EP2047302A1

EP2047302A1 - Flexible materials for optical applications

Info

Publication number: EP2047302A1
Application number: EP06778072A
Authority: EP
Inventors: Robert Beer; Gilbert Gugler; Marc Pauchard; Stefan Schuettel
Original assignee: Ilford Imaging Switzerland GmbH
Current assignee: Wifag-Polytype Holding AG
Priority date: 2006-07-28
Filing date: 2006-07-28
Publication date: 2009-04-15
Also published as: WO2008011919A1; US20100208349A1; CN101501533A; JP2009544491A; CN101501533B

Abstract

Disclosed is a flexible material for optical applications in a wavelength range of λ1 to λ2, λ1 being smaller than λ2. Said flexible material is composed of a flexible support and at least one multilayer that comprises a porous or nanoporous layer which has a low refractive index and contains inorganic nanoparticles and at least one binder, and a non-porous polymer layer which has a high refractive index and is in direct contact with the porous or nanoporous layer. The disclosed flexible material is characterized in that the maximum thicknesses of the boundary layers, in which the refractive index changes from one value to the other and which are located between the porous or nanoporous layers and the non-porous polymer layers that are in direct contact therewith, amount to 0.2 times wavelength λ2. The difference in the refractive indices of the porous or nanoporous layers and the non-porous polymer layers is at least 0.20, 200 nm and 2500 nm being typical values for λ1 and λ2.

Description

Flexible materials for optical applications

Technical area

The present invention relates to flexible materials for optical applications which have on a flexible support at least two thin layers in direct contact, the refractive indices of which differ by at least 0.20. One of these layers is porous or nanoporous and contains inorganic nanoparticles, the other is a non-porous polymer layer.

State of the art

Dielectric thin layers are thin, mostly transparent layers of different chemical compounds with layer thicknesses, which are typically in the micrometer and nanometer range. In optics, dielectric thin films are used to alter the optical properties of surfaces and interfaces. Such interfaces help to partially reflect and partially transmit and refract incident light. The targeted use of the right materials and layer thicknesses can effectively influence the refraction and reflection behavior. The layer thicknesses of interest are all in the range of light wavelengths λi to λ2, which is of interest in a particular application.

In antireflective coatings and in highly reflective dielectric mirrors, preference is given to using so-called λ / 4 layers, ie. H. Layers with a thickness of λ / 4. When using layer thicknesses which are twice or an integer multiple of λ / 4, the desired effect is still present, but it decreases with increasing layer thickness more and more.

By a sequence of layers with high and low refractive indices and suitable layer thicknesses, it is possible, for example, to produce an interference filter which is permeable only for very specific wavelengths of light. Such interference filters are widely used in spectroscopy as dielectric filters, for example.

It is also possible with such multilayer materials to produce Bragg reflectors which selectively and practically completely reflect certain wavelengths, with reflectivities of more than 99% being possible. Such a Bragg reflector can be used, for example, to construct a polymer laser as described by N. Tessler, GJ Denton and RH Friend in "Lasing from conjugated-polymer microcavities", Nature 382, 695-697 (1996). Such interference effects can also be used to create "physical colors," which is exploited, for example, in the manufacture of colored sunglass lenses with high light stability. Among other things, physical colors are also used as optical security features on banknotes or labels for product security.

By a suitable combination of layers with high and low refractive indices, it is also possible to produce waveguide structures which are able to guide specific light wavelengths within these structures into precisely defined zones and to decouple them at another, desired location. In such waveguide structures, a high refractive index (core) layer is surrounded by lower refractive index (cladding) layers. The light is transmitted in the core through total internal reflection. The layer thickness of the core defines how many modes of a light wave can be passed on. Waveguides that can pass only the fundamental mode are called unimodal waveguides or single-mode waveguides. The layer thickness of the core in these waveguides depends on the refractive indices of the materials used and the range of wavelengths of light λi to λ £, which is of interest in a particular application, as described, for example, by X. Peng, L. Liu, J. Wu, Y. Li, Z. Hou, L. Xu, W. Wang, F. Li and M. Ye in "Wide-range amplified spontaneous emission wavelength-tuning in a solid-state dye waveguide", Optics Letters 25, 314-316 (US Pat. 2000). For the materials typically used in glass fibers, the core layer thickness is about 2 to 6 wavelengths. The layer thickness of the core for a single mode waveguide is below a wavelength when the difference in refractive indices of the layers is greater than 0.20. As the layer thickness of the core increases, an increasing number of higher modes are passed and a multimode waveguide is referred to. Single-mode waveguides have a number of advantages over multimode waveguides and are therefore preferred in certain applications. It is therefore of great interest to be able to realize thin waveguide layers and high differences in the refractive indices. Interesting applications of such waveguides can be found, for example, on integrated optical chips for data transmission or on sensor chips for the analysis of samples by the interaction with light. For many of the applications mentioned above, it is of great advantage to achieve the greatest possible difference between the refractive indices between two adjacent layers, with the refractive index having to change as abruptly as possible from one layer to the other. For example, the number of λ / 4 layers required in a dielectric mirror can be increased by increasing the difference in refractive indices of the layers used of the reflection behavior are drastically reduced, as described for example in the patent application US 2004 / 0'096'574.

For inorganic materials, the refractive index varies between 1.45 (silicate glass) and 3.40 (indium phosphide), as reported by N. Kambe, S. Kumar, S. Khirovolu, B. Chaloner-Gill, YD Blum, DB MacQueen and GW Faris in Refractive Index Engineering of Nano-Polymer Composites ", K. Kobayashi," Optical Integrated Devices ", Kyoritsu Publications, Tokyo, pages 26-30 (1999). Within relatively narrow limits, it is possible to change the refractive index of a particular inorganic material by doping. The patent application EP1'116'966 describes how, by doping silicate glasses with B2O3 or P2O5, the refractive index of the pure silicate glass can be slightly lowered or slightly increased.

Common organic polymers have refractive indices between 1.34 and 1.66. The polymer with the highest known refractive index of 1.76 is described in the patent application US 2004 / 0'158'021.

Table 1 summarizes the refractive indices of common or described organic polymers at a wavelength of 550 nm.

Table 1

Table 1 (continued)

By a suitable combination of organic polymers with inorganic elements, refractive indices above 1.76 are also accessible. For example, Y. Wang, T. Flaim, S. Fowler, D. Holmes, and C. Planje describe in "Hybrid High Refractive Index Polymer Coatings," Proceedings of SPIE 5724, 42-49 (2005), the preparation of a hybrid material of titanium dioxide and titanium organic polymer which has a refractive index of 1.94 at 400 nm.

The range of refractive indices between 1.05 and 1.40 can be covered with porous or nanoporous structures which contain a high proportion of air or other gases in the pores of the layers. Patent US Pat. No. 6,204,202 describes, for example, the preparation of porous SiO 2 layers with refractive indices between 1.10 and 1.40, which are obtained by a sol-gel method and the use of thermally decomposable polymers. Such polymer-containing coatings must be heated for 10 to 60 minutes to a temperature of at least 400 ° C, so that the polymer is decomposed and pure SiO 2 layers arise with the desired properties. Aerogels can also be used to prepare such porous, low refractive index layers as described, for example, by A. Köhler, J.S. Wilson and R.H. Friend in "Fluorescence and Phosphorescence in Organic Materials", Advanced Materials .14, 701 (2002).

Large differences in the refractive indices of different layers up to a value of 2.00 can also be achieved by suitable combinations of non-porous inorganic compounds in the various layers.

Such layers are produced, for example, by vacuum evaporation or wet-chemical with a sol-gel process. In the patent application US 2004 / 0'096'574, for example, in a dielectric mirror, a combination of layers of Al 2 O 3 and GaP is described, which has a difference of the refractive indices of 1.87. By suitable combinations of non-porous inorganic and nonporous organic layers, the difference in the refractive indices can be increased still further in some cases, but the amount of realizable layer combinations is limited by the limited compatibility of the compounds to be used and the possible coating methods.

Another possibility for achieving large differences in the refractive indices is the combination of nonporous organic layers with porous or nanoporous inorganic layers. An example of such an application is provided by RL Oliveri, A. Sciuto, S. Libertino, G. D'Arrigo and C. Arnone in "Fabrication and Characterization of Polymeric Optical Waveguides Using Standard Silicon Processing Technology", Proceedings of WFOPC 2005, 4th IEEE / LEOS Workshop on Fibers and Optical Passive Components, 265-270 (2005). Here, a porous layer having a low refractive index made of SiO 2 is produced on a silicon chip, and polymethyl methacrylate is used as a layer having a high refractive index.

However, all of the aforementioned inorganic layers have the effect that such layer packages are brittle and have only a very limited mechanical flexibility. Such materials can only be used where a very high difference in refractive indices is required, but mechanical flexibility does not matter.

The above-mentioned porous layers, which are used in optical applications, also do not have the appropriate mechanical properties and sometimes require inappropriate steps in the manufacturing process (high temperature treatment, supercritical drying, etc.) in order to be able to apply large-scale and cost on flexible support ,

For certain applications, it is necessary that the layers produced have a high mechanical flexibility. Flexible layers can be obtained by applying solutions of suitable organic polymers or suitable melted polymers. For example, in the patent application JP 2005-055'543 a method is described how multiple polymer layers for optical applications can be produced. However, the amount of layer combinations obtainable here too is limited by the limited combinability of the materials to be used (adhesion, solubility in various solvents, etc.) as well as the problem of precise multiple coating. The realizable difference in refractive indices in such organic-only containing structures is therefore well below the theoretical value of 0.42, which is the combination of the lowest refractive index polymer (polytetrafluoroethylene having a refractive index of 1.34) and the highest refractive index (polyimide) with a index of 1.76). For example, the maximum achievable difference in the refractive indices of the polymer layers in patent application JP 2005-055'543 is 0.20.

Fast drying recording materials for ink jet printing use porous or nanoporous ink receptive layers containing inorganic nanoparticles and a low level of binders. Such layers have a high mechanical flexibility.

Ink-jet recording materials having on a flexible support a flexible inorganic nanoparticle-containing porous or nanoporous ink-receiving layer and a polymer layer disposed thereover are also known. Such recording materials with a nonporous polymer layer are described, for example, in the patent applications EP 1'188'572 and EP 1'591 '265, the layer thicknesses of the polymer layer normally being between 3 μm and 15 μm. The layer thickness of 3 μm must not be exceeded in order to obtain the desired ink absorption properties of the polymer film.

A recording material having a porous polymer layer is described, for example, in patent application EP 0761'459. Here, the recording material is thermally treated after printing to seal the porous polymer layer and thereby protect the underlying image.

In the patent US Pat. No. 6,025,068, the polymer film is formed only after the printing of the recording material by the application of a polymer solution or the polymer film is laminated thereon by means of an adhesion promoter. To be of interest for the mentioned optical applications, such polymer layers should not be thicker than a quarter to about a whole wavelength λ of the light used.

The quality of the existing in any case boundary layer between the porous or nanoporous layer and the polymer layer and the homogeneity of the polymer layer are not sufficiently good for optical applications. In recording materials for ink jet printing, too sharp an interface would only disturb, otherwise unwanted color effects would occur.

The patent application EP 1'492'389 describes an optical amplifier material which contains on a carrier a thin, transparent amplifier layer which contains nanocrystalline, nanoporous aluminum oxides or aluminum oxide / hydroxides and optionally a binder, and above that a luminescent layer, preferably consisting of tris- (8-hydroxyquinolino) -aluminum. The luminescent compound is formed by vapor deposition. and the resulting luminescent layer has sufficient mechanical flexibility only at layer thicknesses below 200 nm.

Brief description of the drawings

FIG. 1 schematically shows the simplest structure of a material according to the invention for optical applications. On a flexible carrier (1) there is a porous or nanoporous layer (2) which contains inorganic nanoparticles and, arranged above, a nonporous polymer layer (4). (3) denotes the boundary layer between the porous or nanoporous layer (2) and the non-porous polymer layer (4).

FIG. 2 shows schematically a further material according to the invention for optical applications. In this material, two layer packages from FIG. 1 are arranged one above the other in the reverse order. (1) again denotes a flexible support, (2) and (2 ') each denote a porous or nanoporous layer containing (possibly different) inorganic nanoparticles, (4) and (4') denote (possibly different) non-porous polymer layers and (3) and (3 ') denote the boundary layers between the porous or nanoporous layers (2) and (2') and the non-porous polymer layers (4) and (4 ').

Description of the invention

The aim of the invention is the provision of flexible materials for optical applications, which consist of a flexible carrier and at least two layers applied thereto with a large difference in the refractive indices, which are in direct contact with each other. These materials have a high mechanical flexibility and can be produced inexpensively in large quantities. It has now surprisingly been found that this objective can be achieved by suitable combinations of porous or nanoporous layers having a low refractive index, which contain inorganic nanoparticles, with non-porous polymer layers having a high refractive index.

The difference between the refractive indices of the two layers is at least 0.20 in the range of wavelengths of interest λi to λ £. But preferably higher values, preferably between 0.20 to 0.76 in the region of interest light wavelengths .lambda..sub.i to \ 2 ^'m is further provided always that is .lambda..sub.i smaller than λ2. In each case there is a boundary layer between the two layers, in which the refractive index changes from one value to the other value. The thickness of this boundary layer is extremely important in optical applications and has a great influence on the proportion of light which is reflected. The wavelength of light plays a decisive role here. An optically sharp boundary layer in the materials according to the invention is then used if the thickness of the boundary layer in the region of the wavelengths of interest λi to λ £ is not greater than 1/5 of the wavelength of the light.

The application areas of the materials for optical applications are in the wavelength range between 200 nm (λi) and 2500 nm (λ2).

The visible spectral range of the light between 400 nm and 700 nm, for example, is interesting for all applications where directly visible optical effects are to be generated for humans. For example, this is the case in the production of physical colors for decorative purposes, for color effects in security features or for simple optical sensors based on a color change of a test strip. The range of interesting wavelengths of light λi and λ2 for the materials according to the invention extends here, for example, over the entire visible spectral range between 400 nm and 700 nm. Optically sharp boundary layers must not have a thickness greater than 140 nm for these applications. However, preference is given to a thickness of the boundary layer which is not greater than 70 nm.

For applications where ultraviolet radiation is used, for example for security features which should only be visible under UV light, the range of interesting wavelengths λi and λ £ for the materials according to the invention extends over the range between 200 nm and 400 nm. Optically sharp Boundary layers must not have a thickness greater than 80 nm for these applications. However, preference is given to a thickness of the boundary layer which is not greater than 40 nm. For applications where infrared radiation is used, for example for security features which can only be visualized by means of infrared sensors or infrared detectors, the range of the interesting wavelengths λi and λ2 for the materials according to the invention extends over the range between 700 nm and 2500 nm. Optically sharp boundary layers must not have a thickness greater than 500 nm for these applications. However, preference is given to a thickness of the boundary layer which is not greater than 250 nm.

A layer package consisting of a porous or nanoporous layer with a low refractive index and a non-contact layer in direct contact with it. porous polymer layer with a high refractive index forms the smallest unit of the inventive materials. The materials according to the invention contain at least one such layer package or a sequence of such layer packages, the differences of the refractive indices of the different layers, the order of the layers, the orientation of the layers, the composition of the layers and their thickness depending on the particular application.

The porous or nanoporous layer with the low refractive index, which contains inorganic nanoparticles, has in the material according to the invention a dry film thickness between 0.2 μm and 60.0 μm, preferably between 1.0 μm and 40.0 μm, particularly preferably between 2.0 μm and 20.0 μm.

The non-porous polymer layer with the high refractive index has a dry film thickness of between 0.05 μm and 2.5 μm, preferably between 0.2 μm and 2.0 μm, in the material according to the invention. Layer thicknesses between 0.3 μm and 0.8 μm are particularly preferred.

If appropriate, the materials according to the invention may, between the individual layer packages, if present between the layer packages and the support or on the layer packages, comprise one or more additional layers with different functions (for example luminescent layers, electrically conductive layers, reflective layers, protective layers, mechanical mechanical layers) Stabilization or release layers).

In a preferred embodiment of the invention, the material according to the invention, as shown in FIG. 1, consists of a flexible carrier on which a porous or nanoporous layer with a low refractive index, which contains inorganic nanoparticles, and above it a non-porous polymer layer with a high Refractive index are applied. This embodiment is of interest, for example, for those applications in which the light propagating in the non-porous polymer layer having the high refractive index should be optically decoupled from the flexible support regardless of whether the light is coupled into the non-porous polymer layer having the high refractive index or was created there. An example of such an application is described by T. Tsutsui, M. Yahiro, H. Yokogawa, K, Kawano, and M. Yokoyama in "Döubling Coupling-Öut Efficiency in Oregon Light-Emittinc Thin Siläca Aerogei Layer", Advanced Materials J3, 1149. 1152 ben, where the Auskoplungsseffizienz of light from organic light-emitting diodes was examined. In a further preferred embodiment of the invention, as shown in FIG. 2, the porous or nanoporous layer with the low refractive index, which contains inorganic nanoparticles, and the nonporous polymer layer with the high refractive index again with a layer package consisting of a porous or nanoporous layer a deep refractive index, which contains inorganic nanoparticles, and a non-porous polymer layer with a high refractive index applied in reverse order. This is interesting for such applications, where the influence of the environment on the optical properties of the nonporous polymer layer with the high index of refraction should be controlled in a targeted manner. Such an application where the non-porous polymer layer having the high refractive index functions as an optical waveguide and the porous or nanoporous deep refractive index layers containing inorganic nanoparticles shield the waveguide on both sides (cladding of the waveguide). If the refractive index of the used non-porous layers 4 and 4 'is identical, no additional optical boundary layer is formed between these layers. This makes it possible, for example, to generate a plurality of mutually independent waveguides, each consisting of a core layer and two cladding layers or to control the communication between these waveguides targeted. The jacket of the waveguide also makes it possible, for example, for the flexible material according to the invention to be glued or transferred onto another carrier by means of an adhesive, without influencing the properties of the nonporous polymer layer having the high refractive index.

In addition, because of the porosity or nanoporosity of the deep refractive index layer containing inorganic nanoparticles, compounds having a diameter smaller than the mean pore diameter can penetrate into the pores of the porous or nanoporous layer and target the behavior of a waveguide, for example influence. This principle is well known in the field of application of optical waveguides in sensor technology and optical communications technology and is described, for example, in the book by W. Bludau, "Optical Waveguides in Sensor Technology and Optical Communications", pages 191-198 and 215-227, Springer Verlag 1998 , ISBN 3-540-63848-2 or by PJ Skrdla et. al., in "Planar Integrated Optical Waveguide Sensor for Isopropyl Alcohol in Aqueous Media", Journal of SoI-GeI Science and Technology, 24, 167-173 (2002).

The porous or nanoporous layers having a low refractive index contain inorganic nanoparticles and optionally a small amount of binders and other additives. After drying, they have a specific, measurable pore volume. The pore volume can be determine the BET method. The BET method for pore volume determination has been described by S. Brunauer, PH Emmet and I. Teller in "Adsorption of Gases in Multimolecular Layers", Journal of the American Chemical Society 60, 309-319 (1938). A simpler method is to fill the pores with a suitable solvent of known density and directly determine the pore volume by increasing the weight of the layer. The porous or nanoporous layers according to the invention have a pore volume of between 0.1 ml / g and 2.5 ml / g, the reference value being the unit weight of the porous or nanoporous layer containing inorganic nanoparticles.

In the novel recording materials, pore volumes of between 0.2 ml / g and 2.5 ml / g determined in this way are preferred; pore volumes between 0.4 ml / g and 2.5 ml / g are particularly preferred.

The refractive index of the porous or nanoporous layer containing inorganic nanoparticles is influenced by the porosity. An increase in porosity leads to a decrease in the refractive index. As a result, it is theoretically possible to set refractive indices between 1.00 (air) and that of the inorganic nanoparticles used, for example the value 1.45 when using SiO 2 as inorganic nanoparticles. The relevant in practice for optical applications refractive indices between 1.05 to 1.40 can be achieved in this way.

The effective refractive index of such layers can be approximated by forming the volume weighted sum of the refractive index of the nanoparticle network and the refractive index of the gas filled pores.

For example, such a porous or nanoporous layer with a porosity of 0.80, which mainly contains SiO 2 nanoparticles with a refractive index of 1.45 and air with a refractive index of 1.00, has an effective refractive index of 1.09. After application of the coating solution for the porous or nanoporous layer with the low refractive index, which contains inorganic nanoparticles, during the drying of the layer, a three-dimensional network of these nanoparticles gradually forms. The interstices of this network are filled with the solvent used or dispersants and, if appropriate, the other additives used. During further drying, the solvent used or dispersant is removed. When using sufficiently small amounts of additives, such as the binder, the remaining additives are unable to completely fill the interstices of the nanoparticles and release them. are in the network of nanoparticles filled with gas pores. This consists of two phases, a solid and a gaseous, existing three-dimensional network has structures with dimensions in the submicron range. By a targeted control of the size of these structures, the scattering effects and thus also the transparency of the layers according to the invention can be influenced. These effects can be characterized, for example, on layers on a transparent polymer support by the optical transmission at 550 nm.

In an advantageous embodiment of the invention, the porous or nanosized layer has a transmission value for light of wavelength 550 nm between 60% and 99%. In a preferred embodiment of the invention, the nanoporous layer has a transmission value between 80% and 95%. In a particularly preferred embodiment of the invention, the nanoporous layer has a transmission value between 85% to 95%.

The inventive materials also solve the problems of brittleness and stiffness of the porous or nanoporous layers for optical applications described in the prior art. The desired mechanical properties are achieved by the use of a suitable binder in the porous or nanoporous layers containing inorganic nanoparticles.

As inorganic nanoparticles for producing the porous or nanoporous layers having a low refractive index, for example, natural, precipitated or powdered metal oxides, metal oxide / hydroxide and natural or synthetic zeolites can be used. As metal oxides, for example, SiO 2, Al 2 O 3, TiO 2, ZnO, ZrO 2 and SnO 2 or the mixed oxide indium-tin oxide can be used. It is also possible to use mixtures of all these compounds. As the metal oxide / hydroxide, for example, AIOOH can be used.

Preference is given to inorganic nanoparticles having a refractive index of less than 1.80 at a wavelength of 550 nm. Particularly preferred inorganic nanoparticles are precipitated or dusty silica, alumina, alumina / hydroxide and the zeolites zeolite beta, ZSM-5, mordenite, LTA (Linde Type A ), Faujasites and LTL (Linde Type L).

Official structural designations of the aforementioned zeolites can be found, for example, in the book by C. Bärlocher, WM Meier and DH Olson, "Atlas of Zeolite Framework Types", 5th ed., Elsevier (2001), ISBN 0-444-50701-9. The size of the inorganic nanoparticles (primary particles) can be determined by imaging techniques, such as high-resolution transmission electron microscopy or scanning electron microscopy.

The mean particle diameter of the inorganic nanoparticles (primary particles) is preferably between 5 nm and 200 nm, particularly preferably the size range between 10 nm and 60 nm. The inorganic nanoparticles preferably have a narrow particle size distribution, with at least 90% of the primary particles having a smaller diameter have twice the above-mentioned average particle diameter and practically no primary particles have a larger diameter than three times the aforementioned average particle diameter.

The inorganic nanoparticles can also be present in the form of agglomerates (secondary particles) which have a measurable BET pore volume as the solid substance.

In the particularly preferred silica, two different types can be used, first, a precipitated silica prepared by a wet process and, secondly, a dusty silica produced by a gas phase process. Precipitated silica can be prepared, for example, by wet process by metathesis of sodium silicate by an acid or by passing through a layer of ion exchange resin as silica sol, by heating and ripening this silica sol, or by gelling a silica sol. Dust-form silica is generally prepared in a flame hydrolysis process, for example by combustion of silicon tetrachloride with hydrogen and oxygen. Example of such dusty silica is Aerosil® 200 (SiO 2 having an isoelectric point at pH 2.0) available from DEGUSSA AG, Frankfurt / Main, Germany. According to its data sheet, this substance has a BET specific surface area of about 200 m 2 / g and a primary particle size of about 12 nm. Another example is Cab-O-Sil® M-5 available from Cabot Corporation, Billerica, USA , According to its data sheet, this product has a BET specific surface area of about 200 m 2 / g and a size of the primary particles of about 12 nm. The agglomerates are 0.2 μm to 0.3 μm long. In the present invention, preferably dusty silica having an average size of the primary particles of at most 20 nm and a specific surface area of at least 150 m 2 / g as determined by the BET method is used. The likewise preferred zeolite beta is available in the form of nanoparticles with a mean size of 30 nm from NanoScape AG, Munich, Germany. The other nanocrystalline zeolites (the size of the primary particles is given in parentheses) are ZSM-5 (70 nm - 100 nm), mordenites (500 nm), LTA (90 nm), faujasites (80 nm) and LTL (50 nm) available there.

As the metal oxide / hydroxide, for example, alumina / hydroxide can be used. Particularly preferred is pseudoboehmite.

The preparation of the aluminum oxide / hydroxides in the sol-gel process takes place with advantage in the complete absence of acid, as described, for example, in the patent DE 3'823'895.

A preferred alumina is γ-alumina.

In a particularly preferred embodiment of the invention, the aluminas or alumina / hydroxides incorporated in the crystal lattice elements of rare earths. Their preparation is described for example in the patent application EP 0'875'394. Such aluminas or alumina / hydroxides contain one or more elements of atomic number 57 to 71 of the Periodic Table of the Elements, preferably in an amount between 0.4 and 2.5 mole percent based on Al2O3. A preferred rare earth element is lanthanum.

The surface of the inorganic nanoparticles can be modified in order to break up the possibly present agglomerates of the primary particles during the dispersing process into smaller units and to stabilize them. The size of the dispersed particles has a considerable influence on the transparency of the porous or nanoporous layer containing these nanoparticles. The surface modification can also serve to improve the compatibility of the nanoparticle surfaces with the binders and / or solvents or dispersants used. In such a modification, an uncharged, a positively charged or a negatively charged surface can be generated.

A preferred type of surface modification for producing a positively charged surface of silicon dioxide is that with polyaluminum hydroxychloride, as proposed, for example, in patent application DE 10'020'346. The patent application WO 00/202222 describes the surface modification of gas phase produced silica with aluminum chlorohydrate. Another preferred type of surface modification of silica is that with aminoorganosilanes, as described for example in patent application EP 0'663'620.

A particularly preferred mode of surface modification of silica is described in European Patent Application EP 1'655'348 in which the surface of the silica is reacted with the reaction products of at least one aminoorganosilane and a trivalent aluminum compound.

Preferred compounds of the trivalent aluminum for surface modification with the reaction products of a compound of trivalent aluminum and an aminoorganosilane are aluminum chloride, aluminum nitrate, aluminum acetate, aluminum formate and aluminum chlorohydrate.

The amount of the compound of trivalent aluminum is typically between 0.1 percent by weight and 20 percent by weight based on the amount of silica. A value between 0.5% by weight and 10% by weight is preferred.

Particularly preferred aminoorganosilanes for surface modification with the reaction products of a compound of trivalent aluminum and an aminoorganosilane are 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, (3-triethoxysilylpropyl) -diethylenetriamine, 3-aminopropyltriethoxysilane, N - (2-aminoethyl) -3-aminopropyltriethoxysilane, (3-triethoxysilylpropyl) -diethylenetriamine and mixtures thereof.

The total amount of Aminoorganosilans or the mixture of Aminoorganosilanen is typically between 0.1 weight percent and 10 weight percent based on the amount of silica. A value between 0.5% by weight and 20% by weight is preferred.

The weight ratio between the compound of trivalent aluminum (for example aluminum chlorohydrate) and the aminoorganosilanes is advantageously chosen so that the desired pH is achieved when the two components of the two reagents are mixed. Preference is given to a molar ratio between 0.1 and 2.0, more preferably a molar ratio of between 0.4 and 1.5, based on the number of aluminum atoms and the number of amino groups of the aminoorganosilane.

Particularly preferred for the surface modification with the reaction products of a compound of trivalent aluminum and at least one Aminoorganosilane is dusty silica having a primary particle size of at most 20 nm.

The dispersion at high shear rates gives a uniform distribution of the reaction products on the silica. Furthermore, the theological behavior of the dispersion is improved.

In the porous or nanoporous layers with low refractive index, which contain inorganic nanoparticles, the inorganic nanoparticles are in amounts between 0.2 g / m ^ and 60.0 g / m ^, preferably between 1.0 g / m ^ and 40.0 g / m2, more preferably between 2.0 g / m2 and 20.0 g / m2 available.

The amount of binder present in the porous or nanoporous layer should be sufficiently small to achieve the desired porosity, but also high enough to produce stable, well-bonded coatings on the flexible support without brittleness. Amounts up to 60% by weight of the binder based on the total amount of the inorganic nanoparticles may be used, but preferred are amounts between 0.5% and 40.0% by weight of the binder based on the total amount of the inorganic nanoparticles in the porous or nanoporous layer having the low refractive index. Particular preference is given to amounts between 10.0% by weight and 30.0% by weight, based on the total amount of the inorganic nanoparticles in the porous or nanoporous layer with the low refractive index.

Suitable binders for the porous or nanoporous deep refractive index layer containing inorganic nanoparticles are generally water-soluble hydrophilic polymers.

Synthetic, natural or modified natural water-soluble polymers such as fully or partially hydrolyzed polyvinyl alcohol or copolymers of vinyl acetate and other monomers; modified polyvinyl alcohols; Polyvinylpyrrolidone, polyethylene oxides; Homopolymers or copolymers of (meth) acrylamide; Polyvinyl pyrrolidones, polyvinyl acetals, polyurethanes and starch or modified starch, cellulose or modified cellulose such as hydroxyethyl cellulose, carboxymethyl cellulose and gelatin can be used as well as mixtures of these polymers.

It is also possible to use conductive polymers such as polythiophene, polyaniline, polyacetylene, poly (3,4-ethylene) dioxythiophene, mixtures of poly (3,4-ethylene) dioxythiophene-poly (styrenesulfonate), polyfluorene, polyphenylene, polyphenylene and Polyphenylenevinylene in double strand form and block copolymers of different conductive polymers or block copolymers of conductive and non-conductive polymers. Poly (3,4-ethylene) dioxythiophene is preferred. Particularly preferred synthetic binders for the porous or nanoporous deep refractive index layer containing inorganic nanoparticles are modified and unmodified polyvinyl alcohol, polyvinylpyrrolidone or their mixtures. The above-mentioned binders having crosslinkable groups can be converted to practically water-insoluble layers with the aid of a crosslinker or hardener. Such crosslinks can be covalent or ionic. Crosslinking or curing of the layers permits a change in the physical layer properties, such as, for example, liquid absorption, dimensional stability under the action of liquids, vapors or temperature changes, or resistance to layer damage and brittleness. The crosslinkers and hardeners are selected on the basis of the water-soluble polymers to be crosslinked.

Organic crosslinkers and hardeners include, for. B. aldehydes (such as formaldehyde, glyoxal or glutaraldehyde); N-methylol compounds (such as dimethylolurea or methylol-dimethylhydantoin); Dioxanes (such as 2,3-dihydroxydioxane); reactive vinyl compounds (such as 1,3,5-trisacryloyl-hexahydro-s-triazine or bis (vinylsulfonyl) ethyl ether), reactive halogen compounds (such as 2,4-dichloro-6-hydroxy-s-triazine) ; epoxides; aziridines; Carbamoylpyridinverbindungen or mixtures of two or more of these crosslinkers mentioned.

Inorganic crosslinkers and hardeners include, for example, chrome alum, aluminum alum, boric acid, zirconium compounds or titanocenes.

The layers may also contain reactive substances which crosslink the layers under the influence of UV light, electron beams, X-rays or heat.

The polymers may be blended with water-insoluble natural or synthetic high molecular weight compounds, especially acrylic latices or styrene acrylic latices.

In another embodiment of the invention, the nanoporous layers with the low refractive index may also contain compounds which absorb light in the wavelength range of interest between 200 nm and 2500 nm. In a preferred embodiment of the invention, it is organic compounds which absorb light in the range between 200 nm and 700 nm. In another embodiment of the invention, the nanoporous layers having the low refractive index may also contain luminescent organic molecules, luminescent organic pigments, luminescent organic polymers, luminescent inorganic nanoparticles and organic or inorganic nanoparticles with luminescent compounds contained therein which emit light in the wavelength range of interest between 200 nm and 2500 nm.

The non-porous polymer layer having the high refractive index consists of synthetic, natural or modified natural water-soluble polymers such as fully or partially hydrolyzed polyvinyl alcohol or

Copolymers of vinyl acetate and other monomers; modified polyvinyl alcohols; (Meth) acrylated polybutadiene; Homopolymers or copolymers of

(Meth) acrylamide; Polyvinylpyrrolidone, polyvinyl acetals, polyurethanes and starch or modified starch, cellulose or modified cellulose such as hydroxyethyl cellulose, carboxymethyl cellulose and gelatin or mixtures thereof.

Preferred synthetic polymers are modified polyvinyl alcohol, polyurethane, (meth) acrylated polybutadiene, copolymers of (meth) acrylamide and polyacrylonitriles or their mixtures. Conductive polymers such as polythiophene, polyanilines, polyacetylene, poly (3,4-ethylene) dioxythiophene, mixtures of poly (3,4-ethylene) dioxythiophene-poly (styrenesulfonate), polyfluorene, polyphenylene, polyphenylene and polyphenylenevinylene in double-stranded form, and Block copolymers of different conducting polymers or block copolymers of conducting and non-conducting polymers can also be used. Poly (3,4-ethylene) dioxythiophene is preferred.

Polyelectrolytes, such as salts of polystyrenesulfonic acid, salts of polyvinylsulfonic acid, salts of poly-4-vinylbenzylammonium cation, salts of polyallylamine, salts of polyethyleneimine, salts of poly (dimethyldiallyl) -ammonium cation, poly (allylamine) hydrochloride, Chitosan, polyacrylic acids and their salts, dextran sulfates, alginates, salts of poly (I - [4- (3-carboxyl-4-hydroxyphenylazo) benzenesulfonamido] -1,2-ethane, salts of poly (dimethyldiallylammonium) cations , Block copolymers and their mixtures can also be used.

This layer can also be crosslinked or hardened, as previously described for the layer with the deep refractive index.

In another embodiment of the invention, the non-porous polymer layer having the high refractive index may also consist of water-dispersible thermoplastic polymers. In this case, if necessary, the polymer film is produced in an additional step after the application of the layer by a heat treatment under pressure. This subsequent heat treatment under pressure is not necessary, for example, if the layer during the drying phase reaches or exceeds the glass transition temperature of the thermoplastic polymer for a certain time. The water-dispersible thermoplastic polymers include, for example, particles, latices or waxes of polyethylene, polypropylene, polytetrafluoroethylene, polyamides, polyesters, polyurethanes, acrylonitriles, polymethacrylates such as methyl methacrylates, polyacrylates, polystyrenes, polyvinyl chloride, polyethylene terephthalate, copolymers of ethylene and acrylic acid and paraffin waxes (such as Polysperse, available from Lawter Int., Belgium). Mixtures of these compounds or polymers such as polystyrene and acrylates, ethylene-acrylate copolymers, copolymers of styrene and acrylonitrile may also be used. The particle size of the latices can be between 20 nm and 5 ¹ 000 nm, preferably between 40 nm and 1000 nm, and more preferably between 50 nm and 500 nm. The glass transition temperature is between 30 ° C. and 170 ° C., preferably between 50 ° C and 110 ° C, more preferably between 60 ° C and 90 ⁰ C.

If the layer of latex particles does not already form a transparent film during the manufacturing process, the latex particles may be fused into a film having the facilities and conditions known to those skilled in the art, such as are common in the lamination of photographic and inkjet printing paper. For example, the laminator GBC 3500 Pro, available from GBC European Films Group, Mercuriusstraat 9, Kerkrade, Holland, may be used. This device is particularly suitable for a heat treatment at a temperature of 120 ° C at a flow rate of about 27 cm / min.

The water-dispersible thermoplastic polymers can also be composed of several shells, wherein, for example, the core and an outer shell can have a different swellability or a different glass transition temperature.

The polymer particles or polymer latices may have an uncharged surface or a positive or negative surface charge. The polymer particles can be mixed with water-soluble binders, such as the aforementioned binders, preferably with polyvinyl alcohol or mixtures of different polyvinyl alcohols. Preference is given to polyvinyl alcohols having a viscosity of at least 26 mPasec and a degree of hydrolysis of at least 70%. In another embodiment of the invention, it is also possible to use UV-curable polymer particles which are dispersed in water and then applied to the porous or nanoporous deep refractive index layer containing inorganic nanoparticles. Subsequently, the non-porous polymer layer is produced in an additional step by heat treatment under pressure and / or UV exposure, as described by MMG Antonisse, PH Binda and S. Udding-Louwrier in "Application of UV Curable Powder Coatings on Paperlike Substrates", American Ink Maker 79 (5). 22-26 (2001).

In another embodiment of the invention, the nonporous polymer layers with the high refractive index may additionally contain, in addition to the polymers, non-porous inorganic compounds which may further increase the refractive index. For this purpose, inorganic compounds are used which have a higher refractive index in the wavelength range of interest between 200 nm and 2500 nm than the polymer used in the non-porous polymer layer. The refractive index of the nonporous polymer layer is then increased by adding the inorganic compound. In contrast to the porous or nanoporous layers with low refractive index, which contain inorganic compounds, the proportion of inorganic compounds in relation to the polymer used in the non-porous polymer layer is kept so low that no porosity can arise because the presence of gas-filled pores otherwise the refractive index would reappear. A layer in which the ratio of the pore volume to the total volume is less than 4% is defined as "nonporous". The achievable effective refractive indices of the resulting non-porous layer are always between the refractive index of the non-porous starting layer and the refractive index of the added inorganic compound.

In a preferred embodiment of the invention, the average particle diameter of these inorganic nanoparticles (primary particles) is preferably between 5 nm and 200 nm, more preferably the size range between 10 nm and 60 nm. The inorganic nanoparticles preferably have a narrow particle size distribution, wherein at least 90 % of the primary particles have a smaller diameter than twice the aforementioned average particle diameter and practically no primary particles have a diameter larger than three times the aforementioned average particle diameter. Examples of such preferred nanoparticles in the nonporous polymer layer are PbS, TiO 2, SiO 2, Al 2 O 3, ZrO 2, ZnO and SnO 2.

In another preferred embodiment of the invention, the inorganic compounds are polymers such as poly (dibutyl titanate).

In another embodiment of the invention, the non-porous polymer layers with the high refractive index may also contain, in addition to the polymers, compounds which absorb light in the wavelength range of interest between 200 nm and 2500 nm. In a preferred embodiment of the invention, organic compounds absorb light between 200 nm and 700 nm. In another embodiment of the invention, the non-porous polymer layers with the high refractive index may also contain luminescent organic molecules, luminescent organic pigments, luminescent organic polymers, luminescent inorganic nanoparticles and organic or inorganic nanoparticles with luminescent compounds contained therein, which in the wavelength range of interest 200 nm and 2500 nm emit light.

Flexible carriers for the novel materials are a large variety of flexible carriers, such as those used in the photographic industry, among others. For the preparation of the novel materials, it is possible to use all carriers used in the production of photographic materials, for example transparent carriers of cellulose esters such as cellulose triacetate, cellulose acetate, cellulose propionate or cellulose acetate / butyrate, polyesters such as polyethylene terephthalate or polyethylene naphthalate, polyamides, polycarbonates , Polyimides, polyolefins, polyvinyl acetals, polyethers, polyvinyl chloride and polyvinylsulfones. Preference is given to polyesters, in particular polyethylene terephthalate such as, for example, Cronar® from Du-Pont Tejin Films or polyethylene naphthalate, because of their excellent dimensional stability.

For example, baryta paper, polyolefin-coated papers, white opaque polyesters such as Melinex® from Du-Pont Tejin Films can be used in the opaque supports used in the photographic industry. Particularly preferred are polyolefin-coated papers or white opaque polyester. Furthermore, carriers consisting of acrylonitrile-butadiene-styrene, polycarbonate, polyetherinide, polyether ketone, polymethyl methacrylate, polyoxymethylene and polystyrene can also be used.

It is advantageous to provide these supports, in particular polyesters, with a subbing layer prior to coagulation in order to improve the adhesion of the layers to the support. Such subbing layers are well known in the photographic industry and contain e.g. As terpolymers of vinylidene chloride, acrylonitrile and acrylic acid or vinylidene chloride, methyl acrylate and itaconic acid. The adhesion of the layers to the support can also be improved, for example, by a corona or corona / aerosol treatment of the support before the casting. All of these flexible carriers can also be provided with an electrically conductive layer. Preference is given to metals or indium tin oxide coated plastic carrier.

Flexible metal foils, for example made of aluminum, can also be used. All of these supports can also have three-dimensional surface structures.

The layers according to the invention are generally prepared from aqueous solutions or dispersions containing all the necessary components on the flexible layer

Carrier applied or potted. In many cases, wetting agents are added as casting aids in order to improve the casting behavior and the uniformity of the

To improve layers. Although such surface-active compounds in the

Nevertheless, they form an essential part of the invention.

In order to prevent the brittleness of the layers having a low refractive index, which contain inorganic nanoparticles, it is additionally possible to add plasticizers, for example glycerol.

The novel materials comprise at least one layer package which contains a porous or nanoporous layer with a low refractive index and a non-porous polymer layer with a high refractive index, or several such layer packages, the differences in the refractive indices of the different layers, the sequence of the layers, the orientation of the layers , the composition of the layers and their thickness depend on the particular application. In the case of several layer packages, these can be applied successively or also together to the flexible carrier.

In a first embodiment of the invention, for the production of such a flexible material for optical applications, first the porous or nanoporous layer with the low refractive index, which contains inorganic nanoparticles and a binder and optionally further additives, is applied to the flexible carrier. For this purpose, aqueous, colloidal dispersions of these inorganic nanoparticles, together with the binder and optionally further additives, at temperatures between 0 ° C and 100 ° C, preferably between 15 ° C and 60 ° C on flexible metal, paper or Plastic support, which may also be coated with indium tin oxide or metals, applied and the molded flexible carrier is then dried. In a second step, the nonporous polymer layer with the high refractive index is then applied thereto by adding aqueous solutions of the polymer, which optionally contain further additives, or, when using water-dispersible thermoplastic polymers, colloidal dispersions of these thermoplastic polymers, optionally together with an additional binder temperatures ren between 0 ° C and 100 ° C, preferably between 15 ° C and 60 ° C are applied and the coated flexible carrier is then dried.

In a second embodiment of the invention, to produce such a flexible material for optical applications, first the non-porous high refractive index polymer layer and then the low refractive index porous or nanoporous layer containing inorganic nanoparticles and a binder and optionally further additives are applied to the applied flexible carrier.

In another embodiment of the invention, further layer packages can be applied to the already coated with a layer package flexible carrier by one of the methods described above. In this case, either the non-porous polymer layer with the high refractive index or the porous or nanoporous layer with the low refractive index can be in direct contact with the carrier in the first layer package.

In a preferred embodiment of the invention, two layer packages are applied to the flexible support, the layer order being as follows: flexible support, a porous or nanoporous layer having a low refractive index, a nonporous layer having a high refractive index, then a second nonporous layer having a high refractive index and on it again a second porous or nanoporous layer with a low refractive index.

In a further embodiment of the invention, the layer packages, each containing a porous or nanoporous layer with a low refractive index, which contains inorganic nanoparticles, and a non-porous polymer layer with high refractive index, simultaneously in one step on flexible metal, paper or plastic substrates, which also with Indium tin oxide or metals can be coated, applied. Subsequently, the molded in this way flexible carrier is dried.

In a particularly preferred embodiment of the invention, the layer packages, each containing a porous or nanoporous layer with low refractive index, which contains inorganic nanoparticles, and a non-porous polymer layer with high refractive index, are applied successively in two separate coating steps on the flexible support. The drying can be done, for example, with air, with IR rays, with microwave radiation, by contact drying (the drying energy is introduced by pure heat conduction in contact with the surface of a heated material in the material to be dried) or a combination of these methods. The drying is preferably carried out with a gas mixture, preferably air, wherein the layer temperature during drying does not exceed 100 ° C, preferably 60 ° C.

The casting solutions can be applied to the flexible carrier in various ways. The casting processes include various well-known casting methods such as gravure coating, roll coating, bar brushing, slot casting, extrusion casting, doctor blade casting, cascade casting, curtain casting or other customary casting methods. If the flexible support is fixed on a firm base, dipping or centrifugal casting can also be used.

The casting speed depends on the method used and can be changed within wide limits. Preferably, as a casting method for the materials according to the invention, the curtain casting at speeds between 30 m / min and 2000 m / min, preferably between 50 m / min and 500 m / min.

All of the above-mentioned layer packages may optionally contain further additives in one or more of the layers, such as, for example, luminescent or light-absorbing compounds. All of the above-mentioned layer packages may optionally contain inorganic compounds for increasing the refractive index in the non-porous polymer layer having the high refractive index.

In a further embodiment of the invention, optionally between the individual layer packages, if several are present, between the layer packages and the carrier or on the layer packages one or more additional layers with other functions (for example luminescent layers, electrically conductive layers, reflective layers, protective layers, Layers for mechanical stabilization or release layers) are applied.

Optionally, at the end or as an intermediate step in the multiple coating, a structure can be applied to the individually applied layers. the. Such a structure can be produced by means of inkjet printing, photolithography, offset printing, laser marking or hot stamping.

The present invention will be further described by the following examples without being limited thereby in any way.

Examples Example 1

A porous or nanoporous layer having a low refractive index and the composition listed in Table 1 (in the dried state) was applied to a subbed Cronar® 742 transparent polyester support available from DuPont Teijin Films, Luxembourg.

Table 1

The surface-modified SiO 2 was prepared by the method of Example 1 of patent application EP 1'655'348.

Polyvinyl alcohol C is available as Mowiol 40-88 from Omya AG, Oftringen, Switzerland. The hardener is boric acid, available from Schweizerhall Chemie AG, Basel, Switzerland.

Onto this porous or nanoporous layer having the low refractive index, a non-porous polymer layer of high refractive index consisting of polyvinyl alcohol B having a dry film thickness of about 0.24 μm was applied.

Polyvinyl alcohol B is also available as Mowiol 56-98 from Omya AG, Oftringen, Switzerland. Example 2

A porous or nanoporous layer having a low refractive index and the composition listed in Table 2 (in the dried state) was applied to the subbed transparent polyester support of Example 1.

Table 2

Onto this porous or nanoporous layer having the deep refractive index, a non-porous polymer layer having a high refractive index and the in

Table 3 listed (when dried) applied.

Table 3

Polyvinyl alcohol D is available as Gohsefimer K-210 from Nippon Synthetic Chemical Industry Ltd., Osaka, Japan. The latex is Jonrez E2001, available from MeadWestvaco Corporation, Stamford, USA.

This layer was sealed with the GBC 3500 Pro laminator at a temperature of 120 ° C at a speed of about 27 cm / min.

Example 3

A porous or nanoporous layer having a low refractive index and the composition listed in Table 4 (in the dried state) was applied to the subbed transparent polyester support of Example 1.

Table 4

The lanthanum-containing alumina / hydroxide was prepared by the method of Example 1 of patent application EP 0O67O86.

Onto this porous or nanoporous layer having a low refractive index, a non-porous polymer layer having a high refractive index and the composition listed in Table 5 (in the dried state) was applied:

Table 5

Polyvinylpyrrolidone is Luviskol * K 90, available from BASF AG Wädenswil, Switzerland.

exams

In the case of the flexible materials for optical applications according to the invention, visible interference colors which are visible to the eye occur when viewed in daylight. These interference colors are due to the multiple reflection of the incident light at the interface between the porous or nanoporous deep refractive index layer containing inorganic nanoparticles and the non-porous polymer layer having the high refractive index. They are only clearly visible if the boundary layer is optically sufficient is sharp and the refractive index difference of the layers is at least 0.20.

Examples of tables of such interference colors have been compiled by J. Henrie, S. KeIMs, S.M. Schultz and A. Hawkins in "Electronic color Charts for dielectric films on Silicon", Optics Express 12, 1464-1469 (2004).

Because of the sensitivity of the eye, the visual assessment in the visible region of the spectrum (400 nm - 700 nm) is very meaningful. For the assessment, the interference colors could in principle also be recorded by means of a spectrometer. However, this method would be advantageous only where interference colors occur which are below or above the range visible to the human eye, or where multiple interferences overwhelm the spectral resolution of the human eye.

Results

Table 6 summarizes the evaluations of the interference colors of the test samples under the experimental conditions given above.

Table 6

The results in Table 6 clearly show that clearly visible interference colors occur in all cases. Particularly salient they are in Example 1.

Claims

claims

1. Flexible material for optical applications in a wavelength range between λi and λ2, wherein λi is smaller than λ2, consisting of a flexible support and at least one layer package applied thereon consisting of a porous or nanoporous layer having a low refractive index, which inorganic nanoparticles and at least one binder, and a nonporous high refractive index polymer layer in direct contact therewith, characterized in that the thicknesses of the interfaces between the porous or nanoporous layers and the nonporous polymer layers in direct contact therewith, in which the refractive index is from one to the other changes other value, at most 1/5 of the wavelength λ £.

2. Material according to claim 1, characterized in that λi is greater than 200 nm and λ2 is less than 2500 nm.

3. Material according to one of claims 1 or 2, characterized in that the difference in the refractive indices between the porous or noporösen layer and the non-porous polymer layer at a wavelength λ in the wavelength range between λi and λ £ is at least 0.20.

4. Material according to one or more of claims 1 to 3, character- ized in that the material has a single layer package on the support.

5. Material according to claim 4, characterized in that above the first layer packet, a second is arranged.

6. Material according to claim 5, characterized in that the layer order in the second package is the same as in the first layer package.

7. Material according to claim 5, characterized in that the layer sequence in the second package is reversed in comparison to the first layer package.

8. Material according to one or more of claims 1 to 7, characterized in that the porous or nanoporous layer of the first layer package is in direct contact with the carrier.

9. Material according to one or more of claims 1 to 8, characterized in that the non-porous polymer layer of the first layer packet is in direct contact with the carrier.

10. Material according to one or more of claims 1 to 9, character- ized in that the dry film thickness of the porous or nanoporous

Layers between 0.2 μm and 60 μm and the dry film thicknesses of the nonporous polymer layers are between 0.05 μm and 2.5 μm.

11. Material according to one or more of claims 1 to 10, character- ized in that the inorganic nanoparticles from the group consisting of precipitated or dusty silica, alumina, alumina / hydroxide, the zeolite zeolite beta, the zeolite ZSM-5, the Zeolites Mordenite, the zeolite LTA (Linde Type A), the zeolite faujasite and the zeolite LTL (Linde Type L) or mixtures of these compounds.

12. Material according to claim 11, characterized in that the inorganic nanoparticles have an average particle diameter between 5 nm and 200 nm.

13. Material according to one or more of claims 1 to 12, characterized in that the inorganic nanoparticles from the group consisting of precipitated or dusty silica, alumina, alumina / hydroxide, the zeolite zeolite beta, the zeolite ZSM-5, the zeolite mordenite , the zeolite LTA (Linde Type A), the zeolite

Faujasite and the zeolite LTL (Linde Type L) or mixtures of these compounds.

14. Material according to one or more of claims 1 to 13, character- ized in that the amount of the binder in the porous or nanoporous layer containing inorganic nanoparticles, between 0.5 weight percent and 60 weight percent based on the amount of inorganic nanoparticles in this Layer is.

15. Material according to one or more of claims 1 to 14, characterized in that the binder is selected in the porous or nanoporous layer from the group consisting of modified and unmodified polyvinyl alcohol, polyvinylpyrrolidone or mixtures of these compounds.

16. Material according to one or more of claims 1 to 15, characterized in that the polymer in the non-porous polymer layer from the group consisting of modified polyvinyl alcohol, polyurethane, (meth) acrylated polybutadiene, copolymers of (meth) acrylamide and

Polyacrylonitrile or mixtures of these compounds is selected.

17. Material according to one or more of claims 1 to 15, characterized in that the non-porous polymer layer of water-dispersible thermoplastic polymers having glass transition temperatures between

30 ° C and 170 ° C, from which by a heat and pressure treatment, the non-porous polymer layer is produced.

17. Material according to claim 16, characterized in that the water-dispersible thermoplastic polymers are selected from the group consisting of particles, latices or waxes of polyethylene, polypropylene, polytetrafluoroethylene, polyamides, polyesters, polyurethanes, acrylonitriles, polymethacrylates, polyacrylates, Polystyrene, polyvinyl chloride, polyethylene terephthalate, copolymers of ethylene and acrylic acid and paraffin waxes is selected.

18. A process for producing a material according to claim 1, characterized in that the porous or nanoporous layer, which contains inorganic nanoparticles, and the nonporous non-porous polymer layer are applied to the flexible carrier in two separate coating processes.

19. A method for producing a material according to claim 18, characterized in that the coating of the flexible carrier by means of cascade casting or by curtain coating takes place.