EP2488590A1

EP2488590A1 - Highly refractive, scratchproof tio2 coatings in mono- and multilayers

Info

Publication number: EP2488590A1
Application number: EP10763197A
Authority: EP
Inventors: Karlheinz Hildenbrand; Friedrich-Karl Bruder
Original assignee: Bayer MaterialScience AG
Current assignee: Bayer Intellectual Property GmbH
Priority date: 2009-10-16
Filing date: 2010-10-11
Publication date: 2012-08-22
Also published as: WO2011045275A1; CN102549081A; JP2013507274A; US20120219788A1

Abstract

The invention relates to coated products comprising a substrate (S) having a coating made of a single, highly refractive, and scratchproof layer (A) or having a multilayer construction, wherein layers (A) alternate with less refractive layers (B), wherein the layers (A) are characterized in that they comprise particularly finely distributed TiO2 nanoparticles.

Description

High refractive, scratch resistant TiC coatings in monolayers and multilayers

The invention relates to coated products comprising a substrate (S) provided with a coating consisting of a single, high-index and scratch-resistant layer (A) or provided with a multilayer Au, in which alternating layers (A) with lower refractive layers (B), wherein the layers (A) are characterized in that they contain particularly finely divided T1O ₂ - nanoparticles. The coatings comprising the layer (A) can be produced by a process which enables the agglomeration-free deposition of the nanoparticles. A further subject of the invention is therefore also a process for the production of the products provided with a single layer or with multilayer and their use, for example as "cover layer" in optical data storage or as IR reflection coatings.

High refractive index (HRI) coatings, also referred to as HRI coatings, are known from a variety of applications, such as optical or planar waveguides, where the term "refractive index" is synonymous with "Real part of the complex refractive index", both terms are used interchangeably in the present application and denoted by n. Coatings with high refractive indices can in principle be produced by various methods T1O ₂ , Ta ₂ 0 ₅ , CeÜ ₂ , Y ₂ O ₃ deposited in a high vacuum via plasma processes. While it is easy to achieve refractive indices of more than 2.0 in the visible wavelength range, the method is relatively complex and expensive.

US Pat. No. 6,777,070 B1 describes an antireflective material and a polarizing film, the antistain coating consisting of 3 components: 1. a fluorine-containing methacrylate polymer, 2. a polymer of urethane acrylate and ultrafine particles, and 3. a surface-treated titanium oxide particle resin. Thus, in the examples, a mixture of titanium dioxide and zirconium dioxide is used. The present coated product exclusively contains titanium dioxide nanoparticles in the scratch-resistant layer.

DE 1,982,3732 A1 describes a process for the production of optical multilayer systems, wherein, inter alia, the application of a nanoscale inorganic solid particles containing flowable composition takes place on a glass substrate. In the present application, the substrates are of polymeric material. Chem. Mater 2001, 13, 1137 -1 142 describes the preparation of optical thin films of high-index trialkoxysilane-capped PMMA titanium hybrid and, inter alia, its transmission. It is a scratch resistant coating on potassium bromide pellets. Polycarbonate as a substrate material is not mentioned.

US Pat. No. 6,777,706 Bl describes an optical product which contains a layer of organic material, which contains translucent nanoparticles. The content of nanoparticles, including T1O ₂ , in the cured layer may be 0-50 vol.%. The coated product of the present invention contains in the coating an amount of> 58% by weight of titanium dioxide.

EP 0964019 A1 and WO 2004/009659 A1 disclose organic polymers, for example sulfur-containing polymers or halogenated acrylates (tetrabromophenyl acrylate, Polyscience Inc.), which inherently have a higher refractive index than conventional polymers and which are prepared by simple methods from organic solutions Conventional coating methods can be applied to surfaces. However, the refractive indices are limited to values of up to about 1.7, measured in the visible wavelength range.

Another process variant, which is becoming increasingly important, is based on metal oxide nanoparticles which are incorporated into organic or polymeric binder systems. The corresponding nanoparticle-polymer hybrid formulations can be applied in a simple manner at low cost, for example by means of spin coating, to various substrates. The achievable refractive indices are usually between the first mentioned sputtering surfaces and the layers of high refractive index polymers. With increasing nanoparticle contents, increasing refractive indices can be achieved. For example, US 2002/176169 A1 discloses the preparation of nanoparticle-acrylate hybrid systems, wherein the high-index layers contain a metal oxide, such as titanium oxide, indium oxide or tin oxide, and a UV-crosslinkable binder, for example acrylate-based, in organic solvent. After spin coats, solvent evaporation and UV irradiation, appropriate coatings for optical films / foils containing a scratch resistant coating, an HRI layer (I) in a thickness of 30 to 120 nm and a desired refractive index of 1.70. 1.95, a layer (II) in a thickness of 5 - 70 nm and having a refractive index of 1.60 - 1.70, and containing an LRI layer of a siloxane-based polymer. These films should be suitable as antireflection layers. Although a target refractive index range of up to 1.95 is given for the HRI layer (I), there is no instruction or example of how such a layer could be made. In the examples, the preparation of HRI layers (I) is described, which have only refractive indices of n = 1.71 and 1.72 (according to the manufacturer of the Ti0 ₂ -containing coating solution used are even only refractive indices of max. To achieve 1.59). about the imaginary part k of the refractive index is not stated, it also depends on the size of the nanoparticles, as described below. Therefore, the layers with higher refractive indices claimed in this application are to be regarded as desideratum only, and the disclosure does not satisfy the need for a method of producing such high refractive index layers.

EP-A 2008/040439 describes coated products comprising a substrate (S) and a coating (A) produced from a water-containing nanoparticle suspension. The coatings (A) are characterized by having a real part n of the complex refractive index of at least 1.70, an imaginary part k of the complex refractive index of at most 0.016, a surface roughness of Ra less than 20 nm, and a scratch resistance of less or 0.75 μm scratch depth, the real part and the imaginary part of the refractive index being measured at a wavelength of 400-40 μm (that is to say in the wavelength range of the blue laser) and the surface roughness being denoted as Ra value by means of AFM (FIG. atomic force microscopy). Such HRI coatings can be used as the uppermost layer in optical data storage (ODS), whereby the high refractive index enables the coupling of light in the evanescent field of a near-field lens (solid immersion lens, SIL). However, the higher the real part n of the refractive index and the lower the imaginary part k (k value) of the refractive index of the HRI layer, the better the performance, in particular the storage capacity of such optical data memories. The k value is related to the decay constant of the light intensity α as follows: λ - a

The decay constant α in turn depends on the absorption and scattering (scatter) in the refractive medium. Particularly in the case of nanoparticle-containing systems, k or α can be dominated by scattering (scatter) in the visible wavelength range of 400-800 nm if the primary nanoparticles are too large or agglomerate nanoparticles to form larger particles, even if no molecular mass is present in this spectral range Absorption is present. A low k value thus describes a medium in which light scattering and absorption are low and which has good transmission properties.

One step of the production process for such coatings from EP-A 2008/040439 is the partial replacement of the water of an aqueous nanoparticle suspension with organic solvent. If the water content is not adjusted precisely, this process leads to agglomeration of the nanoparticles and thus to layers with reduced transmission (higher k values). In the course of further investigations, it turned out that agglomerations can not be avoided, especially when solvent is exchanged for water against organic solvents of suspensions containing TiCV nanoparticles. Layers with a real part n of the complex refractive index of at least 1.85 and an imaginary part k of the complex refractive index of at most 0.01 (measured at a wavelength of 400-410 nm) can therefore be combined with HRI according to EP-A 2008/040439. Not achieve layers.

The combination of HRI layers with other coatings that have a significantly lower refractive index ("low reflective index" (LRI) layers) results in birefringent multilayers (alternating sequence of low and high refractive layers), which results in coatings with reflective properties for electromagnetic radiation, for example in the visible part of the solar spectrum or in the range of IR heat radiation The principles of these developments are described in US-A 3610729, 5094788, 5122905, 5122906, 5269995 and 5389324 of the company Dow Films with IR reflection properties are offered for example by the company 3M under the name "Prestige Series Films". These are laminated individual layers of films with different refractive indices, for example of polyester and polyacrylate films whose layer thicknesses are in the range of% of the IR rays to be reflected, ie at approximately 250 nm. Because of the small refractive index difference of not significantly more than 0.1 (polyacrylate: n ~ 1.5 and polyester: n ~ 1.6), a very high number (about 200) of HRI / LRI layer sequences are needed to obtain IR reflectance values of about 90%. With layer sequences whose refractive indices differ more strongly, the number of layer sequences could be significantly reduced on the basis of theoretical calculations. Conventional coating formulations, for example based on acrylate, usually have a real part of the refractive index in the range of about n = 1.5.

For this reason, the higher their refractive index, the higher the suitability of an HRI layer for an HRI / LRI multilayer coating. Efficient reflection properties could thus be made possible with a significantly lower number of layer sequences.

There is therefore a need for HRI layers for substrates such as glass, quartz or organic polymers, which have even better complex refractive indices than the prior art, characterized in that at the same time the real part n of the complex refractive index is higher and the imaginary part k is lower, and simultaneously with the values for surface roughness ("Ra value", measured by AFM (atomic force microscopy) and scratch resistance (determined by measuring the resulting scratch depth when guiding a diamond needle with a tip radius of 50 μm at a feed rate of 1.5 cm / s and a coating weight of 40 g over the coating), at least at a comparable level. The layers should also be made by a simple process.

With a view to novel high-index HRI layers, it has now surprisingly been found that high-indexing, by virtue of the integration of commercially available, anhydrous, organically modified TIO ₂ nanoparticles having a Dio value of <about 100 nm, into UV crosslinkable coating formulations known per se Coating layers (layer (A)) with a real part n of the complex refractive index greater than 1.85, preferably> 1.90 and particularly preferably greater than 1.92 and an imaginary part k of the complex refractive index less than 0.01, preferably <0.008 and particularly preferably < 0.005 (measured at a wavelength of 405 nm) can be produced. The HRI layers according to the invention have a layer thickness of> 120 nm, in particular> 125 nm and> 150 nm. Even in larger layer thicknesses, for example> 200 nm,> 300 nm and greater than 500 nm, good properties are achieved. The layer thickness is preferably <1 μm, particularly preferably <500 nm. For example, the HRI layers according to the invention have a value of the sum of light absorption and light scattering of <1 0 at a layer thickness of about 1 μm and a light radiation having a wavelength of 405 nm % on. At the same time, such high-index lacquer layers are characterized by a very low roughness (surface roughness) of less than 20 nm, determined by AFM (atomic force microscopy) and surprisingly good scratch resistance of less than 0.75 μm scratch depth.

The present invention therefore relates to a coated article comprising a substrate (S) made of an organic polymer, and at least one coating comprising at least one layer (A), characterized in that it contains finely divided TiC nanoparticles in an amount of 58% by weight. to 95 wt.% Based on the coating (A).

In the novel layers, the T1O ₂ nanoparticles are particularly finely dispersed, which is shown by the low k value, their good transparency and the low value for the sum of light absorption and scattering. The transmission of the layers (A) is in the visible wavelength range (400-800 nm) even in a thickness of about 1 μιη preferably more than 70%, more preferably more than 75% and most preferably more than 80%.

These novel HRI layers (layer (A)) are well suited for the production of coatings containing an HRI single layer, as well as for the production of coatings containing a multilayer coating of a combination of lower-breaking HRI layers (A). LRI layers (B), characterized in that their refractive index n (real part) is at least 0.3 units lower than in the high refractive index HRI coating, ie n (B) <1.6 and in particular <1.5 This layer (B), also referred to here as "LRI" (low refractive index), is alternately combined with the high-index layer (A) in that on the substrate (S) HRI / LRI layer sequences [(A) - (B)] _X are formed, where x is an integer between 1 and 100.

The coating of a substrate (S) with single and / or multi-layers can take place on one or more sides. In a multilayer coating, first and last layers on the substrate may independently be HRI layer (A) or LRI layer (B).

The products and methods of the invention will be further described below.

Substrate (S):

The material of the substrate (S) is selected from at least one of the group consisting of glass, quartz (which is preferably used for planar waveguides) and organic polymers. From this group, organic polymers, and among them, in particular, polycarbonate, poly (methyl) methacrylate, polyester or cycloolefin polymer, are preferred.

Polycarbonates for the compositions according to the invention are homopolycarbonates, copolycarbonates and thermoplastic polyestercarbonates.

The polycarbonates and copolycarbonates according to the invention generally have weight average molecular weights of 2,000 to 200,000, preferably 3,000 to 150,000, in particular 5,000 to 100,000, very particularly preferably 8,000 to 80,000, in particular 12,000 to 70,000 g / mol (determined by GPC with polycarbonate calibration ).

For the preparation of polycarbonates for the compositions according to the invention, see for example "Schnell", Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964, DC PREVORSEK, BT DEBONA and Y. KESTEN, Corporate Research Center, Allied Chemical Corporation, Moristown, NJ 07960, "Synthesis of Poly (ester) Carbonate Copolymer" in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 19, 75-90 (1980), on D. Freitag, U. Grigo, PR Müller, N. Nouvertne, BAYER AG, "Polycarbonates" in Encyclopaedia of Polymer Science and Engineering, Vol. 11, Second Edition, 1988, pages 648-718 and finally to Dres. U. Grigo, K. Kircher and PR Müller " Polycarbonates "in Becker / Braun, Plastics Handbook, Volume 3/1, P olycarbonate, polyacetals, polyesters, cellulose esters, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299 referenced. The production preferably takes place according to the phase boundary process or the chemical interesterification process.

Preference is given to homopolycarbonates based on bisphenol A and copolycarbonates based on the monomers bisphenol A and 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane. These or other suitable bisphenol compounds are carbonated, in particular phosgene or in the melt transesterification process, diphenyl carbonate or dimethyl carbonate, reacted to form the respective polymers.

Very particular preference is given to highly transparent substrate wafers, which are produced industrially as compact disc (CD) for optical data storage. For their preparation, inter alia, in CD polycarbonates are - quality used, for example, linear polycarbonate based on bisphenol A, for example, the polycarbonate Makrolon ^® types DPI -1265 (linear bisphenol-A polycarbonate having a melt volume flow rate of 19.0 cm ³ / 10 min at 250 ° C and a load of 2.16 kg, measured according to ISO 1133) or OD 2015 (linear bisphenol-a polycarbonate having a melt volume flow rate of 16.5 cm ^3/10 min at 250 ° C and a Load of 2.16 kg, measured to ISO 1133 and a Vicat softening temperature of 145 ° C at a load of 50 N and a heating rate of 50 ° C per hour according to ISO 306) from. Bayer MaterialScience AG. The substrate (S) may have spirally arranged grooves, depressions and / or elevations and on the surface so-called information layers or storage layers, as are common in optical data storage wear.

HRI layer (A):

The HRI layer (A) is prepared from a casting solution containing the following components:

Nanoparticle suspension: Anhydrous T1O ₂ nanoparticle suspensions in an organic solvent, for example isopropanol, are used. An important boundary condition with regard to optical requirements is the particle size of the T1O ₂ nanoparticles. It has been found that their particle sizes should not exceed values of about 100 nm (dioo value, maximum diameter of 100% of the particles, measured by analytical ultracentrifugation, "AUZ") Advantageously, the dioo values are below 70 nm and the d ₅₀ values (maximum diameter of 50% of the particles) below 25 nm. The method of analytical ultracentrifugation for determining the particle size is described, for example, in "Particle Characterization", Part. Part. Syst. Charact, 1995, 12, 148-157 and thus known to the skilled person. The HRI layer does not contain any Z VP articles.

Such products are marketed, for example, by the Japanese company Tayca, Tokyo under the brand name "Micro Titanium".

If the T1O ₂ nanoparticles are suspended in a low-boiling organic solvent, for example isopropanol (boiling point (bp.) 82 ° C.), the solvent should advantageously be exchanged for a higher-boiling solvent, the solvent exchange advantageously taking place by distillation. The higher-boiling solvent should have a boiling point greater than or equal to 100 ° C. Very particularly preferred are higher-boiling alcohols such as Diacetoalcohol (DAA, bp 166 ° C), l-methoxy-2-propanol (MOP, bp 120 ° C) or propyl glycol (bp 150-152 ° C) or mixtures of these solvents.

Binders: Preference is given to using UV-reactive monomer components which, after coating, can be converted by means of a photochemical reaction into highly crosslinked polymer matrices. For example, the crosslinking takes place with the aid of UV irradiation. Crosslinking by means of UV irradiation is particularly preferred in view of increased scratch resistance. The reactive components are preferably UV-crosslinkable acrylate systems, as described, for example, in PG Garratt in "Strahlenhärtung" 1996, C. Vincentz Vlg., Hannover or BASF Handbuch, Lackiertechnik, A. Goldschmidt, H. Streitberger, Vincentz Verlag, 2002 , Acrylate Resins, page 119 et seq .. Particularly preferred binders are polyfunctional acrylates, for example diacrylates, such as hexanediol diacrylate (HDDA) or the tripropylene glycol diacrylate (TPGDA), triacrylates, such as pentaerythritol triacrylate, tetraacrylates, such as ditrimethylolpropane tetraacrylate (DTMPTTA), pentaacrylates, such as dipentaerythritol pentaacrylate or hexaacrylates, such as dipentaerythritol hexaacrylate (DPHA), in particular DPHA is used In addition to these low molecular weight polyfunctional acrylates, oligomeric or polymeric (meth) acrylates, for example urethane acrylates, can also be used Polyisocyanates, Hers tell methods for urethane acrylates are basically known and described, for. Example, in DE-A-1644798, DE-A 2,115,373 or DE-A-2 737 406. Such products are for example. Bayer MaterialScience sold under the name Desmolux® ^®. It is of course also possible to use mixtures of the polyfunctional acrylates mentioned.

Solvents: The solvents may be selected from the group consisting of alcohols, ketones, diketones, cyc lis ethers, Glyko le, glyco lether, Gly kel ester, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, dimethylacetamide and propylene carbonate used. Preference is given to using 1-methoxy-2-propanol (methoxy alcohol, MOP) and 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol, DAA), whereby mixtures of these two solvents are preferably used.

Additives: The components used are preferably at least one additive selected from the group of photoinitiators and thermal initiators. Based on the sum of the parts by weight of the components of the casting solution, up to 3 parts by weight of additives (A3) are used, preferably 0.05 to 1 part by weight, more preferably 0.1 to 0.5 part by weight. Typical photoinitiators (UV initiators) are α-hydroxy ketones (Irgacure ^® 184, Fa. Ciba) or Monoacylphosphine (Darocure ^® TPO, Fa. Ciba). The amount of energy required to initiate the UV polymerization (energy of UV radiation) is in the range of about 0.5 to 4 J / cm ² , more preferably in the range of 2.0 to 3.0 J / cm ² coated area. As further additives are still so-called. Coating additives, as they are, for example, by the company. Byk / Altana (46483 Wesel, Germany) under the name BYK, for example. BYK 344®, available in question.

The casting solution for the high-index coatings according to the invention is prepared by dissolving at least one binder and optionally further additives in an organic solvent or solvent mixture. The resulting solution (hereinafter referred to as binder solution) is mixed with the above-described nanoparticle suspension, for example with stirring, and optionally filtered and degassed. In a preferred embodiment, the suspension contains the same organic solvent or solvent mixture as the binder solution.

For homogenization, the casting solution is optionally treated with ultrasound, for example up to 5 minutes, preferably 10 to 60 seconds, and / or filtered through a filter, preferably with a 0.2 μm membrane (for example an RC membrane from Sartorius).

The use of the mentioned T1O ₂ nanoparticles and the procedure described here make it possible to prevent agglomeration of the nanoparticles.

A preferred coating composition comprises 15 to 30 parts by weight, preferably 17 to 28 parts by weight, more preferably 22 to 27 parts by weight of the nanoparticles of the invention, 2 to 8 parts by weight, preferably 2.5 to 5 parts by weight of acrylate-containing binder, 0 to 3 parts by weight, preferably 0.05 to 1 parts by weight, more preferably 0.1 to 0.5 parts by weight of further additives, 40 to 80 parts by weight, preferably 45 to 75 parts by weight, particularly preferably 55 to 73 parts by weight of organic solvent, the sum of the parts by weight of the components being 100 normalized.

Based on the cured layer, ie, after evaporation of the solvent and UV crosslinking, the solids content of the T1O ₂ - nanoparticles in the cured layer is 58 to 95 wt.% Preferably 70 to 90 wt.%, In particular 80 to 90 wt.%.

Process for the preparation of the coated products:

The casting solution is applied to the surface of the substrate or the surface of the information and storage layer. Suitable coating technology are the methods known per se, such as flooding, dipping, knife coating, spraying, spin coating and pouring via slot or cascade casters and curtain casters. These processes are described, for example, in BASF Handbuch, Lackiertechnik A., Goldschmidt, H. Streitberger, Vincenz-Verlag, 2002, Chapter Lackverarbeitung p. 494 ff.

After removal, preferably by spin-coating, of the excess casting solution remains on the substrate, a residue of the casting solution, the thickness of the Solids content of the casting solution and in the case of spin coatings depends on the spinning conditions. Optionally, by thermal treatment, the solvent contained in the casting solution may be partially or wholly removed. The subsequent crosslinking of the polymer components of the casting solution is preferably carried out by photochemical (for example UV light) methods. The photochemical crosslinking can be carried out, for example, on a UV exposure system: For this purpose, the coated substrate is placed on a conveyor belt, which at a speed of about 1 m / min at the UV exposure source, (Hg lamp, 80W) is passed. This process can also be repeated to increase the radiant energy per cm ² . A radiation energy of at least 1 J / cm ² , preferably 2 to 10 J / cm ² , is preferred. Subsequently, the coated substrate can still be thermally treated, preferably with hot air, for example, 5 to 30 minutes at 60 ° C - 120 ° C.

The present invention thus also provides a process for producing a product coated with layer (A) comprising the steps

i. Coating the product with a casting solution containing the components

a. an anhydrous suspension of TiCV nanoparticles with a dioo value of approx.

100 nm in an organic solvent with a boiling point> 100 ° C, b. Binder,

c. Photo or thermal initiators,

d. optional additives and

e. organic solvent;

ii. Removing the excess casting solution,

iii. Removing the solvent,

iv. Crosslinking of the coating.

The coating with a single layer (A) described above gives a product with the layer sequence (S) - (A) or, in the case of two-sided coating, a product with the layer sequence (A) - (S ) - (A). These products are also the subject of this invention.

It has been found that these layers have a refractive index> 1.85, in particular> 1.90, measured in a wavelength range from 380 to 420 nm. These are therefore high-index (HRI) layers. The use of the mentioned T1O ₂ nanoparticles and the procedure described here make it possible to prevent agglomeration of the nanoparticles. This ensures that the layers have a low k value. At a wavelength of about 405 nm and a layer thickness of 1 μιη the sum of the measured light scattering and absorption, which determines the height of the ^ value, the HRI layers according to the invention at a value of less than 10%. In this case, it applies that in particular in the nanoparticle-containing Systems k and α in the visible spectral range (400 - 800 nm) are dominated by the scattering (scatter), if the primary nanoparticles are too large or agglomerate nanoparticles into larger particles, even if there is no molecular absorption in this spectral range. This low value for the sum of light absorption and scattering in the layer shows that the T1O ₂ nanoparticles are particularly finely distributed in the HRI layer (A) according to the invention and no agglomeration to larger nanoparticles occurs. The layers have high transparency with transmission values of> 70%, in particular> 75% and very particularly preferably> 80% in the visible spectral range.

Surprisingly, it has been found that the above-described high-index TiC layers (A) according to the invention, hereinafter also referred to as "TiC HRI", readily with layers (B) consisting of coatings prepared from conventional, thermally or photochemically crosslinkable casting formulations whose refractive index Therefore, in addition to the products with the described single-layer, high-index layers (A), there are also substrates with multilayers, which alternately have layers with a high (HRI) and a low (LRI) refractive index content of the present application, wherein the previously described TiC-containing formulations for the layers (A) are used as the HRI layer.

Layer (B): For the so-called LRI layers (B), naturally those formulations are to be preferred whose refractive index is as low as possible and which can be coated and crosslinked as analogously as possible to the TiCVHRI formulation. In principle, all coating formulations which have a significantly lower refractive index n than the T1O ₂ -HRI coating (about 1.90 at 405 nm) are suitable as the low-refractive index layer (LRI). The difference An should be greater than 0.2, preferably greater than 0.25 and particularly preferably greater than 0.3. Layer (B) has a refractive index <1.70, preferably <1.65, particularly preferably <1.60, measured in a wavelength range from 380 to 420 nm.

Accordingly, all conventional formulations (solutions of binders) are suitable as LRI layers, ie formulations which do not contain any refractive index-increasing components, such as high-index nanoparticles. Such formulations are known to the person skilled in the art, for example from "Coatings Compendium, Lackrohstoffkunde" by P. Nanetti, Vincentz Verlag, Hannover, 2000. As described there, the binders may be, for example, polycondensation resins, for example polyesters or polyaddition resins, such as polyurethanes, or In addition to binders and solvents, the LRI-layer formulations may contain further constituents, such as initiators, rheological additives, leveling agents, or flow control agents, such as poly (meth) acrylates Fillers, the latter must be such that highly transparent layers are created. Accordingly, suitable fillers are only those nanoparticles which, in addition to mechanical and rheological effects, also have refractive index-lowering properties, for example silica nanoparticles with particle sizes smaller than (d ₂ s) <25 nm.

Particularly preferred formulations for the LRI layer (B) comprise UV-crosslinkable acrylate or polyurethane acrylate binders which are dissolved in alcoholic solvents and contain, as further components, inter alia UV initiators and low-refractive silica nanoparticles.

The preparation of silica-containing, UV-crosslinkable formulations and coatings thereof is described, for example, in WO-A 2009/010193.

The production of the coatings from the formulations mentioned for layer (A) and (B) can furthermore be carried out by the methods known to the person skilled in the art. An overview of common manufacturing processes can be found, for example, in the BASF Handbook, Lackiertechnik, Vincentz-Verlag, 2002, chapter "The coating", p.333 ff, "in the textbook of coating technology (Brock, Groteklaes, Mischke - Vincentz Verlag, 2. Edition 2000, page 229ff.) Or in the textbook of paints and coating materials, Volume 8 - Production of paints and coating materials (Kittel, Hirzel Verlag, 2nd edition 2005).

Most commonly, the production takes place with stirring. In this case, all components are added in succession to a template and homogenized with constant stirring. To speed up the homogenization process, the mixtures can be heated.

Production of the multilayer coating:

The substrates are coated alternately, for example by spin-coating, with the coating composition for an HRI layer (A) and coating composition for an LRI layer (B), for example a silica-LRI formulation.

The present invention thus also provides a process for producing a coated product, wherein the substrate (S) is coated on one or more sides alternately or several times alternately with layers (A) and (B), wherein the layer (A) after the method described above.

Such multilayers can be used as reflection-reducing coatings, as described, for example, in "Vacuum Coating 4", Gerhard Kienel, VDI Verlag, 1993. The greater the difference in refractive index between the HRI, the lower the number of required multilayers can be. With respect to the target layer thickness d, the rule of thumb d = 7 4 is divided by n. So if one wants IR heat rays of the wavelength 1000 nm, a target layer thickness of about 131 nm results for the HRI layer with n: 1.90 and a target layer thickness of about 167 nm for the HRI layer with n: 1.5.

It is irrelevant whether the application of the multilayer series starts with the HRI or the LRI recipe and whether the total number of multilayers is even or odd.

With regard to the substrates for the multilayers, in principle the selection criteria mentioned in the case of the HRI monolayers come into question, with polycarbonate plates and films being particularly preferred.

With regard to the coating technology for HRI monolayers or multilayers, the methods known per se, such as flooding, dipping, knife coating, spraying and pouring via slot or cascade casters and curtain casters are suitable. These processes are described, for example, in BASF Handbook, Goldschmidt, Streitberger "Lackiertechnik", Vincentz, 2002 Chapter Lackverarbeitung, p. 494 ff. ".

By means of the above-described coatings comprising multilayers of layers (A) and (B), a product with the layer sequence (S) - (B) _y - [(A) - (2) is obtained by mutual, single-sided or multilateral coating of the substrate (S). B)] _x - (A) _z or, in the case of two-sided coating, a product with the layer sequence (A) _z - [(B) - (A)] _x - (B) _y - (S) - (B) _y - [(A) - (B)] _x - A _z , where y, z can each independently be 0 or 1 and x is an integer between 1 and 100. These products are also the subject of this invention. Very effective IR reflection properties will be found on these products according to the invention.

The subject matter of the present application is therefore also a process for producing a coated product containing at least once the above-described steps i. - iv. for applying a layer (A) and additionally containing the step at least once

v. Applying a layer (B) with a refractive index n <1.65,

wherein when performing steps i. - v. the layers (A) and (B) are applied alternately.

In a preferred embodiment, polycarbonate substrates are coated with an alternating sequence of T1O ₂ -HRI / silica LRI multilayers.

As a further field of application for the high-index coatings according to the invention, planar waveguides (PWG) can be used in addition to optical data memories. By definition, a waveguide is an inhomogeneous medium that, by virtue of its physical nature, bundles a wave in such a way that it is guided therein. The functional principle is explained in more detail, for example, in AW Snyder and JD Love, Optical Waveguide Theory, Chapman and Hall, London (1983). Examples

A) Measuring methods for testing

- The coating thickness determination is carried out by means of a white light interferometer (ETA SPB-T, ETA Optics GmbH).

- Determination of the refractive index:

The refractive index n and the imaginary part k of the complex refractive index (k value of the coating) were obtained from the transmission and reflection spectra. For this purpose, approximately 100-300 nm thick films of the coating were spun onto quartz glass substrate from dilute solution. The direct transmission and reflection of this layer package were measured excluding the transmitted and reflected scattered light with a spectrometer from STEAG ETA Optics, CD-Measurement System ETA-RT and then the layer thickness and the spectral course of n and k to the measured transmission and reflection spectra adjusted. This is done with the internal software of the spectrometer and additionally requires the n and k data of the quartz glass substrate, which were determined beforehand in a blind measurement. K is related to the decay constant of the light intensity α as follows: λ - a λ is the wavelength of the light.

In this measuring arrangement, the direct transmission and reflection is determined, excluding the transmitted and reflected scattered light. As a result, the decay constant α or k also contains the components which, by scattering, lead to the attenuation of the light intensity and not only the portions of the pure molecular absorption. Thus, the sum of absorption and scattering can also be determined via the measuring arrangement, which is dominated by the scattering (scattering) in the spectral range (400-800 nm) visible in the nanoparticle-containing systems in question if the primary nanoparticles are too large or Nanoparticles agglomerate to larger particles, even if there is no molecular absorption in this spectral range.

The real part n and the imaginary part k were determined as a function of the wavelength, with a high wavelength dependence expected for high refractive indices (n: 1.88 to 1.93 in the range 380 to 420 nm, n: approx. 1.84 to 1.85 in the range 550 nm and n: about 1, 820 to 1, 825 in the range greater than 800 nm - the scatter of the measured values results from multiple determinations).

Surface roughness: The surface roughness was determined by atomic force microscopy (AFM) according to standard ASTM E-42.14 STM / AFM, where R a values in the range of 15-18 nm were determined.

Scratch resistance: To determine the scratch resistance, a diamond needle with a tip radius of 50 μm was guided onto the coating at a feed rate of 1.5 cm / s and a coating weight of 40 g, and the resulting scratch depth was measured. The measured values were in the range of about 0.58 to 0.65.

B) Preparation of UV-crosslinkable suspensions

Example 1. Solvent Exchange on T1O ₂ Nanoparticles

Starting product: Micro Titanium / IPA Sol "T1O ₂ ND 134" in isopropanol, which is a 45% by weight nanoparticle suspension from Tayca.

The nanoparticle suspension was concentrated on a rotary evaporator at 15-25 mbar at a temperature of 35-40 ° C, with isopropanol (bp. 82 ° C) was distilled off. The decreasing volume was replaced by diacetone alcohol (DAA, 4-hydroxy-4-methyl-2-pentanone, acros, bp .: 166 ° C).

Product: Ti0 ₂ -DAA 34.7% by weight in DAA.

Example 2. Preparation of a crosslinkable UV T1O ₂ -containing suspension (T1O ₂ - HRI formulation)

This is the recipe of a layer A according to the invention.

7.5 g of dipentaerythritol penta / hexaacrylate (DPHA, Aldrich 407283) were weighed into a 250 ml beaker. To this was added 39.4 g of diacetone alcohol (DAA) and stirred by means of a magnetic stirrer to give a clear solution. 0.54 g of Irgacure® 184 (1-hydroxycyclohexylbenzophenone from Ciba) was added and stirred until a clear solution resulted. 131.3 g of the T1O ₂ -DAA nanoparticle suspension prepared according to Example 1 were added with stirring to give a translucent suspension.

Before use, the nanoparticle-containing suspension was homogenized with an ultrasound finger and filtered through a 0.45 μm filter. Example 3. Preparation of an Si0 ₂ -containing UV-crosslinkable suspension (Si0 ₂ -LRI formulation)

A UV-curable formulation with a high content of silica nanoparticles was prepared. Such formulations are content of application WO-A 2009/010193.

There were

1.5 g of DPHA (dipentaerythritol penta / hexaacrylate, Aldrich, 407283),

1.5 g of PETA (pentaerythritol triacrylate, Aldrich, 246794),

7.0 g Desmolux U 100 (urethane acrylate, Bayer MaterialScience),

0.4 g of Irgacure 184 ((1-hydroxycyclohexylbenzophenone, CIBA),

0.1 g of Darocure TPO (diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide,

83.6 g Highlink Nano 401-31, 13 nm silica nanoparticles, 29.8% in methoxypropanol (MOP) from Clariant

0.17 g of sodium dioctylsulfosuccinate (anionic surfactant, Fluka 86139) and

48.0 g of methoxypropanol (1-methoxy-2-propanol, MOP, KMF 12-512)

homogenized by stirring. Before use, the nanoparticle-containing suspension was homogenized with an ultrasound finger and filtered through a 0.45 μιη filter.

C) Coating of quartz substrates to determine the optical properties (n, k)

Preparation of a coated plate with a coating layer thickness> 120 nm:

With the aid of a spin coater (from Steag Hamatech), the nanoparticle suspensions described in the above examples were each applied to a 2.5 × 2.5 cm glass substrate (quartz glass slide) at a rotation speed of 10000 min ^-1 (revolutions per minute) ) and then crosslinked with UV light (Hg lamp, about 3 J / cm ² ).

Example 4. Optical Properties and Layer Thickness of the T1O ₂ - HRI Coating from Example 2

The following values were determined on a quartz substrate coated according to C) with the coating of Example 2 using the methods described in A):

Layer thickness: 156.3 nm

Refractive index: n: 1, 936

* Value: 0.002 Example 5 Optical Properties and Layer Thickness of the SiO ₂ -LRI Coating from Example 3

The following values were determined on a quartz substrate coated according to C) with the coating of Example 3 using the methods described in A):

Refractive index n: 1.485

Layer thickness: 337.4 nm

* Value: 0.015

D) Coating of compact disc (CD) substrates

To determine the scratch resistance of the coating on plastic substrates and to determine the sum of absorption and scattering of the inventive coating of Example 2 in a coating layer thickness of about 1 μιη (accuracy +/- 10%) were the formulations described in Example 2 and 3 at the following spin-coat conditions on CD substrates from Makroion® OD2015 (linear bisphenol A polycarbonate with a melt volume flow rate of 16.5 cm 3/10 min at 250 ° C and a load of 2.16 kg, measured according to ISO 1133 and a Vicat softening temperature of 145 ° C at a load of 50 N and a heating rate of 50 ° C per hour according to ISO 306) coated:

• Dosing of the casting solutions at 50 min ^"1 (revolutions per minute), distributing the sample at 10 min ^{" 1} (revolutions per minute) over a period of 60 sec, centrifuging at 3000 min ^"1 (revolutions per minute) over a period of 15 sec.

The coating was cross-linked with a Hg lamp at 5.5 J / cm ² .

• Subsequently, layer thickness and scratch resistance were determined according to the methods described in A).

Example 6. Properties of the TiCl 2 -containing HRI coating from example 2

The following values were determined on a polycarbonate substrate coated according to D) with the coating of Example 2 using the methods described in A):

Surface roughness Ra: 12 to 18 nm determined by AFM

Scratch depth: 0.6 to 0.65 μιη

Sum of absorption and scattering at a wavelength of 405 nm: approx. 6.5% Example 7. Properties of the SiC ^ -containing LRI coating of Example 3

The following values were determined on a polycarbonate substrate coated according to C) with the coating of Example 2 using the methods described in A):

Surface roughness Ra: 10 to 15 nm determined by AFM

Scratch depth: 0.5 to 0.6 μιη

Example 8. Coating of compact disc (CD) substrates with Ti0 ₂ - HRI / Si0 ₂ - HRI multilayers

a) coating of the first T1O ₂ - HRI layer

The formulation described in Example 2 was applied via a metering syringe to the CD substrate (Makroion OD 2015) using a fully automatic spin coater from the company Steag Hamatech, equipped with a pressure-operated metering device EFD 2000 XL. The spin conditions (centrifugation of the excess lacquer) were selected so that a layer thickness of about 125 nm resulted. For this purpose, the rotational speed of the substrate for 2.1 s at 240 min ^"1 (revolutions per minute), for 3 s to 1000 min ^{" 1} (revolutions per minute) and then for 17 s to 7200 min ^"1 (revolutions per minute) The mixture was then crosslinked with a Hg lamp at 5.5 J / cm ² UV.

b) Coating of the first S1O ₂ - HRI layer on the first T1O ₂ - HRI layer

The S1O ₂ -LRI formulation described in Example 3 was coated analogously to a) and UV crosslinked, although the coating conditions were aligned to layer thicknesses of about 190 nm. In detail, the following conditions were observed for centrifuging: 1.2 sec at 240 min ^-1 (revolutions per minute), 1.5 sec at 1000 min ^-1 (revolutions per minute) and 13 sec at 7000 min ^-1 (revolutions per minute) ).

c) application of the further multilayers

The procedures described in a) and b) were repeated, wherein in each case after a total of 16 and 24 multilayers, a spectroscopic evaluation in accordance with ASTM E 1331 (Standard Test Method for Reflectance Factor and Color by Spectrophotometry Using Hemispherical Geometry) was performed. It was found that the CD substrate provided with 16 multilayers showed a reflection peak reaching up to 72% in the range from 900 to 1150 nm, ie in the infrared range, while after 24 multilayers a reflection of approximately 92% was achieved.

Using TEM (Transmission Electron Microscopy) images, the alternating sequence of the darker HRI and brighter LRI layers could also be documented.

Claims

claims

1. Coated product comprising a substrate (S), made of an organic polymer, and at least one coating containing at least one layer (A), characterized in that it comprises finely divided TiCV nanoparticles in an amount of 58 wt.% To 95 wt.% on the coating (A) contains.

2. Coated product according to claim 1 containing 80 wt.% To 90 wt.% T1O ₂ - nanoparticles based on the coating (A).

3. Coated product according to claim 1, wherein layer (A) has a layer thickness of> 120 nm.

4. Coated product according to claim 1 to 3, characterized in that in layer (A) except TiC nanoparticles no further nano-particles are included.

5. Coated product according to one of claims 1-3, wherein layer (A) at a wavelength of 405 nm has a value for the sum of light absorption and - scattering of <10%.

6. Optical data storage obtainable from a coated product according to claim 1.

A coated product according to claim 1, wherein layer (A) is obtainable from a coating composition containing

i. an anhydrous suspension of TiCV nanoparticles having a dioo value of about 100 nm in an organic solvent having a boiling point> 100 ° C.,

ii. Binder,

iii. Photo or thermal initiators,

iv. optional additives and

v. organic solvent.

A coated product according to claim 1, wherein the product has the layer sequence (S) - (A) or (A) - (S) - (A) measured in a wavelength range of 380 to 420 nm.

9. Coated product according to claim 1 or 8, wherein at least one coating additionally contains at least one layer (B), which has a refractive index n <1.65, measured in a wavelength range of 380 to 420 nm.

A coated product according to any one of the preceding claims, wherein the substrate (S) is an organic polymer selected from the group consisting of polycarbonate, poly (methyl) methacrylate, polyester or cycloolefin polymer.

The coated article of claim 7, wherein the binder is selected from the group consisting of polyfunctional acrylates.

12. A process for producing a coated product according to claim 1 or 7 comprising a layer (A) comprising the steps of applying a layer (A)

i. Coating a substrate (S) of an organic polymer with a casting solution containing the components

a. an anhydrous suspension of TiCV nanoparticles having a Dio value of <about 100 nm in an organic solvent with a boiling point of 100 ° C.,

b. Binder,

c. Photo or thermal initiators,

d. optional additives and

e. organic solvent;

ii. Removing the excess casting solution,

iii. Removing the solvent,

iv. Crosslinking of the coating.

13. Use of a coating composition according to claim 7 containing

i. an anhydrous suspension of TiCV nanoparticles with a dioo value of approx.

100 nm in an organic solvent with a boiling point> 100 ° C, ii. Binder,

iii. Photo or thermal initiators,

iv. optional additives and

v. organic solvent,

for coating a substrate (S), of organic polymers.

14. Coated product according to claim 1, characterized in that it does not contain an antireflective layer.