DE102014018464A1 - THERMOCHROMIC PIGMENTS, THERMOCHROME COATING, METHOD FOR THE PRODUCTION THEREOF AND THEIR USE - Google Patents

Abstract

The invention relates to thermochromic pigments selected from one or more of the pigments of the general formula (1) to (6) and a thermochromic coating comprising at least one layer comprising or consisting of one or more of the thermochromic pigment of the formulas (1) (2), (3), (4), (5) and / or (6), and optionally containing a temperature-resistant matrix based on one or more binders or a glass frit. The thermochromic pigments and the thermochromic coatings produced therefrom are characterized by particularly advantageous combinations of properties, whereby they are also suitable for use in household appliances, in particular as temperature indicators.

Description

The invention relates to thermochromic pigments, to a thermochromic coating containing or consisting of thermochromic pigments, to a process for the preparation of thermochromic pigments and to a thermochromic coating, and to the use thereof.

BACKGROUND OF THE PRIOR ART

Thermochromic materials are today used as temperature indicators in many areas. Thermochromic materials are materials that show a change in color when heated. A distinction is made between irreversible thermochromism, ie the color change is retained even after cooling, and reversible thermochromism, in which the materials return to their original color after cooling. Irreversible thermochromic materials are used, for example, to obtain a visual impression of the temperature history of a product. For example, in the DE 10 2010 026 967 A1 describe the use of an irreversibly thermochromic dye in a machine oil to document the temperature history of the engine oil. Reversibly thermochromic inks, for example, are printed on teacups and show a reversible color change when filling the cup with a hot beverage.

The mechanisms behind these color changes are manifold. Depending on the type of mechanism, the color change occurs continuously over a temperature interval or at a defined transition temperature. While thermochromic effects, which are due to the increasing dispersion of electronic states with increasing temperature, do not have a clear turnover temperature, for those based on phase transitions or coordination changes of the chromophore, accurate turnover temperatures or narrow temperature intervals may be indicated. An example of the former is the thermochromism of ZnO or TiO ₂ , which shows a change in color from white to yellow with increasing temperature. As the temperature increases, the band gap decreases due to the thermally induced broadening of valence and conduction band, so that at higher temperatures, the absorption edge is shifted from the UV-A region into the visible spectral range. As a result, portions of the blue spectral region are increasingly absorbed, which in turn causes a yellow body color. Depending on the position of the band gap, this mechanism allows color changes from white (at low temperatures) to yellow to orange, red to black (at higher temperatures).

Also, a continuous change in color with increasing temperature is observed in materials whose color is based on absorption based on electronic transitions within the electron shell of an atom or ion. For example, the dd absorptions of Cr ³⁺ in the ruby (Al ₂ O ₃ : Cr ³⁺ ) are at least partially in the visible spectral range. When the temperature increases, the crystal field splitting and thus the energy gap between the occupied and unoccupied d orbitals decreases; There is a continuous red shift of the absorption bands with increasing temperature.

If, on the other hand, color changes are based on real structural changes, they are assigned a transition temperature. Thus, copper (II) compounds are known which contain the complex anion [CuCl ₄ ] ^2- and show a change in temperature a color change. For bis (diethylammonium) tetrachlorocuprate (II) [(C ₂ H ₅ ) ₂ NH ₂ ] ₂ [CuCl ₄ ] the transition temperature for the color change from green to yellow is 43 ° C, at which temperature the coordination geometry changes in [CuCl ₄ ] ^2- anion of distorted square-planar (T <43 ° C) distorted tetrahedral (T> 43 ° C).

There are a variety of organic thermochromic materials and inorganic thermochromic complexes, but their application is limited to low temperatures. For use at higher temperatures, eg. As in household appliances such as an oven, a stove, a hob, etc., but inorganic thermochromic materials must be provided, which are durable at temperatures of ≥ 200 ° C. In extreme load cases (eg an empty pot with activated hob), these inorganic materials must be resistant even at temperatures of 600 to 700 ° C.

The known inorganic thermochromic materials include, for example, HgI ₂ , Agl, Ag ₂ HgI ₄ , Cu ₂ HgI ₄ and the Ag ₂ HgI ₄ -Cu ₂ HgI ₄ eutectoid containing 43 mol% of Cu ₂ HgI ₄ . CdS and CdSe also show a color change with temperature change. However, these show disadvantages. On the one hand, mercury- and cadmium-containing pigments are undesirable for use in the household appliance sector because of their toxicity, on the other hand, the temperature stability of these iodides, sulfides and selenides in extreme load cases is not given, since this is so-called "softframework crystals ", So materials with a soft or strongly polarizable network. Noble metal halides tend to dissociate under heating to release the elemental halogen, and these materials may be susceptible to hydrolysis. In the concept "Principles of soft and hard acids and bases" (HSAB concept) (s. Holleman-Wiberg: Textbook of Inorganic Chemistry, 101st Edition, Publisher Walter de Gruyter (Berlin, New York, 1995), p. 245 ff. ) cations and anions are then called soft when they are in low charge at the same time large ion radius and with free valence electrons (pairs), such as. B. external d-electrons, and thus are easily polarized. Examples are Cd ^2+, Hg ^2+, Pb ²⁺ and Br ^-, I ^-, S ^2-.

Another known inorganic thermochromic material is the ruby, ie Cr-doped Al ₂ O ₃ . At room temperature, two absorption bands (dd-transitions of Cr ³⁺ with the electron configuration [Ar] 3d ³ ) causing the body color lie in the UV-A and green spectral range, giving the impression of a magenta color. With increasing temperature, the crystal field splitting becomes smaller, which leads to a red shift of the two absorption bands, so that the absorption then lies in the blue and red spectral range, whereby a green color impression is produced. A particular problem with Cr-doped Al ₂ O ₃ (ruby) is that it has a color change from red (cold) to green (hot). The color change behavior of this material is just reversed from that expected by a temperature indicator color change, which is why this material precipitates as an indicator of the hot area.

Another known example of an inorganic material with color change upon temperature change is VO ₂ , which shows a semiconductor-metal transition at temperatures of 65 to 69 ° C, which is accompanied by a change in the optical constant. In the US 2013/0150238 A1 For example, a thermochromic substrate is described which discloses a nanolayer with a thermochromic substance VO ₂ , Ti ₂ O ₃ , NbO ₂ or NiS, preferably VO ₂ , and is to be used as a so-called smart window, ie a window containing infrared radiation Reflected above a certain critical temperature and thus prevents a rise in temperature in the building. The cause of the change in optical properties is a first-order crystallographic phase transition from a monoclinic to a tetragonal crystal structure, as a result of which the absorption properties in the NIR as well as electrical and magnetic properties change to turn a semiconductor into a material with metallic properties. In a nanolayer of VO ₂ (Ti ₂ O ₃ , NbO ₂ , NiS), no true color change is obtained, but an envelope changes from transparent to specular.

Furthermore, the disclosure US 2013/0149441 A1 a nanolayer of VO ₂ (Ti ₂ O ₂ , NbO ₂ ) in a layered structure with non-thermochromic oxides / nitrides. Even with these materials, no real color change is achieved, but an envelope from transparent to specular.

Furthermore, the describes EP 2 610 368 A2 a reflective substrate based on a nano-layer of VO ₂ (Ti ₂ O ₃ , NbO ₂ , NiS) doped with Mo, W, Cr, Ni or Zr in a layered structure with non-thermochromic oxides / nitrides. Again, there is no real color change, but only an envelope from transparent to specular.

The thermochromism of bismuth vanadate (BiVO ₄ ) is also known. BiVO ₄ shows a reversible color change at approx. 255 ° C (s. Bierlein et al., Solid State Comm. 1, 69-70, 1975 ). BiVO ₄ , however, is valued and used mainly as a non-toxic yellow pigment (s. DE 27 27 864 A1 . DE 33 15 850 A1 . DE 41 19 668 A1 ). Furthermore, from the DE 32 21 338 A1 Molybdenum- and tungsten-containing BiVO ₄ pigments known. In the DE 27 27 865 A1 For example, a pigment composition consisting of BiVO ₄ , Al ₂ O ₃ and SiO _{2 is} described. The DE 40 40 849 A1 describes zirconium-containing BiVO ₄ pigments. From the DE 42 00 925 A1 and the EP 0 441 101 A1 Phosphorus-containing BiVO ₄ pigments are known. In particular, the coloristic character of the pigments at room temperature and their chemical resistance are positively influenced by the addition of the dopants to the pure BiVO ₄ . From the DE 19 502 196 A1 Furthermore, coated BiVO ₄ pigments are known. Furthermore, Sun et al. monoclinic BiVO ₄ quantum tubes, which show a color change from yellow to red at 270 ° C (s. Sun et al., Nano Res. 3, 620-631, 2010 ). The influence of a partial substitution of Bi ³⁺ by Ce ⁺ in BiVO ₄ with respect to the color effect was also studied (s. Neves et al., Dyes and Pigments, 59, 181-184, 2003 ). In addition, doped bismuth vanadates according to BiVO ₄ : RE ³⁺ with RE = La, Ce, Ho, Yb, Eu, Sm, Nd, Gd (s. Xu et al., Appl. Surf. Sci., 256, 597-602, 2009 ) or BiVO ₄ : Ln with Ln = Eu, Gd, Er (s. Zhang et al., Chin J. Inorg. Chem., 25, 2040-2047, 2009 ) have been studied for their photocatalytic activity.

Also in connection with heatable surfaces in the household appliance sector, the use of thermochromic materials has become known:
So will in the US 5,499,597 A an optical temperature display with thermochromic semiconductor material according to (Cd _y Zn _(1-y) S _b Se _1-b ) with 0.5 ≤ y ≤ 1.0 and 0.5 ≤ b ≤ 1.0) included in a vitreous enamel , which can be used to warn the user of a hotplate against a hot surface.

In the US 7,304,008 B2 discloses a thermochromic material consisting of a binder and a thermochromic component, wherein the thermochromic component is selected from the group of bismuth-metal mixed oxides, niobates, tantalates, molybdate, tungstates and chromates. In this case, the US patent refers both to bismuth-rich ternary mixed oxides, ie those with a proportion of more than 50 mol% Bi ₂ O ₃ , based on the total oxide content, as well as quaternary or quinary mixed oxides in which the sum of Proportions of Bi ₂ O ₃ and (Nb, Ta) ₂ O ₅ or Bi ₂ O ₃ and (Mo, W) O _{3 is} above 50 mol%. The thermochromic component may be mixed with a thermostable component (eg, CoAl ₂ O ₄ or other Co ²⁺ -containing aluminates or silicates). Furthermore, an article with the thermochromic material will be described. In contrast, the compounds of the invention have no bismuth, molybdenum or tungsten or bismut-, molybdenum or tungsten low, ie, the proportion of Bi ₂ O ₃ , MoO ₃ or WO ₃ is below 50 mol% based on the total oxide composition.

The problem with bismuth-rich oxides is generally that they show a bismuth loss at high temperatures because of the high vapor pressure. In the case of pigment production, cross-contamination easily occurs due to the evaporation of bismuth, which has a particularly disadvantageous effect on cost efficiency, since the bismuth-containing pigments have to be processed separately. The doping of bismutreicher oxides with, for example, sodium can lead to an enhancement of the thermochromic effect. At the same time, however, this leads to a lowering of the melting point, which increases the evaporation problem of bismuth and leads to a reduced temperature stability.

In the JP 2006-104319 A For example, a temperature gauge on a heated body with a thermo-reversible colored layer based on zirconium and praseodymium-containing pigments in a binder will be described. The disadvantage of this document is that the color change for ZrO ₂ : Pr is not clear enough.

In the DE 10 2005 025 896 B4 a hob plate is described which has a different optical transmission at different temperatures and is coated on the upper side with a material having thermochromic properties.

In the WO 2011/086504 A2 a domestic appliance device, in particular cooktop device is described, which contains at least one thermochromic and / or thermoluminescent element having at least one vanadium-containing material, in particular VO ₂ . Taking advantage of the transition from VO ₂ of transparent semiconducting to non-transparent or opaque metallic state with increasing temperature, a method is described here, with the help of electronic components to be protected from heat radiation. The WO document also mentions a temperature indicator function based on the change from transparency at low to opacity at higher temperatures.

The vanadium-containing material, in particular VO ₂ , has no real color change, but rather a transition from transparent to specular.

In the US 8,647,735 A1 describes a heatable article provided with a coating comprising thermochromic pigments such as Bi ₂ O ₃ , Al ₂ O ₃ , V ₂ O ₅ , WO ₃ , CeO ₂ , In ₂ O ₃ , Y _1,28 Ca _{0, 16} Ti _1.84 V _0.16 O _1.84 or BiVO ₄ , which have an oxide shell to make them fat and oil resistant.

In the EP 2 587 166 A2 a cooking device is described with optical temperature display, wherein the thermochromic material is applied to a separate carrier. In the EP 2 587 166 A2 Furthermore, the CHROMAZONE pigment is named as a thermochromic material, which, however, decomposes at temperatures greater than 50 ° C.

So far there are no products on the market that provide suitable properties. The transition point for the display of an elevated temperature for the known materials is usually too high, for example well above 200 ° C, so that these materials are not suitable for the home appliance sector. Furthermore, the materials provided must be approved for the conditions of use. In doing so, the relevant EC directive (RoHS Directive 2011/65 / EU or RoHS 2) must be observed to limit the use of certain hazardous substances in electrical and electronic equipment, which regulates the use of hazardous substances in equipment and components. For example, cadmium or mercury-containing pigments such as these in the EP 0 287 336 A1 , of the US 5,547,283A . US 5,499,597 A and the US 5,772,328 A are not suitable; these materials are not RoHS compliant.

The present invention is therefore based on the object to provide a thermochromic material which overcomes the above-described disadvantages of the prior art. In particular, a material is to be made available, which can also be used in the household appliance sector, to warn the user of the household appliance or other object against hot surfaces, without having to be installed in the household appliance or object for additional electronics or sensors. It should show a clearly perceptible color change with increasing temperature, preferably in the range above 60 ° C, and the color change behavior should not change as far as possible over the service life of the household appliance or the duration of use of the object. Furthermore, the thermochromic material should be inexpensive to produce and processable.

DESCRIPTION OF THE PRESENT INVENTION

The object according to the invention is achieved according to the invention by a thermochromic pigment selected from one of the pigments of the general formula (1) to (6): A ₄ B ₉ X ₂₀ : n% C, (1) where A comprises or represents one or more elements of the group A = Li, Na or
B comprises or represents one or more elements of the group B = Si, Ge, Zr, Sn, Hf
X comprises or represents one or more elements of the group X = O, S, N and
C comprises or represents one or more elements of the group C = Mn (IV), Cr (IV), Mo (VI), Ru (II), Nb (V), Fe (III),
and 0 <n ≤ 10; A ₃ BX ₆ : n% C, (2) wherein A comprises or represents one or more elements of the group A = Mg, Ca, Sr, Ba, Zn,
B comprises or represents one or more elements of the group B = Mo, W
X comprises or represents one or more elements of the group X = O, S, N and
C comprises or represents one or more elements of the group C =Eu, Fe, Mn, Co, Ni, Cu, Ru
and 0 <n ≤ 20; (Bi _1-x A _x ) (V _{1 -y} B _y ) O ₄ , (3) where A comprises or represents one or more elements of the group A = La, Pr, Nd, Er, where 0 <x ≦ 0.2, and
B comprises or represents one or more elements of the group B = P, Mo, W, Nb, Ta, where 0 ≤ y ≤ 0.2; (Bi _1-x A _x ) (V _{1 -y} B _y ) O ₄ , (4) wherein A comprises or represents Ce, where 0 <x ≤ 0.2 and
B comprises or represents one or more elements of the group B = P, Mo, W, Nb, Ta, where 0 <y ≤ 0.2; L _x M _y N _{(2x + 4y) / 3} : n% R, (5) where R = Ce, Pr, Sm, Eu, Tb, Tm, Yb and / or Bi and 0 <n ≤ 50,
wherein L comprises or represents one or more elements of the group L = Mg, Ca, Sr, Ba, with 1 ≤ x ≤ 10 and
M comprises one or more elements of the group M = C, Si, Ge or represents with 1 ≤ y ≤ 10; or L _x M _y O _z N _{(2x + 4y-2z) / 3} : n% R, (6) where R = Ce, Sm, Eu, Tm and / or Yb and 0 <n ≤ 50,
wherein L comprises or represents one or more elements of the group L = Mg, Ca, Sr, Ba, with 1 ≤ x ≤ 10 and
M comprises or represents one or more elements of the group M = C, Si, Ge, where 1 ≦ y ≦ 10 and 0 <z ≦ 10.

A pigment of group (1) is preferably Na ₄ Ge ₉ O ₂₀ : Mn ⁴⁺ (2Na ₂ O.9GeO ₂ doped with Mn ⁴⁺ ). A pigment of group (2) is preferably Sr ₂ MgMoO ₆ : Eu ²⁺ (2SrO.MgO.MoO ₃ doped with Eu ²⁺ ).

The invention also provides a thermochromic coating comprising at least one layer comprising or consisting of one or more of the thermochromic pigments of the formulas (1), (2), (3), (4), (5) and / or (6 ), optionally containing a temperature-resistant matrix, based on one or more binders or a glass frit.

The invention also relates to the use of the thermochromic coating comprising at least one layer, containing or consisting of one or more of the pigments of the general formulas (1) to (6), on a glass and / or glass ceramic substrate as a temperature indicator, preferably Surfaces of (domestic) appliances or objects of all kinds which may become hot or hot, in particular cooking hobs of cookers, hobs, the inside or outside of oven panes, oven windows or fireplace panes, cookware, bakeware, (ceramic) baking trays, and / or heatable plates of irons, curling irons, straighteners and the like.

The thermochromic pigments or the thermochromic coating according to the present invention thus fulfill their purpose to warn the user of a household appliance or object against hot surfaces without having to install additional electronics or sensors in the household appliance.

Hereinafter, the present invention will be explained in detail.

DETAILED DESCRIPTION OF THE INVENTION

THERMOCHROME PIGMENTS

The thermochromic pigments according to the invention are selected from one or more pigments of the general formulas (1) to (6), as indicated above. These pigments show a color change as the temperature increases. This color change is reversible, d. H. the pigments return to their original color after cooling. The thermochromic pigments of the present invention exhibit a distinct and visually discernible color change as the temperature is increased by 50 K or more, starting from room temperature. The color change is reversible and clearly visible, d. H. the materials show a marked shift of color point (according to CIE-Luv color space system of 1976) with temperature change. When the temperature increases, the color change or color change temperature may be different than when cooling, d. H. There may be a hysteresis.

Thus, the thermochromic pigments show a noticeable change in color when the temperature rises from room temperature to temperatures in the range of 60 to 200 ° C, so that color differences can be visually detected from an increase in temperature by 50 K and these can be used as temperature indicators in hot areas. The color change is determined by measuring the temperature-dependent diffuse reflection. To evaluate the color change effect, the color points are shown in a color diagram according to the CIE-Luv color space system (also L * u * v *) of 1976, which offers the advantage of visualizing the color point shift under the premise of comparability, since in the two-dimensional representation the normalized color coordinates u 'and v' have the same color tone differences in accordance with an approximately identical geometric color point distance (s. Poynton, C. Digital Video and HDTV Algorithms and Interfaces, Morgan Kaufmann Publishers, 2007, San Francisco, p. 226ff. ). Another key parameter in assessing the perceivability of color differences is the brightness of a pigment, which is described by the L * value in the CIE-Luv color space system. This produces a three-dimensional color space in which a hue difference ΔE * _uv can be quantified as the Euclidean distance between two points E * _uv (1) and E * _uv (2) and can be calculated as follows:

For the calculation of the color difference, the normalized color coordinates u 'and v' are not used, but derived values u * and v *, which among other things also include the white point and the brightness. E * _uv values of 4 or greater are described as visually perceptible. The particularly good color change effects which are achieved for the pigments according to the invention in comparison with pigments from the prior art are given in the examples.

The pigments of the invention meet the requirements of the above-mentioned EU Directive, ie they are RoHS compliant and generally for use on heated surfaces in (household) appliances suitable. In general, the pigments of the invention do not contain Zr, Cd, Se, Te, Hg, Tl, As, Sb, U, Th.

The thermochromic pigments according to the invention are preferably bismuth-free or bismutarm, vanadium-free or vanadium-poor, tungsten-poor and molybdenum-poor. In the present invention, bismuth, molybdenum or tungsten-free means that, except for unavoidable impurities, there is no bismuth, molybdenum or tungsten in the pigment or pigments of the invention. Bismuth, molybdenum or tungsten arm in the context of the present invention means that the proportion of Bi ₂ O ₃ , MoO ₃ or WO _{3 is} below 50 mol%, based on the total oxide composition.

The thermochromic pigments contain coloring or color-enhancing ionic dopants, eg. As Mn ⁴⁺ , Eu ²⁺ or Ce ³⁺ , whose absorption bands deepen or change the color impression of the undoped host lattice. The energetic position of the absorption bands depends strongly on the metal-anion distances, which in turn are influenced by the temperature. In addition, the thermal dependence of the band gap is observed. Since the vast majority of materials thermally expand, a color shift is observed in the heating.

The use of nitridic and oxinitridischen thermochromic materials according to the general formula (5) and / or (6) is particularly advantageous because they contain with the nitride an softer and thus more easily polarizable anion compared to the Oxidanion according to the already discussed HSAB concept, which in turn results in a stronger dependence of the band gap on the temperature and thus a pronounced thermochromic effect. Owing to the greater polarizability of the nitride anion in comparison to the oxide anion, the thermochromic effect is therefore enhanced in oxinitridic and nitridic compounds.

The thermochromic pigment of the present invention may be blended with one or more further pigments to obtain a blend color and / or enhance the contrast enhancement thermochromic effect in the "right direction" in the color chart. That is, in addition to the thermochromic pigments other, non-thermochromic and thermostable pigments can be added, for. B. CoAl ₂ O ₄ , BaMgAl ₁₀ O ₁₇ : Co ²⁺ or other Co ²⁺ -containing aluminates, borates or silicates.

The thermochromic pigments preferably have an average particle diameter d ₅₀ of 0.1 μm to 100 μm, more preferably 0.5 μm to 5 μm and preferably a maximum particle diameter d _max of <200 μm, more preferably <100 μm, particularly preferably <10 μm , Alternatively, it is also possible to use nanopigments whose dimensions are preferably in one, two or three spatial directions <100 nm, for example nanoparticles, nanowires, nanotubes or nanoplates.

According to a preferred embodiment, the thermochromic pigments according to the general formulas (1), (2), (3), (4), (5) and (6) may additionally be enveloped. The shell may be organic or inorganic. The shell may for example consist of silica, alumina, tin oxide, titanium oxide, aluminum phosphate, aluminum-zinc phosphate, an organopolysiloxane, silicon nitride, silicon carbide and / or aluminum nitride. The thermochromic pigments may also be surrounded by multiple shells. Preferably, the shell is oxidic, nitridic, oxynitridic or consists of an organopolysiloxane. Such an encapsulation increases the temperature and hydrolysis resistance and the resistance of the pigments to oils and greases. The encapsulation of the pigment particles can take place both via wet-chemical (sol-gel methods) and gas-particle conversion methods (plasma, MO or fluidized-bed CVD processes). While the first in an inert solvent aimed at the deposition of layers for the coating of the primary particles (pigment), in the latter reactive gaseous reactants are added to the pigment particles, which react immediately due to their high reactivity under the present reaction conditions and thus produce layered coatings of the pigment particles.

The preparation of the thermochromic pigments can take place by wet-chemical processes or by solid-state reaction. In the case of wet-chemical preparation method, the starting materials are homogeneously mixed in a solvent and then converted by precipitation, complexation, sol-gel process or other processes in a precursor, which then at temperatures above 400 ° C for at least four hours to form the desired crystallographic structure is thermally treated in one or more calcination steps. Likewise, production via solid-state reactions is suitable. For this purpose, the starting materials in the form of oxidic, nitridic or sulfidic compounds, optionally with exclusion of air and moisture, ground and optionally with the addition of sintering aids at temperatures above 400 ° C for at least four hours to form the desired crystallographic structure in one or thermally treated several calcination steps. Both at the wet chemical and at The solid state methods, the thermal treatment in oxidizing (air, oxygen), inert (nitrogen, argon, other noble gases) or in reducing (carbon monoxide, forming (N ₂ / H ₂ ), hydrogen, ammonia, other reducing agents) atmosphere, wherein Different atmospheres can be used in several calcining steps.

THERMOCHROME COATING

The thermochromic coating according to the invention comprises at least one layer comprising or consisting of one or more of the thermochromic pigments according to the invention of the formulas (1), (2), (3), (4), (5) and / or (6). The thermochromic coating may be composed of one or more layers.

According to one embodiment of the present invention, the thermochromic coating may comprise or consist of only one layer containing or consisting of the pigments of the invention. The thermochromic coating can be applied directly to a glass and / or glass ceramic substrate, which is generally preferred. According to a preferred embodiment, the pigments may be present in the thermochromic coating in a temperature-resistant matrix.

Preferably, the temperature-resistant matrix is selected from one or more binders or a glass frit, in which the pigment (s) are incorporated and then applied to the glass and / or glass-ceramic substrate together with the matrix, preferably directly.

The coating according to the invention is characterized by the presence of the pigments for the thermochromic coating, in particular for the reversibly thermochromic coating.

The coating of the present invention meets the requirements for the performance characteristics of a thermochromic temperature indicator, which is preferably used in the context of special glasses / glass ceramics; For example, the thermochromic coating is suitable for cooking surfaces. The coating fulfills the required conditions for this: The coating has a temperature resistance greater than 400 ° C. The thermochromic coating has a high thermal resistance, i. H. the necessary durability of 400 ° C for 100 h, for a short time even 500 ° C can be tolerated. There is no color point change at room temperature and no change in color change behavior with a temperature change. In addition, when using a heatable surface, especially in household appliances, loads of water vapor occur, which can be highly corrosive. It has further been found that the coating according to the invention is resistant to hot steam and also to oil filtration for at least 1 hour, ie. H. the coating exhibits condensation resistance in contact with wet media. The required high mechanical resistance (scratch resistance above 500 g in the skierometer test) and chemical resistance, in particular against oil and water vapor, are also present.

It is understood that if more than one layer is present in the coating of the present invention, all layers should have the appropriate properties for the intended use.

Preferably, the thermochromic coating, comprising or consisting of at least one layer consisting of or containing the thermochromic pigments according to the invention, fully or partially applied to a hob, an oven disc, a furnace window or a chimney panel. The thermochromic coating fulfills the purpose of warning the user of the (household) device or object against hot surfaces, without having to install additional electronics or sensors for this purpose. The temperature indicator therefore represents an electrically self-contained temperature display device.

The thermochromic coating is preferably applied directly to the heatable or hot-going surface, without interlayer or intermediate layer. In other embodiments, also intermediate layers or intermediate layers are possible.

It has been found according to the invention that the thermochromic coating has an excellent durability, not only in terms of durability and durability, but also their color change behavior does not change over 10 years, d. H. no human-perceivable color point change was observed at room temperature or elevated temperature.

The properties of the thermochromic pigments and thus also of the thermochromic coating can be improved in part if the thermochromic pigments are surrounded by an inorganic or organic shell, as already explained in detail. The thermochromic coating may therefore contain the thermochromic pigments encapsulated or unencapsulated.

The mass fraction of the thermochromic pigment or pigments in the cured or baked ink / layer is 0.5 to 50 wt .-%, preferably 2 to 40 wt .-% and particularly preferably 10 to 30 wt .-%.

In addition to the thermochromic pigments, one or more further thermostable pigments can be incorporated into the matrix to obtain a mixed color and / or enhance the thermochromic effect by increasing the contrast. By incorporating these thermostable pigments in a temperature and chemical resistant matrix, the color impression of the temperature display is optimized.

If further additives are contained in the matrix, they are temperature-stable and have no adverse effect on the thermochromic coating or the thermochromic pigments.

MATRIX

The temperature-resistant matrix according to the invention is preferably selected from one or more binders or a glass frit. The matrix is preferably transparent with a transmission of the light in the visible range of more than 75% with a layer thickness of the matrix of 1 mm. The matrix is colorless according to the invention or may be colored. A colorless matrix ensures that a maximum color impression is obtained by the thermochromic or the pigments. A dyed matrix, together with the color through the thermochromic or the pigments, leads to a mixed color and a desired overall color impression. By selecting the matrix, it is therefore possible to optimize the color impression.

For the production of a thermochromic coating according to the invention on a glass or glass-ceramic substrate, the thermochromic / n pigments and optionally additives are distributed in a liquid or pasty matrix-forming material or a matrix precursor and applied to the substrate in one or more coating steps.

The matrix gives the thermochromic coating thereby an optimal adhesion and a high scratch resistance on the substrate and meets the performance characteristics in terms of thermal, mechanical and chemical resistance. The scratch resistance, determined by means of a sclerometer test, preferably gives layers with a scratch resistance> 500 g, particularly preferably> 700 g.

Examination of the resistance of the thermochromic coating to hot steam by exposing the coating to hot steam for at least one hour shows that the thermochromic coating also meets this criterion.

The provision of a matrix is particularly advantageous since the matrix additionally protects the thermochromic pigments from degradation (protection against oxygen, sulfur, H ₂ O, acid attack, oil, grease) or corrosion. As a result, the long-term stability of the color-changing effect of the coated substrate is additionally improved and ensured.

As matrix material, for example, one or more binders are used, preferably one or more polymers. In particular, UV or thermally curable polymers can be used, such as polyacrylate, polymethacrylate, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetals, polyvinylpyrrolidone, polystyrene, polyolefins, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, perfluorinated polymers such as polytetrafluoroethylene, polyurethanes such as silicone-modified polyurethanes, polyesters , Epoxy resins, methacrylate resins, polyimides, polyamides, polycarbonate, cycloolefin copolymers, polyethersulfone and mixtures of these,
Polysiloxanes, such as, for example, methylpolysiloxane, phenylpolysiloxanes, methyl / phenylpolysiloxanes, acrylate-modified, polyester-modified, polyurethane-modified, epoxy-modified or nanoparticle-functionalized polysiloxanes and / or silicones, silicone resins, polyester-modified, polyether-modified or epoxide-functionalized silicone resins, silazanes, silicans, and / or
Sol-gel materials, preferably UV or thermally organically crosslinkable hybrid polymer sol-gel materials, hybrid polymer sol-gel materials, nanoparticle-functionalized sol-gel materials, sol-gel materials with nanoparticulate fillers, inorganic sol-gel materials. These are nanoparticulate Fillers contain additives that are not incorporated into the sol-gel network, whereas nanoparticles in nanoparticle-functionalized sol-gel materials are reactively incorporated into the matrix network.

The sol-gel starting materials used are preferably metal alcoholates, preferably alkoxysilanes, for example TEOS: tetraethoxysilane, aluminum alkoxides, titanium alcoholates, zirconium alcoholates and / or organometalic alcoholates. Preference is given to a tetraalkoxysilane Si (OR ¹ ) ₄ (with R ¹ = methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, phenyl) or an aluminum alcoholate or a titanium alkoxide or a zirconium alcoholate in combination with an alkoxysilane Si (OR ¹ ) ₃ R ² (R ² = glycidoxy, methacryloxy, acrylic, vinyl, allyl, amino, mercapto, isocyanato, epoxy, ...), which has an organically crosslinkable functionality used. Organic linkable alkoxysilanes may be, for example: GPTES: glycidoxypropyltriethoxysilane, MPTES: Methacryloxypropyltriethoxysilane, GPTMS: Glycidyloxypropyltrimethoxysilane, MPTMS: methacryloxypropyltrimethoxysilane, VTES: vinyltriethoxysilane, ATES: allyltriethoxysilane, APTES: aminopropyltriethoxysilane, MPTES: mercaptopropyl, ICPTES: 3-isocyanatopropyltriethoxysilane. Optionally, a further metal alcoholate is used, for example Zr (OR ¹ ) ₄ , Ti (OR ¹ ) ₄ , Al (OR ¹ ) ₃ , such as zirconium tetrapropylate, titanium tetraethylate, alumimium sec-butoxide. Optionally, a further organoalkoxysilane is used, for example Si (OR ¹ ) ₃ R ³ , Si (OR ¹ ) ₂ R ³ ₂ , Si (OR ¹ ) R ³ ₃ , (where R ¹ = methyl, ethyl, propyl, butyl, butyl, R ³ : methyl, phenyl, ethyl, iso-propyl, butyl, sec-butyl), for example MTEOS: methyltriethoxysilane, PhTEOS: phenyltriethoxysilane, DEMDEOS: dimethyldiethoxysilane, mercaptosilane, APTES aminosilanes.

The preparation of the (sol-gel) hydrolyzate is carried out by the specific reaction of the monomers with H ₂ O. This is preferably carried out in the presence of an acid, for example HCl, H ₂ SO ₄ , p-toluenesulfonic acid, acetic acid. The aqueous hydrolysis solution preferably has a pH <4. In a particular embodiment, the hydrolysis can also be carried out in an alkaline environment (eg NH ₃ , NaOH). In a further specific embodiment, the hydrolysis is carried out with an aqueous nanoparticle dispersion. The degree of crosslinking of the hydrolyzate is adjusted via the ratio of H ₂ O to hydrolyzable monomers. The degree of crosslinking is preferably 5-50%, preferably 11-40%, most preferably 15-35%. The degree of crosslinking is determined by ²⁹ Si NMR spectroscopy. The viscosity of the hydrolyzate is 5-30 mPas, preferably 9-25 mPas. The residual solvent content is preferably <10% by weight.

The coating solution may include UV-activatable or thermal initiators for cationic or free-radical polymerization such as triarylsulphonium salts, diaryliodinium salts (e.g., Irgacure 250), ferrocenium salts, benzoin derivatives, alpha-hydroxyalkylphenones (e.g., Irgacure 184), alpha-aminoacetophenones (e.g. 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropanone), acylphosphine oxides (e.g., Irgacure 819) or 1,5-diazabicyclo [4.3.0] non-5-ene (DBN) become.

To improve screen printability, dispersibility, avoidance of defects and Bernardian cells, auxiliary and anodic substances, defoamers, deaerators, levelers, wetting and dispersing additives, lubricants, leveling agents and substrate wetting additives may be added to the coating solution.

Depending on the coating process, it is also possible to add various leveling agents, defoamers, deaerators or dispersing additives such as, for example, PEG, BYK 302, BYK 306, BYK 307, DC11, DC57 or Airex 931 or Airex 930 in order to achieve homogeneous layer thicknesses and a homogeneous distribution of the additives in to achieve the coating.

For example, methanol, ethanol, isopropanol, ethoxynonafluorobutane or else high-boiling solvents having a low vapor pressure of <5 bar, preferably <1 bar, particularly preferably <0.1 bar, can be used as the solvent. Solvents which have a boiling point of more than 120 ° C. and an evaporation number of> 10 are preferably added. Preferably, a solvent having a boiling point above 150 ° C and an evaporation number of> 500, more preferably having a boiling point above 200 ° C and an evaporation rate of> 1000 is used. Such high-boiling solvents are in particular glycols and glycol ethers, terpenes and polyols, as well as mixtures of several of these solvents. It may be butyl acetate, methoxybutyl acetate, butyl diglycol, butyl diglycol acetate, butyl glycol, butyl glycol acetate, cyclohexanone, diacetone alcohol, diethylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, propylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monoethyl ether, ethoxypropyl acetate, hexanol, methoxypropyl acetate, 1,3-diethoxy-2-propanol, 1,5- Pentanediol, 1-methoxy-2-propanol, 2- (2-butoxyethoxy) ethyl acetate (carbitol acetate), 2-butoxyethyl acetate, 4-hydroxy-4-methyl-2-pentanone, ethyl acetoacetate, butyl carbitol acetate F4789, N, N-dimethylacetamide, polyethylene glycol 200, propylene carbonate, monoethylene glycol, ethylpyrrolidone, methylpyrrolidone, dipropylene glycol dimethyl ether, propylene glycol, propylene glycol monomethyl ether, mixtures of paraffinic and naphthenic hydrocarbons, aromatic hydrocarbon mixtures, mixtures of alkylated aromatic Hydrocarbons and mixtures of n-, i- and cyclo-aliphatic be used as solvent. In particular, polyethylene glycol ethers such as diethylene glycol monoethyl ether, tripropylene glycol monomethyl ether and terpineol may be used as the solvent. Furthermore, mixtures of two or more of these solvents can be used. In this case, the solvents can be added both to the matrix precursor and to the additives.

The matrix may additionally contain nanoparticles of oxidic materials such as TiO ₂ (anatase and / or rutile), ZrO ₂ (amorphous monoclinic and / or tetragonal phase), Ca or Y ₂ O ₃ doped ZrO ₂ , MgO doped ZrO ₂ , CeO ₂ , Gd ₂ O ₃ doped CeO ₂ , Y doped ZrO ₂ , SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ (alpha, gamma or amorphous form), SnO ₂ , ZnO, Bi ₂ O ₃ , Li ₂ O, K ₂ O, SrO, NaO, CaO, BaO, La ₂ O ₃ and / or HfO ₂ , boehmite, andalusite, mullite and their mixed oxides. The matrix may preferably contain SiO ₂ -containing nanoparticles.

Non-nanoscale fillers may also be added to the matrix; these may be, in particular: SiO _x particles, alumina particles, pyrogenic silicas, soda-lime, alkali aluminosilicate or borosilicate glass spheres, glass hollow spheres.

The matrix material can be based on glass frits or glass flows. The glass frit is a fine-grained glass, which was obtained by melting a mixture of raw materials and subsequent grinding (for example, grain sizes ≤ 20 microns).

The resulting glass frit is optionally mixed with additives. The glass frit can be added to pigments, pigment mixtures, fillers and structuring particles. The pigments used are preferably metal oxides, which in particular can produce black, gray, white, blue, green, yellow, orange, red, pink and brown colors. These may be, in particular: cobalt oxides / spinels, cobalt-aluminum spinels, Co-Al-Zn oxides, Co-Al-Si oxides, cobalt-titanium spinels, cobalt-chromium spinels, cobalt-aluminum spinels. Cr oxides, cobalt nickel manganese iron chromium oxides / spinels, cobalt nickel zinc titanium aluminum oxides / spinels, iron oxides, iron chromium oxides, iron chromium tin Titanium oxide, copper-chromium spinels, nickel-chromium-antimony-titanium oxides, titanium oxides, zirconium-silicon-iron oxides / spinel, etc. Suitable pigments are also all conceivable absorption pigments, in particular platelet or rod-shaped pigments. It is also possible to use coated effect pigments.

The powder thus obtained is then admixed, for example, with a dispersant adapted to the application process and applied to the substrate by means of a suitable process. In order to ensure optimal processability, depending on the coating method, various auxiliaries, dispersants, additives, solvents, thixotropic agents, etc. may be added. Subsequently, the baking process takes place, wherein the glass frit softens and the additives are embedded and fixed on the carrier substrate.

As a glass frit, the following types of glass are preferably used, for. B. alkali-free and alkaline glasses, silicate glasses, borosilicate glasses, zinc borate glasses, zinc phosphate glasses, bismuth borate glasses, phosphate glasses, lithium aluminum silicate glasses, aluminosilicate glasses.

Table 1 below shows particularly preferred compositions of glass frits which can be used as matrix materials for the production of a thermochromic coating according to the invention, preferably on a glass-ceramic substrate. Table 1: Compositions of glass frits in wt .-% as matrix materials for use on a glass ceramic substrate Wt .-% Glass A Glass B Glass C Glass D Glass E Glass F SiO ₂ 44-57 53-63 57-62 47-52 40-50 63-73 Al ₂ O ₃ 5-25 15-25 5-8 2-6 9-15 0-7 B ₂ O ₃ 0-27 15-22 18-23 17-21 10-15 12-29 Li ₂ O 0-10 2-7 2-6 3-5 0-4 0-6 Na ₂ O 0-10 0-1 0-1 1-5 1-4 0-8 K ₂ O 0-10 0-1 0-4 5-10 0-3 0-8 CaO 0-4 1-4 1-2 0-2 0-3 0-5 MgO 0-3 1-4 0-2 0-1 0-3 0.1-5 BaO 0-4 0-1 0-2 0-2 16-24 0-5 SrO 0-4 1-4 0.5-2 0-1 0-2 0-4 ZnO 0-15 1-4 0-2 0-3 8-15 0-15 TiO ₂ 0-3 0-1 0-2 0-2 0-3 0-5 ZrO ₂ 0-7 1-4 2-5 0-2 0-4 0-5 As ₂ O ₃ 0-1 0-1 0-1 0-1 0-1 0-1 Sb ₂ O ₃ 0-15 0-1 0-1 0-1 0-15 0-1 F 0-3 0-1 0-1 0-1 0-1 0-1 H ₂ O 0-5 0-3 0-3 0-3 0-3 0-3

In particular for use on glass substrates, the compositions listed in Table 2 below are preferred. Table 2: Composition of glass frits in% by weight as matrix materials for use on a glass substrate Wt .-% Glass G Glass H Glass I Glass J Glass K SiO ₂ 25-55 35-65 30-54 6-20 6-15 Al ₂ O ₃ 3-18 - 0 to 17.5 0-5 - B ₂ O ₃ 5-25 - 13-28 20-38 20-28 Li ₂ O 0-12 0-6 3-6 - - Na ₂ O 3-18 0-6 4-10 - - K ₂ O 3-18 0-6 0-2 - - CaO 3-17 0-12 0-6 - - MgO 0-10 0-12 0-4 - - BaO 0-12 0-38 - - - SrO - 0-16 0-4 - - ZnO - 17.5 to 38 3-13 35-70 58-70 TiO ₂ 0-5 - 0-2 0-5 - ZrO ₂ 0-3 - 0-2 0-5 - Bi ₂ O ₃ - - - 0-20 - CoO - - - 0-5 - Fe ₂ O ₃ - - - 0-5 - MnO - - - 0-10 0.5-1 CeO ₂ - - - - 0-3 F - - 0-3.3 0-6 -

PREPARATION OF COATING

As (coating) method for applying the matrix material with the thermochromic pigments dispersed therein, printing methods, in particular screen printing, doctoring, off-set printing, inkjet or pad printing, as well as spraying, roll coating and spin coating are preferably used. It can therefore be used according to the invention, a cost-effective method, with which the thermochromic coating is applied.

Preferably, the thermochromic coating is cured. The curing of the thermochromic coating can be carried out by UV irradiation or thermally. A thermal curing is preferably carried out in the temperature range of 150-500 ° C for 10 min to 3 h.

According to a preferred embodiment of the invention, a coating solution in the form of a screen printing ink is used for producing a thermochromic coating according to the invention on a substrate, consisting of a matrix-forming material and thermochromic pigments of the formulas (1), (2), (3), (4), (5) and / or (6), optionally further thermochromic or thermostable pigments and further additives, wherein the additives are preferably selected from dispersants, surface reactants (surfactants), solvents, thickeners, flow control agents, deaerators, defoamers, crosslinkers, hardeners, Starters, corrosion inhibitors, adhesion promoters and the like.

The thermochromic coating preferably has a thickness of 10 nm to 500 .mu.m, preferably 20 nm to 100 .mu.m, more preferably from 50 nm to 10 .mu.m.

The thermochromic coating can be applied partially or completely. The thermochromic coating may also be structured (for example, provided with structures in the nm, μm, mm or cm range) in one or more partial areas or even over the entire surface. For example, the cooking zones of a hob can be highlighted by circular structures.

In a preferred embodiment, the substrate is additionally provided with one or more additional coatings which serve decorative and / or functional purposes, and may or may not be pigmented. These coatings may be located on the same side of the substrate as the thermochromic coating or on the opposite side of the substrate. The further coatings may be applied over part of the area or over the entire surface and may also be structured. These coatings can be applied next to one another and / or also above one another.

Substrate

As the substrate for the thermochromic coating according to the invention, glasses are preferably so-called special glasses, and / or glass ceramics are used. The substrate is preferably transparent and may also be colored, by which is meant any kind of dyeing. In certain embodiments, the substrate may be translucent or opaque.

The shape and size of the substrate are initially not limited: preferred are plate-shaped or disc-shaped substrates or also forms suitable for cooking and / or baking. The substrate may be part of a device or article or form the article.

Preferred glass ceramics are, in particular, transparent-colored lithium aluminosilicate (LAS) glass ceramics, transparent LAS glass ceramics or magnesium aluminosilicate glass ceramics or lithium disilicate glass ceramics. Preferred glasses are silicate glasses, for example borosilicate glasses, zinc borosilicate glasses, boroaluminosilicate glasses, aluminosilicate glasses, alkali-free glasses, soda-lime glasses, or laminates composed of several of the materials indicated above.

Is preferred as the substrate, a thermal shock resistant glass or a glass ceramic, preferably with a thermal expansion coefficient of less than 5.0 10 ^-6 / K, preferably less than 4.0 10 ^-6 / K, particularly preferably less than 3.4 10 ^-6 / K. A borosilicate glass or a lithium aluminum silicate glass ceramic with high quartz mixed crystal phase or keatite is preferably used. The crystal phase content is preferably between 60-85%.

In a particular embodiment, a preloaded substrate is used, particularly preferred are boroalumosilicate glasses (eg SCHOTT Xensation ^™ , Corning Gorilla ^™ I-III, Asahi Dragontrail ^™ ). The bias voltage can be obtained chemically or thermally.

The substrate may be rigid or flexible, bent or deformed. The substrate may have surface structures such as elevations and / or depressions.

Preferred thicknesses of the substrate are in the range of 10 .mu.m to 6 cm, more preferably 30 .mu.m to 2 cm, most preferably 50 .mu.m to 6 mm, particularly preferably 1 mm to 6 mm.

It can be used both sides smooth or one-sided knopped substrates.

For transparent substrates, the substrate transmission is selected at 4 mm substrate thickness and wavelengths greater than 450 nm in the visible range, preferably greater than 80%, more preferably greater than 90%. The thermochromic coating according to the invention can be applied to the top side and / or the underside of a transparent substrate.

For substrates, for example consisting of transparent colored glass ceramic, the light transmission of the substrate in the visible (light transmission according to ISO 9050: 2003 , 380-780 nm) at a substrate thickness of 4 mm at 0.8-10%. Preferably, the thermochromic coating according to the invention is applied only on the upper side of a transparent colored glass ceramic.

USE

The invention also relates to the use of the thermochromic coating comprising at least one layer comprising or consisting of the thermochromic pigments of the general formulas (1), (2), (3), (4), (5) and / or ( 6) on a glass or glass-ceramic substrate as a temperature indicator, preferably on surfaces of (household) appliances or items that can be heated or heated, in particular stoves of cookers, hobs, the inside or outside of oven panes, oven windows or fireplace viewing panes, cookware , Baking molds, (ceramic) baking trays, and / or heatable plates of irons, curling irons, straighteners and the like.

The present on the substrate thermochromic coating serves as a temperature indicator for either heated surfaces, eg. As a cooking surface, or for hot-expectant surfaces, eg. B. a fireplace cover. Depending on the application, the substrate can be provided on the top or outside and / or the bottom or inside with a thermochromic coating. A transparent colored glass ceramic is preferably provided on the upper side with a thermochromic coating.

The advantages of the present invention are extremely complex:
According to the invention, thermochromic pigments of the general formulas (1) to (6) are provided which can serve as reversible temperature indicators. The thermochromic pigments of the present invention exhibit a noticeable color change upon increasing the temperature from 60 ° C to 200 ° C and are suitable for use on heated or hot surfaces in (household) appliances or objects of all kinds.

Thermochromic coatings comprising the thermochromic pigments, optionally together with a temperature-stable matrix, can be applied directly to a substrate, for example of glass and / or glass ceramic. The matrix is for example selected from a temperature-stable, preferably transparent material, in particular one or more polymers, sol-gel materials or glass frits.

The thermochromic coating has a high thermal, mechanical and chemical resistance, which is reflected in particular in a high durability. The properties of the thermochromic pigments and thus also of the thermochromic coating can be partially improved if the thermochromic pigments are surrounded by an inorganic or organic shell, i. H. be encapsulated.

In addition to the thermochromic pigments, another thermostable pigment may be present in the matrix to obtain a mixed color and / or enhance the thermochromic effect by increasing the contrast.

In contrast to organic materials which do not have sufficient temperature resistance in applications in the hot region, for example a cooktop, the inorganic thermochromic materials according to the invention exhibit a significantly increased temperature resistance.

Also known inorganic complexes can not achieve the properties of the thermochromic pigments of the invention. Thus, they often have organic ligands, which results in a much larger distance between cation and ligand than in crystalline solids. This leads to a significantly reduced bond strength between cation and ligand, whereby the stability and, in turn, the temperature resistance of inorganic complexes for applications at elevated temperatures is insufficient. More stable inorganic complexes can be used, for example, with ruthenium or iridium Metal cation can be synthesized. However, both these metals themselves and the preparation of complexes with these cations are extremely expensive. In contrast, the thermochromic pigments according to the invention have the required temperature stability. Furthermore, they consist of significantly cheaper basic materials and can be produced by inexpensive methods.

The thermochromic coating of the invention can indicate the change in temperature autonomously by direct application to a heatable or hot-going surface, d. H. without having to install additional electronics (eg LEDs) or sensors (eg temperature sensors).

The invention will be further illustrated by means of drawings which are not intended to limit the present invention.

The 1a to 8a show reflection spectra, where the diffuse reflection (in%) against the wavelength (in nm) is plotted, and the 1b to 8b calculated color points at different temperatures of thermochromic pigments according to the invention. The figures are explained in detail in the following embodiments.

The present invention will be described below with reference to embodiments which are not intended to limit the present invention.

EMBODIMENTS

EMBODIMENT 1

For the synthesis of Na ₄ (Ge _0.99 Mn _0.01 ) ₉ O ₂₀ , 2.1198 g (20 mmol) of Na ₂ CO ₃ , 9.3233 g (89.100 mmol) of GeO ₂ and 0.1611 g (0.900 mmol) MnC ₂ O ₄ • 2H ₂ O triturated with addition of acetone. The powder was dried and calcined at 600 ° C for 2 hours. The resulting powder was mixed with 5 wt% NaF, resorbed and heated at 800 ° C for 4 hours. The pigment shows a color change from orange to a bluish red with temperature increase. The color change is clearly noticeable from a temperature of 75 ° C.

1a shows the diffuse reflection measured against BaSO ₄ and 1b the calculated color points at different temperatures. The reflection spectra and the color points of Na ₄ Ge ₉ O ₂₀ : Mn show a redshift with increasing temperature.

EMBODIMENT 2

For the synthesis of (Sr _0.95 Eu _0.05 ) ₂ MgMoO ₆ , 2.8049 g (19.000 mmol) SrCO ₃ , 1.4835 g (10.000 mmol) MgC ₂ O ₄ · 2H ₂ O, 1.4394 g (10,000 mmol) MoO ₃ and 0.1760 g (0.500 mmol) Eu ₂ O _{3 were} triturated with the addition of acetone. The powder was dried and heated in air at 1300 ° C for 8 hours. The pigment shows a color change from blue to green with temperature increase. The color change is clearly noticeable from a temperature of 100 ° C.

2a shows the diffuse reflection measured against BaSO ₄ and 2 B the calculated color points at different temperatures. The reflection spectra and color points of Sr ₂ MgMoO ₆ : Eu show a green shift with increasing temperature.

EMBODIMENT 3

For the synthesis of (Bi _0.96 Nd _0.04 ) VO ₄ , 6.70981 g (14.4 mmol) of Bi ₂ O ₃ , 0.20189 g (0.6 mmol) of Nd ₂ O ₃ and 2.7282 were obtained g (15 mmol) V ₂ O ₅ triturated with the addition of acetone. The powder was dried and heated in air at 500 ° C for 24 hours. The pigment shows a color change from orange to red with temperature increase. The color change is clearly noticeable from a temperature of 75 ° C.

3a shows the diffuse reflection measured against BaSO ₄ and 3b the calculated color points at different temperatures. The reflection spectra and color points of BiVO ₄ : Nd show a significant red shift with increasing temperature.

EMBODIMENT 4

For the synthesis of (Bi _0.96 Er _0.04 ) (V _0.9 Mo _0.1 ) O ₄ , 6.70981 g (14.4 mmol) Bi ₂ O ₃ , 0.222951 g (0.6 mmol) of Er ₂ O ₃ , 2.45538 g (13.5 mmol) of V ₂ O ₅ and 0.43181 g (3 mmol) of MoO ₃ with the addition of acetone. The powder was dried and heated in air at 500 ° C for 24 hours. The pigment shows a color change from orange to red with temperature increase. The color change is clearly noticeable from a temperature of 75 ° C.

4a shows the diffuse reflection measured against BaSO ₄ and 4b the calculated color points at different temperatures. The reflection spectra and color points of Bi (V, Mo) O ₄ : show a clear redshift with increasing temperature.

EMBODIMENT 5

For the synthesis of (Bi _0.95 Er _0.05 ) VO ₄ , 6.63992 g (14.25 mmol) Bi ₂ O ₃ , 0.28689 g (0.75 mmol) Er ₂ O ₃ and 2.7282 were obtained g (15 mmol) V ₂ O ₅ triturated with the addition of acetone. The powder was dried, heated for 8 hours at 600 ° C in air, triturated again in a mortar and heated for 8 hours at 650 ° C in air. The pigment shows a color change from orange to a bluish red with temperature increase. The color change is clearly noticeable from a temperature of 75 ° C.

5a shows the diffuse reflection measured against BaSO ₄ and 5b the calculated color points at different temperatures. The reflection spectra and color points of BiVO ₄ : It shows a clear color point shift with increasing temperature.

EMBODIMENT 6

For the synthesis of (Bi _0.975 Er _0.025 ) VO ₄ , 6.81465 g (14.625 mmol) of Bi ₂ O ₃ , 0.144344 g (0.375 mmol) of Er ₂ O ₃ and 2.7282 g (15 mmol) of V ₂ O were added ₅ triturated with the addition of acetone. The powder was dried and heated in air at 500 ° C for 24 hours. The pigment shows a color change from orange to a bluish red with temperature increase. The color change is clearly noticeable from a temperature of 75 ° C.

6a shows the diffuse reflection measured against BaSO ₄ and 16b the calculated color points at different temperatures. The reflection spectra and color points of BiVO ₄ : It shows a clear color point shift with increasing temperature.

EMBODIMENT 7

For the synthesis of (Bi _0.995 Ce _0.005 ) (V _0.9 P _0.1 ) O ₄ , 6.9544 g (14.925 mmol) Bi ₂ O ₃ , 0.02582 g (0.15 mmol) CeO ₂ , 2 , 45538 g (13.5 mmol) of V ₂ O ₅ and 0.34508 g (3 mmol) of NH ₄ H ₂ PO _{4 are} triturated with the addition of acetone. The powder was dried, heated in air at 550 ° C for 24 hours, triturated in a mortar and heated in air at 600 ° C for 12 hours. The pigment shows a color change from orange to red with temperature increase. The color change is clearly noticeable from a temperature of 75 ° C.

7a shows the diffuse reflection measured against BaSO ₄ and 7b the calculated color points at different temperatures. The reflection spectra and color points of Bi (V, P) O ₄ : Ce show a significant red shift with increasing temperature.

EMBODIMENT 8

For the synthesis of (Bi _0.96 Ce _0.04 ) (V _0.9 P _0.1 ) O ₄ , 6.70981 g (14.4 mmol) of Bi ₂ O ₃ , 0.222951 g (0.6 mmol) of Er ₂ O ₃ , 2.45538 g (13.5 mmol) of V ₂ O ₅ and 0.34508 g (3 mmol) of NH ₄ H ₂ PO _{4 are} triturated with the addition of acetone. The powder was dried, heated in air at 550 ° C for 24 hours, triturated in a mortar and heated in air at 600 ° C for 12 hours. The pigment shows a color change from orange to red with temperature increase. The color change is clearly noticeable from a temperature of 75 ° C.

8a shows the diffuse reflection measured against BaSO ₄ and 8b the calculated color points at different temperatures. The reflection spectra and color points of Bi (V, P) O ₄ : show a significant red shift with increasing temperature

EMBODIMENT 9

To prepare a thermochromic coating based on pigments according to embodiment 4, 9 g of binder based on glycidoxypropyltriethoxysilane and tetraethoxysilane in a ratio of 4: 1.18.43 g of SiO ₂ nanoparticles and 8.25 g of diethylene glycol monoethyl ether with 14.46 g of thermochromic pigment mixed. After addition of a UV initiator thermochromic layers were printed with a 140 sieve and dried for 1 h at 400 ° C. The thermochromic layers showed a reversible color change from yellow to orange, which is clearly perceptible at a temperature change of 50 K.

EMBODIMENT 10

The color tone differences were calculated for the pigments according to the invention according to the embodiments 1 to 9 compared to a pigment from the prior art. ΔE * _uv values of 4 or greater are visually noticeable. The particularly good color change effects which are achieved for the pigments according to the invention in comparison to a pigment of the prior art are summarized in the following Table 3: TABLE 3 Quantification of the color difference ΔE * _uv of pigments according to the invention composition ΔE * _uv at a temperature increase of 300 K embodiment 350K 400K State of the art BiVO ₄ 4.6676 11.88162 - Inventive pigments Na ₄ Ge ₉ O ₂₀ : Mn 6.48881 9.65905 1 Sr ₂ MgMoO ₆ : Eu 3.9589 9.75209 2 Bi (V, P) O ₄ : Ce 4.23938 9.34906 7 BiVO ₄ : Nd 4.69288 9.31209 3 Bi (V, P) O ₄ : He 3.33894 8.86926 8th BiVO ₄ : He (1) 6.06689 12.32382 5 BiVO ₄ : He (2) 4.01746 12.1018 6 Bi (V, Mo) O ₄ : He 5.13077 12.30758 4

As shown in Table 3, the pigments of the present invention have Na ₄ G ₉ O ₂₀ : Mn, BiVO ₄ : Nd, BiVO ₄ : Er, and Bi (V, Mo) O ₄ : Er as the temperature increases from 300 to 350K higher color point difference ΔE * _uv than the indicated pigment of the prior art. The Er-doped samples also achieve a greater color change than the prior art pigment as the temperature is increased to 400K. The reason for the enhancement of the thermochromic effect by doping with rare earths such as neodymium compared to undoped BiVO ₄ is the additional absorption in the orange-red spectral range. Furthermore, a marked influence of the co-doping with molybdenum or phosphorus on the direction of the color shift becomes clear (see color point diagrams in the embodiments 5 and 6 in comparison with FIG. 4).

The inventive pigment Sr ₂ MgMoO ₆ : Eu shows a color change from blue to green with increasing temperature, which can be perceived very well due to the high sensitivity of the eyes. However, since this pigment has only very low brightness values, the quantification of color differences with the aid of ΔE * _{uv reaches} its limits here, since the perceivable color difference is greater than the comparatively low value for ΔE * _uv suggests. This is also clear in the representation of the calculated color coordinates u 'and v' (see embodiment 2).

The present invention thus provides for the first time thermochromic pigments having particularly advantageous combinations of properties as well as thermochromic coatings which can be produced therewith. The thermochromic pigments and coatings made therewith are also suitable for use in household appliances, especially as temperature indicators.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

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Claims (18)

Thermochromic pigments selected from one or more of the pigments of general formula (1) to (6): A ₄ B ₉ X ₂₀ : n% C, (1) wherein A comprises or represents one or more elements of the group A = Li, Na, B comprises or represents one or more elements of the group B = Si, Ge, Zr, Sn, Hf, X is one or more elements of the group X = O, S, N comprises or represents and C comprises or represents one or more elements of the group C = Mn (IV), Cr (IV), Mo (VI), Ru (II), Nb (V), Fe (III), and 0 <n ≤ 10; A ₃ BX ₆ : n% C, (2) wherein A comprises or represents one or more elements of the group A = Mg, Ca, Sr, Ba, Zn, B comprises or represents one or more elements of the group B = Mo, W, X represents one or more elements of the group X = O, S, N includes or represents and C comprises or represents one or more of the group C = Eu, Fe, Mn, Co, Ni, Cu, Ru, and 0 <n ≤ 20; (Bi _1-x A _x ) (V _{1 -y} B _y ) O ₄ , (3) wherein A comprises or represents one or more elements of the group A = La, Pr, Nd, Er, where 0 <x ≦ 0.2, and B comprises one or more elements of the group B = P, Mo, W, Nb, Ta or represents, wherein 0 ≤ y ≤ 0.2; (Bi _1-x A _x ) (V _{1 -y} B _y ) O ₄ , (4) wherein A comprises or represents Ce, where 0 <x ≦ 0.2 and B comprises or represents one or more elements of the group B = P, Mo, W, Nb, Ta, where 0 <y ≦ 0.2; L _x M _y N _{(2x + 4y) / 3} : n% R, (5) wherein R = Ce, Pr, Sm, Eu, Tb, Tm, Yb and / or Bi and 0 <n <50, wherein L comprises or represents one or more elements of the group L = Mg, Ca, Sr, Ba, with 1 ≤ x ≤ 10 and M comprises one or more elements of the group M = C, Si, Ge or represents with 1 ≤ y ≤ 10; or L _x M _y O _z N _{(2x + 4y-2z) / 3} : n% R, (6) wherein R = Ce, Sm, Eu, Tm and / or Yb and 0 <n ≤ 50, wherein L comprises or represents one or more elements of the group L = Mg, Ca, Sr, Ba, with 1 ≤ x ≤ 10 and M comprises one or more elements of the group M = C, Si, Ge, where 1 ≤ y ≤ 10 and 0 <z ≤ 10. Thermochromic pigments according to Claim 1, characterized in that they have an average particle diameter d ₅₀ of 0.1 μm to 100 μm, more preferably 0.5 μm to 5 μm, and preferably a maximum particle diameter d _max of <200 μm, more preferably <100 μm , particularly preferably <10 μm, or that they represent nanopigments whose dimensions are preferably in one, two or three spatial directions <100 nm, particularly preferably selected from nanoparticles, nanowires, nanotubes or nanoplates. Thermochromic pigments according to claim 1 or 2, characterized in that they are surrounded by one or more shells of organic or inorganic material, wherein the material of the sheath preferably consists of one or more constituents of the group consisting of silica, alumina, tin oxide, titanium oxide, Aluminum phosphate, aluminum-zinc phosphate, silica, alumina, an organopolysiloxane, silicon nitride, silicon carbide and / or aluminum nitride is selected, more preferably an oxide, nitridic or oxinitridisches material is present. Thermochromic pigments according to at least one of the preceding claims 1 to 3, characterized in that in the thermochromic pigments, the proportion of Bi ₂ O ₃ , MoO ₃ and / or WO ₃ below 50 mol%, based on the total oxide composition, or that is present, except for unavoidable impurities no Bi ₂ O ₃ , MoO ₃ or WO ₃ in the pigments. Thermochromic coating comprising at least one layer containing or consisting of one or more of the thermochromic pigments of the formulas (1), (2), (3), (4), (5) and / or (6) according to any one of claims 1 to 4, optionally containing a temperature-resistant matrix, based on one or more binders or a glass frit or A thermochromic coating comprising at least one layer containing or consisting of one or more of the thermochromic pigments of the formulas (1), (2), (3), (4), (5) and / or (6) according to any one of claims 1 to 4 and one or more thermostable pigments, optionally containing a temperature-resistant matrix, based on one or more binders or a glass frit. Thermochromic coating according to claim 5, characterized in that the mass fraction of the thermochromic or pigments in the layer 0.5 to 50 wt .-%, preferably 2 to 40 wt .-% and particularly preferably 10 to 30 wt .-% is. Thermochromic coating according to one of the preceding claims 5 or 6, characterized in that the temperature-resistant matrix is based on one or more binders, preferably one or more polymers, in particular UV or thermally curable polymers selected from polyacrylate, polymethacrylate, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetals , Polyvinylpyrrolidone, polystyrene, polyolefins, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, perfluorinated polymers such as polytetrafluoroethylene, polyurethanes such as silicone modified polyurethanes, polyesters, epoxy resins, methacrylate resins, polyimides, polyamides, polycarbonate, cycloolefin copolymers, polyethersulfone and mixtures thereof, polysiloxanes such as Methyl-polysiloxane, phenyl-polysiloxanes, methyl / phenyl-polysiloxanes, acrylate-modified, polyester-modified, polyurethane-modified, epoxy-modified or nanoparticle-functionalized polysiloxanes and / or Silicones, silicone resins, polyester-modified, polyether-modified or epoxy-functionalized silicone resins, silazanes, silixanes, and / or sol-gel materials, preferably UV or thermally organically crosslinkable hybrid polymer sol-gel materials, hybrid polymeric sol-gel materials, nanoparticle-functionalized sol-gel Materials, sol-gel materials with nanoparticulate fillers, inorganic sol-gel materials. Thermochromic coating according to one of the preceding claims 5 to 7, characterized in that the thermochromic coating, comprising or consisting of at least one layer, fully or partially applied to a glass and / or glass ceramic substrate, preferably directly to a glass and / or glass ceramic substrate is applied. Thermochromic coating according to at least one of the preceding claims 5 to 8, characterized in that the thermochromic coating has at least one of the following features: a thickness of 10 nm to 500 μm, preferably 20 nm to 100 μm, particularly preferably 50 nm to 10 μm and / or a scratch resistance, determined by means of a sclerometer test, of> 500 g, more preferably> 700 g and / or present in one or more partial areas or over the entire surface of the substrate and / or in a structured manner. Thermochromic coating according to at least one of the preceding claims 5 to 9, characterized in that the substrate comprises or consists of glass ceramic, preferably selected from transparent colored lithium aluminosilicate (LAS) glass ceramic, transparent LAS glass ceramic, magnesium aluminosilicate glass ceramic or lithium disilicate glass ceramic or the Substrate glass comprises or consists thereof, preferably selected from silicate glasses, in particular borosilicate glasses, zinc borosilicate glasses, Boroalumosilikatgläsern, aluminosilicate glasses, alkali-free glasses, soda-lime glasses, or the substrate comprises a laminate or consists thereof, composed of several of the above materials. Thermochromic coating according to at least one of the preceding claims 5 to 10, characterized in that the substrate has at least one of the following features: - is thermo shock resistant and / or - a coefficient of thermal expansion less than 5.0 10 ^-6 / K, preferably less than 4.0 10 ^-6 / K, more preferably less than 3.4 10 ^-6 / K and / or - is chemically or thermally prestressed and / or - is rigid or flexible and / or - bent or not bent and / or - has surface structures on one or both surface sides such as elevations and / or depressions and / or - a thickness in the range of 10 microns to 6 cm, more preferably 30 microns to 2 cm, most preferably 50 .mu.m to 6 mm, particularly preferably 1 mm to 6 mm. Process for the preparation of the thermochromic pigments according to at least one of the preceding claims 1 to 4 - By a wet chemical process, wherein the starting materials are homogeneously mixed in a solvent and then transferred by precipitation, complexation, sol-gel process or other processes in a precursor, which then at temperatures above 400 ° C for at least four hours for the purpose of education the desired crystallographic structure is thermally treated in one or more calcination steps or - About a solid state reaction, wherein the starting materials in the form of oxidic, nitridic or sulfidic compounds, optionally with exclusion of air and moisture, and optionally with the addition of sintering aids at temperatures above 400 ° C for at least four hours to form the desired crystallographic Structure are thermally treated in one or more calcination steps. Process for producing a thermochromic coating according to at least one of the preceding claims 5 to 11 on a glass and / or glass ceramic substrate, wherein the thermochromic pigments and optionally additives are distributed in a liquid or pasty matrix-forming material and applied to the substrate in a coating step and preferably cured, in particular by UV irradiation or thermally. A method according to claim 13, characterized in that a coating solution in the form of a screen printing ink is used which consists of a matrix-forming material and thermochromic pigments of the formulas (1), (2), (3), (4), (5) and / or (6) and if necessary additives. A method according to claim 13 or 14, characterized in that methanol, ethanol, isopropanol, ethoxynonafluorobutane or high-boiling solvents having a low vapor pressure of <5 bar, preferably <1 bar, more preferably <0.1 bar are used as solvent, preferably solvent which have a boiling point of more than 120 ° C and an evaporation number of> 10, more preferably solvent having a boiling point above 150 ° C and an evaporation number of> 500, more preferably having a boiling point above 200 ° C and an evaporation number of> 1000 or mixtures thereof be used. Method according to at least one of the preceding claims 12 to 15, characterized in that the additives in the liquid or pasty matrix-forming material are selected from - further thermochromic or non-thermochromic thermostable pigments; Nanoparticles of oxidic materials, preferably selected from TiO ₂ , ZrO ₂ , Ca or Y ₂ O ₃ doped ZrO ₂ , MgO doped ZrO ₂ , CeO ₂ , Gd ₂ O ₃ doped CeO ₂ , Y doped ZrO ₂ , SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , SnO ₂ , ZnO, Bi ₂ O ₃ , Li ₂ O, K ₂ O, SrO, NaO, CaO, BaO, La ₂ O ₃ and / or HfO ₂ , boehmite, andalusite, mullite and their mixed oxides, particularly preferably SiO ₂ -containing nanoparticles; - Additives, preferably selected from wetting and dispersing additives, surface reactants (surfactants), solvents, thickeners, flow control agents, deaerators, defoamers, auxiliaries and anesthetics, levels, crosslinkers, lubricants, hardeners, starters, corrosion inhibitors, adhesion promoters and the like. Method according to at least one of the preceding claims 12 to 16, characterized in that the coating step for applying the matrix-forming material with the distributed therein thermochromic pigments on the substrate is selected from a printing process, in particular screen printing, knife coating, off-set printing, inkjet, pad printing, a spray process, roll coating and spin coating. Use of the thermochromic coating according to at least one of the preceding claims 5 to 11, comprising at least one layer comprising or consisting of the thermochromic pigments of the general formula (1), (2), (3), (4), (5) and / or (6) on a glass and / or glassmask substrate as a temperature indicator, preferably on surfaces of (domestic) appliances or items that may be heated or heated, in particular stoves of cookers, hobs, the inside or outside of oven panes, oven windows or fireplace viewing panes, cookware, baking pans, (ceramic) baking trays, and / or heatable plates of irons, curling irons, straighteners and the like.

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