WO2008104389A2

WO2008104389A2 - Layer system for wipe-resistant reflectors

Info

Publication number: WO2008104389A2
Application number: PCT/EP2008/001573
Authority: WO
Inventors: Torsten Schmauder
Original assignee: Leybold Optics Gmbh
Priority date: 2007-02-28
Filing date: 2008-02-28
Publication date: 2008-09-04
Also published as: TWI417565B; DE102007010124A1; WO2008104389A3; TW200900726A

Abstract

In the layer system for wipe-resistant optical reflectors on a substrate, comprising an optically reflective material layer and a transparent upper layer structure disposed on the side of the metal layer opposite the substrate, wherein the layer structure comprises a cover layer made of a hard layer deposited based on a plasma method, the hard layer being based on at least one silicone-organic compound and optionally having at least one intermediate layer, it is provided that the layer thickness of the upper layer structure is selected such that a spectral mean reflection level Rs dependent on the layer thickness of the upper layer structure has a maximum Rmax, that a spectral mean value Rs of a reflection level dependent on the layer thickness of the upper layer structure has a value of > Rmetal - 1/3 ΔR, wherein Rmetal is a spectral mean value Rmetal, determined in an analog fashion to Rs, of a reflection level of the unprotected metal layer determined in an analog fashion to Rs and wherein ΔR = Rmetal - Rmin is true, and Rmin refers to the minimum of the reflection level dependent on the layer thickness of the upper layer structure, or is a color difference ΔE* = root[(L*s - L*m)**2 + (a*s - a*m) **2 + (b*s - b*m)**2] < 2.0 between a color impression Fs = (L*s, a*s, b*s) dependent on the layer thickness of the upper layer structure and the color impression of the unprotected metal layer Fm = (L*m, a*m, b*m). The invention further relates to a method for producing such a layer system.

Description

description

Layer system for smudge-proof reflectors

The invention relates to a layer system and a method for producing a layer system according to the features of the preambles of the independent claims.

Many luminaires use, in addition to the actual light source (lamp), one or more reflective surfaces (reflectors) for influencing the light path and thus the illumination effect and distribution. Many such reflectors today consist of a plastic molding whose surface receives the reflector function by metallization. In some applications, the reflectors described are exposed to mechanical stresses during manufacture - for example, during the item transport and the installation of the lamp - or during the entire life of the lamp - for example, for cleaning - exposed.

Naturally, for the reflectors, the highest possible reflection of the light is usually aimed for, at least in the wavelength range in which the luminaire is to be used as the light source - typically in the visible range of about 400 nm to about 800 nm for humans.

Plastic surfaces as well as the coatings usually produced by vacuum metallization are extremely scratch sensitive mechanically. In order to avoid premature destruction of the component - often even during the assembly of the luminaire - an additional mechanical protective coating is required. So far, this is usually made by painting.

Coatings of indoor downlight reflectors with a transparent hard topcoat are known. As described for example in DE 196 34 334 C1, there are different relevant methods for the production of reflection coatings with an optical reflection layer and a final protective layer. According to a first method, a vacuum metallization by a reflective layer is made of a metal on which in turn by means of a dipping or spraying a final protective coating is applied, which protects the reflective layer against mechanical stress, such as wiping. In this method, there is an increased capital expenditure due to the separate process steps of vacuum coating and painting, each of which makes a vacuum coating chamber and a dipping or spraying system necessary. Since in the painting process quality losses due to dust and droplet formation lead to an increased reject rate, the costs increase further. Furthermore, not infrequently low durability of the coatings are observed.

In a second method, a reflective coating is provided with a plasma-deposited protective layer. In this case, a hard covering layer is produced on a reflective metal layer produced by means of vacuum metallization by means of a plasma polymerization method.

A mechanical protective layer can be produced, for example, by plasma decomposition (PECVD) of organosilicon compounds with oxygen. As the organosilicon compound, for example, hexamethyldisiloxane (HMDSO) or tetramethyldisiloxane (TMDSO) are used. In addition to oxygen (O ₂ ), ozone (O ₃ ), nitrogen oxide (N ₂ O) or other oxygen-donating substances can also be used as the oxygen source. A description of the production of hard coatings by means of PECVD of siloxanes is given, for example, by the documents DE 3 413 019 A1 and EP 007 48 259 B1.

The production of siloxane-based hard layers as protective layers against mechanical stress, in particular abrasion, is to be distinguished from the production of chemical protective layers, in particular corrosion protection layers, by PECVD of organosilicon compounds without the addition of oxygen. Such anticorrosion layers are used, for example, to protect the reflective aluminum layers on reflectors for vehicle lights and described, for example, in DE 2 537 416 A1.

The layers obtained by PECVD of siloxanes without added oxygen are similar in their properties to a silicone rubber: they are soft, elastic, chemically very resistant. In the context of the present invention, such layers are referred to below as siloxane anticorrosive coatings

By contrast, the layers obtained by PECVD from oxygen-added siloxanes are more like glass. They are transparent, hard and brittle. In the following, these layers are referred to as siloxane hard layers.

It is also known, for example, to achieve an advantageous adaptation of the hard layer to the likewise comparatively soft plastic substrate, for example by means of gradient layers with a stepped or stepless transition from an elastic base layer to a scratch-resistant cover layer. An example of this is the mentioned DE 3413019 A1. An important aspect of the design of a layer system for mechanically protected metal reflector layers on plastic substrates is the layer sequence. Good protection is achieved by applying the hard layer to the metal layer on the side of the metal layer facing away from the substrate. The disadvantage here, however, that the protective layer must be traversed by the light to be reflected, so that there is a loss of reflectance, such as by absorption in the hard layer or by interference. These losses are also often wavelength-dependent and lead to undesirable color effects.

In order to ensure an adequate abrasion-protective effect of a plasma CVD (PCVD) layer in practice, a certain layer thickness is required, with thicker layers causing color distortions of the reflected light. In DE 196 34 334 C1, in order to increase the mechanical stability of thin HMDSO layers, it has been proposed to place as much of the abrasion-protective layer as possible under the reflective metal layer and to apply only a small portion as a hard covering layer to the reflective metal layer. Therefore, according to DE 196 34 334 C1, a thin HMDSO cover layer with thicknesses of 50 to 100 nm is supported by a thick hard base layer under the metal layer and, when manufactured, terminates the deposition of the HMDSO cover layer at a thickness at which the formation of interference colors just starts.

The invention is based on the object to provide a layer system for smudge-proof optical reflectors and a method for producing such a layer system, which has a hard top layer with a sufficient abrasion resistance and at the same time has a relation to the protected metal layer as unadulterated optical impression.

The object is achieved with the features of the independent claims.

In the inventive layer system for smear-resistant optical reflectors on a substrate, comprising an optically reflective metal layer and on the substrate opposite side of the metal layer arranged transparent upper layer structure with a cover layer of a plasma-deposited hard layer deposited on at least one silicon-organic compound based and optionally with at least one intermediate layer, the layer thickness of the upper layer structure is selected so that a spectral reflectance has a predetermined for the particular application maximum.

The invention is based on the recognition that with increasing layer thickness of the upper layer structure and in particular the cover layer undesirable effects, such as Increasing color falsification by wavelength-dependent interference with a varying degree of reflection on the respective spectrum occurs and the reflectance decreases, but that decrease in the range of a certain thickness of the cover layer, these effects and a relation to the unprotected metal layer largely neutral color impression of the reflection occurs. If the layer thickness of the upper layer structure is further increased beyond the said range, a sharp drop in the degree of reflection is obtained, in particular at short wavelengths, and thus an increased color distortion of the reflected light. With an even further increase in the layer thickness, reflected light with a largely neutral color impression is obtained again. Surprisingly, it is possible to achieve a very low color distortion by selecting the layer thickness of the upper layer structure such that a mean spectral reflectance assumes a maximum R _ma χ.

The mentioned demand for the highest possible reflection of the generated reflector is often combined with the requirement to admit no undesired color impressions by spectrally uneven absorption or interference. This combination of requirements requires a qualification criterion adapted to the particular application for assessing the suitability of a given layer system, wherein a spectral mean value of the reflectance R _{5 is} used as a criterion according to the invention.

As the spectral mean of the reflectance R, the average of the measured reflectance formed with a suitable weighting function over a predetermined wavelength range of the reflected radiation is defined, for applications in the visible spectrum preferably in the range of 360nm to 830nm, but at least the range of 400nm to 700nm includes. The averaging is performed with a weighting function dependent on the specific application. For example, in the simplest case an arithmetic mean can be used, although other functions are useful.

The specific method of spectral mean value formation of the reflectance is adapted to the respective specific task of the reflector layer with respect to the wavelength range and the relative weighting of the wavelengths contained therein in which the reflector is to operate. One known method is the determination of the color coordinates L ^* , a ^* and b ^* :

The L ^* a ^* b ^* color system is the standard system for psychophysical color stimulus specification developed by the CIE Commission (Commission Internationale de l'Eclairage, Publication CIE no. 15.2, Colorimetry, 2nd Ed., Central Bureau of the CIE, Vienna, 1986), as described, for example, in ASTM Designation 308-01 (Standard Practice for Computing the Colors of Objects by Using the CIE System, November 2001).

In the present invention, the color impression L ^* a * b ^{* is determined} with one of the CIE standard illuminants, preferably D65 and a 2 ° or 10 ° observer. For the measurements of the spectral reflectance, for example, a colorimeter from X -Rite Inc. (4300 44 ^th Street SE, Grand Rapids, MI, 49512 USA) model SP60 can be used.

Since the reflectance depends on the viewing and incident angle of the reflected radiation, it is preferred to determine the reflectance in the direction of a typical viewing position of the reflector and for a typical angle of incidence of the incident radiation.

According to a further aspect of the invention, the layer thickness of the upper layer structure is selected such that

a spectral average value R _s of a dependent on the layer thickness of the upper layer structure reflectance a value> R _meta i - having 1/3 .DELTA.R, wherein R _me t _a i a same way as R _s educated spectral average value R _me tai an analog as R _s specific Reflectance of the unprotected metal layer and ΔR = R _meta i - R _m i _n and R _m j _n denotes the minimum of the layer thickness of the upper layer structure dependent reflectance R _s or

between one of the layer thickness of the upper layer structure dependent color impression F _s = (L ^* _s , a ^* _s , b * _s ) and the color impression of the unprotected metal layer F _m = (L ^* _m , a ^* _m , b * _m ) a color difference ΔE ^* = root [(L ^* _s -L ^* _m ) ^** 2 + (a ^* _s -a ^* _m ) ^** 2 + (b ^* _s -b ^* _m ) ** 2] <2.0.

The spectral average R _me tai formed analogously to R _{s is} formed with the same weighting function and over the same wavelength range as R ₅ . The reflectance of the unprotected metal layer, which is determined analogously to R _{s, is} determined under the same conditions and with the same measuring method as the reflectance dependent on the layer thickness of the upper layer structure.

The L ^* a ^* b ^* color system is the standard system for psychophysical color-stimulus specification developed by the CIE Commission (Commission Internationale de l'Eclairage, Publication CIE No. 15.2, Colorimetry, 2nd ed., Central Bureau of the CIE, Vienna, 1986), as described, for example, in ASTM Designation 308-01 (Standard Practice for Computing the Colors of Objects by Using the CIE System, November 2001).

In the present invention, the color impression L ^* a * b * is determined with one of the CIE standard illuminants, preferably D65 and a 2 ° or 10 ° observer. For the measurements of the spectral reflectance, for example, a colorimeter from X-Rite Inc. (4300 44 * Street SE, Grand Rapids, MI, 49512 USA) model SP60 can be used.

If, according to the invention, a layer thickness of the upper layer structure is chosen such that a spectral mean R _{s of} a reflectance dependent on the layer thickness of the upper layer structure has a value> R _meta -1/3 ΔR, an optical reflector is obtained whose reflected light is largely unadulterated is and at the same time has a high resistance to wiping and scratching. Here, R is a _meta i analogous to R _s educated spectral average value of an analog as R _s specific reflectance of the metal layer and unprotected .DELTA.R = Rmetai - Rmin. wherein R _min denotes the minimum of the layer thickness of the upper layer structure dependent reflectance R _s . In a preferred embodiment, a layer thickness of the upper layer structure is selected for which the spectral mean R _{5 of} a reflectance dependent on the layer thickness of the upper layer structure has a value> R _me tai - c ΔR with c in a range of 1/10 to Y * ,

Surprisingly, the global parameters R _meta ι and ΔR are suitable to determine the layer thickness of the upper layer structure so that a largely color neutral impression of the layer system is realized.

Alternatively, it is proposed to use the L * a ^* b * color system to characterize the reflected light and to select the layer thickness of the upper layer structure such that between a color impression dependent on the layer thickness of the upper layer structure F _s = (L ^* _s , a ^* _s , b * _s ) and a color impression of the unprotected metal layer F _m = (L ^* _m , a * _m , b * _m ) is a color difference ΔE ^* of less than 2.0.

According to this aspect of the invention, the color impression is compared with the color impression of the unprotected metal layer as a function of the layer thickness of the upper layer structure. The L ^* a ^* b ^* color system is based on the characteristics of human perception and is better suited for characterizing the color impression of optical reflectors than, for example, an arithmetic mean of the reflectance. L ^* is a measure of the brightness, a ^* for the red-green and b ^* for the yellow-blue value of the color impression. De layer thickness of the upper layer structure is in a range between 110nm and 200nm. A thickness of 130 nm to 150 nm is preferred, in particular for siloxane-based hard coatings.

The layer thickness of the cover layer is preferably in a range between 110 nm and 190 nm, so that a high abrasion resistance of the layer system can be achieved.

The invention can be applied to different reflectors.

A car headlight reflector, which is the primary reflector, is designed for the best reflection of the specific radiation of the light source used, whereby the averaging weights the relatively short-wave (blue) halogen or xenon radiation more strongly than relatively long-wave radiation.

Decorative parts (bezels) have hitherto often been electroplated in the prior art, for example by means of chromium plating, in order to achieve a hard coating. Since the galvanic coating, in particular the Chromgalvanik requires larger amounts of toxic substances, the application of this method is associated with a high cost of process safety and disposal and should therefore be avoided in principle.

A bezel should reflect the defined, decorative color of the metal layer, so erfindungsgernäß a color difference ΔE * <2 is achieved.

A ceiling light for the distribution of pleasant-looking white light will be optimized for the best possible reflection with a spectral averaging according to the sensitivity of the human eye.

According to the invention it is possible to use thicker upper protective layers than before, since the usual color distortions and reflection losses can be avoided with the layer system according to the invention. Since the abrasion resistance of the layer system increases with the thickness of the cover layer, it is possible according to the invention to provide optical reflectors with high wipe and scratch resistance and at the same time high optical quality.

In an advantageous development of the invention, it is provided that a base layer is provided on the side of the metal layer facing the substrate, which increases the adhesion of the metal layer to the substrate or the mechanical stability of the layer system. The base layer can be a plasma-deposited layer, based on at least one silicon-organic compound. Furthermore, the base layer may be a lacquer layer. Preferably, a hard base layer is used, which prevents mechanical breakdown of the layers arranged above it and makes it possible to further increase the abrasion resistance, if an increase in the thickness of the cover layer is to be avoided, since otherwise the optical impression of the reflector would deteriorate.

In a further development of the invention, at least one upper intermediate layer is arranged between the cover layer and the metal layer. Preferably, this upper intermediate layer has an oxygen protection function for the metal layer.

Furthermore, at least one additional lower intermediate layer can be arranged between the base layer and the metal layer, in particular with an oxygen protection function for the metal layer.

The lower and / or upper intermediate layer preferably has a layer thickness between 10 nm and 20 nm. Appropriately, here is the use of the above-referred to as Siloxan Korrossionsschutzschicht, known protective coatings

The silicon-organic compound is preferably HMDSO or TMDSO, which are broken up by means of a plasma and deposited as a layer or layer constituents. In the production of the hard plasma-deposited layer, oxygen and / or nitrogen is incorporated in the layer, which is supplied as a reactive component during production. Preferably, the reactive component is supplied at a flow rate ratio of 1: 0.5 to 1: 20 of HMDSO or TMDSO to the reactive component, as is known per se.

Particularly suitable for optical reflectors is a metal layer which comprises at least one member of the group formed from aluminum, copper, silver, gold, titanium, magnesium, iron, steel, chromium or the alloys formed from them, since these form highly reflective metallic layers , The metal layer preferably has a thickness between 20 and 150 nm. The layer system according to the invention can be effectively produced inexpensively and in high quality using medium- to low-frequency electromagnetic excitation, for example with a frequency of 40 kHz in a conventional single-chamber coating system. Other aspects and advantages of the invention will become apparent from the following description of embodiments with reference to drawings independently of their summary in the claims.

Show it:

Figure 1 is a schematic representation of a layer system according to the invention

Figure 2 is an illustration of a layer thickness-dependent reflectance

FIG. 3 shows a measured reflectance of a substrate with a layer system plotted against the wavelength of the reflected light for different layer thicknesses

1 schematically shows the construction of a layer system according to the invention comprising a substrate 10, a metal layer 20, a cover layer 30, an upper intermediate layer 40, a lower base layer 50 and a lower intermediate layer 60. The substrate is preferably a plastic substrate, for example Polycarbonate or a metal substrate for an optical reflector. The metal layer 20 may be aluminum, copper, silver, gold, titanium, magnesium, iron, steel, chromium, or an alloy formed therefrom deposited by a sputtering process, a physical or chemical vaporization process, or an ion beam process. The cover layer 30 is a plasma-deposited hard layer based on at least one silicon-organic compound and having a high abrasion resistance. The base layer 50 is a plasma-supported deposited silicon-organic compound or a lacquer layer. Preferably, these are hard layers. The upper intermediate layer 40 and the lower intermediate view 60 are preferably deposited plasma-based and are based on an organosilicon compound. As the silicon-organic compound, HMDSO or TMDSO is preferably selected.

FIG. 2 shows the typical layer thickness dependency of a mean reflectance R for a layer system with a layer structure comprising a cover layer and optionally an intermediate layer. Typically, the degree of reflection initially decreases with increasing layer thickness, starting from the value of an unprotected metal layer, and reaches a minimum R _{min in} order subsequently to assume a first maximum and later further maxima. With increasing layer thickness, the value of the maxima decreases while the value decreases the minimum lying between the maxima increases. In the layer system according to the invention, the value of the layer thickness of the layer structure is chosen such that the mean reflectance R> R _meta i is 1/3 ΔR. Particularly preferred is a layer system with a layer thickness which leads to an average reflectance in the region of the first or second maximum. In the representation of FIG. 3, there are layer thicknesses in the range of S ₁ and S ₂ .

To produce a layer system according to the invention, an optical reflector is introduced into a vacuum chamber of a coating installation, for example a PylonMet 1 V system of the Applicant, in which there are glow electrodes for feeding in electromagnetic energy and magnetron sputtering cathodes with aluminum targets. The reflector is placed opposite the targets, with the surface to be coated facing the targets. The plasma-assisted deposition of the layers takes place by means of two plate electrodes, which are connected to a 40 kHz generator with a maximum power of 5 kW.

On a 3mm thick polycarbonate substrate, the application of a smudge-resistant layer system with the following process steps.

plasma treatment

The vacuum chamber is evacuated to a pressure of 3 x 10 ^"2 mbar. Argon gas is introduced into the vacuum chamber sccm about 800, wherein by means of electromagnetic energy having a power of 5 kW and a frequency of 40 kHz for approximately 30 seconds, a plasma The substrate is cleaned by the plasma and activated for better adhesion of the subsequent layer.

Plasma CVD of a hard base layer

A 350 nm thick hard layer by means of electromagnetic energy by an electromagnetic excitation of 40 kHz with a power of 4.5 kW and gas flows of 150 sccm HMDSO and 750 sccm of oxygen at a process pressure of about 4 x 10 ^"2 mbar at a process time of Applied 240 seconds.

Plasma CVD of an intermediate layer At a process pressure of 4 x 10 ^'2 mbar, HMDSO is introduced into the vacuum chamber at a flow rate of 100 sccm and a plasma is ignited by means of electromagnetic energy with a power of 4.5 kW and a frequency of 40 kHz for about 20 seconds , wherein an intermediate layer is deposited on the substrate of about 5 to 10 nm layer thickness.

Spitting a metal layer

The vacuum chamber is evacuated to a base pressure of less than 10 ⁵ mbar and then carried out at an argon flow of 540 sccm at 3 x 10 ^"3 mbar process pressure and 70 kW sputtering the application of a reflective aluminum layer with a layer thickness of about 80 nm at a Process duration of 15 s.

Plasma CVD of an intermediate layer

At a process pressure of 4 x 10 ^-2 mbar HMDSOO sccm with a flow rate of 100 introduced into the vacuum chamber and ignited by means of electromagnetic energy with a power of 4.5 kW and a frequency of 40 kHz for approximately 20 seconds, a plasma, wherein an intermediate layer is deposited on the substrate of about 5 to 10 nm layer thickness.

Plasma CVD of the topcoat

HMDSO at a flow rate of 150 sccm and oxygen at a flow rate of 600 sccm of a 40 kHz excitation with 4 kW plasma power are introduced into the vacuum chamber. With a duration of this step of 90 seconds, the deposition of a 160 nm thick protective layer takes place. Shorter or longer process times lead to a thinner or thicker protective layer.

After aeration of the chamber, the coated substrate can be removed.

The reflection spectrum of such a treated substrate gave the color coordinates L ^* = 94.3, a ^* = -1, 8 and b ^* = 1.5 at an average reflectance of 83%, with an arithmetic mean at a wavelength range of 400-700 nm took place. The coating consisted of several tape-pulls on a Tesa 4124 package tape attached to a previously attached grid without delamination and a 30 minute exposure to I percent NaOH solution with no visible damage. FIG. 3 shows the spectral reflectance of a layer system applied to a polycarbonate plate of about 3 mm thickness, plotted for different layer thicknesses of an upper layer structure comprising a hard outer layer and an intermediate layer in a wavelength range between 400 nm and 700 nm. The measurements were carried out with an SP-X spectral photometer from X-Rite for a D65 illuminator and a 2 ° observer. The metal layer consisted of magnetron-sputtered aluminum with a layer thickness of 100 nm. The layer system was produced by the method described above with an upper intermediate layer of 10 nm.

It can be seen from FIG. 3 that the reflectance of the unprotected metal layer, that is to say a layer system with a thickness of the covering layer of 0, is highest over the entire wavelength range considered. Already with a cover layer with a layer thickness of 40 nm, a drop in the reflectance at short wavelengths is observed. With a further increase in the layer thickness of the cover layer, a reduction in the degree of reflection toward longer wavelengths is observed. With a layer thickness of 160 nm, a higher degree of reflection can be seen in a medium wavelength range between 450 and 600 nm. At a layer thickness of 180 nm, there is again a sharp drop in the degree of reflection towards shorter wavelengths.

Table 1 shows the numerical values corresponding to FIG. 3 for the CIE L * a ^* b * color impression, ΔE * and the mean reflectance in% relative to the intensity of the incident radiation. In addition, an assessment of the subjective color impression is added in a column "Remarks." The layer system with a layer thickness of 160 nm has a maximum reflectance and a ΔE * <1.4 .. It can be seen that, with a cover layer of 180 nm, a relative high brightness L ^* occurs, but has a yellowish color impression.

Claims

claims

1. A layer system for smear-proof optical reflectors on a substrate, comprising an optically reflective metal layer and on the substrate opposite side of the metal layer arranged transparent upper layer structure with a cover layer of a plasma-deposited hard layer based on at least one silicon-organic compound and optionally with at least one intermediate layer, characterized in that the layer thickness of the upper layer structure is selected such that

a spectral average reflectance R ₅ dependent on the layer thickness of the upper layer structure has a maximum R _max ,

a spectral mean R ₅ a is dependent on the layer thickness of the upper layer structure reflectance a value> R _meta i - having 1/3 .DELTA.R, wherein R _meta i a analogously as R ₅ formed spectral mean R _me tai an analogous _R5 determined reflection degree of unprotected metal layer and ΔR = R _me tai - R _m m and R _min denotes the minimum of the layer thickness of the upper layer structure dependent reflectance or

between one of the layer thickness of the upper layer structure dependent color impression F _s = (L * _s , a * _s , b ^* _s ) and the color impression of the unprotected metal layer F _m = (L ^* _m> a * _m , b * _m ) a color difference ΔE * = root [(L ^* _s -L * _m ) ^** 2 + (a% -a ^* _m ) ^** 2 + (b * _s -b * _m ) ^** 2] <2.0.

2. Layer system according to claim 1, characterized in that on the side facing the substrate of the metal layer between the metal layer and the substrate, a base layer is provided.

3. Layer system according to claim 2, characterized in that the base layer is a plasma-deposited deposited, preferably hard layer, which is based on at least one silicon-organic compound or a preferably hard lacquer layer.

4. Layer system according to one of the preceding claims, characterized in that at least one upper intermediate layer is arranged between the cover layer and the metal layer.

5. Layer system according to one of the preceding claims 2 to 4, characterized in that between the base layer and the metal layer at least one additional lower intermediate layer is arranged.

6. Layer system according to one of the preceding claims, characterized in that a lower and / or upper intermediate layer is provided with an oxygen protection function for the metal layer.

7. Layer system according to one of the preceding claims, characterized in that the silicon-organic compound is hexamethyldisiloxane or tetramethyldisiloxane.

8. Layer system according to one of the preceding claims, characterized in that in at least one of the hard layers oxygen and / or nitrogen is incorporated.

9. Layer system according to claim 8, characterized in that the metal layer comprises at least one member of the group of aluminum, copper, silver, gold, titanium, magnesium, iron, steel, chromium or the alloys formed from them.

10. Layer system according to one of the preceding claims, characterized in that the layer thickness of the upper layer structure is in a range between 110nm and 200nm.

11. A method for producing a layer system for smear-resistant optical reflectors on a substrate, wherein on an optically reflecting metal layer on the side opposite the substrate of the metal layer, a transparent upper layer structure with a cover layer of a plasma-deposited hard layer deposited on at least one silicon organic compound based and optionally with at least one intermediate layer, is applied, characterized in that the layer thickness of the upper layer structure is chosen so that a dependent on the layer thickness of the upper layer structure spectral mean reflectance R _{s has} a maximum R _ma χ,

a spectral mean value R _{s of} a reflectance which depends on the layer thickness of the upper layer structure has a value> R _meta -1/3 ΔR, wherein R _meta 1 denotes a spectral mean R _meta 1 of an analogous to R _s formed as R _s Reflectance of the unprotected metal layer and ΔR = R _meta i - R _m i _n and R _m m denotes the minimum of the layer thickness of the upper layer structure dependent reflectance or

between one of the layer thickness of the upper layer structure dependent color impression F _s = (L * _s , a * _Sl b ^* _s ) and the color impression of the unprotected metal layer F _m = (L * _mi a * _m , b * _m ) a color difference ΔE ^* = Root [(L% -L ^* _m ) ^** 2 + (a ^* _s -a * _m ) ** 2 + (b ^* _s -b * _m ) ** 2] <2.0.

12. The method according to claim 11, characterized in that the vacuum remains unbroken during production.

13. The method according to any one of claims 11 or 12, characterized in that the metal layer is applied by a sputtering method, a physical or chemical evaporation method or an ion beam method.

14. The method according to any one of claims 11 to 13, characterized in that the silicon-organic compound is hexamethyldisiloxane or tetramethyldisiloxane, wherein in the preparation of the cover layer, a reactive component such as oxygen and / or nitrogen is supplied.

15. The method according to claim 14, characterized in that the reactive component is supplied in a flow rate ratio of 1: 0.5 to 1: 20 of hexamethyldisiloxane or tetramethyldisiloxane to the reactive component.

16. The method according to any one of claims 1 1 to 15, characterized in that an upper layer structure is applied with a layer thickness in a range between 110nm and 200nm.