Patent Application
20080247046
The invention concerns a glare free mirror pane and a method for the manufacturing the same, as well as a glare free rear view mirror for motor vehicles.
Reflectant coatings of silver on conventional mirror panes, in spite of sealing, are frequently subject to corrosion, which is detrimental to viewing in the field of sight and, eventually, can lead to a complete loss of functionality of a mirror so affected. Further, a reduction of the disturbing effect of glare would be of advantage in both day and night rear view service. Consequently, efforts have been made to provide glare prevention over the entire wavelength range of visible light. In the bright ambience of daylight the human eye possesses a maximum spectral sensitivity at 555 nm, which wave length encompasses yellowish-green colorations. Conversely, in dark surroundings, for instance at night, when light is largely excluded, the maximum spectral sensitivity tends to migrate into the blue range of the spectrum. On this account, a mirror, with a high degree of reflectivity in the blue spectral range is considered to be particularly adaptable for both day and night service. It is also true, that from none other than aesthetic grounds, mirrors often are designed to reflect in the said blue range.
A mirror of this kind has been made known by EP-B-1099671. This disclosed front surface mirror employs chromium as the reflecting coating and consequentially is very resistant to corrosion. Disturbing dazzling effects are minimized by means of additional coatings, namely Al2O3, ZrO2, SnO2, and TiO2. The reflection factor of mirrors incorporating such coatings is found to be greater in the short-wave spectrum (blue) of visible light than in the long wave spectrum (red) of visible light. For this reason, such mirrors provide a bluish reflection. Difficulties with these blue-oriented mirrors lie in providing a satisfactory homogeneity of reflectance over the entire surface of the mirror.
In order to achieve a reduction of a glare effect, it is customary to block an overly blue toned portion of the spectrum, which, as said above, is that range of the visible spectrum most adaptable to night service. If this is done, then the reflecting factor of a mirror of this design is less in the blue spectrum than in the long-wave red spectrum. Unfortunately, mirrors are purposely designed to tend toward a red reflection. Disadvantageously, however, even in highly rated mirror classifications, such a mirror exhibits its maximum intensity of reflected light in the red, i.e., long wave spectrum. Essentially, this results in an excessive quantity of light, which, in turn, promotes excess glare in daytime reflectance.
Thus it is the purpose of the present invention to create a mirror pane of reduced glare and thereby a glare free rearview mirror for motor vehicles, wherein a reasonable compromise between glare activity in night and day operation can be found.
The objectives of the invention are accomplished by means of the combination of a coating of niobium pentoxide (Nb2O5), applied onto a transparent substrate, a color rendering layer of silicon nitride (Si3N4) laid thereon and finally a chromium layer to serve as a reflecting surface, it is possible to create a glare diminishing effect of a sufficient degree to be employed in both day and night services. A further attribute of this combination is that the said blue tinge is very well homogenized over the entire pane surface.
The mirror pane possesses over the entire spectral range of visible light a somewhat reduced reflection factor, for instance, at 700 nm wave length, the reflectance runs some 32%, at 400 nm wave length the reflectance is 65%. The sought after blue tinge exhibits an unchangeable rendition of color, Thereby, for the first time, it becomes possible to fashion a reflecting surface effective in the blue tinge range by using niobium pentoxide and silicon nitride. This here described surface, because of its basic chrome deposit, can offer an excellent resistance to corrosion.
The realization of the invention, giving consideration to the compromises made between a reduced glare effect in both night and day services is very advantageous.
By means of the advantageous construction of the invention the desired degree of reflectance and the desired blue tinting is satisfactorily achieved.
By means of slight curvature the described glare free mirror adapts itself very well as a rear view mirror for motor vehicles.
Glass is especially preferred as the substrate or the carrier of the individually mentioned coatings of the mirror since glass possesses outstanding optical characteristics as well as an excellent mechanical strength. It is, however, entirely possible to employ a transparent plastic as a substrate for the same purpose.
The method in accord with the invention presents an advantageous possibility for the manufacture of the invented mirror pane.
The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof, wherein an example of the invention is shown and wherein:
Referring now in more detail to the drawings, the invention will now be described in more detail.
The niobium pentoxide layer 4 has a thickness of 38 nm±10 nm, the silicon layer 6 is 49 nm thick, ±20 nm and the reflecting layer 8, this being of chromium, has a thickness of 50 nm with a variance of ±10 nm. The thicknesses of the individual layers 4, 6 and 8 are so selected that the desired reflectant degree exceeds 40% mm—this being a condition suitable for installation as motor vehicle rear vision mirrors—and the mirror a whole can assure service day and night with a sufficient freedom from glare.
The deposition of the layers 4, 6 and 8 is carried out by sputtering. For this operation, inline sputtering devices of the firm Leybold Optics are used. With these said devices, substrate 2 and the individual targets for the various for the different layers are stratified vertically, next to one another. The different targets are stationarily located continguently to one another, while the substrate is moved linearly along the said targets. For the niobium pentoxide layer 4, a target of niobium pentoxide is made and for the reflecting layer 8 of chromium a target of that metal is used. The silicon reacts in an atmosphere containing nitrogen in accord with the reaction formula:
3Si+2N2→Si3N4
thus forming in transit silicon nitride, which then precipitates itself on the niobium pentoxide layer 4.
While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202006015876.6 | Oct 2006 | DE | national |
