WO2010012664A1

WO2010012664A1 - Heat-absorbing pmma pane

Info

Publication number: WO2010012664A1
Application number: PCT/EP2009/059601
Authority: WO
Inventors: Clemens Dransfeld; Erich Kramer; Peter Studer
Original assignee: Mecaplex Ag
Priority date: 2008-07-28
Filing date: 2009-07-24
Publication date: 2010-02-04

Abstract

A heat-absorbing polymer pane essentially consisting of PMMA and one or more IR absorbers and one or more UV absorbers and, preferably one or more fluorescent whitening agents (optical brighteners) is described, which is particularly useful for making the windows of automobiles, vessels or airplane, in particular helicopters.

Description

Heat-absorbing PMMA pane

The present invention relates to heat-absorbing window panes, in particular for vehicles like automobiles, vessels and airplanes, and to a method for making such panes.

Many transparent materials useful for the manufacture of window panes have also a high transmittance for IR radiation, particularly IR radiation having a wavelength of about 750nm to about 2500 nm (near infrared radiation, NIR) . This leads to an undesirable temperature rise inside of a room which is glazed with such panes under the influence of sunlight because the solar IR radiation is absorbed by objects inside of the glazed room which are heated thereby to temperatures in the range of about 25 to 80⁰C and emit a corresponding long-wave heat radiation, for which conventional transparent materials exhibit far a less transparency, so that this heat radiation cannot dissipate to the outside and warms up the inner of the glazed room (greenhouse effect) . In addition to IR radiation UV radiation also contributes considerably to the mentioned temperature increase inside of a glazed room.

One approach for overcoming this problem is to apply a coating to the window pane, which reflects IR and/or UV radiation. This approach, however, can normally not be used for vehicle panes, in particular for the cockpit panes of vehicles because it reduces the transparency of the panes for visible light too to an extent, which is not acceptable. The EP 0 679 614 A discloses another way for dealing with this problem. A glass pane is coated with a coating comprising a synthetic resin an IR absorber, an UV absorber and a fluorescent brightening agent. This coating absorbs the undesired radiation but is transparent for visible radiation. The brightening agent is added to sharply cut long-wavelength ultraviolet rays until the upper limit of the UV region (about 400nm) . Although this layered window pane provides a certain improvement when compared with the aforementioned panes with reflective coating, it is still suboptimal because reflection and scattering of radiation at the boundary between the glass layer and the absorbing polymer layer reduces the transparency of the laminated pane for visible light. Furthermore laminated pane structures have the general disadvantage that they cannot be shaped by use of heat.

EP 0 682 082 A2 discloses a polymer composition for vehicle and building panes obtained by kneading a polymethacrylacrylate resin or a polycarbonate resin uniformly with an IR absorber and an UV absorber. The panes deter IR and UV radiation but let visible light pass. It is however difficult to disperse the IR and UV absorbing compounds uniformly by simply kneading them with a prefabricated polymer material, in particular because the absorbers cannot withstand kneading temperatures necessary for obtaining a uniform distribution of the compounds for a sufficiently long time period. This applies particularly to IR absorber materials. Furthermore, it is generally difficult to produce panes of excellent optical quality without vision- impeding streaks from a prefabricated polymer material, as required in particular for use as cockpit glazing. A sufficient transparency for visible light is particularly critical for vehicle glazing, i.e. automotive glazing, glazing for vessels and, in particular, aircraft glazing, where a minimum transparency of 50 to 55 percent and even 75 percent in the visible range is required for window panes in the passenger cabin and the pilot cockpit, respectively.

On the other side, US 2007/0210287 Al describes a method for making a transparent thermoplastic article, e.g. a window pane, e.g. for use in vehicles or airplanes, having controlled solar energy transmittance, which includes providing a liquid thermoplastic material and adding thereto from 0.003 to 0.1 percent by weight of a blend of a perylene dye and a nanoparticulate metal hexaboride-based IR absorber like e.g. YE>6, LaE>6 and others, and cooling said mixture to form the transparent thermoplastic article. They have the disadvantage that pigments are used as the IR absorber, which scatters the radiation passing the pane and causes a rather unclear, cloudy visibility, which is not desirable, in particular, for cockpit panes.

It has now been found that methylmethacrylate (MMA) monomers are excellently suited to dissolve conventional IR absorber compounds as well as UV absorber compounds and/or fluorescent brightening agents (in the following also collectively referred to as "PMMA additives") . When such solutions are polymerized, they form polymethylmethacrylate material (PMMA, Plexiglas) , wherein the absorber substances and/or the brightener are much more equably distributed or dispersed than they would be if the PMMA additives would be incorporated into the thermoplastic material after finishing - A -

the polymerization. This PMMA material is excellently suited to meet the requirements for window panes of all kinds of vehicles, in particular of airplanes.

Accordingly the present invention relates to a heat- absorbing polymer pane essentially consisting of PMMA and one or more IR absorbers and one or more UV absorbers and, optionally but particularly preferred, one or more fluorescent brighteners .

The use of pigments as PMMA additives according to the invention is at least not preferred because of their light scattering effect of such pigments and, more preferably, the use of pigments is entirely avoided. The near-absorbing polymer panes according to the invention are generally about 1 to about 15 mm thick, preferably about 3 to 5 mm. In certain cases they may even be thinner, e.g. in case of a laminate comprising a different core material on which a PMMA pane according to the invention is laminated as described in more detail below.

"Essentially consisting of" means for the purposes of this application that panes according to the invention substantially do not contain components other than those explicitly mentioned with the exception of substances which are not avoidable, e.g. an initiator for the free radical polymerization of the MMA monomers . Heat-absorbing PMMA panes according to the invention show excellent optical quality without any visible streaks or haze. In addition, the requirements for sufficient transparency for visible light can easily be met by these panes, in particular by panes based on PMMA comprising fluorescent brighteners, because these brighteners absorb generally UV radiation and convert it to radiation having a wavelength in the visible range so that, in sum, more visible light reaches the interior of a room glazed with panes according to the invention. The PMMA panes according to the invention can furthermore be heat- shaped in almost any desired way on contrary to conventional laminated panes, in particular based on inorganic glass. It is therefore possible to manufacture curved large area heat- absorbing panes of uniform and excellent optical quality with said PMMA material as e.g. required for the cockpit glazing of helicopters.

The exact nature of the IR absorber (s) , UV-absorber (s) and fluorescent whitening agent (s) is not particularly critical as long as the compounds do substantially not absorb light having a wavelength in the visible range and are sufficiently soluble in MMA (which is generally the case if no pigment-compounds are used) .

Figure 1 shows a comparison of the transmission characteristic of a heat-absorbing PMMA pane according to the invention with reference material, pure PMMA, PMMA and IR absorber .

Figure 2 shows the influence of a heat-absorbing PMMA pane according to the invention on the inner temperature of a box covered with said panes and irradiated with radiation of an IR source, in comparison to reference material.

Preferred IR absorbers include e.g. Quaterrylenes (as described e.g. in A. Bδhm "IR-Absorber, Konzepte und Lδsungen fur ein effektives Warmemanagement, Presse-Information BASF, 26.10.2004), Chinophthalones, Anthrachinones and Dioxazins or mixtures of such compounds . Preferred concentrations of the IR absorber component range from about 0.001 to about 1, more preferably 0.001 to 0.5 %bw, still more preferably 0.002 to 0.05 %bw, most preferably 0.0025 to 0.03 of IR absorber.

Suitable IR absorbers are e.g. available under the registered trademarks LUMOGEN from BASF like LUMOGEN 765 or 788, two quaterrylenes having absorption maxima at 765 nm and 788 nm respectively, Minatec from Merck, SMARTLIGHT from CIBA, or from LANXESS (IR-Absorber 2052, a combination of two compounds, namely N, N, N ' , N ' -Tetrakis- (p-di-n- butylaminophenyl) -p-phenylenediamin) and N, N, N ' , N ' -Tetrakis- (p-di-n-butylaminophenyl) -p-benzochinon-bis- (immonium- hexafluoroantimonat) which are added separately, so that the ratio between the two components can be easily adapted to specific demands.

A particularly preferred combination of IR absorbers consists of a quaterrylene and the afore-mentioned combination of N, N, N ' , N ' -Tetrakis- (p-di-n-butylaminophenyl) - p-phenylenediamin) and N, N, N ', N ' -Tetrakis- (p-di-n- butylaminophenyl) -p-benzochinon-bis- (immonium- hexafluoroantimonat) , wherein the quaterrylene component is present in an amount of about 0.001 to about 0.008, preferably 0.002 to 0.006 %bw, based on the PMMA pane, and N,N,N',N'-Tetrakis- (p-di-n-butylaminophenyl) -p- phenylenediamin) and N, N, N ', N ' -Tetrakis- (p-di-n- butylaminophenyl) -p-benzochinon-bis- (immonium- hexafluoroantimonat) together are present in an amount of about 0.008 to about 0.025 %bw, preferably 0.01 to 0.02 %bw, e.g. about 0.02 %bw, all afore-mentioned percentages again based on the PMMA pane, The ratio of N, N, N ' , N ' -Tetrakis- (p- di-n-butylaminophenyl) -p-phenylenediamin) and N,N,N',N'- Tetrakis- (p-di-n-butylaminophenyl) -p-benzochinon-bis- (immonium-hexafluoroantimonat) can be adapted to the specific needs and ranges e.g. from about 2:1 to about 1:4, preferably from about 1,5:1 to about 1:4, more preferably from 1:1.25 to 1:1.75. A particular corresponding combination consists of about 0.0025 %bw of LUMOGEN IR765, i.e. the compound of formula :

about 0.008 %bw of N, N, N ', N ' -Tetrakis- (p-di-n-butylaminophenyl) -p-phenylenediamin) and 0.012 %bw of N,N,N',N'- Tetrakis- (p-di-n-butylaminophenyl) -p-benzochinon-bis- (immonium-hexafluoroantimonat) .

Preferred UV absorbers include e.g.

Hydroxybenzophenones, Benzotriazoles, which are specifically, preferred, Hydroxyphenyltriazines and mixtures thereof.

The UV absorbers are generally used at concentrations which allow UV radiation to enter the pane for a distance of about one fifth to about two thirds of the total thickness of the pane, e.g. for about 1.5 to 3 mm in case of a pane of 2 to 5 mm thickness. In this way a sufficient distance is provided inside of the pane for the UV radiation to interact with the fluorescent whitening agent (optical brightener) component in order to convert penetrating UV radiation into visible radiation to enhance the total amount of visible radiation passing through the pane. Preferably the UV absorbers are used at concentrations ranging from about 0.1 to about 2 %bw, preferably 0.01 to 0.5, most preferably 0.05 to 0.15 %bw of UV absorber, based on the PMMA pane. .

Examples of suitable Hydroxybenzophenones are e.g. 2- Hydroxybenzophenone and its 4-hydroxy, 4-methoxy, 4-octyloxy, 4-decyloxy, 4-dodecyloxy, 4-benzyloxy, 4, 2 ' , 4 ' -trihydroxy and 2 ' -hydroxy-4, 4 ' -dimethoxy derivatives .

Examples of suitable Benzotriazoles include e.g. /- [/ ' -Hyorcxy-3 ' , ^r-> ' -o: - ( J , 1 -o: metr.y lbenry . ) phenyl _ -/H- benztii3z Die, 2- (2 ' -Hydroxyphenyl) benzotriazoles, for example 2- (2 ' -hydroxy-5 ' -methylphenyl) -benzotriazole, 2- (3 ' , 5 ' -di- tert-butyl-2 ' -hydroxyphenyl) benzotriazole, 2- (5' -tert-butyl- 2 ' -hydroxyphenyl) benzotriazole, 2- (2 ' -hydroxy-5 ' - (1, 1, 3, 3- tetramethylbutyl) phenyl) benzotriazole, 2-(3',5'-di-tert- butyl-2 ' -hydroxyphenyl) -5-chloro-benzotriazole, 2- (3 ' -tert- butyl-2 ' -hydroxy-5 ' -methylphenyl) -5-chloro-benzotriazole, 2- (3 ' -sec-butyl-5 ' -tert-butyl-2 ' -hydroxyphenyl) benzotriazole, 2- (2 ' -hydroxy-4 ' -octyloxyphenyl) benzotriazole, 2-(3',5'-di- tert-amyl-2 ' -hydroxyphenyl) benzotriazole, 2- (3 ' , 5 ' -bis- ( , - dimethylbenzyl) -2 ' -hydroxyphenyl) benzotriazole, 2- (3 ' -tert- butyl-2 ' -hydroxy-5 ' - (2-octyloxycarbonylethyl) phenyl) -5- chloro-benzotriazole, 2- (3 ' -tert-butyl-5 ' - [2- (2-ethylhexyl- oxy) -carbonylethyl ] -2 ' -hydroxyphenyl) -5-chloro-benzotriazole, 2- (3 ' -tert-butyl-2 ' -hydroxy-5 ' - (2-methoxycarbonylethyl) - phenyl) -5-chloro-benzotriazole, 2- (3 ' -tert-butyl-2 ' -hydroxy- 5 ' - (2-methoxycarbonylethyl) phenyl) benzotriazole, 2- (3 '-tert- butyl-2 ' -hydroxy-5 ' - (2-octyloxycarbonylethyl) phenyl) - benzotriazole, 2- (3 ' -tert-butyl-5 '- [2- (2-ethylhexyloxy) - carbonylethyl] -2 ' -hydroxyphenyl) benzotriazole, 2- (3 ' -dodecyl- 2 ' -hydroxy-5 ' -methylphenyl) benzotriazole, 2- (3 ' -tert-butyl- 2'-hydroxy-5'- (2- isooctyloxycarbonylethyl) phenylbenzotriazole, 2,2' -methylene- bis [4- (1, 1, 3, 3-tetramethylbutyl) -6-benzotriazole-2-ylphenol] ; the transesterification product of 2- [3 ' -tert-butyl-5 ' - (2- methoxycarbonylethyl) -2 ' -hydroxyphenyl] -2H-benzotriazole with

polyethylene glycol 300; [R-CH₂CH₂-COO-CH₂CH₂-^- , where R =

3 ' -tert-butyl-4 ' -hydroxy-5 ' -2H-benzotriazol-2-ylphenyl, 2- [2 ' -hydroxy-3 ' - (CC, CC-dimethylbenzyl) -5 ' - (1, 1, 3, 3- tetramethylbutyl) -phenyl] benzotriazole; 2- [2' -hydroxy-3 ' - (1, 1, 3, 3-tetramethylbutyl) -5 ' - (GC, CC-dimethylbenzyl) - phenyl] benzotriazole.

Examples of suitable Hydroxyphenyltriazines included e.g. 2- (2-Hydroxyphenyl) -1, 3, 5-triazines, for example 2,4,6- tris (2-hydroxy-4-octyloxyphenyl) -1, 3, 5-triazine, 2- (2- hydroxy-4-octyloxyphenyl) -4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5- triazine, 2- (2, 4-dihydroxyphenyl) -4, 6-bis (2, 4- dimethylphenyl) -1, 3, 5-triazine, 2, 4-bis (2-hydroxy-4-propyl- oxyphenyl) -6- (2 , 4-dimethylphenyl) -1 , 3, 5-triazine, 2- (2- hydroxy-4-octyloxyphenyl) -4, 6-bis (4-methylphenyl) -1, 3, 5- triazine, 2- (2-hydroxy-4-dodecyloxyphenyl) -4, 6-bis (2, 4- dimethylphenyl) -1, 3, 5-triazine, 2- (2-hydroxy-4-tri- decyloxyphenyl) -4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazine, 2- [2-hydroxy-4- (2-hydroxy-3-butyloxypropoxy) phenyl] -4, 6- bis (2, 4-dimethyl) -1, 3, 5-triazine, 2- [2-hydroxy-4- (2-hydroxy- 3-octyloxypropyloxy) phenyl] -4, 6-bis (2, 4-dimethyl) -1,3,5- triazine, 2- [4- (dodecyloxy/tridecyloxy-2-hydroxypropoxy) -2- hydroxyphenyl ] -4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazine, 2- [2-hydroxy-4- (2-hydroxy-3-dodecyloxypropoxy) phenyl] -4, 6- bis (2, 4-dimethylphenyl) -1, 3, 5-triazine, 2- (2-hydroxy-4- hexyloxy) phenyl-4 , 6-diphenyl-l , 3, 5-triazine, 2- (2-hydroxy-4- methoxyphenyl) -4, 6-diphenyl-l, 3, 5-triazine, 2,4, 6-tris [2- hydroxy-4- (3-butoxy-2-hydroxypropoxy) phenyl] -1, 3, 5-triazine, 2- (2-hydroxyphenyl) -4- (4-methoxyphenyl) -6-phenyl-l, 3, 5-triazine, 2- { 2-hydroxy-4- [3- (2-ethylhexyl-l-oxy) -2-hydroxy- propyloxy] phenyl } -4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazine, 2, 4-bis (4- [2-ethylhexyloxy] -2-hydroxyphenyl) -6- (4-methoxyphenyl) -1, 3, 5-triazine.

Suitable UV absorbers are e.g. available from Ciba AG under the registered trademarks CHIMASORB and TINUVIN.

A specifically preferred UV absorber is 2 ^■■ [ 2 ' --Hydroxy ^■■ 5 ' , 5 ' ^~Ό.^~ (L, l-dxr.Chylbcr.-iyl) phcr.yl] -2K-oonz;,^i.a_iJol.c (7JNl]V JN /34) w"n-}] r_^n ddvarr .-iσeousl y oe used e . u , it.

r/,,5 to about: 0.? ³-bw, preferaoJy L. TS t"> 0.12 -bw, o.cf. m a" 3:iiDurt c± about 0.1- cw.

Preferred fluorescent whitening agents (optical brighteners) include e.g. Bis-benzooxazles like Styryl-bis- benzooxazoles and Thiophene-bis-benzooxazoles, Triazin- phenylcoumarines, Methylcoumarin, Naphthotriazolecoumarines, Naphthotriazolphenylcoumarines, Benzotriazole-coumarines, Bis- (styryl) biphenyles, Pyrene-triazines and the like.

The optical brighteners are preferably used at concentrations ranging from about 0.03 to about 0.3, preferably from 0.05 to 0.1 %bw again based on the PMMA pane.

Specific examples of suitable fluorescent agents include e.g. 4-Methyl-7-diethylaminocoumarine, 3-Phenyl-7- (4- methyl-6-butyloxybenzoxazole) coumarine, 4,4' -bis (benzo- oxazole-2-yl) stilbene, 2, 4-dimethoxy-6- (1 ' -pyrenyl) -1, 3, 5- triazine, 1, 4-bis (benzoxazol-2-yl) naphthalene, 3-phenyl-7- (2H-naphtho- [ [1,2-d] ]triazol-2-yl) coumarine, 4 , 4 ' -bis (2- methoxystyryl) -biphenyl, 4, 4 ' -bis (2-sulfostyryl) -biphenyl disodium salt and 2, 5-bis- (5-tert-butyl-benzoxazol-2-yl) - thiophene (TINOPAL OB; Fluorescent Brightener 184) which is particularly preferred.

Suitable optical brighteners are readily available commercially, e.g. from Ciba AG under the registered trademark TINOPAL.

Examples of PMMA panes according to the present invention include e.g. PMMA panes comprising the following PMMA additives according to the invention: A

0.005 % Lumogen IR765 0.1 % TINUVIN 234 0.05 % TINOPAL OB

B

0.01 % Lumogen IR765 0.1 % TINUVIN 234 0.1 % TINOPAL OB

C

0.0025 % Lumogen IR765 0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.05% TINOPAL OB

*[3:2] is the weight ratio between of N, N, N ' , N ' -Tetrakis- (p- di-n-butylaminophenyl) -p-benzochinon-bis- (immonium- hexafluoroantimonat) and N, N, N ' , N ' -Tetrakis- (p-di-n- butylaminophenyl) -p-phenylenediamin) . D

0.03 % Lumogen IR765

0.1 % TINUVIN 234

0.15 % TINOPAL OB E

0.005 % Lumogen IR765

0.005 % Smartlight

0.1 % TINUVIN 234

0.05% TINOPAL OB

0.005 % Lumogen IR765 0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.05% TINOPAL OB

0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.05% TINOPAL OB

H

0.0025 % Lumogen IR765 0.015 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.05% TINOPAL OB

I

0.0025 % Lumogen IR765 0.02 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.05% TINOPAL OB

J

0.005 % Lumogen IR765 0.015 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.1% TINOPAL OB

K

0.0025 % Lumogen IR765 0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.1% TINOPAL OB L

0.005 % Lumogen IR765 0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.1% TINOPAL OB

M

0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.1% TINOPAL OB

N

0.0025 % Lumogen IR765 0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.1% TINOPAL OB

O

0.0025 % Lumogen IR765 0.015 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.1% TINOPAL OB

P

0.005 % Lumogen IR765 0.01 % Lanxess 2052 [3 :2]* 0.1 % TINUVIN 234 0.2% TINOPAL OB

Compounds which absorb both IR and UV radiation can of course also be used for the present invention, in particular as auxiliary absorbers, e.g. for fine tuning the colour shade of the pane. Such broadband absorbers, which are frequently used in the field of agro technology are also commercially available, e.g. under trade names like SMART LIGHT (Ciba) .

The PMMA panes according to the present invention can e.g. be manufactured with a process comprising the free radical polymerization of a solution essentially consisting of methylmethacrylate and one or more IR absorbers, one or more UV absorbers and, preferably, one or more fluorescent whitening agents (optical brighteners) in the presence of an initiator for the free radical polymerization and forming a PMMA pane therefrom.

Formation of the pane can e.g. be achieved by casting the monomer composition comprising initiator between two glass plates, e.g. plates of securit glass or float glass, wherein the final polymerization is carried out

Preferably, PMMA panes according to the invention are manufactured using a two step free radical polymerization including a prepolymerization step for obtaining a prepolymerized slightly to moderately viscous but still liquid PMMA material which is then cast into an appropriate mould, e.g. between two glass plates, preferably float glass, wherein the final polymerization is carried out. This two- step polymerization has e.g. the advantage, that the polymerization shrinkage can be better controlled.

For the prepolymerization methylmethacrylate (MMA) is mixed with the desired amounts of IR absorber (s) and UV absorber (s) and optionally the optical whitening agent (s). Generally, a clear solution is obtained. An initiator for the free radical polymerization is added to said solution, e.g. azo-iso-butyronitril (AIBN) at a concentration of about 0.01 to 1 %bw, e.g. about 0.05 %bw and the mixture is heated to a temperature of about 40 to 90⁰C, e.g. about 80⁰C for about 30 90 minutes, e.g. about 1 hour. The prepolymerization conditions must be chosen in a way that the prepolymerized material is slightly to moderately viscous, so that it can still be blended with further initiator compound and is still pourable. Preferably, the viscosities are in the range of 30 to 100 mPas s, preferably 40 to 60, e.g. about 50 mPas s, each time measured at 80⁰C.

For the final polymerization the prepolymerized material is blended with further initiator, e.g. 0.05 %bw of AIBN, and poured into a mould consisting e.g. of two glass plates of appropriate size and a seal between them having a thickness corresponding to the desired thickness of the pane to be manufactured, which seals off the room between the plates to the environment. The inner sides of the glass plates are lined with a release or separating agent, preferably a polyethyleneterephthalate (PET) foil having e.g. a thickness of 15 to 50 μm.

The final polymerization can be performed at one temperature like the prepolymerization and usually takes about 24 to 100 h. Preferably however the final polymerization is performed at increasing temperatures, e.g. in three steps, an initial polymerization of e.g. 14 to 20 hours or longer at about 40⁰C, followed by a second polymerization step of e.g. 15 to 20 hours or longer at a somewhat increased temperature, e.g. 50 ⁰C and a final polymerization step of e.g. 15 to 40 hours or longer at further increased temperature, e.g. at about 60 to 80⁰C. This mentioned stepwise final polymerization is advantageous in view of optimizing the optical quality of the panes.

After finishing the polymerization the plane can be removed from the mould and further processed, if desired, e.g. polished and/or warped to a desired shape. A further embodiment of the present invention is therefore a heat absorbing PMMA pane obtainable by an embodiment of the aforementioned processes.

The PMMA panes of the invention can also be used to manufacture laminated polymer panes. By the way of example a polycarbonate (PC) core can be laminated at one or both sides with a PMMA pane according to the invention using e.g. polyvinylbutyral (PVB) as a transparent intermediate bonding layer. PC has better mechanical properties than PMMA and would therefore willingly be used, in particular for manufacturing large curved window panes, cannot be sufficiently polished however so that it is not really suitable for manufacturing cockpit windows particularly for airplanes. The aforementioned PMMA/PC or PMMA/PC/PMMA layer structures provide a suitable remedy for this lack in polishability of PC.

A heat absorbing laminated (window) pane consisting of a core of polycarbonate, which is lined on one, or both sides with a PMMA pane as described herein is therefore a further embodiment of the invention.

A further embodiment of the present invention is a heat-absorbing window pane, in particular for an automobile, a vessel or an airplane comprising a heat absorbing PMMA pane as described above.

Preferably, said window panes exhibit an overall transparency for light of a wavelength between 400 and 780 nm (visible range) of 50% or more, preferably 75% or even 80% and more. Most preferably, the heat-absorbing PMMA panes according to the invention are used for manufacturing the glazing of airplanes, in particular helicopters therefrom. In this sense the present invention accordingly relates to the use of an appropriately shaped heat-absorbing window pane as described herein including laminated panes consisting of PC and PMMA layers for the glazing of an airplane, in particular a helicopter.

Example 1 :

A PMMA pane of the dimensions 800 x 600 x 3.3 mm is manufactured according to following scheme:

Prepolymerisation :

Preparation of a clear solution of 0.005 %bw LUMOGEN IR 765 (a commercial IR absorber available from BASF), 0.1 %bw TINUVIN 234 (a commercial UV absorber available from CIBA and 0.05 %bw of TINOPAL OB (a commercial optical brightener available from CIBA in methylmethacrylate (MMA) ) is prepared and prepolymerized for 1 hour at 80⁰C in a reactor in the presence of 0.05%bw AIBN as initiator for the free radical polymerization.

Final polymerization:

The viscous pre-polymerised material obtained is blended with 0.05%bw AIBN and cast into a mould consisting of two glass plates (1000 x 1000 x 3 mm) with a seal between them which seals off the room between the plates to the environment. The inner sides of the glass plates are lined with a PET foil of 19 or 40μm. The mold is heated to 40⁰C and left at said temperature for about 18 hours. Then the temperature is raised to 50⁰C for another 18 hours and finally to 70⁰C for about 24 hours.

The transparent panes obtained are entirely uniform and of excellent optical quality show no streaks or haze.

Similarly, a PMMA pane of the same dimensions is prepared containing 0.005%bw of LUMOGEN IR765 and a corresponding PMMA pane of the same dimensions is prepared containing 0.005%bw of LUMOGEN IR765 and 0.1%bw TINUVIN 234 as well as a pure PMMA plane.

Example 2

The transparency of the panes of Example 1 is determined in the range of 250 to 5023.95 nm. The results are shown in Table 1. Table 2 shows the mean transmission of the panes over a wavelength from 250 to 5023.95 nm as well as the transmission for visible light of a wavelength from 250 to 780nm.

Table 1

Wavelength Absorption Transmission

0.005%Lumogen 0.005% Lumogen IR 765+

0.005% Lumogen PMMA IR765+ 0.1% Tinuvit 7 0.1% Tinuvin 234 + 0.05%

IR765 Reference 234 Tinopal OB

[nm] % % % %

250.00 0.0 0.0 0.0 0.0

260.00 0.4 0.9 0.0 0.0

270.00 0.0 4.3 0.1 0.1

280.00 0.1 5.0 0.3 0.1

290.00 6.3 9.6 0.4 0.1

300.00 20.9 22.0 0.3 0.1

310.00 31.9 35.8 0.4 0.3

320.00 37.7 49.0 0.5 0.4

330.00 41.4 67.0 0.7 0.5

340.00 45.5 77.0 0.6 0.5 350.00 46.2 79.0 0.7 0.5

360.00 46.1 83.0 2.6 1.7

370.00 44.0 87.0 5.6 4.0

380.00 46.3 89.0 45.0 27.0

390.00 56.4 89.4 53.0 49.0

400.00 61.3 89.6 60.0 56.0

410.00 63.6 89.7 61.0 60.0

420.00 65.4 89.8 65.0 69.0

430.00 66.8 89.8 64.0 73.0

440.00 67.6 90.0 65.0 77.0

450.00 68.5 90.3 66.0 78.0

470.00 69.5 90.5 67.0 79.0

480.00 69.1 90.7 68.0 79.0

490.00 70.5 90.9 69.0 80.0

500.00 70.4 91.0 70.0 80.0

510.00 69.5 91.1 70.0 81.0

520.00 71.0 91.1 72.0 81.2

530.00 72.6 91.0 71.0 82.0

540.00 72.6 91.1 71.5 83.0

550.00 72.1 91.1 71.0 82.0

560.00 71.0 91.2 71.0 81.0

570.00 69.2 91.1 69.5 80.3

580.00 67.1 91.1 66.0 78.0

590.00 64.8 91.2 65.0 76.0

600.00 61.6 91.2 60.0 73.0

610.00 56.7 91.3 56.0 70.0

620.00 50.7 91.2 45.9 64.0

630.00 45.5 91.3 44.7 59.0

640.00 41.2 91.3 41.0 53.0

650.00 37.2 91.4 36.0 48.0

660.00 31.8 91.4 30.1 42.0

670.00 24.3 91.5 24.0 36.0

680.00 17.5 91.5 16.5 29.0

690.00 13.6 91.6 13.0 24.0

700.00 11.9 91.6 11.2 22.0

710.00 11.5 91.5 11.0 21.4

720.00 11.7 91.5 11.0 18.0

730.00 10.6 91.6 10.3 16.0

740.00 7.1 91.6 7.0 12.0

750.00 3.5 91.7 3.0 7.0

760.00 1.9 91.8 2.0 5.0

770.00 1.8 91.7 2.0 5.0

780.00 3.8 91.8 3.0 6.0

790.00 10.1 91.7 9.6 13.0

800.00 22.5 91.8 20.7 25.0

810.00 38.3 91.9 37.0 40.0

820.00 52.7 91.9 50.5 54.0

830.00 63.0 91.9 60.2 64.0

840.00 69.1 91.8 67.0 70.0

850.00 72.4 91.8 70.1 73.0

860.00 76.5 92.0 75.3 77.0 870.00 77.9 91.9 77.0 78.0

880.00 78.8 91.6 77.4 79.0

890.00 78.8 91.2 77.4 79.0

900.00 79.4 91.0 78.0 80.0

910.00 80.4 91.4 78.8 80.5

920.00 81.5 91.8 79.4 82.0

930.00 82.1 91.9 80.6 82.0

940.00 82.7 92.1 81.0 83.0

950.00 82.8 92.0 81.0 82.8

960.00 83.1 91.9 82.0 83.0

970.00 83.0 91.8 82.1 83.0

980.00 83.0 91.8 82.1 83.0

990.00 82.7 91.5 82.0 82.8 "000.00 82.5 91.3 81.4 82.3 '020.00 82.8 91.4 81.3 82.5 '040.00 83.2 91.6 81.5 83.0O60.00 83.6 91.9 82.0 83.2 '080.OO 83.9 92.0 82.1 83.4 '100.OO 83.6 91.8 82.5 83.2 '120.00 81.0 90.1 80.2 81.0 '140.00 74.4 86.1 73.1 76.0 '160.00 68.2 81.2 67.0 69.0 '180.00 66.7 80.0 65.8 67.0 '200.00 77.0 86.7 75.6 78.0 '220.00 82.7 90.3 81.0 83.0 '240.00 84.1 91.1 82.0 84.0 '260.00 84.8 91.5 83.0 85.0 '280.00 84.7 91.5 83.0 86.0 '300.00 84.9 91.5 83.0 86.0 '320.00 83.9 91.0 82.7 85.0 '340.00 72.5 83.1 73.0 75.0 '360.00 65.7 78.7 67.0 67.0 '380.00 63.7 76.9 64.0 65.0 '400.00 68.0 80.0 66.0 67.0 '420.00 68.0 79.7 66.0 67.0 '440.00 70.5 81.6 69.0 69.0 '460.00 78.0 86.5 75.3 77.0 '480.00 79.9 87.8 77.2 79.0 '500.00 81.9 89.1 80.1 81.0 '520.00 83.2 89.8 82.4 82.0 '540.00 83.4 89.8 82.0 83.0 '560.00 82.5 89.1 81.0 82.0 '580.00 80.9 88.2 79.5 81.0 '600.00 78.4 86.7 77.0 79.0 '620.00 61.3 82.2 60.7 64.0 '640.00 66.9 79.2 65.8 68.0 '660.00 30.0 50.1 30.0 32.0 '680.00 12.0 29.3 13.0 14.0 '700.OO 19.3 38.3 20.0 18.0 '720.OO 21.8 40.4 22.0 20.7 '740.OO 30.3 49.9 29.0 28.0 1'760.OO 43.9 61.4 42.0 42.0

1'780.OO 44.7 61.6 43.0 43.0

1'800.00 54.2 68.5 53.0 51.0

1'820.00 61.1 73.5 60.6 59.0

1'840.00 60.1 73.0 60.0 58.0

1'850.00 57.4 71.4 57.0 56.0

1 '851.68 57.0 70.9 56.0 55.5

1 '900.55 39.9 52.7 40.0 40.0

1 '952.08 49.2 64.0 48.0 47.0

2O00.27 58.1 72.4 57.0 56.0

2O50.91 54.6 69.3 55.0 55.0

2^*104.18 28.7 47.1 26.4 27.0

2^*153.12 21.5 38.7 20.8 22.0

2'204.38 8.5 20.2 8.2 9.0

2'250.31 0.0 0.6 0.2 0.1

2'306.37 0.1 0.2 0.1 0.1

2'356.69 0.1 0.2 0.1 0.0

2'400.33 0.0 0.2 0.1 0.0

2'454.88 0.4 0.8 0.5 0.2

2'502.27 1.2 3.3 1.0 1.0

2^*551.53 3.5 9.0 3.2 2.6

2'602.77 7.3 16.0 7.1 6.0

2'656.10 11.0 22.6 12.6 10.4

2700.37 6.3 12.4 6.9 7.0

2757.83 0.0 0.1 0.1 1.0

2'805.58 0.0 0.0 0.0 0.1

2'855.02 0.0 0.2 0.2 0.0

2^*906.23 0.0 0.3 0.1 0.0

2^*959.31 0.6 3.5 0.5 0.3

3^*000.41 0.8 4.0 0.8 0.5

3^*057.02 0.7 3.6 0.7 0.7

3'100.90 0.3 2.2 0.4 0.3

3'208.36 0.0 0.1 0.1 0.1

3'306.58 0.0 0.0 0.0 0.0

3'410.99 0.0 0.0 0.0 0.0

3'503.18 0.0 0.0 0.0 0.0

3'600.49 0.0 0.4 0.4 0.0

3703.37 0.6 3.4 0.4 0.3

3'812.29 0.2 1.6 0.2 0.1

3^*904.15 0.2 1.8 0.2 0.1

4^*000.55 1.1 5.6 0.9 0.5

4^*101.83 0.6 3.3 0.8 0.4

4'208.37 0.1 1.5 0.2 0.2

4'320.59 0.3 2.2 0.3 0.1

4'408.77 0.6 3.4 0.5 0.3

4'500.62 0.6 3.7 0.6 0.4

4'629.21 0.2 1.6 0.3 0.2

4730.58 0.1 0.6 0.1 0.1

4'800.66 0.1 0.4 0.1 0.0

4^*909.76 0.1 0.1 0.1 0.0

5^*023.95 0.1 0.2 0.0 0.0 Table 2

It can particularly be seen that the transmission of the PMMA comprising the optical brightener is significantly increased for visible light as compared to heat-absorbing PMMA panes comprising only the IR absorber or only the IR and the UV absorber component.

Figure 1 is a graphical representation of the above table in the range from 200 to 1000 nm.

Example 3

The heat-absorbing properties of panes according to Example 1 are determined. An IR lamp is used as the heat source. A box having the dimension 20 x 12 x 7 cm and equipped with a PC- fan and a thermo couple was covered with a pane according to Example 1 leaving a gap of about 4 mm between the top of the box and the pane to allow some convection. The thermo couple was linked to a Laptop to provide the data to a software program for analysis. The distance between pane and IR lamp is 50 cm.

After about 30 min an influence of the absorber in the pane can be determined. After 100 min a maximum difference in temperature of 0.95⁰C can be determined. At 100 min the fan is switched off. The temperature difference at 150 min. is 2.41°C.

The results are summarized in Table 3 and graphically shown in Figure 2.

Table 3:

Claims

What is claimed is:

1. A heat-absorbing polymer pane essentially consisting of PMMA, one or more IR absorbers, one or more UV absorbers and one or more fluorescent whitening agents (optical brighteners) .

2. A heat-absorbing polymer pane according to claim 1 or 2, comprising 0.001 to 0.5 %bw, , preferably 0.002 to 0.05 %bw, most preferably 0.0025 to 0.03 of IR absorber.

3. A heat-absorbing polymer pane according to any one of claims 1 to 3, comprising 0.01 to 0.5, preferably 0.05 to

0.15 %bw of UV absorber.

4. A heat-absorbing polymer pane according to any one of claims 1 to 3, comprising 0.01 to 0.2 %bw, preferably 0.04 - 0.15 most preferably 0.05 to 0.15 of fluorescent whitening agent (optical brightener) .

5. A heat-absorbing polymer pane according to any one of claims 1 to 4, wherein the one or more IR absorbers are selected from Quaterrylenes, Chinophthalones, Anthrachinones, Dioxazins and mixtures of such compounds

6. A heat-absorbing polymer pane according to any one of claims 1 to 5, wherein the one or more UV absorbers are selected from Hydroxybenzophenones, Benzotriazoles, Hydroxyphenyltriazines and mixtures thereof.

7. A heat-absorbing polymer pane according to any one of claims 1 to 6, wherein the one or more fluorescent whitening agents (optical brighteners) are selected from Bis- benzooxazles, Triazin-phenylcumarines, Naphthotriazol- phenylcumarines, Bis- (styryl) biphenyles and mixtures thereof.

8. A heat-absorbing polymer pane according to any one of claims 1 to 7, comprising 0.002 to 0.05 %bw, most preferably 0.0025 to 0.03 of IR absorber, 0.01 to 0.5, preferably 0.05 to 0.15 %bw of UV absorber and 0.04 - 0.15 most preferably 0.05 to 0.15 of fluorescent whitening agent (optical brightener) .

9. A heat-absorbing polymer pane according to any one of claims 1 to 8 and, in particular to claim 8, wherein the IR absorber is selected from Quaterrylenes, a combination of N,N,N',N'-Tetrakis- (p-di-n-butylaminophenyl) -p- phenylenediamin) and N, N, N ', N ' -Tetrakis- (p-di-n- butylaminophenyl) -p-benzochinon-bis- (immonium- hexafluoroantimonat) and mixtures thereof, the UV absorber is selected from Benzotriazoles, and the fluorescent whitening agent (optical brightener) is a Bis-benzooxazle, in particular 2, 5-bis- (5-tert-butyl-benzoxazol-2-yl) thiophene .

10. A process for manufacturing a polymer pane according to anyone of claims 1 to 8 comprising the free radical polymerization of a solution essentially consisting of methylmethacrylate and one or more IR absorbers, one or more UV absorbers and, optionally, one or more fluorescent whitening agents (optical brighteners) in the presence of an initiator for the free radical polymerization and forming a PMMA pane therefrom.

11. A process according to claim 10, wherein the polymerization of the solution essentially consisting of methylmethacrylate and one or more IR absorbers, one or more UV absorbers and, optionally, one or more fluorescent whitening agents (optical brighteners) is carried out in two steps :

(a) a prepolymerization of said solution essentially consisting of methylmethacrylate (MMA) and one or more IR absorber (s) , one or more UV absorber (s) and, optionally, one or more whitening agent (s) in the presence of an iniator for the free radical polymerization under conditions wherein a prepolymerized material if formed which is only so viscous, that it can still be blended with further initiator compound and is still pourable; and

(b) the final polymerization of said prepolymerized material, wherein said material is blended with further initiator, poured into an appropriate mould to form a pane, heated to temperatures of 40 to 90⁰C and held at said temperatures for a time sufficient to finalize the polymerization .

12. A process according to claim 11, wherein wherein the prepolymerzation is carried out in the presence of azo- iso-butyronitril (AIBN) at a concentration of about 0.01 to 1 %bw at a temperature of about 50 to 90⁰C during about 30 90 minutes, and the final polymerization is carried out in the presence of 0.05 %bw of AIBN, in a mould consisting of two glass plates of appropriate size with a seal between them having a thickness corresponding to the desired thickness of the pane to be manufactured, which seals off the room between the plated to the environment, wherein the inner sides of the glass plates are lined with a release agent, preferably a polyethylene terephthalate (PET) foil having a thickness of 15 to 50 μm, wherein the final polymerization is furthermore performed in three steps, an initial polymerization step of about 14 to 20 hours at about 40⁰C, followed by a second polymerization step of about 15 to 20 hours or longer at about 50⁰C and an ultimate polymerization step of about 15 to 40 hours or longer at a temperature of about 60 to 80⁰C.

13. A heat absorbing PMMA pane obtainable according to any one of claims 10 to 12.

14. A heat-absorbing window pane, in particular for an automobile, a vessel or an airplane comprising a heat absorbing PMMA pane according to any one of claims 1 to 9 or 13.

15. A heat-absorbing window pane according to claim 13, which exhibits an overall transparency for light of a wavelength between 400 and 780 nm (visible range) of 50% or more, preferably 75%.

16. A heat-absorbing laminated window pane consisting of a core of polycarbonate which is lined on one or both sides with a PMMA pane according to any one of claims 1 to 9 or 13.

17. Use of an appropriately shaped heat-absorbing window pane according to any one of claims 13 to 16 for the glazing of an airplane, in particular a helicopter.