EP1095080A1

EP1095080A1 - Method for producing thermotropic casting resin systems and utilization thereof

Info

Publication number: EP1095080A1
Application number: EP99924875A
Authority: EP
Inventors: Taner Bicer; Christoph Schwitalla; Holger GÖDEKE
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 1998-06-10
Filing date: 1999-05-04
Publication date: 2001-05-02
Also published as: US6489377B1; DE19825984C1; WO1999064488A1

Abstract

The invention relates to a method for producing thermotropic casting resin systems that comprise at least one matrix polymer including at least one thermotropic monomer compound which cannot be mixed with the matrix polymer, whereby the matrix polymer and the thermotropic monomer compound are selected in such a way that their refraction indices are almost the same in a temperature range that is below the temperature required for structural change and that reaches the temperature of structural change of the thermotropic monomer compound, the casting resin system being translucent or transparent in this temperature range. After dissolving the monomer thermotropic compound in a matrix solution containing a photohardening oligomer, reactive diluents and photoinitiators and a liquid, photohardenable system is obtained, photoradiation with exclusion of oxygen is carried out for hardening.

Description

Process for the production of thermotropic cast resin systems and its application

The present invention relates to a process for producing thermotropic casting resin systems comprising at least one matrix polymer which includes at least one (thermotropic) monomeric compound which is immiscible with the matrix polymer and which can be influenced by the change in temperature in its structure, the matrix polymer and the thermotropic monomeric compound being selected in this way are that their refractive indices are approximately the same in the temperature range below the temperature relevant for the structural change up to the temperature of the structural change of the thermotropic monomeric compound, and thus the casting resin system is translucent or transparent in this temperature range, and the use of such thermotropic casting resin systems. Various thermo-optical systems are already known, particularly in connection with the shading of glass surfaces.

A thermo-optical polymer material is known from the generic DE 44 33 090 A1, which consists of at least one matrix polymer and a monomeric compound, the matrix polymer and the monomeric compound being selected such that their refractive indices in the temperature range below the temperature relevant for the structural change up to the temperature of the structural change of the monomeric compound are approximately the same and the polymer material is thus translucent and transparent in this temperature range. As matrix polymers

Polyester proposed and as monomeric compounds preferably alkanes with CIO to C25.

From German patent application DE 196 42 886.6 it is known that thermotropic systems can be formulated on the basis of completely segregated polymers which are used for the production of thermotropic coatings. Here, a coating solution is first prepared (for example with xylene as a solvent). The application of the

Coating solution is carried out using known coating technology, such as knife coating, spraying or flooding. After the coating solution has been applied, the solvent is evaporated off and the crosslinking is then thermally induced. After cooling and intermediate storage, a top layer is preferably applied. The disadvantage of this method is that toxic vapors can arise when the solvent is evaporated. This can lead to environmental degradation as well require increased investment costs for occupational safety. In addition, due to the complex drying process, the manufacturing process can only be carried out for open areas or for coatings with a limited thickness, so that the large-scale industrial application is limited.

A further development is based on a thermotropic gel, which mainly consists of colloidal particles of a polyether-water mixture, which is enclosed by a gel layer made of a vinyl-carboxyl-water mixture. A surfactant surface serves as a solubilizer. When a critical temperature is exceeded, the water bound to the macromolecules is split off into the external solvent. At the same time, temperature-dependent matting of the macromolecules takes place. In addition to this particle growth, the relative refractive index of the particles is also increased by the elimination of water (see also European Patent 86 904

133). These thermotropic gels can, for example, be filled into a space between the panes to produce thermo-optical glazing. The disadvantage of the development, however, is that the generally highly viscous systems can only be filled with great effort and the edge seals have to be made water-vapor diffusion-tight as well as resistant to chemicals in order to prevent drying out. In addition to high production costs, the long-term stability of the corresponding glazing is generally severely restricted.

Starting from DE 44 33 090 AI, the present invention has for its object to provide a method for producing thermotropic cast resin systems create that makes it possible to produce long-term resistant thermotropic cast resin systems of any shape and size in a fast and environmentally friendly manner.

This object is achieved by a manufacturing method according to claim 1 and in relation to the use by the features of claim 15.

The fact that the thermotropic cast resin systems

(T-OPAL) by dissolving the monomeric compound in a photo-curing oligomer, reactive diluent and photoinitiator-containing matrix solution to form a liquid, photo-curable system and subsequent photo-irradiation with exclusion of oxygen for curing, there is no need for a solvent to be evaporated. This means that there are no (often toxic) solvent emissions, which means that the workload is low without the need for additional protective measures. The elimination of the drying process, which is very time-consuming with solvent-containing coating solutions or only enables coatings of small thickness, can significantly reduce the process times. Appropriate variation of the parameters (for example increased addition of photoinitiators) allows very short curing times to be achieved. The process is also characterized by the very simple process control and the low outlay on equipment, and the hardened cast resin system, in contrast to thermotropic gels according to the prior art, has significantly improved long-term stability. During the curing process taking place under photoirradiation, the reactive thinner enters into the curing reaction in the present production process (depending on the intensity of the radiation, addition of appropriate photoinitiators and

The filling form of the cast resin system requires a photo-irradiation period of 1 to 20 minutes). The thermotropic compound or component precipitates out very finely and is thus built into the matrix in the crystalline state. In order to enable the desired precipitation, the matrix solution must have an appropriate solubility for the thermotropic component. The solvency of the matrix in combination with the crosslinking speed determines the particle size distribution and the number of separation zones, which in turn have a significant influence on the radiation properties of the layers. Both the temperature-dependent reduction in the level of radiation transmission and the wavelength dependency of the transmission can be specifically varied using these parameters.

In any case, however, care must be taken that the optical density of the resulting matrix is matched to the thermotropic component, that is to say that the refractive index of the matrix corresponds to that of the thermotropic component below the temperature relevant for the structural change in the thermotropic component (for For example, the refractive index of the matrix when using paraffins is preferably 1.5 <n _D ²⁰ <1.58). It is advantageous or necessary here that the refractive index of the matrix is constant over a wide temperature range (for example between 10 and 40 ° C.). Since no thermal treatment is necessary to cure the matrix solution, the entire production process, that is to say the dissolution of the thermotropic monomeric compound in the matrix solution and the subsequent photoirradiation, can take place at room temperature. For processing reasons, an ambient temperature range of 10 to 30 ° C must be maintained, preferably 20 ° C.

The photoirradiation can be carried out with light of different wavelengths, but the irradiation with UV light in the wavelengths from 200 to 500 nm is particularly advantageous.

The matrix solution can be composed in many different ways. For the photo-curing resins, acrylic-modified, saturated, aliphatic systems such as e.g. To use polyester, urethane or polyether, 20 to 80 parts being advantageously used in the formulation. Acrylic acid, ethyl acrylate, s-butyl acrylate, 2-hydroxyethyl acrylate, ethoxyethoxyethyl acrylate, tetrahydrofurfury1-acrylate or methyl methacrylate, for example, are used as reactive diluents. 80 to 20 parts of reactive diluent are preferably added to the formulation. Commercial photoinitiators such as e.g. Phosphine oxides and ketones. An initiator content of 0.5 to 1 part is advantageously chosen.

Commercially available thermotropic monomeric compounds can be considered as the thermotropic component in the production process according to the invention. These are preferably aliphatic compounds, especially alkanes of the general formula C _n H _{2n + 2} with n = 10 to n = 25. Depending on the choice of the thermotropic monomeric compound, the temperature which is decisive for the structural change and thus for the changed optical properties can be in the range from 10 to 50 ° C., preferably in the range from 20 to 40 ° C.

The mixed liquid casting resin system which already contains the thermotropic component can be filled in various ways. In addition to filling into any transparent filler, it is possible, for example, to fill the liquid system in an intermediate space between the two transparent glass or plastic panes, which is sealed all the way around before the photo-irradiation. In this way, the outflow of oxygen during the curing of the cast resin system is ensured in a particularly simple manner. When using organic multi-wall sheets, the hollow chambers of which are filled, a separate edge seal can be dispensed with. In any case, techniques that are already established in the glazing industry can be used because, for example, the filling of inter-pane spaces for sound insulation purposes is already state of the art.

After the curing process induced by photo-irradiation, the panes surrounding the filling can remain or can also be removed. If the surrounding panes remain, the adhesion between the filling and the panes can preferably be further improved by commercially available adhesion promoters, such as silanes, which at the same time increases the strength of the overall arrangement. This can be done, for example, by applying suitable adhesion promoters to the corresponding inner surfaces of the surrounding panes respectively. The fact that the surrounding panes remain has the advantage that the thermotropic layer is protected from mechanical, chemical and radiation-related attack, and a consistently high surface quality is also guaranteed.

However, it is of course also possible to use the hardened cast resin system as an independent pane after removing the surrounding panes.

Another possibility is to openly apply the liquid system to a substrate before the photo irradiation. This can be done by methods customary in the paint industry, such as spraying, flooding or

Squeegees happen. In any case, however, care must be taken that the photo-irradiation takes place in a room with the exclusion of oxygen or that a gas-tight film is placed on the applied layer outside such a room during the photo-irradiation.

Regardless of whether the liquid system is poured into a closed mold or applied to a free surface before the photo-irradiation, layer thicknesses can be achieved in a very wide range of sizes. It is therefore easily possible to achieve layer thicknesses in the range from 0.1 mm to 10 mm. Corresponding fillings or coatings can be used in all areas of technology, especially in sun-exposed structures and motor vehicles. The coating or filling according to the invention of transparent components, for example made of glass or plastic, can thus provide a screen or shade which is opaque at high temperatures. becomes more casual and thus makes the use of energy-intensive air conditioning systems unnecessary or enables a smaller dimensioning. Because of the low raw material costs, the costs of the fillings or coatings according to the invention are comparatively low.

The invention is explained in more detail below using two exemplary embodiments:

Example 1:

16.9 parts of methacrylic acid methyl ester (from Merck) are added to 80.9 parts of an acrylic-modified saturated polyester (viaktin, from Vianova Resins) and 1.9 parts of n-octadecane (from Merck) are dissolved in this mixture. 1.0 part of the UV initiator IRGACURE (from Ciba Specialty Chemicals) is added to the resulting solution. The edge of two float glass panes is sealed with the help of a double-sided adhesive tape, which also serves as a spacer, except for a small fill opening. The fluid solution described above is poured into the space between the panes. This composite pane is then exposed to UV radiation (Vitalux, from Osram) at a temperature of about 20 ° C. for about 5 minutes.

Example 2:

16.9 parts of divinylbenzene (from Merck) are added to 80.9 parts of an acrylic-modified saturated polyester (viaktin, from Vianova Resins) and 1.9 parts of n-eicosan (from Merck) are dissolved in this mixture. The resulting solution is blended with 1.0 part UV Initiator IRGACURE (from Ciba Specialty Chemicals) added. The edge of two float glass panes is sealed with the help of a double-sided adhesive tape, which also serves as a spacer, except for a small fill opening. The fluid solution described above is poured into the space between the panes. Finally, this composite pane is exposed to UV radiation (Vitalux, Osra) at a temperature of approx. 30 ° C for approx. 5 minutes.

Example 3:

48.8 parts of an aliphatic urethane acrylate (Rahn Chemie) become 4.8 parts of acrylic acid (Fluka) 24.2

Parts of acrylic acid methyl ester (Fluka) and 19.4 parts of acrylic acid tetrahydrofurfurylacrylate (Cray Valley) were added and 2.4 parts of n-octadecane (Fluka) were dissolved in this mixture. 0.8 part of the UV initiator IRGACURE (Ciba Specialty Chemicals) is added to the resulting solution. The edge of two float glass panes is sealed with the help of a double-sided adhesive tape, which also serves as a spacer, except for a small fill opening. The thin solution described above is poured into the space between the panes. Finally, this composite pane is exposed to UV radiation (UVA Black, Radium) at a temperature of approx. 25 ° C for approx. 10 minutes.

Example 4:

19.5 parts of a polyethylene glycol diacrylate (Cray Valley) become 14.6 parts of acrylic acid (Fluka), 14.6 parts of dianoldiacrylate (Akcros) and 48.8 parts of acrylic Acid tetrahydrofurfurylacrylat (Cray Valley) added and 2 parts of n-octadecane (Fluka) dissolved in this mixture. 0.5 part of the UV initiator IRGACURE (Ciba Specialty Chemicals) is added to the resulting solution. The edge of two float glass panes is sealed with the help of a double-sided adhesive tape, which also serves as a spacer, except for a small fill opening. The fluid solution described above is poured into the space between the panes. Finally, this composite pane is exposed to UV radiation (UVA Black, Radium) at a temperature of approx. 25 ° C for approx. 10 minutes.

The transmission properties of a cast resin pane according to the invention are illustrated below with the aid of a figure. This shows:

FIG. Transmission measurements on a thermotropic cast resin disc according to Example 2.

The figure shows the directional-hemispherical transmission of light of different wavelengths through a 2 mm thick thermotropic cast resin disc. The upper curve (filled squares) shows the transmission at 20 ° C, the lower curve (empty squares) the transmission at 35 ° C. It can be clearly seen that in this temperature range, which is relevant for technical applications, there is a significant reduction in transmission for all wavelengths with increasing temperature. In addition, the transmission T, which reproduces the radiation flow of the emerging light beam in relation to the radiation flow of the incoming light beam, is specified. This is 0.69 at 20 ° C, but only 0.24 at 40 ° C.

Claims

claims

1. A process for the preparation of thermotropic casting resin systems comprising at least one matrix polymer which includes at least one (thermotropic) monomeric compound which is immiscible with the matrix polymer and which can be influenced by the change in temperature in its structure, the matrix polymer and the thermotropic monomeric compound being selected in this way that their refractive indices are approximately the same in the temperature range below the temperature relevant for the structural change up to the temperature of the structural change in the thermotropic monomeric compound, and thus the cast resin system is translucent or transparent in this temperature range, characterized by

a) dissolving the thermotropic monomeric compound in a matrix solution containing photo-curing oligomers, reactive diluents and photoinitiators to form a liquid, photo-curable system,

b) Photo irradiation of the liquid system with the exclusion of oxygen for curing.

2. The method according to claim 1, characterized in that the photo-irradiation is carried out with UV light of the wavelength 200 to 500 nm.

3. The method according to at least one of the preceding claims, characterized in that the The duration of the photo-irradiation for curing the cast resin system is 1 to 20 minutes.

4. The method according to at least one of the preceding claims, characterized in that the photocuring resins are acrylic-modified e.g. Polyester or urethane.

5. The method according to at least one of the preceding claims, characterized in that the

Reactive thinners are selected from thinners which contain at least one unsaturated group, e.g. Acrylic acid, methacrylic acid ester, divinylbenzene.

6. The method according to at least one of the preceding claims, characterized in that the photoinitiators are ketones or phosphine oxides.

7. The method according to at least one of the preceding claims, characterized in that the thermotropic monomeric compound is an aliphatic compound.

8. The method according to at least one of the preceding claims, characterized in that the thermotropic monomeric compound is selected from alkanes of the general formula C _n H _{2n + 2} with n = 10 to n = 25.

9. The method according to at least one of the preceding claims, characterized in that for the structural change of the thermotropic mono- The relevant temperature is 10 to 50 ° C.

10. The method according to at least one of the preceding claims, characterized in that the temperature for the structural change of the thermotropic monomeric compound is 20 to 40 ° C.

11. The method according to at least one of the preceding claims, characterized in that the liquid system before process step b) in a space between two transparent panes, circumferentially sealed at the edge or another transparent space

Filler is filled.

12. The method according to at least one of the preceding claims, characterized in that the liquid system is applied to a substrate after process step a).

13. Use of thermotropic cast resin systems, produced by a process according to at least one of claims 1 to 12, characterized in that it is used as a screen or shading in the form of a coating on transparent components or in the form of a filling between transparent components, for example made of glass or plastic , with a layer thickness of 0.1 mm to 10 mm.