Color converters

Abstract

A color converter comprising at least one layer comprising at least one organic fluorescent colorant and at least one barrier layer having a low permeability to oxygen.

Claims

1. An illumination device, comprising: an LED; and a color converter, wherein the color converter comprises: at least one layer comprising at least one organic fluorescent colorant, the at least one organic fluorescent colorant embedded into a matrix of an organic polymer which is polystyrene, polycarbonate, polymethyl methacrylate, polyvinylpyrrolidone, polymethacrylate, polyacrylate, polyvinyl acetate, polybutene or polyethylene glycol; and at least one barrier layer having a low permeability to oxygen of less than 100 mL/m.sup.2*d, wherein the at least one barrier layer is selected from the group consisting of a glass, quartz, a metal oxide, SiO.sub.2, titanium nitride, a SiO.sub.2/metal oxide multilayer material, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, a liquid-crystal polymer, polybutylene terephthalate, polyethylene terephthalate, polyvinyl butyrate, polyvinyl chloride, a polyamide, a polyoxymethylene, a polyimide, a polyetherimide, and an epoxy resin, wherein the at least one organic fluorescent colorant is selected from the group consisting of: ##STR00005## ##STR00006## ##STR00007## wherein R.sup.1 is a linear or branched C.sub.1-C.sub.18 alkyl radical, a C.sub.4-C.sub.8 cycloalkyl radical which is optionally mono- or polysubstituted by halogen or by a linear or branched C.sub.1-C.sub.18 alkyl, phenyl, or naphthyl, where the phenyl or naphthyl is optionally mono- or polysubstituted by halogen or by a linear or branched C.sub.1-C.sub.18 alkyl; X represents a substituent in an ortho, para, or both ortho and para positions and is a linear or branched C.sub.1-C.sub.18 alkyl; and y is a number from 0 to 3; wherein the at least one layer comprising the at least one organic fluorescent colorant is surrounded on all sides by the at least one barrier layer having a low permeability to oxygen; wherein the LED and the color converter are present in a remote phosphor structure; wherein air, noble gases, nitrogen or other gases or mixtures thereof are present between the color converter and the LED; and wherein the distance between the LED and the color converter is from 0.1 to 10 cm.

2. The illumination device according to claim 1, wherein the at least one barrier layer consists essentially of at least one barrier material having a low specific oxygen permeability of less than 1000 mL*100 m /m.sup.2*d.

3. The illumination device according to claim 1, wherein the at least one barrier layer has a low permeability to water vapor of less than 1 g/m.sup.2*d.

4. The illumination device according to claim 1, wherein the organic fluorescent dye is at least one selected from the group consisting of 3,9-dicyanoperylene-4,10-bis(isobutyl carboxylate) and 3,10-dicyanoperylene-4,9-bis(isobutylcarboxylate).

5. The illumination device according to claim 1, wherein the color converter is a film, a plate, or a sheet.

6. A method for converting light produced by an LED, the method comprising: passing light produced by the LED through a color converter, the color converter comprising: at least one layer comprising at least one organic fluorescent colorant, the at least one organic fluorescent colorant embedded into a matrix of an organic polymer which is polystyrene, polycarbonate, polymethyl methacrylate, polyvinylpyrrolidone, polymethacrylate, polyacrylate, polyvinyl acetate, polybutene or polyethylene glycol; and at least one barrier layer having a low permeability to oxygen of less than 100 mL /m.sup.2*d, wherein the at least one barrier layer is selected from the group consisting of a glass, quartz, a metal oxide, SiO.sub.2, titanium nitride, a SiO.sub.2/metal oxide multilayer material, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, a liquid-crystal polymer, polybutylene terephthalate, polyethylene terephthalate, polyvinyl butyrate, polyvinyl chloride, a polyamide, a polyoxymethylene, a polyimide, a polyetherimide, and an epoxy resin, wherein the at least one organic fluorescent colorant is selected from the group consisting of: ##STR00008## ##STR00009## ##STR00010## wherein R.sup.1 is a linear or branched C.sub.1-C.sub.18 alkyl radical, a C.sub.4-C.sub.8 cycloalkyl radical which is optionally mono- or polysubstituted by halogen or by a linear or branched C.sub.1-C.sub.18 alkyl, phenyl, or naphthyl, where the phenyl or naphthyl is optionally mono- or polysubstituted by halogen or by a linear or branched C.sub.1-C.sub.18 alkyl; X represents a substituent in an ortho, para, or both ortho and para positions and is a linear or branched C.sub.1-C.sub.18 alkyl; and y is a number from 0 to 3; wherein the at least one layer comprising the at least one organic fluorescent colorant is surrounded on all sides by the at least one barrier layer having a low permeability to oxygen; wherein the LED and the color converter are present in a remote phosphor structure; wherein air, noble gases, nitrogen or other gases or mixtures thereof are present between the color converter and the LED; and wherein the distance between the LED and the color converter is from 0.1 to 10 cm.

7. The illumination device according to claim 1, wherein the matrix material consists essentially of polystyrene and/or polycarbonate.

8. The illumination device according to claim 1, wherein the matrix material is poly(methyl methacrylate).

9. A method for protecting the lat least one layer comprising at least one organic fluorescent colorant of the illumincation device of claim 1, the method comprising: surrounding the at least one layer comprising at least one organic fluorescent colorant on all sides by the at least one barrier layer, thereby obtaining the color converter.

Description

EXAMPLES

(1) Materials Used

(2) Polymer 1: transparent homopolymer of methyl methacrylate having a Vicat softening temperature of 96 C. to DIN EN ISO 306, (Plexiglas 6N from Evonik)

(3) Polymer 2: transparent polystyrene based on a homopolymer of styrene having a density of 1048 kg/m.sup.3 and a Vicat softening temperature of 98 C. to DIN EN ISO 306 (PS 168 N from BASF SE)

(4) Dye 1: greenish-yellow-fluorescing fluorescent dye consisting of a mixture of 3,9-dicyanoperylene-4,10-bis(isobutyl carboxylate) and 3,10-dicyanoperylene-4,9-bis(isobutyl carboxylate).

(5) Dye 2: yellow-fluorescing fluorescent dye with the name 9-Cyano-N-(2,6-diisopropylphenyl)perylene-3,4-dicarboxylic monoimide.

(6) Dye 3: red-fluorescing fluorescent dye with the name N,N-bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboximide.

(7) Barrier material 1: plates of borosilicate glass of thickness 1 mm with an area of 3 cm3 cm.

(8) Barrier material 2: barrier film ESCAL (composed of polypropylene (PP)/metal oxide coated PVA (polyvinyl alcohol)/polyethylene (PE), film thickness: approx. 112 m), supplier Dry&Safe GmbH, Oensingen, Switzerland.

(9) Barrier material 3: barrier film Saranex (available from Dow, USA), which are multilayer blown coextruded films with polyolefin skin layers and a PVDC (polyvinylidene chloride) barrier layer; film thickness 102 m.

(10) Barrier material 4: EVAL L films, ethylene vinyl alcohol (EVOH) copolymer films, supplier EVAL Europe nv, Antwerpen, Netherlands.

(11) Titanium dioxide: TiO.sub.2 rutile pigment by the sulfate process with a mean scattering power to DIN 53165 of 94.0 to 100 (Kronos 2056 from Kronos Titan)

(12) Exposure of the Samples:

(13) The samples were exposed with a self-constructed exposure apparatus composed of 16 commercially available GaN-LEDs of the Rebel series (from Lumileds Lighting, wavelength approx. 451 nm). Two light-scattering plates of opal glass were arranged in front of the exposure apparatus. The luminance at each sample position was homogenously distributed and approx. 0.08 W/cm.sup.2.

(14) Determination of the Photostability of the Samples:

(15) For analysis, the samples were removed from the exposure stations and analyzed in the C9920-02 quantum yield measuring system (from Hamamatsu). This involved illuminating each of the samples in an integrating sphere (Ulbricht sphere) with light of 450 to 455 nm. By comparison with the reference measurement in the Ulbricht sphere without sample, the non-absorbed fraction of the excitation light and the fluorescent light emitted by the sample are determined by means of a calibrated CCD spectrometer. Integration of the intensities over the non-absorbed excitation light or over the emitted fluorescent light gives the degree of absorption or fluorescence intensity or fluorescence quantum yield of each sample.

(16) Each of the specimens was exposed constantly over a period of 20 days and removed from the exposure apparatus only to determine the degree of absorption, the fluorescence intensity and the fluorescence quantum yield of the color converters.

(17) Production of the Color Converters 1-4:

(18) Approx. 2.5 g of polymer and the desired amount of dye were dissolved in approx. 5 mL of methylene chloride, and 0.5% by weight of TiO.sub.2, based on the amount of polymer used was dispersed therein. The resulting solution/dispersion was coated onto a glass surface with a box-type coating bar (wet film thickness 400 m). After the solvent had dried off, the film was detached from the glass and dried at 50 C. in a vacuum drying cabinet overnight. Two circular film pieces each with a diameter of 22 mm were punched out of this film, and then served as test samples.

(19) Encapsulation with Glass:

(20) The thus obtained film pieces were transferred with the barrier material 1 into a nitrogen-filled glovebox. After about 2 hours, the film pieces were placed between two sheets of barrier material 1 and pressed on using fingers. Subsequently, the thus obtained test samples enclosed in a sandwich-like manner were sealed at the edges of the glass plates with a photocurable epoxy adhesive, and removed again from the glovebox.

(21) The following samples were produced and examined:

(22) TABLE-US-00001 Film Poly- TiO.sub.2 thick- Barrier No. mer Dye Dye content* content* ness layers 1 1 1 0.014% by wt. 0.5% by wt. 84 m top and bottom 1a 1 1 0.02% by wt. 0.5% by wt. 96 m none 2 2 1 0.014% by wt. 0.5% by wt. 82 m top and bottom 2a 2 1 0.014% by wt. 0.5% by wt. 82 m none 3a 2 1 0.03% by wt. 0.5% by wt. 79 m none 4 1 2 0.02% by wt. 0.5% by wt. 91 m top and bottom 4a 1 2 0.02% by wt. 0.5% by wt. 91 m none 5 2 2 0.03% by wt. 0.5% by wt. 73 m top and bottom 5a 2 2 0.03% by wt. 0.5% by wt. 73 m none *based on the amount of polymer used

(23) FIGS. 1 and 3 show, on the abscissa, the exposure time in days and, on the ordinate, the percentage of the incident light (450 to 455 nm) which has been absorbed.

(24) The numbers beside the three curves correspond to the sample numbers.

(25) It was found that the absorption of light in the case of the samples which had no barrier layer on the top and bottoms sides (samples with the suffix a) decreased significantly with exposure time.

(26) In the case of the inventive color converters which had a barrier layer on both the top and bottom sides (samples without suffix a), the absorption remained virtually constant over the exposure period with a much weaker overall decrease in absorption compared to color converters having no barrier layer on both the top and bottom sides.

(27) FIGS. 2 and 4 show, on the abscissa, the exposure time in days and, on the ordinate, the relative fluorescence intensity.

(28) The numbers beside the three curves correspond to the sample numbers.

(29) It was found that the fluorescence intensity in the case of the samples which had no barrier layer on the top and bottoms sides (samples with the suffix a) decreased significantly with exposure time.

(30) In the case of the inventive color converters which had a barrier layer on both the top and bottom sides (samples without suffix a), the fluorescence remained virtually constant over the exposure period with a much weaker overall decrease in fluorescence compared to color converters having no barrier layer on both the top and bottom sides.

(31) Production of the Color Converter 6 and 7:

(32) The desired amount of dye(s), polymer and TiO.sub.2 (see table 1 below) were fed into a double shaft extruder of the Collin ZSK 25-30D type and processed to granules. A single shaft extruder of the Collin Teach line E 20 T was charged with these granules. The granules were processed to a film having a thickness of approx. 400 m via slot type nozzles. Circular film pieces each with a diameter of 22 mm were punched out of this film, and then served as test samples.

(33) TABLE-US-00002 TABLE 1 TiO.sub.2 film No. polymer dye content of dye 1* dye content of dye 3* content* thickness 6 1 1 0.008% by wt. 3 0.50% by 400 m wt. 7 1 1 0.008% by wt. 3 0.0015% by wt. 0.50% by 400 m wt. *based on the amount of polymer used
Encapsulation with Barrier Material 2
Route a)

(34) The punched film pieces were transferred with the barrier material 2 (ESCAL film) into a nitrogen-filled glove-box with yellow light conditions. After about 2 hours, a photocurable adhesive was applied to the top side of the film piece. The barrier material 2 was placed onto the adhesive side and pressed on using rollers. The adhesion was cured with UV-A light and visible light. The same procedure was repeated on the bottom side of the film piece. Finally, the top and bottom barrier materials passing over the color converter were sealed with the aid of heat sealing pliers. The thus obtained color converters had a barrier layer on both the top and bottom sides.

(35) Route b)

(36) The punched film pieces were transferred with the barrier material 2 (ESCAL film) into a nitrogen-filled glove-box. The glove-box comprised a hetseal laminator. After about 2 hours, the film pieces and the barrier material 2 (ESCAL L film, the PE side of the barrier material faced the film piece) were pressed together at 150 C. and sealed in the hot seal laminator. The same procedure was repeated on the bottom side of the film piece.

(37) Production of the Color Converter 8 and 9:

(38) Approx. 20 g of polymer and the desired amount of dye were dissolved in approx. 60 mL of methylene chloride, and 0.1% by weight of TiO.sub.2, based on the amount of polymer used, was dispersed therein (see table 2). The resulting solution/dispersion was coated onto a glass surface. After the solvent had dried off, the film was detached from the glass, crushed, dried at 50 C. in a vacuum drying cabinet overnight, ground in a laboratory mill and the powder obtained was dried at 50 C. in a vacuum drying cabinet overnight. The powder was hot pressed at 200 C. at a pressure of 3 bar (for 6 minutes) and then at a pressure of 100 bar (5 min) using a metal pressing frame to give circular polymer film pieces each with a diameter of 1.5 mm.

(39) TABLE-US-00003 TABLE 2 TiO.sub.2 film No. polymer dye content of dye 1* dye content of dye 3* content* thickness 8 2 1 0.0048% by wt. 3 0.10% by 1.5 mm wt. 9 2 1 0.0048% by wt. 3 0.00105% by wt. 0.10% by 1.5 mm wt. *based on the amount of polymer used
Encapsulation with Barrier Material 2:

(40) The encapsulation process described above using barrier material 2 was repeated but using color converter 8 and 9 instead of color converter 6 and 7.

(41) The specimens no. 6, 6a, 7, 7a, 8, 8a, 9 and 9a were exposed with the exposure apparatus constantly over a period of 20 days as described above. Table 3 below shows the photostability and the remaining fluorescence.

(42) TABLE-US-00004 TABLE 3 photostability No remaining fluorescence (%) after x days of exposure 6 after 20 days: >90% 6a after 10 days: <50% 7 after 20 days: >90% 7a after 10 days: <50% 8 after 20 days: >90% 8a after 10 days: <50% 9 after 20 days: >90% 9a after 10 days: <50%

(43) It was found that the fluorescence intensity in the case of the samples which had no barrier layer on the top and bottoms sides (samples with the suffix a) decreased significantly with exposure time.

(44) In the case of the inventive color converters which had a barrier layer both on the top and bottom sides (samples without suffix a), the fluorescence remained virtually constant over the exposure period with a much weaker overall decrease in fluorescence compared to color converters having no barrier layer both on the top and bottom sides.

(45) Production of the Color Converters 10 and 11:

(46) The encapsulation process described above for color converter 6 and 7 was repeated but using barrier material 3 instead of barrier material 2.

(47) Production of the Color Converters 12 and 13:

(48) The encapsulation process described above for color converter 6 and 7 was repeated but using barrier material 4 instead of barrier material 2.

(49) Production of the Color Converters 14 and 15:

(50) The encapsulation process described above for color converter 8 and 9 was repeated but using barrier material 3 instead of barrier material 2.

(51) Production of the Color Converters 16 and 17:

(52) The encapsulation process described above for color converter 8 and 9 was repeated but using barrier material 4 instead of barrier material 2.

(53) In the case of the inventive color converters 10, 11, 12, 13, 14, 15, 16 and 17 which had barrier layers both on the top and bottom sides, the fluorescence remained virtually constant over the exposure period with a much weaker overall decrease in fluorescence compared to comparison color converters having no barrier layer on both the top and bottom sides.