Temperature Indicator

Abstract

The invention relates to a coating comprising at least one functional decorative layer. The decorative layer comprises a thermochromic composition exhibiting a reversible variation of optical and/or colorimetric properties when part or all of the coating is subjected to a temperature variation between a cold temperature and a hot temperature, the cold temperature being between 0° C. and 40° C. and the hot temperature being between 80° C. and 400° C., and comprising at least one thermochromic compound of the family of silver halides. The invention also relates to a functional decorative layer composition, to an article comprising the coating or the decorative layer composition, and to the use of the coating or the decorative layer composition as a temperature indicator.

Claims

1. A coating, comprising: at least one functional decorative layer comprising a thermochromic composition, wherein the thermochromic composition exhibits reversible changes in the optical and/or colorimetric properties when the coating is subjected, partially or fully, to a change in temperature between a cold temperature and a hot temperature, the cold temperature being between 0° C. and 40° C. and the hot temperature being between 80° C. and 400° C., and wherein the thermochromic composition comprises at least one thermochromic compound in the silver halide family.

2. The coating according to claim 1, wherein the thermochromic compound is silver bromide or silver iodide.

3. The coating according to claim 1 wherein the hot temperature is between 120° C. and 280° C.

4. The coating according to claim 1, wherein the thermochromic composition comprises at least one other thermochromic compound and/or at least one thermostable pigment.

5. The coating according to claim 1, wherein the decorative layer is free of binder.

6. The coating according to claim 1, wherein the decorative layer comprises at least one binder.

7. The coating according to claim 6, wherein the binder comprises at least an enamel, a fluorocarbon resin, a resin adhesive, an inorganic or hybrid organic-inorganic polymer synthetized by sol/gel method, a lacquer, and a condensed tannin

8. The coating according to claim 6, wherein a weight ratio of the dry content of the thermochromic composition to the dry content of the binder is less than 3.

9. A functional decorative layer, comprising: a thermochromic composition exhibiting reversible changes in the optical and/or colorimetric properties when the functional decorative layer is subjected, partially or fully, to a change in temperature between a cold temperature and a hot temperature, the cold temperature being between 0° C. and 40° C. and the hot temperature being between 80° C. and 400° C.; and at least one binder, wherein the thermochromic composition comprises at least one thermochromic compound in the silver halide family.

10. The functional decorative layer according to claim 9, wherein the thermochromic compound is silver bromide or silver iodide.

11. The functional decorative layer according to claim 9, wherein the hot temperature is between 120° C. and 280° C.

12. The functional decorative layer according to claim 9, wherein the thermochromic composition comprises at least one other thermochromic compound and/or at least one thermostable pigment.

13. The functional decorative layer according to claim 9, wherein the binder comprises at least an enamel, a fluorocarbon resin, a resin adhesive, an inorganic or hybrid organic-inorganic polymer synthetized by sol/gel method, a lacquer, and a condensed tannin.

14. The functional decorative layer according to claim 9, wherein a weight ratio of the dry content of the thermochromic composition to the dry content of the binder is less than 3.

15. An item comprising the coating according to claim 1.

16. (canceled)

17. An item comprising the functional decorative layer according to claim 9.

Description

[0103] Other advantages and special features of this invention will be seen in the following description, which is provided as a non-limiting example and refers to the figures appended hereto:

[0104] FIG. 1 is a schematic cross-section view of an example of an embodiment of a pan according to the invention;

[0105] FIG. 2 is a schematic cross-section view of the pan in FIG. 1 with an example of a single-layer coating according to the invention; and

[0106] FIG. 3 is a schematic cross-section view of the pan in FIG. 1 with an example of a multi-layer coating according to the invention.

[0107] FIG. 1 shows an example of a cooking utensil according to the invention, a pan 1 comprising a support 3 shown as a shallow bowl equipped with a handle 4. The support 3 comprises an inner side 31 which is the side turned towards the food that may be placed in the pan 1, and an outer side 32 that is to be placed near an external source of heat. Support 3 comprises, on its inner side 31, a coating 2 according to the invention.

[0108] FIG. 2 is a schematic cross-section view of the pan in FIG. 1 with an example of a single-layer coating 2 according to the invention. The coating 2 comprises a decorative layer 20 comprising at least one thermochromic component in the silver halide family.

[0109] FIG. 3 is a schematic cross-section view of the pan in FIG. 1 with an example of a multi-layer coating 2 according to the invention. The coating 2 comprises an undercoat 22, a finishing coat 21 and a decorative layer 20 comprising at least one thermochromic component in the silver halide family. The invention is illustrated in greater detail in the following examples.

EXAMPLES

Example 1: Preparation of an AgI-Based Decorative Layer Composition, with No Thermostable Binder

[0110] A decorative AgI-based layer composition with no thermostable binder is prepared from the components listed below:

TABLE-US-00001 Components Weights (g) Water 52.73 AgI 30.64 Thickener 4.90 pH adjuster 0.69 Solvent 11.04

[0111] A decorative paste is prepared first by dispersing the AgI in the water.

[0112] Then the decorative layer composition is prepared by mixing the decorative paste with the other components.

Example 2: Preparation of an AgI-Based Decorative Layer Composition, with No Thermostable Binder

[0113] A decorative layer composition comprising AgI with no thermostable binder is prepared from the components listed below:

TABLE-US-00002 Components Weights (g) Water 50.0 AgI 37.5 Thickener 5 pH adjuster 0.5 Solvent 7

[0114] A decorative paste is prepared first by dispersing the AgI in the water.

[0115] Then the decorative layer composition is prepared by mixing the decorative paste with the other components.

Example 3: Preparation of an AgI-Based Decorative Layer Composition with a Thermostable Binder

[0116] A decorative AgI-based layer composition with a thermostable binder, PTFE, is prepared from the components listed below:

TABLE-US-00003 Components Weights (g) Aqueous dispersion of 59.06 PTFE (60% dry content by weight) AgI 23.62 Thickener 2.19 Water 3.13 pH adjuster 0.48 Solvent 11.22 Foam inhibitor 0.30

[0117] A decorative paste is prepared first by dispersing the AgI in the water.

[0118] Then the decorative layer composition is prepared by mixing the decorative paste with the other components

Example 4: Preparation of Fluorocarbon Resin-Based Coatings Comprising at Least One Decorative Layer Comprising AgI

[0119] Various decorative layer compositions were formulated. These compositions have a common base formulation comprising in particular a solvent, water and thickeners. AgI and PTFE were added to this base formulation in respective proportions which are detailed below. The decorative layer compositions are obtained by first dispersing the AgI in water, then mixing the paste obtained with the other ingredients.

TABLE-US-00004 Without PTFE PTFE PTFE PTFE Content 1 Content 2 Content 3 AgI 10 10 10 10 (dry content in g) PTFE 0 4.41 9.68 25.78 (dry content in g) Ratio AgI/PTFE n/a 2.27 1.03 0.39

[0120] Each of these compositions was applied by pad printing in one or three or five layers on a PTFE-based primer deposited on a support.

[0121] A transparent PTFE-based finish was then deposited and the coating was fired at 430° C. for 11 minutes.

[0122] The coatings obtained have a vert-de-gris-colored decoration at room temperature (20° C.) on a black background (corresponding to the undercoat). The coatings for which the decorative layer compositions were deposited in a single layer have a lighter vert-de-gris-colored decoration than the coatings for which the decorative layer compositions were deposited in multiple layers.

[0123] Various aging tests were performed on the coatings obtained.

[0124] Color-change test: the coated samples were fired to 250° C. A gradual change in the color of the decoration, from the initial vert-de-gris to a yellow/orange color, was observed during heating, with the colorimetric properties of the black background remaining unchanged. The contrast in the color change is most obvious when the decoration comprises PTFE. The samples were left to cool to room temperature; a gradual color change from yellow/orange to the initial vert-de-gris color was observed during cooling, with the colorimetric properties of the black background remaining unchanged.

[0125] Peanut oil test at 250° C.: the coated samples were immersed for fifteen hours in peanut oil heated to 250° C. The appearance of the pad-printed areas was examined before and after the test. There was a clear yellowing of the pad-printed areas in the three- and five-layer configurations. Moreover, particular soiling was observed in the three- and five-layer configurations on the pad-printed areas without PTFE and with PTFE content 1 (AgI/PTFE ratio=2.27). The decorative layer compositions comprising an AgI/PTFE ratio<2.27 were protected from soiling.

[0126] Water test at 82° C.: the coated samples were immersed for forty-eight hours in water at 82° C. The appearance of the pad-printed areas was examined before and after the test. Uniform whitening was observed in the configurations without PTFE and with PTFE content 1 (AgI/PTFE ratio=2.27). The decorative layer compositions comprising an AgI/PTFE ratio<2.27 seem to have been protected from this effect and the color of the corresponding pad-printed areas was uniform with no defects.