IE57107B1

IE57107B1 - Rear-view mirror for vehicles,particularly motor vehicles,having a coating on the rear face

Info

Publication number: IE57107B1
Application number: IE2400/85A
Authority: IE
Original assignee: Flachglas Ag
Priority date: 1984-10-01
Filing date: 1985-09-30
Publication date: 1992-04-22
Also published as: EP0176935B1; DE3583908D1; IE852400L; ATE66751T1; EP0176935A2; DE3436011C1; EP0176935A3

Abstract

This rear view mirror has a transparent layer carrier consisting preferably of soda silicate glass and has a rear coating which exhibits a highly reflective mirror layer of a metal or a metal alloy, particularly silver or aluminium, and an interference layer of dielectric material arranged between the layer carrier and the mirror layer, wherein the dielectric interference layer (14) is constructed in its thickness as anti-reflection layer for the long wave visible spectral band; and between the transparent layer carrier (10) and the dielectric interference layer (14) is arranged an additional layer (12) of a metal or a metal alloy of such a thickness that the light transparency of the compound arrangement consisting of the transparent layer carrier (10) and the additional layer (12) is less by 10 to 55% than that of the transparent layer carrier (10) alone. <IMAGE>

Description

FLACEGLAS AKTIBNGBSELLSCHAFT, A BODY CORPORATE ORGANISED UNDER THE LANS OF THE FEDERAL REPUBLIC OF GERMANY, OF 10 14» OTTO-SBELING-PROtfSNADE, 8510 SURTB/BAYSRN, GERMANY.

I > > < - 1 The invention relates to a rear-view mirror for vehicles, more particularly motor vehicles or the like, the mirror having a transparent coating support or substrate which is preferably of soda silicate glass, and a rear coating comprising a highly reflective mirror layer of a metal of aluminium, and a dielectric interference layer between the a substrate and the reflecting layer.

It is well known that layers of the highly reflective metals 10 silver Selective Optical Services for Solar Energy Converters by 20 M.M. Koltun, New York, 1961, page 39, discloses a milror 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 a f 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 e of wavelength, it results in drivers being dazzled at night by the headlights of following vehicles. j j 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 non-metallic 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 ι ί proportion of radiation in the long-wave visible range, is reduced.

However, one disadvantage of such dazzle-free rear-view 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 a 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-metal 1ic interference coatings, it is not possible to achieve the necessary piotcction of the coating by following the method of coating the rear of the substrate; the interference coatings are transparent and their rear would have lo 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. tf, on the other hand, in a rear-view mirror for vehicles, the mirror having a transparent coating support or substrate which is preferably of soda silicate glass, and a rear coating comprising a highly reflective mirror layer of a metal or metal alloy, more particularly silver or aluminium, and a dielectric interference layer between the substrate * and the reflecting layer, the attempt is made to achieve the above-described selectivity in the reflection by forming the J 4 interference layer as a high-refraction non-reflecting coating adapted to the long-wave visible range, for example from TiO2, CeO2, Ta2O5, Bi2O3 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 15 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, the mirror having a transparent coating support or substrate which is preferably of soda silicate glass, and a rear coating comprising a highly reflective mirror layer of a metal or metal alloy, more particularly silver or aluminium, and a dielectric interference layer between the substrate and the reflecting lt^yer, wherein the dielectric interference layer is devised in its thickness as a non-reflecting coating for the visible long-wave range of the sped ruin, and an additional layer of a metal or a metal alloy is disposed between the transparent substrate and the dielectric interference layer and is of a thickness such that the light transmittance of the composite comprising the transparent substrate and the additional layer is from 10 to 55% less than that of the transparent substrate alone.

In one special embodiment of the invention, the light transmittance of the composite comprising the transparent substrati' and the additional layer is from 15 to 45% less than that of the transparent substrate alone.

According Lo the invention, the additional layer may consist of chromium, nickel, iron, titanium, alloys of these metals or an alloy of the metals chromium, aluminium and iron.

Alternatively, according to the invention, the additional layer may consist of silver.

ALso, «according to the invention, the additional layer may consist of aluminium.

With the additional layer used according to the invention, il has surprisingly been possible to achieve the selective ' spcclia, cuivc required for dazzle- free vision, i.e. having > a lower degree of reflection in the long-wave visible spectral range than in the short-wave visible range, in , i conjunction with an average light reflection of such a mirror.

Unlike the case of known interference filters having a melal/dielectric/metal construction, for example of the kind described in DE-PS 716 153, an essential feature of the invention is the cooperation of the high reflection amplitude at the interface between the dielectric interference layer and the rear highly reflective layer, with the front weaker reflection amplitude of the additional layer by way of interference. This layer construction surprisingly makes it possible to achieve the required selective spectral curve for the rear-view mirror according to the invention, with a degree of reflection decreasing continuously from the blue to the long-wave visible range.

Generally, coating of the transparent substrate for the production of the coating according to the invention is all * i carried out by the vacuum-coating. Preferably, the metal or metal alloy layers may be applied by vaporisation from resistance-heated vaporisation devices or by electron beam vaporisation. Cathode sputtering in the form of D.C., low-frequency and high-frequency atomisation, and the particularly economic MAGNETRON cathode sputter process, are 4 also suitable. The dielectric interference layers may be applied either by direct vaporisation or cathode sputtering ' of the corresponding dieLectric materials. The known processes of reactive vaporisation or reactive cathode sputtering of the corresponding metals can aLso be used.

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 Lo the coating in order to improve the resistance of the rear-view mirror according to the invention to corrosion. This may, for example, be < ft 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.

The light attenuation adjustable by the additional layer in the range indicated according to the invention depends, on the one hand, on the degree of light reflection required for the dazzle-free rear-view mirror. The light attenuation required by the additional layer is all the greater within the indicated range, the lower the degree of light reflect ion selected. There is also a certain dependency according to whether silver or aluminium is used for the rear mirror layer. Somewhat higher light attenuation values are required for silver than aluminium, to give the same 1ight reflection. Λ number of dielectric materials have proved suitable for the dielectric interference layer provided that they are substantially absorption-free only in the visible range and hence they do not cause an additional unwanted light attenuation. Not only dielectric layers having a high refraction index above 1.7 are suitable, of the kind used for effective non-reflection on the air side of highly reflective single metal layers, for example T1O2, ZnS, CeO2r U±2Oj or Ί^Ο^, but also layers having a lower refractive index, eg silicon dioxide and magnesium fluoride.

With the three-layer construction provided according to the invention it is obviously sufficient for the dielectric interference layer to act as a spacing layer between the two metal layers, i.e., the reflecting layer and the additional layer, its thickness being equivalent to that of a quarter-wavelength layer' for the long-wave visible range.

The materials preferably used according to the invention for the additional layer, i.e., chromium, nickel, iron, titanium, alloys of these metals or an alloy of the metals chromium, aluminium and iron, are distinguished, when applied in a vacuum, by good adhesion to the glass substrate and the adjoining dielectric interference layer, and thus give the complete coating good resistance to abrasion. Also suitable, however, are layers of other metals and metal alloys, for example including layers of the metals silver or aluminium used for the rear mirror coating.

The use of the same material for the reflecting layer and for the additional layer provides a particularly economic application of the coating system, since the same vapour-coating devices and targets can be used for the I coating operation.

Further fealuics and advantages oi. the invention will be apparent from the claims and from the following description, in which exemplified embodiments are explained in detail ' with refcience to the diagrammatic drawings wherein: i ' Fig. 1 is a first exemplified embodiment of a rear-view mirror according to the invention in diagrammatic section at right angles to the plane 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 of rear-view mirrors according to the invention.

Figure 1 shows an exemplified embodiment of a rear-view 20 mirror according to the invention, in which an additional layer 12 of chromium, followed by a dielectric non-reflecting layer 14 of ZnS, in turn followed by a reflecting layer 15 of silver, are disposed on a transparent substrate 10 consisting of soda-silicate glass.

In the exemplified embodiment shown in Figure 2, a protective layer 16, in this case a coat of varnish, also follows the reflecting layer 15.

The rear-view mirror according to the invention can be produced in the manner described in the following examples: 1 I.

Example 1 ' Λ chromium-nickeL layer 12 of the composition 80% by weight of nickel and 20% by weight of chromium, was first applied to a 3 mm thick clear glass plate 10 in a high-vacuum vapour-coating plant. The coating process was concluded when the light transmittance of the plate, which was 91% before the start of the vapour-coating operation, had dropped fo 60%. A zinc sulphide layer 14 of a thickness of nm was then applied by vapour coating. Coating with silver was then carried out (reflecting layer 15) in a thickness such that the light transmission of the coated plate was less than 1%.

The spectral reflection with a ray incidence from the glass side of the coated plate gave the curve 1 in Figure 3. This has the selective spectral gredation required for dazzle-free vision, with the degree of reflection decreasing s in the long-wave visible range as compared with the short-wave visible spectral range. Accordingly, when viewed from the glass side the plate has a distinct blue cast. The brightness level of the plate, which has a degree of light reflect.ion of 0.6, is at the top limit of the required j range. With Light reflections between 0.5 and 0.6, the double image effects produced by the somewhat laterally offset additional reflection produced at the outside of the mirror are no longer significant.

Example 2 Λ chromium layer 12, ίΐ t. Itanium dioxide layer 14, and an al uin in Lum layer 15 wore successfully applied by vapour j 5 coating to a clear glass plate 10, 3 mm thick. The chromium layer 12 was of a thickness such that it reduced the light transmittance of the uncoated plate from 91% to 76%. The thickness of the titanium dioxide layer 14 was 64nm. The light transmittance was reduced to a value below 1% by the 2Q aluminium layer 15. When viewed from the glass side the coated plate also had a distinct blue cast as did the plate in example 1. The spectral reflection of the plate measured from the glass side is shown as curve 2 in figure 3 and has the required selective reflection with the degree of reflection decreasing with longer visible spectral j wavelengths. The brightness level of this plate, with a light reflection of 0.54, is also in the required middle range .

Claims

CLAIMS:

1. A rear-view mirror for vehicles, the mirror having a transparent coating support or substrate which is preferably 5 of soda silicate glass, and a rear coating comprising a J highly reflective mirror layer of a metal or metal alloy, more particularly silver or aluminium, and a dielectric ) interference layer between the substrate and the reflecting layer, wherein the dielectric interference liiyer is devised Ί θ in its thickness as a non-reflecting coating for the visible long-wave range of the spectrum, and an additional layer of a metal or a metal alloy is disposed between the transparent substrate and the dielectric interference layer and is of a thickness such that the light transmitLance of the composite comprising the transparent substrate and the additional layer is from 10 to 55% less than that of the transparent substrate alone.

2. Λ rear-view mirror according to claim 1, wherein the 20 light transmittance of Lhe composite comprising the transparent. substrate and the additional layer is from 15 to 45% less than that of the transparent substrate alone.

3. A rear-view mirror according to claim 1 or 2, wherein 25 the additional layer consists of chromium, nickel, iron, I titanium, alloys of these metals or an alloy of the metals chromium, ίΐΐυιηΐ nium and i ron.

4. A rear-view mirror according to claim Ί or 2, wherein 5. The additional layer consists of silver. i.

5. A rear-view mirror according to claim 1 or 2, wherein the additional layer consists of aluminium. 10

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

7. A rear-view mirror according to any of the previous 15 claims, wherein «at least one of the layers <»f the rear coating is applied by vacuum coating.

8. A rear-view mirror substantially in accordance with any of the embodiments herein described with reference to the 20 accompanying drawings and/or the examples. MACLACHLAN & DONALDSON,