ACRYLIC GLASS HAVING PHOTOCHROMIC PROPERTIES

VERRE ACRYLIQUE PRESENTANT DES PROPRIETES PHOTOTROPIQUES

English Abstract

The invention relates to polymethyl methacrylate that has photochromic
properties, to methods for producing it and to uses thereof.

French Abstract

La présente invention concerne du polyméthylméthacrylate présentant des propriétés phototropiques ainsi que des procédés de fabrication de ce composé et son utilisation.

Claims

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claims
1. Polymethyl methacrylate sandwich elements
comprising two polymethyl methacrylate sheets and
an intermediate layer which comprises phototropic
dyes.
2. Polymethyl methacrylate sandwich elements
according to Claim 1, characterized in that the
intermediate layer comprises polyacrylates or
alkylated polymethacrylates, preferably polybutyl
methacrylates.
3. Polymethyl methacrylate sandwich elements
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
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
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
to 5 mm, preferably from 0.1 to 3 mm.
7. Polymethyl methacrylate sandwich element according
to Claim 6, characterized in that the intermediate
lay~r comprises amounts of from 0.001 to 10% of
phototropic dyes.
8. Polymethyl methacrylate sandwich element according
to Claim 1, characterized in that the polymethyl
methacrylate sheets comprise light stabilizers.

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9. Polymethyl methacrylate sandwich element according
to Claim 1, characterized in that the polymethyl
methacrylate sheets comprise dyes.
10. Polymethyl methacrylate sandwich element according
to Claim 1, characterized in that the polymethyl
methacrylate sheets comprise comonomers, in
particular crosslinking agents.
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
polymethacrylate sheets and the materials are
bonded to one another by way of a heat-
conditioning process.
12. Process for production of polymethyl methacrylate
sandwich elements according to Claim 1,
characterized in that internal coextrusion is used
to produce two polymethacrylate sheets with an
intermediate layer.
13. Use of polymethyl methacrylate sandwich elements
in the construction sector.

Description

CA 02580765 2007-03-16
WO 2006/048089 PCT/EP2005/010556
Acrylic glass having photochromic properties
The invention relates to acrylic sheet with phototropic
properties, production processes, and uses.
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
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.
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-
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.
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
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
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.

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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
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.
The intermediate layer has to be sufficiently soft to
leave enough freedom for the dye molecules to produce
the colour change via isomerism.
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
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
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-
alkylated polymethacrylates. Propyl, butyl and longer-
chain methacrylates have been found to be particularly
suitable.
Any of the known phototropic dyes may be introduced
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,

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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
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
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.
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
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
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.
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
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

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sandwich elements can be produced by this process using
an appropriately designed extrusion die.
The invention therefore also comprises the cell casting
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
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
illustration of the present invention, but are not
intended to restrict the invention to the features
disclosed herein.
Examples
Example 1
Colourless acrylic sheet for outer panes of the
sandwich element
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
Light stabilizers may also be optionally added in order
to protect the photochromic inner layer.
Suitable products for this purpose are HALS products,
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

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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 C. Completion of the polymerization
takes place in a heat-conditioning cabinet for 4h at
115 C.
Example 2
Photochromic inner layer of the sandwich element:
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
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
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 C.
This gives a transparent, slightly yellowish sheet with
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
to brown colour.