time. Such UV additives, known as stabilizers, are transparent in the visible region and work to absorb UV radiation, quench the free radicals which are generated in the polymer and prevent oxidation reactions which lead to polymer degradation. For example, UV stabilizing additives drawn from benzophenones, cinnamic acid derivatives, esters of benzoin acids, salicylic acid, terephthalic and isophthalic acids with resorcinol and phenols, pentamethyl piperidine derivatives, salicylates, benzotriazoles, cyanoacrylates, benzilidenes, malonates and oxalanilides are effective to block UV radiation and stabilize the polymer layer when impregnated in such layer, included in separate coatings in addition to such layer or incorporated directly in front element 12 such as when it is cast from plastic. Other additives may be combined with the above materials such as nickel chelates and/or hindered amines. The following table shows several combinations of commercially available polymers and UV additives which may be used: Polymer Stabilizer Polyolefins 2-hydroxy-4-octoxybenzophenones nickel chelates hindered amines Styrenics hindered amines 2-hydroxyphenylbenzotriazole PVC benzotriazoles benzophenones acrylonitriles Unsaturated Polyesters 2-hydroxybenzotriazole benzophenone Polyurethanes benzotriazole pentamethyl piperidine derivatives Polycarbonate 2-hydroxy-phenylbenzotriazole Polyamides tetramethyl piperidyl sebacate Acrylic 2-hydroxyphenylbenzotriazole In many instances, two or more of such additives are combined together for increased, synergistic effects in UV radiation reduction and stabilization. UV stabilizers/blockers/filters/absorbers are incorporated directly into the polymer anti-lacerative layer(s) 14, 36 in a variety of ways. For polyvinylbutyral, UV blocking additives are compounded with the PVB resin. Alternately, the UV blockers are dissolved in plasticizers which are then used to plasticize the PVB. PVB can also be dissolved in a suitable solvent, with UV stabilizers next added to the PVB solution and a UV stabilized PVB film/sheet can be cast from this solution. UV blockers can also be incorporated into polyester either through compounding or by solvent casting. Polyurethane anti-lacerative sheeting is a thermoset usually formed from reaction of isocyanate and polyols. Since both of these starting materials are liquids, UV blockers/stabilizers/filters/absorbers can be added to either the isocyanate component or the polyol component or to both. Concentrations of the various additives for combination with the various polymers are conventionally known such as are disclosed in U.S. Patent No. 4,657,769 to Musil et al. As an alternative, UV blockers, filters or screens, or absorbers may be coated directly onto the front element 12, preferably on the first surface 11, regardless of whether it is glass or plastic (see Fig. 9). A clear transparent coating packed with UV blockers/filters/ absorbers may be cast, spun, dipped, brushed, painted or sprayed onto glass surfaces through which UV radiation must pass before reaching the electro-optically active medium. A suitable solution can be made by dissolving a clear thermoplastic acrylic, polystyrene, NAS (70% polystyrene; 30% acrylic copolymer), polycarbonate, TPX (polymethylpentene), or SAN (styrene acrylonitrile copolymer) in a suitable solvent such as acetone, ethyl acetate, acetonitrile, tetrahydrofuran or any other common volatile solvent. To this, UV blockers are added such as Cyasorb™ UV1084 or UV5411, available from American Cyanamid of Stamford, Connecticut, or any suitable material drawn from known UV blockers up to concentrations close to their solubility limit. Cyasorb™ UV5411 is a benzotriazole while Cyasorb™ UV1084 is an organo-nickel complex or nickel chelate. The solution so constituted can then be cast, spun, sprayed, brushed, painted or dipped onto, for instance, the outer surface of front glass element 12 followed by application of anti-lacerative layer 14 or 36 either with or without UV reducing additives as described above. For example, a 2.5% weight/volume casting solution was prepared by dissolving commercial acrylic sheeting in a 50:50 mixture of acetone and toluene. To 100 mls of this acrylic solution, 1.6 g of Cyasorb™ UV1084 and 1.89 g of Cyasorb™ UV5411 were added. When cast onto a piece of one mm thick ITO coated glass in a thickness of about eight microns, the acrylic was UV stabilized and yielded the transmission spectrum shown in Fig. 11. Transmission through such coated glass in the region from about 280 nm to about 350 nm was markedly reduced compared to similar transmission spectra generated when only a 2.5% non-UV stabilized acrylic solution was cast onto ITO coated glass (Fig. 12) or when no acrylic was cast and a spectrum of ITO coated glass itself was generated (Fig. 4). In spite of low UV transmission, the UV stabilized cast acrylic coating was highly transparent in the visible portion of the electromagnetic spectrum. Alternatively, UV stabilizers/blockers/filters/absorbers can be incorporated into the polysiloxane solutions, such as Dow Corning ARC™ coatings, available from Dow Corning Inc. of Midland, Michigan. These are commonly available to impart a transparent anti-abrasion coating onto optical plastics which can be used for front element 12 to further reduce fragment scattering and laceration-type injuries. Alternately, UV stabilizers/absorbers/blockers/filters can be added to thermosetting optical plastics such as CR-39™ (allyl diglycol carbonate) or optical nylons or polysulfones. With thermosetting materials such as CR-39™ optical plastic, available from PPG Industries, Inc. of Pittsburgh, Pennsylvania, the UV absorbing, blocking or screening additive is incorporated in the initial plastic components and cast onto the front surface of front element 12 prior to assembly followed by suitable curing in the conventionally known manner. If a UV absorbing/blocking/screening material such as CR-39™ above is cast as a separate sheet, it may then be mounted on and adhered to front surface 11 of a clear plastic front element 12 with an adhesive bonding substance such as Versilok™ acrylics available from Lord Corporation of Erie, Pennsylvania. In such case a UV reducing additive such as benzotriazoles or hindered amines can also be incorporated directly in the adhesive bonding agent. Alternately, the sheet may be press laminated to the surface under increased pressure and modest heat. As an alternative to adding the UV reducing additive materials to the scatter preventing, anti-lacerative layers 14, 36 or other polymers, or as coatings in combination with such anti-lacerative layers, or as coatings in combination with the addition of the above mentioned types of additives to such layers, other materials may be used to decrease the ultraviolet radiation passing through the front element 12 to the interior of the mirror assemblies as shown in Figs. 5-10. In Fig. 5, where like numerals indicate like parts to those described above, a laminate, electro-optic rearview mirror assembly 45 has front glass 12 replaced with a laminate glass assembly comprised of a front glass element 12a having parallel front and rear surfaces adhered to an intermediate glass element 12b also having parallel surfaces by an interlayer 12c of polyvinylbutyral (PVB). Layer 12c is adhered to the rear surface of glass element 12a and the front surface of glass element 12b by heat and pressure lamination such as with the conventionally known autoclave method or the like. Glass elements 12a, 12b may be conventional soda lime window glass. The rear surface of glass element 12b is coated with indium tin oxide layer 13 which is, in turn, sealed with the front ITO coated surface of rear glass element 16 by seal 29 to provide the space 18. A scatter preventing, anti-lacerative, ultraviolet radiation reducing layer such as that shown above at 14 or 36 may be adhered to the front surface of front glass element 12a by suitable adhesives, heat, pressure or curing to provide the additional advantages noted above. However, the laminate glass assembly of assembly 45 inherently affords extra safety advantages by contributing to the reduction of ultraviolet radiation transmission into the assembly and providing greater shatter resistant strength for the assembly while providing scatter protection due to the use of the PVB layer 12c together with the anti-lacerative protection of layers 14 or 36. With reference to Figs. 6 and 7, where like numerals indicate like parts, it is also possible to incorporate sheet polarizers in the mirror assembly to further prevent ultraviolet radiation transmission into the assembly. In Fig. 6, a laminate electro-optic rearview mirror assembly 50 includes a layer of light polarizing sheet material 52 applied to the front surface 11 of front glass element 12 prior to adherence of the anti-scatter, anti-lacerative layer 14 or 36 mentioned above. A suitable H-sheet polarizer material is that sold under Product No. HN-38 by Polaroid Corporation of Cambridge, Massachusetts. Such sheet polarizers act to block and screen out ultraviolet radiation below wavelengths of about 380 nm. Alternately, a sheet polarizer material 57 like that above may be incorporated in the laminate electro-optic rearview mirror assembly 55 of Fig. 7 where it is laminated and adhered as an interlayer between the front and rear surfaces of intermediate and front glass elements 12b′ and 12a′ to provide a glass laminate assembly. That glass assembly is substituted for front glass element 12 just as assembly 45 of Fig. 5. As with assembly 45, mirror assembly 55 has increased mechanical strength due to the laminate construction of the front glass panel, may incorporate scatter preventing, anti-lacerative layers 14 or 36 on the front surface of the front glass element 12a′ for safety purposes, and reduces UV radiation transmitted into the assembly due to the UV absorbing and blocking function of the sheet polarizer layer 57 and any layer 14 or 36 to increase the lifetime of the assembly. In Fig. 8, where like numerals indicate like parts to those described above, mirror assembly 60 includes a front glass element 62 formed from one of several types of specialized glass rather than conventional soda lime window glass. For example, front glass element 62 may have a higher iron oxide content of within the range of about 0.2% to 0.9% by weight thereby increasing the ultraviolet radiation absorption, blockage and/or screening effect. Similar improvement can be obtained using higher cerium oxide content of 0.2% to 0.9% by weight concentration. Other specialized glasses which have high visible transmission but are strong absorbers in the ultraviolet electromagnetic region can be used including NOVIOL glasses as described in "Spectral-Transmissive Properties and Use of Eye-Protecting Glasses" by R. Stair in National Bureau of Standards Circular 471 (1948). A two millimeter thick sheet of NOVIOL 0 CG306 (National Bureau of Standards Circular, 471 (1948)) transmits only about 12% of the incident ultraviolet radiation at 380 nanometers in contrast to transmission of approximately 70% of the incident ultraviolet radiation at 360 nanometers with a conventional soda lime window glass sheet. This is true even when such NOVIOL glass is coated with indium tin oxide as an electrical conductor. Conventional soda lime glass begins to screen out significant amounts of ultraviolet radiation only below about 300 nm. Other useful specialty glasses include UV-36™ glass available from Hoya Corporation of Tokyo, Japan having an average transition wavelength of about 360 nm such that it cuts off ultraviolet radiation below that wavelength. Transition wavelength is the wavelength at the midpoint of the transition interval where glass goes from being highly transmitting to visible radiation to being highly absorbing for UV radiation. Other glasses which can be used include L-1B™ also available from Hoya Corporation having an average transition wavelength of 420 nm. Other examples include CS0501, No. 0-51 available from Corning Glass Works, Corning, New York having a transmittance less than 0.5% at 334 nm and lower at shorter wavelengths but being highly transmitting in the visible electromagnetic region and FG-62™ available from Ohara Optical Glass Manufacturing Company, Ltd. of Tokyo, Japan, having a UV cutoff just slightly below 400 nm. Such ultraviolet radiation reducing glasses may be used either with or without scatter preventing, anti-lacerative, UV reducing layers 14 or 36 or the UV reducing coatings mentioned above. When used, however, the scatter preventing, anti-lacerative layers have the added advantage of significantly strengthening such glass which, in many instances, are mechanically weaker than conventional window glass. In addition such speciality glasses may be used in the laminate assemblies substituted for front element 12 as described with Figs. 5 and 7. As mentioned above, elements 12, 16 may also be cut or cast from clear plastic sheet material such as acrylic or polycarbonate and used in place of front element 62 of Fig. 8. Additives such as benzothiazoles and benzophenones may be incorporated in the plastic to reduce UV radiation transmission. Other UV reducing layers or coatings as described herein, including polymer layers 14, 36, may also be used in combination with the plastic elements. As shown in Fig. 9, wide band, ultraviolet radiation, dielectric, dichroic or reflective filter materials may also be used in conjunction with the front glass or plastic elements 12 or 62. Suitable dichroic filter or reflective materials include thin film coatings 67 which significantly reduce ultraviolet transmission. Thin film layers 67 can be applied to any glass or plastic surface ahead of the UV vulnerable electro-optic mirror medium 20 but preferably on front or first surface 11. A suitable thin film coating is the ultraviolet wide band dichroic filter available from Optical Coatings Laboratory, Inc. of Santa Rosa, California. When applied to the rear surface of front element 12 or 62 as shown in Fig. 9 in solid lines, coatings 67 are interposed between the element rear surface and ITO coating 13a. When applied to the front surface 11, however, thin film coatings 67 are interposed between the front surface and the scatter preventing, anti-lacerative layer 14 or 36 as illustrated in phantom. Thin film coatings 67 have a transmission of visible light over 80% at 550 nm with a sharply lowered transmission of about 5% at 400 nm at which level the thin films become reflecting to UV radiation. As a substitute for the thin film coatings 67, ultraviolet radiation blocking paints or lacquers can be applied to the element surfaces provided such paints or lacquers are transparent to visible light. A suitable material for layer 70 is a lacquer supplied as ZLI-2456 transparent UV protecting lacquer by E. M. Industries of Hawthorne, New York. Such lacquer substantially reduces UV radiation transmitted into the assembly and is preferably applied to front surface 11 of element 12 to avoid dissolving in medium 20. For example, the above UV protecting lacquer ZLI-2456 was coated on a one mm thick sheet of ITO conductive glass to a thickness of about 30 microns. The transmission spectrum of such coated glass is shown in Fig. 3. It has a sharp transmission cutoff below about 400 nm and greatly reduces UV radiation in the 290-400 nm region as compared to that normally transmitted by ITO coated glass (see Fig. 4). Thin film coatings or UV reducing paint or lacquer layers 67, 70 may be used with conventional soda lime window glass as front glass element 12, or with specialized UV radiation reducing or higher iron oxide containing glass, or other UV reducing elements 62 such as the plastic elements mentioned above. As shown in Fig. 10, a further embodiment 75 of the laminate electro-optic rearview mirror assembly is illustrated including a scatter preventing, anti-lacerative layer 77 similar to the polyvinylbutyral/polyester composite layer 36 described above in connection with Fig. 2 but also including silicone moieties chemically incorporated in the anti-lacerative composite. Polymer layer 77 including the silicone additive prevents condensation and/or beading up of condensed water on the coated front surface 11 of front mirror element 12, 62 in high humidity conditions thereby providing an anti-fogging, anti-misting result. A material found useful as anti-lacerative, anti-fogging layer 77 is silicone impregnated polyurethane supplied under the trade name CLARIFLEX™ by Saint-Gobain Vitrage of Paris, France. UV reducing additives such as those described above in connection with Fig. 2 may also be incorporated in the anti-lacerative, anti-fogging layer to increase the lifetime of the assembly. Alternately, front glass element 12, 62 may be fashioned from conventional soda lime glass, UV reducing specialized glasses, or polymer plastics. It is also possible to utilize thin film coatings or UV reducing paints or lacquers 67, 70 on at least one surface of front element 12, 62 when the anti-lacerative, anti-fogging layer is incorporated. In addition to the foregoing, UV radiation reducing or absorbing stabilizers are incorporated directly in the electro-optic medium 20 injected or otherwise inserted in space 18. Such absorbers are dissolved directly in the medium, e.g., an electrochemichromic liquid. The UV absorbers are selected to be compatible with the ingredients of the medium 20, such that they do not affect the electrical performance and function of the medium or oxidize or reduce in the assembly. In a further embodiment a laminate electrochemichromic mirror was fabricated as described in the above example in connection with Fig. 2 except that no anti-lacerative layer was used over front glass element 12. In addition, UV stabilizers Cyasorb™ UV1084 and Cyasorb™ UV5411 were added to the electrochemichromic active solution prior to filling into the gap 20 between front glass 12 and back glass 16. Concentration for the UV1084 was 0.6% by volume and the UV5411 was 0.6% by volume g/cc. As shown in Fig. 14, where like numerals indicate like parts to those described above, another embodiment 85 of the laminate, electro-optic rearview mirror assembly also includes a laminate glass assembly substituted for the front glass as is the case in embodiments 45 and 55 in Figs. 5 and 7 above. The front or first, laminate assembly 86 includes a front or first glass panel 12d having parallel front and rear surfaces adhered to an intermediate glass panel 12e also having parallel surfaces by an interlayer 12c of polyvinylbutyral (PVB) or another interlayer as described below. As in the prior embodiments, layer 12c is adhered to the rear surface of glass panel 12d and to the front surface of glass panel 12e by heat and pressure lamination such as with the conventionally known autoclave method or the like. In embodiment 85, however, glass panel 12d is formed from a blue tinted specialized glass which significantly reduces UV radiation transmission while maintaining high visible light transmission. The rear surface 13 of glass panel 12e is coated with an indium tin oxide layer 13a which is, in turn, sealed with the front ITO coated surface 17 of rear glass element 16 by seal 29 to provide electro-optic media receiving space 18 as in the above embodiments. Preferably, the blue tinted specialized glass 12d is formed from Solextra 7010™ blue tinted glass available from Pittsburgh Plate Glass Industries, Pittsburgh, Pennsylvania. Graphs illustrating the percent transmission of both ultraviolet and visible light for a 2.3 mm thick pane of Solextra 7010™ glass are shown in Figs. 22a and 22b. Solextra 7010™ glass is highly visibly transmitting at the 2.3 mm thickness, i.e., 83% transmission overall using a Standard Illuminant C and a photopic detector (Fig. 22b). Also, this glass appears light blue in transmission and strongly absorbs UV radiation below about 340 nm (Fig. 22a). At this thickness, Solextra 7010™ passes only about 2% of the incident solar energy in the 250-350 nm range. In the 350-400 nm region, it passes about 67% of the incident solar energy. Alternately, glass panel 12d may be formed from Sunglas™ Blue from Ford Glass Co., Detroit, Michigan. The spectral transmission for a 3 mm pane of Sunglas™ Blue is shown in Figs. 23a and 23b. This glass is highly visibly transmitting at this thickness, i.e., 72% transmission overall with Standard Illuminant C and a photopic detector (Fig. 23b), appears light blue in transmission and strongly absorbs ultraviolet radiation below about 330 nm (Fig. 23a). Such thickness of Sunglas™ Blue passes only about 11% of the incident solar energy in the 250-350 nm range and 67% of the incident solar energy in the 350-400 nm range. The above specialized glasses may also be used for second glass panel 12e or both panels 12d and 12e. Whether or not to use such specialized glass in both panels 12d and 12e is dictated by the degree of UV radiation protection desired, and by the degree of attenuation allowable in visible transmission of light that is concurrent with use of even thicker panes or multiple panes of blue tinted or similar light filtering panels. Mirror assembly 85 incorporating one or more blue glass panels provides a unique advantage. As described above, a UV radiation stabilizer is added to enhance the UV radiation stability of the electrochemichromic solution used in a rearview mirror assembly. Broad UV radiation stabilizers such as Cyasorb 24™ from American Cyanamid Company of Wayne, New Jersey, Uvinul D-50™ from BASF Wyandotte Corporation, Parsippany, New Jersey, or Tinuvin 327™ from Ciba Geigy, Hawthorne, New York, impart a yellow color to electrochromic or electrochemichromic solutions or materials, especially when they are added in high concentrations where they are most effective in protecting UV vulnerable materials. Yellow is aesthetically displeasing in many applications and is particularly displeasing when used in rearview mirrors. Also, when electrochemichromic solutions are exposed to prolonged dosages of high intensity UV radiation, such as occur during natural weathering in sunny climates, those solutions frequently turn a yellowish hue which is aesthetically displeasing to the consumer. It has been found that use of specialized blue glass, such as that described above, allows use of higher concentrations of broad UV radiation stabilizers in electrochemichromic solutions than otherwise would be consumer tolerable due to yellowing. As an example of an electrochemichromic device constructed according to Fig. 14, an electrochemichromic solution was formed from 0.025M methylviologen perchlorate, 0.025M 5,10-dihydro-5,10-dimethylphenazine, 0.025M tetraethylammonium perchlorate and 12.5% wt/vol Cyasorb 24™ UV radiation stabilizer, all dissolved in 2-acetylbutyrolactone. When filled in cavity 18 of embodiment 85 as shown in Fig. 14, cavity 18 having a 150 micron thickness and using 15 ohms/sq indium tin oxide (ITO) transparent coatings 13a, 17a and with glass panels 12d and 12e both fabricated of 1.6 mm standard, clear, soda lime glass laminated together with a commercially available, clear PVB interlayer 12c Saflex™ SR#11 from Monsanto Company of St. Louis, Missouri, at zero potential and with a silver mirror reflector such as reflective layer 26 behind the assembly, the light reflected off mirror embodiment 85 has a distinct yellow tint and measures about 80% reflectivity using Standard Illuminant A and a photopic detector. Because consumers in automobiles are accustomed and appreciative of "silvery" reflection such as is found on interior and exterior automotive mirrors of conventional design, the marked yellow tint makes use of high concentrations of broad UV radiation absorbers commercially disadvantageous. Yet, such high concentrations of UV absorbers have the advantage of affording greater UV protection and, therefore, prolong the commercial life of electrochemichromic rearview mirror devices, particularly when used on the outside of a vehicle. However, when a 2.3 mm pane of Solextra 7010™ was substituted as the first glass panel 12d, with all other factors being the same for the example of embodiment 85 as described above, the reflection as seen in the mirror reflector was no longer yellow but had a color or tint described as gun metal blue to neutral silvery. This is a much more acceptable and commercially desirable reflective color than the Yellowish tint previously obtained. Because Solextra 7010™ glass panel 12d naturally filters out yellow light thereby absorbing undesirable yellow tint, the integrated reflection at zero potential in this version of the assembly is lower than that using clear glass, i.e., about 63% reflectivity using Standard Illuminant A and a photopic detector. However, such transmission is still sufficiently high to allow successful use in vehicles, particularly as outside mirrors. Yet another advantage is obtained using embodiment 85 and the specialized glass panels 12d or 12e therein. Blue mirrors are particularly well-suited to night driving. Fig. 24 illustrates the relative spectral power output versus wavelength of a CIE Standard Illuminant A and for CIE Standard Illuminant C. Illuminant A is a Planckian radiator at 2856K and, thus, is similar to an automobile headlamp. Illuminant C provides light similar to average daylight. Also included on Fig. 24 are the wavelengths of light which form the main bands of color in the visible spectrum. By day, rearview mirror illumination is natural daylight (similar to Illuminant C). By night, however, mirror illumination will be that of headlamp output (similar to Illuminant A) superimposed upon nighttime ambient light which is essentially spectrally unbiased. Vision from a mirror is also dependent on the spectral sensitivity of the driver's eye. The spectral sensitivity of the human eye depends on its light adaptation. If bright adapted, vision is photopic and the spectral sensitivity is as shown in Fig. 25. If dark adapted, however, vision is scotopic and sensitivity shifts toward the blue. Between these two extremes vision is mesopic. Almost all night driving is in the mesopic range of adaptation because the reflection of the driver's own headlights from the road provide sufficient illumination to maintain the adaptation level above the scotopic range even on a very dark, unlit road. Because a headlamp emits efficiently in the yellow/orange/red region of the visible spectrum, but relatively poorly in the blue region as shown in Figs. 24 and 25, and because a driver's eyes when driving at night are somewhat more sensitive to blue light, mirrors which optimize reflectance in the blue spectral region but minimize reflectance in the yellow/orange/red region best match human eye sensitivity in day and night conditions, are most efficient at reducing headlamp glare and are desirable as both inside and outside rearview mirrors. Therefore, embodiment 85, which includes the specialized tinted glass panel or panels, is efficient in absorbing or filtering out substantially more light in the yellow/orange/red regions of the visible spectrum than in other regions of the visible spectrum. It tends to mask yellowness due to any inclusion of UV radiation absorbers, or due to any degradation of the EC or ECC material itself, efficiently absorbs headlamp glare, provides a pleasing, attractive reflective color, and allows matching to visible blue tinted colors on outside mirrors when one side of the vehicle has an electro-optic mirror assembly for the driver and the other has a conventional, blue tinted, passenger-side mirror. In addition, the blue tinted embodiment 85 of the present mirror assembly is more restful on a user's eyes since any yellowness otherwise present in an electro-optic mirror assembly incorporating UV radiation stabilizers is a more efficient reflector of light from a yellow headlight and, thus, would reflect more glare to a user's eyes than a comparable blue tinted mirror. Also, a commercially useful advantage of Solextra 7010™ and Sunglas™ Blue glass panels is that they are relatively inexpensive, namely, generally about two to three times the already low commodity cost of conventional, clear, soda lime glass. Alternately, SunBlue™ glass from Asahi Glass Company, Tokyo, Japan, can be used for one or both panels 12d and 12e. SunBlue™ is a blue tinted float glass incorporating added iron content and has a visible light transmission of 83% at a 3 mm thickness (per JIS-R-3106) and a UV radiation cutoff below about 330 nm. Also, Sunglas™ Green from Ford Glass, Detroit, Michigan, could be used for either or both of glass elements 12d and 12e in embodiment 85. As shown in Fig. 26b, such glass, in a 3 mm thickness, is highly light transmitting in the visible spectrum, i.e., 82% transmission overall with Standard Illuminant C and a photopic detector. It is also slightly green tinted and cuts off UV radiation transmission below about 330 nm as shown in Fig. 26a. This glass in such thickness transmits only about 6% of the incident solar energy in the 250-350 nm region, and about 60% in the 350-400 nm region. A preferred material for the interlayer 12c of embodiment 85 is commercially available polyvinylbutyral (PVB) sheeting such as Saflex™ SR#11 PVB mentioned above. Such commercially available PVB sheeting is commonly used in automotive and architectural products and is formed by combining PVB resin with added UV absorbers, as described earlier. Figs. 27a and 27b illustrate the ultraviolet and visible spectral transmission of a sheet of Saflex™ SR#11 PVB adhered between two 1.6 mm conventional, clear, soda lime glass panels. Such a laminated assembly, using clear glass and Saflex™ SR#11, transmits only about 8% of the incident solar energy in the 250-350 nm region and about 54% of such energy in the 350-400 nm region. When laminated, Saflex™ SR#11 is water clear in light transmission. In general, various forms of Saflex™ polyvinylbutyral sheeting interlayers are acceptable for use in this invention as UV reducing interlayers. These include Saflex SR™, Saflex TG™ and Saflex TL™ sheeting in thickness ranges between about 0.015 and 0.060 inch. Thicker PVB interlayers provide better UV radiation shielding but may cause visible distortion. Yet, thicker sheeting is acceptable if due care is taken during lamination. Generally, such Saflex™ sheeting is preferably shipped and stored in a refrigerated or cold condition to prevent the sheeting from sticking to itself while easing handling and use. Other commercially available clear PVB sheeting can be used. For instance, Butacite™ 14 NC-10 clear PVB sheeting from E. I. DuPont de Nemours and Company of Wilmington, Delaware is a suitable choice. When laminated between two panels of 2.3 mm conventional, clear, soda lime glass as shown in Figs. 35a and 35b, Butacite™ 14 NC-10 clear PVB sheeting transmits less than 0.1% of the incident solar energy in the 250-350 nm region and only about 25% in the 350-400 nm region. Alternatively, Butacite™ 140 NC-10 or Butacite™ 14 UV clear PVB sheeting can be used. Alternately, a blue or blue/green tinted interlayer 12c′ may be substituted to form embodiment 85′ of the mirror assembly as shown in Fig. 14. Preferably, Butacite™ Cobalt Blue 0547800 polymeric interlayer sheeting available from E. I. DuPont de Nemours and Company of Wilmington, Delaware can be used. The ultraviolet and visible spectral transmission of Butacite™ Cobalt Blue, when laminated between two 2.3 mm standard, clear, soda lime glass panels is shown in Figs. 28a and 28b. Such sheeting is a highly light transmitting polymeric material having 78% overall visible light transmission with Illuminant C and a photopic detector (Fig. 28b). It is blue in tint and highly absorbing in the UV radiation range below about 375 nm (Fig. 28a). It transmits only 0.01% of the incident solar energy in the 250-350 nm region and about 24% of such energy between 350 and 400 nm. By reason of its blue tint, Butacite™ Cobalt Blue also provides the advantage of masking yellowness in the mirror to provide a commercially acceptable silvery or silver-blue reflection from assembly 85′, while reducing headlamp glare and also matching existing blue exterior rearview mirrors commonly used in many vehicles. Butacite™ Cobalt Blue could be used alone or in combination with one or both panels 12d, 12e of embodiment 85 being specialized blue or green tinted glass. Other suitable blue tinted polymeric sheeting interlayers include Butacite™ Automotive Blue Green 0377800, Butacite™ Automotive Green Blue 1107800 and Butacite™ Light Blue Green 0377300 also available from E. I. Dupont in Wilmington, Delaware. In addition, Saflex TR Blue Green 377300 available from Monsanto Company of St. Louis, Missouri may be used. The ultraviolet and visible spectral transmission of Saflex™ Blue Green 377300 is shown in Figs. 29a and 29b. Alternately, Saflex™ Cool Blue 637600 or Saflex™ Solar Blue 755800 could also be used. With reference to Fig. 15, another embodiment 95 of the electro-optic rearview mirror assembly of the present invention, where like numerals indicate like parts to those described above, incorporates a single glass panel 97 having parallel front and rear surfaces but formed from one of the blue or green tinted specialized glasses described above in connection with embodiments 85 and 85′. Thus, for example, front glass element 97, which also includes a coating of indium tin oxide 13a on its rear or inner surface 13, may be formed from Solextra 7010™ blue tinted glass, Sunglas™ Blue glass, SunBlue™ glass or Sunglas™ Green glass. When the blue tinted glasses are used, the resultant yellow absorbing light advantages described above in connection with embodiments 85 and 85′ result in embodiment 95 as well. These glasses are highly efficient in absorbing or filtering out substantially more light in the yellow/orange/red regions of the visible spectrum than in other regions of the visible spectrum. With reference to the visible spectrum in Fig. 24, such specialized glasses preferentially absorb visible light with wavelengths generally higher than about 560 nm. In other respects, the embodiment 95 remains substantially the same as embodiment 60 of the mirror assembly. Optionally, panel 97 could be a panel of specialized blue or green tinted safety glass that has been tempered and/or toughened by conventional means which include thermal tempering, contact tempering and chemical tempering. An alternate form 100 of the UV radiation reducing embodiment 65 shown in Fig. 9 is illustrated in Fig. 16. Mirror assembly 100, where like numerals indicate like parts to those described above, includes a UV absorbing paint or lacquer which is transparent to light in the visible spectrum and may be applied as coatings 102, 104 on one or both of the inwardly facing surfaces of glass elements 12a, 12b or 12d, 12e. These are the surfaces of the glass panels which face one another and adhering interlayer 12c. A preferred UV absorbing lacquer is PC-60 from American Liquid Crystal Chemical Corporation of Kent, Ohio. The ultraviolet spectral transmission of an approximately 32 microns thick coating of PC-60 lacquer when applied to one surface of a 1.6 mm thick single panel of conventional, clear, soda lime glass is illustrated in Fig. 30. When applied as a coating, PC-60 is highly visibly transmitting, i.e., about 89% overall transmission with Illuminant C and a photopic detector, has a slight yellow tint, and absorbs sharply in the UV radiation region below about 390 nm. Between 250 and 350 nm, such a coating of PC-60 transmits essentially none of the solar energy incident in that region. For incident solar energy between 350 nm and 400 nm, PC-60 transmits only about 5%. Overall, such a coating of PC-60 transmits only about 3% of the incoming solar energy in the 250-400 nm region. An alternate UV absorbing lacquer is ZLI-2456 mentioned above in layer 70 and useful to form embodiment 100′ (Fig. 16). A 12 microns thick coating of ZLI-2456 transmits only about 2% of the incident solar energy in the 250-350 nm region, and only about 9% of the solar energy normally incident between 350 and 400 nm. ZLI-2456 is slightly more yellowish in color and transmission than is PC-60. Of course, UV absorbing paint/lacquer coatings such as those described above may be used with UV absorbing/filtering interlayers 12c or 12c′ as described above, or when either of glass panels 12a, 12d or 12b, 12e are formed from blue or green tinted specialized glass as described above. Indeed, in a preferred form of embodiment 100, glass panel 12d will be formed from Solextra 7010™ or Sunglas™ Blue glass while the electro-optic media in space 18 will include UV absorbing additives as described above. The ultraviolet spectral transmission of ZLI-2456 is shown in Fig. 31. As a specific example of mirror assembly 100 shown in Fig. 16, an electrochemichromic solution was formulated consisting of 0.02M methylviologen hexafluorophosphate and 0.02M 5,10-dihydro-5,10-dimethylphenazine dissolved in 2-acetylbutyrolactone. To this was added 12.5% wt/vol Cyasorb24™ UV radiation absorber. This was filled into a 150 micron thick cavity between panels 16, 12b of ITO transparent coated, 1.6 mm thick, conventional, clear, soda lime glass. The ITO coating on each glass panel was 15 ohms/sq and had a visible transmission of 85%. A coating of UV absorbing ZLI-2456 lacquer was spray coated on the front facing surface 103 of rear glass panel 12b and on the rear facing surface 101 of front glass panel 12a each to a thickness of about 11 microns. Glass panels 12a, 12b were then laminated by an interlayer 12c of Saflex™ SR#11 PVB sheeting. When tested under mercury UV radiation lamps at a temperature of about 80 C. for a period of approximately two weeks, such a mirror assembly was found to be exceptionally UV radiation stable. Integrated irradiation in the 295-400 nm region within the UV radiation chamber used to accelerate natural weathering was around 100W/m2. Initially electrochemichromic mirror devices with such UV and anti-scatter protection had a reflection of approximately 81% at zero potential which dimmed to a reflectivity of approximately 8% when one volt potential was applied across ITO coatings 13a, 17a which enclose the electrochemichromic solution. After over 336 hours in the UV radiation chamber, the zero potential reflectivity remained high at around 80% and the mirror continued to dim to about 8% reflectivity when one volt was applied. The appearance of the mirror remained essentially unchanged after such prolonged exposure to high intensity ultraviolet radiation. Also, when the safety performance of the mirror assembly was tested by impacting it with a 0.9 kg steel ball dropped from a height of 1 meter, the Saflex™ SR#11 laminating interlayer securely retained all shards of glass such that they did not fly away and such that they remained securely held to the laminate interlayer. Also, the Saflex™ SR#11 laminate interlayer did not fracture nor tear and was effective in ensuring that contact with chemicals used within the electrochemichromic mirror assembly is minimized should the mirror glass break in an accident. Because of the high concentration (12.5% wt/vol) of broad UV absorber Cyasorb 24™ used in this embodiment, and because of the slight yellow tint inherent to ZLI-2456 UV absorbing lacquer, the reflection from this example of mirror assembly 100 had a somewhat yellow tint which is cosmetically undesirable in some applications. However, when the front glass panel 12a was replaced with a blue tinted glass panel 12d as described in embodiment 85, the benefits described above were achieved. Specifically, when a 2.3 mm panel of Solextra 7010™ glass was used as front glass panel 12d, reflectance at zero potential remained close to its initial 64% in spite of over 336 hours of UV accelerated weathering testing as mentioned above. Because of the use of blue tinted glass, the reflector looked more silvery-blue and was more consumer acceptable. Also, when dimmed by applying one volt to the transparent coatings 13a, 17a, the mirror continued to dim to its low reflection state of about 7% reflectivity, even after prolonged exposure to the intense UV radiation. Also with reference to Fig. 16, an alternate embodiment 110 substitutes different layers for paint/lacquer layers 102, 104 preferably in the form of a polymeric film such as clear Scotchtint™ SH2CLX available from 3M Corporation, St. Paul, Minnesota. Such Scotchtint™ film may be adhered as layers 112, 114 to one or both of the inner facing surfaces of glass panels 12a, 12b or specialized glass panels 12d, 12e as described above, said placement on inner surfaces having the added advantage of protecting the potentially scratchable polymeric film behind glass panels 12a, 12d. Film layers 112, 114 (Fig. 16) provide assembly 110 with similar UV reducing advantages while maintaining strength and scatter preventing advantages due to the laminate front assembly as in embodiments 100 and 100′. The ultraviolet spectral transmission of a single layer film of Scotchtint™ SH2CLX adhered to a sheet of 1.6 mm conventional, clear, soda lime glass is shown in Fig. 32. Scotchtint™ SH2CLX is a highly visibly transmitting film, i.e., about 82% overall transmission using Illuminant C and a photopic detector. It is also clear and absorbs sharply and intensely in the UV region below about 380 nm. Preferably, Scotchtint™ SH2CLX is used in a form including a pressure sensitive adhesive applied to one surface such that it may be easily adhered to the rear facing surface of glass panel 12a or 12d and the front facing surface of glass panel 12b or 12e. Likewise, such polymeric film adds to the anti-scatter effect of the mirror assembly 110 by retaining shards or splinters from glass panel 12a, 12d should it be broken upon impact. Also, by serving as a barrier film, they are effective in ensuring that contact with the chemicals used within the electro-optical mirror is minimized should the mirror glass break in an accident. Alternately, polymeric film such as Scotchtint™ SH2CLX may be used in combination with clear or tinted UV reducing interlayers 12c or 12c′ such as Saflex™ as described above. As an alternative to using polymeric sheeting 112, 114 in mirror assembly embodiments 100, 100′ or 110 as described above in Fig. 16, a UV curable, pourable adhesive can be used to retain the glass panels 12a, 12b or 12d, 12e together while simultaneously reducing UV transmission as embodiment 120 (Fig. 16). A suitable ultraviolet curing modified polyurethane adhesive is Norland 65 available from Norland Products, Inc., New Brunswick, New Jersey, which is water clear, highly transparent to visible light, includes a moderate modulus of elasticity when cured such that it is not overly brittle and does not fracture upon impact, and includes an index of refraction of 1.54 matched closely to that of soda lime glass (which has a refractive index of 1.52). Norland 65 also adheres well to glass, is of relatively low viscosity (1,200 centipoise) such that it easily pours and spreads between two glass panels to allow lamination once cured. It also has a relatively low modulus of elasticity (20,000 psi). Its ability to be cured with UV radiation is well-suited to manufacturing processing. Fig. 33 illustrates the ultraviolet spectral transmission of a 35 microns thick coating of cured Norland 65 on a 1.6 mm conventional, clear, soda lime glass panel. Ultraviolet radiation transmission is cut off below about 310 nm while only about 19% of the incident solar energy in the 250-350 nm region is transmitted while about 62% of the incident solar energy in the 350-400 nm region is transmitted. Alternately, Norland NOA68, also available from Norland Products, Inc., can be used instead of Norland 65. NOA68 has a refractive index of 1.52 which is matched perfectly with clear soda lime glass. It has a modulus of 20,000 psi when cured and has an excellent adhesion to glass. Norland NOA61 can also be used although, with a modulus when cured of 135,000 psi, it is somewhat more brittle. Alternately, Dymax #478™ available from Dymax Corporation, Torrington, Connecticut can be used. This is a UV curing acrylic that has a refractive index very close to that of soda lime glass when cured. Alternately, conventionally known UV curing optical epoxies, preferably of low modulus or with their modulus reduced through addition of reactive diluents and reactive flexibilizers, as is commonly known, can be used. Should it be desired to further reduce the modulus of elasticity of the cured adhesive, clear plasticizers or clear low molecular weight epoxies can be added to the UV curing adhesives so that they are less brittle after curing, and such that they have even better lamination safety performance. For example, cyclohexanedimethanol diglycidyl ether such as Heloxy MK107™ from Wilmington Chemical Corporation of Wilmington, Delaware can also be added to NOA61, NOA65 or NOA68 in quantities up to 30% wt/wt or more (i.e., % grams of MK107 added to grams of NOA61, etc.) to plasticize them. Heloxy MK107™ has a refractive index close to 1.48 which is also well-matched to that of clear soda lime glass. At high concentration of added MK107, the UV cured NOA61, NOA65 or NOA68 materials are quite flexible and somewhat elastic such that they are well-suited for use as anti-lacerative layers and as laminate interlayers. As an alternative to the UV curing adhesives described above, thermally or catalytically cured adhesives can also be used to retain glass panels 12a, 12b and 12d, 12e together while simultaneously acting as a UV radiation reducing agent. As with the UV curing adhesives, the thermally or catalytically cured adhesives are preferably water clear, highly transparent to visible light, closely matched to the index of refraction of glass, while being of moderate modulus of elasticity when cured so as not to be overly brittle nor to fracture upon impact and thus impair retention of any glass fragments or shards. A suitable system includes a modified epoxy adhesive formed from 15% wt/wt EPON 828™ epoxy resin, mentioned above in embodiment 10, 35% wt/wt Heloxy MK107™, and 50% wt/wt Capcure 3-800™ mercaptan curing agent available from Diamond Shamrock Chemicals Company, Morristown, New Jersey. These ingredients are mixed together in a container and subsequently spun in a centrifuge at approximately 4,500 rpm for about ten minutes to remove entrained air. The resultant viscous mixture is clear and is applied between panels 12a, 12b or 12d, 12e. The resultant assembly so formed is fired at about 110 C. for about one hour followed by firing at 140 C. for a further hour. Such firing causes the adhesive mixture to cure to an adhering but moderate modulus of elasticity, somewhat flexible, optically clear laminate. The ultraviolet transmission of a 500 microns thick cured coating of this adhesive mixture, coated onto a 0.063 inch conventional, clear, soda lime glass panel is shown in Fig. 34. Such material transmits about 35% of the incident ultraviolet solar energy in the 250-350 nm region thereby providing good inherent UV absorbing properties. Also, it is possible to enhance the already good inherent UV radiation absorbing properties of these UV, thermally, or catalytically cured adhesives by adding any of the UV absorbing materials such as Uvinul D-50™, Uvinul D-49™, Uvinul 400™, Tinuvin P™, Tinuvin 327™, Tinuvin 328™, or Cyasorb 24™ to the liquid adhesives prior to their cure. The UV, thermally, or catalytically cured adhesives can also be optionally dyed so that they have a slight bluish tint and provide the desirable properties for the electro-optic mirror assemblies including specialized blue tinted glass panels or blue tinted interlayers. For example, taking the specific adhesive mixture of EPON 828™/Heloxy MK107™/Capcure 3-800™ described above, such mixture can be dyed blue using Neozapon Blue™ 807, a phthalocyanine dye available from BASF Wyandotte Corporation, Parsippany, New Jersey, added in about 0.5% to 1% by weight. When laminated between two 0.063 inch thick panels of clear, conventional, soda lime glass, such a dyed mixture, at 0.5% dye concentration, was highly visibly transmitting (78% transmission using Illuminant C and a photopic detector), was tinted blue, and was highly absorbing in the UV region with only 30% transmission of incident solar UV energy in the 250-350 nm region. In any of the above mirror assembly embodiments, and especially those utilizing one or more panels of clear soda lime glass not already tinted blue or green as in embodiments 85, 85′, 100′, 110 or 120, a blue, electrochemically inert dye may be added to the electrochromic or electrochemichromic solution itself to provide the advantages of absorbing more light in the yellow/orange/red region of the visible spectrum than in other regions of the visible spectrum. Such a dyed assembly will provide similar advantages to those including specialized blue tinted glass or blue tinted interlayers. For example, a suitable material such as Neopen 808 is available from BASF Wyandotte, Parsippany, New Jersey. Such material, dissolved to a concentration of 0.1% wt/vol in propylene carbonate (a common solvent used in electrochemichromic solutions), and when placed in a 1 mm pathlength cell, transmits about 60% of the visible spectrum (Standard Illuminant C and a photopic detector), and transmits only about 9% of the incoming solar UV energy in the 250-350 nm region. Also, for additional scatter protection and safety, in any of the above disclosed mirror assembly embodiments, any of the glass panels of the assemblies could be formed from safety glass that has been tempered and/or toughened by conventional means including thermal, contact and chemical tempering. Also, such tempered, safety glass can be blue or green tinted to provide the advantages described above. While several forms of the invention have been shown and described, other forms will now be apparent to those skilled in the art. Therefore, it will be understood that the embodiments shown in the drawings and described above are merely for illustrative purposes, and are not intended to limit the scope of the invention which is defined by the claims which follow.

Claims: A vehicular rearview mirror assembly comprising: first and second spaced, optically transparent elements (12, 16) each having front and rear surfaces and defining a space (18) between the rear surface of said first element and the front surface of said second element, an electro-optic medium (20) confined in said space (18) whose light transmittance is variable upon the application of an electric field thereto, means (13a, 17a) for applying an electric field to said electro-optic medium to cause variation in the light transmittance of said medium, a reflective coating (26) on one surface of said second element (16) adapted to reflect light incident thereon through said first element (12) and said electro-optic medium (20), and ultra-violet radiation absorption means for reducing ultra-violet radiation degradation of said electro-optic medium, characterised in that: the rearview mirror assembly is an exterior rearview mirror; said electro-optic medium (20) is an electrochemichromic solution comprising an anodic electrochemichromic compound and a cathodic electrochemichromic compound dissolved in solution in an organic solvent, said ultra-violet radiation absorption means includes an ultraviolet radiation absorber also dissolved in solution in said organic solvent, said ultraviolet absorber being compatible with the other ingredients of the electrochemichromic solution, and said electrochemichromic solution in said space being sufficiently stable to exposure to natural weathering for said rearview mirror assembly to be used on the outside of a vehicle. A mirror assembly as claimed in claim 1, further including absorbing/filtering means for absorbing or filtering out substantially more light in the yellow/orange/red regions of the visible spectrum than in other regions of the visible spectrum. A mirror assembly as claimed in claim 2, wherein said first element (12) is a laminate assembly including a pair of optically transparent panels (12d, 12e) secured to one another by an intermediate layer (12c). A mirror assembly as claimed in claim 3, wherein at least one of said panels (12d, 12e) is formed from highly light transmitting glass that absorbs ultraviolet radiation. A mirror assembly as claimed in claim 3, wherein at least one of said panels (12d, 12e) is formed from glass which absorbs substantially more visible light in wavelengths higher than about 560 nanometers than in other regions of the visible spectrum and has a blue or green tint. A mirror assembly as claimed in any one of claim 3, 4 or 5, wherein the intermediate layer (12c) is a polymeric layer. A mirror assembly as claimed in claim 5, wherein said absorbing/filtering means includes the intermediate layer (12c) which absorbs ultraviolet radiation. A mirror assembly as claimed in claim 5, wherein the intermediate layer (12c) is highly light transmitting. A mirror assembly as claimed in claim 5, wherein the intermediate layer (12c) absorbs substantially more visible light in wavelengths higher than about 560 nanometers than in other regions of the visible spectrum and has a blue or green tint. A mirror assembly as claimed in any one of claims 3 to 9, wherein the intermediate layer (12c) is a layer of cured adhesive incorporating a blue dye. A mirror assembly as claimed in any one of claims 3 to 10, wherein at least one of said panels (12d, 12e) includes a coating (102, 104) of UV radiation reducing paint/lacquer on at least one surface thereof. A mirror assembly as claimed in claim 11, wherein each of said panels (12d, 12e) includes a coating of said UV radiation reducing paint/lacquer on at least one surface which faces the other of said panels. A mirror assembly as claimed in any one of claims 3 to 10, wherein each of said panels (12d, 12e) includes a layer of UV radiation reducing polymeric film (112,114) on at least one surface thereof. A mirror assembly as claimed in any one of claims 2 to 13, wherein said absorbing/filtering means includes a dye dissolved in said electrochemichromic solution. A mirror assembly as claimed in claim 14, wherein said dye is a blue dye. A mirror assembly as claimed in claim 1 or 2, wherein said first element (12) is formed from highly light transmitting glass having an iron oxide content of at least 0.2% to 0.9% by weight or a cerium oxide content of at least 0.2% to 0.9% by weight. A mirror assembly as claimed in claim 2, wherein said absorbing/filter means includes said first element (12) being formed from glass which absorbs substantially more visible light in wavelengths higher than about 560 nanometers than in other regions of the visible spectrum and has a blue or green tint. A mirror assembly as claimed in claim 1, 16, or 17, wherein at least one of said first and second elements (12, 16) is formed from tempered safety glass. A mirror assembly as claimed in any one of claims 3 to 13, wherein at least one of said panels (12d, 12e) is formed from tempered safety glass. A mirror assembly as claimed in any preceding claim, wherein said cathodic electrochemichromic compound is a viologen. A mirror assembly as claimed in any preceding claim, wherein said anodic electrochemichromic compound is a phenazine. A mirror assembly as claimed in claim 21, wherein said phenazine is 5,10-dihydro-5,10-dimethylphenazine or 5,10-dihydro-5,10-diethylphenazine. A mirror assembly as claimed in any preceding claim, wherein said ultraviolet absorber is dissolved in said solvent at a concentration of at least 0.6% wt/vol. A mirror assembly as claimed in claim 23, wherein said ultraviolet absorber is dissolved in said solvent at a concentration of at least 1.2% wt/vol. A mirror assembly as claimed in claim 24, wherein said ultraviolet absorber is dissolved in said solvent at a concentration of at least 12.5% wt/vol. A mirror assembly as claimed in claim 23, wherein said ultraviolet absorber is dissolved in said solvent at a concentration of between about 0.6% wt/vol and 12.5% wt/vol. A mirror assembly as claimed in any preceding claim, wherein at least said first element (12) comprises glass of thickness about 3mm or less. A mirror assembly as claimed in claim 27, wherein at least said first element (12) comprises glass of thickness about 1.6mm or less. A mirror assembly as claimed in claim 28, wherein both said first element (12) and said second element (16) comprises glass of thickness about 1.6 mm or less. A mirror assembly as claimed in any preceding claim, wherein at least said rear surface of said first element (12) is coated with a thin film transparent conductor (13a). A mirror assembly as claimed in claim 30, wherein said thin film transparent conductor has an electrical sheet resistance of about 15 ohms/square or less. A mirror assembly as claimed in claim 31 wherein said thin film transparent conductor comprises indium tin oxide. A mirror assembly as claimed in any preceding claim, wherein said organic solvent comprises propylene carbonate.

Inventors: LYNAM NIALL RICHARD, LYNAM, NIALL RICHARD
Applicants: DONNELLY CORP, DONNELLY CORPORATION
Application year: 1990
Main classification: B60R1
IPC codes: G02F1, G02B5, B32B27, B32B17, B60R1, B60J3