Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1998-07-08
2000-10-31
Berman, Susan W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
522 84, 522 85, 522 74, 522114, 522116, 522117, 522120, 522121, 523300, 524458, 524460, 524529, 524530, 524533, 524534, 524535, C09K 328, C08F 250, C08F27102, C08F29112
Patent
active
061403873
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to gels for thermotropic layers, obtainable by irradiating a mixture comprising the sum of a), b) and c),
The present invention furthermore relates to a process for the production of the gels and to their use for the production of thermotropic layers.
The necessity for efficient use of energy and also utilization of solar energy for heating buildings requires highly effective and intelligent systems which match the solar-energy systems (windows, collectors, house walls) optimally to the weather conditions and user requirements. A high-quality window in an office wall ensures pleasant temperatures in winter and consequently results in a saving of energy. In spring at the latest, the same window will cause overheating and consequently expenditure of cooling energy, negating the energy saving in winter. It is therefore clear that optimized systems require control mechanisms for regulating the radiation or heat flow. This control can be partly passive, such as shading by roofs or balconies, or actively/mechanically by roller blinds or awning systems. However, many of these systems are not sufficiently effective, are too expensive or have an inadequate service life, which in turn results in increased costs.
The idea of using electro- or thermo-optical systems for control is repeatedly put forward, but has hitherto not resulted in a decisive breakthrough owing to material-related or technical problems.
An effective and inexpensive method of controlling the radiation and heat flow comprises using thermotropic layers. These layers are transparent in the unswitched state and only become cloudy above a certain switching temperature. The clouding is fully reversible, ie. the thermotropic layers become fully transparent again on cooling to temperatures below the switching temperature.
EP-A-678 534 describes gels for thermotropic layers which are obtainable from mixtures of monomers, thermotropic polymers and solvents by irradiation with high-energy light. The minimum amount of thermotropic polymer is 5% by weight, based on the mixture.
The resultant gels still have disadvantages concerning stability of the network formed from the monomers by irradiation and concerning transparency below the clear/cloudy switching temperature. The switching temperature should of course be above room temperature, preferably from 20 to 90.degree. C.
It is an object of the present invention to provide a gel for thermotropic layers and a process for the production thereof, by means of which the abovementioned disadvantages can be overcome.
We have found that this object is achieved by the gel defined at the outset, by a process for the production thereof, and by the use of the gel for the production of thermotropic layers.
The novel gels are obtainable by irradiating a mixture comprising components a), b) and c) with high-energy light.
Suitable uncrosslinked polymers as component a) are in particular those which have thermotropic properties such that a 10% strength by weight solution of this polymer in the selected solvent c), ie. in water or an organic solvent or a mixture thereof, has, in a switching range covering less than 20.degree. C., a change in the transmission of light having a wavelength of 600 nm so that, at a layer thickness of 10 mm, less than 50% of the incident light is transmitted above the switching range and at least 70% of the incident light is transmitted below the switching range. (During measurements with rising or falling temperature for determining the transmission, attainment by the polymer or gel of the new temperature is in each case awaited.)
The switching range or switching temperature is preferably in the range from 20 to 90.degree. C., particularly preferably from 20 to 50.degree. C., very particularly preferably, in the case of glazing systems, from 20 to 40.degree. C.
The switching range should preferably be less than 10.degree. C., particularly preferably less than 5.degree. C., very particularly preferably only 1.degree. C. or less.
Below the switching range, the transmissio
REFERENCES:
patent: 5587404 (1996-12-01), Kroner et al.
BASF - Aktiengesellschaft
Berman Susan W.
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