MXPA98001411A - Solar collectors fluorescent, duran - Google Patents

Abstract

The present invention relates to a solar collector that exhibits long-lasting fluorescent properties, characterized in that it comprises a polymeric matrix, a dye and a hindered amine light stabilizer, wherein the colorant comprises at least one of the dyes selected from the group of thioxanthone, perylene imide and thioindigoid compounds and the polymer matrix comprises polycarbonate

Description

SOLAR FLUORESCENT, DURABLE COLLECTORS FIELD OF THE INVENTION The invention relates to articles that have increased fluorescence durability. In particular, the invention relates to fluorescent solar concentrators or concentrators which exhibit increased fluorescence durability.

BACKGROUND OF THE INVENTION It is commonly known that solar radiation causes colorants to degrade. This is a particularly acute problem for articles exposed to solar radiation for extended periods of time, such as solar collectors. Color degradation occurs in articles colored with conventional dyes, as well as articles colored with fluorescent dyes. However, this is a particularly acute problem for fluorescent articles. Fluorescent dyes degrade, often becoming colorless more quickly than conventional dyes. The effective life REF .: 26824 of fluorescent materials exposed to daily solar radiation is short, and is typically measured in terms of days or months. Fluorescent dyes are frequently used in flat-plate solar collectors, because fluorescent dyes more effectively absorb light of lower wavelength in the ultraviolet and visible wavelength ranges, and emit that energy at long wavelengths. higher wave. The higher wavelength light emitted by the fluorescent-colored solar collector is more easily converted to electrical energy than light at lower wavelengths by the solar cells. The silicon solar cells commonly used have optimal efficiency at wavelengths between 500-900 nanometers, and are very inefficient below 400 nanometers. At ground level, solar radiation comprises electromagnetic radiation having wavelengths greater than about 290 nanometers, with the range of about 400 to about 700 nanometers typically considered the range of visible light. Radiation that has wavelengths shorter than visible light is believed to damage conventional and fluorescent dyes. Attempts to maintain the color of a fluorescent article have included the addition of ultraviolet filters which selectively filter radiation below the range of 340 nm to 380 nm. Japanese Patent Application Kokai No. 2-16042, No. 63-165914 (Koshiji, et al.), Discloses fluorescent articles comprising a filter layer and a layer containing a fluorescent coloring agent, wherein the filter layer it only allows a defined interval of light transmission. U.S. Patent No. 5,387,458 also discloses a retroreflective article comprising an ultraviolet filtration layer and a color layer contained in a defined polymer matrix. The article shows durable fluorescence in daylight and resistance to degradation from exposure to sunlight. It is known that polycarbonate is easily degraded when exposed to solar energy. Attempts to stabilize the polycarbonate include the addition of ultraviolet bizbenzophenone absorbers to the polycarbonate, as described in U.S. Patent No. 5,306,456 ("Patent 56") which is incorporated by reference herein. The '56 patent does not take precautions in adding spherically hindered amines to the polycarbonate resin or to a polycarbonate copolymer. U.S. Patent No. 4,110,123, which is incorporated by reference herein, teaches fluorescent centers (light concentrators) which consist of thin layers of transparent solid or liquid materials with embedded fluorescent centers, and which in conjunction with the Solar cells serve to convert solar energy to electrical energy. Solar collectors are needed that show improved fluorescence durability. In particular, fluorescent solar collectors that retain their fluorescent properties without requiring the use of protective topcoats are also necessary.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides, in brief summary, solar collectors that show improved retention of fluorescent properties, without the use of protective topcoats. That is, the solar collectors of the invention retain their ability to fluoresce for a longer period than is normally expected when exposed to direct sunlight. The invention further includes a method for manufacturing such durable, fluorescent solar collectors. The solar collectors of the invention comprise (1) a polymeric matrix, (2) a dye, and (3) a light stabilizer, hindered amine, wherein the polymeric matrix is comprised of polycarbonate and the dye contains at least one of the compounds selected from the group of thioxanthone, perylene-imide, and dyes of the thioindigoid type. The hindered amine light stabilizer is comprised of compounds of the 2, 2, 6, 6-tetraalkyl-piperidine class in a preferred embodiment. In one embodiment, the solar collectors of the present invention also include mirrors or retroreflective elements. The resulting articles show light concentration and durable fluorescent properties. Such materials show prolonged ability to collect and / or concentrate light.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further explained with reference to the drawings, wherein: Figure 1 is a cross-sectional view of an apparatus for the concentration of light, for use in solar cells, Figure 2 is an alternative embodiment of the invention showing a light concentrator, Figure 3 is a modality similar to that of Figure 2, which also includes a protective top layer.

These figures, which are idealized, are not to scale and are intended to be merely illustrative and not limiting.

Definitions As referred to herein, the term "colorant" will mean the pigment or colorants or other substances used to impart hue and intensity of color and value to an article. As used herein, the term "conventional dye" will mean dyes that do not show fluorescent properties with the naked eye. As referred to herein, the term "colorant" will mean substances that impart color to a substrate by selective absorption of light. The dyes are. soluble and / or undergo an application process which, at least temporarily, destroys any crystalline structure of the colored substances. The dyes are conserved in the substrate by absorption, solution and mechanical retention, or by ionic or covalent chemical bonds. As referred to herein, the term "durable" will refer to improved color retention or fluorescence after exposure to environmental conditions. As referred to herein, the term "hindered amine light stabilizer" refers to spherically hindered amines of the class of compounds typically represented by 2, 2, 6, 6-tetraalkyl-piperidines.

As referred to herein, the term "solar collector" refers to an article useful for absorbing solar energy. As referred to herein, the term "solar concentrator" will be used interchangeably with the term "solar collector" but will also refer to useful articles for concentrating energy. As referred to herein, the term "resistance to environmental conditions" will mean the exposure of an article to either natural environments or artificial environments which include heat, light, humidity, and ultraviolet radiation.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE MODALITIES OF THE INVENTION The present invention combines a polymeric matrix containing the hindered amine light dye and stabilizer to create a solar collector that exhibits more durable fluorescence. The polymer matrix of the invention is first discussed, followed by a discussion of suitable dyes and suitable hindered amine light stabilizers.

POLYMERIC MATRIX Polycarbonate is the preferred polycarbonate matrix of the invention, because it is substantially transparent and is easily colored with fluorescent and conventional dyes. In addition, the polycarbonate exhibits good optical properties such as good light transmittance, which is important for the present invention. Although polycarbonate exhibits these desirable characteristics, it is surprising that polycarbonate is the polymeric matrix of choice for the present invention. As is commonly known in the art, polycarbonate is photosensitive and degrades when exposed to ultraviolet radiation.

COLORING In a preferred embodiment, the fluorescent dyes of the invention are dyes of the class of compounds of thioxanthone, perylene imide and thioindigoid. The invention anticipates that a simple fluorescent dye or pigment may be used to color an article of the invention, or that a combination of one or more fluorescent dyes and one or more conventional dyes may be used. Typically, the article of the present invention contains between about 0.01 and about 2.00 weight percent, and preferably between about 0.05 and about 0.70 weight percent, and more preferably between about 0.1 and about 0.5 weight percent of colorant fluorescent. It will be understood that articles with dye charges outside this range can be used according to the invention. As is known to those of skill in the art, articles having heavier dye loads will show brighter fluorescence than items with lighter dye loads of the same dye will show. However, articles that have very high fluorescent dye charges may show a self-extinguishing phenomenon, which occurs when fluorescent dye molecules absorb energy emitted by neighboring fluorescent dye molecules. This auto-off causes an undesirable decrease in fluorescent brightness. In some embodiments, the colorant in the articles of the present invention will consist essentially of one or more dyes selected from the class of perylene imide, thioindigoid, and thioxanthone compounds. In other cases, the article may also contain other coloring agents such as pigments or other colorants, in addition to those described to adjust the color and appearance of the article. For example, polycarbonate typically has a yellow appearance. Minor amounts, for example, of about 0.01 weight percent or less, of the pigments often referred to as "bluing agents" may be incorporated to neutralize the yellow appearance. Other non-fluorescent or conventional dyes or pigments may also be added to the present invention, however, care must be taken in selecting such dye and pigment fillers, so that the dyes do not significantly interfere with the operation of the fluorescent dyes.

Amined Light Stabilizers The hindered amine light stabilizers (HALS) are included in the solar collector of the present invention. This is a somewhat surprising combination because, as one skilled in the art will recognize, it is not recommended to combine amines with polycarbonate. It has traditionally been known that amines attack the carbonyl group of polycarbonate, thereby degrading polycarbonate (for example see Schnell, Chemistry and Physics of Polycarbonates, page 183, 1964). Without wishing to be bound by theory, it is believed that the combination of the spherically hindered amine, the polycarbonate matrix and the colorant in the present invention prevents otherwise indefinite degradation and / or reaction between the dye and the polycarbonate. . As far as we are concerned, the advantages of the present invention are achieved through the combination of the dye, the polymeric matrix material, and the hindered amine light stabilizer described herein. It is thought that the dyes in the present invention act as singlet oxygen sensitizers. The energy transfer, which occurs in general from the triplet state of the dye, is turned off by the molecular oxygen in the basal state, to produce active singlet oxygen. The singlet oxygen is then free to react with the dye, causing degradation of the dye. Alternatively, singlet oxygen may react with the polymer, leading to degradation of the polycarbonate. However, the hindered amine light stabilizer present in the invention is capable of directly quenching the singlet oxygen formed, preventing the onset of degradation reactions. The hindered amine light stabilizers can also prevent secondary reactions initiated by the oxidation of the polymer from proceeding. These reactions include a number of chain reactions based on free radicals or peroxide, which are thought to occur in the photooxidation of the polycarbonate, which can result in degradation of the polymer and dye. The prevention of these reactions increases the durability of polycarbonate and dye in the colorful system. Any hindered amine light stabilizer is suitable for the present invention, such as the 2, 2, 6, 6-tetraalkyl-piperidine compounds but preferably the 2, 2, 6, 6-tetramethyl-piperidine compounds were used as the light stabilizers of hindered amine, due to the easy availability of the compounds. Hindered amine light stabilizers are included in the articles of the present invention from about 0.05 to about 1.00 percent by weight, and preferably from about 0.10 to about 0.75 percent by weight, and still more preferably from about 0.1 to about 0.5. percent in weight.

Solar Collectors Solar collectors are typically used in conjunction with solar cells. Solar or silicon cells convert light energy into electrical energy. Conventional silicon cells suffer from problems of inefficiency. Therefore, solar collectors which are generally comprised of a thin polymeric film having mirror edges or other means, concentrate or direct the incident sunlight towards the silicon solar cells. Luminescent solar collectors can use fluorescent dyes to absorb the lowest wavelengths in the ultraviolet and visible wavelength ranges, and they emit that energy at higher wavelengths so the silicon solar cell is more efficient in the conversion to energy. The use of the articles of the present invention in the solar collectors allows more efficient use of solar energy and also provides more photostable solar collectors due to the fluorescent durability of the articles of the present invention. A simple embodiment is shown in Figure 1. The sunlight 2 is absorbed in the light concentrator 10 and is converted with a quantum yield of approximately 100 percent in fluorescent light 3, and is deflected in the reflectively coated notches 5 of so that it leaves the plate and collides with a solar cell 7, where it is converted to electrical energy. Another effective embodiment is shown in Figure 2. The plate-shaped light concentrator 10 is reflectively coated on both faces 4 and has no reflection on the two remaining faces. On faces without reflection, the fluorescent light is emitted and collides with the solar cells 7. The use of such a concentrator initially causes a substantial reduction in the price of the complete energy conversion system, since the area of the solar cell can be smaller by a factor of 10 to 2000 from the area of energy collection. The plastic plate is materially cheaper than the solar cell. Therefore, optimum solar cells can be used with high efficiency. US Patent No. 4,110,123 which is incorporated by reference herein, describes numerous embodiments of solar concentrators or solar collectors, which when used in conjunction with solar cells convert light energy to electrical energy.

Superior Coatings Protects Against Ultraviolet Light Although not necessary, the articles of the present invention may optionally include a top layer which may or may not include ultraviolet light absorbing agents. Some further improvement in degradation resistance is observed, when the article of the present invention is covered by an upper layer which includes ultraviolet light absorbing agents and is exposed to sunlight. The upper layer is preferably substantially transparent to visible light and includes a means for filtering substantial portions of the incident ultraviolet radiation. Figure 3 illustrates a retroreflective embodiment of the present invention, similar to that shown in Figure 1, and which further includes an upper layer 12. The solar collector which is comprised of the polymer matrix / dye / light stabilizer of hindered amine is it shows as a plate 10. The upper layer 12 is preferably coextensive with the composite plate 10 to provide the greatest protection to the collector 10.

Eg emplos The invention is further explained by the following illustrative examples, which are intended not to be limiting. Unless stated otherwise, all quantities are expressed in parts by weight.

The following abbreviations are used in the examples.

Abbreviation Meaning PC Polycarbonate; PMMA Polymethyl methacrylate; S063 HOSTASOL RED GGMR Solvent Orange 63 Thioxanthone dye from Hoechst Celanese; RED 41 HOSTASOL RED 5BMR-Red Vampiro 41, thioindigoid dye from Hoechst Celanese; Pl 240 LUMOGEN F240K Orange-perylene imide of BASF; SY 160: 1 MACROLEX 10GNMR Yellow Solvent 160: 1, benzoxazole-coumarin dye from Mobay Corp. SG 5 FLUOROL GREEN GOLD 084MR Green Solvent 5, perylene dye from BASF. HALS1 Dimethyl succinate polymer with 4-hydroxy-2, 2,6,6-tetramethyl-1-piperidineethanol available as TINUVIN 622 from Ciba-Geirjy Corp., Hawthorne, NY.

HALS2 Poly- [6 [(1,1,3,3-tetramethylbutyl) amino] -s- triazin-2,4-di] -1- [2, 2, 6,6-tetramethyl-4-piperidyl) imino] hexamethylene [ (2,2,6,6-tetramethyl-4-piperidyl) imino)] available as CHIMASORB 944FL from Ciba-Geigy Corp. HALS3 Bis (2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate available as TINUVIN 770 from Ciba-Geigy Corp.

Unless stated otherwise, the following test methods were used.

Accelerated Environmental Wear In order to simulate outdoor exposure to sunlight on an accelerated basis, the samples in Examples 1 to 6 and 8 were exposed according to ASTM G 26-Type B, Method A, with a xenon arc device cooled with water with internal and external borosilicate filters for periods of 102 minutes of exposure to a Black Panel temperature of approximately 63 ° C, followed by 18 minutes of exposure while the sample was sprayed with deionized water. It is believed that a thousand hours of exposure in this cycle are equivalent to at least several months of exposure to direct sunlight outdoors.

Fluorescence Fluorescence was determined by the following technique. A spectrophotometer of Hunter's Labscan 6000 was used at the following settings and conditions: Illuminator D6 ^, Geometry 0/45, Gate 25 mm, Standard Observer 2 degrees CIÉ, with measurements taken every 10 nanometers in a range of 400 to 700 nanometers The percentage of Initial Maximum Total Spectral Radiance Factor (% PTSR) was calculated as the proportion, in percentage, of the maximum total spectral radiance factor of the sample after exposure for the indicated time (time t) to the spectral radiance factor maximum total of a sample not exposed to the wavelength of the initial maximum total spectral radiance. This is best illustrated by the following equation. ° sPTSR = Maximum Spectral Radiance of exposed X 100 Maximum Spectral Radiance of the unexposed The maximum total spectral radiance factor is a relative measure of the fluorescence content. The fluorescence content is directly correlated to the amount of fluorescent dye, therefore, the maximum reflectance is a relative measure of the remaining fluorescent dye content. The difference in the percent of PTSR of about 5 or less is generally not considered significant for measurements made on constructions.

Preserved fluorescence Fluorescence was measured using an SLM AB2 Luminescence Spectrophotometer (SLM Instruments, Rochester, NY) using a 150 watt continuous Xenon lamp. The Preserved Fluorescence was calculated as the proportion, in percent, of the fluorescent intensity of the sample after exposure for the indicated length of time at the fluorescent intensity of an unexposed sample, at the wavelength of the maximum emission of the sample not exposed.

Molecular weight Molecular weight was measured by gel permeation chromatography (GPC) using a group of columns of the MICROSTYRAGEL brand available from Waters Division of Millipore Corp. Milford, MA and polystyrene standards for calibration. The samples were dissolved and run in tetrahydrofuran at 30 ° C at a flow rate of 1.0 milliliter per minute. A UV detector set at 266 nm was used for the detection of the polycarbonate.

Degradation by the Environmental Conditions in Exteriors The degradation by environmental conditions in exteriors was carried out on samples of size of approximately 7 x 12 centimeters. The samples were adhered to a piece of aluminum, which was mounted on a panel painted black facing upwards at 45 ° from the vertical and facing south.

The samples were exposed for 12 months in Wittmann, Arizona.

Time Determination for Loss of 50% of Colorant Films were mounted on aluminum skid structures, surface coated with a polyolefin film transparent to ultraviolet light, which was a 0.005 cm (2 mil) thick film of an ethylene / acrylic acid copolymer made from Primacor 3440 available from Dow Corporation of Midland, MI and set forth in accordance with ASTM G26, Type B, Method A, as described at the beginning. The concentration of the dye in each sample was measured initially and then every 500 hours of exposure. The samples were exposed for a total of 2000 hours. The time for the 50% loss of the dye for each sample was graphically interpolated from the graphs of dye concentration versus total exposure (for example [S063] versus hours). The dye concentrations were determined from the UV-Visible spectroscopic measurements of the sample films using the Beer-Lambert Law. All measurements were made on a Beckman UV-Visible Spectrophotometer Model DU-70.

Example 1 Example 1 illustrates the improved durability of the fluorescent properties and the color of fluorescent dye S063 with a hindered amine light stabilizer, and compares the durability of a sample with a sample that includes a top layer of ultraviolet light protection. The films were prepared for Example 1 as follows. The fluorescent dye and HALS (if present) were mixed ^ cp pellets with polycarbonate resin beads. The fluorescent dye was added to the polycarbonate resin pellets at a load of 0.2 weight percent. The hindered amine light stabilizer, if present, was incorporated into the mixture at a load of 0.26% by weight. The resin pellets used were Makrolon FCR-2407 available from Miles Inc. of Pittsburgh, PA. The dye / resin / HALS mixture was dried overnight to remove moisture. After drying overnight, the mixture was extruded into the film approximately 0.1-0.15 mm (4-6 mils) thick using a single screw extruder with three heating zones set at 260 ° C, 260 ° C. and 304 ° C and a film die set at 304 ° C. The extruder was a 19 mm (3/4 inch) single screw extruder for the Haake Rheocord as available from HaaJe of Karlsruhe, Germany. The film was then laminated on a 3M Diamond Grade 3M Retrorreflector laminate construction by Scotchlite ™ (as manufactured by 3M Company of Saint Paul, Minnesota) using a clear acrylic adhesive. A top layer film consisting of the urethane-acrylic film with or without an ultraviolet light absorber (indicated in Table 1) was laminated onto the fluorescent / retroreflective construction with acrylic adhesive. The hindered amine light stabilizer (HALS) used for the samples of Example 1, was HALS 1 (Tinuvin 622), an oligomeric tertiary amine.

They were also prepared comparable movies without HALS as described at the beginning, and laminated to form samples having fluorescent / retroreflective / top layer constructions, and all samples were degraded under ambient conditions in accelerated testing devices as described above. Fluorescence retention was assessed by color measurements on the Hunter Labscan 6000. Fluorescence durability is correlated to% of PTSR.

TABLE 1 All samples contained S063 dye at a loading of 0.2 wt.% HALS 1 at a load of 0.26 wt.%. The UV absorber was Uvinol 400 from BASF at a load of 3 wt.%.

The results shown in Table 1 show that HALS offers a substantial improvement in the fluorescence durability of S063 with or without a superior protective layer of ultraviolet light. Samples containing HALS showed improvement in fluorescence durability compared to those samples without HALS. In addition, improvement was observed in the samples containing HALS, while a superior ultraviolet light absorbing layer was added to the sample.

Example 2 Example 2 illustrates the improved durability of the fluorescent properties of the RED41 dye in the articles of the present invention. Samples 2E to 2H of Example 2 were prepared as described in Example 1, except that the polycarbonate resin used was Lexan 123R-112 as available from GE Plastics of Mt. Vernon, IN. The hindered amine light stabilizer used for the samples in Example 2 was HASL 1. The samples were degraded to environmental conditions using accelerated environmental degradation devices for the periods of time noted. The results are recorded in Table 2 below.

TABLE 2 1 Samples 2E-2H include Red 41 dye at a load of 0.2% by weight HALS 1 at a load of 0.26% by weight Urethane-acrylic top coat with 3% Uvinol 400.

The results shown in Table 2 show that Red dye 41 benefits by the addition of HALS 1 (Samples 2-F and 2-H).

Example 3 Example 3 illustrates different amine light stabilizers hindered at different charges, which are suitable for increasing the durability of fluorescent dye S063. Films were prepared as described in Example 1. The amount and type of HALS and colorant added to each film is designated in Table 3 below. Samples were exposed in an accelerated environmental degradation device as described at the beginning.

The results in Table 3 illustrate that the different hindered amine light stabilizers, including HALS 2 and HALS 1, are effective in increasing the durability of fluorescent dye S063.

Example 4 Example 4 illustrates a range of dye charges that is appropriate for the present invention. Samples were prepared as described in Example 3. Dye S063 and HALS 1 were used to prepare the samples. In samples containing HALS, 0.50% by weight of HALS 1 was included. The amount of colorant added to each sample is listed below. The samples were degraded under environmental conditions by exposing them to accelerated degradation by environmental conditions.

The results in Table 4 demonstrate that HALS is effective at different dye charges.

Example 5 Example 5 illustrates different hindered amine light stabilizers with a range of fillers that are suitable for the present invention. The films were prepared as described in Example 1. The resin used was Makrolon FCR-2407 from Miles Incorporated of Pittsburgh, PA. The samples were prepared by hot-rolling the colored films to a clear layer with retroreflective elements embedded in a second side and hot-laminating a top layer of PMMA to the first side of the colored films. All the colored films contained S063 dye at 0.20 weight percent. HALS 1 was added to the films as designated in Table 5 below. The samples were degraded under environmental conditions by exposing them in an accelerated degradation device for 1000 hours. The results are shown in Table 5.

TABLE 5 The results illustrate that HALS 1 is effective at a variety of fillers, to increase the durability of the fluorescent properties of S063 dye.

Comparative Example 6 Comparative Example 6 illustrates that polymethyl methacrylate is not a polymeric matrix suitable for making articles of the present invention because such articles do not show increased durability of fluorescent or color properties. Films for Comparative Example 6 were prepared as described in Example 1, except that the polymer matrix used was polymethyl methacrylate (PMMA) instead of polycarbonate. The PMMA used was either Perspex GP924 or CP923 from ICI Acrylics (Saint Louis, MO) or Lucite 47K from Dupont (Wilmington, DE), all containing approximately 0.3% by weight of UV absorber of a type of benzotriazole. The HALS (if any) was HALS 1 added to a load of 0.25 percent by weight. The extrusion temperatures for the PMMA were from 249 ° C to 260 ° C. Samples were prepared by hot lamination for either the four 0.075 mm (3 mil) colored films or two 0.15 mm (6 mil) colored films together, and recording the retroreflective elements on the second side of the film. laminated construction. The samples were subjected to degradation under environmental conditions exposing them to accelerated degradation under environmental conditions for the times listed in Table 6.

TABLE 6 Polymethyl methacrylate The dye was added to the samples at a 0.20 percent by weight filler, except that the 6C-1 sample was 0.29 percent by weight. HALS 1 was added to 0.25 percent by weight.

As discussed above, no increase in color or fluorescence durability is observed (Table 6) when a HALS and a fluorescent dye is added to the polymethyl methacrylate.

Example 7 Example 7 illustrates that polycarbonate is more durable if a hindered amine light stabilizer is included together with the polymer matrix and a fluorescent dye. The samples for Example 7 were prepared as described in Example 5. The resin used was Makrolon FCR-2407 from Miles Inc. The S063 dye was added to the samples at a loading of 0.2 weight percent. The hindered amine light stabilizer and the amount added to each sample are listed below in Table 7. The samples were subjected to degradation under ambient conditions by exposure abroad for 12 months as described above.

TABLE 7 The molecular weight results shown in Table 7 illustrate fluorescent dye samples and < polycarbonate containing HALS, which did not degrade as easily as the control that did not contain HALS. In this way, the present invention helps increase the durability of polycarbonate. The results in Table 7 further show that the fluorescent properties in the samples containing the HALS do not change the color as easily as the samples that did not contain the HALS.

Example 8 Example 8 illustrates the effect of several different hindered amine light stabilizers on the durability of the fluorescent color with outdoor exposure. Samples were prepared as in the Example 5, except that a second colored layer was used instead of the clear layer, and this was embedded with the retroreflective elements. The resin used was Makrolon FCR-2407 from Miles Inc. All the colored films contained S063 dye at 0.25 weight percent polycarbonate, the aggregated hindered amines are designated in Table 8 and were added at 0.25 weight percent. The samples were exposed in Arizona for 1 year as described above, and measurements were taken for the Initial Maximum Total Spectral Radiance Percentage and the color change. The results of the color change are given in Table 8.

TABLE 8 Example 9 Example 9 illustrates the durability of the improved fluorescence samples of the present invention, as measured by a spectrofluorometer. The samples were prepared as in Example 5, and exposed to accelerated environmental degradation. The readings were taken initially and at 2500 hours. The HALS, the colorant and the respective fillers are listed in Table 9 below, together with the results. 1 The polycarbonate was comprised of Makrolon 2407. The polycarbonate was comprised of 80% Makrolon 2407 and 20% Lexan 123R.

Comparative Example 10 Comparative Example 10 illustrates that the fluorescent dyes SY 160: 1 and SG 5 are not suitable dyes for the present invention. The films were prepared as described in Example 1. Samples 10A, 10B and 10D were prepared by hot rolling two colored films of 0.1 mm (4 mils) together. A top layer of PMMA of 0.5 mm (2 mils) containing 1.8% Tinuvin 327 (UV absorber available from Ciba-Geigy) was hot rolled to a first side of the laminated dye. Sample 10C was prepared by hot rolling a top layer of 0.75 mm (3 mil) PMMA containing 1.2 weight percent of Tinuvin 327 to a first side of a 0.3 mm (12 mil) film and embedding retroreflective elements on the second side of the film. The polycarbonate resin used in samples 10A and 10B was Makrolon 2407 and Lexan 123R-112 was used in samples 10C and 10D. Samples 10E and 10F are samples that are provided for comparison purposes. Samples 10E and 10F are prepared according to the present invention, and demonstrate that the perylene imide dyes are suitable for use in the present invention. Sample 10E was formed from a Lexan 123R-112 polycarbonate resin. A 0.3 mm (12 mil) polycarbonate film was formed with a surface layer of 0.075 mm (3 mils) PMMA hot rolled to the first side of the colored film, with the retroreflective elements embedded within the second side of the colored film. Sample 10-F was formed from Lexan polycarbonate resin 123R-112. The sample was prepared by hot rolling two colored films of 0.10 mm (4 mils) together, and by laminating a surface layer of PMMA of 0.05 mm (2 mils) to a first surface of the colored film resulting. The retroreflective elements were embedded within the second surface of the colored film. The upper or surface layers for samples 10-E and 10-F were made to have the same filtering ability of ultraviolet light. The 0.075 mm (3 mil) top layer included 1.2 wt% Tinuvin 327 available from Ciba Geigy Corp., while the 0.05 mm (2 mil) top layer contained 1.8 wt% Tinuvin 327. The HALS used for all the samples was HALS 1. The samples were subjected to degradation under environmental conditions exposing them to accelerated degradation under environmental conditions. The results are given in Table 10.

TABLE 10 The data were not measured due to severe color degradation. Samples were not measured in the 1500 hour interval.

One of skill in the art will recognize that the details of the prior embodiment may be varied without departing from the spirit and scope of the invention.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. A solar collector showing durable fluorescent properties, comprising a polymeric matrix, colorant and a hindered amine light stabilizer, characterized in that the colorant contains at least one of the dyes selected from the group of thioxanthone, perylene imide and thioindigoid compounds, and The polymer matrix comprises polycarbonate.

2. The solar collector according to claim 1, characterized in that the solar collector contains about 0.01 to about 2.00 weight percent of said dye.

3. The solar collector according to claim 1, characterized in that the solar collector contains about 0.05 to about 1.00 weight percent of the hindered amine light stabilizer.

4. The solar collector according to claim 3, characterized in that the solar collector contains approximately 0.10 to 0.75 weight percent of the hindered amine light stabilizer.

5. The solar collector according to claim 1, characterized in that the hindered amine light stabilizer is comprised of a 2, 2, 6,6-tetramethyl-piperidine compound.

6. The solar collector according to claim 1, further characterized in that it includes a top or surface layer.

7. An apparatus for converting light energy into electrical energy, comprised of a solar cell, means for directing light to the solar cell, and a solar collector, the collector is comprised of the polymer matrix, the dye and the amine light stabilizer hindered, characterized the dye because it contains at least one of the dyes selected from the group of thioxanthone, perylene imide and thioindigoid compounds, and the polymer matrix comprises polycarbonate.

8. The apparatus according to claim 7, characterized in that the means for directing the light towards the solar cell comprises at least one reflecting surface.

9. The solar collector according to claim 1, further characterized in that it includes a means to direct the light coming out of the collector.

10. The solar collector according to claim 9, characterized in that the means for directing the light comprises at least one reflecting surface.