System consisting of two UV-curing dry-transfer coating layers for the protection of a hologram in a photopolymer film composite

Abstract

The invention relates to a scaled holographic medium comprising a layer construction B′-C1′-C2′, to a process for producing the sealed holographic medium, to a kit of parts, to a layer construction comprising a protective layer and a substrate layer and to the use thereof.

Claims

1. A sealed holographic medium comprising a layer construction B′-C1′-C2′, wherein B′ is a photopolymer layer containing a volume hologram, C1′ is a protective layer at least partly cured by actinic radiation obtained by reaction of I) at least one thermoplastic mainly linear and semicrystalline polyurethane resin C1-I, II) at least one multifunctional acrylate reactive diluent C1-II, and III) at least one photoinitiator C1-III and C2′ is a protective layer at least partly cured by actinic radiation obtainable by reaction of I) at least one thermoplastic resin C2-I selected from the group consisting of polyvinyl butyral and polymethyl methacrylate, II) at least one multifunctional acrylate reactive diluent C2-II, and III) at least one photoinitiator C2-III.

2. The sealed holographic medium according to claim 1, wherein the layer construction according to the invention consists of at least four layers at least partly joined to one another, wherein the layers are arranged directly atop one another in the sequence substrate layer A, photopolymer layer B′, cured protective layer C1′ and cured protective layer C2′.

3. The sealed holographic medium according to claim 1, wherein the layer construction consists of at least four layers at least partly joined to one another, wherein the layers are arranged directly atop one another in the sequence photopolymer layer B′, cured protective layer C1′, cured protective layer C2′ and substrate layer D2.

4. The sealed holographic medium according to claim 1, wherein the layer construction consists of at least five layers at least partly joined to one another, wherein the layers are arranged directly atop one another in the sequence substrate layer A, photopolymer layer B′, cured protective layer C1′, cured protective layer C2′ and substrate layer D2.

5. A layer construction comprising a curable protective layer C1 and an areal substrate layer D1 at least partly joined to the protective layer C1, wherein the protective layer C1 comprises I) at least one thermoplastic mainly linear and semicrystalline polyurethane resin C1-I, II) at least one multifunctional acrylate reactive diluent C1-II, and III) at least one photoinitiator C1-III.

6. A process for producing the sealed holographic medium according to claim 1, wherein initially an uncured protective layer C1 is applied atop a photopolymer layer B′ containing a volume hologram to afford a layer composite B′-C1, in a further step an uncured protective layer C2 is applied atop the protective layer C1 to afford a layer composite B′-C1-C2 and subsequently the layer composite B′-C1-C2 is at least partly cured with actinic radiation to obtain a layer composite B′-C1′-C2′, wherein C1′ and C2′ are the at least partly cured protective layers C1 and C2 respectively, wherein the uncured protective layer C1 comprises I) at least one thermoplastic mainly linear and semicrystalline polyurethane resin C1-I, II) at least one multifunctional acrylate reactive diluent C1-II, and III) at least one photoinitiator C1-III and the uncured protective layer C2 comprises I) at least one thermoplastic resin C2-I selected from the group consisting of polyvinyl butyral and polymethyl methacrylate, II) at least one multifunctional acrylate reactive diluent C2-II, and III) at least one photoinitiator C2-III.

7. The process according to claim 6, wherein in a first step a layer composite A-B′ is provided, wherein A is a substrate layer and B′ is the photopolymer layer containing the volume hologram, in a second step the uncured protective layer C1 is applied atop a substrate layer D1 to afford a layer composite C1-D1, in a third step the layer composite A-B′ is areally joined to the layer composite C1-D1 to afford a layer composite A-B′-C1-D1, in a fourth step the substrate layer D1 is removed from the layer composite A-B′-C1-D1 to afford a layer composite A-B′-C1, in a fifth step the uncured protective layer C2 is applied atop a substrate layer D2 to afford a layer composite C2-D2, in a sixth step the layer composite A-B′-C1 is areally joined to the layer composite C2-D2 to afford a layer composite A-B′-C1-C2-D2, and in a seventh step the layer composite A-B′-C1-C2-D2 is at least partly cured with actinic radiation to afford a layer composite A-B′-C1′-C2′-D2.

8. The process according to claim 7, wherein in an eighth step the substrate layer D2 is removed from the layer composite A-B′-C1′-C2′-D2 to afford a layer composite A-B′-C1′-C2′.

9. A kit of parts containing at least one uncured protective layer C 1, at least one uncured protective layer C2 and an areal photopolymer layer B′ containing a volume hologram, wherein the protective layers C1 and C2 are different.

10. The kit of parts according to claim 9, wherein the photopolymer layer B′ is disposed on a substrate layer A, wherein the photopolymer layer B′ is on one side at least partly joined to the substrate layer A.

11. The kit of parts according to claim 9, wherein the uncured protective layer C1 is disposed on a substrate layer D1, wherein the protective layer C1 is on one side at least partly joined to the substrate layer D1 , and the uncured protective layer C2 is disposed on a substrate layer D2, wherein the protective layer C2 is on one side at least partly joined to the substrate layer D2.

12. A method comprising utilizing the layer construction according to claim 5 to produce a sealed holographic medium.

13. An optical display comprising the sealed holographic medium according to claim 1, wherein the optical display is selected from the group consisting of autostereoscopic and/or holographic displays, projection screens, displays with switchable restricted emission characteristics for privacy filters and bidirectional multiuser screens, virtual displays, head-up displays, head-mounted displays, illumination symbols, warning lamps, signal lamps, floodlights/headlights and display panels.

14. A security document comprising the sealed holographic medium according to claim 1.

Description

EXAMPLES

(1) The invention will now be more particularly elucidated by means of examples.

(2) Test Methods:

(3) Solids content: The reported solids contents were determined according to DIN EN ISO 3251. colour number: The colour number was determined according to DIN ISO 6271-2:2002 and evaluated as Hazen.
Chemicals:

(4) In each case, the CAS number, if known, is reported in square brackets.

(5) Raw Materials for Photopolymer Layer B

(6) Fomrez® UL 28 Urethanization catalyst, commercial product of Momentive Performance Chemicals, Wilton, Conn., USA. Borchi® Kat 22 Urethanization catalyst, [85203-81-2] commercial product of OMG Borchers GmbH, Langenfeld, Germany. BYK-310 silicone-containing surface additive, product of BYK-Chemie GmbH, Wesel, Germany. Desmodur® N 3900 product of Covestro AG, Leverkusen, DE, hexane diisocyanate-based polyisocyanate, proportion of iminooxadiazinedione at least 30%, NCO content: 23.5%. CGI-909 tetrabutylammonium tris(3-chloro-4-methylphenyl)(hexyl)borate [1147315-11-4], product of BASF SE

(7) Dye 1 (3,7-bis(diethylamino)phenoxazin-5-ium bis(2-ethylhexyl)sulfosuccinate) was produced as described in WO 2012062655.

(8) Polyol 1 was produced as described in WO2015091427.

(9) Urethane acrylate 1, simultaneously also RD 2, (phosphorothioyltris(oxybenzene-4,1-diylcarbamoyloxyethane-2,1-diyl) trisacrylate, [1072454-85-3]) was produced as described in WO2015091427.

(10) Urethane acrylate 2, (2-({[3-(methylsulfanyl)phenyl]carbamoyl}oxy)ethyl prop-2-enoate, [1207339-61-4]) was produced as described in WO2015091427.

(11) Additive 1, bis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl)-2,2,4-trimethylhexane-1,6-diyl)biscarbamate [1799437-41-4] was produced as described in WO2015091427.

(12) Raw Materials for Layer C

(13) Physically Drying Resins

(14) Desmocoll 406—resin 1 A linear thermoplastic flexible polyurethane from Covestro Deutschland AG, Leverkusen, Germany. Desmocoll 400/3—resin 2 A linear thermoplastic flexible polyurethane from Covestro Deutschland AG, Leverkusen, Germany. Mowital B75H—resin 3 A linear thermoplastic amorphous polyvinyl butyral having an Mw of 240 000 from Kuraray Europe GmbH, Hattersheim, Germany Degacryl M547—resin 4 A linear thermoplastic amorphous polymethyl methacrylate having an Mw of 500 000 from Evonik Industries, Marl, Germany
Acryloyl-Functional Reactive Diluents
Abbreviation RD=Reactive Diluents DPHA—RD 1 [29570-58-9] Dipentaerythritol hexaacrylate from Cytec Surface Specialties, Brussels, Belgium. RD 2 Phosphorothioyltris(oxybenzene-4,1-diylcarbamoyloxyethane-2,1-diyl) trisacrylate, [1072454-85-3]) was produced as described in WO2015091427. Sartomer SR444D— RD 3 [3524-68-3] Pentaerythritol triacrylate (PETIA) from the SARTOMER Division of CRAY VALLEY, Paris, France (Arkema Group). Sartomer SR494— RD 4 Quadruply ethoxylated pentaerythritol tetraacrylate (PPTTA) from the SARTOMER Division of CRAY VALLEY, Paris, France (Arkema Group).
Photoinitiators Esacure One— Initiator 1 [163702-01-0] Oligo[2-hydroxy-2-methyl-1-((4-(1-methylvinyl)phenyl)propanone] from Lamberti S.p.A., Albizzate, Italy. Irgacure 4265— Initiator 2 A mixture of Irgacure® TPO (50% by weight) and Irgacure® 1173 (50% by weight) from BASF, SE, Ludwigshafen, Germany.
Additives BYK 333— Flow control agent Silicone-containing surface additive from BYK Chemie GmbH, Wesel, Germany
Solvent Butyl acetate (BA) Butyl acetate from Brenntag GmbH, Mülheim an der Ruhr, Germany. Methoxypropanol (MP-ol) l-Methoxy-2-propanol from Brenntag GmbH, Mülheim an der Ruhr, Germany.

(15) Purification of Urethane Acrylate 1 (Simultaneously Also RD 2):

(16) The 40% solution of urethane acrylate 1 in ethyl acetate has a colour number of 300 to 700 Hazen (DIN ISO 6271-2:2002) which is not acceptable for the optical lacquers based thereon. For purification the solution is diluted with cyclohexane and additional ethyl acetate, the resulting 10% solution is filtered in a solvent mixture of ethyl acetate and cyclohexane (1.4 to 1 parts by weight) through a layer of Kieselgel 60 (Merck) and subsequently the purified original 40% solution in ethyl acetate is re-obtained by distillative removal of cyclohexane and excess ethyl acetate. The thus obtained solution of RD 2 has a colour number of 40-50 Hazen.

(17) Production of Holographic Media (Photopolymer Film)

(18) 7.90 g of the above-described polyol component were melted and mixed with 7.65 g of the particular urethane acrylate 2, 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, so that a clear solution was obtained. This was followed by addition of 1.50 g Desmodure® N 3900 and renewed mixing.

(19) This solution was applied to a PET film of 36 μm in thickness in a roll-to-roll coating plant where by means of a knife coater the product was applied 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 polyethylene film of 40 μm in thickness. This film was then light-tightly packaged.

(20) Production of the Latent Protective Layer C1 on Substrate D1/Protective Layer C2 on Substrate D2

(21) The formulations reported in table 1 were produced when the physically drying resins, dissolved at 100° C. in the reported organic solvent and cooled to room temperature, were mixed with the reactive diluent. The photoinitiators and flow control agents were then added in darkness.

(22) TABLE-US-00001 TABLE 1 Coating composition * got producing the latent protective layer C Resin/RD Solids content Viscosity of weight (% by weight) solution at 23° C. Sample Resin RD ratio Solvent [mPas] Inventive examples C1-01 1 RD 1 30/70 25% 170 butyl acetate C1-02 2 RD 2 40/60 26% 1120 butyl acetate C2-01 3 RD 3 50/50 20% 4400 1-methoxy-2- propanol C2-02 3 RD 2 20/80 28% 950 1-methoxy-2- propanol C2-03 4 RD 4 25/75 25% 169 1-methoxy-2- propanol C2-04 3 RD 3 .sup. 47/48.sup.# 20% 3020 1-methoxy-2- propanol Noninventive examples C1-N01 2 RD5 50/50 25% 2220 butyl acetate * All coating compositions contain initiator 1 (3.0% by weight based on solids content of lacquer), initiator 2 (1.5% by weight based on solids content of lacquer) and flow control agent (0.2% by weight based on solids content of lacquer); .sup.#contains 5% by weight of PGM-ST-UP SiO nanoparticles (Nissan Chemical)

(23) The coating compositions C1-01 and C1-02 for the latent protective layer C1 were applied atop a 36 μm-thick silicone-modified PET film D1 (Hostaphan RN30 2PRK from Mitsubishi Polyester Film GmbH, Wiesbaden, Germany) in a roll-to-roll coating plant by means of a knife coater. With a drying temperature of 85° C. and a drying time of 5 minutes, the coated film was dried and then protected with a polyethylene film of 40 μm in thickness. The coating thickness was generally 15-16 μm. Subsequently, this film was light-tightly packaged.

(24) The coating compositions C2-01, C2-02, C2-03 and C2-04 for the latent protective layer C2 were analogously applied atop a 36 μm-thick PET film D2 (RNK 36 from Mitsubishi Polyester Film GmbH, Wiesbaden, Germany) followed by drying, laminating and packaging. The coating thickness was generally 15-16 μm.

(25) Production of Test Holograms in the Film Composite A-B

(26) The test holograms were prepared as follows: the photopolymer films with the layer construction A-B were in darkness cut to the desired size and using a rubber roller laminated onto a glass sheet having dimensions of 50 mm×70 mm (3 mm thick). The test holograms were produced using a test apparatus which produces Denisyuk reflection holograms using green (532 nm) laser radiation. The test apparatus consists of a laser source, an optical beam guide system and a holder for the glass coupons. The holder for the glass coupons is mounted at an angle of 13° relative to the beam axis. The laser source generated the radiation which, widened to about 5 cm by means of a specific optical beam path, was guided to the glass coupon in optical contact with the mirror. The holographed object was a mirror about 2 cm×2 cm in size, so the wavefront of the mirror was reconstructed on reconstructing the hologram. All examples were irradiated with a green 532 nm laser (Newport Corp, Irvine, Calif., USA, cat. no. EXLSR-532-50-CDRH). A shutter was used to irradiate the recording film in a defined manner for 2 seconds. This forms a film composite A-B* comprising a hologram in layer B.

(27) Subsequently, the samples were placed onto the conveyor belt of a UV source with the B side facing the lamp and irradiated twice at a belt speed of 2.5 m/min. The UV source employed was a Fusion UV “D Bulb” No. 558434 KR 85 iron-doped Hg lamp having a 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). After this fixing step the film composite A-B′ is formed.

(28) Characterization of Test Holograms The holograms in layer B′ of the film composite A-B′ were then analysed for quality by spectroscopy.

(29) On account of the high diffraction efficiency of the volume hologram, the diffractive reflection of such holograms may be analysed in transmission with visible light with a spectrometer (USB 2000 instrument, Ocean Optics, Dunedin, Fla., USA, is employed) and appears in the transmission spec-trum as a peak with reduced transmission T.sub.Red. Evaluating the transmission curve makes it possible to determine the quality of a hologram according to ISO standard 17901-1:2015(E) taking account of the following measured values; all results are summarized in table 3 in the section “spectral quality of holograms”, column “in A-B”: T.sub.Red=100−T.sub.peak(A-B′)(1) Maximum depth of the transmission peak, this corresponds to the highest diffraction efficiency. Thus, 100−T.sub.peak(A-B′) serves as a measure for the reflection power (or visible “strength” or “quality”) of the hologram. FWHM The width of the transmission peak is determined as “full width at half maximum” (FWHM) in nanometres (nm). λ.sub.peak Spectral position of the transmission minimum of the hologram in nanometres (nm).

(30) The films having the layer structure A-B′ were then provided with the two successive protective layers C1′ and C2′ in the process according to the invention. The holograms were then also reana-lysed for quality in the layer construction A-B′-C1′-C2′ and compared with the original values for the layer construction A-B′ (tab. 3).

(31) Production of a Film Composite with Layer Construction A-B′-C1′-C2′

(32) Production of a film composite with the layer construction A-B′-C1′-C2′ comprises lamination of side B′ of the film A-B′ onto side C1 of the film composite C1-D1. This is effected by pressing together the two films between the temperature controlled rubber rollers of a laminator. The temperature of the rollers was set to 30° C., 60° C. or 90° C. The produced multilayer film was cooled to room temperature. The substrate film D1 was then peeled off from the film composite A-B′-C1-D1. Side C2 of the film composite C2-D2 was then laminated onto side C1 of the film composite A-B′-C1 in analogous fashion.

(33) Subsequently, the samples A-B′-C1-C2-D2 were placed onto the conveyor belt of a UV source with the D2 side facing the lamp and irradiated twice at a belt speed of 2.5 m/min. The UV source employed was a Fusion UV “D Bulb” No. 558434 KR 85 iron-doped Hg lamp having a 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). After this curing step the film composite A-B′-C1′-C2′-D2 is formed, from which the substrate film D2 is subsequently peeled off.

(34) TABLE-US-00002 TABLE 2 Applicability of the protective layer C1 and C2 onto the holographic film A-B and protective quality of coatings C2′ Lamination of Lamination of Adhesion of layer layer C1 onto layer C2 onto Removability construction B′- Solvent resistance (1 h) Coating composition T.sub.Lam layer B′ and layer C1/onto of film D2 C1′-C2′ evaluated of layer C2′ against Sample Layer C1 Layer C2 [° C.] removal of film D1 layer B′ from layer C2′ by cross cut NEP/MEK/butanol/EA Comparative example none none − − − − − 5/5/1/5 (after 10 min) Inventive examples 01-01 C1-01 C2-01 60 + + + 1 0/0/0/0 01-02 C1-01 C2-01 60 + + + 1 0/0/0/0 01-03 C1-01 C2-01 60 + + + 1 0/0/0/0 02-01 C1-01 C2-02 60 + + + 0 0/0/0/0 02-02 C1-01 C2-02 60 + + + 0 0/0/0/0 02-03 C1-01 C2-02 60 + + + 0 0/0/0/0 03-01 C1-02 C2-03 60 + + + 1 0/1/0/0 03-02 C1-02 C2-03 60 + + + 1 0/1/0/0 04-01 C1-02 C2-04 60 + + + 1 0/0/0/1 04-02 C1-02 C2-04 60 + + + 1 0/0/0/1 Noninventive examples N01 C1-N01 C2-01 60 + − N02 C1-01 none 60 + + 0 2/4/0/2 N03 C1-02 none 60 + + 1 4/4/4/4 N04 none C2-01 60 + + 5 0/0/0/0 N05 none C2-03 60 + + 1 0/0/0/0 N06 none C2-04 30 + + 5 0/0/0/0

(35) Table 2 shows that all inventive examples may be readily produced by two successive lamination steps. The noninventive example N01 cannot be produced. Noninventively constructed layer C1 has the result that lamination of layer C2 does not succeed. Further inventive examples N02 to N06 are those comprising only one protective layer, either only C1 or only C2. They may all be readily produced but fail due to inadequate solvent resistance (N02, N03), adhesion (N04, N06) or holographic performance (N05).

(36) Quantitative Analysis of the Adhesion of Protective Layers C1′ and C2′ and of the Protective Layer Composite C1′-C2′ on the Layer B′ of the Holographic Film A-B′ According to ISO 2409 (Cross Cut Test)

(37) An adhesive tape peel test (adhesive tape used: 3M Scotch 898) with cross cut (as per DIN EN ISO 2409:2013-06) was performed. The performance values range from full adhesion (performance value: 0) to inadequate adhesion (performance value: 5).

(38) Evaluation of Solvent Resistance of Protective Layer C2′ or C1′

(39) The solvent resistance of the coatings was typically tested with technical quality N-ethyl-2-pyrrolidone (NEP), methyl ethyl ketone (MEK), 1-butanol and ethyl acetate (EA). The solvents were applied to the coating with a soaked cotton bud and protected from vaporization by covering. Unless stated otherwise, a contact time of 60 minutes at about 23° C. was observed. After the end of the contact time, the cotton bud is removed and the test surface is wiped clean with a soft cloth. The inspection is immediately effected visually and after gentle scratching with a fingernail.

(40) A distinction is made between the following levels: 0=unchanged; no change visible; not damageable by scratching. 1=slight swelling visible, but not damageable by scratching. 2=change clearly visible, barely damageable by scratching. 3=noticeable change, surface destroyed after firm fingernail pressure. 4=severe change, scratched through to substrate after firm fingernail pressure. 5=destroyed; lacquer already destroyed on wiping off the chemical; the test substance is not removable (eaten into surface).

(41) Within this assessment, the test is typically passed with performance values of 0 and 1. Performance values of >1 represent a “fail”.

(42) As is shown by the corresponding column of table 2 all inventive coatings C2′ register a very high level of solvent resistance.

(43) Samples N04 to N06, wherein layer C2′ is applied directly atop A-B′ without an interlayer C1′, show equally good values. Such samples fail due to inadequate adhesion (N04 and N06) or holographic performance (N05).

(44) Samples N02 and N03, wherein the layers C1′ are not covered with the layers C2′, show insufficient solvent resistance.

(45) Characterization of Test Holograms

(46) The holograms in layer B′ of the film composite A-B′ which are initially measured before application of any protective layers are analysed by spectroscopy for possible loss of quality in the layer composite A-B′-C1′-C2′.

(47) TABLE-US-00003 TABLE 3 Quality of holograms inscribed in A-B film composite then UV-VIS-fixed; this forms the film composite A-B′; this is followed by lamination of C1-D1 and removal of D1; this is followed by lamination of film composite C2-D2; then the film composite A-B′-C1-C2-D2 is fixed by irradiation to afford the film composite A-B′-C1′-C2′-D2 and then, by removal of D2, the film composite A-B′-C1′-C2′ Spectral quality of holograms in A-B′-C1′-C2′ (after 1 h) in A-B′-C1′-C2′ (after 3 days) in A-B′ Δ Δ 100- 100- λ.sub.peak 100- λ.sub.peak Coating composition T.sub.Lam T.sub.peak FWHM λ.sub.peak T.sub.min FWHM λ.sub.peak [nm] T.sub.peak FWHM λ.sub.peak [nm] Sample Layer C1 Layer C2 [° C.] [%] [nm] [nm] [%] [nm] [nm] to A-B′ [%] [nm] [nm] to A-B′ Inventive examples 01-01 C1-01 C2-01 60 92.9 23.9 528 85.6 18.0 533 4.5 84.1 17.3 527 −1.4 01-02 C1-01 C2-01 60 93.6 23.8 528 89.1 17.2 536 7.9 86.6 18.9 528 0.0 01-03 C1-01 C2-01 60 91.4 24.2 528 89.0 17.5 536 7.9 81.1 15.7 525 −3.1 02-01 C1-01 C2-02 60 90.4 23.4 529 88.0 19.1 535 6.6 83.8 18.8 525 −3.8 02-02 C1-01 C2-02 60 89.7 23.4 529 89.6 18.4 539 10.1 85.5 16.8 530 1.4 02-03 C1-01 C2-02 60 92.5 22.9 528 89.2 18.3 534 5.9 88.0 17.9 527 −1.0 03-01 C1-02 C2-03 60 91.9 21.7 529 90.1 18.4 538 8.6 91.2 21.3 537 8.3 03-02 C1-02 C2--03 60 91.9 22.0 529 93.2 19.1 538 9.0 90.7 20.8 536 7.3 04-01 C1-02 C2-04 60 93.8 21.6 529 92.9 19.7 532 3.1 92.4 20.5 530 1.3 04-02 C1-02 C2-04 60 91.5 24.3 529 94.0 19.52 536 7.3 91.9 20.6 534 5.9 Noninventive examples N01 C1-N01 C2-01 60 93.0 19.9 529 — — — — — — — — N02 C1-01 none 60 90.9 24.0 528 90.5 18.6 530 1.4 90.5 18.7 526 −2.1 N03 C1-02 none 60 94.3 20.9 529 94.2 19.9 533 4.2 91.7 19.3 532 3.1 N04 none C2-01 60 93.2 23.0 528 88.9 19.8 544 16.3 91.9 19.9 542 14.2 N05 none C2-03 60 79.2 20.3 529 47.0 32.5 557 28.4 31.8 159.7.sup.# 549 19.7 N06 none C2-04 60 91.7 22.0 526 87.4 21.9 534 8.0 84.0 22.5 534 7.3 .sup.#spectral peak nonuniform, several additional peaks

(48) The values of T.sub.Red=100−T.sub.peak(A-B′-C1′-C2′) (2) for the inventive examples differ only minimally from the corresponding values for A-B′ and only in individual cases is a deviation of about 10% observed. A large loss in hologram quality is recorded only for the noninventive example N05.

(49) The same tendency also affects the spectral position of the transmission peak λ.sub.peak. As is shown by the difference
Δλ.sub.peak=λ.sub.peak(A-B′-C1′-C2′)−λpeak.sub.(A-B′)  (3)
the deviation from λ.sub.peak is not more than 10 nm. Some noninventive examples (N04 and N05) show substantially higher values.