MOISTURE-STABLE HOLOGRAPHIC MEDIA

Abstract

The invention relates to novel compounds which are especially suitable for use as writing monomers in holographic media. The invention further provides a photopolymer and a holographic medium comprising the inventive compounds, and an optical display, a security document and a holographic optical element comprising an inventive holographic medium.

Claims

1-15. (canceled)

16. A photopolymer comprising matrix polymers, writing monomers and photoinitiators, wherein the writing monomers comprise compound of formula (I) ##STR00009## in which R.sup.1 is an aliphatic hydrocarbyl radical having 1-8 carbon atoms; R.sup.2 is hydrogen or methyl; Ar is an aromatic radical of the formula (II) ##STR00010## in which R.sup.3 are independently radicals selected from the group of substituted or unsubstituted phenyl, substituted or unsubstituted phenylthiyl, branched or unbranched alkyl, branched or unbranched alkylthiyl, halogen, where at least one of the R.sup.3 radicals is a radical selected from the group of substituted or unsubstituted phenyl, substituted or unsubstituted phenylthiyl; n=1 or 5; or Ar is an aromatic radical of the formula (III) ##STR00011## in which R.sup.3 are independently radicals selected from the group of substituted or unsubstituted phenyl, substituted or unsubstituted phenylthiyl, branched or unbranched alkyl, branched or unbranched alkylthiyl, halogen, where at least one of the R.sup.3 radicals is a radical selected from the group of substituted or unsubstituted phenyl, substituted or unsubstituted phenylthiyl; o=1 or 3; p=1 to 4, wherein the compound of the formula (I) has only one radiation-curing group.

17. The photopolymer according to claim 16, wherein at least one of the R.sup.3 radicals is selected from the group of phenyl, phenylthiyl, phenylthiylphenylthiyl, alkylphenyl, alkylphenylthiyl, biphenyl.

18. The photopolymer according to claim 16, wherein Ar is a radical of the formula (II).

19. The photopolymer according to claim 16, wherein o=1.

20. The photopolymer according to claim 16, wherein R.sup.1 is a radical selected from the group of —CH.sub.2—CH.sub.2—, —CH.sub.2—CH.sub.2—CH.sub.2—, —CH.sub.2—CHCH.sub.3—, —CH.sub.2—CH.sub.2—CH.sub.2—CH.sub.2—.

21. The photopolymer according to claim 16, wherein the matrix polymers are crosslinked matrix polymers, preferably three-dimensionally crosslinked matrix polymers and most preferably are three-dimensionally crosslinked polyurethanes.

22. The photopolymer according to claim 16, wherein it comprises monomeric fluorourethanes.

23. A holographic medium comprising a photopolymer according to claim 16.

24. The holographic medium according to claim 23, wherein it is a film, preferably with a film thickness of 0.3 μm to 500 μm, more preferably with a film thickness of 0.5 μm to 200 μm and yet more preferably with a film thickness of 1 μm to 100 μm.

25. The holographic medium according to claim 23, wherein at least one hologram was recorded into the holographic medium.

26. An optical display comprising a holographic medium according to claim 23.

27. A security document comprising a holographic medium according to claim 23.

28. A holographic optical element comprising a holographic medium according to claim 23.

29. A compound of the formula (I′) ##STR00012## in which R.sup.1 is an aliphatic hydrocarbyl radical having 1-8 carbon atoms; R.sup.2 is hydrogen or methyl; Ar is an aromatic radical of the formula (II′) ##STR00013## in which R.sup.3′ are independently radicals selected from the group of unsubstituted phenyl, substituted or unsubstituted phenylthiyl, branched or unbranched alkyl, branched or unbranched alkylthiyl, halogen, where at least one of the R.sup.3′ radicals is a radical selected from the group of substituted or unsubstituted phenyl, substituted or unsubstituted phenylthiyl; n=1 to 5; or Ar is an aromatic radical of the formula (III) ##STR00014## in which R.sup.3 are independently radicals selected from the group of substituted or unsubstituted phenyl, substituted or unsubstituted phenylthiyl, branched or unbranched alkyl, branched or unbranched alkylthiyl, halogen, where at least one of the R.sup.3 radicals is a radical selected from the group of substituted or unsubstituted phenyl, substituted or unsubstituted phenylthiyl; o=1 to 3; p=1 to 4, wherein the compound of the formula (I′) has only one radiation-curing group.

30. A method comprising utilizing the compound of the formula (I) as writing monomer in photopolymers, holographic media and/or holographic optical elements.

Description

EXAMPLES

[0145] The invention will now be more particularly elucidated by means of examples.

[0146] The drawings show:

[0147] FIG. 1 the geometry of a holographic media tester (HMT) at λ=532 tun (DPSS laser=diode pumped solid state laser),

[0148] FIG. 2 the measured diffraction efficiency n as circles plotted against the angle detuning ΔΩ and the fit to the Kogelnik theory as a solid line. The figure shows Example 2.

[0149] FIG. 3 the measured diffraction efficiency η as circles plotted against the angle detuning ΔΩ and the fit to the Kogelnik theory as a solid line. The figure shows Example 4.

[0150] FIG. 4 a setup for writing of Denisyuk holograms.

METHODS OF MEASUREMENT

[0151] Determination of Viscosity:

[0152] Viscosity was determined with a Physica MCR 51 (from Anton Paar) viscometer. For this purpose, the sample was equilibrated and a ball was suspended (for low viscosities η<10 000 mPas: 23° C., ball diameter 25 mm (CP-25) and for high viscosities η>10 000 mPas: 50° C., ball diameter 60 mm (CP-60)). About 0.5-1 g of product was placed onto the plate, and the ball was allowed to drop down, such that the ball was fully wetted with product. Excess product was wiped off. The shear rate (about 500 1/s at lower viscosities and about 100 1/s at higher viscosities) was set automatically by the instrument. 20 measurements were made in each case and the mean was determined.

[0153] Isocyanate Content

[0154] Reported NCO values (isocyanate contents) were quantified to DIN EN ISO 11909.

[0155] The full conversion of NCO groups, i.e. the absence thereof, in a reaction mixture was detected by IR spectroscopy. Thus, complete conversion was assumed when no NCO band (2261 cm.sup.−1) was visible in the IR spectrum of the reaction mixture.

[0156] Measurement of the Holographic Properties of Diffraction Efficiency DE and Refractive Index Contrast Δn of the Holographic Media by Means of Twin-Beam Interference in a Reflection Arrangement.

[0157] A holographic test setup as shown in FIG. 1 was used to measure the diffraction efficiency (DE) of the media. The beam of a DPSS laser (emission wavelength 532 nm) was converted to a parallel homogeneous beam with the aid of the spatial filter (SF) and together with the collimation lens (CL). The final cross sections of the signal and reference beam are fixed by the iris diaphragms (I). The diameter of the iris diaphragm opening is 0.4 cm. The polarization-dependent beam splitters (PBS) split the laser beam into two coherent beams of identical polarization. By means of the λ/2 plates, the power of the reference beam was set to 0.87 mW and the power of the signal beam to 1.13 mW. The powers were determined using the semiconductor detectors (D) with the sample removed. The angle of incidence (α.sub.0) of the reference beam is −21.8°; the angle of incidence (β.sub.0) of the signal beam is 41.8°. The angles are measured proceeding from the sample normal to the beam direction. According to FIG. 1, therefore, α.sub.0 has a negative sign and β.sub.0 a positive sign. At the location of the sample (medium), the interference field of the two overlapping beams produced a pattern of light and dark strips perpendicular to the angle bisectors of the two beams incident on the sample (reflection hologram). The strip spacing A, also called grating period, in the medium is ˜225 nm (the refractive index of the medium assumed to be ˜1.504).

[0158] FIG. 1 shows the geometry of a holographic media tester (HMT) at λ=532 nm (DPSS laser): M=mirror, S=shutter, SF=spatial filter, CL=collimator lens, λ/2=λ/2 plate, PBS=polarization-sensitive beam splitter, D=detector, I=iris diaphragm, α.sub.0=−21.8°, β.sub.0=41.8° are the angles of incidence of the coherent beams measured outside the sample (outside the medium). RD=reference direction of turntable.

[0159] Holograms were recorded in the medium in the following manner: [0160] Both shutters (S) are opened for the exposure time t. [0161] Thereafter, with the shutters (S) closed, the medium is allowed 5 minutes for the diffusion of the as yet: unpolymerized writing monomers.

[0162] The written holograms were then read out in the following manner: The shutter of the signal beam remained closed. The shutter of the reference beam was opened. The iris diaphragm of the reference beam was closed to a diameter of <1 mm. This ensured that the beam was always completely within the previously recorded hologram for all angles of rotation (Ω) of the medium. The turntable, under computer control, swept over the angle range from Ω.sub.min to Ω.sub.max with an angle step width of 0.05°. Ω is measured from the sample normal to the reference direction of the turntable. The reference direction of the turntable is obtained when the angles of incidence of the reference beam and of the signal beam have the same absolute value on recording of the hologram, i.e. α.sub.0=−31.8° and β.sub.0=31.8°. In that case, Ω.sub.recording=0°. When α.sub.0=−21.8° and β.sub.0=41.8°, Ω.sub.recording is therefore 10° . In general, for the interference field in the course of recording of the hologram:

α.sub.0=θ.sub.0+Ω.sub.recording.

θ.sub.0 is the semiangle in the laboratory system outside the medium and, in the course of recording of the hologram:

[00001]${\theta }_0=\frac{{\alpha }_0-{\beta }_0}{2}.$

[0163] Thus, in this case, θ.sub.0=−31.8°. At each setting for the angle of rotation Ω, the powers of the beam transmitted in the zeroth order were measured by means of the corresponding detector D, and the powers of the beam diffracted in the first order by means of the detector D. The diffraction efficiency was calculated at each setting of angle Ω as the quotient of:

[00002]$\eta =\frac{P_D}{P_D+P_T}$

[0164] P.sub.D is the power in the detector for the diffracted beam and P.sub.T is the power in the detector for the transmitted beam.

[0165] By means of the process described above, the Bragg curve, which describes the diffraction efficiency η as a function of the angle of rotation Ω, for the recorded hologram, was measured and saved on a computer. In addition, the intensity transmitted into the zeroth order was also recorded against the angle of rotation Ω and saved on a computer.

[0166] The maximum diffraction efficiency (DE=η.sub.max) of the hologram, i.e. the peak value thereof, was determined at Ω.sub.reconstruction. In some cases, it was necessary for this purpose to change the position of the detector for the diffracted beam in order to determine this maximum value.

[0167] The refractive index contrast Δn and the thickness d of the photopolymer layer were now determined by means of coupled wave theory (see: H. Kogelnik, The Bell System Technical Journal, Volume 48, November 1969, Number 9 page 2909-page 2947) from the measured Bragg curve and the angle profile of the transmitted intensity. In this context, it should be noted that, because of the shrinkage in thickness which occurs as a result of the photopolymerization, the strip spacing A′ of the hologram and the orientation of the strips (slant) can differ from the strip spacing A of the interference pattern and the orientation thereof. Accordingly, the angle α.sub.0′ and the corresponding angle of the turntable Ω.sub.reconstruction at which maximum diffraction efficiency is achieved will also differ from α.sub.0 and from the corresponding Ω.sub.recording. This alters the Bragg condition. This alteration is taken into account in the evaluation process. The evaluation process is described hereinafter:

[0168] All geometric parameters which relate to the recorded hologram and not to the interference pattern are shown as parameters with primes.

[0169] For the Bragg curve η(Ω) of a reflection hologram, according to Kogelnik:

[00003]$\eta =\{\begin{array}{cc}\frac{1}{1-\frac{1-{\left(\xi /v\right)}^2}{{\sin }^2\left(\sqrt{{\xi }^2-v^2}\right)}},& \mathrm{for}.Math..Math.v^2-{\xi }^2<0\\ \frac{1}{1+\frac{1-{\left(\xi /v\right)}^2}{{\sinh }^2\left(\sqrt{v^2-{\xi }^2}\right)}},& \mathrm{for}.Math..Math.v^2-{\xi }^2\ge 0\end{array}.Math..Math.\mathrm{with}.Math.\text{:}.Math..Math.v=\frac{\pi .Math.\Delta .Math..Math.n.Math.d^{\prime }}{\lambda .Math.\sqrt{.Math.c_s.Math.c_r.Math.}}.Math..Math.\xi =-\frac{d^{\prime }}{2.Math.c_s}.Math.\mathrm{DP}.Math..Math.c_s=\cos \left({\vartheta }^{\prime }\right)-\cos \left({\psi }^{\prime }\right).Math.\frac{\lambda }{n.Math.{\Lambda }^{\prime }}.Math..Math.c_r=\cos \left({\vartheta }^{\prime }\right).Math..Math.\mathrm{DP}=\frac{\pi }{{\Lambda }^{\prime }}.Math.\left(2.Math.\cos \left({\psi }^{\prime }-{\vartheta }^{\prime }\right)-\frac{\lambda }{n.Math.{\Lambda }^{\prime }}\right).Math..Math.{\psi }^{\prime }=\frac{{\beta }^{\prime }+{\alpha }^{\prime }}{2}.Math..Math.{\Lambda }^{\prime }=\frac{\lambda }{2.Math.n.Math.\cos \left({\psi }^{\prime }-{\alpha }^{\prime }\right)}$

[0170] The following holds for the reading out (“reconstruction”) of the hologram similarly to the above explanation:

′.sub.0=θ.sub.0+Ω

sin(′.sub.0=n.Math.sin(′)

[0171] Under the Bragg condition, the “dephasing” DP=0. And it follows correspondingly that:

α′.sub.0=θ.sub.0+Ω.sub.reconstruction

sin(α′.sub.0)=n.Math.sin(α′)

[0172] The as yet unknown angle β′ can be determined from the comparison of the Bragg condition of the interference field in the course of recording of the hologram and the Bragg condition in the course of reconstruction of the hologram, assuming that only shrinkage in thickness takes place. It then follows that:

[00004]$\sin \left({\beta }^{\prime }\right)=\frac{1}{n}.Math.\left[\sin \left({\alpha }_0\right)+\sin \left({\beta }_0\right)-\sin \left({\theta }_0+{\Omega }_{\mathrm{reconstruction}}\right)\right]$

[0173] ν is the grating intensity, ξ is the detuning parameter and ψ′ is the orientation (slant) of the refractive index grating written. α′ and β′ correspond to the angles α.sub.0 and β.sub.0 of the interference field during the recording of the hologram, but measured in the medium and valid for the grating of the hologram (shrinkage in thickness). n is the average refractive index of the photopolymer and was set equal to 1.504. λ is the wavelength of the laser light in a vacuum.

[0174] The maximum diffraction efficiency (DE=η.sub.max), when ξ=0, is then calculated to be:

[00005]$\mathrm{DE}={\tanh }^2\left(v\right)={\tanh }^2\left(\frac{\pi .Math.\Delta .Math..Math.n.Math.d^{\prime }}{\lambda .Math.\sqrt{\cos \left({\alpha }^{\prime }\right).Math.\cos \left({\alpha }^{\prime }-2.Math.\psi \right)}}\right)$

[0175] FIGS. 2 and 3 show the measured transmitted power P.sub.T (right-hand y-axis) plotted as a lit solid line against the angle detuning ΔΩ; the measured diffraction efficiency η (left-hand y-axis) is plotted as filled circles against the angle detuning ΔΩ (to the extent allowed by the finite size of the detector), and the fitting to the Kogelnik theory as a broken line (left-hand y-axis).

[0176] The measured data for the diffraction efficiency, the theoretical Bragg curve and the transmitted intensity are, as shown in FIGS. 2 and 3, plotted against the centred angle of rotation ΔΩ=Ω.sub.reconstruction−Ω=α′.sub.0−′.sub.0, also called angle detuning.

[0177] Since DE is known, the shape of the theoretical Bragg curve, according to Kogelnik, is determined only by the thickness d′ of the photopolymer layer. Δn is corrected via DE for a given thickness d′ such that measurement and theory for DE are always in agreement. d′ is then adjusted until the angle positions of the first secondary minima of the theoretical Bragg curve correspond to the angle positions of the first secondary maxima of the transmitted intensity, and there is additionally agreement in the full width at half maximum (FWHM) for the theoretical Bragg curve and for the transmitted intensity.

[0178] Since the direction in which a reflection hologram also rotates when reconstructed by means of an Ω scan, but the detector for the diffracted light can cover only a finite angle range, the Bragg curve of broad holograms (small d′) is not fully covered in an Ω scan, but rather only the central region, given suitable detector positioning. Therefore, the shape of the transmitted intensity, which is complementary to the Bragg curve, is additionally employed for adjustment of the layer thickness d′.

[0179] FIGS. 2 and 3 show the plot of the Bragg curve η according to the coupled wave theory (broken line), the measured diffraction efficiency (filled circles) and the transmitted power (black solid line) against the angle detuning ΔΩ.

[0180] For a formulation, this procedure was repeated, possibly several times, for different exposure times t on different media, in order to find the mean energy dose of the incident laser beam in the course of recording of the hologram at which DE reaches the saturation value. The mean energy dose E is calculated as follows from the powers of the two component beams assigned to the angles α.sub.0 and β.sub.0 (reference beam where P.sub.r=0.87 mW and signal beam where P.sub.s=1.13 mW), the exposure time t and the diameter of the iris diaphragm (0.4 cm):

[00006]$E\left(\mathrm{mJ}.Math.\text{/}.Math.{\mathrm{cm}}^2\right)=\frac{2.Math.\left[P_r+P_s\right].Math.t\left(s\right)}{\pi .Math.{0.4}^2.Math..Math.\mathrm{cm}}$

[0181] The powers of the component beams were adjusted such that the same power density is attained in the medium at the angles α.sub.0 and β.sub.0 used.

[0182] Chemicals:

[0183] In each case, the CAS number, if known, is stated in square brackets.

TABLE-US-00001 2-Hydroxyethyl acrylate [818-61-1] - Sigma-Aldrich Chemie GmbH Steinheim, Germany Hydroxypropyl acrylate [25584-83-2] - BASF SE, Ludwigshafen Germany 2,6-Di-tert-butyl-4- [128-37-0] - Merck KGaA, methylphenol Darmstadt, Germany 2-Aminobiphenyl [90-41-5] - Sigma-Aldrich Chemie GmbH Steinheim, Germany 2-Aminobiphenyl phenyl [1134-94-7] - Sigma-Aldrich sulphide Chemie GmbH Steinheim, Germany 3 -(Methylthio)phenyl [28479-19-8] - Sigma-Aldrich isocyanate Chemie GmbH Steinheim, Germany 1-Isocyanato-3-(methyl- [28479-19-8] - Sigma-Aldrich sulphanyl)benzene Chemie GmbH, Steinheim, Germany Desmodur ® RFE Tris(p-isocyanatophenyl) thiophosphate, 27% in ethyl acetate, product from Bayer MaterialScience AG, Leverkusen, Germany Dibutyltin dilaurate [77-58-7] - Sigma-Aldrich Chemie GmbH Steinheim, Germany Fomrez ® UL 28 Momentive Performance Chemicals, Wilton, CT, USA. Borchi ® Kat 22 [85203-81-2] - OMG Borchers GmbH, Langenfeld, Germany. BYK-310 BYK-Chemie GmbH, Wesel, Germany Phenyl chloroformate [1885-14-9] - Acros Organics, Geel, Belgium Desmodur ® N 3900 Bayer MaterialScience AG, Leverkusen, DE, hexane diisocyanate-based polyisocyanate, proportion of iminooxadiazinedione at least 30%, NCO content: 23.5%. Desmodur 2460M Bayer MaterialScience AG, Leverkusen, DE, bis(isocyanatophenyl)methane (MDI)-based isocyanate Desmorapid ® SO [301-10-0] - Rhein Chemie Rheinau GmbH, Mannheim, Germany CGI-909 tetrabutylaminonium tris(3-chloro-4- methylphenyl)(hexyl)borate [1147315- 11-4], BASF SE Trimethylhexamethylene [28679-16-5] - ABCR GmbH & Co KG, diisocyanate Karlsruhe, Germany 1H, 1H-7H- [335-99-9] - ABCR GmbH & Co KG, Perfluoroheptan- Karlsruhe, Germany 1-ol Astrazon Rosa FG 200% [3648-36-0] - DyStar Colours Deutschland GmbH, Frankfurt am Main, Germany Sodium bis(2- [45297-26-5] Sigma-Aldrich ethylhexyl)sulphosuccinate Chemie GmbH, Steinheim, Germany

[0184] Preparation of 2-phenylthiophenyl isocyanate

[0185] In a three-neck flask with precision glass stirrer, under nitrogen, 720 g of 2-aminobiphenyl phenyl sulphide were dissolved in 4.2 kg of toluene and 519 g of potassium carbonate were added while stirring, and the mixture was equilibrated to 10° C. Then 560 g of phenyl chloroformate were added dropwise. The product was filtered off and dried under reduced pressure. This gave 1.15 kg of phenyl [2-(phenylsulphanyl)phenyl]carbamate in the form of a crystalline precipitate.

[0186] 950 g of phenyl [2-(phenylsulphanyl)phenyl]carbamate were initially charged in a three-neck flask provided with a precision glass stirrer, a silvered Vigreux column and a distillation system. A reduced pressure of about 1 mbar was applied and the mixture was heated gradually to 168° C. At a top temperature of 143° C., first of all, 257 g of phenol were distilled off. Thereafter, a total of 592 g of crude product having an NCO content of 16.5% was obtained. The crude product was subjected to fine distillation at 1 mbar and top temperature 118-121° C. to obtain a total of 502 g of 2-phenylthiophenyl isocyanate.

[0187] Preparation of 2-biphenyl isocyanate

[0188] A three-neck flask with dropping funnel, precision glass stirrer and distillation attachment was initially charged with 1500 g of Desmodur 2460M and heated to 140° C. Then, within 50 minutes, 243.7 g of 2-aminobiphenyl were added and the reaction temperature was kept below 160° C. Subsequently, the product was distilled off under high vacuum (about 0.03 mbar), and 203.2 g of 2-biphenyl isocyanate, a clear liquid, were obtained.

[0189] Preparation of 1-isocyanato-2-{[3-(phenylsulphanyl)phenyl]sulphanyl}benzene

[0190] 100 g of 2-{[3-(phenylsulphanyl)phenyl]sulphanyl}aniline (prepared as described in Advanced Synthesis & Catalysis (2009), 351(14+15), 2369-2378) and 0.1 g of tetrabutylammonium bromide were dissolved in 470 g of dichloromethane/water (1:1), and 49.1 g of potassium carbonate were added. At 10° C., 53.1 g of phenyl chloroformate were added dropwise to the vigorously stirred mixture. After the reaction had ended, 0.52 g of methanol was added and the mixture was stirred at room temperature for a further hour. The crude product was discharged onto 1 1 of water and the aqueous phase was extracted three times with 500 ml each time of dichloromethane. The organic phases were dried and the solvent was distilled off under reduced pressure. This gave 133 g of phenyl (2-{[3-(phenylsulphanyl)phenyl]sulphanyl}phenyl)carbamate as a colourless solid.

[0191] 100 g of phenyl (2-{[3-(phenylsulphanyl)phenyl]sulphanyl}phenyl)carbamate were initially charged in a Kugelrohr distillation apparatus and heated at 160° C. and 0.1 mbar. The phenol formed was discarded and 72 g of crude product were obtained. After distillation in a Kugelrohr distillation apparatus, 65.3 g of 1-isocyanato-2-{[3-(phenylsulphanyl)phenyl]sulphanyl}benzene were obtained as a colourless liquid.

Example 1: 2-({[2-(Phenylsulphanyl)phenyl]carbamoyl}oxy)propyl acrylate

[0192] A three-neck flask with condenser, precision glass stirrer and nitrogen gas inlet was initially charged with 16.0 g of 2-phenylthiophenyl isocyanate, and the reaction vessel was purged with nitrogen and then heated to 80° C. Then 5 mg of 2,6-di-tert-butyl-4-methylphenol and 1 mg of Bochi-Kat 22 were added. After stirring for 15 minutes, 9.01 g of hydroxypropyl acrylate were added dropwise thereto within 20 minutes. The mixture was stirred for 18 hours and 2-({[2-(phenylsulphanyl)phenyl]carbamoyl}oxy)propyl acrylate was obtained as a clear liquid which no longer contained any isocyanate.

Example 2: 2-({[2-(Phenylsulphanyl)phenyl]carbamoyl}oxy)ethyl acrylate

[0193] A three-neck flask with condenser, precision glass stirrer and air inlet was initially charged with 45.9 g of 2-phenylthiophenyl isocyanate, 13.5 mg of 2,6-di-tert-butyl-4-methylphenol and 33.8 g of dibutyltin dilaurate, then heated to 60° C., After stirring for 20 minutes, 21.6 g of hydroxyethyl acrylate were added dropwise thereto within 10 minutes. The mixture was stirred for 19 hours and a further 30 mg of dibutyltin dilaurate were added. After a further 32 hours, a further 1.08 g of hydroxyalkyl acrylate were added and, after stirring for a further 5 hours, 2-({[2-(phenylsulphanyl)phenyl]carbamoyl}oxy)ethyl acrylate was obtained as a clear liquid which no longer contained any isocyanate.

Example 3: 2-[(Biphenyl-2-ylcarbamoyl)oxy]propyl acrylate

[0194] A three-neck flask with condenser, precision glass stirrer and air inlet was initially charged with 7.8 g of biphenyl 2-isocyanate and 2.6 mg of 2,6-di-test-butyl-4-methylphenol, and then heated to 60° C. Then, with gradual introduction of air, 5.2 g of hydroxypropyl acrylate were added dropwise thereto within 30 minutes. After 1.5 hours, 6.5 mg of dibutyltin dilaurate were added thereto. The mixture was stirred for 46 hours and 2-[(biphenyl-2-ylcarbamoyl)oxy]propyl acrylate was obtained as a clear liquid which no longer contained any isocyanate.

Example 4: 2-[(Biphenyl-2-ylcarbamoyl)oxy]ethyl acrylate

[0195] A three-neck flask with condenser, precision glass stirrer and air inlet was initially charged with 7.8 g of biphenyl 2-isocyanate and 2.4 mg of 2,6-di-tert-butyl-4-methylphenol, and then heated to 60° C. Then, with gradual introduction of air, 4.3 g of 2-hydroxyethyl acrylate were added dropwise thereto within 30 minutes. After 1.5 hours, 6.1 mg of dibutyltin dilaurate were added thereto. The mixture was stirred for 70 hours and 2-[(biphenyl-2-ylcarbamoyl)oxy]ethyl acrylate was obtained as a clear liquid which no longer contained any isocyanate and crystallized gradually to give a solid having a melting range of 110-120° C.

Example 5: 2-{[(2-{[3-(Phenylsulphanyl)phenyl]sulphanyl}phenyl)carbamoyl]oxy}ethyl acrylate

[0196] A 100 ml round-bottom flask was initially charged with 0.01 g of 2,6-di-tert-butyl-4-methylphenol, 0.01 g of dibutyltin dilaurate and 7.50 g of 1-isocyanato-2-{[3-(phenylsulphonyl)phenyl]sulphanyl}benzene in 30 ml of ethyl acetate and heated to 60° C. Subsequently, 2.50 g of 2-hydroxyethyl acrylate were added dropwise and the mixture was still kept at 60° C. until the isocyanate content had fallen below 0.1%. This was followed by cooling and complete removal of the ethyl acetate under reduced pressure. The product was obtained as a partly crystalline solid.

Example 6:2-{[(2-{[3-(Phenylsulphanyl)phenyl]sulphanyl}phenyl)carbamoyl]oxy}propyl acrylate

[0197] A 100 ml round-bottom flask was initially charged with 0.01 g of 2,6-di-tert-butyl-4-methylphenol, 0.01 g of dibutyltin dilaurate and 7.30 g of 1-isocyanato-2-{[3-(phenylsulphanyl)phenyl]sulphanyl}benzene in 30 ml of ethyl acetate and heated to 60° C. Subsequently, 2.70 g of hydroxypropyl acrylate were added dropwise and the mixture was still kept at 60° C. until the isocyanate content had fallen below 0.1%. This was followed by cooling and complete removal of the ethyl acetate under reduced pressure. The product was obtained as a partly crystalline solid.

Comparative Example A: 2-({[3-(Methylsulphanyl)phenyl]carbamoyl}oxy)ethyl prop-2-enoate

[0198] A 100 ml round-bottom flask was initially charged with 0.02 g of 2,6-di-tert-butyl-4-methylphenol, 0.01 g of dibutyltin dilaurate, 11.7 g of 3-(methylthio)phenyl isocyanate, and the mixture was heated to 60° C. Subsequently, 8.2 g of 2-hydroxyethyl acrylate were added dropwise and the mixture was still kept at 60° C. until the isocyanate content had fallen below 0.1%. This was followed by cooling. The product was obtained as a colourless liquid.

[0199] Urethane acrylate 1: Phosphorothioyltris(oxybenzene-4,1-diylcarbamoyloxyethane-2,1-diyl) triacrylate

[0200] A 500 ml round-bottom flask was initially charged with 0.1 g of 2,6-di-tert-butyl-4-methylphenol, 0.05 g of dibutyltin dilaurate and 213.1 g of a 27% solution of tris(p-isocyanatophenyl) thiophosphate in ethyl acetate (Desmodur® RFE, product from Bayer MaterialScience AG, Leverkusen, Germany), which were heated to 60° C. Subsequently, 42.4 g of 2-hydroxyethyl acrylate were added dropwise and the mixture was still kept at 60° C. until the isocyanate content had fallen below 0.1%. This was followed by cooling and complete removal of the ethyl acetate under reduced pressure. The product was obtained as a partly crystalline solid.

[0201] Polyol Component:

[0202] A 1 1 flask was initially charged with 0,037 g of Desmorapid® SO, 374.8 g of ε-caprolactone and 374.8 g of a difunctional polytetrahydrofuran polyether polyol, which were heated to 120° C. and kept at this temperature until the solids content (proportion of nonvolatile constituents) was 99.5% by weight or higher. Subsequently, the mixture was cooled and the product was obtained as a waxy solid.

[0203] Dye 1:

[0204] 5.84 g of anhydrous sodium bis(2-ethylhexyl)sulphosuccinate were dissolved in 75 ml of ethyl acetate. 14.5 g of the dye Astrazon Rosa FG 200%, dissolved in 50 ml of water, were added. The aqueous phase was removed and the organic phase was stirred three times with 50 ml of fresh water at 50° C. and the aqueous phase was removed each time, the last time at room temperature. After the aqueous phase had been removed, the solvent was distilled off under reduced pressure and 8.6 g of 3H-indolium, 2-[2-[4-[(2-chloroethyl)methylamino]phenyl]ethenyl]-1,3,3-trimethyl-1,4-bis(2-ethylhexyl)sulphosuccinate [153952-28-4] were obtained as an oil of high viscosity.

[0205] Fluorinated urethane: bis(2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl)-(2,2,4-trimethylhexane-1,6-diyl) biscarbamate

[0206] A 6 1 round-bottom flask was initially charged with 0.50 g of Desmorapid Z and 1200 g of trimethylhexamethylene diisocyanate, and the mixture was heated to 80° C. Subsequently, 3798 g of 1H,1H,7H-perfluoroheptan-1-ol were added dropwise and the mixture was still kept at 80° C. until the isocyanate content had fallen below 0.1%. This was followed by cooling. The product was obtained as a colourless oil.

[0207] Preparation of the Inventive and Noninventive Holographic Media (Examples I-VI and Comparative Example I)

[0208] 7.90 g of the above-described polyol component were melted and mixed with 7.65 g of the particular writing monomer (writing monomer 1 to 6 and Comparative Example A), 2.57 g of the above-described urethane acrylate 1, 5.10 g of the above-described fluorinated urethane, 0.91 g of CGI 909, 0.232 g of dye 1, 0.230 g of BYK 310, 0.128 g of Fomrez UL 28 and 3.789 g of ethyl acetate, such that a clear solution was obtained. This was followed by addition of 1.50 g Desmodur® N 3900 and mixing again.

[0209] Then this solution was applied in a roll-to-roll coating system to a 36 μm-thick PET film, where the product was applied by means of a coating bar in a wet film thickness of 19 μm. With a drying temperature of 85° C. and a drying time of 5 minutes, the coated film was dried and then protected with a 40 μm-thick polyethylene film. Subsequently, this film was packaged with exclusion of light.

[0210] Determination of the Moisture Stability of the Holograms Which Were Recorded in the Inventive and Noninventive Media.

[0211] The media produced as described in the “Preparation of the inventive and noninventive holographic media” section were then tested for their holographic properties as follows using a measuring arrangement according to FIG. 4:

[0212] The beam of a laser (emission wavelength 532 nm) is expanded to a diameter of ˜3-4 cm with the aid of an optional expanding lens (AF) and the collimation lens (CL) positioned after the shutter S. The diameter of the expanded laser beam is determined by the aperture of the open shutter. An inhomogeneous intensity distribution of the expanded laser beam is deliberately ensured. Thus, the edge intensity P.sub.R is ˜ only half of the intensity P.sub.Z in the centre of the expanded laser beam. P should be understood here as power/area. The expanded laser beam at first passes through a glass plate placed at an oblique angle to the beam, which serves as shearing plate (SP). On the basis of the interference pattern reflected upward, which is produced by the two glass surface reflections of the SP, it is possible to see whether the laser emits in a stable manner in single mode. In that case, on an above the SP positioned diffusing screen composed of dark and light stripes is observed. Only when there is single mode emission are holographic exposures conducted. In the case of the DPSS laser, the single mode can be achieved by adjusting the pump power. The expanded beam passes through the holographic medium (P) at an oblique angle of about 15°; this portion forms the reference beam, in order then to be reflected by the object (O) arranged parallel to P back into P. This portion then forms the signal beam of the Denisyuk arrangement.

[0213] The interference of signal beam and reference beam in P creates the hologram in the holographic medium. O consists of a metal plate covered with white paper, with the paper side P facing forward. On the paper is a square pattern produced by black lines. The edge length of a square is 0.5 cm. This pattern is imaged in the hologram as well in the holographic exposure of P,

[0214] The mean exposure dose E.sub.ave is adjusted via the opening time t of S. With fixed laser power I, t is therefore the parameter proportional to E.sub.ave. Since the expanded laser beam has an inhomogeneous (bell-shaped) intensity distribution, the local dose E for creation of the hologram in P varies. Together with the oblique arrangement of P and O relative to the optical axis, the effect of this is that the written hologram has an elliptical form. Since O is a diffuse reflector, the hologram is easily reconstructed by illumination with a point light source (e.g. pocket torch), and it is likewise possible to examine the holograms in the transmission mode of a UV-VIS spectrometer and compare them with one another.

[0215] Subsequently, the samples were placed onto the conveyor belt of a UV source with the substrate side facing the lamp and exposed twice at a belt speed of 2.5 m/min. The UV source used was an iron-doped Hg lamp of the Fusion UV type “D Bulb” No. 558434 KR 85 with total power density 80 W/cm.sup.2. The parameters corresponded to a dose of 2×2.0 J/cm.sup.2 (measured with an ILT 490 Light Bug).

[0216] The media thus obtained were examined in a UV-VIS spectrometer. For this purpose, a transmission measurement through the medium was conducted and recorded. Via the evaluation of the transmission curve, it is possible to determine the lowest transmission; this corresponds to the highest diffraction efficiency. Then the resonance frequency (in nm) in the transmission spectrum at the lowest transmission is determined and reported as T.sub.min.

[0217] The transmission spectra of the written holograms of Inventive Examples 1-6 and Comparative Example A were determined thereafter. The media containing the holograms produced as described above were stored at various temperatures and air humidities and T.sub.min was determined again on completion of the storage.

[0218] Study of Thermal Stability:

[0219] The samples were stored at 100° C. In an oven for two days and cooled within 2 minutes, and T.sub.min(1) was determined. Subsequently, the samples were stored at about 20° C. and 40%-50% relative humidity for 7 days and T.sub.min(2) was determined. Finally, the difference in the peak wavelengths of the two measurements ΔT.sub.min(1) was calculated.

[0220] Study of Moisture Stability:

[0221] The samples were stored at 60° C./95% relative air humidity for two days and cooled within 2 minutes, and T.sub.min(3) was determined. Subsequently, the samples were stored at about 20° C. and 40%-50% relative humidity for 7 days and T.sub.min(4) was determined. Finally, the difference in the peak wavelengths of the two measurements ΔT.sub.min(2) was calculated.

[0222] Study of Holographic Performance (see Table 1)

[0223] The determination of the refractive index modulation Δn was conducted by the process described above in the “Test methods” section. Inventive Examples 1-6 and Comparative Example A show good holographic performance with a refractive index modulation Δn>0.025. In the study of thermal stability, a value of <2 nm ΔT.sub.min(1) was consistently found. In the study of moisture stability, for the inventive examples, a value of <5 nm ΔT.sub.min(2) was consistently found. The comparative example has a ΔT.sub.min(2) of 7.4 nm. Thus, the inventive examples of the formula (1) have a maximum change in the reconstruction wavelength of less than 5 nm based on a reflection hologram which has been written by interference of two planar waves having a wavelength of 532 nm.

TABLE-US-00002 TABLE 1 Δn T.sub.min T.sub.min(1) T.sub.min(2) ΔT.sub.min(1) T.sub.min(3) T.sub.min(4) ΔT.sub.min(2) Unit — [nm] [nm] [nm] [nm] [nm] [nm] [nm] Example 1 0.029 530.7 529.0 530.0 −1.0 534.8 530.7 4.1 2 0.033 529.3 527.8 528.4 −0.6 533.1 528.4 4.7 3 0.028 529.0 527.4 527.8 −0.4 532.3 527.8 4.5 4 0.027 527.1 525.3 525.9 −0.6 531.5 526.7 4.8 5 0.034 530.7 528.2 530.0 −1.9 533.5 529.8 3.7 6 0.036 529.7 527.2 528.6 −1.4 532.9 529.6 3.3 Comparative Example A 0.033 526.9 524.5 525.1 −0.6 532.7 525.3 7.4