ADHESIVE-FREE PHOTOPOLYMER LAYER STRUCTURE

Abstract

The invention relates to a process for producing a layer construction with adhesive-free bonding, to a layer structure comprising an exposed photopolymer layer B and a substrate layer C of (co)polycarbonate, to a sealed optical medium comprising the layer structure, and to an optical display and a security document comprising the sealed optical medium.

Claims

1.-15. (canceled)

16. A process for producing an at least part-bonded layer construction comprising a photopolymer layer B containing a hologram, and a substrate layer C of (co)polycarbonate, wherein the process comprises the following steps: a) directly contacting an unexposed photopolymer layer B or a part-exposed photopolymer layer B containing a hologram with the substrate layer C, so as to form a layer composite B-C, b) heating the layer composite B-C to a temperature of 70 C. to 110 C., c) optionally exposing a hologram into the unexposed photopolymer layer B comprising matrix polymers, writing monomers, photoinitiators, optionally at least one non-photopolymerizable component and optionally catalysts, free-radical stabilizers, solvents, additives and other assistants and/or added substances, d) subjecting the part-exposed layer composite B-C containing a hologram to actinic radiation, wherein step d) is always conducted as the last step.

17. The process according to claim 16, wherein process steps a)-d) are conducted in the sequence a), b), c) and d) or in the sequence a), c), b) and d) or in the sequence c), a), b) and d).

18. The process according to claim 16, wherein the layer composite B-C is heated in step b) for 0.2 second to 60 minutes.

19. The process according to claim 16, wherein the layer composite after step b) has a bonding force in accordance with ISO/IEC 10373 using a tensile tester according to DIN EN ISO 527-1 between the photopolymer layer B and the substrate layer C of at least 0.5 N/10 mm.

20. The process according to claim 16, wherein the temperature in step b) is 75 C. to 110 C.

21. The process according to claim 16, wherein step b) is conducted in a heated space, or by means of a laminator.

22. The process according to claim 16, wherein step a) and step b) are conducted in a joint step.

23. The process according to claim 16, wherein the photopolymer layer B is present on a substrate layer A, and where the layers A and B are bonded to one another in an adhesive-free manner.

24. The process according to claim 16, wherein the substrate layer C is present on a substrate layer D and is at least part-bonded thereto, and where the substrate layer D consists of a transparent thermoplastic material or a material composite.

25. The process according to claim 16, wherein the glass transition temperature T.sub.g of the substrate layer C is higher than the temperature in process steps a)-d) for production of the layer composite B-C.

26. The process according to claim 16, wherein the substrate layer C is an aromatic polycarbonate layer.

27. A layer construction comprising a photopolymer layer B containing a hologram and a substrate layer C of (co)polycarbonate, obtained by the process of claim 16.

28. A sealed holographic medium comprising a layer construction according to claim 27.

29. An optical display comprising a sealed holographic medium according to claim 28, wherein the optical display is selected from the group consisting of autostereoscopic 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.

30. A security document comprising a sealed holographic medium according to claim 29.

Description

EXAMPLES

Chemicals:

[0164] In each case, the CAS number, if known, is reported in square brackets.

TABLE-US-00001 Raw materials for photopolymer layer B 2-Hydroxyethyl acrylate [818-61-1]Sigma-Aldrich Chemie GmbH Steinheim, Germany 2,6-Di-tert-butyl-4- [128-37-0]Merck KGaA, Darmstadt, methylphenol Germany 3-(Methylthio)phenyl [28479-19-8]Sigma-Aldrich Chemie isocyanate GmbH Steinheim, Germany Desmodur RFE [141-78-6] tris(p-isocyanatophenyl) thiophosphate, 27% in ethyl acetate, product from Covestro Deutschland 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. Desmodur N 3900 [28182-81-2] Covestro Deutschland AG, Leverkusen, DE, hexane diisocyanate-based polyisocyanate, proportion of iminooxadiazineclione at least 30%, NCO content: 23.5%. Desmorapid SO [301-10-0]Rhein Chemie Rheinau GmbH, Mannheim, Germany CGI-909 [1147315-11-4] tetrabutyl ammonium tris (3- chloro-4-methylphenyl)(hexyl)borate, BASF SE Trimethylhexamethylene [28679-16-5]ABCR GmbH & Co KG, diisocyanate Karlsruhe, Germany 1H,1H-7H- [335-99-9]ABCR GmbH & Co KG, Perfluoroheptan-1-ol Karlsruhe, Germany Astrazon Rosa FG 200% [3648-36-0]DyStar Colours Deutschland GmbH, Frankfurt am Main, Germany Sodium bis(2- [45297-26-5] Sigma-Aldrich Chemie GmbH, ethylhexyl)sulfosuccinate Steinheim, Germany Polytetrahydrofuran polyether polyols Additives BYK 310leveling agent silicone-containing surface additive from BYK Chemie GmbH, Wesel, Germany Tinuvin 292light a sterically hindered amine from BASF SE, stabilizer Ludwigshafen, Germany. Irganox 1135antioxidant a phenolic antioxidant from BASF SE, Ludwigshafen, Germany. Solvent Butyl acetate (BA) butyl acetate from Brenntag GmbH, Miilheim an der Ruhr, Germany. Methoxypropanol (MP) 1-methoxy-2-propanol from Brenntag GmbH, Miilheim an der Ruhr, Germany. MPA-EEP (M/E) a 50:50% by weight mixture of 1-methoxy-2- propyl acetate (DOWANOL PMA GLYCOL ETHER ACETATE) from DOW Deutschland Anlagengesellschaft mbH, Schwalbach, Germany, and ethyl 3- ethoxypropionate from Brenntag GmbH, Miilheim an der Ruhr, Germany. Films Makrofol DE 1-1 a bisphenol A (BP-A-PC)-based polycarbonate film from Covestro Deutschland AG, Leverkusen, DE, with a smooth surface on the front and reverse sides. Bayfol OX503 a bisphenol A (BP-A-PC)-based polycarbonate film from Covestro Deutschland AG, Leverkusen, DE, with a smooth surface on the front and reverse sides. Hostaphan polyethylene glycol terephtalate (PET) film from Mitsubishi Chemical Europe GmbH, Dusseldorf, Germany. Tacphan cellulose triacetate (TAC) film from LOFO High Tech Film GmbH, Weil am Rhein, Germany. Transphan polyamide (PA) film from LOFO High Tech Film GmbH, Weil am Rhein, Germany. Pokalon polycarbonate (PC) film from LOFO High Tech Film GmbH, Weil am Rhein, Germany. Plexiglas polymethylmethacrylat (PMMA) sheet from Evonik Industries AG, Essen, Germany.
Urethane acrylate 1: Phosphorothioyltris(oxybenzene-4,1-diylcarbamoyloxyethane-2,1-diyl)trisacrylate

[0165] 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 Covestro Deutschland 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.

Urethane acrylate 2: 2-({[3-(Methylsulphanyl)phenyl]carbamoyl}oxy)ethyl prop-2-enoate

[0166] 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.

Polyol Component:

[0167] A 1 l flask was initially charged with 0.037 g of Desmorapid SO, 374.8 g of -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.

Dye 1:

[0168] 5.84 g of anhydrous sodium bis(2-ethylhexyl)sulfosuccinate 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)sulfosuccinate [153952-28-4] were obtained as an oil of high viscosity.

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

[0169] A 6 l round-bottom flask was initially charged with 0.50 g of dibutyltin dilaurate 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.

Production of Holographic Media (Photopolymer Film)

[0170] 7.90 g of the above-described polyol component were melted and mixed with 7.65 g of the respective urethane acrylate 2, 2.57 g of the above-described urethane acrylate 1, 5.10 g of the abovedescribed 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 to obtain a clear solution. This was followed by addition of 1.50 g Desmodur N 3900 and mixing again.

[0171] Then this solution was applied in a roll-to-roll coating system to a 66 m-thick polycarbonate carrier film, where the product was applied by means of a coating bar in a wet film thickness of 19 pm. 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 m-thick polyethylene film. Subsequently, this film was light-tightly packaged.

Production and Characterization of Test Holograms

[0172] Test holograms were prepared as follows: the photopolymer films were cut to the desired size in the dark and laminated with the aid of a rubber roller onto a glass plate of dimensions 50 mm70 mm (thickness 3 mm).

[0173] 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 cm2 cm in size, and so the wavefront of the mirror was reconstructed on reconstructing the hologram. All 15 examples were exposed 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.

UV Exposure/Exposure with Actinic Radiation

[0174] The samples were placed onto the conveyor belt of a UV source with the carrier layer side facing the lamp and exposed 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 of 80 W/cm.sup.2. The parameters corresponded to a dose of 22.5 J/cm.sup.2 (measured with an ILT 490 Light Bug).

Analysis of the Hologram for Frequency Shift

[0175] Because of the high efficiency of the volume hologram, this diffractive reflection can be analysed in transmission with visible light with a VIS spectrometer (USB 2000, Ocean Optics, Dunedin, Fla., USA), and it appears in the transmission spectrum as a peak with reduced transmission. The quality of the hologram can be ascertained via the evaluation of the transmission curve: The width of the peak was determined as the full width at half maximum (FWHM) in nanometres (nm), the depth of the peak (Tmin) was reported as 100%Tmin in per cent (1T.sub.min), and the region with the lowest transmission indicates the wavelength (.sub.peak) of highest diffraction efficiency.

Study of Adhesion in Film Composite

[0176] The cohesion of all layers of the film composite was tested and evaluated by an in-house method. This involved pulling apart the photopolymer film B and the substrate film C applied thereto by hand. The results were quantified in the following grades from full adhesion (index: 0) down to no adhesion (index: 5). [0177] 0adhesion is so strong that the film composite cannot be separated without destruction; [0178] 1strong adhesion, can be peeled off only with considerable use of manual force; [0179] 2moderately strong adhesion, can be peeled off with use of manual force; [0180] 3moderate adhesion, can be peeled off with use of low force; [0181] 4slight adhesion, can be peeled off with use of slight force; [0182] 5very weak or zero adhesion. Film composite has contact adhesion only.

Noninventive Examples A-C, Inventive Example 1

[0183] A film piece of size 5 cm7 cm of the photopolymer film was cut to size in the dark (57 cm) and the PE lamination was removed. Subsequently, the photopolymer surface was laminated together with a polycarbonate film (Makrofol DE 1-1, thickness 125 m) by means of a roll laminator (Dumor Trident 46; lamination speed: 0.3 m/min, roll pressure setting: high; contact time: about 0.5 sec) at various roll temperatures. Thereafter, a reflection hologram was written at 532 nm and the sample was fully bleached with UV light (5 J/cm.sup.2). The samples were characterized by spectrometry and with regard to the adhesion between the photopolymer and polycarbonate film (Makrofol DE 1-1, thickness 125 m). The results are compiled in Table 1.

TABLE-US-00002 TABLE 1 Characterization of Examples A-C and 1 with regard to hologram and adhesion Adhesion Shift vs. 0 (very strong) Lamination 1-T.sub.min .sub.peak reference to Example temperature [%] [nm] [nm] 5 (very low) A 60 C. 85.5 532 2.1 5 1 100 C. 84.4 533 2.8 3 B 120 C. bubble formation C 140 C. bubble formation

[0184] In Inventive Example 1, a low hologram shift (vs. reference sample) was measured, with measurement of moderate adhesion between photopolymer and polycarbonate film. In Noninventive Example A, no improvement in adhesion is found. In Noninventive Examples B and C, the films exhibited significant bubble formation.

Noninventive Examples D-F, Inventive Example 2

[0185] A film piece of size 5 cm7 cm of the photopolymer film was cut to size in the dark (57 cm) and the PE lamination was removed. Subsequently, the photopolymer surface was laminated together with a polycarbonate film (Makrofol DE 1-1, thickness 125 m) by means of a roll laminator (Dumor Trident 46; lamination speed: 0.3 m/min, roll pressure setting: high) at room temperature. Thereafter, a reflection hologram was written at 532 nm and the sample was laminated once again by means of the roll laminator at various roll temperatures and then fully bleached with UV light (5 J/cm.sup.2). The samples were characterized by spectrometry and with regard to adhesion. The results are compiled in Table 2.

TABLE-US-00003 TABLE 2 Characterization of Examples D-F and 2 with regard to hologram and adhesion Adhesion Shift vs. 0 (very strong) Lamination 1-T.sub.min l.sub.peak reference to Example temperature [%] [nm] [nm] 5 (very low) D RT 82.6 535 4.9 5 2 100 C. 81.4 533 3.5 3 E 120 C. bubble formation F 140 C. bubble formation

[0186] In Inventive Example 2, moderate adhesion was determined, with measurement of a slight hologram shift (vs. reference sample). In Noninventive Example D no adhesion was found; in Noninventive Examples E and F significant bubble formation was found.

Noninventive Examples G-I, Inventive Examples 3-6

[0187] A film piece of size 5 cm7 cm of the photopolymer film was cut to size in the dark (57 cm) and the PE lamination was removed. Subsequently, the photopolymer surface was laminated together onto glass and a reflection hologram was written at 532 nm. Subsequently, the film was delaminated from the glass and the photopolymer surface was laminated onto a polycarbonate film (Makrofol DE 1-1, thickness 125 m) by means of a roll laminator (Dumor Trident 46; lamination speed: 0.3 m/min, roll pressure setting: high) at various laminator roll temperatures. This was followed by complete bleaching with UV light (5 J/cm.sup.2). The samples were characterized by spectrometry and with regard to adhesion. The results are compiled in Table 3.

TABLE-US-00004 TABLE 3 Characterization of Examples G-I and 3-6 with regard to hologram and adhesion Adhesion Shift vs. 0 (very strong) Lamination 1-T.sub.min .sub.peak reference to Examples temperature [%] [nm] [nm] 5 (very low) G RT 93.4 529 1.0 5 3 70 C. 93.5 529 1.0 4 4 80 C. 93.9 529 1.0 3-4 5 100 C. 94.5 530 0.3 3 6 110 C. 94.7 530 0.3 2 H 120 C. bubble formation I 140 C. bubble formation

[0188] In Inventive Examples 3 to 6, a small hologram shift (vs. reference sample) was measured, while there was a distinct rise in the adhesion between the photopolymer and polycarbonate film with temperature. In Noninventive Example G, no adhesion is observed. In Noninventive Examples H and I, the films exhibited significant bubble formation.

Noninventive Example L, Inventive Examples 7-12

[0189] A film piece of size 5 cm7 cm of the photopolymer film was cut to size in the dark (57 cm) and the PE lamination was removed. Subsequently, the photopolymer surface was laminated together onto glass and a reflection hologram was written at 532 nm. Subsequently, the film was delaminated from the glass and the photopolymer surface was laminated with a polycarbonate film (Makrofol DE 1-1, thickness 125 m) by means of a roll laminator (Dumor Trident 46; lamination speed: 0.3 m/min, roll pressure setting: high) at room temperature. This was followed by heat treatment of the construction at various temperatures in the oven. The samples were exposed by UV light treatment (5 J/cm.sup.2) directly after the heating in the oven. Finally, the samples were characterized by spectrometry and with regard to adhesion. The results and the experimental parameters are summarized in Table 4.

TABLE-US-00005 TABLE 4 Characterization of Inventive Examples 7-12 and Noninventive Example L with regard to hologram stability and adhesion Storage Time Adhesion time in between 0 (very Oven the oven Shift vs. strong) temp. oven and UV 1-T.sub.min .sub.peak reference to 5 Example ( C.) (sec.) step min [%] [nm] [nm] (very low) 7 100 20 5 min 93.3 527 3.4 4 8 100 30 5 min 96.2 529 1.3 4 9 100 50 5 min 96.4 528 1.7 3 10 100 70 5 min 95.3 529 0.6 3 11 100 90 5 min 95.5 528 2.4 2 12 100 120 5 min 95.9 529 1.0 2 L 120 30 5 min bubble formation

[0190] In Inventive Examples 7 to 12, a small, acceptable hologram shift was measured, while there was a rise in the adhesion between the photopolymer and polycarbonate film with temperature. In Noninventive Example L, significant bubble formation was observed. Examples 9-12 are preferred (storage time>50 seconds at oven temperature 100 C.), and Examples 11-12 (storage time>90 seconds at oven temperature 100 C.) are particularly preferred.

Noninventive Examples M-S, Inventive Examples 13-15

[0191] A film piece of size 5 cm7 cm of photopolymer film was cut to size in the dark (57 cm) and the PE lamination was removed. Subsequently, the photopolymer surface was laminated together onto various thermoplastic polymer films by means of a roll laminator (Dumor Trident 46; lamination speed: 0.3 m/min, roll pressure setting: high) at room temperature. Subsequently, the construction was subjected to heat treatment in the oven at 100 C. for 20 seconds. Details of the experiments and the results are collated in Table 5.

TABLE-US-00006 TABLE 5 Adhesion between photopolymer layer and various laminated-on thermoplastic polymer films and glass Adhesion 0 (very strong) Laminated-on Material of the to Example polymer films substrate film 5 (very low) 13 Bayfol OX503 66 m BP A polycarbonate 2 14 Makrofol 1-1 125 m BP A polycarbonate 2 M Transphan 60 m Polyamide 5 N Tacphan 50 m Cellulose triacetate 5 15 Pokalon 60 m BP TMC polycarbonate 2-3 O Hostaphan 36 m Polyethylene glycol 5 terephthalate P Hostaphan 23 m Polyethylene glycol 5 terephthalate Q Hostaphan 50 m Polyethylene glycol 5 terephthalate R Plexiglas 1.5 mm Polymethylmethacrylat 5 S Glass Soda glass 5

[0192] Good adhesion was generated only in Inventive Examples 13, 14 and 15 with PC-based films. In Noninventive Examples M to S with non-polycarbonate-based materials, adhesion after processing remains low.

Noninventive Example T, Inventive Examples 16-19

[0193] A film piece of size 15 cm20 cm of a photopolymer film with thickness 25 m was cut to size in the dark (1520 cm) and the PE lamination was removed. Subsequently, the photopolymer surface was laminated together on a polycarbonate film (Makrofol DE 1-1, thickness 125 m) (Dumor Trident 46; lamination speed: 0.3 m/min, roll pressure setting: high) at room temperature. This was followed by heat treatment of the construction with various temperatures and times in the oven. Subsequently, the samples were fully bleached with UV light (5 J/cm.sup.2). Each film was cut into at least 6 different strips of width 10 mm. The bonding forces between the photopolymer and polycarbonate film were measured in accordance with ISO/IEC 10373 with a tensile tester according to DIN EN ISO 527-1. Details of the experiments and the results are collated in Table 6. The bonding force figures in the table correspond to the mean from six individual measurements on identically prepared samples.

TABLE-US-00007 TABLE 6 Bonding forces (in N/10 mm) measured between photopolymer layer B and laminated-on polycarbonate film (substrate layer C) Adhesion Thermal Bonding 0 (very strong) Oven temp. treatment force to Examples ( C.) time [N/10 mm] 5 (very low) T 60 5 min 0.3 5 16 70 30 sec 1.3 3 17 100 30 sec 4.8 1 18 100 10 min 13.0 0 19 110 30 sec 4.6 1

[0194] In Inventive Examples 17 to 19, a very good bonding force was obtained, and this rose as a function of oven temperature and time. In Example 19, a very high bonding force of 13 N/10 mm was obtained, and so the layer construction can no longer be separated without destruction.

Inventive Examples 20 and 21

[0195] A film piece of size 15 cm20 cm of photopolymer film in thickness 15 m was cut to size in the dark (1520 cm) and the PE lamination was removed. Subsequently, the photopolymer surface was laminated onto glass and reflection holograms were written with variable writing dose at 532 nm. Subsequently, the latter were delaminated from the glass in the dark and laminated onto a polycarbonate film (Makrofol DE 1-1, thickness 125 m) (Dumor Trident 46; lamination speed: 0.3 m/min, roll pressure setting: high) at room temperature. This was followed by heat treatment in the oven at 100 C. for 20 seconds. Subsequently, the samples were fully bleached with UV light (5 J/cm.sup.2). Each film was cut into 6 different strips of width 10 mm. The bonding forces between the photopolymer and polycarbonate film were measured in accordance with ISO/IEC 10373 with a tensile tester according to DIN EN ISO 527-1. Details of the experiments and the results are collated in Table 7.

TABLE-US-00008 TABLE 7 Bonding forces (in N/10 mm) measured between photopolymer layer B and laminated-on PC film (substrate layer C) Adhesion Writing Bonding 0 (very strong) dose force to Examples (mJ/cm.sup.2) [N/10 mm] 5 (very low) 20 29.6 3.5 3 21 177.8 3.5 3