DE102015114877A1 - Scratch-resistant antireflective coating - Google Patents

Abstract

The invention relates to a transparent element with an antireflection coating (5). The anti-reflection coating (5) with four layers (51, 52, 53, 54) is designed so that the color location of reflected light has a reduced dependence on layer thickness fluctuations.

Description

The invention relates generally to optical interference coatings. In particular, the invention relates to antireflection or antireflection coatings with high scratch resistance.

Chemically tempered glasses for displays of mobile electronic devices, such as smartphones or tablet PCs are known. As a rule, aluminosilicate glasses are used as coverslips for these displays. These aluminosilicate glasses typically have a refractive index of greater than 1.5 at a wavelength of 550 nm.

It is also known and customary to chemically bias cover glasses for optical displays. By chemical toughening, in which Na ions of the glass are exchanged for potassium ions from a salt bath, the potassium accumulates in a near-surface zone of several micrometers. The potassium content is in the range up to a few percent by mass. By chemical toughening an increase in flexural strength and scratch resistance is achieved. Nevertheless, after a short period of use of a typical product damage to the surface in the form of scratches can be seen. Although chemical tempering prevents easy breakage of the glass under bending stress, since the compressive prestressing prevents or delays propagation of a crack caused by a scratch, for example, scratches are avoided.

An antifingerprint coating (AFP), which is either oleophobic or hydrophobic or amphiphobic, can be applied to the glass, so that fingerprints do not arise or at least can be cleaned very easily. Today's products typically have a non-durable AFP, so the effect of easy cleanability or reduced fingerprint conspicuousness is lost after a few months. The AFP is generally a partially organic layer that is applied very thin so that it is optically inactive. The reflection of the product is therefore given primarily by the glass surface. At the top of the glass, therefore, about 4 percent of the light is reflected at normal incidence, which is particularly disturbing in bright lighting, such as sunshine, and limits the readability of the content of the display.

Antireflective coatings for antireflecting glass surfaces are known. Depending on the embodiment, they consist of several layers, which are applied to the glass substrate on one or both sides. Depending on the field of application of the product, a mechanically stable, ie damage-resistant or scratch-resistant version of the antireflection system is desirable. The general objective of an antireflective optical coating is to suppress uniformly the reflection of the visible part of the electromagnetic spectrum, so that as far as possible no color conspicuousness arises due to an uneven residual reflection. An example of such a color neutral, scratch resistant, antireflective coating is in US 2012/0212826 A1 specified.

In the course of the mobile phone cover manufacturing process, said glasses can be provided with a decorative print on the side facing away from the user, the so-called back of the cover, which is typically black or white. Often the company name or the product name is printed in silver lettering.

Antireflection systems usually consist of more than one layer, in particular if a large part of the visual spectrum is to be uniformly antireflected and not only at a specific wavelength. Two consecutive layers have different refractive indices. Layers of high and low refractive index alternate. The wavelength-dependent reflection curve is the result of the interaction of the individual reflections at the interfaces. A uniform, color-neutral reflection is the result of a perfectly matched sequence of optical layer thicknesses, i. the product of refractive index and layer thickness. The change of one or more layer thicknesses changes the reflection conditions and thus also the reflection result, in particular also the color location of the reflection.

Process-related layer thickness fluctuations, as they occur, for example, at different positions within a sample holder (English: Carrier) or fluctuations of Produktionslos to Produktionslos, therefore, can lead to a strong color change. Depending on the thickness of the layer thickness variation, there are strongly noticeable color location variations, which reduce the production yield.

The invention is therefore based on the object to provide an antireflection system, which has a good adhesion to the glass substrate, has a high scratch resistance, provides a good basis for a Antifingerprintbeschichtung and especially in typical process-related layer thickness variations has only a small change in color location. The invention specifically relates to a transparent element with a four-layer anti-reflection coating. This antireflection coating is designed in accordance with the above-mentioned object so that the color location of reflected light has a reduced dependence on layer thickness fluctuations.

The antireflective interference layer system according to the invention comprises a sequence of alternating high and low refractive layers. As the position progresses, the refractive index becomes alternately higher and lower. The layer system comprises at least four layers. High scratch resistance is achieved by using a transparent hard material for at least one high refractive index layer.

It can be seen that the layer thickness-dependent chromaticity variation in a four-layer antireflective coating can be achieved by using more than two materials. In this case, the first high-index layer applied to the substrate should have a refractive index n _m which lies between the refractive index of the further high-index layer n _h and the refractive index of the low-refractive index n _n .

• – einem im sichtbaren Spektralbereich transparenten scheibenförmigen Substrat und
• – einer auf dem Substrat abgeschiedenen Antireflexbeschichtung vor, wobei die Antireflexbeschichtung
• – vier aufeinanderfolgende Lagen umfasst, bei welcher aneinander angrenzende Lagen sich jeweils in ihrem Brechungsindex unterscheiden, derart, dass der Brechungsindex von Lage zu Lage abwechselnd ansteigt und abnimmt und sich Lagen mit niedrigerem Brechungsindex mit Lagen mit höherem Brechungsindex abwechseln.

Accordingly, the invention provides a disk-shaped element

• - A transparent in the visible spectral disc-shaped substrate and
• An anti-reflection coating deposited on the substrate, the anti-reflection coating
• Comprises four successive layers in which adjacent layers each differ in their refractive index, such that the refractive index alternately increases and decreases from layer to layer, and layers of lower refractive index alternate with layers of higher refractive index.

The lowermost of the four layers is a layer of higher refractive index and thus has a higher refractive index than the adjacent second lowest layer.

The four layers now have at least three different refractive indices such that the refractive index of the lowermost layer of the higher refractive index layer is lower than the refractive index of the further layer of higher refractive index. In this case, the lowermost layer with a higher refractive index is preferably formed from an oxygen-containing material. As a result of these features, the disk-shaped element shows, in particular, a slight color change in the case of layer thickness variation.

The lowermost, the substrate next layer of the antireflection coating is preferably an oxynitride layer or an oxide layer. Oxinitride layers with silicon or aluminum or with a mixture of both materials are particularly suitable because these materials are very transparent and at the same time hard, whereby the refractive index can be well adjusted and adjusted by the oxygen content during the coating process. In general, several components can be used for the composition of the layer. Thus, according to one embodiment of the invention, it is provided that the lowest layer contains at least three different components in oxinitridischer or oxidic form, which contribute to more than 1 atomic percent of the total composition.

The use of oxynitrides facilitates the production of a multilayer antireflective layer system in that silicon oxynitride or aluminum nitride, aluminum oxynitride or a nitride or oxynitride of a mixture of aluminum and silicon can also be used for the further refractive index hard material layer. Since their refractive index should be higher, the oxygen content is correspondingly lower. According to one embodiment of the invention, it is therefore provided that both layers with a higher refractive index are silicon oxynitride layers or aluminum oxynitride layers or a mixture of silicon and aluminum oxynitride, wherein the lowermost layer with a higher refractive index has a higher oxygen content than the further layer with higher refractive index.

If a purely oxidic layer system is to be produced via a sputtering process, then only oxygen can be used as the reactive gas. A mixture of the reactive gas is eliminated. Nevertheless, it is possible to produce an antireflective layer system according to the invention by using an alloy target which consists of at least two materials such that the oxide of one material is high-refractive and the oxide of the other material is low-refractive. By skillful choice of composition of the Alloy targets can now be a mixed oxide produced by the sputtering process in oxygen-containing process atmosphere, which meets the above requirements for a higher refractive index, but lower than the refractive index of the other high refractive index layer is sufficient. As an example, without limitation to other possibilities here is a target of silicon with an admixture of zirconium called or a target of aluminum with an admixture of zirconium.

As already stated above, more than two components can also be involved in the construction of the lowest layer. In particular, at least three different components may be present in oxinitridic or oxidic form, contributing to greater than 1 atomic percent of the total composition. For example, in addition to Si and Al, a further component with one or more atomic percent may be present and incorporated in oxidic or oxinitridischer form.

The sequence of the four layers of the antireflection coating is particularly preferably applied directly to the substrate.

Accordingly, the substrate surface directly adjoins the sequence of the four layers of the antireflective coating.

On the antireflection coating according to a particularly preferred embodiment of the invention, a fluoroorganic layer can be applied. In particular, such a layer can also be formed as a monolayer of fluoroorganic molecules, preferably with a layer thickness of 1 nm to 20 nm, particularly preferably with a layer thickness of 1 nm to 10 nm. The fluoroorganic layer can be, for example, an oleophobic coating

It has been found that a layer system in which an additional fluoroorganic layer is added to an antireflection coating with a thick, upper layer of hard material, in particular with the largest layer thickness of the antireflection coating, is not only effective in reducing fingerprinting or cleaning easily let, but that the thus coated, chemically toughened glass substrate and thus the element according to the invention supports in particular the avoidance of scratches.

This is attributed to the fact that the additional fluoroorganic layer presumably reduces the coefficient of friction of the surface so that damage to the surface is less pronounced.

In order to deposit the antireflection coating according to the invention, it is preferable to use sputtering, in particular reactive sputtering.

The invention will be explained in more detail below with reference to the figures and exemplary embodiments. In the figures, like reference characters designate the same or similar layers.

Show it:

1 a substrate with a four-layer antireflective coating,

2 a variant of in 1 shown embodiment,

3 a development of the invention with a light-absorbing backside coating,

4 Color locus changes to different elements depending on the structure of the anti-reflection coating and the presence or absence of a light absorbing backsize coating;

5 Color locus changes in antireflective layer systems with SiO ₂ / TiO ₂ layers.

1 shows an example of a disk-shaped element according to the invention. The element 1 generally includes, but is not limited to, the particular example illustrated, a transparent substrate in the visible spectral region 3 and one on the substrate 1 on a side surface 30 deposited anti-reflective coating 5 ,

The anti-reflective coating 5 includes four consecutive layers 51 . 52 . 53 . 54 , Neighboring layers differ in their refractive index. In particular, the refractive index changes from Position to position so that it alternately increases and decreases. If you go the layers from top to bottom to the substrate 3 through, so the refractive index of the top layer increases 54 to the second highest position 53 on, sinks to the next location 52 off and climbs to the bottom 51 again, being below the refractive index level 53 remains.

The lowest of the four layers 51 . 52 . 53 . 54 (ie location 51 ) is a layer of higher refractive index and thus has a higher refractive index than the adjacent second lowest layer 52 ,

Without limitation to the specific embodiment of 1 In any case, in the case of an antireflection coating according to the invention, such a sequence consists of four layers 51 . 52 . 53 . 54 available. The coating preferably contains 5 as optically effective layers only these four layers. However, it is not excluded that further layers at the top and / or bottom, or on the substrate side follow this sequence.

The four layers 51 . 52 . 53 . 54 have at least three different refractive indices, such that the refractive index of the lowest, the substrate 3 next location 51 with higher refractive index is lower than the refractive index of the other layer 53 with higher refractive index. This is the lowest position 51 with higher refractive index preferably formed from an oxygen-containing material.

The terms "lower refractive index" and "higher refractive index" apply relative to the adjacent layers. A layer with a lower refractive index consequently adjoins one layer (when the low-index layer completes the layer system) or two layers (when the low-index layer adjoins other layers of the layer system at both interfaces) with a higher refractive index.

The substrate 3 is particularly preferably an inorganic, oxidic substrate, in particular a glass substrate. The antireflective layer system according to the invention is particularly suitable for chemically toughened glass substrates.

It can be seen that a good bonding of the first hard material layer to the substrate can be achieved if it is an oxidic hard material layer (for example ZrO ₂ or a Zr-Si mixed oxide, ie a mixture of ZrO ₂ and SiO ₂ or a mixed oxide with ZrO ₂ and Al ₂ O ₃ ) or when the first hard material layer is an oxygen-containing nitride in the form of an oxynitride. Suitable oxynitrides are, for example, silicon oxynitride (SiO _x N _y ) or aluminum oxynitride (AlO _x N _y ) or silicon aluminum oxynitride (Si AlO _x N _y ).

These materials mentioned, ZrO ₂ or a mixture of ZrO ₂ and SiO ₂ or Al ₂ O ₃ ) and oxynitrides of silicon or aluminum or a mixture of aluminum and silicon are particularly preferred for the lowest layer with a higher refractive index. For example, ZrO ₂ can be combined with a TiO ₂ layer as a further or upper layer with a higher refractive index. Another possibility is to use a titanium-containing oxide, for example a mixed oxide with titanium and another element, for the lower layer with a higher refractive index. One possibility is a titanium / silicon mixed oxide. A preferred variant of an antireflective system according to the invention provides for the use of a ZrO ₂ layer as the uppermost layer with a higher refractive index in combination with a mixed oxide of zirconium and silicon or zirconium and aluminum or zirconium and silicon and aluminum as the lower layer 51 with higher refractive index.

According to a preferred embodiment of the invention is therefore the lowest, the substrate 3 next location 51 the anti-reflective coating 5 an oxynitride or oxide layer. In this case, this layer is formed, in particular, from an oxide or oxynitride of at least one of the elements silicon aluminum or a mixture thereof. An oxide layer as a lower layer 51 The higher refractive index may be formed from an oxide of titanium and / or zirconium mixed with aluminum and / or silicon. A particularly good adhesion is generally achieved on chemically tempered glass substrates.

Anyway, the two layers 51 . 53 Although layers with higher refractive index, but differ in that the refractive index of the two layers, as explained above, is different.

Both layers can 51 . 53 quite the same ingredients, but in different compositions. If the constituents are at least partially the same, the production can be facilitated thereby, since both layers can in principle be deposited using the same production method, with only the process parameters being adapted.

A preferred embodiment of the invention is based on the fact that both layers 51 . 53 with higher refractive index silicon, nitrogen and oxygen containing layers are, the lowest layer 51 having a higher refractive index has a higher oxygen content than the further layer 53 with higher refractive index.

In the case of an oxynitride layer, it can be seen that sufficient adhesion of the layer can be achieved even at a low oxygen content of about 5-10 atomic percent compared to nitrogen. In other words, according to this embodiment of the invention, the content of oxygen to nitrogen in the bottom layer 51 at least 5 atomic percent but below 10 atomic percent. According to a further embodiment, the ratio of the oxygen to nitrogen contents of the oxynitride (contents in atomic percent), preferably of a silicon oxynitride, is in the range of 0.41 to 1.02.

In general, without limitation to the exemplary embodiments, aluminum may be present in all silicon-containing layers in addition to silicon. Preferably, in the upper three layers, so the layers 52 . 52 . 54 the proportion of aluminum is less than the proportion of silicon, each in atomic percent. The ratio of the molar amounts of aluminum to silicon is preferably greater than 0.05, preferably greater than 0.08, wherein the molar amount of silicon but outweighs the molar amount of aluminum. Preferably, the ratio of the molar amounts of aluminum to silicon is about 0.075 to 0.5, more preferably about 0.1.

For the lowest position 51 with higher refractive index can also be the above ratio of the amounts of substance can be used, but is also suitable any ratio of the amounts of Al and Si.

The scratch resistance of the antireflection coating can be further improved by applying to an antireflective coating according to the invention 5 still an additional fluoroorganic layer 6 is applied. This fluoroorganic layer is also effective to reduce fingerprinting or to be easily cleaned.

The increased scratch resistance is attributed to the fact that the additional fluoroorganic layer presumably reduces the coefficient of friction of the surface so that damage to the surface is less pronounced.

2 shows a variant of in 1 shown embodiment. Either 1 , as well as 2 are examples of an embodiment of the invention in which the uppermost layer of higher refractive index, which is the second uppermost layer 53 the four-layer anti-reflective coating 5 forms, has a greater thickness than the layers 51 and 52 ,

In the embodiment of the 2 but is the layer thickness of the second uppermost layer 53 again significantly larger than the in 1 shown example. In general, layer designs can be found in which one of the higher-refractive layers is very thick and nevertheless has good antireflection properties. The large layer thickness of one of the hard, higher refractive layers, preferably the second uppermost layer 53 leads to a high scratch resistance of the coating system. However, it proves favorable if the layer thickness of the second uppermost layer 53 not more than half of the total layer thickness of all four layers 51 . 52 . 53 . 54 is. According to another example in the example of 2 also realized embodiment has the situation 52 That is, the lower refractive index layer that exists between the two layers 51 . 53 with higher refractive index, the smallest layer thickness of the four layers. It turns out that, in fact, this layer should preferably be as thin as possible in order to achieve a comparatively minimal chromaticity variation with layer thickness variation.

As layers 52 . 54 With lower refractive index, generally without limitation to the specific embodiments, SiO ₂ layers may serve. In other words, in a four-layer antireflection coating 5 then the topmost location 54 and the second lowest location 52 formed of SiO ₂ . Silicon oxide is particularly suitable because of its relatively low refractive index to obtain high refractive index jumps at the interfaces of the antireflective coating. These silicon oxide layers may preferably contain a small amount of Al ₂ O ₃ , wherein the ratio of the contents in atomic percent of aluminum to silicon in the range of 0.05 to 0.3, preferably in the range 0.1. Such a small admixture of Al ₂ O ₃ to SiO ₂ leads only to a very small increase in the refractive index.

In the embodiment of 2 Yet another embodiment of the invention is realized. According to this embodiment, the layer thickness is the lowest layer 51 greater than the layer thickness of second lowest location 52 , This general relationship of the layer thicknesses, in conjunction with the design of the refractive indices, also leads to an improved stability of the antireflection effect in the case of production-related layer thickness fluctuations. This embodiment is independent of the specific ones in FIG 2 shown layer thicknesses.

3 shows a development of the invention. According to this embodiment is generally on the page 31 of the substrate 3 which of the page 30 with the anti-reflective coating 5 opposite, a light-absorbing coating 7 , preferably applied a black coating. This decorative coating preferably serves as an opaque decor and typically frames a display area 32 a, within which a display, such as an LCD or OLED display is visible to a viewer. The opaque decor conceals components, such as a peripheral attachment of the substrate 3 or even at the edge of the display lying connections.

As a starting point for clarification of the invention serves as an example a cover glass with an antireflection coating known from the prior art with the layer sequence glass / Si ₃ N ₄ / SiO ₂ / Si ₃ N ₄ / SiO ₂ . Accordingly, on a glass plate as a substrate 3 first a silicon nitride layer as a layer 51 , then as a layer 52 an SiO ₂ layer, then another silicon nitride layer 53 and thereon SiO ₂ layer as the uppermost layer 54 the anti-reflective coating 5 deposited. As in 1 shown, can be on the topmost position 54 the anti-reflective coating 5 still be applied a fluoro-organic layer.

4 shows color changes to different elements 1 depending on the structure of the anti-reflective coating 5 and the presence or absence of a light absorbing or light blocking coating 7 on the website 31 of the substrate 3 , The measured values are denoted by reference numerals in parentheses individually.

An optimal case of uniform reflection is, for example, when for the substrate 3 an aluminosilicate glass is used, and the layer thicknesses from the glass are as follows: Location (51) Si ₃ N ₄ 15 nm Location (52) SiO ₂ 32 nm Location (53) Si ₃ N ₄ 132 nm Location (54) SiO ₂ 87 nm

In this case, a color location according to CIE-Lab on the pure glass without decor, or without light-absorbing coating 7 with the coordinates a and b of 1.0 and 3.7 (measured value 40 ).

If one deviates in the layer thicknesses by + 1nm (16nm (Lage 51 ), 33nm (location 52 ), 133nm (location 53 ), 88nm (location 54 )), the color locus values 1.5 and 2.8 (measured value 41 ). Reduction of the layer thickness by 1 nm (14nm, 31nm, 131nm, 86nm) results in a and b of 0.1 and 4.7. The three measurements discussed above 40 . 41 . 42 are in 4 drawn with triangular symbols.

With a black decor, respectively in the area of an as in 3 drawn light-absorbing coating 7 On the back of the cover glass, the color location values fluctuate significantly more with the same coating. The corresponding measured values 43 . 44 . 45 are marked with diamond symbols. Greater chromaticity variations also occur with a switched off and then dark display, as well as in dark areas of the switched-on display, so for example with a dark screen background.

The color values of the optimal case are here:
a = -0.2, b = 2.1 (measured value 43 ); at +1 nm layer thickness:
a = 1.7 and b = -0.7 (measured value 44 ); at -1 nm layer thickness
a = -2.6 and b = 4.6 (measured value 45 ).

This greater fluctuation and dependence on the layer thickness is due to the hidden by the decor back reflex. In the case of pure glass, its backside reflects about 4% (uniformly over the wavelength range of visible light), contributing about ten times as much to the overall reflection as the non-reflective front side (about 0.5%). The color location variations caused by the layer thickness variation are "outshined" by the back and are less noticeable. in the In case of a black back decoration, the back reflection is almost suppressed. Thus, the color point almost exclusively by the anti-reflection coating 5 determined and caused by layer thickness variations color location changes are more significant.

The measured values 60 to 62 (Cross symbols) and 63 to 65 (square symbols) are for comparison calculated color location changes to antireflective coatings according to the invention 5 which have the same layer thickness variations.

The first layer of the antireflective coatings of the invention 5 is in each case an oxygen-containing silicon nitride layer. Here, the ratio of oxygen to nitrogen, O / N, is adjusted so that a refractive index at 550 nm of about 1.71 results. With higher refractive indices in the direction of Si ₃ N ₄ , the color locus fluctuation increases. If there is too much oxygen in the SiO _x N _y , good antireflection conditions no longer result for a four-layer antireflective coating. Generally, without limitation to the composition of the lowest layer 51 it is favorable if the refractive index of the lowest layer 51 with higher refractive index between 1.665 and 1.795. The refractive index is preferably less than 1.790, more preferably less than 1.785.

The measured values 60 - 62 affect a glass substrate without decor and are therefore with the readings 40 . 41 . 42 to compare. It can be seen that in the case of a layer system according to the invention, the color loci are much closer to one another with the same layer thickness fluctuations than with an antireflection coating with similar higher refractive index layers. Also in an antireflection coating according to the invention 5 with different high refractive index layers in terms of material and refractive index 52 . 53 increases in the range of a light-absorbing coating 7 the color locus fluctuation (measured values 63 - 65 ). But here, the Farbortschwankungen are much lower than in an antireflection coating with respect to material and refractive index similar higher refractive index layers 52 . 53 ,

A concrete example of an antireflection system according to the invention with AR systems of lower color order variation with layer thickness variation compared to the prior art is shown in the following table: Location (51) SiO _x N _Y (n = 1.77) 33 nm Location (52) SiO ₂ 24 nm Location (53) Si ₃ N ₄ 132 nm Location (54) SiO ₂ 87 nm

5 shows color loci of the light reflections of substrates with TiO ₂ / SiO ₂ - based antireflective coatings. The color loci were returned to one with a back light absorbing coating 7 provided disc-shaped element 1 calculated.

Also these anti-reflective coatings 5 each have four layers. For the layers 51 . 53 with higher refractive index were in the in 5 registered color location values 46 . 47 . 48 Titanium dioxide layers (TiO ₂ ) used. The color location values 66 . 67 . 68 belong to an antireflective coating according to the invention 5 in which the four layers 51 . 52 . 53 . 54 the coating have at least three different refractive indices, such that the refractive index of the lowest, the substrate 3 next location 51 with higher refractive index is lower than the refractive index of the other layer 53 with higher refractive index, the lowest layer 51 is formed with a higher refractive index of an oxygen-containing material.

In the present case was for the lowest position 51 a SiO _x N _y , that is selected an oxygen-containing silicon nitride, wherein the refractive index is about 1.77. In contrast, pure silicon nitride has a refractive index of about n = 2. With a value of 1.77, the refractive index of the layer is 51 between the values of SiO 2 (ie the refractive index of the layers 52 . 54 ), and TiO ₂ (ie the refractive index of the layer 53 ).

A possible example for the construction of an inventive AR system from the aforementioned materials SiO _x N _y , SiO ₂ and TiO ₂ is given by way of example in the following table: Location (51) SiO _x N _Y (n = 1.733) 61 nm Location (52) SiO ₂ 10 nm Location (53) TiO ₂ 102 nm Location (54) SiO ₂ 89 nm

The result is a similar picture as in the examples of 4 , When using only two different refractive indices in the 4-layer AR system (color locus values 46 . 47 . 48 ) variations of the layer thicknesses of the layers by ± 1 nm result in a greater chromaticity variation than when using three refractive indices (color location values) 66 . 67 . 68 ) When as previously described, in the order viewed from the substrate _medium n, n _low n _high, n run _low. At the in 2 As shown, the ratios of the layer thicknesses correspond to the values of the above table.

Good antireflective properties can still be achieved if the above-mentioned layer thicknesses each deviate by 10%. According to one embodiment of the invention, therefore, the layer thicknesses for the lowest layer 51 61 ± 6.1 nm, for the second lowest layer 52 10 ± 1 nm, for the upper, higher refractive position 53 102 ± 10.2 nm and for the topmost layer 54 89 ± 8.9 nm.

It is clear from these examples that it is favorable if a certain minimum difference in the refractive indices of the two layers 51 . 53 is present with higher refractive index. In general, without limitation to the examples described with reference to the figures, it is provided according to a development of the invention that the refractive index of the lowest layer 51 the four layers 51 . 52 . 53 . 54 the anti-reflective coating 5 smaller than 1.79 is to choose and at the same time to adjust so that the neighboring situation 52 a layer thickness between 1 and 20 nm, preferably between 5 and 15 nm. A small layer thickness of the situation 52 proves to be particularly effective in reducing the sensitivity of the AR system to chromaticity variations with variation of layer thicknesses. According to one embodiment of the invention, it is therefore provided that the layer thickness of the layer 52 with lower refractive index, which is located between the two layers 51 . 53 is located with a higher refractive index, or the second lowest layer is below 20 nm, preferably below 18 nm, more preferably below 15 nm.

At the bottom, this difference is limited by the refractive index of the lower refractive index layers. Depending on the materials used in the structure of the antireflection system are here for the bottom layer 51 Refractive indices of from about 1.66 are preferred.

The refractive index of the layer 51 is thus preferably in the range between 1.66 and 1.79.

6 shows a typical application for the invention. According to one embodiment of the invention, without limitation to the illustrated example, a mobile electronic device 20 with an electronic display 21 , preferably a matrix display, or a pixel-controlled display provided, wherein the electronic device 20 an inventive disk-shaped element 1 which has the electronic display 21 covering, taking the page 30 the disc-shaped element 1 with the anti-reflective coating 5 turned to the outside. In this way, the antireflection coating 5 to exert their effect in the reduction of disturbing light reflections on the one hand and protection against scratching by external mechanical effects on the other hand.

The example shown is a mobile device in the form of a tablet PC. To the same extent, the invention is also suitable for mobile phones, in particular so-called smart phones, mobile navigation devices and mobile media players, in particular music and video players, and for smart watches.

Particular mechanical loads occur in such devices, especially when the devices are equipped with a user interface with a touch-sensitive screen, so that the page 30 with the anti-reflective coating 5 of the element according to the invention 1 at the same time also represents a user interface of the interface. Just in this embodiment of the invention is also a further coating in the form of the above and in the example of 1 shown fluoroorganic layer 6 ,

Often, the cover of the electronic display should not be completely transparent, but, as well as on the basis of 3 explained, certain areas are covered. This is a light-absorbing coating 7 provided, which are the edge areas of the element 1 covered and the electronic display 21 framed. Especially in these 6 black bordered, provided with a light-blocking coating edge color variations are particularly clearly visible, as shown by the examples of 4 and 5 was shown. Although the light reflections are due to the anti-reflection coating 5 in itself only very weak. This is countered by the fact that the dark background due to the light-absorbing coating provides a high contrast, so that even very weak light reflections are noticeable. With the inventive design of the anti-reflection coating 5 is now ensured that the remaining visible light reflections appear in a uniform color.

It will be apparent to those skilled in the art that the invention is not limited to the embodiments shown in the figures, but rather varied within the scope of the subject-matter of the claims. In particular, the features of the individual embodiments can also be combined with each other. So can for a mobile electronic device 20 both a coating according to 1 , as well as with the further features of the example of 2 be used. A fluoroorganic coating 6 may be present in any of the illustrated embodiments. This possibility is also expressly preferred.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2012/0212826 A1 [0005]

Claims (17)

Disc-shaped element ( 1 ) with - a transparent in the visible spectral range disc-shaped substrate ( 3 ) and - one on the substrate ( 1 ) deposited antireflection coating ( 5 ), the antireflective coating ( 5 ) - four successive layers ( 51 . 52 . 53 . 54 ), wherein mutually adjacent layers each differ in their refractive index, such that the refractive index increases and decreases alternately from layer to layer and layers ( 52 . 54 ) with lower refractive index with layers ( 51 . 53 ) alternate with higher refractive index, and where - the lowest ( 51 ) of the four layers ( 51 . 52 . 53 . 54 ) is a layer of higher refractive index and has a higher refractive index than the adjacent second lowest layer ( 52 ), The four layers ( 51 . 52 . 53 . 54 ) have at least three different refractive indices, such that the refractive index of the lowest, the substrate ( 3 ) next situation ( 51 ) with a higher refractive index than the refractive index of the further layer ( 53 ) with higher refractive index, and wherein the lowest layer ( 51 ) is formed with a higher refractive index from an oxygenous material, whereby this disk-shaped element ( 1 ) shows in particular a small color change in layer thickness variation. Disc-shaped element ( 1 ) according to the preceding claim, characterized in that the substrate ( 3 ) is a glass substrate, in particular a chemically toughened glass substrate. Disc-shaped element ( 1 ) According to one of the two preceding claims, characterized in that the bottom (the substrate 3 ) next location ( 51 ) of the antireflective coating ( 5 ) is an oxynitride layer, preferably with silicon or aluminum or with aluminum and silicon, or an oxide layer, in particular a ZrO ₂ -containing layer. Disc-shaped element ( 1 ) according to the preceding claim, characterized in that both layers ( 51 . 53 ) with higher refractive index silicon oxynitride layers, wherein the lowest layer ( 51 ) having a higher refractive index has a higher oxygen content than the further layer ( 53 ) with higher refractive index. Disc-shaped element ( 1 ) according to one of the two preceding claims, characterized in that oxygen in the lowest layer ( 51 ) in the range of 5 to 10 atomic percent, or that the ratio of the contents in atomic percent of oxygen to nitrogen of the oxynitride in atomic percent is in the range of 0.41 to 1.02. Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that the uppermost layer of higher refractive index, which is the second uppermost layer of the four-layer antireflection coating ( 5 ), the layer with the greatest layer thickness under the four layers ( 51 . 52 . 53 . 54 ). Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that on the antireflective coating ( 5 ) a fluoroorganic layer 6 is applied. Disc-shaped element according to one of the preceding claims, characterized in that on the side ( 31 ) of the substrate ( 3 ) which of the page ( 30 ) with the antireflection coating ( 5 ), a light-absorbing coating ( 7 ), preferably a decorative coating is applied. Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that the layers ( 52 . 54 ) are SiO ₂ layers with lower refractive index. Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that the layers ( 52 . 54 ) having lower refractive index are SiO ₂ layers additionally containing Al ₂ O ₃ such that the ratio of the contents of Al / Si in atomic percent is in the range of 0.05 to 0.3, preferably about 0.1. Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that the refractive index of the lowest layer ( 51 ) having a higher refractive index between 1.665 and 1.795, preferably less than 1.790, more preferably less than 1.785. lies. Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that the layer thickness of the second lowest layer ( 52 ) is below 20 nm, preferably below 18 nm, particularly preferably below 15 nm. Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that the layer thickness of the lowest layer ( 51 ) greater than the layer thickness of the second lowest layer ( 52 ). Disc-shaped element ( 1 ) according to one of the preceding claims, characterized in that the anti-reflection coating ( 5 ) has the following layer thicknesses: 61 ± 6.1 nm for the lowest layer ( 51 ) of the four successive layers, 10 ± 1 nm for the second lowest layer ( 52 ) of the four successive layers, 102 ± 10.2 nm for the upper, higher refractive index layer ( 53 ) of the four successive layers and 89 ± 8.9 nm for the uppermost layer ( 54 ) of the four successive layers. Disc-shaped element according to one of the preceding claims, characterized in that the substrate surface directly to the sequence of the four layers ( 51 . 52 . 53 . 54 ) of the antireflective coating ( 5 ) adjoins. Mobile electronic device ( 20 ) with an electronic display ( 21 ), preferably a matrix display, wherein the electronic device ( 20 ) a disk-shaped element ( 1 ) according to one of the preceding claims, which comprises the electronic display ( 21 ), whereby the page ( 30 ) of the disc-shaped element ( 1 ) with the antireflection coating ( 5 ) is turned to the outside. Mobile electronic device ( 20 ) according to the preceding claim, characterized by a user interface with a touch-sensitive screen, the page ( 30 ) of the element ( 1 ) with the antireflection coating ( 5 ) represents a user interface of the interface.

Images