Layer System with Anti-Fog and Antireflective Properties and Method for Manufacturing a Layer System

Abstract

In an embodiment a layer system includes a substrate with an anti-fog material on at least one surface, a water-permeable intermediate layer arranged on the surface and a water-permeable nanostructure including a plurality of pillars arranged side by side, the water-permeable nanostructure arranged on the water-permeable intermediate layer.

Claims

1. A layer system comprising: a substrate with an anti-fog material on at least one surface; a water-permeable intermediate layer arranged on the surface; and a water-permeable nanostructure comprising a plurality of pillars arranged side by side, the water-permeable nanostructure arranged on the water-permeable intermediate layer.

2. The layer system according to claim 1, wherein the anti-fog material comprises a structuring which, together with the water-permeable nanostructure, is configured to produce an anti-reflective property.

3. The layer system according to claim 1, wherein the water-permeable nanostructure is formed by a layer which is inorganic or partially inorganic.

4. The layer system according to claim 1, wherein at least some of the pillars comprise cavities.

5. The layer system according to claim 1, wherein the pillars are stochastically randomly distributed over the surface, and wherein at least for some of the pillars a distance to the closest pillar is between 20 nm and 70 nm inclusive.

6. The layer system according to claim 1, wherein the pillars comprise a height-to-width ratio of at least 1.0.

7. The layer system according to claim 1, wherein an effective refractive index of the water-permeable nanostructure is smaller than an effective refractive index of the intermediate layer.

8. The layer system according to claim 1, wherein the anti-fog material is a water-absorbing polymer and comprises a thickness of at least 1 μm.

9. The layer system according to claim 1, wherein the anti-fog material is an inorganic-organic network which is rendered highly hydrophilic by admixtures.

10. A method for manufacturing a layer system, the method comprising: providing a substrate comprising an anti-fog material on at least one surface; forming a water-permeable intermediate layer on the surface; and forming a water-permeable nanostructure with a plurality of pillars arranged side by side on the water-permeable intermediate layer.

11. The method according to claim 10, wherein the intermediate layer is an inorganic or partially inorganic layer applied by a plasma, and wherein deposition parameters are adjusted such that the intermediate layer is water-permeable.

12. The method according to claim 10, wherein the anti-fog material is structured before the water-permeable intermediate layer is applied.

13. The method according to claim 12, further comprising: applying a temporary layer prior to structuring the anti-fog material; and subsequently performing a material removal, which varies locally with respect to a removal depth, over the surface, with which the temporary layer is removed and the anti-fog material is structured.

14. The method according to claim 10, wherein the anti-fog material is unstructured when the intermediate layer is applied.

15. The method according to claim 10, wherein forming the water-permeable nanostructure comprises: forming a nanostructured layer on the intermediate layer, overlaying the nanostructured layer with a layer, and performing a post-treatment in which the nanostructured layer is at least locally decomposed or removed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Further embodiments and expediencies become apparent from the following description of the exemplary embodiments in connection with the figures.

[0054] In the Figures:

[0055] FIGS. 1A to 1I show an exemplary embodiment for a method for manufacturing a layer system by means of intermediate steps each shown in schematic sectional view, wherein FIG. 1I shows a completed layer system according to an example of embodiment;

[0056] FIG. 2 shows an exemplary embodiment of a layer system; and

[0057] FIGS. 3 to 7 each show a reflection spectrum of an example of a layer system.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0058] The figures are each schematic illustrations and therefore not necessarily true to scale. Rather, various elements, in particular layer thicknesses, may be shown exaggeratedly large for improved illustration and/or better understanding.

[0059] Elements that are the same, similar or have the same effect are indicated in the figures with the same reference signs.

[0060] In the exemplary embodiment shown schematically on the basis of FIGS. 1A to 1I, a substrate 1 is provided, for example a glass substrate or a plastic substrate (FIG. 1A). An anti-fog material 2 is applied to the substrate so that the anti-fog material is present on a surface 10. Deviating from this exemplary embodiment, the substrate 1 may itself be formed by an anti-fog material, so that the surface 10 is formed by the substrate 1 and no additional layer with an anti-fog material is required.

[0061] A temporary layer 3 is applied to the surface 10. The temporary layer 3 has, for example, a layer thickness between 1 nm and 2 nm inclusive and is deposited, for example, by evaporation in vacuum or by another method. A suitable material for the temporary layer 3 is, for example, a dielectric material such as titanium dioxide (FIG. 1B).

[0062] Subsequently, a pattern 20 with irregularly arranged depressions 21 is formed at the surface 10. This irregularly formed structuring 20 can be achieved, for example, by ion bombardment, which completely removes the temporary layer 3 and produces the irregular structuring 20 of the anti-fog material 2 (FIG. 1C).

[0063] As illustrated in FIG. 1D, an intermediate layer 4 is applied to the surface 10. The intermediate layer 4 comprises, for example, a thickness between 10 nm and 200 nm inclusive and is selectively deposited so as to be water-permeable.

[0064] The intermediate layer 4 may be produced by a plasma process, wherein the adjustment of the water permeability of the intermediate layer 4 is performed by adjusting the coating rate R and the ion energy during the deposition in the plasma deposition apparatus.

[0065] A corresponding matrix with variation of the coating rate R and the average ion energy is shown in Table 1 for a silicon dioxide layer. Here, a (−) indicates that dense water-impermeable layers tend to be produced with the specified values for the coating rate and the average ion energy of the gas bombarding the substrate during the growth of the layer, while a plus (+) indicates that water-permeable layers were produced.

TABLE-US-00001 TABLE 1 Ionenenergie in eV Beschichtungsrate R in nm/s 1 nm/s 0.5 nm/s 0.2 nm/s  0 eV +++ +++ +++  80 eV +++ +++ ++ 100 eV ++ + − 120 eV + − − 150 eV − − −

[0066] Thus, low ion energies and large deposition rates tend to improve the water permeability of the layer. In a similar way, the subsequent layers of the layer system can also be made water-permeable. In principle, this can also be applied to other materials, wherein the parameters have to be adjusted to the materials and the properties of the deposition system.

[0067] The depressions 21 are at least partially not filled with material of the intermediate layer 4. The cavities thus created cause a reduction in the effective refractive index in the region of the structuring 20 compared with the underlying unstructured anti-fog material 2.

[0068] As illustrated in FIG. 1E, an initial layer 510 for a nanostructured layer is applied. The nanostructured layer 51 preferably comprises an organic material, but may also comprise inorganic components as long as the material for the nanostructured layer 51 is more easily patterned by a plasma etching process than the underlying intermediate layer.

[0069] As illustrated in FIG. 1F, the initial layer 510 is patterned into the nanostructured layer 51 by a plasma process to form a plurality of spaced apart pillars 55. The pillars 55 extend perpendicularly or at least substantially perpendicularly to the surface 10. Between the pillars 55, the intermediate layer 4 is exposed at least in places. The nanostructured layer 51 comprises, for example, a thickness between 40 nm and 250 nm, inclusive.

[0070] As illustrated in FIG. 1G, the pillars 55 are overcoated with an inorganic or at least partially inorganic layer as layer 52. As in connection with the intermediate layer 4, this layer is preferably deposited specifically in such a way that it is permeable to water, for example in the form of a porous layer. The pores of the intermediate layer 4 and of the porous layer 52 are illustrated by dots in the figures.

[0071] Subsequently, as illustrated in FIG. 1H, a post-treatment is performed in which the nanostructured layer 51 is decomposed or removed at least in places. This results in an inorganic-organic hybrid material. Preferably, the organic components are completely removed during the post-treatment. In contrast to the structuring in the intermediate step shown in FIG. 1F, the geometry of the nanostructured layer 5 with the pillars 55 is largely retained. In particular, the height-to-width ratio of the pillars 55 does not change or does not change significantly.

[0072] The post-treatment creates cavities 56 in the pillars 55. Via the cavities 56, a particularly low effective refractive index results for the nanostructure 5.

[0073] The post-treatment can be achieved by a plasma etching process. Here, in contrast to the intermediate step shown in FIG. 1F, the layer to be processed is covered by an overlying layer, the porous layer 52. Alternatively or in addition to a post-treatment with a plasma etching process, a thermal treatment, for example at a temperature of at least 70° C., can also be performed.

[0074] A cover layer 6 can optionally be applied to the nanostructure 5 (FIG. 1I). The cover layer is specifically designed to be water-permeable, as described in connection with the intermediate layer 4.

[0075] Preferably, the same plasma source is always used for all plasma processes, for example a plasma source of the Leybold APS type.

[0076] The finished layer system 100 combines the anti-fog property of the anti-fog material 2 with a good anti-reflective property, which is achieved by the structuring 20 of the anti-fog material 2 in conjunction with the water-permeable layers arranged above it.

[0077] The anti-reflective property of the layer system 100 is achieved via the course of the effective refractive index profile. The effective refractive index of the sub regions of the layer system 100 is significantly influenced by the volume fraction of cavities. The nanostructure 5 comprises the highest percentage of cavities. The intermediate layer 4 preferably comprises the lowest percentage of cavities and, correspondingly, a comparatively high refractive index. For example, the intermediate layer 4 forms a local maximum of the refractive index curve. The proportion of cavities in the region of the structuring 20 of the anti-fog material 2 is preferably between the proportion of cavities in the nanostructure 5 and the proportion of cavities in the intermediate layer 4. For example, the proportion of cavities in the region of the structuring 20 is between 20% and 30% inclusive, in the intermediate layer 4 between 2% and 8% inclusive, for example at about 5%, and in the region of the nanostructure 5 between 60% and 80% inclusive.

[0078] The effective refractive index of the intermediate layer 4 comprises, for example, between 1.37 and 1.45. The effective refractive index of the nanostructure 5 comprises, for example, an effective refractive index between 1.1 and 1.25. In the region of the cover layer 6, the effective refractive index is preferably greater than the effective refractive index of the nanostructure 5. As a result, the minimum of the effective refractive index profile of the layer system 100 is spaced from the interface with the surrounding medium.

[0079] In the described exemplary embodiment, the anti-fog material 2 with the patterning 20 together with the nanostructure 5 provides an anti-reflective property. It has been found that the anti-reflective properties can thus be significantly improved compared to structuring the anti-fog material 2 alone. In addition, there are much better possibilities in terms of the achievable optical properties, for example with regard to the target wavelength, spectral width, dependence on the angle of incidence and combinations of these properties.

[0080] However, structuring of the anti-fog material 2 is not mandatory.

[0081] This is illustrated with reference to FIG. 2. In this exemplary embodiment, the surface 10 of the anti-fog material 2 is unstructured. The substrate 1 is formed by the anti-fog material 2. Deviating from this, however, the anti-fog material 2 can also be arranged in the form of a coating on the substrate 1, as in the previous exemplary embodiment. This embodiment is particularly preferred if the anti-fog material 2 is difficult to structure chemically. The anti-reflective property is achieved by the nanostructure 5 applied to the surface 10. If necessary, in this exemplary embodiment as in the previous exemplary embodiment, a further nanostructure may be arranged on the nanostructure 5. This further nanostructure can be formed largely analogously to the nanostructure 5. Also in this exemplary embodiment, a cover layer may additionally be applied.

[0082] The anti-fog property of the layer system 100 can be tested by the anti-fog test described in the following.

[0083] First, water is heated to a temperature of about 40° C. in a narrow tall vessel that is half-filled. This causes a volume with a high humidity to form above the interface with the water inside the tall vessel. The layer system to be tested is held above the volume with the high humidity for 30 s and the transmission of the layer system is then measured for 5 s.

[0084] If a substrate 1 without a layer system is subjected to the anti-fog test, a temporary haze will occur due to the surface of the substrate 1 being fogged with water.

[0085] In the anti-fog test, the layer system 100 produced by the method described comprises the same properties as a surface covered only with the anti-fog material 2. In other words, neither the structuring 20 of the anti-fog material 2 nor the further layers applied thereto affect the anti-fog properties of the layer system 100.

[0086] In particular, the anti-fog property is confirmed if there is no visible fogging or other clouding even after three times of exposure.

[0087] Five examples of specific layer sequences with different requirements for the antireflection properties are described below, wherein the respective reflection spectra are shown in FIGS. 3 to 7.

[0088] Example 1 involves an antireflection coating optimized for a target wavelength of 950 nm and a light incidence angle range of 0° to 50°. A 3 μm thick polymer layer is applied as an anti-fog material 2 (type HCF 100, Exxene Corporation) to a glass pane as substrate 1.

[0089] A dielectric layer of, for example, titanium dioxide is applied as a temporary layer 3. This layer causes a subsequent etching process with a plasma source to result in the structuring 20 of the anti-fog material 2. This etching process is performed in a layer system of the type APS 904 from the manufacturer Leybold-Optics. The following parameters for the coating refer to this type of system and can be adjusted accordingly for other types of system. The etching time is about 300 seconds in an argon/oxygen plasma at a pressure range between 1×10.sup.−4 mbar and 1×10.sup.−3 mbar with a gas flow for argon of about 14 sccm and for oxygen of about 30 sccm. The voltage with which the ions of the plasma are accelerated, which is a measure of the average energy of the ions impinging on the surface, is 120 V, while the discharge current of the plasma is about 50 A.

[0090] A 50 nm thick silicon dioxide layer is applied as an intermediate layer 4, wherein the parameters are chosen as described above so that the layer is permeable to water. Thus, a first sub-layer system is formed with the patterned anti-fog material 2 and the intermediate layer 4. The patterning extends about 130 nm in the vertical direction, i.e. perpendicular to the surface 10, and achieves an average effective refractive index of 1.32.

[0091] Xanthine with a thickness of 250 nm is vapor-deposited as the initial layer 510 for the nanostructured layer 51. A 150 nm high structure is formed from the organic layer within 400 seconds by plasma etching. This is overlaid with 20 nm of porous silicon dioxide as porous layer 52.

[0092] A plasma etching process is then performed as a post-treatment to remove the organic constituents. About 60 nm of silicon dioxide is then applied as a cover layer 6. The cover layer is applied by electron beam evaporation and, like the previous layers, is formed in such a way that water transport remains possible.

[0093] The transmission of the layer system 100 is monitored by in-situ measurement and the deposition of the last layer is stopped exactly when the reflection minimum is in the desired spectral range. As FIG. 3 shows, the minimum of the residual reflection is at about 950 nm and at this wavelength also below 0.3% for all light incidence angles from 0° to 50° (represented in angular steps of 10° by the curves R0 at 0°, R10, R20, R30, R40 and R50).

[0094] In the anti-fog test, the surface shows the same properties as the original anti-fog material without the layers applied to it.

[0095] The second example is an antireflection coating for the spectral range from 400 nm to 1000 nm, for which the reflectance spectrum is shown in FIG. 4.

[0096] In each of FIGS. 4 to 7, the curve R0 represents the residual reflectance of an uncoated substrate, while the curves R1 show the residual reflectance for the respective layer system 100.

[0097] In this example, the substrate 1 is a plastic substrate, namely a polycarbonate sheet, to which a 3 μm thick polymer layer is applied as an anti-fog material 2 (HCF 100, Exxene Corporation). The application is carried out by dipping.

[0098] The anti-fog material 2 is structured as described in connection with the first example. A 30 nm thick silicon dioxide layer is applied as an intermediate layer 4, which in turn is deposited in such a way that the intermediate layer is water-permeable. The vertical extent of the resulting patterning 20 with the intermediate layer is about 120 nm in total. The average effective refractive index is 1.32.

[0099] Xanthine is applied as the initial layer for the nanostructured layer 51 with a layer thickness of 150 nm. A 90 nm high structure is formed from the initial layer 510 by plasma etching within 400 seconds, which is overlaid with 30 nm of porous silicon dioxide as a porous layer 52. The organic components are then removed by plasma etching. As FIG. 4 shows, the residual reflectance achieved is less than 0.5% over the entire desired spectral range. In the anti-fog test, the surface shows the same properties as the original anti-fog material 2 without layers applied to it.

[0100] The third example is an antireflection coating for the spectral range from 350 to 600 nm, for which the resulting spectrum is illustrated in FIG. 5.

[0101] A quartz disk is used as substrate 1, which is coated with an acrylate-based layer about 3 μm thick as anti-fog material 2. A 0.5 nm thick dielectric layer of titanium dioxide is applied as a temporary layer. The structuring of the anti-fog material 2 is carried out as described above.

[0102] Subsequently, a 30 nm thick silicon dioxide layer is applied as an intermediate layer 4, which in turn is deposited so that it is permeable to water. The resulting structure extends 80 nm in the vertical direction towards the substrate 1.

[0103] By means of optical simulation, the average effective refractive index of 1.34 is verified. The nanostructure 5 is formed as in the previous examples, but with an initial layer thickness of the initial layer 510 of 100 nm xanthine. The resulting structure with hollow silica pillars is overlaid with a 20 nm thick cover layer 6 of silica, resulting in a total layer thickness of 100 nm with an average effective refractive index of 1.13.

[0104] As FIG. 5 shows, the average residual reflectance in the spectral range from 350 nm to 650 nm is extremely low, less than 0.05%. The surface shows excellent anti-fog properties even after the layers have been applied to the anti-fog material 2.

[0105] The fourth example, the spectrum of which is shown in FIG. 6, is an antireflection coating for the spectral range from 400 nm to 800 nm. For this purpose, a glass pane made of crown glass with a refractive index of 1.53 is coated with a layer of a siloxane-based anti-fog material 2 about 1 to 3 μm thick.

[0106] In contrast to the preceding examples, the anti-fog material 2 is not structured as described in connection with FIG. 2. A 60 nm silicon dioxide layer is applied as an intermediate layer 4, which in turn is deposited so that it is water-permeable. The effective refractive index of the layer is 1.43.

[0107] A nanostructure 5 is applied to this as described in the previous examples, wherein xanthine with an initial layer thickness of 140 nm is generated as the initial layer 510. The resulting structure with hollow silicon dioxide pillars about 150 nm high is overlaid with a 16 nm thick silicon dioxide layer as a cover layer 6, so that a total of 116 nm with an average effective refractive index of 1.13 is achieved. The average residual reflectance in the spectral range from 400 to 800 nm is less than 0.15%. Excellent anti-fog properties were again confirmed in the anti-fog test.

[0108] The fifth example represents an antireflection coating with a target wavelength of 1100 nm.

[0109] Here, as in example 4, a pane of crown glass is coated with a siloxane-based layer about 1 to 4 μm thick as an anti-fog material 2. This layer is again not patterned. Xanthine with an initial layer thickness of 280 nm is used as the initial layer 510. On the resulting hollow nanostructure 5 with a height of about 200 nm, a 26 nm thick silicon dioxide layer is applied as a cover layer 6. Thus, a total of 226 nm layer thickness is achieved with an average effective refractive index of 1.23. The average residual reflectance for the target wavelength of 1100 nm is less than 0.5%. Again, excellent anti-fog properties are shown in the anti-fog test.

[0110] The above examples demonstrate that various application-specific anti-reflective properties can be achieved with excellent anti-fog properties at the same time. This cannot be achieved with conventional layer systems. In particular, high requirements for the parameters of the residual reflection can be met, for example a particularly low value for the residual reflection for the target wavelength, possibly also in combination with a broad spectral range, for example of 400 nm or more, and/or a large range for the angle of incidence, for example of 30° or more. Furthermore, the layer system is suitable not only for the visible spectral range, but also for target wavelengths in the near infrared. Of course, the materials and layer thicknesses used for producing one or more nanostructures 5 on the anti-fog material can be varied within wide limits in order to adjust the layer system to specified anti-reflective properties. In particular, the materials listed in the general part of the description can be used for the layers of the layer system.

[0111] The invention is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses any new feature as well as any combination of features, which in particular includes any combination of features in the patent claims, even if that feature or combination itself is not explicitly specified in the patent claims or the exemplary embodiments.