AU2005300858A1

AU2005300858A1 - Acrylic glass having photochromic properties

Info

Publication number: AU2005300858A1
Application number: AU2005300858A
Authority: AU
Inventors: Gunther Ittmann; Hans Lichtenstein
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 2004-11-04
Filing date: 2005-09-30
Publication date: 2006-05-11
Also published as: ZA200703580B; CA2580765A1; JP2008518809A; KR20070074597A; WO2006048089A1; EP1807261A1; CN101022950A; BRPI0517270A; DE102004053817A1

Description

IN THE MATTER OF an Australian Application corresponding to PCT Application PCT/EP2005/010556 RWS Group Ltd, of Europa House, Marsham Way, Gerrards Cross, Buckinghamshire, England, hereby solemnly and sincerely declares that, to the best of its knowledge and belief, the following document, prepared by one of its translators competent in the art and conversant with the English and German languages, is a true and correct translation of the PCT Application filed under No. PCT/EP2005/010556. Date: 6 October 2006 C. E. SITCH Acting Managing Director For and on behalf of RWS Group Ltd WO 2006/048089 PCT/EP2005/010556 Acrylic glass having photochromic properties The invention relates to acrylic sheet with phototropic properties, production processes, and uses. 5 For some time there have been dyes which exhibit a light-dependent change in shade and intensity. The use of these dyes in plastics is known. However, the dyes cannot be incorporated into any desired plastics 10 matrix. In order to become effective, the dye molecule has to be allowed sufficient freedom for the colour effect to be developed via isomerism. Polyurethanes are mostly used because they provide a suitable matrix for the dyes. 15 The hardness of polymethyl methacrylate makes it an unsuitable plastics matrix for these dyes, because it does not allow the dye molecules the necessary freedom of movement. The system becomes effective when rela 20 tively large amounts of plasticizers or of plasticizing comonomers are added. However, the material here becomes so soft that it no longer complies with the requirements for the respective applications. 25 It was therefore an object to produce a polymethyl methacrylate with phototropic properties. The object has been achieved via polymethyl meth acrylate sandwich elements comprising two polymethyl 30 methacrylate sheets and an intermediate layer which comprises phototropic dyes. Surprisingly, it has been found that by using a sandwich structure it is possible to produce polymethyl 35 methacrylate (PMMA) with phototropic properties. The two outer PMMA sheets here provide the mechanical stability, and the soft intermediate layer permits introduction of phototropic dyes.

- 2 It has been found that the outer PMMA sheets can be modified with the known additives. Light stabilizers may preferably be incorporated. Particularly suitable additives are those which filter only short-wave UV 5 light, examples being bisoxanilines or compounds from the HALS (Hindered Amine Light Stabilizers) group. The PMMA sheets may moreover comprise dyes which are permeable to UV light. 10 The intermediate layer has to be sufficiently soft to leave enough freedom for the dye molecules to produce the colour change via isomerism. 15 Surprisingly, it has been found that polymethyl meth acrylates with plasticizers and/or with comonomers are suitable for the intermediate layer. Plasticizers which may be used are any of the commercially available additives, such as adipates, phthalates, phosphates or 20 citrates. Plasticizers particularly preferably added are di-n-butyl adipate and diisobutyl phthalate. Comonomers which may be used are a wide variety of PMMA-compatible monomers. Particularly suitable 25 compounds are those from the class of the acrylates or of the higher-alkylated methacrylates. It has been found that the intermediate layer can also be composed entirely of polyacrylates or of higher 30 alkylated polymethacrylates. Propyl, butyl and longer chain methacrylates have been found to be particularly suitable. Any of the known phototropic dyes may be introduced 35 into the intermediate layer. It is preferable to use dyes from the group of the spironaphthoxazines and naphthopyrans. Particular preference is given to photo chromic Reversacol dyes from J. Robinson (Huddersfield, England), e.g. Gray 219, Gray 208, Gray 306, Gray 195, - 3 Brown 105, Flamme 29 B, Sea Green 5, Velvet Blue, Sunflower, Graphite and Palatinate Purple. The amount of these dyes added to the plastics matrix 5 is a function of the layer thickness. A very small thickness requires a high concentration. By way of example, the amounts added of the dyes are from 0.001% to 0.3% at a thickness of 3 mm. At very small layer thicknesses, up to 10% of dyes may be added. It has 10 been found that good phototropic properties are detectable when the thickness of the intermediate layer is from 0.01 to 5 mm. The best results were achieved with layer thicknesses of from 0.1 to 3 mm. Mixtures of various dyes may also be used. 15 It has been found that the inventive sandwich elements can be produced by various processes. A particularly suitable process is the cell casting process. The cell casting process here is used to produce the polymethyl 20 methacrylate sheets separately. The temperature and time for heat-conditioning are set as a function of the thickness of the sheets. The conventional additives, e.g. UV filters, initiators, dyes or stabilizers, may be added. The intermediate layer is then cast with the 25 appropriate additives, e.g. phototropic dyes and, if appropriate, plasticizers, between the polymethyl meth acrylate sheets. The bond is produced via swelling processes. The PMMA sheets may be treated with cross linking agents in order to regulate the swelling. 30 Another suitable process for producing the inventive sandwich elements is the internal coextrusion process. EP1270176 describes a process for producing multilayer hollow-chamber profiled sheets. This process produces 35 an upper and a lower layer from a plastics melt and a layer situated within the hollow-chamber profile and composed of a plastics melt by coextrusion of the plastics melt and use of an extrusion die, and then calibration of the resultant extrudate. The inventive - 4 sandwich elements can be produced by this process using an appropriately designed extrusion die. The invention therefore also comprises the cell casting 5 process and the internal coextrusion process for producing the inventive sandwich elements. The polymethyl methacrylate sandwich elements with phototropic dyes are versatile. By way of example, they 10 can be used for automatic shading systems in the construction sector, e.g. greenhouses, conservatories, glazing (e.g. skylights), display windows. The examples given below are given to provide better 15 illustration of the present invention, but are not intended to restrict the invention to the features disclosed herein. Examples 20 Example 1 Colourless acrylic sheet for outer panes of the sandwich element 25 The following additives are dissolved, with stirring, in 998 parts of methyl methacrylate prepolymer (viscosity about 1000 cP): 1 part of 2,2'-azobis(2,4-dimethylvaleronitrile) 1 part of glycol dimethacrylate 30 Light stabilizers may also be optionally added in order to protect the photochromic inner layer. Suitable products for this purpose are HALS products, 35 such as Tinuvin 770, and UV absorbers which are particularly effective in the short-wavelength UV region, e.g. Sanduvor VSU. The mixture is vigorously stirred, charged to a - 5 silicate glass cell of 400 x 500 mm format with a 3 mm thickness separating bead, and polymerized in a water bath for 16 h at 45 0 C. Completion of the polymerization takes place in a heat-conditioning cabinet for 4h at 5 1150C. Example 2 Photochromic inner layer of the sandwich element: 10 The following additives are dissolved, with stirring, in 9988 parts of butyl methacrylate: 5 parts of 2,2'-azobis(isobutyronitrile) 5 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) 1 part of Reversacol Sunflower Bt 278/13 (photochromic 15 dye from James Robinson, England) 1 part of Reversacol Palatinate Purple (photochromic dye from James Robinson, England) The mixture is vigorously stirred, charged to a cell 20 composed of colourless acrylic sheet from Experiment 1 with a 3 mm-thickness bead as separator, and poly merized in a water bath for 22 h at 50 0 C. This gives a transparent, slightly yellowish sheet with 25 the high mechanical strength typical of poly methacrylate. The result of irradiation with sunlight is that, depending on light intensity, the sheet becomes markedly more strongly coloured after from about 30 seconds to 2 minutes, and assumes a grey-brown 30 to brown colour.

Claims

1. Polymethyl methacrylate sandwich elements comprising two polymethyl methacrylate sheets and 5 an intermediate layer which comprises phototropic dyes.

2. Polymethyl methacrylate sandwich elements according to Claim 1, characterized in that the 10 intermediate layer comprises polyacrylates or alkylated polymethacrylates, preferably polybutyl methacrylates.

3. Polymethyl methacrylate sandwich elements 15 according to Claim 2, characterized in that the intermediate layer comprises comonomers.

4. Polymethyl methacrylate sandwich element according to Claims 1 to 3, characterized in that the 20 intermediate layer comprises plasticizers.

5. Polymethyl methacrylate sandwich element according to Claims 1 to 4, characterized in that the inter mediate layer comprises spironaphthoxazines or 25 naphthopyrans.

6. Polymethyl methacrylate sandwich element according to Claims 1 to 5, characterized in that the thickness of the intermediate layer is from 0.01 30 to 5 mm, preferably from 0.1 to 3 mm.

7. Polymethyl methacrylate sandwich element according to Claim 6, characterized in that the intermediate layer comprises amounts of from 0.001 to 10% of 35 phototropic dyes.

8. Polymethyl methacrylate sandwich element according to Claim 1, characterized in that the polymethyl methacrylate sheets comprise light stabilizers. - 7

9. Polymethyl methacrylate sandwich element according to Claim 1, characterized in that the polymethyl methacrylate sheets comprise dyes. 5

10. Polymethyl methacrylate sandwich element according to Claim 1, characterized in that the polymethyl methacrylate sheets comprise comonomers, in particular crosslinking agents. 10

11. Process for production of polymethyl methacrylate sandwich elements according to Claim 1, characterized in that, in the cell casting process, an intermediate layer is cast between two 15 polymethacrylate sheets and the materials are bonded to one another by way of a heat conditioning process.

12. Process for production of polymethyl methacrylate 20 sandwich elements according to Claim 1, characterized in that internal coextrusion is used to produce two polymethacrylate sheets with an intermediate layer. 25

13. Use of polymethyl methacrylate sandwich elements in the construction sector.