IMPROVED FADING

Description

[0001] The present invention relates to UV / VIS photopolymerizable compositions and elements produced therefrom, as well as their use. In particular, it relates to recording materials for optical elements with refractive index modulation, especially holograms.

[0002] In order for photopolymerizable compositions to be cured with visible light, they need a suitable photoinitiator system that absorbs the energy of the light, forms radicals and initiates the chain reaction of radical polymerization.

[0003] Such systems are known and are described, for example, in the application DE 69032682 T2 by DuPont, WO 2010091795 A1 by Bayer and in the EP 1779196 B1 by Xetos.

[0004] They use a dye as a sensitizer and a borate salt as a co-initiator. The color determines which light the system is sensitive to. Fluorescent dyes with the complementary color of the exposure wavelength are preferred to effectively absorb the light energy. For example, a magenta dye is used for green light, a blue dye for red, and a yellow dye for blue. Combinations are also possible for exposure to different wavelengths.

[0005] To achieve advantageously high light sensitivity, sufficient and distinct coloration of the photopolymerizable composition is necessary. However, for most applications of the exposed elements, a clear, transparent, and colorless layer is desirable. It is advantageous that these dyes are not lightfast and fade to a greater or lesser extent under UV light. However, this can take some time and high irradiance levels, depending on the dye, and thus a clearly perceptible residual coloration usually remains after UV curing, which takes place after laser exposure. Description of the invention

[0006] The present invention therefore aims to provide a system that bleaches faster and more effectively under UV light, without any loss of quality or additional work steps.

[0007] The object is achieved according to the invention by a photopolymerizable composition that can be cured by UV / VIS irradiation, comprising: a) 80 to 99.8 wt% of a radically curable monomer-containing mixture, b) 0.1 to 10 wt% of a photoinitiator system, and c) 0.1 to 10 wt% of a bleaching agent, wherein the total amount of a), b) and c) is 100 wt% and wherein the bleaching agent is effective under actinic irradiation, wherein component c) contains photoinitiators and the photoinitiators used in component c) generate benzoyl and alcohol radicals under the influence of actinic radiation and liquid photoinitiators at room temperature are used which can simultaneously serve as solvents for dyes.

[0008] Further preferred embodiments are defined in the dependent claims.

[0009] Actinity (actinic radiation) refers to the photochemical effectiveness of electromagnetic radiation of different wavelengths.

[0010] 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.

[0011] "Effective under actinic irradiation" can, in the context of the present invention, mean that a brightening occurs.

[0012] Preferably, the photopolymerizable composition according to the invention is used for the production of elements with a refractive index modulation, in particular holograms. These elements are generally produced by applying spatially or interferometrically modulated radiation to a layer of the photopolymerizable composition applied to a support substrate or a template. Suitable support substrates for the production of the elements according to the invention include glass, plastic (in particular PET, PP, PMMA, polycarbonate, or cellulose di- or triacetate), or paper. During exposure, the photopolymerizable composition can, for example, be located between two glass plates.

[0013] A preferred element is one containing a component obtainable by the action of UV / VIS radiation, preferably actinic UV / VIS radiation, on the photopolymerizable composition according to the invention.

[0014] Particularly preferred is an element comprising a hologram obtainable by the action of spatially or interferometrically modulated radiation on the photopolymerizable composition according to the invention.

[0015] Particularly preferred is an element according to the invention comprising a hologram that is obtainable in this way and is bleached by UV radiation.

[0016] Preferably, a manufacturing process is used which bleaches the element again with UV light after UV / VIS exposure.

[0017] Preferably, the element is used as a film, lens, grating, prism, mirror, beam splitter, diffuser, surface relief, optical switch, or sensor. It is particularly preferably used for a head-up display, a laminated glass pane, smart glasses, a light guidance system, a spectrometer, a detection system, a security element, or a label.

[0018] Another object of the invention is a method for forming a light-resistant hologram in a photopolymerizable layer on a substrate surface or a copy template, comprising the action of a modulated radiation carrying holographic information on a layer of the photopolymerizable composition according to the invention. Bleach

[0019] Surprisingly, it was found that the decay products of certain photoinitiators produced during actinic irradiation contribute to better and faster bleaching of the dyes.

[0020] These are photoinitiators structured as follows. An arylketone compound, represented by the following general formula (1), wherein Rx and Ry are the same or different and represent a straight or branched alkyl group having 1 to 8 carbon atoms and optionally substituted with a hydroxyl group, a cycloalkyl group having 1 to 8 carbon atoms and optionally substituted with a hydroxyl group, an alkoxy group having 1 to 8 carbon atoms and optionally substituted with a hydroxyl group, an alkoxycarbonyl group (whose alkoxy group has 1 to 8 carbon atoms) and optionally substituted with a hydroxyl group, a carbamoyl group, optionally substituted with a phosphate group, a phosphoryl group, optionally substituted by an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 8 carbon atoms, an acyl group or a condensed acyl group, optionally substituted with a hydroxyl group, or a group represented by formula (2); wherein in formula (2) R 1z< to R 5z< are the same or different and represent a hydrogen atom, an alkyl group with 1 to 8 carbon atoms, an alkenyl group with 2 to 8 carbon atoms, an alkoxy group with 1 to 8 carbon atoms, an alkyl group with 1 to 8 carbon atoms and substituted with halogen atoms, an alkoxy group with 1 to 8 carbon atoms and substituted with halogen atoms, a halogen atom, a hydroxyl group, a nitro group, a cyano group, an amino group, wherein in formula (2) any two adjacent groups of R 1z< to R 5z< optionally bond together to form a fused ring selected from naphthalene ring, quinoline ring, isoquinoline ring, tetrahydronaphthalene ring, indane ring, tetrahydroquinoline ring and tetrahydroisoquinoline ring together with the benzene ring to which they bond, and the carbon atoms to which bind two adjacent groups from R 1z< to R 5z<,are optionally substituted with 1 to 4 of the same or different substituents, selected from an alkyl group with 1 to 8 carbon atoms, a cycloalkyl group with 3 to 8 carbon atoms, an alkenyl group with 2 to 8 carbon atoms, an alkoxy group with 1 to 8 carbon atoms and optionally substituted with halogen atoms, hydroxyl group, nitro group, cyano group, amino group, wherein at least one of Rx and Ry is represented by formula (2).

[0021] The following photoinitiators and reactions are preferred.

[0022] And especially preferred is 2-hydroxy-2-methyl-1-phenylpropanone.

[0023] The bleaching agent c) in the photopolymerizable composition comprises one or more of these photoinitiators or their decomposition products or a mixture of these components.

[0024] The proportion of suitable photoinitiators in the bleaching agent can be more than 50% by weight, preferably more than 90% by weight. Particularly preferably, the bleaching agent consists exclusively of one or more suitable photoinitiators.

[0025] The decomposition products are benzoyl derivatives and alcohols; particularly favored decomposition products are benzaldehyde and 2-propanol.

[0026] Preferably, component c) of the photopolymerizable composition according to the invention contains photoinitiators, wherein the photoinitiators used in component c) particularly preferably generate benzoyl and alcohol radicals under the influence of actinic radiation.

[0027] To obtain the desired decomposition products, a mixture of two photoinitiators can also be used, whereby under irradiation the first photoinitiator forms the benzoyl radical and the second photoinitiator forms the alcohol radical.

[0028] It is particularly preferred that the bleaching substances and the bleaching effect only arise through actinic irradiation. For these substances to be effective, a corresponding dosage is necessary, which may exceed the usual recommended amount for photoinitiators. A proportion of at least 1 wt% is preferred, and at least 3 wt% is particularly preferred.

[0029] Liquid photoinitiators are used at room temperature and can simultaneously serve as solvents for the dyes. Preferably, component c) can therefore be used as a component of a solvent for a dye concentrate.

[0030] Another object of the invention is therefore a method in which component c) of the photopolymerizing composition according to the invention is used as a solvent or as a component of a solvent for the dye.

[0031] Photoinitiators that yellow as little as possible under UV light are also preferred. Monomer-containing mixture

[0032] The radically curable, monomer-containing mixture contains ethylene-unsaturated monomers capable of radical addition polymerization. The proportion is preferably at least 5 wt.%, more preferably at least 40 wt.%, and particularly preferably at least 80 wt.%.

[0033] The monomer-containing mixture can also contain polymeric binders such as vinyl acetate (DE 69032682 T2), PMMA, or polyols in a proportion of less than 95%, preferably less than 60% by weight, and particularly preferably less than 20% by weight. Instead of being embedded in a polymeric binder, the monomers can also be embedded in a polyurethane matrix (WO 2008 / 125229 A1, WO 2012 / 062655 A2).

[0034] Plasticizers and additives such as leveling agents and deaerators, which improve film properties, may also be included. Other inert, non-crosslinking components, such as triglycerides (EP 1 779 196 B1), may also be present. The ingredients of the mixture are selected such that the photopolymerizable composition forms a solid layer, at the latest upon actinic irradiation. Preferably, the components of the monomer-containing mixture ensure that, upon suitable exposure of the photopolymerizable composition, refractive index differences of at least 0.005, preferably at least 0.01, and particularly preferably at least 0.02 can be generated. Refractive index modulations with a resolution of over 1000 lines / mm for recording holograms are particularly preferably achieved.

[0035] Preferably, the photopolymerizable composition according to the invention can form a refractive index modulation with an amplitude or Δn of at least 0.005.

[0036] The refractive index modulation Δn is calculated using the Coupled Wave Theory of Kogelnik (see; H. Kogelnik, The Bell System Technical Journal, Volume 48, November 1969, Number 9 page 2909 - page 2947) based on the measured diffraction efficiency (DW) η and the layer thickness d.

[0037] 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.

[0038] The diffraction efficiency can be measured with a spectrometer (e.g., CAS 140 B from Instrument Systems) at room temperature using transmitted light. This should be done with perpendicular illumination. Since the hologram only reflects the wavelength that satisfies the Bragg condition, a distinct absorption peak is visible in the spectral curve at this point.

[0039] 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

[0040] The layer thickness d can be measured with a digital micrometer screw gauge. The refractive index modulation is calculated from the two measurements as follows: Δn = λ π ⋅ d ⋅ arctanh η ,

[0041] The monomer-containing mixture forms essentially clear and transparent layers that can be solid at room temperature. Monomer-containing mixtures that are liquid in a temperature range of 20°C to 150°C are particularly preferred. The viscosity should be at least 2000 mPa s at 20°C, preferably 10000 mPa s, and most preferably at least 20000 mPa s.

[0042] 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).

[0043] Preferably, the monomer-containing mixture contains multifunctional monomers with at least two ethylene unsaturated groups. The monomer-containing mixture can consist exclusively of one or more difunctional or higher-functional monomers; that is, the composition can be free of monofunctional ethylene unsaturated monomers. Preferably, the content of monomers with at least two ethylene unsaturated groups in component c) of the composition according to the invention is more than 10 wt.% and particularly preferably more than 30 wt.%.

[0044] 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.

[0045] Preferred monomers with at least two ethylene-unsaturated groups are ethoxylated bisphenol-A diacrylates, in particular compounds of the following formula wherein with n, m = 0-12, preferably 1-12; o = 0, 1; and Ar a mono- or polynuclear substituted or unsubstituted aromatic or heterocyclic aromatic residue and R 1 is an H, methyl or ethyl.

[0046] One particularly preferred monomer is the compound with the following structural formula:

[0047] Preferably, the viscosity of the monomer or monomer mixture at room temperature is at least 900 mPa·s. Photoinitiator system

[0048] The photoinitiator system, which activates the polymerization of the monomers upon exposure to actinic radiation, consists of a photoinitiator or a co-photoinitiator and a dye. Preferably, it contains all three components. The photoinitiator differs from the photoinitiator that may be used in the bleaching agent. Particularly preferably, the photoinitiator system or component b) contains only the co-photoinitiator and the dye. The terms "co-photoinitiator" and "co-photoinitiator" are used interchangeably within the scope of the present invention.

[0049] The dye acts as a sensitizer, absorbing the energy of radiation from the near-UV, visible or near-infrared range and initiating the radical formation reaction with the help of the co-photoinitiator. dye

[0050] The dye serves as a sensitizer for the co-photoinitiator. Suitable for this purpose are, for example, methylene blue and the sensitizers 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-inden-1-one; and Safranin O, i.e., 3,7-diamino-2,8-dimethyl-5-phenylphenazinium chloride.

[0051] Preferably, the dye in the photopolymerizable composition according to the invention is a fluorescent dye, which can consist, for example, of a cationic dye and an anion. The cationic dye can be represented by the formula F+<.

[0052] Therefore, a cationic dye of the formula F+ is preferably understood to be one of the following formulas: wherein X1< represents O, S, NR6< or CR6< aR6b<, X2< represents N or CR5<, R5< represents hydrogen, cyano, C1- to C4-alkyl, C4- to C7-cycloalkyl, a C6- to C10-aryl possibly substituted by C1- to C4-alkoxycarbonyl or NR7< R8<, a heterocyclic residue or C6- to C10-aryl substituted with a carboxyl group, R6< represents hydrogen, C1- to C16-alkyl, C4- to C7-cycloalkyl, C7- to C16-aralkyl, C6- to C10-aryl or a heterocyclic residue, R6a< and R6b< independently represent methyl, ethyl or together a -CH2-CH 2-CH2- or -CH2-CH2-CH2-CH2-bridge or for C6- to C10-aryl substituted with a carboxyl group, until R4<, R7< and R8< independently represent hydrogen, C1- to C16-alkyl, C4- to C7-cycloalkyl, C7- to C16-aralkyl, C6- to C10-aryl or a heterocyclic residue, or NR1< R2< ,NR 7< R 4< and NR 7< R 8< independently represent a five- or six-membered saturated ring linked via N, which may additionally contain an N or O and / or be substituted by nonionic groups, or until R 4< , R 7< and R 8< independently form a two- or three-membered bridge with a C atom of the benzene ring adjacent to the N atom, which may contain an O or N and / or be substituted by nonionic groups, R 9< , R 9a< , R 9b< , R 10< , R 10a< and R 10b< independently represent hydrogen, halogen or C 1 to C 4 alkyl, , wherein R 15< represents hydrogen, halogen, C 1 to C 4 alkyl, C 1 to C 4 alkoxy or NR 18< R 19<, R 11< to R 14<, R 18< and R 19< independently represent hydrogen, C 1 to C 16 alkyl, C 4 to C 7 cycloalkyl, C 7 to C 16 aralkyl, C 6 to C 10 aryl or a heterocyclic residue, or NR 11< R 12<, NR 13< R 14< and NR 18< R 19< independently represent a five- or six-membered saturated ring linked via N, which may additionally contain an N or O and / or may be substituted by nonionic residues, or R 12< ; R 17b< , R 13< ; R 17c< and R 18< ;R 17a< independently form a two- or three-membered bridge which may contain an O or N and / or may be substituted by nonionic groups, R 16< stands for hydrogen, chlorine, methyl, methoxycarbonyl or ethoxycarbonyl, R 16a< stands for hydrogen, chlorine or methyl, R 17a<, R 17b< and R 17c< independently stand for hydrogen, chlorine, methyl or methoxy. ;

[0053] Non-ionic residues are C1- to C4-alkyl, C1- to C4-alkoxy, halogen, cyano, nitro, C1- to C4-alkoxycarbonyl, C1- to C4-alkylthio, C1- to C4-alkanoylamino, benzoylamino, mono- or di-C1- to C4-alkylamino.

[0054] Alkyl, alkoxy, cycloalkyl, aryl, and heterocyclic residues may optionally bear further residues such as alkyl, halogen, nitro, cyano, CO-NH₂, alkoxy, trialkylsilyl, trialkylsiloxy, or phenyl; the alkyl and alkoxy residues may be straight-chain or branched; the alkyl residues may be partially or perhalogenated; the alkyl and alkoxy residues may be ethoxylated, propoxylated, or silylated; adjacent alkyl and / or alkoxy residues on aryl or heterocyclic residues may jointly form a three- or four-membered bridge; and the heterocyclic residues may be benzannelated and / or quaternized.

[0055] Halogens are understood to be fluorine, chlorine, bromine or iodine, preferably fluorine, chlorine or bromine.

[0056] Examples of substituted alkyl groups are trifluoromethyl, chloroethyl, cyanomethyl, cyanoethyl, and methoxyethyl. Examples of branched alkyl groups are isopropyl, tert-butyl, 2-butyl, and neopentyl. Examples of alkoxy groups are methoxy, ethoxy, and methoxyethoxy.

[0057] Preferred optionally substituted C1 to C4 alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, iso-butyl, tert-butyl, perfluorinated methyl, perfluorinated ethyl, 2,2-trifluoroethyl, 3,3,3-trifluoroethyl, perfluorobutyl, cyanoethyl, methoxyethyl, chloroethyl.

[0058] Preferred aralkyls include, for example, benzyl, phenethyl or phenylpropyl.

[0059] Examples of C6 to C10 aryl groups are phenyl and naphthyl. Examples of substituted aryl groups are tolyl, chlorophenyl, dichlorophenyl, methoxyphenyl, nitrophenyl, cyanophenyl, dimethylaminophenyl, and diethylaminophenyl.

[0060] Examples of heterotary residues, especially five- or six-membered heterocyclic residues, are indolyl, pyridyl, quinolyl, and benzthiazolyl. Examples of substituted heterocyclic residues are 1,2-dimethylindol-3-yl and 1-methyl-2-phenylindol-3-yl.

[0061] Anions for the cationic dyes of the formula F+< can be, for example, anions of the halogens, sulfates, carbonates or nitrates.

[0062] Particularly suitable cationic dyes are malachite green, methylene blue, safranin O, and rhodamines of formula III. wherein R a , R b , Re , R d , Re , R f and R g each represent H or an alkyl group, and X -< represents chloride ion, trifluoromethanesulfonate, naphthalene disulfonate, para-toluenesulfonate, hexafluorophosphate, perchlorate, meta-nitrobenzenesulfonate or meta-aminobenzenesulfonate, e.g. Rhodamine B, Rhodamine 6 G or Violamin R, also Sulforhodamine B or Sulforhodamine G, as listed below.

[0063] Other suitable dyes are fluorones, such as those described by Neckers et al. in J. Polym. Sci., Part A, Poly. Chem., 1995, 33, 1691-1703. Of particular interest is

[0064] Examples of other suitable dyes are cyanines of formula IV. where R IV = alkyl; n 1 ≤ 0, 1, 2, 3 or 4 and Y 1 = CH=CH, N-CH 3 , C(CH 3 ) 2 , O, S or Se. Cyanines are preferred, where Y 1 in formula IV is C(CH 3 ) 2 or S.

[0065] Preferably, the dye in the photopolymerizable composition according to the invention is selected from the group consisting of acriflavins, diaminoacridines, rhodamine B, safranin-O, diethyl safranin and methylene blue. Photoinitiator

[0066] Preferably, the photoinitiator system or component b) of the photopolymerizable composition contains a photoinitiator.

[0067] Preferably, the photoinitiator in the photopolymerizable composition according to the invention can form radicals when irradiated with a wavelength between 100 nm and 480 nm, preferably between 150 nm and 460 nm and particularly preferably between 200 nm and 380 nm.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.% are 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

[0072] The photoinitiators mentioned above can be used alone or in combination.

[0073] Preferably, the photoinitiator is liquid and / or selected from the group consisting of 1,2-octanedione-1-[4-(phenylthio)phenyl]-2-(O-benzoyl oxime), (1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone-O-acetyl oxime, methyl benzoyl formate), 2,4,6-trimethylbenzoyl diphenyl phosphine oxide, ethyl (2,4,6-trimethylbenzoyl) phenyl phosphinate), 2-hydroxy-2-methyl-1-phenylpropanone, a mixture of 2-hydroxy-2-methyl-1-phenylpropanone (80%) and 1-hydroxycyclohexyl phenyl ketone (20%), 1-hydroxycyclohexyl phenyl ketone, bis(2,4,6-trimethylbenzoyl) phenyl phosphine oxide, a mixture of 2-Hydroxy-2-methyl-1-phenylpropanone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate), and 4,4'-dimethyl-diphenyl-iodonium hexafluorophosphate.

[0074] Preferably, the photoinitiator system or component b) of the photopolymerizable composition contains a co-photoinitiator. Co-photo initiator

[0075] Preferably, the co-photoinitiator used in the composition according to the invention comprises a compound of formula (I) wherein R 1c means C 1-C 20 alkyl, C 3-C 12 cycloalkyl, C 2-C 8 alkenyl, phenyl-C 1-C 6 alkyl or naphtyl-C 1-C 3 alkyl, wherein the C 1-C 20 alkyl, C 3-C 12 cycloalkyl, C 2-C 8 alkenyl, phenyl-C 1-C 6 alkyl or naphtyl-C 1-C 3 alkyl residues may be interrupted by one or more groups O, S(O) p or NR 5c, or wherein the C 1-C 20 alkyl, C 3-C 12 cycloalkyl, C 2-C 8 alkenyl, phenyl-C 1-C 6 alkyl or naphtyl-C 1-C 3 alkyl residues may be unsubstituted or interrupted by C 1-C 12 -alkyl, OR 6 , R 7c S(O) p , R 7c S(O) 2 O, NR 8c R 9c , SiR 10c R 11c R 12c , BR 13c R 14c or R 15c R 16c P(O) q , are substituted; R2c, R3c and R4c independently denote phenyl or biphenyl, where the residues are unsubstituted phenyl or biphenyl, or unsubstituted or substituted with OR6c, NR8c, R9c or halogen, C1-C12 alkyl, OR6c, R7c, S(O)p, R7c, S(O)2O, R8c, R9c, NS(O)2, NR8c, R9c, NR3c, R8c, CO. SiR 10c R 11c R 12c , BR 13c R 14c , Halogen, R 15c R 16c P(O) q , oder are substituted; R 5c means hydrogen, C 1 -C 12 alkyl, unsubstituted or one to five times substituted with C 1 -C 6 alkyl, C 1 -C 12 alkoxy or halogen phenyl-C 1 -C 6 alkyl or unsubstituted or one to five times substituted with C 1 -C 6 alkyl, C 1 -C 12 alkoxy or halogen; R 6c and R 7c represent unsubstituted or halogen-substituted C 1 -C 12 alkyl, unsubstituted or one- to five-fold C 1 -C 6 alkyl, C 1 -C 12 alkoxy or halogen-substituted phenyl-C 1 - C 6 alkyl, or unsubstituted or one- to five-fold C 1 -C 6 alkyl, C 1 -C 12 alkoxy or halogen-substituted phenyl;R8c, R9c, R10c, R11c, R12c, R13c, R14c, R15c and R16c independently represent C1-C12 alkyl, C3-C12 cycloalkyl, unsubstituted or one- to five-fold substituted with C1-C6 alkyl, C1-C12 alkoxy or halogen phenyl-C1-C6 alkyl or unsubstituted or one- to five-fold substituted with C1-C6 alkyl, C1-C12 alkoxy or halogen phenyl, or R8c and R9c together with the N atom to which they are bonded form a 6-membered aliphatic ring, which may also contain oxygen or sulfur as a further heteroatom; R17c, R18c, R19c and R20e independently denote hydrogen, unsubstituted or C1-C12-alkoxy-substituted C1-C12-alkyl, phenyl or phenyl-C1-C6-alkyl, wherein the phenyl or phenyl-C1-C6-alkyl residues are unsubstituted or one to five times substituted with C1-C6-alkyl, C1-C12-alkoxy or halogen; p represents a number from 0 to 2;r represents a number from 0 to 5; R 21c represents hydrogen or C 1-C 12 alkyl; R 22c, R 22a, R 23c and R 24c independently represent hydrogen, unsubstituted C 1-C 12 alkyl or C 1-C 12 alkyl substituted with C 1-C 12 alkoxy, OH or halogen, or unsubstituted phenyl or C 1-C 12 alkyl substituted with C 1-C 12 alkoxy, OH or halogen; q represents 0 or 1; and G represents a residue that can form positive ions.

[0076] Preferably, the co-photoinitiator in the photopolymerizing composition 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.

[0077] A particularly preferred co-photoinitiator with the structural formula aa, which was developed under the name "CGI 7460" by Ciba Specialty Chemicals Inc. and is now available from BASF AG under the name SEC LCA 1460, is described as follows: Examples

[0078] The following dyes were used for the bleaching experiments. Dyes

[0079] dye CAS molecule Saffron-O 477-73-6 Diethyl saffranine 4569-86-3 Rhodamin-B 81-88-9 Methylene blue 61-73-4 Acriflavine 8048-52-0 UV initiators

[0080] These UV initiators were compared with each other in the bleaching tests. Liquid UV initiators

[0081] Brand name CAS molecule Omnirad MBF (IGM) 15206-55-0 Omnirad 1173 (IGM) 7473-98-5 Powdered UV initiators

[0082] Brand name CAS molecule Omnirad 184 (IGM) 947-19-3 Omnirad 819 (IGM) 162881-26-7 Omnirad 659 (IGM) 106797-53-9 Omnirad TPO (IGM) 75980-60-8 OXE-01 (BASF) 253585-83-0 solvent

[0083] The following solvents were also used in the bleaching experiments for the dyes and the powdered UV photoinitiators. A low-molecular-weight polycaprolactone (PCL-triol) was used as a solvent that had no effect on bleaching. Designation CAS molecule Benzaldehyd 100-52-7 2-Propanol 7473-98-5 Polycaprolactone triol, (PCL-triol), M n ~300 37625-56-2 Bleaching experiments

[0084] To test the suitability of the photoinitiators and solvents for improved dye bleaching, saturated dye solutions were prepared. One to two spoon spatula tips (approx. 0.1 to 0.2 g) of dye were added to small 1.5 ml cuvettes. Two to four spoon spatula tips (approx. 0.2 to 0.4 g) of powdered UV photoinitiators were also added, and the mixtures were then filled to the brim with polycaprolactone triol (PCL-triol). For the mixtures with the liquid UV photoinitiators and solvents, it was sufficient to completely fill the cuvettes. The pure PCL-triol dye mixtures served as a reference, as no improved bleaching was observed in these solutions.

[0085] These mixtures were thoroughly blended and stored in a 120°C oven for one to two hours. The samples were then centrifuged to allow the undissolved components to settle. Small amounts of the liquid at the top were pipette-loaded and placed as drops onto a microscope slide. A drop of the reference solution was placed to the right and left of these drops for comparison. The entire assembly was then covered with a second microscope slide.

[0086] These samples could now be measured and bleached. For bleaching, the samples were placed under a UV bridge with an arc length of 70 mm and a power of 120 W / cm² for 30 seconds. Before and after bleaching, the samples were visually inspected and the spectral absorption curves were measured with a spectrometer.

[0087] All tests showed that the dyes bleached best in the Omnirad 1173 and benzaldehyde mixtures. The addition of 2-propanol to the other UV photoinitiator mixtures partially improved their bleaching effect. Photopolymerizable compositions

[0088] As an example of the effect according to the invention, two photopolymerizable compositions with the Safranin-O dye were prepared. For this purpose, two dye concentrates and a monomer-containing mixture were first mixed. Table 1 Dye concentrates FK1 Quantity [g] Crowd[%] Designation CAS 14,7 73,5% PCL-triol, M n ~300 37625-56-2 5,0 25,0% OXE-01 253585-83-0 0,3 1,5% Saffron-O 477-73-6 20,00 100,00% Table 2 Dye concentrate FK2 Quantity [g] Crowd[%] Designation CAS 9,85 49,25% PCL-triol, M n ~300 37625-56-2 9,85 49,25% Omnirad 1173 7473-98-5 0,30 1,5% Saffron-O 477-73-6 20 100,00% Table 3 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%

[0089] For the holographic exposures, two photopolymerizable compositions were prepared from the monomer-containing mixture listed above and the two dye concentrates. The mixture containing dye concentrate FK1 was used as a comparison example. Table 4 Photopolymerizable composition A Quantity [g] Crowd[%] component name 5 97,09% MM1 Monomer-containing mixture 0,15 2,91% FK1 Dye concentrate 5,15 100,00% Table 5 Photopolymerizable Composition B Quantity [g] Crowd[%] component name 5 97,09% MM1 Monomer-containing mixture 0,15 2,91% FK2 Dye concentrate 5,15 100,00% preparation

[0090] First, the color concentrates and the monomer-containing mixture are prepared. The respective components are added one after the other to a beaker containing a magnetic stirrer. The beaker is placed on a scale to ensure the correct amount of liquid is added. The mixture is then heated to 120°C on a heated magnetic stirrer and stirred. The powdered substances are measured using weighing dishes and added to the mixture while stirring. The mixture is stirred for approximately one hour at 120°C before the solution is filtered and bottled.

[0091] The photopolymerizable compositions are formed from the dye concentrates and the monomer-containing mixture by mixing (for example by shaking with a speed mixer or stirring with a stirring stick). Exposures

[0092] Table 6 Laser exposures material Peak [nm] BWG[%] Thickness [µm] Transparency[%] A 536 86 % 90 60 B 536 92 % 77 75

[0093] Photopolymerizable compositions A and B were exposed to a laser with a wavelength of 532 nm at temperatures ranging from 20°C to 21°C. The compositions were stored in an oven at 80°C and exposed shortly after application. Following laser exposure and rapid UV curing with a UV flash, the spectral absorption curves were measured using a spectrometer. The compositions were then post-cured under UV light for 30 seconds and bleached. The different bleaching rates of the two samples were clearly visible and confirmed by a subsequent measurement of the spectral absorption. The diffraction efficiency (DEF) was also determined from the spectral absorption curve. Transparency was measured using a hazemeter, and layer thickness was measured with a digital micrometer. Exposure setup

[0094] The laser beam with a measured power of 4.0 W was horizontally widened using a Po-Iygon scanner and focused by a cylindrical lens to cover an exposure width of 23 cm. Figure 1 shows the schematic exposure setup. Reference symbols in Figure 1:

[0095] 1Laser 532nm 2Mirror 3Polygon scanner 4Cylinder lens 5Scan beam 6Scanner mirror

[0096] 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.

[0097] The Figure 2 shows the path of the rays. Reference symbols in Figure 2:

[0098] 1 Scan beam 532nm 2 Scanner mirror 3 Exposure direction 4 Exposure angle, 22° 5 Substrate, glass or film 6 Photopolymer (photopolymerizable composition) 7 Master, mirror sheet

[0099] 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 photopolymerizable composition in the form of a refractive index modulation, resulting in a so-called Lippmann-Bragg hologram.

[0100] 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, 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 photopolymerizable composition is cured with UV light. A UV flash with an intensity of 3000 WS was used for the first curing step. This is sufficient to subsequently remove the hologram and the substrate from the plate. To ensure adhesion to the glass, it should be pretreated with a primer.

[0101] For the final hardening and bleaching of the sample, a UV bridge with an arc length of 70 mm and a power of 120 W / cm² was used. The light source was a mercury vapor bulb. The exposure / bleaching time was 30 seconds. Measurement setup

[0102] 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.

[0103] 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

[0104] Figure 3 The measurement curve shows the corresponding measurement points of sample B.

[0105] The tabulated exposure values ​​(Table 6) show that both samples achieve a high diffraction efficiency of over 80%, but sample B is significantly more transparent. Figure 4 shows the spectral absorption curves of the two photopolymerized compositions A and B before and after 30s of bleaching under the UV bridge.

[0106] The transparency values ​​were measured with a hazemeter (haze-gard i from BYK) using a 4mm aperture diaphragm according to the ASTM D 1003 standard procedure.

Claims

1. Photopolymerisable composition curable by UV / VIS irradiation, comprising: a) 80 to 99.8% by weight of a radically curable monomer-containing mixture, b) 0.1 to 10% by weight of a photoinitiator system, and c) 0.1 to 10% by weight of a bleaching agent, wherein the total amount of a), b) and c) is 100% by weight and wherein the bleaching agent is effective under actinic irradiation, wherein component c) contains photoinitiators and the photoinitiators used in component c) generate benzoyl and alcohol radicals under the action of actinic radiation and photoinitiators which are liquid at room temperature and can simultaneously serve as solvents for dyes are used.

2. Photopolymerisable composition according to claim 1, wherein the photoinitiator system contains a dye and a co-initiator.

3. Photopolymerisable composition according to claim 1 or 2, 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.

4. Photopolymerisable composition according to any one of claims 1 to 3, wherein the dye is selected from the group consisting of acriflavines, diaminoacridines, rhodamine B, safranin O, diethylsafranin and methylene blue.

5. Photopolymerisable composition according to any one of claims 1 to 4, wherein bleaching substances are formed from component c) by the action of actinic radiation.

6. Photopolymerisable composition according to any one of claims 1 to 5, wherein the photopolymerisable composition can form a refractive index modulation with an amplitude or Δn of at least 0.005.

7. Element containing a component which is obtainable by the action of UV / VIS radiation, preferably actinic UV / VIS radiation, on the photopolymerisable composition according to any one of claims 1 to 6.

8. Element according to claim 7, comprising a hologram obtainable by exposing the photopolymerisable composition according to any one of claims 1 to 6 to spatially or interferometrically modulated radiation.

9. Use of the element according to any one of claims 7 and 8 as a film, lens, grating, prism, mirror, beam splitter, diffuser, surface relief, optical switch or sensor.

10. Use of the element according to any one of claims 7 and 8 for a head-up display, a laminated glass pane, data glasses, a light guide system, a spectrometer, a detection system, a security element or a label.

11. Method for producing an element according to any one of claims 7 and 8, in which the element is post-cured by UV light.

12. Method in which component c) of the photopolymerising composition according to any one of claims 1 to 6 is used as a solvent or as a component of a solvent for the dye.

13. Method for forming a light-resistant hologram in a photopolymerisable layer on a substrate surface or a copy template, comprising exposing a layer of a photopolymerisable composition according to any one of claims 1 to 6 to modulated radiation carrying holographic information.