WO2009106352A1

WO2009106352A1 - Thermochromic coated substrates and method for the production thereof

Info

Publication number: WO2009106352A1
Application number: PCT/EP2009/001432
Authority: WO
Inventors: Arno Seeboth; Ralf Ruhmann
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2008-02-27
Filing date: 2009-02-27
Publication date: 2009-09-03
Also published as: EP2262593A1; DE102008011444A1

Abstract

An organic thermochromic complex, comprising at least one colorant, at least one developer, and at least one flux, is deposited on a substrate in the vacuum process. The substrate can comprise glass, ceramic, metal and the complexes and/or oxides thereof, doped and undoped semiconductor material, or plastic. The combination of different thermochromic layers is possible. The thermochromic layer can be combined with further functional layers, wherein these are also vapor deposited, or can be deposited using sputtering or CVD/OVPD technology or can be applied by screen printing, spraying, spinning, and/or common technology methods. The thermochromic effect is reversible, wherein the switching range can be determined beforehand.

Description

Thermochrome coated substrates and process for their preparation

The invention relates to the production of a layer with intrinsically reversible thermochromic properties using vacuum vapor deposition with organic thermochromic complexes. Such thermochromic coatings are used in particular for electro-optical or photovoltaic modules use.

Thermochromism involves the property of a material to reversibly or irreversibly change its color depending on the temperature. This can be done both by changing the intensity and / or the wavelength maximum.

There has been a tremendous demand for thermochromic materials, especially since the last decade. These are used, for example, as thermochromic inks, lacquers or plastics of all kinds, in particular films. As a rule, a coating of the outer substrate surface or a doping into the respective material volume takes place. For coating surfaces with thermochromic components, in particular screen printing technology or inkjet printing is used. In the case of thermoplastics, either a co-extrusion with a second thermochromic polymer or the doping of a thermochromic material takes place directly into the polymer melt. Thermochromic thermosets are preferably produced by doping the resin with thermochromic microcapsules.

Thermochromic inks are described in WO 2007/089554 in combination with regular color inks for the packaging industry and in US 2007167325 involving classical donor-acceptor systems based on spirolactones and phthalide derivatives. JP 2006335848 and JP 2006168244 include water-based thermochromic inks consisting of microcapsules of 0.5-2.0 μm or thermochromic laminate films for the packaging industry by using inorganic pigments embedded in a resin.

Inorganic and organic thermochromic materials differ in principle in their properties and functional action. The advantage of inorganic ther- mochromic materials is their high thermal resistance and light stability. However, they are, in part, mercury salts, ie extremely toxic. The advantage of organic reversible thermochromic materials is their mode of action. In contrast to inorganic materials, the switching temperature between the different color states is freely selectable - not fixed - and a multi-shell th between different color states is possible.

Many products, especially in information and communication technology, essentially require the switching properties of thermochromic organic materials, which are further enhanced by the requirement for high transparency. Thus, for example, the combination of transparent electrodes, or reflecting metal layers or ordered liquid crystal layers or hologram layers with thermochromic layers with simultaneously high transparency and, if possible, the additional option of several switching states, can not be realized so far. For optical recording materials, systems having thermochromic properties in combination with vacuum technology are described in US 5,576,084. However, these are limited exclusively to 2-component systems, ie in each case only the combination of dye and developer.

Proceeding from this, it was an object of the present invention to provide a method for thermochromic coating, which allows thermochromic coatings with freely selectable switching temperature between the different color states and a multi-switching between the color states. At the same time, the process should be easy to handle and provide high reproducibility.

This object is achieved by the method having the features of claim 1 and by the thermochromic coated substrate having the feature of claim 17. The further dependent claims show advantageous developments. In claim 20 a use according to the invention is mentioned. According to the invention, a method for the thermochromic coating of substrates is provided, in which a substrate and at least one organic thermochromic precursor containing at least one colorant, at least one developer and at least one fluxing agent are introduced into a vacuum chamber. In the vacuum chamber is then carried out by thermal excitation, evaporation of the precursor, wherein this vapor is then deposited on the substrate as a thermochromic complex.

It could be surprisingly shown that the use of vapor depositions in vacuum high reproducibility in terms of thermochromic coatings could be achieved and at the same time for the first time the combination of dye, developer and flux could be prepared as organic components with the advantages described in a simple manner.

The deposition is preferably carried out by physical or chemical vapor deposition. In this case, both the thermal vacuum deposition, an electron beam vapor deposition or sputtering come into question.

Preferred dyes are substances of the group consisting of triphenylmethane dyes, pyridinium phenolate betaines, pyranines, sulfophthaleins, Reichardt dyes, indicator dyes, azo dyes. The dyes may also be used in the form of mixtures thereof.

As flux, preferably substances of the group consisting of hydrocarboxylic acids, amines and amides, hydroxy compounds such as octadecanol, dodecanol, Hexadecanol or paraffins and mixtures thereof are used.

As the developer, preferred are substances such as esters of gallic acid, hydroxycarboxylic acids, bis-4-hydroxyphenyl derivatives and mixtures thereof.

Hydrocaboxylic acids in mixtures with hydroxy compounds, in particular the aliphatic structures, are suitable both as a developer or as a flux.

Preferably, the thermochromic precursor additionally comprises at least one organosilane. This organosilane preferably has the general formula

With

X is independently selected from the group consisting of C 1 -C ₁₆ -alkyl, C 1 -C ₆ -alkoxy, aryloxy, hydroxy or halogen,

R are independently selected from the group consisting of C 1 -C ₁₆ -alkyl, C 1 -C ₁₆ -alkoxy, amino, cyano, mercapto or glycidic structures.

More preferably, the organosilane is selected from the group consisting of dimethyldichlorosilane, trimethylchlorosilane, 3-chloropropyltrichlorosilane, 3-cyanopropyltri-chlorosilane, diphenylsilanediol, N-docosyltri-chlorosilane, vinyltriethoxysilane, gamma-aminopropyltrichlorosilane, hexamethyldisilazane, triphenylsilanol, and mixtures thereof.

The organosilanes act as adhesion promoters, whereby preferably organosilanes with high reactivity are used. The reactivity increases in the order chlorosilane <silanols <alkoxysilanes.

It is also possible to use several organosilanes, in which case the different organosilanes preferably have the same group X, while the group R varies.

The precursor preferably contains from 0.3 to 15% by weight of the dye, from 0.3 to 18% by weight of the dye

Developer, 67 to 99.4 wt .-% of the flux and 0 to 1.5 wt .-% of the organosilane.

The chosen molecular relationship between the individual components and the ability of the resulting total complex to form internal dimer / agglomerates, especially formed only by the flux, are crucial prerequisites for the continuing reversibility of the thermochromic effect of the deposited layer in a previously defined temperature range

To increase the thermal stability of the thermochromic complex consisting of dye, developer and flux, a surfactant may be added. In general, the surfactants can increase the possibility of forming dimers / agglomerates, ie the formation of superordinate structures. Suitable for this are, for example, hexadecylammonium bromide

(CTAB), sodium dodecyl sulfate (SDS) or anhydride compounds and their derivatives such as maleic anhydride and succinic acid esters. Particularly suitable is the sodium salt bis (2-ethylhexyl sulphosuccinate (AOT). The substrate surfaces to be vapor-deposited with thermochromic material can consist of glass, ceramics, metals and their complexes or oxides, doped and undoped semiconductor material or a polymer material.

The polymer material is preferably formed from the group consisting of polyethylene, polypropylene, cyclic olefins, polyesters, polycarbonate, poly (meth) acrylates, polyamide, acrylonitrile-butadiene-styrene copolymers and blends thereof.

During a vapor deposition process, if required, several thermochromic layers with different properties such as color, intensity or switching temperature for the color change can be deposited directly after one another or separated by functional layers such as transparent electrodes, electrochromic layers, protective layers or, for example, reflection layers. A variety of technology combinations is possible, including the combination of vacuum evaporation, sputtering and / or CVD / OVPD processes. The vacuum-deposited thermochromic layers can have almost any layer thickness, as they are technologically feasible in the UHV process. For applications in electrooptical modules, the layer thickness is preferably in the nm range, preferably in the range from 250 to 2000 nm, in particular from 250 to 1000 nm.

Suitable materials for coupled transparent electrodes are, for example, indium or cadmium derivatives, for electrochromism vanadium or tungsten oxides, for protective layers SiO, SiO _x or for reflection Al or Ag. The vacuum deposited organic thermochromic layer can be combined with additional functional layers - also by screen printing, lacquer, ink and polymer foils - for further specific applications. The polymer film may be a thermochromic polythiophene layer. Paint or ink may contain thermochromic capsules. The deposited thermochromic layer may also be part of a multilayer system with all layers deposited in a vacuum. Thus, for example, first a transparent electrode can be deposited on a substrate as first layer, in the second step a thermochromic organic layer, in the third step a protective layer of silicon oxide and finally in the fourth step an Al reflection layer. Such a layer system is free of oxygen (and its radicals) and gases such as CO ₂ or SO ₂ . As a result, the long-term stability of the thermochromic layer is increased enormously.

According to the invention, a thermochromic coated substrate is likewise provided, which can be produced by the method as described above. The thermochromic layer preferably has a thickness in the range from 100 to 3000 nm, in particular from 150 to 1000 nm.

The thermochromic complex is preferably in the form of connected dimers or an agglomerate.

The thermochrome-coated substrates are used in the production of electro-optical or photovoltaic modules.

Reference to the following examples, the subject invention is to be explained in more detail, without To limit this to the specific embodiments shown here.

example 1

On a ceramic surface (Pyrope), a black thermochromic layer is deposited, consisting of the thermochromic complex consisting of tetradecanol: bis (4hydroxyphenyl) sulfides: Pergascript Black = 14.5: 2: 1.5% by weight. The deposition takes place at 105 ^° C. and 6.5 × 10 ^-7 mbar. It is worked at a constant evaporation rate of 55%. The homogeneous layer is black at room temperature. When heated to over 40 ^° C., the layer becomes colorless, with different shades of gray becoming visible. The thermochromic effect is reversible.

Example 2

On a glass substrate coated with a transparent electrode consisting of ITO, a red thermochromic layer is deposited from a thermochromic complex consisting of octadecanol: 2,2Bis (4-hydroxyphenyl) -2,2-propane: commercial dye Pergascript Red: AOT = 10: 2 : 1: 0.2 weight percent. For the deposition in vacuo at 100 ⁰ C and 8.6 x 10 ^{~ η} mbar a tungsten boat is used. In the sourcel phase, the power is 45% and in the source2 phase it is 60%. At room temperature, the thermochromic layer is red. The temperature increase takes place by applying a voltage. At 4.5 volts, the ITO layer A of thermochromic switching effect sufficiently heated to approximately 55 ⁰ C. from red to colorless is visually apparent and is reversible Example 3

On a glass substrate, CdS is vapor-deposited in a first step. In a second step, a thermochromic layer is vapor-deposited analogously as in Example 2, and in a third step, a silicon oxide layer is deposited on the thermochromic layer. These three steps are done by thermal vacuum deposition. As a final fourth step, an Al layer is applied to the silicon oxide layer by electron beam evaporation. Throughout the coating, the recipient remains closed. It is worked oxygen-free. The coating system switches from red to colorless at approx. 55 ° C. The effect is reversible. Optionally, the color circuit can also be created by applying a voltage of 4.8 volts to the transparent electrode.

Example 4

On a polypropylene film, a reflective silver layer is evaporated. Subsequently, the evaporation takes place with a green thermochromic layer consisting of octadecanoic acid amide:

Bis (4-hydroxyphenyl) sulfides: commercial dye Pergascript Green: CTAB = 10: 1.5: 1: 0.08 in analogous conditions as in Example 2. In the second step, the vaporization source is changed and directly over the thermochromic layer, without aerating the recipient Protective layer of SiO vaporized. The green at room temperature is colorless when heated to about 78 ° C. The effect is visually visible and is reversible.

Claims

claims

1. Process for the thermochromic coating of

Substrates in which a substrate and at least one organic thermochromic precursor containing at least one dye, at least one developer and at least one flux is introduced into a vacuum chamber, the precursor is vaporized and deposited on the substrate as a thermochromic complex.

2. The method according to claim 1, characterized in that the deposition takes place by physical or chemical vapor deposition.

3. The method according to claim 1 or 2, characterized in that the deposition by thermal Vakuumbedampfung, electron beam vapor deposition and / or sputtering takes place.

4. The method according to any one of claims 1 to 3, characterized in that the dye is selected from the group consisting of triphenyl nylmethanfarbstoffen, Pyridiniumphenolatbetaine, pyranines, sulfophthaleins, Reichhardt dyes, indicator dyes, azo dyes and mixtures thereof.

5. The method according to any one of claims 1 to 4, characterized in that the developer is selected from the group consisting of esters of gallic acid, hydroxycarboxylic acids, bis-4-hydroxyphenyldrivate and mixtures thereof.

6. The method according to any one of claims 1 to 5, characterized in that the flux is selected from the group consisting of hydroxycarboxylic acids, amines, amides, hydroxy compounds, in particular octadecanol, dodecanol or hexadecanol, paraffins and mixtures thereof.

7. The method according to any one of claims 1 to 6, characterized in that the thermochromic precursor additionally at least one organosilane of the general formula

With

X is independently selected from the group consisting of Cx-Ciε-alkyl, Ci-Ci ₆ alkoxy, aryloxy, hydroxy or halogen, R is independently selected from the group consisting of Ci-Ci ₆ alkyl, _Ci-6 alkoxy Ci .

Amino, cyano, mercapto or Glycidstrukturen contains.

8. The method according to claim 7, characterized in that the organosilane is selected from the group consisting of dimethyldichlorosilane, trimethylchlorosilane, 3-chloropropyltrichlorosilane, 3-cyanopropyltrichlorosilane, diphenylsilanediol, N-docosyltri- chlorosilane, vinyltriethoxysilane, gamma-aminopropyltrichlorosilane, hexamethyldisilazane, triphenylsilanol and mixtures thereof.

9. The method according to any one of claims 1 to 8, characterized in that the precursor of 0.3 to 15 wt .-% of the dye, 0.3 to 18 wt .-% of the developer and 67 to 99.4 wt. Contains% of the flux.

10. The method according to any one of claims 1 to 9, characterized in that the precursor has at least one surface-active substance.

11. The method according to claim 10, characterized in that is used as a surfactant bis (2-ethylhexylsulfosuccinat), hexadecylammonium bromide, sodium dodecyl sulfate and / or anhydrides, in particular maleic anhydride or succinic acid ester.

12. The method according to any one of claims 1 to 11, characterized in that the substrate is selected from the group consisting of glass, ceramics, metals, semiconductors, polymer materials and their composite systems.

13. The method according to claim 12, characterized in that the polymer material is selected from the group consisting of polyethylene, polypropylene, cyclic olefins, polyesters, polycarbonate, poly (meth) acryla- polyamide, acrylonitrile-butadiene-styrene copolymers and their blends.

14. The method according to any one of claims 1 to 13, characterized in that in vacuum a further functional layer is deposited before or after the deposition of the thermochromic layer.

15. The method according to claim 14, characterized in that as functional layers transparent electrodes, electrochromic layers, protective layers or reflective layers are deposited.

16. Thermochromic coated substrate preparable by the method according to any one of the preceding claims.

17. Thermochromic coated substrate according to claim 16, characterized in that the layer has a thickness in the range of 100 to 3000 nm, in particular from 150 to 1000 nm.

18. Thermochromic coated substrate according to claim 16 or 17, characterized in that the thermochromic complex is in the form of connected dimers or an agglomerate.

19. Use of the thermochromic coated substrates according to any one of claims 16 to 18 for the production of electro-optical or photovoltaic modules.