PHOTOPOLYMERIZABLE HOE COMPOSITION

Description

Field of invention

[0001] The present invention relates to photopolymerizable compositions and elements produced therefrom, as well as their use. The photopolymerizable compositions are particularly suitable as recording material for optical elements with refractive index modulation, especially holograms.

[0002] A variety of holograms are known, such as reflection holograms, embossing holograms, transmission holograms, or volume holograms.

[0003] A volume hologram is produced, for example, by interfering with two light waves of the same wavelength, also called the object beam and reference beam, and exposing a holographic recording medium, usually photographic film, with the resulting interference pattern, which is typically an intensity pattern. The holographic exposure process and the replication of the hologram are technically complex optical processes that require specialized application knowledge. Methods for generating holograms and the underlying theory are comprehensively described in the literature [Howard M. Smith, "Principles of Holography", Wiley (1969)] [Fred Unterseher, et al. "Holography Handbook: Making Holograms the Easy Way", Ross Books (1982)] [Graham Saxby, "Practical Holography", Inst, of Physics Pub. (2004)].

[0004] Known recording materials with varying property profiles and applications include: silver halide emulsions, hardened dichromate gelatin, ferroelectric crystals, photochromic and dichroid materials, and photopolymers [Howard M. Smith, "Principles of Holography", Wiley (1969).]. For high-volume applications, materials that can be easily integrated into hologram production and duplication systems and that allow for simple holographic exposure and development are of interest. Photopolymers are considered particularly preferred due to their high efficiency, ease of handling, and good storage stability. The best-known photopolymers are from DuPont, e.g., Omnidex HRF 600 [SM Schultz, et al. "Volume grating preferential-order focusing waveguide coupler", Opt. Lett., vol. 24, pp. 1708-1710, Dec. 1999].Omnidex materials belong to the class of self-evolving photopolymer films based on radical polymerization and monomer diffusion (see EP 0324480 A2).

[0005] Omnidex photopolymers have been further developed over the years, primarily with the aim of increasing the refractive index contrast and achieving a high diffraction efficiency in the film (see US 49421 12 A and DE 69032682 T2). However, the application-relevant diffraction efficiencies of well over 2 / 3 are achieved at the cost of a high proportion of thermoplastic binder.

[0006] In film production, the binder for the coating must be liquid. A solvent is used for this purpose, and its evaporation after coating leads to a significant reduction in film thickness. The wet film applied is therefore considerably thicker than the resulting film layer, corresponding to the solvent content. The solvent content is typically around 80%. To achieve a 20 µm layer suitable for volumetric holographic exposure, a 100 µm wet film layer must be applied in this case. The required high thickness of the wet film prevents or hinders the use of common printing processes such as flexographic or gravure printing. In screen printing, the use of fast-drying solvents can cause the mesh to clump together.

[0007] Furthermore, the film can only be processed or wound up once all the solvent has evaporated. Therefore, production requires a long drying line with a health- and environmentally-friendly extraction system, as well as a dust- and explosion-proof environment. This effort means that film production and holographic exposure typically take place at separate locations and times.

[0008] For binder-containing materials, a thermal post-treatment ("tempering") of the exposed and UV-fixed photopolymer is also necessary to achieve maximum refractive index contrast (see DE 68905610 T2). Tempering is an additional time-consuming processing step that, in addition to the complex film production, slows down, complicates, and increases the cost of hologram production and also limits the choice of substrate materials to those that are not temperature-sensitive.

[0009] Other photopolymer materials for volume holography have been developed by Polaroid (see US 5759721 A), Fuji Photo Film (see EP 1510862 A2), Konica Minolta Medical & Graphic (see US 200505891 A1), Dai Nippon Printing (see EP 123151 A1), Nippon Paint (see EP 21 1615 A2), Nissan Chemical Industries (see US 20050068594 A1), Bayer (see WO 2010091795 A1), Xetos (see WO 2003036389 A1), and InPhase Technologies (see US 2002142227 A1). The prior art includes photopolymers that differ from Omnidex in their holographic properties or processing. The technological progress is documented by reduced oxygen sensitivity, reduced material shrinkage during exposure, adapted spectral sensitivity, solvent-free film production, higher diffraction efficiency without annealing and / or better temperature and storage stability.

[0010] A newer and commercially available holographic photopolymer is the "Bayfol HX" film developed by Bayer MaterialScience. This film contains a polyurethane as its polymer matrix, which holds the holographically exposed writing monomers, rather than a thermoplastic binder. The polyurethane is formed by polyaddition from a polyisocyanate and polyol mixture. The reactive components are mixed together shortly before coating and cure on the substrate. While it does not have the high solvent content of the previously described binder-containing materials, the curing time of up to one hour presents the same challenge: providing a sufficiently long, dust-free drying and curing area in the coating system.

[0011] As with all commercially available photopolymer films, the user cannot freely choose and coat the base material themselves, but must process the supplied film assembly. In addition to the base film, a lamination film is applied to the light-sensitive film layer to prevent sticking and contamination. Removing this lamination film can cause static electricity, which attracts dust particles. Since the film must be laminated onto either glass or a master for exposure, where every dust particle creates a defect, an extremely dust-free environment is required for clean and flawless processing.

[0012] Photopolymer systems containing a polymeric binder or polymeric matrix form an essentially solid film layer. In contrast, binder-free systems have also been presented that are essentially liquid until exposure (see, e.g., US Patent 3,993,485 A or N. Smirnova, Optics in Information Systems, February 2004, p. 9, or Xetos (see WO 2003036389 A1)).

[0013] In most essentially solid monomer-binder / matrix photopolymers, after holographic laser exposure, unexposed writing monomers located in the region of the dark interference lines diffuse into the exposed polymerized areas. This creates a refractive index difference whose spatial modulation corresponds to the interference pattern to be recorded. However, the diffusion of the writing monomers in the solid matrix takes time. An increase in temperature can accelerate this process. DuPont specifies a curing time of one hour at 120 °C for the aforementioned OmniDex® material. For the Bayfol HX material, the patent applications (EP 2 372 454 A1 p.13

[0127] , EP 2 219 073 A1 p.15

[0102] ) specify a waiting time of 5 minutes before the material is finally completely cured with UV light.

[0014] However, many production processes require the shortest possible times or the highest possible throughput and a simple, cost-effective process for the production of holograms, so that cumbersome and time-consuming post-treatments or waiting times are a disadvantage.

[0015] For this reason, photopolymerizable compositions were developed that exhibit effective refractive index modulation during laser exposure and can be immediately fixed with UV light, as described in EP 1 779 196 B1. Various triglycerides, such as castor oil, were used in this application.

[0016] Castor oil is an inert component that does not cross-link during exposure. This means it can later migrate out of the layer. To reliably prevent this, the hologram layer is usually subsequently sealed with a UV varnish layer.

[0017] However, if the castor oil content is too high, this can occur during or shortly after exposure. An excessively high content also leads to clouding. The higher the castor oil content, the higher the exposure temperature must be to ensure a clear layer. However, increasing the temperature reduces the viscosity of the photopolymerizable composition, which negatively affects holographic exposure. Therefore, there is an upper limit for both the castor oil content and the exposure temperature, which must not be exceeded for holographic exposure.

[0018] Besides the disadvantage that the exposed layer must be sealed relatively quickly with a UV varnish to prevent the castor oil from seeping out, these photopolymerizable compositions have a relatively high turbidity. The turbidity becomes more noticeable the thicker the layers are and the higher the triglyceride content.

[0019] For security features and labels applied to an opaque substrate, this isn't as noticeable. However, especially with holographic optical elements (HOEs), unobstructed transparency is desirable and often necessary, for example, when the holograms are used in head-up displays or augmented / mixed reality glasses. Unlike holographic security features, where very thin layers of less than 20 µm are targeted, HOE layers can be significantly thicker, exceeding 100 µm. Thick layers are sometimes even desirable to compensate for tolerances in the optical components that are to be combined with or bonded to the hologram layer. Thick layers are also often necessary when only a very narrow spectral range of light is to be reflected.Depending on their viscosity, liquid photopolymerizable compositions only exhibit high refractive index differences up to a certain layer thickness. Beyond a certain thickness, the dynamics of the liquid and the shrinkage during curing are simply too great to effectively and uniformly record a pattern in the range of light wavelengths. This is particularly true for holographic dual-beam or master exposures. In contrast, the large-scale production of essentially solid film materials with layer thicknesses above 20 µm is very complex and, due to the currently low demand, not profitable. Covestro's Bayfol HX 200 material is offered with a layer thickness of 16 µm. The haze value is specified as <2% (Product Information Sheet - Bayfol HX 200, Edition 2018-03-01).

[0020] Besides having the lowest possible haze value, a holographic element integrated into a car's windshield for a head-up display must meet further requirements. During manufacturing, the laminated glass pane is subjected to temperatures of up to 140°C and pressures of 12 bar for up to 90 minutes in an autoclave (WO 03033583 A1). The holographic material and the embedded hologram must also withstand this without damage or loss of quality.

[0021] The diffraction efficiency (DEE) η of volume holograms depends on their layer thickness d and on Δn. Δn denotes the amplitude of the refractive index modulation within the hologram layer. According to Kogelnik's Coupled Wave Theory (see H. Kogelnik, The Bell System Technical Journal, Volume 48, November 1969, Number 9, pages 2909–2947), the higher the Δn value, the thinner the layers can be to achieve a high DEE. For reflection holograms of surface mirrors or Lippmann-Bragg holograms, where the refractive index modulation runs parallel to the surface, the following relationship applies. η = tanh 2 π ⋅ Δn ⋅ d λ , where λ is the wavelength of the light. For thick layers, the Δn value of the holographic recording materials can therefore be lower than for thin layers in order to achieve the same diffraction efficiency.

[0022] The photopolymerizable composition can be used to record both transmission and reflection holograms. The achievable amplitude of the refractive index modulation Δn in Lippmann-Bragg holograms with a layer thickness of over 100 µm, whose grid lines run parallel to the surface, is greater than 0.001, preferably greater than 0.002, and particularly preferably greater than 0.003.

[0023] Based on the wavelength λ of the absorption peak measured in the spectrometer during perpendicular irradiation, the diffraction coefficient η (DWG) and the layer thickness d, Δn for these holograms can be calculated as follows. Δn = λ π ⋅ d ⋅ arctanh η , Description of the invention

[0024] The present invention is therefore based on the objective of providing a photopolymerizable composition that avoids the aforementioned disadvantages of known recording materials and advantageously enables holographic exposure of thick layers greater than 20 µm, preferably greater than 50 µm, and particularly preferably greater than 100 µm. As with the liquid holographic material known from application EP1779196B1, very rapid processing suitable for mass production should be possible. The holographic elements produced from the photopolymerizable composition should also exhibit high long-term stability as well as thermal and mechanical stability. Furthermore, additional sealing should not be strictly necessary. Particularly preferably, the hardened material and the hologram recorded therein should withstand the autoclave process for the production of a laminated glass pane without damage.Preferably, the photopolymerizable composition should be usable for processes in which pressures above 5 bar and temperatures above 100°C, and particularly preferably pressures above 10 bar and temperatures above 120°C, act on the photopolymerizable composition or elements produced therefrom.

[0025] Surprisingly, it was found that the inert components such as the castor oil in the formulation described in EP 1 779 196 B1 can be advantageously replaced by suitable aliphatic urethane acrylates, which also crosslink upon exposure to light and therefore cannot seep out.

[0026] The problem is thus solved according to the invention by a photopolymerizable composition that can be cured by UV / VIS irradiation, comprising: a) 25 to 74.9 wt.% of at least one monomer M comprising at least one ethylene unsaturated group or of a monomer mixture comprising at least two monomers M comprising different ethylene unsaturated groups, wherein the monomer M is selected from the group consisting of (meth)butyl methacrylate, (meth)phenyl methacrylate, (meth)benzyl methacrylate, (meth)isobornyl methacrylate, (meth)cyclohexyl methacrylate, (meth)2-phenoxyethyl methacrylate, (meth)1H,1H,2H,2H-perfluorooctyl methacrylate, 2,2,2-trifluoroethyl(meth)acrylate, heptafluoropropyl(meth)acrylate, 1,1,1,3,3,3-hexyfluoroisopropyl(meth)acrylate, 2,2,3,3-tetrafluoropropyl(meth)acrylate). 2,2,3,3,4,4,4-heptafluorobutyl (meth)acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl (meth)acrylate, acrylic acid N,N-diethylaminoethyl ester, acrylic acid ethoxyethoxyethyl ester, acrylic acid 2-(p-chlorophenoxy)ethyl ester, p-chlorophenyl acrylate, 2-phenylethyl (meth)acrylate, Pentachlorophenyl acrylate, phenyl acrylate,p-chlorostyrene, n-vinylcarbazole, 1-vinyl-2-pyrolidone, 2-chlorostyrene, 2-bromostyrene, methoxystyrene, phenol ethoxylate acrylate, 2-(p-chlorophenoxy)ethyl acrylate, hydroquinone monomethacrylate and 2-[β-(N-carbazolyl)propionyloxy]ethyl acrylate, and also contains a bisphenol A diacrylate with a proportion of more than 25 wt%, based on the total weight of component a), b) 25 to 74.9 wt% of an aliphatic urethane acrylate or a mixture of different aliphatic urethane acrylates, c) 0.1 to 10 wt% of a photoinitiator that activates the polymerization of the monomers and urethane acrylates upon exposure to actinic radiation; d) 0.01 to 20 wt% additives, , the photopolymerizable composition is liquid at standard pressure in the range of 15°C to 150°C.

[0027] Unless otherwise stated, values ​​given in wt.% refer to the total weight of the photopolymerizable composition.

[0028] Further preferred embodiments are defined in the dependent claims. Actinity (actinic radiation) can be understood as the photochemical effectiveness of electromagnetic radiation of different wavelengths.

[0029] The term is used, for example, in evaluating the physiological effects of laser light of different colors or the spectral sensitivity of photographic films and papers. In photochemistry, actinic chemicals are those that are sensitive to light or radiation.

[0030] Component a) contains a bisphenol A diacrylate with a proportion within this component of over 25 wt.%, preferably over 50 wt.% and particularly preferably over 90 wt.%, based on the total weight of component a).

[0031] Particularly preferred as component b) is an aliphatic urethane diacrylate resin, in particular Ebecryl 230 from Allnex, or a difunctional aliphatic urethane diacrylate resin, in particular CN9002 from Sartomer.

[0032] Preferably, the aliphatic urethane acrylate or the urethane acrylate mixture has a significantly slower crosslinking rate than the monomer or monomer mixture. During holographic exposure, the slower-reacting component is displaced from the bright areas of the interference pattern. This separation results in a higher urethane acrylate content in the dark areas of the interference pattern than in the bright areas. Since the urethane acrylate or urethane acrylate mixture has a different refractive index than the monomer or monomer mixture, the refractive index in the layer is modulated according to the interference pattern, and a hologram is created. The difference between the refractive indices of the two components should be at least 0.02, preferably at least 0.05, and particularly preferably at least 0.07 at 20°C. Preferably, the difference between the refractive indices of component a) and component b) at 20°C is at least 0.02.

[0033] The refractive index can be measured with a refractometer, e.g. with an analog Abbe refractometer.

[0034] The Abbe refractometer is an optical instrument for determining the refractive index n of liquids. The measuring principle is based on determining the critical angle for total internal reflection. For this purpose, the liquid is enclosed between two glass prisms and, by default, illuminated with light of a wavelength of 589 nm (sodium D-line) at a temperature of 20°C. After setting the critical angle, the refractive index can be read from a scale.

[0035] Preferably, the urethane acrylates can be reaction products of (meth)acrylic acids, polyols and multifunctional isocyanates.

[0036] Urethane acrylates are produced, for example, from alcohols containing (meth)acrylolyl groups and di- or polyisocyanates. Manufacturing processes for urethane acrylates are generally known and described, e.g., in DE-A-1 644 798, DE-A 2 115 373, or DE-A-2 737 406. Alcohols containing (meth)acrylolyl groups include both esters of acrylic acid or methacrylic acid with dihydric alcohols containing a free hydroxyl group, such as 2-hydroxyethyl, 2- or 3-hydroxypropyl, or 2-, 3-, 4-hydroxybutyl (meth)acrylate, as well as any mixtures of such compounds. Furthermore, alcohols containing monovalent (meth)acryloyl groups or reaction products consisting essentially of such alcohols are also considered, which are obtained by esterification of n-valent alcohols with (meth)acrylic acid, which are obtained by esterification of n-valent alcohols with (meth)acrylic acid and possibly other substances.further dicarboxylic acids are obtained, wherein mixtures of different alcohols can also be used as alcohols, such that n represents an integer or fractional number greater than 2 to 4, preferably 3, and wherein n-1 mol of (meth)acrylic acid is used per mol of the aforementioned alcohols, in particular preferably.

[0037] Surprisingly, it was found that the clarity of the exposed layer depends on the exposure time and intensity used for exposure and curing. If the layer is exposed quickly (for less than 1 second) with sufficient intensity, it is less hazy than if it is exposed for several seconds at lower intensities. The haze is measurable and is expressed as a percentage. At an exposure temperature of 21°C and a layer thickness of 1 mm, measured according to the ASTM D 1003 standard method, the difference between the quickly and slowly exposed areas should be at least 50%, preferably at least 60%, and most preferably at least 70%. Temperature also influences haze. The lower the temperature, the milkier the result.Exposing different areas to light at different temperatures can therefore also make a difference or further enhance the intensity-dependent effect.

[0038] The sensitivity of the photopolymerizable composition should be better than 150mJ / cm 2< , preferably better than 100mJ / cm 2< and particularly preferably better than 50mJ / cm 2< .

[0039] The sensitivity indicates the minimum exposure dose required to create a hologram. The laser must have the appropriate wavelength for the dyes used in the initiator system. For example, methylene blue is used with a red laser at 633 nm, and safranin-O with a green laser at 532 nm. The laser wavelength should be close to the spectral absorption maximum of the corresponding dye. The sensitivity can be determined by comparing the exposed holograms. Once the measured diffraction efficiency can no longer be improved by increasing the exposure dose at the same layer thickness, the required minimum dose has been reached or exceeded.

[0040] Preferably, with the composition according to the invention, no time is required for the evaporation of volatile solvents, for chemical reactions, or for thermal treatments after application to a substrate or a copying template. Exposure can occur immediately after application of the composition to a substrate or copying template. Wet application of the composition to the substrate can be carried out by doctor blades, doctor blades, or slot-dye coating. For thin layers of less than 20 µm, known printing processes such as screen printing, gravure printing, etching, pad printing, or flexographic printing can also be used. Preferably, the photopolymerizable composition is laminated directly onto the master to be copied using a transparent and clear film. The layer thickness is adjusted either by the contact pressure and lamination speed or by the slot width. When coating thick and rigid substrates such as, for example,Glass plates can be coated using a spin coating process. Application via inkjet printing or CNC-controlled dispensing devices is also possible. Direct injection into cavities is another option.

[0041] In particular, the photopolymerizable composition is also suitable for application to curved surfaces. It can also be pressed between two matching bodies and simultaneously used as a filler or adhesive.

[0042] The user also has complete freedom to choose which substrate materials and layer structures to use, as the coating process takes place in the exposure unit. The photopolymerizable composition, which is essentially free of volatile organic solvents and preferably contains less than 5% by weight, and more preferably at most 1% by weight, can be exposed immediately after application. Multilayer exposures are also not a problem, as a new layer can be applied and holographically exposed after curing using the same principle. This can be used, for example, to create true-color holograms from three layers representing the primary colors red, green, and blue.

[0043] Aliphatic urethane acrylates with a relatively slow reaction rate and high flexibility are preferred. The flexibility of the hardened layer is helpful for removing the exposed hologram from rigid surfaces such as glass or metal. The easy and clean removal is very advantageous for mass production because it allows the use of wear-free copy masters, such as conventional nickel shims with a fine holographic surface structure or volume holograms sealed with thin glass, for contact printing. The complete removal of the non-sticky layer keeps cleaning effort to a minimum.

[0044] The photopolymerizable composition is particularly suitable for contact printing. Because the liquid photopolymerizable composition is printed directly onto the master, index matching is unnecessary. Index matching refers to the application of a liquid between the master and the hologram layer with approximately the same refractive index. In conventional contact printing with film materials, index matching prevents the occurrence of disruptive interference patterns (Newton's rings). These arise from reflections, which occur particularly where the two layers do not directly touch, for example, due to dust inclusions or minor irregularities, resulting in bubbles or air inclusions. Furthermore, compensating for scratches and other imperfections on the substrate and master improves the optical quality of the copy.Small dust particles with dimensions smaller than the layer thickness are embedded in the liquid and do not produce noticeable pressure marks or defects like those found in film materials. This significantly reduces rejects and the cleanroom requirements for the production environment.

[0045] The liquid photopolymerizable composition can therefore also be advantageously used as an index match material for the exposure of holographic film materials. Because it hardens during exposure, cleaning or evaporation is unnecessary. Furthermore, the holographic recording is supported and enhanced by the combination of the two holographic recording materials, as a hologram is formed in both layers.

[0046] Because the liquid material conforms to any surface, unlike film materials, it allows for the simultaneous imprinting of holograms and the use of complexly shaped surfaces. These surface structures can include embossed holograms or Fresnel structures. This makes it possible to physically and holographically copy both the surface structure and the volume holographic or optical information of the master in a single processing step.

[0047] In this way, optical elements such as prisms or lenses with integrated hologram structures can also be manufactured.

[0048] Because the photopolymerizable composition can be exposed immediately after application, compact coating and exposure times with very short transport distances and times between these two stations are achievable. This reduces the risk of unintentional pre-exposure by ambient light. Therefore, the requirements for a dark environment are not stringent. The photopolymerizable composition can be applied and exposed within 1 minute, preferably within 20 seconds, and most preferably within 5 seconds.

[0049] The invention relates to a method in which the photopolymerizable composition according to the invention is applied and exposed within one minute.

[0050] The photopolymerizable composition according to the invention comprises at least one monomer M comprising at least one ethylene unsaturated group, preferably one monomer M comprising at least two ethylene unsaturated groups.

[0051] Particularly preferably, the photopolymerizable composition comprises at least one monomer M comprising at least one ethylene unsaturated group, and one monomer M1 comprising at least two ethylene unsaturated groups, wherein M1 preferably differs from M only by the second ethylene unsaturated group.

[0052] The monomer, comprising at least one ethylene unsaturated group, can have the following general structural units. or or or or or where where n, m = 0-12, preferably 1-12; o = 0, 1; and Ar is a mono- or polynuclear substituted or unsubstituted aromatic or heterocyclic aromatic residue, wherein residue R1 is H, methyl, or ethyl, and wherein residues R2 and R3 are independently selected from the group consisting of alkyl, alkenyl, alkynyl, alkoxy, acyl, and acyloxy residues, which may be straight- or branched-chain, unsubstituted or substituted, substituted or unsubstituted aryloxy residues, substituted or unsubstituted aromatic or heterocyclic residues, unsubstituted or substituted alicyclic hydrocarbon residues, aliphatic, aromatic, and aliphatic aromatic amino, carboxylic acid, amido, and imido residues, hydroxy, amino, cyano, nitro, halogen atoms, or hydrogen atoms, and combinations of the aforementioned residues, wherein the substituted residues may be substituted with C 1 -C 12 alkyl, C 1 -C 12 alkoxy, hydroxy, carboxy,Carbonyl, amino, amido, imido residues, halogen atoms, aromatic residues, or combinations thereof.

[0053] Examples of suitable monomers M are substituted or unsubstituted styrene monomers, acrylic acid, α-alkylacrylic acid, acrylic acid esters, α-alkylacrylic acid esters, the alcohol component of which may be a substituted or unsubstituted aliphatic or aromatic residue with 2-50 carbon atoms, acrylamides, α-alkylacrylamides, where alkyl has the meaning given above, vinyl esters, vinyl alcohols, vinyl ethers and other substituted vinylic monomers, substituted with substituted or unsubstituted aliphatic or aromatic residues with 2-50 carbon atoms.

[0054] Monomers M are selected from the group consisting of (meth)butyl acrylate, (meth)phenyl acrylate, (meth)benzyl acrylate, (meth)isobornyl acrylate, (meth)cyclohexyl acrylate, (meth)2-phenoxyethyl acrylate, (meth)1H,1H,2H,2H-perfluorooctyl acrylate, 2,2,2-trifluoroethyl(meth)acrylate, heptafluoropropyl(meth)acrylate, 1,1,1,3,3,3-hexyfluoroisopropyl(meth)acrylate, 2,2,3,3-tetrafluoropropyl(meth)acrylate, 2,2,3,3,4,4,4-heptafluorobutyl(meth)acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl(meth)acrylate, and N,N-diethylaminoethyl acrylate. Acrylate ethoxyethyl ester, acrylate 2-(p-chlorophenoxy)ethyl ester, p-chlorophenyl acrylate, 2-phenylethyl(meth)acrylate, pentachlorophenyl acrylate, phenyl acrylate, p-chlorostyrene, n-vinylcarbazole, 1-vinyl-2-pyrolidone, 2-chlorostyrene, 2-bromostyrene, methoxystyrene, phenol ethoxylate acrylate, 2-(p-chlorophenoxy)ethyl acrylate, 2-(1-naphthyloxy)ethyl acrylate, hydroquinone monomethacrylate and 2-[β-(N-carbazolyl)propionyloxy]ethyl acrylate.

[0055] Particularly preferred monomers M are N-vinylcarbazole, ethoxyethoxyethyl acrylate, phenol ethoxylate acrylate, 2-(p-chlorophenoxy)ethyl acrylate, p-chlorophenyl acrylate, phenyl acrylate, 2-phenylethyl acrylate, 2-(1-naphthyloxy)ethyl acrylate, t-butyl acrylate, isobornyl acrylate, cyclohexyl acrylate, N,N-diethylaminoethyl acrylate, ethoxyethoxyethyl acrylate, 1H,1H,2H,2H-perfluorooctyl methacrylate.

[0056] Preferably, the monomer M comprises at least two ethylene unsaturated groups; therefore, the monomer is preferably difunctional.

[0057] Difunctional ethylene unsaturated monomers have two C-C double bonds in the molecule, meaning they contain, for example, two of the structural units listed above. A difunctional ethylene unsaturated monomer can, for example, contain two acrylate or methacrylate groups.

[0058] The monomer M in the photopolymerizable composition according to the invention can consist exclusively of one or more difunctional or higher-functional monomers, i.e., the composition can be free of monofunctional ethylene-unsaturated monomers. Preferably, the content of monomers M with at least two ethylene-unsaturated groups in the composition according to the invention is more than 10 wt.%, preferably more than 20 wt.%, and particularly preferably more than 30 wt.%, based on the total weight of the composition.

[0059] The use of difunctional or higher functional monomers leads in particular to a particularly high thermal and mechanical stability of the manufactured holographic elements and is especially advantageous in the production of reflection holograms.

[0060] Preferred bisphenol-A diacrylates are ethoxylated bisphenol-A diacrylates, in particular compounds of the following formula where R 1 , Q and Ar have the meanings given above.

[0061] One particularly preferred monomer M is the compound with the following structural formula:

[0062] Preferably, the viscosity of the monomer M or monomer mixture at room temperature is at least 900 mPa·s.

[0063] The photopolymerizable composition according to the invention comprises an aliphatic urethane acrylate or a mixture of different aliphatic urethane acrylates.

[0064] The suitable urethane acrylates are generally compounds of the following general structural formula: where R is a long polyol segment and NHCOO is the urethane compound. Particularly preferred aliphatic urethane acrylates are the commercially available products Ebecryl 230 from Allnex and CN 9002 from Sartomer; and n1 = 0-1000, preferably 0-100, particularly preferably 1-12.

[0065] The urethane acrylate mixture contains 25%, preferably over 50%, of one of these products, or most preferably consists of only one of these two products.

[0066] The viscosity of the photopolymerizable composition at 20°C is at least 2000mPa s, preferably 10000mPa s and particularly preferably at least 20000mPa s.

[0067] Viscosity can be determined using a plate-plate rotation rheometer (e.g., from Haake, type 006-2805). In this test, the material is placed between two coaxial, circular plates, one of which rotates. The plates are, for example, 1 mm apart and have a diameter of 35 mm. The viscosity can be determined from the measurement of the torque and rotational speed (e.g., 10 revolutions / second) (DIN 53018, ISO 3210).

[0068] The photopolymerizable composition according to the invention comprises at least one photoinitiator, which preferably activates the polymerization of the monomer(s) M and the aliphatic uretanacrylate(s) upon exposure to (actinic) radiation. This is preferably a radical-forming polymerization initiator.

[0069] Radical-forming polymerization initiators are known, see e.g. Timpe, HJ and S. Neuenfeld, "Dyes in photoinitiator systems", Kontakte (1990), pages 28-35 and Jakubiak, J. and JF Rabek, "Photoinitiators for visible light polymerization", Polimery (Warsaw) (1999), 44, pages 447-461.

[0070] Suitable radical-forming polymerization initiators, which can be activated by UV radiation and are generally inactive at temperatures up to 185°C, include the substituted or unsubstituted polynuclear quinones; These are compounds with two intracyclic carbon atoms in a conjugated carbocyclic ring system, e.g., 9,10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, octamethylanthraquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone, 2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, sodium salt of anthraquinone α-sulfonic acid. 3-Chloro-2-methylanthraquinone, retenquinone, 7,8,9,10-tetrahydronaphthacenequinone and 1,2,3,4-tetrahydrobenz[a]anthracene-7,12-dione.Other photoinitiators that are also useful, although some are thermally active at temperatures as low as 85°C, are described in US patent 2,760,663, and these include vicinal ketaldonyl alcohols such as benzoin, pivaloin, acyloin ethers, e.g., benzoin methyl and ethyl ethers, α-hydrocarbon-substituted aromatic acyloins, including α-methylbenzoin, α-allylbenzoin, and α-phenylbenzoin.

[0071] Photoreducible dyes and reducing agents such as those disclosed in US patents 2 850 445, 2 875 047, 3 097 096, 3 074 974, 3 097 097, 3 145 104 and 3 579 339, as well as dyes from the class of phenazines, oxazines and quinones, can be used as photoinitiators; Michler's ketone, benzophenone, 2,4,5-triphenylimidazolyl dimers with hydrogen donors and mixtures thereof, as described in US patents 3,427,161, 3,479,185, 3,549,367, 4,311,783, 4,622,286, and 3,784,557. A useful discussion of dye-sensitized photopolymerization can be found in "Dye Sensitized Photopolymerization" by DF: Eaton in Adv. in Photochemistry, Vol. 13, DH Volman, GS Hammond, and K. Gollnick, eds., Wiley-Interscience, New York, 1986, pp. 427–487. Similarly, the cyclohexadienone compounds of US patent no. 4,341,860 are also suitable as initiators. Suitable photoinitiators include CDM-HABI, i.e.,, 2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)-imidazole dimer; o-Cl-HABI, i.e., 2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-biimidazole; and TCTM-HABI, i.e., 2,5-bis(o-chlorophenyl)-4-(3,4-dimethoxyphenyl)-1H-imidazole dimer, each typically used with a hydrogen donor, e.g., 2-mercaptobenzoxazole.

[0072] Particularly preferred UV photoinitiators are IRGACURE® < OXE-01 (1,2-octanedione-1-[4-(phenylthio)-phenyl]-2-(O-benzoyl oxime)) and IRGACURE® < OXE-02 (1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone-O-acetyl oxime) from BASF AG, as well as OMNIRAD-MBF (methylbenzoyl formate), OMNIRAD-TPO (2,4,6-trimethylbenzoyl diphenyl phosphine oxide), OMNIRAD-TPO-L (ethyl-(2,4,6-trimethylbenzoyl) phenyl phosphinate), OMNIRAD-1173 (2-hydroxy-2-methyl-1-phenylpropanone), and OMNIRAD 1000 (mixture of 2-hydroxy-2-methyl-1-phenylpropanone). (80%) and 1-hydroxycyclohexyl phenylketone (20%)), OMNIRAD 184 (1-hydroxycyclohexyl phenylketone), OMNIRAD 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), OMNIRAD 2022 (mixture of 2-hydroxy-2-methyl-1-phenylpropanone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate) and OMNICAT 440 (4,4'-dimethyl-diphenyl-iodonium hexafluorophosphate), which are available from IGM Resins and preferably in an amount of 0.1 to 10 wt.-% will be used. IRCACURE ®< OXE-01 OMNIRAD MBF IRGACURE ®< OXE-02 OMNIRAD TPO-L OMNIRAD TPO OMNIRAD 819 OMNIRAD 184 OMNIRAD 1000 OMNICAT 440 OMNIRAD 1173 OMNIRAD 2022

[0073] The photoinitiators mentioned above can be used alone or in combination.

[0074] Preferably, the photoinitiator contains a dye and a borate salt as a co-photoinitiator. The terms "co-photoinitiator" and "co-photoinitiator" are used interchangeably within the scope of the present invention.

[0075] A particularly preferred photoinitiator comprises the combination of the following structural formula I (co-photoinitiator) and dyes (sensitizing agents), such as methylene blue, and the sensitizing agents disclosed in US patents 3,554,753 A, 3,563,750 A, 3,563,751 A, 3,647,467 A, 3,652,275 A, 4,162,162 A, 4,268,667 A, 4,454,218 A, 4,535,052 A and 4,565,769 A, as well as the dyes and co-photoinitiators mentioned in application WO 2012062655 A2, to which express reference is made herein. Particularly preferred sensitizing agents include the following: DBC, i.e., 2,5-bis[(4-diethylamino-2-methylphenyl)methylene]cyclopentanone; DEAW, i.e., 2,5-bis[(4-diethylaminophenyl)methylene]cyclopentanone; Dimethoxy-JDI, i.e., 2,3-dihydro-5,6-dimethoxy-2-[(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-9-yl)methylene]-1H-in-den-1-one; and Safranin O, i.e., 3,7-diamino-2,8-dimethyl-5-phenylphenazinium chloride.

[0076] The compound with structural formula I, which was developed by Ciba Specialty Chemicals Inc. under the name "CGI 7460" and is now available from BASF AG under the name SEC LCA 1460, is represented as follows:

[0077] The dyes are particularly preferably supplied as dye concentrates (see Tables 2 and 3) in a mixture without volatile solvents. This simplifies the preparation of the photopolymerizable compositions, as boiling off the volatile substances is unnecessary and dosing is simpler and more precise.

[0078] Preferably, the dye in the photopolymerizable compositions according to the invention is selected from the group consisting of acriflavins, diaminoacridines, rhodamine B, safranin-O, diethyl safranin and methylene blue.

[0079] Preferably, the co-photoinitiator in the photopolymerizable compositions according to the invention is selected from the group consisting of tetrabutylammonium tetrahexyl borate, tetrabutylammonium triphenylhexyl borate, tetrabutylammonium tris-(3-fluorophenyl)-hexyl borate and tetrabutylammonium tris-(3-chloro-4-methylphenyl)-hexyl borate or mixtures thereof.

[0080] The photoinitiator system, which activates the polymerization of the monomers and urethane acrylates upon exposure to actinic radiation, consists of a photoinitiator or a co-photoinitiator and a dye. Preferably, it contains all three components.

[0081] To adapt to the chosen processing method or the application area of ​​the photopolymerizable composition and to improve printability, surface adhesion, viscosity, film formation, flexibility, hardness, cold, heat and weather resistance, the composition may contain various additives known per se.

[0082] Therefore, the photopolymerizable composition includes an additive.

[0083] The additives include solvents, fillers, dyes, plasticizers, surfactants, common components used in photopolymer systems, polymeric binders, wetting agents, leveling agents, defoamers, adhesion promoters, surface additives, nanoscale particles, optical brighteners or mixtures thereof.

[0084] These additives should mix well and not impair the diffraction efficiency. Non-volatile substances can even permanently improve the diffraction efficiency in thin films, particularly by selecting additives that increase the refractive index difference between the ethylene-unsaturated monomer and the other components of the photopolymerizable composition. If the urethane component has a lower refractive index than the ethylene-unsaturated monomer component, the additive(s) should also have the lowest possible refractive index. Therefore, in this case, in addition to well-known polymers with a low refractive index such as polyvinyl acetate, fluorinated or silanized polymers are particularly suitable. To achieve good diffusion properties, the molecular weight of the additives under consideration should not be too high.

[0085] The additives mentioned above and specified in detail below are used in an amount of 0.01 to 20 wt.%, preferably 0.01 to 10 wt.%, based on the total weight of the composition.

[0086] The photopolymerizable composition may contain a plasticizer to enhance the modulation of the refractive index of the imaged composition. Plasticizers may be used in amounts ranging from about 0.01 to about 10 wt%, preferably 5 to about 10 wt%, based on the total weight of the composition. Suitable plasticizers include triethylene glycol, triethylene glycol diacetate, triethylene glycol dipropionate, triethylene glycol dicaprylate, triethylene glycol dimethyl ether, triethylene glycol bis(2-ethylhexanoate), tetraethylene glycol diheptanoate, polyethylene glycol, polyethylene glycol methyl ether, isopropyl naphthalene, diisopropyl naphthalene, polypropylene glycol, glyceryl tritributyrate, diethyl adipate, diethyl sebacinate, dibutyl suberinate, tributyl phosphate, tris(2-ethylhexyl) phosphate, Brij®< 30 [C 12 H 25 (OCH 2 CH 2 ) 4 OH], Brij®< 35 [C 12 H 25 (OCH 2 CH 2 ) 20 OH], and n-butyl acetate.Particularly preferred plasticizers are polyethylene glycol, triethylene glycol diethylhexanoate (3G8), triethylene glycol dicaprylate, tetraethylene glycol diheptanoate, diethyl adipate, Brij® < 30 and tris(2-ethylhexyl) phosphate.

[0087] If desired, other common components used in photopolymer systems can be combined with the compositions and elements of this invention. These components include: optical brighteners, ultraviolet absorbing materials, thermal stabilizers, hydrogen donors, oxygen scavengers, and release agents. These additives may also include polymers or copolymers.

[0088] Useful optical brighteners include those disclosed in US Patent 3,854,950 A. A preferred optical brightener is 7-(4'-chloro-6'-diethylamino-1',3',5'-triazine-4'-yl)amino-3-phenylcoumarin. Ultraviolet radiation-absorbing materials useful for this invention are also disclosed in US Patent 3,854,950 A.

[0089] Useful thermal stabilizers include: hydroquinone, phenidone, p-methoxyphenol, alkyl- and aryl-substituted hydroquinones and quinones, tert-butylcatechol, pyrogallol, copper resinate, naphthylamines, β-naphthol, copper(I) chloride, 2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine, nitrobenzene, dinitrobenzene, p-toluquinone, and chloranil. The dinitroso dimers described in US Patent 4,168,982 A are also suitable. An inhibitor for thermal polymerization is usually also present to increase the stability of the photopolymerizable composition during storage.

[0090] Hydrogen donor compounds suitable as chain transfer reagents include: 2-mercaptobenzoxazole, 2-mercaptobenzothioazole, etc., as well as various types of compounds, e.g., (a) ethers, (b) esters, (c) alcohols, (d) compounds containing allylic or benzylic hydrogen such as cumene, (e) acetals, (f) aldehydes, and (g) amides, as disclosed in column 12, lines 18 to 58 of US Patent 3,390,996 A, to which reference is expressly made herein.

[0091] Compounds that have proven useful as release agents are described in US Patent 4,326,010 A. A preferred release agent is polycaprolactone.

[0092] The photopolymerizable composition may also contain one or more polymeric binders selected from the group comprising polymethyl methacrylate and polyethyl methacrylate, polyvinyl esters such as polyvinyl acetate, polyvinyl acetate / acrylate, polyvinyl acetate / methacrylate and partially hydrolyzed polyvinyl acetate, ethylene / vinyl acetate copolymers, vinyl chloride / carboxylic acid ester copolymers, vinyl chloride / acrylic acid ester copolymers, polyvinyl butyral and polyvinyl formal, butadiene and isoprene polymers and copolymers, and polyethylene oxides from polyglycols with an average molecular weight of about 1,000 to 1,000.000 g / mol, epoxides, such as epoxides containing acrylate or methacrylate residues, polystyrenes, cellulose esters, such as cellulose acetate, cellulose acetate succinate and cellulose acetate butyrate, cellulose ethers, such as methylcellulose and ethylcellulose, polycondensates, such as polycarbonates, polyesters, polyamides, such as N-methoxymethylpolyhexamethylene adipamide, polyimides, polyurethanes. The aforementioned polymeric binders can be used, for example, in an amount of 0.001 to 10 wt%, based on the total weight of the composition.

[0093] The photopolymerizable composition may also include one or more wetting agents (especially fluorocarbon polymers, such as Schwego-Fluor 8038™<, or fluorosurfactants, such as 3M Fluorad FC-4430™<), leveling agents (especially glycolic acid n-butyl esters or polyether-modified polydimethylsiloxanes, such as ADDID 130™<), defoamers (especially fluorosilicone oil-based defoamers, such as ADDID 763™<), adhesion promoters (especially diamino-trimethoxy-functional silane adhesion promoters, such as ADDID 900™< or glycidyl-trimethoxy-trifunctional silane adhesion promoters, such as ADDID 911™<, vinyltriethyoxysilane or 3-methacryloxypropyltrimethoxysilane), or surface additives (especially Polyether-modified acrylic functional polydimethylsiloxanes, such as BYK-UV 3500™< , polyether-modified polydimethylsiloxanes, such as BYK-UV 3510™< or polyether-modified acrylic functional polydimethylsiloxanes,such as BYK-UV 3530™<). The products mentioned, with the trade names "ADDID" and "BYK", are available from Wacker and BYK Chemie, respectively.

[0094] The photopolymerizable composition may also contain nanoscale particles such as TiO2, SiO2 or Au, which may be coupled to monomers (such materials are available, for example, under the trade name "Nanocryl").

[0095] Preferably, the additive can be an amine synergist. An amine synergist, in combination with other photoinitiators, can increase the curing rate of UV varnishes (see DE60216490T2).

[0096] Preferably, the additive can be a peroxide. A thermally activatable peroxide, in combination with other photoinitiators, can improve the curing of UV varnishes, especially in shaded areas (see US 5017406 A or DE 60030223 T2).

[0097] Preferably, the additive can also be a marker selected from fluorescent pigments or lanthanide compounds. For example, europium or terbium trisdipicolinate complexes can be used as lanthanide compounds.

[0098] For the purposes of the present invention, a marker is understood to be a forensically detectable substance that can be used to determine the authenticity or origin of a product, or its producer or seller. Provided that the layers to be produced are thick enough to embed the corresponding microparticles, even small, individualized particles, colorful microplastics also known as taggants, can be incorporated.

[0099] Preferably, the photopolymerizable composition is liquid at standard pressure in a range of 20°C to 150°C, most preferably 25°C to 120°C.

[0100] In a further embodiment, the invention comprises an element containing a component that is obtainable by exposure of the photopolymerizable composition according to the invention to (actinic) UV / VIS radiation.

[0101] Preferably, the element according to the invention comprises a component that has transparent and / or translucent areas.

[0102] If the photopolymerizable composition is exposed to a light source of no more than 50 mW / cm² for a period of at least 1 second to 5 minutes, preferably 2 seconds to 2 minutes, it can become milky. This creates a ground glass screen whose scattering properties can be selectively and locally modified by the chosen exposure method (duration, intensity, temperature, etc.). It also makes a difference whether coherent laser light (speckles) or white or UV light is used for exposure. The speckle size, for example, can be used to precisely control the grain size. The achievable resolution is very high. Therefore, components comprising transparent and / or translucent areas can preferably be provided.

[0103] Mask exposure allows for the creation of any structures, texts, and images that can be recognized by their matte finish, independent of holographic reproduction.

[0104] In another embodiment, the invention relates to the use of the element according to the invention as a film, lens, grating, prism, mirror, beam splitter, diffuser, surface relief, optical switch or sensor.

[0105] By exposing the film to a directed beam and a line pattern, milky lamellae, positioned vertically or at an angle and spaced regularly within the layer, can be exposed to create a venetian blind film. This film is transparent in the direction corresponding to the exposure angle and milky in all other directions. Such a film can be used, for example, as a privacy film for screens.

[0106] This process can also be combined with holographic properties by quickly and transparently exposing the unexposed areas holographically. The resulting film then reacts, for example, to a specific illumination angle. Beam deflection and scattering can be coordinated. The use of multiple layers applied sequentially and exposed at different times is also conceivable.

[0107] Furthermore, a surface, such as a lens structure, can be molded simultaneously. This makes it possible to create structures that, for example, focus the light from an LED array and reproduce it as a directed beam, while scattering other light from LEDs not located within the lens array. This scattering can be enhanced by the matte areas outside the lens beam paths. Using a honeycomb structure with matte walls would be one possible implementation.

[0108] One application would be light sources that mimic the natural sky, emitting direct, directional, yellowish-white sunlight as well as blue diffused light. The LED array of this artificial "skylight" could, of course, also locally vary its brightness and color, similar to a screen, allowing for the simulation of different lighting moods, times of day, cloudy skies, and passing clouds.

[0109] The blue light could also be filtered from the directed white light beam by a reflection hologram and focused onto the scattering centers or surfaces. All of this—mapping, light focusing, scattering, and hologram—can be achieved with the photopolymerizable composition in a single exposure process or combined by repeated application and exposure in multiple layers.

[0110] Automobiles also require both directed and diffused light. Directed light is needed for headlights, which illuminate the road, while diffused light, such as from turn signals, brake lights, or taillights, needs to be visible to other road users across a wide angle. By using the special film described above, a headlight, for example, could be designed to function as a turn signal across its entire surface. The headlight would simultaneously emit directed beams and, if necessary, diffused yellow light in all directions.

[0111] Particularly preferred is an element according to the invention comprising a hologram obtainable by the action of a holographic information-carrying, modulating radiation on the photopolymerizable composition according to the invention.

[0112] The holograms are generally produced by exposing a layer of photopolymerizable composition, which is applied to a support substrate or a template, to modulated radiation carrying holographic information. Glass, plastic (in particular PET, PP, PMMA, polycarbonate, or cellulose diacetate or triacetate), or paper can be used as support substrates for the production of the elements according to the invention. During exposure, the photopolymerizable composition can, for example, be located between two glass plates.

[0113] The invention relates to methods for producing an element or photopolymerizable composition according to the invention, in which the element or composition is exposed to a temperature of more than 100°C and a pressure of more than 2 bar.

[0114] The invention further relates to a method for forming a light-resistant hologram in a photopolymerizable layer on a substrate surface or copy template, comprising the action of a modulated radiation carrying holographic information on a layer of a photopolymerizable composition according to the invention.

[0115] Particularly preferred is an element comprising a hologram, wherein the hologram is treated with a swelling agent. A swelling agent within the meaning of the present invention is a substance that causes the hologram to swell by means of diffusion and, in the case of reflection holograms, causes a spectral shift of the reflected light to a higher wavelength.

[0116] For example, a green reflective hologram can be transformed into a red one.

[0117] The same method can also be used with a flash. Applied substances evaporate and penetrate the layer in a flash. Surprisingly, this also works when the photopolymer layer is already sealed with a UV varnish layer.

[0118] This can be used to wonderfully personalize a finished hologram. The swelling agent is applied, for example, using a standard inkjet printing process. The subsequent intense UV flash causes the active substances to vaporize, penetrating the areas where they were applied and creating swelling and local color changes within the hologram. The added information can be, for example, an image, a number, or a label. Since these changes are irreversible and only affect the hologram, this quick and easy method is a good way to increase the counterfeit protection of ID cards, seals, or vignettes. This is especially useful for products that are personalized at the point of issue and where this needs to be done easily.

[0119] Instead of an inkjet printer and a flash, a thermal sublimation printer can also be used, which vaporizes the source materials via a suitable printer ribbon.

[0120] In thick layers, a concentration gradient can develop. The intruded material then causes the upper layer to swell more than the lower layers. This leads to a broadening of the absorption peak in the absorption spectrum. A double peak is also possible if the swelling region ends abruptly and the degree of swelling does not decrease gradually.

[0121] A broadening of the peak indicates that a larger wavelength range is reflected, and the viewing angle for a given wavelength also becomes wider. The ability to modify these important parameters of a hologram after the fact is useful for many technical applications, such as HUDs that need to function even at wider viewing angles.

[0122] The hologram layer can also be brought into contact with a material containing the swelling agent. This could be, for example, a PVB film with a high plasticizer content such as triethylene glycol diethylhexanoate (3G8). Depending on the swelling chemicals used and the layer applied to the hologram that contains and releases this swelling agent, its concentration can change after diffusing into the hologram layer depending on the temperature, as the diffusion equilibrium and the concentration gradient between the two layers are temperature-dependent. With the shift in the absorption peak, the rendering angle for a specific wavelength also changes; this reversible effect can therefore be used as a sensor or optical switch.

[0123] If this effect is not desired, for example within a laminated glass pane, a sealant, e.g. a UV varnish, can preferably be applied to the hologram, which serves as a protective and barrier layer against diffusing substances.

[0124] The use of the element according to the invention is particularly preferred for a head-up display, a laminated glass pane, data glasses, a light guidance system, a spectrometer, a detection system, a safety element or a label. Examples List of abbreviations

[0125] BWG, η Diffraction efficiency CGI 7460 Tetrabutylammonium tris(3-fluorophenyl)hexyl borate, SEC LCA 1460, BASF CN 9002 Aliphatic urethane acrylate Ebecryl 230 Aliphatic urethane diacrylate NPG N-Phenylglycin Omnirad 1173 2-Hydroxy-2-methyl-1-phenylpropanone PCL-triol Poly(caprolactone)triol, M n -300 PolyCLO Capromer PT-05, Polycaprolactone, M n -540 Saffron-O 3,7-Diamino-2,8-dimethyl-5-phenylphenazinium chloride Schwego-Fluor 8038 Ethanolic solution of a polyether-based fluorosurfactant from Schwegmann GmbH SEC LCA 1460 Tetrabutylammonium tris(3-fluorophenyl)hexyl borate, borate salt, co-initiator SR 349 Ethoxylated bisphenol A diacrylate T Peak Peak value, transmission at the wavelength that satisfies the Bragg condition T Ref Reference value, transmission without hologram

[0126] The following examples are not covered by the wording of the claims, but are considered to facilitate understanding of the invention. A composition according to Table 1 is known from the prior art. Table 1 Comparison example VB1 Quantity[g] Crowd[%] Designation CAS 91,93 91,93 % SR 349 64401-02-1 0,03 0,03 % Saffron-O 477-73-6 0,34 0,34 % CGI 7460 3,75 3,75 % castor oil 8001-79-4 3,75 3,75 % Palm kernel oil 8023-79-8 0,2 0,20 % Schwego-Fluor 8038 - 100 100,00 % The composition consists of the EP 1 779 196 B1 known. Examples of invention

[0127] Table 2 Dye concentrates FK1 Quantity [g] Crowd[%] Designation CAS 19,55 65,17% PolyCLO TMP540 37625-56-2 10,00 33,33% Omnirad 1173 7473-98-5 0,15 0,50% NPG 103-01-5 0,30 1,00% Methylene blue 61-73-4 30,00 100,00% Table 3 Dye concentrate FK2 Quantity [g] Crowd[%] Designation CAS 12,00 40,00% PCL-triol 37625-56-2 12,00 40,00% Omnirad 1173 7473-98-5 5,40 18,00% Benzaldehyd 100-52-7 0,60 2,00% Methylene blue 61-73-4 30,00 100,00% Table 4 Monomer-containing mixture MM1 Quantity [g] Crowd[%] Designation CAS 287,5 57,16% SR 349 64401-02-1 212,5 42,25% Ebecryl 230 3 0,60% SEC LCA 1460 503,00 100,00% Table 5 Monomer-containing mixture MM2 Quantity [g] Crowd[%] Designation CAS 23 57,07% SR 349 64401-02-1 17 42,185% CN 9002 0,3 0,74% SEC LCA 1460 40,30 100,00%

[0128] For the exposure of samples A, B, and C, the following photopolymerizable compositions were prepared from the monomer-containing mixtures and dye concentrates listed above. As a comparison, the known formulation from Table 1 was used without Safranin-O. Instead of Safranin-O, the dye concentrate FK2 with methylene blue was added to mixture A.

[0129] Samples D, E, and F were cured using only UV light. Therefore, instead of the dye concentrate, only the UV photoinitiator Omnirad 1173 was added. Table 6 Photopolymerizable composition A Quantity [g] Crowd[%] component name 5 97,09% VB1 without saffron O Monomer-containing mixture from the comparison example 0,15 2,91% FK2 Dye concentrate 5,15 100,00% Table 7 Photopolymerizable Composition B Quantity [g] Crowd[%] component name 5 97,09% MM1 Monomer-containing mixture 0,15 2,91% FK1 Dye concentrate 5,15 100,00% Table 8 Photopolymerizable composition C Quantity [g] Crowd[%] component name 5 97,09% MM2 Monomer-containing mixture 0,15 2,91% FK2 Dye concentrate 5,15 100,00% Table 9 Photopolymerizable composition D Quantity [g] Crowd[%] component name 5 97,09% VB1 without saffron O Monomer-containing mixture from the comparison example 0,1 1,96% Omnirad 1173 Photoinitiator 5,1 100,00% Table 10 Photopolymerizable composition E Quantity [g] Crowd[%] component name 5 97,09% MM1 Monomer-containing mixture 0,1 1,96% Omnirad 1173 Photoinitiator 5,1 100,00% Table 11 Photopolymerizable composition F Quantity [g] Crowd[%] component name 5 97,09% MM2 Monomer-containing mixture 0,1 1,96% Omnirad 1173 Photoinitiator 5,1 100,00% Exposures

[0130] Table 12 Laser exposures material Peak [nm] BWG[%] Thickness [µm] Δn A 574 80 % 124 0,0021 B 578 87 % 138 0,0022 C 578 96 % 115 0,0037

[0131] The photopolymerizable compositions A, B, and C were exposed to a laser with a wavelength of 577 nm at a temperature of 20°C to 21°C. The photopolymerizable compositions were stored in an oven at 80°C and exposed to light shortly after application. After laser exposure and UV curing, the diffraction efficiency (DEF) was determined using a spectrometer based on the spectral absorption curve. The layer thickness was measured with a digital micrometer.

[0132] To demonstrate the exposure-dependent opacity effect, samples D, E, and F were cured using UV light sources of varying intensities. For rapid curing, the UV bridge described above was used again. Although a significantly shorter curing time is sufficient, the samples were irradiated for 30 seconds. For slow exposure, the Hamamatsu UV spot light source LC6 was used. The UV light exits the end of a flexible light guide at an intensity of 3.5 W / cm². The samples were exposed for 120 seconds at a distance of 6 cm from the exit aperture. As a precaution, they were then post-cured for another 30 seconds under the UV bridge. Table 13 UV exposures material Haze value of slow exposure Sample thickness of slow exposure [µm] Haze value of the fast exposure Rapid exposure sample thickness [µm] Haze difference Temperature [°C] D 82 % 948 2 % 936 80 % 26 D 89 % 890 70 % 855 19 % 21 E 80% 935 2% 928 78 % 21 F 80% 950 2 % 889 78 % 21

[0133] The photopolymerizable compositions for UV exposure were stored at room temperature (21°C). Only for the first exposure was the reference material D stored and processed at 26°C. The second exposure at 21°C with photopolymerizable composition D, despite the rapid exposure time, resulted in a high haze value of 70%, because the liquid formulation is already milky at this temperature. Exposure setup

[0134] The laser beam with a measured power of 1.43W was horizontally widened using a polygon scanner and focused by a cylindrical lens to cover an exposure width of 23cm. Figure 2 shows the schematic exposure setup. Reference symbols in Figure 2:

[0135] 1Laser 577nm 2Mirror 3Polygon scanner 4Cylinder lens 5Scan beam 6Scanner mirror

[0136] The samples were scanned and exposed to this line using a movable mirror. The scanning speed was set to 9 mm / s. The laser beam struck the sample surface at an angle of 22° to the normal.

[0137] The Figure 3 shows the path of the rays. Reference symbols in Figure 3:

[0138] 1 Scan beam 577nm 2 Scanner mirror 3 Exposure direction 4 Exposure angle, 22° 5 Substrate, glass or film 6 Photopolymer (photopolymerizable composition) 7 Master, mirror sheet

[0139] To create a reflection hologram, the sample material was applied to a mirror plate, which reflects the laser light back. The interference of the incident and reflected beams creates a line pattern of light and dark areas parallel to the mirror's surface. This interference pattern is recorded by the material in the form of a refractive index modulation, resulting in a so-called Lippmann-Bragg hologram.

[0140] In laser exposure, the photopolymer layer is sandwiched between the mirror plate and a transparent substrate, such as PET film or glass. For the examples, specimen glass slides were used. The glass covers a droplet applied to the mirror plate. The layer thickness is determined by the droplet quantity and its expansion. The size of the circular expansion can be controlled by the contact pressure, temperature, and exposure time. Spacers can also be used to achieve a specific layer thickness. After laser exposure, the material is cured with UV light. For the initial curing step, we use a UV flash with an intensity of 3000 WS. This is sufficient to subsequently remove the hologram and the substrate from the plate. To ensure adhesion to the glass, it should be pre-treated with a primer.

[0141] For the final hardening of the sample, we use a UV bridge with an arc length of 70 mm and a power of 120 W / cm and an exposure time of 30s. Measurement setup

[0142] The samples were measured using a spectrometer (CAS 140 B from Instrument Systems) in transmitted light, specifically under perpendicular illumination. Since the hologram only reflects the wavelength that fulfills the Bragg condition, a distinct absorption peak is visible in the spectral curve at this point.

[0143] The diffraction efficiency (DEE) η is calculated from the peak value Tpeak and a nearby reference value Tref on the upper baseline as follows: η = T Ref − T Peak / T Ref

[0144] Figure 4 The measurement curve shows the corresponding measurement points of sample C.

[0145] The exposure values ​​in Table 12 show that all samples achieve a high diffraction efficiency of over 80% at a layer thickness of over 100 µm. The exposure values ​​of the photopolymerizable compositions B and C according to the invention even reach a higher value than the comparison mixture A.

[0146] The haze values ​​of the UV exposure samples D, E, and F were measured using a hazemeter (haze-gard i from BYK) with a 4 mm aperture diaphragm according to the ASTM D 1003 standard method. The tabulated values ​​(Table 13) show that different turbidity levels can be achieved by varying the exposure intensities. At a layer thickness of approximately 0.9 mm, the difference can exceed 70%. The two measurements of the reference sample D show that the exposure temperature also has an influence. In contrast to the compositions E and F according to the invention, the liquid reference mixture D is not clear at 21°C. production

[0147] Figure 1 shows the schematic structure of a compact roll-to-roll machine for the production of holographic contact copies from the claimed photopolymerizable composition. Reference symbols in Figure 1:

[0148] 1 Storage container 2 Filter and degasser 3 Dosing unit 4 Carrier film 5 Photopolymer (photopolymerizable composition) 6 Carrier film with hologram 7 Film unwinding 8 Laser light 9 Master 10 UV light 11 Film winding

Claims

1. A photopolymerisable composition curable by UV / VIS irradiation consisting of: a) 25 to 74.9% by weight of at least one monomer M comprising at least one ethylenically unsaturated group or of a monomer mixture comprising at least two monomers M comprising different ethylenically unsaturated groups, wherein monomer M is selected from the group consisting of (meth)acrylic acid butyl ester, (meth)acrylic acid phenyl ester, (meth)acrylic acid benzyl ester, (meth)acrylic acid isobornyl ester, (meth)acrylic acid cyclohexyl ester, (meth)acrylic acid 2-phenoxyethyl ester, (meth)acrylic acid 1H,1H,2H,2H-perfluorooctyl ester, 2,2,2-trifluoroethyl (meth)acrylate, heptafluoropropyl (meth)acrylate, 1,1,1,3,3,3-hexyfluoroisopropyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate), 2,2,3,3,4,4,4-heptafluorobutyl (meth)acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl (meth)acrylate, acrylic acid N,N-diethylaminoethyl ester, acrylic acid ethoxyethoxyethyl ester, acrylic acid 2-(p-chlorophe-noxy)ethyl ester, p-chlorophenyl acrylate, 2-phenylethyl (meth)acrylate, pentachlorophenyl acrylate, phenyl acrylate, p-chlorostyrene, n-vinylcarbazole, 1-vinyl-2-pyrrolidone, 2-chlorostyrene, 2-bromostyrene, methoxystyrene, phenol ethoxylate acrylate, 2-(p-chlorophenoxy)ethyl acrylate, hydroquinone monomethacrylate, and 2-[β-(N-carbazolyl)pro-pionyloxy]ethyl acrylate, and also contains bisphenol A diacrylate in an amount exceeding 25% by weight, based on the total weight of component a), b) 25 to 74.9% by weight of an aliphatic urethane acrylate or a mixture of different aliphatic urethane acrylates, c) 0.1 to 10% by weight of a photoinitiator which activates the polymerisation of the monomers and urethane acrylates upon exposure to actinic radiation; d) 0.01 to 20% by weight of additives; wherein the photopolymerisable composition is liquid at a standard pressure in the range of 15°C to 150°C.

2. The photopolymerisable composition according to claim 1, wherein the difference between the refractive indices of component a) and component b) at 20°C is at least 0.02.

3. The photopolymerisable composition according to claim 1 or 2, wherein the photoinitiator contains a dye and as co-initiator a borate salt.

4. The photopolymerisable composition according to any one of claims 1 to 3, wherein the co-initiator is selected from the group consisting of tetrabutylammonium tetrahexylborate, tetrabutylammonium triphenylhexylborate, tetrabutylammonium tris-(3-fluorophenyl)-hexylborate and tetrabutylammonium tris-(3-chloro-4-methylphenyl)-hexylborate or mixtures thereof.

5. The photopolymerisable composition according to any one of claims 1 to 4, wherein the viscosity of the photopolymerisable composition at 20°C is at least 2000mPa·s.

6. The photopolymerisable composition according to any one of claims 1 to 5, wherein component b) is an aliphatic urethanediacrylate resin or a difunctional aliphatic urethanediacrylate resin.

7. An element comprising a component obtainable by exposure of the photopolymerisable composition according to any one of claims 1 to 6 to UV / VIS radiation, preferably actinic UV / VIS radiation.

8. The element of claim 7, comprising a component having transparent and / or translucent regions.

9. The element according to claim 7 or 8, comprising a hologram obtainable by exposing the photopolymerisable composition according to any one of claims 1 to 6 to modulated radiation carrying holographic information.

10. Use of the element according to any one of claims 7 to 9, as a film, lens, grating, prism, mirror, beam splitter, diffuser, surface relief, optical switch or sensor.

11. Use of the element according to any one of claims 7 to 9 for a head-up display, a laminated glass panes, data glasses, a light guidance system, a spectrometer, a detection system, a security element or a label.

12. A process for the preparation of an element according to any one of claims 7 to 9 or the photopolymerisable composition according to any one of claims 1 to 6 in which the element or composition is subjected to a temperature of more than 100°C and a pressure of more than 2 bar.

13. A method of forming a light stable hologram in a photopolymerisable layer on a substrate surface or copy master, comprising exposing a layer of a photopolymerisable composition according to any one of claims 1 to 6 to modulated radiation carrying holographic information.

14. A process in which the photopolymerisable composition of any one of claims 1 to 6 is applied and exposed within one minute.