IE57083B1

IE57083B1 - Rear-view mirror for vehicles,particularly motor vehicles

Info

Publication number: IE57083B1
Application number: IE2399/85A
Authority: IE
Original assignee: Flachglas Ag
Priority date: 1984-10-01
Filing date: 1985-09-30
Publication date: 1992-04-22
Also published as: EP0177834A3; IE852399L; EP0177834A2; DE3583911D1; EP0177834B1; DE3436016C1; ATE66752T1

Abstract

This rear view mirror has a transparent layer carrier consisting preferably of soda silicate glass and has a rear coating which exhibits an interference layer of dielectric material arranged on the transparent layer carrier and an adjoining reflection layer of a metal or of a metal alloy, wherein the interference layer (12) is constructed in its thickness as anti-reflection layer for the long wave visible spectral band; the index of refraction of the interference layer (12) is >/= 2.1; and the degree of light reflection of the transparent layer carrier with the reflection layer (14) alone is within a range of between 0.6 and 0.8, measured from the front of the transparent layer carrier (10). <IMAGE>

Description

The invention relates to a rear-view mirror for vehicles, more particularly motor vehicles or the like, comprising a transparent coating support or substrate, preferably consisting of soda silicate glass, and a rear coating, which comprises a dielectric interference layer disposed on the transparent substrate, followed by a reflecting layer i# consisting of a metal or metal alloy.

I It is well known that layers of the highly reflective metals 10 silver and aluminium can be used as a rear coating for motor vehicle mirrors, such rear coating generally having the advantage over a front-coated rear-view mirror that the coating is protected by the mirror mounting from direct atmospheric action, more pari icularly dirt. The highly reflective metals indicated give rear-view mirrors having reflecting values of more than 85% in the visible spectral range.

Selective Optical Services for Solar Energy Converters by 20 M.M. Koltun, New York, 1961, page 39, discloses a mirror having the above-described layer construction in which, in order further to increase reflecting power to more than 90%, a reflection-increasing single-layer or two-layer dielectric interference layer is disposed between the transparent substrate, hereinafter referred to as the glass substrate V for short, and the metal reflecting layer, which consists of aluminium there.

However, although the high degree of reflection is quite 5 desirable during daylight, and is substantially independent of wavelength, it results in drivers being dazzled at night by the headlights of following vehicles.

) On the other hand, dazzle-free rear-view mirrors are known (DE-AS 10 36 672; DE--AS 24 49 763), in which a coating in the form of a nori-metu I I ic and preferably metal oxide interference coating is applied to the front, of the transparent substrate, which is preferably of glass, and the rear is provided, if required, with a dark absorbent coating. The interference coating may, for example, consist of three sub-layers in the following sequence: high-refraction coating - low-refraction coating high-refraction coating. If the thicknesses of these sub-layers are adjusted, as λ/4-layers, to the short-wave visible spectral range, such mirrors have a higher reflecting power in the blue spectral range as compared with the long-wave yellow-red range. A selectively reflecting blue coating of this kind produces an adequately bright image in daylight, while the dazzle effect from the headlights of following vehicles at night, with their high proportion of radiation in the long-wave visible range, is reduced.

However, one disadvantage of such dazzle-free rear-view 5 mirrors having front interference coating is that the coating is directly exposed to the external atmosphere. The coating may easily be scratched, particularly when dirt is removed from the coated front of the mirror, and this greatly interferes with the function of such rear-view mirror, since scratches on a highly reflective coating produce much greater optical disturbance than, for example, at the interface between a normal glass surface and air having a reflecting power of just 4%.

With the above-mentioned non-metallic interference coatings, it is not possible to achieve the necessary protection of the coating by following the method of coating the rear of the substrate; the interference coatings are transparent and their rear would have to be covered by a dark coating. As a result, however, the outer interface between the interference coating and air, which is important to the effect of the interference filter, would be eliminated, thus having an adverse effect on the function of the filter.

If, on the other hand, in a rear-view mirror for vehicles, V comprising a transparent coating support or substrate, preferably consisting of soda silicate glass, and a rear coating which comprises a dielectric interference layer disposed on the transparent substrate followed by a reflecting layer consisting of a metal or metal alloy, the attempt is made to achieve the above-described selectivity ί in the reflection by forming the interference layer as a high-refraction non-reflecting coating adapted to the long-wave visible range, for example from TiO->, CeO?, Ta^O^, Β^·2θ3 and/or ZnS, the result would be a mirror having a faint blue cast without any appreciable anti-dazzle effect.

The object of the invention, therefore, is to create a dazzle-free rear-view mirror for vehicles, more particularly motor vehicles, which, while avoiding the disadvantages of the known rear-view mirrors having a front interference coating, has a light reflection in the range between the minimum light reflection of 0.4 - as required by the European Community directives - and about 0.6.

Accordingly, the present invention provides a rear-view mirror for vehicles, comprising a transparent coating support or substrate, preferably consisting of soda silicate glass, and a rear coating which comprises a dielectric interference layer disposed on the transparent substrate J followed by a reflecting layer consisting of a metal or metal alloy, wherein the interference layer is devised in its thickness as a non-reflecting layer for the visible long-wave range of the spectrum, the refractive index of the interference layer is >,2.1 and the degree of light reflection of the transparent substrate with the reflecting I layer alone is in the range of between 0.6 and 0.8, measured from the front of the transparent substrate.

As a result of the material selection according to the invention, for the non-reflecting layer on the one hand, and the reflecting layer on the other hand, it has surprisingly been possible to find an optimal solution simultaneously for the above requirements of the rear-view mirror.

In a preferred embodiment of the invention, the degree of light reflection of the transparent substrate with the reflecting layer alone is in the range between 0.65 and 0.75, measured from the front of the transparent substrate.

According to the invention, the reflecting layer may consist of zinc.

Alternatively, the invention proposes that the reflecting layer should consist of tin.

V According to the invention, the reflecting layer may consist of an aluminium-copper alloy.

Alternatively, the invention proposes that the reflecting layer should consist of a tin-copper alloy.

In another embodiment of the invention, a thickness of the i reflecting layer is such that the transmission of the transparent substrate provided with the interference layer and the reflecting layer should be less than 3%.

The materials preferably used for the dielectric interference layer constructed as a non-reflecting layer comprise TiO2, ZnS, CeO2, Bi2O-j an<^ Ta2°5' According to the invention, the reflecting layer may be foLiowed by a protective layer.

Finally, the invention also proposes that at least one of the layers of the rear coating should be applied by vacuum-coating .

Generally, coating of the transparent substrate for the production of the coating according to the invention is all j carried out by the vacuum-coating. Preferably, the metal or metal, alloy layers may be applied by vaporisation from r<‘S is tance h Apart from vacuum deposition, it is also possible to use other deposition processes, for example wet chemical processes, by deposition from suitable feed solutions.

The substrates used may, in addition to silicate glass, be other transparent materials, preferably plastics, eg polymethylmethacrylate, polyesters, polycarbonates and the like .

The invention also covers the case in which a protective layer is additionally applied to the coating in order to improve the resistance of the rear-view mirror according to the invention to corrosion. This may, for example, be another metal, metal alloy or metal oxide layer, which is applied in the vacuum process immediately after application of the actual selective coating, or a coat of varnish. A combination of both steps is also possible.

Other features and advantages of the invention will be J > apparent from the following description, in which exemplified embodiments are explained in detail with reference to the diagrammatic drawings wherein: Fig. 1 is a first exemplified embodiment of a rear-view mirror according to the invention in diagrammatic section at right «ingle.*; to the pi.inc of the transparent, substrate.

Fig. 2 shows a second exemplified embodiment of a rear-view mirror according to the invention in a section corresponding to Fig. 1, and Fig. 3 are graphs showing the degree of reflection against the wavelength in the case of rear-view mirrors produced by examples I rind 2.

Figure 1 illustrates an exemplified embodiment of an rear-view mirror according to the invention, in which a non-reflecting layer 12 of dielectric material and having a u J refractive index equal to or greater than 2.1, followed by a reflecting layer 14 of a metal or metal alloy, are applied to a transparent substrate Ί0 consisting of soda-silicate glass.

In the exemplified embodiment, shown in Figure 2, the y reflecting layer 14 is followed by a protective layer 16, in this case a coat of varnish. j.

The rear-view mirror according to the invention can be produced in the manner described in the following examples: Example 1 A zinc sulphide non-reflecting layer 12 in a thickness of nm was applied to a 3 mm thick glass plate 10 in a high-vacuum vapour-coating plant. A zinc layer 14 was then applied to the zinc sulphide layer 12 in a thickness such that the transmission of the coated plate was less than 1%.

The spectral reflection was then measured on the coated plate for approximately perpendicular ray incidence in the visible spectral range from the glass side. The measured spectral curve is shown in curve 1 in Figure 3. The selective spectral curve required for dazzle-free vision, V with the degree of reflection decreasing continuously from the short-wave to the long-wave visible range, will be apparent from curve 1. Accordingly, the plate has a visually clearly apparent blue tint when viewed from the glass side. The degree of brightness of the plate is also in the required medium range. Thus the degree of light reflection of the plate is 0.56. With such light reflections of between 0.5 and 0.6, the double image effects produced by the somewhat laterally offset additional reflection on significant. the outer surface of the mirror are no longer Example 2 15 The procedure was as in example 1 except that the titanium dioxide non-reflecting layer 12 of a thickness of 59 nm was applied instead of the zinc sulphide layer. The coating was then continued with a lciyer of tin of a thickness such that the transmission of the coated plate was below 1%. The spectral reflection - again when measured from the glass side of the plate - is shown as curve 2 in Figure 3. There is a similar selective reflection curve to the coating according to example 1. Only the brightness level in the reflection is somewhat, lower. The degree of light reflection in this case was accordingly 0.45.

Claims

CLAIMS:

1. A rear-view mirror for vehicles, comprising a transparent coating support or substrate, preferably consisting of soda silicate glass, and a rear coating which comprises a dielectric interference layer disposed on the transparent substrate followed by a reflecting layer consisting of a metal or metal alloy, wherein the interference layer is devised in its thickness as a non-reflecting layer for the visible long-wave range of the spectrum, the refractive index of the interference layers is >2.1, and the degree of light reflection of the transparent substrate with the reflecting layer alone is in the range of between 0.6 and 0.8, measured from the front of the transparent substrate.

2. A rear-view mirror according to claim 1, wherein the degree of light reflection of the reflecting layer alone is in the range of between 0.65 and 0.75, measured from the front of the transparent substrate.

3. A rear-view mirror according to claim 1 or 2, wherein the reflecting layer consists of zinc.

4. A rear-view mirror according to claim 1 or 2, wherein the reflecting layer consists of tin.

5. - A rear-view mirror according to claim 1 or 2, wherein the reflecting layer consists of aluminium-copper alloy.

6. A rear-view mirror according to claim 1 or 2, wherein the reflecting layer consists of a tin-copper alloy.

7. A rear-view mirror according to any one of the preceding 10 claims, having a thickness of the reflecting layer such that the transmission of the transparent substrate provided with the interference layer and the reflecting layer is < 3%.

8. A rear-view mirror- according to any one of the preceding 15 claims, wherein the reflecting layer is followed by a protective layer.

9. A rear-view mirror according to any one of the preceding claims, wherein at least one of the layers of the rear 20 coating is applied by vacuum-coating.

10. A rear-view mirror substantially in accordance with any of the embodiments herein described with reference to the accompanying drawings and/or Examples.