Stock material or miscellaneous articles – Structurally defined web or sheet
Reexamination Certificate
1999-08-27
2001-10-02
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Structurally defined web or sheet
C524S081000, C524S113000, C524S284000, C524S297000, C524S366000, C524S442000, C524S539000, C524S543000, C525S185000, C525S191000, C525S398000, C525S420000, C525S437000, C525S440030, C525S450000, C428S101000, C428S141000, C428S221000, C428S357000, C428S411100, C428S474400, C428S480000
Reexamination Certificate
active
06296920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reversible thermotropic plastics molding compound, to a method for its manufacture and to its utilization. Plastics molding compounds of this kind are needed for shading systems for regulating the amount of light and the temperature. They can be used in particular for the glazing of buildings, greenhouses, cars, solar collecting systems and the like.
2. Description of the Prior Art
According to prior art, the following systems are used for thermotropic glazing of this kind. From DE 19 719 224 A1, WO 9725358 A1 and WO 9725357 A1 it is known that thermotropic gels are introduced between two sheets of glass, the thermotropic gels separating with increasing temperature, forming thus scattering centers and thus reducing the light transmission. As they cool, the thermotropic gels mix with one another again and the scattering centers disappear, as a result of which the transmission increases again. What is disadvantageous about this system is the fact that the diffusion processes occurring in the hydrogel during the separation and mixing are slow, such that only low transition times can be achieved. Furthermore, hydrogels of this kind cannot be processed thermoplastically and themselves have none of the usual functional properties for plastics.
Furthermore liquid crystals embedded in polymers are known from Solar Energie Mater. Sol. Cells (1993) volume 31, pages 197 to 214. In a similar manner, in Proc. SPIE. Int. Soc, Opt. Eng. (1992) volume 1728, pages 261 to 271, films are described which have been manufactured from liquid crystals of this type embedded in polymer. In this case, the desired thermotropic effect is based on an alteration in the structure of the liquid-crystalline phase at a corresponding temperature. Since the molecular re-arrangement of the liquid-crystalline phase is hindered with increasing viscosity of the environment, those systems also have long transition times. Furthermore, liquid-crystalline polymers of this kind are expensive materials with complex structures, which are difficult to process and which have a negative influence on the mechanical properties of the matrix polymer.
From DE 38 31 873 A1 are known mixtures of thermotropic liquid-crystalline polymers, polycarbonate and polyester. The disadvantage of these mixtures consists in the fact that the liquid-crystalline polymers, as a result of the rigid anisotropic segments, are hard and brittle, and thus have a negative effect on the toughness of glass manufactured from same.
OBJECT OF THE INVENTION
The object of the present invention is, therefore, to make available reversible thermotropic molding compounds, methods for manufacturing same and uses of such plastics molding compounds, which can be realized in a simple and inexpensive manner without the listed disadvantages of prior art.
This object is achieved by the thermotropic transparent molding compound according to claim
1
, the method according to claim
23
and the uses according to claim
26
. Advantageous developments of the plastics molding compound, method and uses according to the invention, are given in the dependent claims.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The thermotropic transparent molding compound according to the invention consists of two components, the first component consisting of a transparent plastics material. The second component consists of material which is not thermodynamically miscible with the first component and is therefore available within the working temperature always in a separate phase from the first component. This second component has a dependence of the refractive index on temperature which is different from the dependence of the first component. If the temperature of the molding compound is increased, the refractive index of the second component changes in a different way from the refractive index of the first component, and the transparency of the molding compound is reduced. With this principle, a new way of generating thermotropism of the whole molding compound comprising the first and second component becomes available, which is not based on diffusion processes nor does it require complicated liquid-crystalline polymers with suitable nematic transition, and which thus renders possible a greater choice of second components, since the latter does not have to be liquid-crystalline.
The thermotropism of the molding compound according to the invention is reversible and has short transition times, since no rearrangement of crystals or separating/mixing processes occur.
The clouding intensity or the degree of darkening at a raised temperature of the molding compound may thus be simply adjusted via the amount of the second compound in the whole molding compound. Through the use of a plastics base, in particular the mechanical and electrical properties of the molding compound can be easily adjusted. It can, for example, be made weather-resistant, resistant to chemicals, or scratch-resistant through the addition of suitable additives or its flowing or sliding properties can be modified. In this way, the manufacture of impact resistance modified glass is possible.
The molding compound according to the invention can be forcibly mixed by compounding, for example in a kneader or an extruder, or be polymerized as a diblock or multiblock copolymer. Its processing into any kind of molded part is possible by means of all the standard thermoforming processes, such as injection molding, multicomponent injection molding, injection blow molding, extrusion. By this means, connecting the molding compound in the form of films or sheets or fibers to other materials is also possible, or laminating of the molded parts or coinject or coating or varnishing.
With the molding compound according to the invention, therefore, all the shapes possible with known processing techniques for thermoplastic materials may be manufactured.
If the refractive index of the second component alters strongly at a specific clouding temperature, a kind of optical switch or switching effect can be achieved. Such switching effects can be particularly simply achieved in that the second component has in the relevant temperature range a phase transition, for example a transition glass/melt or solid/liquid. Since the two components are thermodynamically incompatible, the microphases of the two components also remain stable and separated in the melt or the glass. Thus there is a spontaneous particularly strong clouding at the phase transition temperature. This clouding temperature may be adjusted through appropriate choice of component B and may be adapted to the respective application purpose of the thermotropically transparent molding compound. In a plurality of successive arising phase transitions, the clouding of the whole system can be constantly guided with the temperature.
A plurality of successive phase transitions can be achieved in particular with cladded core block copolymers having at least two phase separated shells with different conversion temperatures.
The molding compound has advantageously 1 to 99 wt % of the first component, 99 to 1 wt % of the second component and if necessary further additives with a weight proportion of 0 to 50 wt %, the shares being so selected that altogether 100 wt % is produced. Advantageously, the share of the first component is between 50 and 99 wt %, preferably between 70 and 99 wt %.
The first component consists advantageously of one or more polymers which are compatible with one another, such that the matrix of the molding compound can be adjusted at will between the properties of a transparent rubber and those of a transparent glass. The second component also consists advantageously of one or more polymers which are compatible with one another. This polymer can, for example, be simultaneously an impact resistance modifier, such that the mechanical properties of the molding compound are improved. If the molding compound consists in this way of a two-phase polymer system, according to the volume ratios of the two components
Buehler Friedrich
Hewel Manfred
Acquah Samuel A.
Ems-Chemie AG
Marshall & Melhorn LLC
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