Rear view mirror for vehicles, in particular motor vehicles, with a back layer.

The invention relates to a rearview mirror for vehicles, particularly motor vehicles, or the like, with a transparent layer support, preferably of soda silicate glass consisting, and a back coating which is a arranged a highly reflective mirror layer of a metal or aluminum, and between the substrate and the reflective layer having interference layer of dielectric material.

As back coating for auto mirrors can be known layers of highly reflective metals silver and aluminum insert, wherein such back coating generally towards a front side coated rearview mirror has the advantage that the _Be- Is protected by coating the mirror enclosure from direct atmospheric exposure, especially pollution. By means of the aforementioned highly reflective metals obtained rearview mirror_Reflexionswerten in the visible spectral range of more than 85%.

From "Selective Optical Surfaces for Solar Energy Converters", MM Koltun, New York, 1961, page 39, a reflection of the layer structure described above is known in which to further increase the reflectivity on top 90 between the transparent layer support, in the following, inter alia, also abbreviated as glass slides, and there made of aluminum metal reflective layer is disposed a reflexerhöhende, one- or two-layer, dielectric interference coating.

However, such levels lead because of the daylight quite desirable high (and essentially wavelength-independent) reflectance during night driving glare for the driver through the headlights of following vehicles.

On the other hand, anti-glare rearview mirror is known (DE-_AS ₁₀ 36 672; DE-AS 24 49 763), in which on the front of which preferably consists of transparent glass_Schichtträgers applied a lining in the form of a non-metallic, preferably metal oxide interference coating and the back is optionally provided with a dark, absorbent coating. The interference coating can, for example, of three sub-layers in the order of high refractive index layer - low refractive index layer -_Hochbrechende layer exist. If the thicknesses of these partial layers set as λ / 4 layers on the short wavelength visible spectral region, so have such mirrors in the blue spectral range compared to the long-wave yellow-red range, a higher reflectivity on. By thus selectively reflecting blue haze a sufficiently bright image is generated while reducing driving at night the glare from the headlamps of following vehicles, with its high proportion of radiation in the long wavelength visible area in daylight yet.

A disadvantage of such anti-glare rearview mirror with front-side interference coating, however, is that the coating is exposed directly to the outside atmosphere. In particular, it can at removing dirt easily come from the coated front of the rearview mirror to scratching of the coating, which interfere with the functioning of such a rearview mirror in particularly because scratches rise to a highly reflective layer significantly stronger optical interference as, for example, at the interface of a normal glass panel to air having a reflectivity of only 4%.

The way to achieve by back arrangement of the coating on the support the need to protect the coating, can not be pursued in the aforementioned non-metallic interference coatings; they are transparent and would have to be covered on its rear side by a dark top bar. This, however, which is important for the effect of the interference filter outer interface would eliminate interference coating / air, whereby the function of the filter would be affected disturbing.

If you try the other hand, in a generic mirror with rear reflective layer of aluminum or even silver and between substrate and reflective layer disposed dielectric interference layer, the selectivity described above in reflection to achieve in that the interference layer as the _langwellige, visible area adapted high-index _ent _spi_egelungsschicht, for example, TiO₂, CeO₂, Ta₂O₅, Bi₂O₃_U.Nd / or ZnS is formed, this leads to a possibly weak bluish mirror without significant anti-glare effect.

The invention is therefore based on the object to provide an anti-glare rearview mirror for vehicles, in particular motor vehicles, which while avoiding the drawbacks of known rearview mirror with front-side interference coating a light reflectance in the range between the required according to the guidelines of the European Community minimum light reflectance of 0 , 4 and having about 0.6.

This object is achieved in that the dielectric interference layer in thickness _entspiegelungsschicht is designed for the long-wave visible spectral region; and in that between the transparent substrate and the dielectric interference layer is an additional layer of a metal or a metal alloy such thickness is arranged as_ß the light transmittance of the transparent layer from the support and the additional layer existing network by 10 to 55% lower than that of the transparent layer support alone.

A particular embodiment of the invention provides that the light transmittance of the transparent layer from the support and the additional layer existing network by 15 to 45% lower than that of the transparent layer support alone.

According to the invention it can be provided that the additional layer of chromium, nickel, iron, titanium, alloys of these metals or of an alloy of the metals chromium, aluminum and iron.

Alternatively, the invention also proposes that the additional layer consists of silver.

Furthermore, the invention can be provided that the additional layer is made of aluminum.

With the additional layer according to the invention it is surprisingly possible to obtain the desired glare-free viewing selective spectral lower reflectance in the long wavelength visible spectral range compared to short-wavelength visible region in conjunction with an average luminous reflectance of such a mirror.

The invention is characterized, in contrast to known interference filters of the structure metal / dielectric / metal, as described for example in DE-PS 716 153, the interaction of the high reflection amplitude at the interface between the dielectric interference layer and the back, highly reflective mirror layer with the front weaker reflection amplitude of the additional layer through interference. Through this layer structure, it is surprisingly possible with continuously visible from the blue to the longwave region to achieve the desired spectral selective of erfindungsgemäB-en rearview mirror decreasing reflectivity.

The coating of the transparent carrier layer for producing the coating according to the invention is generally effected by vacuum total coating. Preferably, the metal or metal alloy layers can by evaporation from resistively heated_Vbe erdampfervorrichtungen or deposited by electron beam evaporation. In addition, sputtering are as direct, low-frequency and high-frequency sputtering and the most economic method of Magnetron sputtering. The dielectric interference layers can be carried out either by direct evaporation or sputtering of the corresponding dielectric materials. The known method of reactive evaporation or reactive sputtering of the corresponding metals can be dropped.

In addition to the vacuum deposition Further, other deposition methods, such as. For example, wet chemical methods may be used by deposition from suitable starting solutions.

As the support, in addition to silicate glass and other transparent materials, preferably of plastic, such as. For example, polymethyl methacrylates, polyesters, polycarbonates and the like may be used.

Within the concept of the invention may further also be provided to improve the corrosion resistance of the rear-view mirror according to the invention, in addition to apply to the coating a protective layer. This can eg. B. be another metal, metal alloy layer or a metal oxide layer, which is then applied by the same application of the actual coating in selective vacuum process, or even a paint coating. A combination of both measures is provided.

The light attenuation to be set by the additional layer in accordance with the invention the specified range depends again on the light reflectance to be obtained for the anti-glare rearview mirror. The required light attenuation by the additional layer is greater, the lower the light reflectance is chosen within the stated range. In addition, there is also a certain dependency, depending on whether silver or aluminum is used for the back reflecting layer. For silver slightly higher light attenuation values ​​are needed for the same light reflection level than aluminum.

For the dielectric interference layer to a variety of dielectric materials have been found to be suitable, provided that they are substantially free of absorption in the visible region and thus not through them an additional undesirable attenuation of light is caused. Suitable not only dielectric layers with a high refractive index> 1.7, such as those used for the effective antireflection coating of highly reflective metal single layers on the air side, such as Ti0₂, ZnS, Ce0₂, Bi₂0₃ or Ta₂O₅But also layers having a lower refractive index, such. As silicon dioxide and magnesium fluoride.

In the inventively provided 3-layer structure, it is obvious enough that the dielectric interference film fulfills a role as a spacer layer between the two metal layers, namely the reflection layer and the additional layer, wherein its thickness corresponds to a quarter wavelength layer of the long-wavelength visible region.

The materials according to the invention are preferably used for the additional layer, namely, chromium, nickel, iron, titanium, alloys of these metals or an alloy of the metals chromium, aluminum and iron, are distinguished when applied in a vacuum by a good adhesion to the glass substrate and the subsequent dielectric interference layer and thus give the whole a good layer

Abrasion resistance. but are also suitable layers of other metals and metal alloys, for example, layers of the metals silver or aluminum used for the back mirror coating.

The use of same material for the mirror layer as well as for the additional possible by the fact that in each case the same evaporation facilities or targets can be used for the coating, a particularly economical application of the layer system.

Further features and advantages of the invention will be apparent from the claims and from the description below, are explained in the embodiments with reference to the schematic drawing. In which:<ul><li>1 shows a first embodiment of a rearview mirror according to the invention in schematic section perpendicular to the transparent carrier layer level.</li><li>2 shows a second embodiment of a rearview mirror according to the invention in Figure 1 corresponding section..; and</li><li>Fig. 3 is a graph of the reflectance rearview mirror according to the invention. </li></ul>

Fig. 1 shows an embodiment of a rearview mirror according to the invention, in which consisting on a transparent substrate 10 made of soda silicate glass, an additional layer 12 of chromium, subsequently a dielectric anti-reflection layer 14 made of ZnS, and, subsequently a reflective layer 15 of silver disposed are.

In the embodiment of FIG. 2 in connection with the reflective layer 15 is still a protective layer 16, in this case, a varnish coating disposed.

The preparation of the rearview mirror according to the invention can be carried out in the manner described in the following examples:

Example 1:

On a clear lens 10 is 3 mm thick, a stainless layer was 12 wt .-% of the composition 80 nickel and 20 wt .-% chromium vapor deposited in a high vacuum vapor deposition first. The coating process was stopped when the light transmittance of the disc, which was 91% before the start of vapor deposition was reduced to 60%. Then a zinc sulfide layer 14 was deposited to a thickness of 65 nm. Then, the coating with silver (reflection layer 15) was in a thickness such that the light transmission of the coated pane was below 1%.

The measurement of the spectral reflectance at incident radiation from the glass side of the coated pane gave the reproduced as curve 1 in FIG. 3 curve. This results in the desired glare-free viewing selective spectral running with decrease in reflectivity in the long wavelength visible compared to the short-wave visible spectral range. Accordingly, when viewed from the glass side, the disc has a distinct blue cast. The brightness level of the disc, which has a luminous reflectance of 0.6, is at the upper limit of the desired range. In light reflectance levels between 0.5 and 0.6 in particular are also the double image effects that are caused by the somewhat laterally offset additional reflection on the outside of the mirror is no longer important.

Example 2:

On a clear glass sheet 10 of 3 mm, a titanium dioxide layer 14 and an aluminum layer 15 were successively a chrome layer 12 is evaporated. The chromium layer 12 was doing a thickness such that the light transmittance of the uncoated plate was lowered from 91% to 76% through them. The thickness of the titanium dioxide layer 14 was 64 nm. The aluminum layer 15, the light transmittance was lowered to a value of &lt;1%. The coated pane exhibited when viewed from the glass side as the disk in Example 1 also on a distinct blue cast. The spectral reflectance curve of the disc, measured from the glass side is reproduced as curve 2 in Fig. 3 and shows the desired selective reflection history with decrease in reflectivity at the longer wavelengths of the visible spectral range. Also, the brightness level of this disc with a light reflectance value of 0.54 is desired in the central region.

The features disclosed in the foregoing description, in the drawing and in the claims the invention may also be material for realizing the invention in its various embodiments in any combination, both separately.