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(19) TZZ_ZZ T

(11) EP 1 405 890 B2

(12) NEW EUROPEAN PATENT SPECIFICATION After opposition procedure

(45) Date of publication and mention (51) Int Cl.: of the opposition decision: G01K 11/14 (2006.01) C09K 9/00 (2006.01) 15.03.2017 Bulletin 2017/11 C04B 35/63 (2006.01) C04B 35/626 (2006.01) C04B 35/495 (2006.01) C04B 35/48 (2006.01) (2006.01) (2006.01) (45) Mention of the grant of the patent: C04B 35/457 C04B 35/453 (2006.01) (2006.01) 17.10.2012 Bulletin 2012/42 C04B 35/42 C03C 8/00

(86) International application number: (21) Application number: 01958693.2 PCT/RU2001/000196 (22) Date of filing: 15.05.2001 (87) International publication number: WO 2002/092721 (21.11.2002 Gazette 2002/47)

(54) THERMOCHROMIC MATERIAL THERMOCHROMES MATERIAL MATIERE THERMOCHROMIQUE

(84) Designated Contracting States: (74) Representative: Le Roux, Martine et al DE FR Cabinet Beau de Loménie 158, rue de l’Université (43) Date of publication of application: 75340 Paris Cedex 07 (FR) 07.04.2004 Bulletin 2004/15 (56) References cited: (73) Proprietor: EUROKERA EP-A1- 0 287 336 JP-A- 2 022 144 02400 Château-Thierry (FR) JP-A- 4 140 622 JP-A- 4 140 622 JP-A- 63 107 817 JP-A- 63 122 779 (72) Inventors: US-A- 4 722 510 US-A- 4 722 510 • BELYKH, Anna Vasilievna US-A- 4 983 810 St.Petersburg, 197349 (RU) • EFREMOV, Alexandr Mikhailovich • DATABASE WPI Week 198245 Derwent St.Petersburg, 199004 (RU) Publications Ltd., London, GB; AN 1982-96047E • MIKHAILOV, Mikhail Dmitrievich XP002410579 & JP 57 158834 A (OSAKA St.Petersburg, 199397 (RU) PREFECTURE) 30 September 1982 (1982-09-30) EP 1 405 890 B2

Printed by Jouve, 75001 PARIS (FR) 1 EP 1 405 890 B2 2

Description is used as the inner standard of transition in the thermochromic component upon heating. [0001] This invention relates to thermochromic mate- rials, in particular, thermochromic coatings, change of [0006] It was already mentioned above that cadmium color in which may be used for indication. 5 compositionsare toxicand cannot meetthe requirements One of the fields for thermochromic materials application of sanitary engineering norms in respect of toxicity valid is household appliances with coating of thermochromic for household appliances. Regarding the compound materials. The use of thermochromic materials permits Zn1-yMnyO according to the Specification it is stable upon to simply and efficiently warn a customer about danger heating to 400°C only and has no full reversibility of color of touching a certain portion of an article. 10 transition due to oxidation. The prior art also discloses a [0002] Requirements to thermochromic coatings of reversible temperature indicating material including poly- household appliances are as follows: crystalline sintered mixed bismuth and oxides that can be mixed into glass or ceramics (US patent 4 • The coating should signal about temperature of the 722 510). surface within the range of from 100 to 400°C, which 15 [0007] The purpose of this invention consists in crea- may cause a burn. Higher temperature, for instance, tion of a thermochromic material, non toxic, the color of on cooking top of stove surface may be felt on ac- which is reversible at temperature change from room count of radiation or visible color of the sur- temperature to 400°C, and, of which the color transition face. should permit to reflect temperature changes of less than • Change of color should be reversible in the heating 20 by 200°C, and which is stable when heated to 700°C. cycles - cooling without effects of aging and solari- [0008] This purpose is attained by that a thermochro- zation (discoloration). mic material is disclosed which contains as a thermo- • The coating should be stable up to maximum oper- chromic component based on crystal of heavy metals of ation temperature (700°C for cooking tops, 400° for I, II, III, IV, V, VI, VII, VIII groups of the Periodic System, other devices). 25 and as the binder - mixtures or pure components on the • The coating should meet sanitary engineering re- basis of silicates, borates, phosphates of alkali or alkaline quirements and norms in respect of toxicity. earth metals, the weight ratio of the thermochromic com- ponent to binder being from 2:98 to 98:2. [0003] With such requirements the art-known thermo- [0009] For intensification of thermochromic features chromic materials based on organic compounds and liq- 30 the thermochromic materials additionally comprise a uid crystals cannot be used, since they are not stable at thermostable non-thermochromic or thermochromic high (up to 700°C) , therefore they are not component, in which the reflectance maximum resides considered in the background of the invention. in the same spectral area where thermochromic compo- [0004] Known in the art are thermochromic materials nent edge shift occurs. on the basis of cadmium and mercury sulfides and sele- 35 [0010] In this context, the present invention is as de- nides as thermochromic components and lead-silicate fined in the appended claims. A distinctive feature of the enamels (USA Patents No. 5 772 328 and No. 5 499 597) claimed invention is the thermochromic component or borosilicate glass (USA Patent No. 4 983 810) as a which is selected from the group of the following com- binder. The art-known thermochromic materials permit pounds: to obtain coatings stable to temperatures up to 700°C. 40 However, in accordance with the current norms the coat- i) Based on bismuth oxide compound of the general ings on their base cannot be used for applying onto the formula (Bi2O3)1-z(CrO3)z where z=0 or 0.5. surfaces of household appliances because of high tox- icity rates of cadmium and mercury. [0011] According to the claimed invention, the stable [0005] The solution disclosed in USA Patent No. 4 983 45 non-thermochromic or thermochromic is 810 is believed to be the closest to the claimed one, in cobalt CoAl2O4 or CoWO4 or Co1-xZnxWO4 or CoMoO4 compliance with this solution the thermochromic materi- for thethermochromic compound Bi 2O3 orthe thermosta- als comprises: ble pigment is Cr 2O3 for the mixture (Bi 2O3)0.5 (CrO3)0.5 as a thermochromic component. • as thermochromic component the compounds of for- 50 [0012] Traditionally, the phenomenon of thermo- mula Cd1-x-Sex, wherein x=0-0.8, or formula Zn1-y is connected with in solid sate MnyO wherein y=0.05-0.15; (polymorphic transformation). Typical representatives of • as binder glasses or glass ceramic, in particular, solid thermochromic compounds of this type are some borosilicate glass; of iodomercurates, iodides of tallium, mercury, silver, • as non-thermochromic or low-thermochromic com- 55 which have clear and reversible color change in the point pound the color of which is close to that of thermo- of phase transition (J.H. Day. of Inor- chromic component, for instance, Pb3(SbO4)2 or ganic Compounds. Chem. Rev., 68(1968), 669; K. Sone, ZrO2 alloyed with praseodymium. This component Y. Fukuda, Inorganic Thermochromism. Springer-Ver-

2 3 EP 1 405 890 B2 4 lag, Berlin e.a., 1987). These compounds have high con- mochromic compounds were tested, taking spectra of trast of color changes with temperature, but they are sta- powders diffusion reflection with respect to temperature, ble only at low temperatures. For most thermochromic which was changed within the range from room to 400°C. compounds, such as Ag2HgI4 maximum allowable tem- For measurement purposes spectrophotometer SF-26 perature does not exceed 200°C (D. Negoin, T. Rosu, 5 was used provided with a special cell with a heater, ar- Electric, thermal and thermochromic properties of ranged in spectrophotometer in place of standard holder MxHgl4-type compounds. Rev. Chem., 45 (1994), 201). for powder samples.Shift of the diffusionabsorption band It is not sufficient for application of thermochromic coat- or change in spectrum shape indicated thermochromic ings in such articles as kitchen ovens, temperature of the effect. cooking-top in which may reach 700°C. 10 [0020] Coating thermochromic properties may be [0013] Known in the art are heat resistant thermochro- characterized by two methods depending on the type of mic oxides on the basis of the compounds based on the diffusion spectrum and its behavior upon temperature structures of aluminium-chromium substitution, for in- variations of the sample: stance, rubies and spinels (C.P. Poolle. The optical spec- tra and color of Chromium containing solids. J. Phys. 15 1. Speed of color change with temperature. Coating Chem. Dolids, 25 (1964), 1169). color is characterized by a point with coordinates (x, [0014] Thermochromism of art-known compositions of y) on the color graph (), which are cal- rubies d-elements 2-xCr (AlxO3) and spinels culated from the reflection spectrum (M.M. Gurevich, (MgAl2-xCrxO4), as well as of the claimed ones, is stipu- E.F. Itsko, M.M. Seredenko. Optic properties of var- lated not by the phase transition with the temperature 20 nish-paint coatings. "Khimiya", L. 1984). Thermo- changes, but with the change in ligands field force. Color chromism rate may be characterized with a velocity change takes place with chromium in- of this point along the color graph with temperature, crease on account of aluminum atoms with chromium i.e. the value atoms substitution, which is accompanied by lattice de- formation due to greater radius of chromium atoms25 against aluminum atoms. Hereupon, the phenomenon of such thermochromism is known for chromium only. [0015] If chromium concentration in these compounds is not high, they have color. At high chromium con- An ordinary specialist is capable of distinguishing up centrations the color of these compounds is . Pink 30 to ten thousand if he compares two colors crystals have thermochromism: upon heating their color between them. It means, if TX ≈ 2 x 10 -4, the operator graduallychanges from pink atlow temperatures to green can see the difference in temperatures between cool at high temperatures. However, this change takes place and hot surfaces of about 100°C. For cadmium very slowly within wide range of temperatures from 200 sulfide applied according to the above mentioned to 900°C. Within the range of temperatures from room 35 USA Patents this value is about 3 x 10 -4. The advan- temperature to about 400°C, which is the most substan- tage of estimating thermochromic features by this tial for warning a customer, change of color in rubies and method consists in its absolute nature: the basis for spinels is not sufficient for using them as thermochromic comparing different coatings is their color. However, components of the coatings. this method is labor consuming, since its practicing [0016] Thermochromic component disclosed in this 40 requires integration of sophisticated functions along work have the feature of reversibly changing their color the whole spectrum. Moreover, an operator eye feels within wide range of temperatures and in such way that color changes differently in different ranges of the temperature change by 100 becomes visible, hereupon, spectrum: smaller TX values are seen in the range the coatings based on them have thermal stability of up of blue colors, bigger - in red. to 700°C. 45 2. In many cases changes of reflection spectrum take [0017] Herefor the firsttime not only theabove features place gradually as the edge of absorption shifts upon have been found, but for the first time such solid com- heating, in most cases towards the longwave area pounds have been found which manifest strong contrast of the spectrum. Such behavior of the reflection color change with the temperature and are stable in the spectrum is specific for semi-conductors, for in- air at the temperature up to 700°C. 50 stance, for cadmium, zinc and mercury sulfides and [0018] The above compounds were obtained by a selenides used as thermochromic component (see standard method of pressing the mixture of initial oxides the above mentioned USA Patents). In the temper- followed by heat treatment at 700-1100°C for 4-100 ature range of from room and above position of the hours, depending on the composition. Phase composi- absorption edge (or the same, edges of diffuse re- tion of the resultant compounds was defined by x-ray 55 flectance) is linear dependent on the temperature, if phase analysis on difractometer DRON-2, chemical com- expressed in energy units: position was controlled by x-ray spectral analysis. [0019] Thermochromic features of the resultant ther-

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of a thermochromic coating of the present invention, based on bismuth oxide and cobalt blue, described in Example 8, infra, at various temperatures; wherein β is the temperature coefficient character- izing absorption edge shift with temperature. Ther- 5 Example 1 (not part of the invention) mochromic properties of the compound are ex- pressed the stronger the greater is β value. For cad- [0024] This Example illustrates in detail the process mium sulfide, for instance, this value is: for preparing thermochromic coating and the features thereof. Bismuth, lead, tantalum oxide powders were 10 mixed at molar ratio of 1:1:1, total charge mass being 20 grams. The mixture was pressed into a tablet with the help of a hydraulic press at the pressure of about 1000 [0021] After estimation of thermochromic properties of kg/cm2. The tablet was placed into the oven the temper- the compounds their powders were mixed with a binder ature of which was being increased gradually from room selected from silicates, phosphates, borates and mix- 15 temperature to 800°C within five hours. At this tempera- tures thereof, the total ratio of thermochromic component ture the tablet was left for 100 hours. After cooling of the to binder being from 2:98 to 98:2, doped with water and stove the tablet was again grounded into powder, mixed, the resultant composition was applied onto the surface pressed and again kept for 100 hours at the temperature of glass, metal, or glass-ceramic. For improving cohesion of 800°C. X-ray phase analysis supports homogeneous of the coating with the glass-ceramic, glass or ceramic 20 nature of the resultant crystalline compound the latter was roughed by abrasive powder treatment or PbO·Bi2O3·Ta2O5. Thiscompound is thermochromic: up- by means of groove cutting with the help of a disc. Plate on heating from 20 to 400°C its color changed from with the coating applied thereon was placed into stove to . Powder of this compound was mixed and heated to a temperature of from 500 to 970°C for 10 with glass frit of the following composition: 25 minutes to 1 hour depending on the compounds compo- 78Ba(PO3)2·22Pb(PO3)2, mass ratio being 90:10, then sition. Thereafter, spectra of coating diffuse reflectance water was added to the mixture and the resultant com- depending on temperature were tested. position was applied onto the surface of a glass-ceramic [0022] Results of the spectral assays indicate that the plate. The glass-ceramic plate with the coating applied claimed metal oxides and the coatings on the basis there- was placed into the oven, the temperature of which was of have thermochromic properties, expressed in revers- 30 gradually increased to 500°C, and at this temperature able, strong and contrast color change upon change of the plate was kept for 1 hour. The coating so obtained the temperature from room temperature to 400°C, stay- had light yellow color. Fig. 1 discloses reflectance spec- ing stable upon heating up to 700°C, hereupon, temper- tra, which indicate gradual shift of the absorption edge ature change by 100°C becomes visible. towards the long wave area of the spectrum upon tem- [0023] In the accompanying drawings: 35 perature increase, i.e. the resultant coating has thermo- chromic properties. As a characteristic of thermochromic FIG. 1 is a diagram showing the reflectance spectra properties of the coating it is possible to consider the of a thermochromic coating of the present invention dependence of the edge position on the temperature, for described in Example 1, infra, at various tempera- instance, at the level of reflectance coefficient of 0.5. This tures; 40 dependence is disclosed in Fig. 2. It is evident that posi- FIG. 2 is a diagram showing the dependence of the tion of the claimed coating absorption edge is in linear absorption edge on temperature of the thermochro- dependence on the temperature, as it is in semiconduct- mic coating of FIG. 1; ing compounds. Temperature coefficient of the edge shift FIG. 3 is a diagram showing the reflectance spectra coefficient of the considered coating is: of a thermochromic coating of the present invention 45 described in Example 4, infra, at various tempera- tures; FIG. 4 is a diagram showing the dependence of the absorption edge on temperature of the thermochro- [0025] Thermochromism of the coating may be char- mic coating of FIG. 3; 50 acterized also by the speed of color change TX = 2.3 x FIG.5a, 5b and 5c are diagrams showing the reflect- 10-4. These values are comparable with the thermo- ance spectra of a thermochromic compound at two chromism value, which may be attained of the coatings temperatures, the reflectance spectra of a non-ther- containing cadmium sulfide. mochromic pigment, and the reflectance spectra of the mixture thereof at two temperatures, respective- 55 Example 2 (not part of the invention) ly; FIG. 6 is a diagram showing the reflectance spectra [0026] Similar to Example 1, the compound of the fol-

4 7 EP 1 405 890 B2 8 lowing composition: PbO·Bi2O3·2Ta2O5. The resultant includes, at least, two components with definite ratio of compound was mixed with aluminophosphate binder reflectance spectra. The principle consists in the follow- having approximate final formula Al 2O3·3P2O5. Prepara- ing. Let the coating have within its composition a ther- tion and use of this binder was made in compliance with mochromic compound characterized by gradual shift of literature recommendations (M.M. Sychev. Non-organic 5 absorption edge towards the long-wave area of spec- glues, L. Khymia, 1986). Mass ratio of the binder (recal- trum. Moreover, the coating contains a pigment which culated to solid matter) and thermochromic component may have no thermochromic properties at all, and in in the mixture used for coating application was equal to which the reflectance maximum resides in the same 1:9. The mixture was applied onto the glass-ceramic sur- spectral area where thermochromic component edge face prepared similar to the method disclosed in Example 10 shift occurs (Fig. 5b). Reflectance spectrum of the mix- 1. The coating was dried by heating to 450°C and main- ture in this case will be the superposition of reflectance tained at this temperature for 1 hour. Properties of the spectra of two compounds (Fig. 5, c). In the initial position coating were examined by the method similar to one pre- pigment reflectance band will be distinguishable on the sented in Example 1. According to measurements, the mixture reflectance spectrum, since at low temperature value of temperature coefficient of absorption edge shift 15 it is in the area of thermochromic component transpar- for this coating is: ency. Upon heating the thermochromic component ab- sorption edge shifts towards the long-wave area of spec- trum and starts absorption in the pigment reflectance ar- ea. Eventually reflectance intensity in this spectral area 20 falls to background level. This effect corresponds to color Example 3 (not part of the invention) variation from shade of color of the colored pigment to the color of thermochromic component at high tempera- [0027] This Example illustrates preparation of thermo- ture. Naturally, thermochromism will be still higher if the chromic coating on the basis of a compound containing colored pigment is also thermo-chromic, for instance, the bismuth oxide and having maximum thermochromism 25 proposed in this invention compounds of zinc and cobalt. value. Using the same synthesis conditions as above in [0031] The Example given bellow, demonstrates em- Examples 1 and 2 thermochromic component was ob- bodiment of the claimed compound. tained with the composition 7Bi2O3.Nb2O5. The coating was applied as in Example 2. Its reflectance spectrum in Example 4 the temperature range of from room temperature to30 400°C is given in Fig. 3, and temperature reliance of the [0032] 15 g of bismuth oxide pre-annealed in air at absorption adge position - in Fig. 4. It is evident that for 700°C, is mixed with 1g of commercial heat-stable blue this particular coating thermochromism value is: pigment

35 - cobalt blue (CoAl 2O4) and 0.3 g of potassium silicate is added as the binder. The mixture is vigorously stirred, water is added and deposited onto a metallic [0028] It corresponds to color change upon heating surface and dried. Reflectance spectra of the result- from light yellow at room temperature to dark orange at ant material are given in Fig. 6. The color of coating 400°C. 40 changes from blue at room temperature to orange at 400°C. Thermochromism rate calculated on the Table 1 basis of the data given in Fig. 6, is TX = 6.0 x 10-4. Hence, mixing of thermochromic component - bis- Thermochromic properties of coatings making use of muth oxide bismuth oxide compound as a thermochromic 45 - with non-thermochromic pigment - cobalt blue, led component to intensification of thermochromism twice as much COMPOSITION βx 104, ev/K in comparison with the thermochromism of pure bis- muth oxide. Bi2O3 11.1

50 [0029] Table 1 indicates the temperature coefficient Claims value of the absorption layer shift for the coating com- prising in its composition bismuth oxide. The coating is 1. A thermochromic material comprising a thermochro- thermochromic, and its thermochromism relies upon the mic component and a binder, with the ratio in terms absorption edge shift to long-wave area of the spectrum 55 of weight percentage of thermochromic component upon heating. versus binder being from 2:98 to 98:2, wherein: [0030] According to the invention more intensive color change may be attained if the thermochromic compound - the thermochromic component is crystal phas-

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es of Bi2O3 and additionally comprises a ther- in dem die Flankenverschiebung der thermo- mostable non-thermochromic or thermochromic chromen Komponente auftritt, wobei das Pig- pigment in which the reflectance maxium re- ment aus CoAl 2O4, CoWO4, CO1-xZnxWO4 und sides in the same spectral area where thermo- CoMoO4 ausgewählt ist, oder chromic component edge shift occurs; said pig- 5 - die thermochrome Komponente Kristallphasen

ment being selected from CoAl2O4, CoWO4, aus (Bi2O3)0,5(CrO3)0,5 ist und zusätzlich ein Co1-xZnxWO4 and CoMoO4; or thermostabiles nicht-thermochromes oder ther- - the thermochromic component is crystal phas- mochromes Pigment umfasst, bei dem sich das es of (Bi2O3)0.5(CrO3)0.5 and additionally com- Reflexionsmaximum in demselben Spektralbe- prises a thermostable non-thermochromic or 10 reich befindet, in dem die Flankenverschiebung thermochromic pigment in which the reflectance der thermochromen Komponente auftritt, wobei

maximum resides in the same spectral area das Pigment aus Cr2O3 besteht. where thermochromic component edge shift oc-

curs, said pigment consisting in Cr2O3. 2. Materialnach Anspruch 1, wobei das Bindemittel aus 15 der aus Silikaten, Boraten, Phosphaten der Alkali- 2. The material according to claim 1, wherein the binder oder Erdalkalimetallen und Mischungen davon be- is selected from the group consisting of silicates, bo- stehenden Gruppe ausgewählt ist. rates, phosphates of alkali or alkaline earth metals and mixtures thereof. 3. Verwendung, in einem thermochromen Material, 20 umfassend eine thermochrome Komponente und 3. Use, in a thermochromic material comprising a ther- ein Bindemittel, wobei das Verhältnis ausgedrückt mochromic component and a binder, with the ratio in Gewichtsprozenten der thermochromen Kompo- in terms of weight percentage of thermochromic nente zu dem Bindemittel von 2:98 bis 98:2 reicht, component versus binder being from 2:98 to 98:2, wobei die thermochrome Komponente Kristallpha- wherein the thermochromic component is crystal25 sen ist phases, - aus Bi2O3, - of Bi2O3; wobei die thermochrome Komponente zusätz- said thermochromic component additionally lich ein thermostabiles nicht-thermochromes comprising a thermostable non-thermochromic 30 oder thermochromes Pigment umfasst, bei dem or thermochromic pigment in which the reflect- sich das Reflexionsmaximum in demselben ance maximum resides in the same spectral ar- Spektralbereich befindet, in dem die Flanken- ea where thermochromic component edge shift verschiebung der thermochromen Komponente occurs, said pigment being selected from auftritt, wobei das Pigment aus 2 CoAlO4, 35 CoAl2O4, CoWO4, Co1-xZnxWO4 and CoMoO4; CoWO4, CO1-xZnxWO4 und CoMoO4 ausge- or wählt ist, oder

- of (Bi2O3)0.5(CrO3)0.5; - aus (Bi2O3)0,5(CrO3)0,5, said thermochromic component additionally wobei die thermochrome Komponente Kristall- comprising a thermostable non-thermochromic phasen zusätzlich ein thermostabiles nicht-ther- or thermochromic pigment in which the reflect- 40 mochromes oder thermochromes Pigment um- ance maximum resides in the same spectral ar- fasst, bei dem sich das Reflexionsmaximum in ea where thermochromic component edge shift demselben Spektralbereich befindet, in dem die

occurs, said pigment consisting in Cr2O3. Flankenverschiebung der thermochromen Komponente auftritt, wobei das Pigment aus 45 Cr2O3 besteht. Patentansprüche

1. Thermochromes Material, umfassend eine thermo- Revendications chrome Komponente und ein Bindemittel, wobei das Verhältnis ausgedrückt in Gewichtsprozenten der 50 1. Matériau thermochromique comprenant un compo- thermochromen Komponente zu dem Bindemittel sant thermochromique et un liant, dans un rapport von 2:98 bis 98:2 reicht, wobei en termes de pourcentage en poids du composant thermochromique au liant de 2:98 à 98:2, dans - diethermochrome Komponente Kristallphasen lequel : 55 aus Bi2O3 ist und zusätzlich ein thermostabiles nicht-thermochromes oder thermochromes Pig- - le composant thermochromique correspond à ment umfasst, bei dem sich das Reflexionsma- des phases cristallines de (Bi 2O3) et comprend, ximum in demselben Spektralbereich befindet, en plus, un pigment thermostable non thermo-

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chromique ou thermochromique dans lequel la réflectancemaximale réside dans la mêmezone spectrale que celle où le décalage de front du composant thermochromique se produit ; ledit 5 pigment étant choisi parmi CoAl2O4, CoWO4, Co1-xZnxWO4 et CoMoO4 ; ou - le composant thermochromique correspond à

des phases cristallines de (Bi 2O3)0,5(CrO3)0,5 et comprend, en plus, un pigment thermostable non thermochromique ou thermochromique10 dans lequel la réflectance maximale réside dans la même zone spectrale que celle où le décalage de front du composant thermochromique se

produit ; ledit pigment consistant en du Cr 2O3. 15 2. Matériau selon la revendication 1, dans lequel le liant est choisi dans le groupe constitué par les silicates, les borates, les phosphates de métaux alcalins ou alcalino-terreux et leurs mélanges. 20 3. Utilisation, dans un matériau thermochromique com- prenant un composant thermochromique et un liant, dans un rapport en termes de pourcentage en poids du composant thermochromique au liant de 2:98 à 98:2, dans lequel le composant thermochromique 25 correspond à des phases cristallines,

- de Bi2O3 ; ledit composant thermochromique comprenant, en plus, un pigment thermostable non thermo- 30 chromique ou thermochromique dans lequel la réflectancemaximale réside dans la mêmezone spectrale que celle où le décalage de front du composant thermochromique se produit ; ledit 35 pigment étant choisi parmi CoAl2O4, CoWO4, Co1-xZnxWO4 et CoMoO4 ; ou - de (Bi2O3) 0,5 (CrO3) 0,5; ledit composant thermochromique comprenant, en plus, un pigment thermostable non thermo- chromique ou thermochromique dans lequel la 40 réflectancemaximale réside dans la mêmezone spectrale que celle où le décalage de front du composant thermochromique se produit ; ledit pigment consistant en du Cr2O3. 45

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• US 5772328 A [0004] • US 4983810 A [0004] [0005] • US 5499597 A [0004] • US 4722510 A [0006]

Non-patent literature cited in the description

• J.H. DAY. Thermochromism of Inorganic Com- • C.P. POOLLE. The optical spectra and color of Chro- pounds. Chem. Rev., 1968, vol. 68, 669 [0012] mium containing solids. J. Phys. Chem. Dolids, 1964, •K.SONE; Y. FUKUDA. Inorganic Thermochromism. vol. 25, 1169 [0013] Springer-Verlag, 1987 [0012] • M.M. GUREVICH ; E.F. ITSKO ; M.M. SERE- • D. NEGOIN ; T. ROSU. Electric, thermal and thermo- DENKO. Optic properties of varnish-paint coatings. chromic properties of MxHgl4-type compounds. Rev. Khimiya, 1984 [0020] Chem., 1994, vol. 45, 201 [0012]

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