Non-Stick Coating Comprising at Least One Functional Decorative Layer and Item Provided with Such a Coating

Abstract

Provided is a non-stick coating including at least one functional decorative layer, including a pigment composition having a reversible variation of optical and/or colorimetric properties when the coating is subjected to a temperature variation between a cold temperature of 0 C. to 40 C. and a hot temperature of 80 C. to 400 C. The pigment composition includes at least one compound of formula Y.sub.(3-x)M.sub.xFe.sub.(5-y)Q.sub.yO.sub.12 in the form of particles, in which M is selected from the lanthanides, alkaline metals, alkaline-earth metals and metalloids with a degree of oxidation (DO) +3; Q is selected from the group made up of the lanthanides, non-metals with degree of oxidation +4, metals with DO +3 or +4, transition metals with DO +2 or +4, alkaline-earth metals and alkaline metals; and wherein x is between 0 and 0.3 and y is between 0 and 3.

Claims

1. Non-stick coating (2) comprising at least one functional decorative layer (20), characterized in that the decorative layer (20) comprises a pigment composition displaying a reversible change in optical and/or colorimetric properties when the coating (2) is subjected, in part or in whole, to a temperature change 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 in that the pigment composition comprises at least one compound of formula (I) being in the form of particles:
Y.sub.(3-x)M.sub.xFe.sub.(5-y)Q.sub.yO.sub.12(I) in which: M is selected from the group consisting of lanthanides, alkaline metals, alkaline earth metals and metalloids with a degree of oxidation of +3; Q is selected from the group consisting of lanthanides, non-metals with a degree of oxidation of +4, metals with a degree of oxidation of +3 or +4, transition metals with a degree of oxidation of +2 or +4, alkaline earth metals and alkaline metals; x is between 0 and 0.3; and y is between 0 and 3.

2. Coating (2) according to claim 1, in which: M is selected from the group consisting of La, Ce, Ca and Sr, and combinations thereof; and Q is selected from the group consisting of Si, Al, Ga, Ge, Ti, Cr, Ca, Sr and La, and combinations thereof.

3. Coating (2) according to any of the preceding claims, in which the compound of formula (I) possesses a garnet-type structure.

4. Coating (2) according to any of the preceding claims, in which the compound of formula (I) is selected from among the following compounds: Y.sub.3Fe.sub.5O.sub.12 Y.sub.3Fe.sub.4.75Ga.sub.0.25O.sub.12 Y.sub.2.85La.sub.0.15Fe.sub.5O.sub.12 Y.sub.2.75Sr.sub.0.25Fe.sub.4.75Ge.sub.0.25O.sub.12 Y.sub.2.9Sr.sub.0.1Fe.sub.4.9Ge.sub.0.1O.sub.12 Y.sub.2.75Sr.sub.0.25Fe.sub.4.75Si.sub.0.25O.sub.12 Y.sub.2.9Sr.sub.0.1Fe.sub.4.9Si.sub.0.1O.sub.12 Y.sub.2.9Sr.sub.0.1Fe.sub.4.9Ti.sub.0.1O.sub.12 Y.sub.2.85Sr.sub.0.15Fe.sub.4.85Ti.sub.0.1O.sub.12 Y.sub.2.75Ca.sub.0.25Fe.sub.4.75Ge.sub.0.25O.sub.12 Y.sub.2.75Ca.sub.0.25Fe.sub.4.75Si.sub.0.25O.sub.12 Y.sub.3Fe.sub.4.5Al.sub.0.5O.sub.12 Y.sub.3Fe.sub.4.75Al.sub.0.25O.sub.12 Y.sub.3Fe.sub.4.4Al.sub.0.5Cr.sub.0.1O.sub.12 Y.sub.3Fe.sub.4.65Al.sub.0.25Cr.sub.0.1O.sub.12 Y.sub.3Fe.sub.4.75Ge.sub.0.25O.sub.12 Y.sub.3Fe.sub.4.75Si.sub.0.25O.sub.12 Y.sub.3Fe.sub.4.85Cr.sub.0.15O.sub.12 Y.sub.3Fe.sub.3Al.sub.2O.sub.12 Y.sub.3Al.sub.3Fe.sub.2O.sub.12

5. Coating (2) according to any of the preceding claims, in which y is between 0 and 0.5.

6. Coating (2) according to any of the preceding claims, in which the hot temperature is between 120 C. and 240 C.

7. Coating (2) according to any of the preceding claims, in which the decorative layer (20) does not contain a heat-stable binder.

8. Coating (2) according to any of claims 1 through 6, in which the decorative layer (20) comprises, in addition to the pigment composition, at least one heat-stable binder.

9. Coating (2) according to claim 8, in which the heat-stable binder is selected from the group consisting of enamels, fluorocarbon resins (alone or in a mixture), inorganic polymers or organic-inorganic hybrid polymers synthesized through a sol-gel process, silicones, silicone-polyesters, polyimides, polyphenylene sulfides (PPS), polyethylene sulfides (PES), polyether ether ketones (PEEK), polyether ketones (PEK), polyamide-imides (PAI), fluorosilicones and polybenzimidazoles (PBI), and mixtures thereof.

10. Coating (2) according to any of the preceding claims, in which the pigment composition also comprises at least one other thermochromic compound.

11. Coating (2) according to claim 10, in which the pigment composition also comprises bismuth oxide.

12. Item (1) characterized in that it comprises a medium (3) having two opposite surfaces (31, 32), at least one of which is covered in a coating (2) as defined according to any of claims 1 through 11.

13. Item (1) according to claim 12, characterized in that it is a cooking tool in which the medium (3) has a concave interior surface (31) intended to be positioned on the side where food might be placed in the item (1), and a convex exterior surface (32) intended to be positioned toward a heat source.

14. Process of synthesizing a compound of formula (I) in the form of particles by a solid process:
Y.sub.(3-x)M.sub.xFe.sub.(5-y)Q.sub.yO.sub.12(I) in which: M is selected from the group consisting of lanthanides, alkaline metals, alkaline earth metals and metalloids with a degree of oxidation of +3; Q is selected from the group consisting of lanthanides, non-metals with a degree of oxidation of +4, metals with a degree of oxidation of +3 or +4, transition metals with a degree of oxidation of +2 or +4, alkaline earth metals and alkaline metals; x ranges from 0 to 0.3; and y ranges from 0 to 3; the process comprising the following steps: a) Co-grinding in an alcoholic medium of oxide powders of the elements making up the compound of formula (I); b) Heating of the product of step (a) to a temperature of between 1200 C. and 1500 C. for 4 to 10 hours; and c) Cooling of the product of step (b) to room temperature.

15. Process of synthesizing a compound of formula (I) in the form of particles through a sol-gel process:
Y.sub.(3-x)M.sub.xFe.sub.(5-y)Q.sub.yO.sub.12(I) in which: M is selected from the group consisting of lanthanides, alkaline metals, alkaline earth metals and metalloids with a degree of oxidation of +3; Q is selected from the group consisting of lanthanides, non-metals with a degree of oxidation of +4, metals with a degree of oxidation of +3 or +4, transition metals with a degree of oxidation of +2 or +4, alkaline earth metals and alkaline metals; x ranges from 0 to 0.3; and y ranges from 0 to 3; the process comprising the following steps: a) Mixing of salts of the elements making up the compound of formula (I) and at least one organic acid to form a gel; b) Drying of the gel from step (a); c) Calcination of the product of step (b) at a temperature of between 500 C. and 700 C.; d) Re-baking of the product of step (c) at a temperature of between 800 C. and 1000 C. for at least 4 hours; and e) Cooling of the product of step (d) to room temperature.

16. Process according to claim 15, in which the salts used are nitrates.

17. Process according to either claim 15 or 16, in which the organic acid is citric acid.

Description

[0122] Other advantages and particularities of this invention will become apparent in the description below, which is provided as a non-limiting example, and in reference to the attached drawings:

[0123] FIG. 1 is a schematic cross-section view of one example embodiment of a frying pan according to the invention;

[0124] FIG. 2 depicts a schematic cross-section view of the frying pan in FIG. 1, provided with a single-layer coating according to the invention; and

[0125] FIG. 3 depicts a schematic cross-section view of the frying pan in FIG. 1, provided with a single-layer non-stick coating according to the invention.

[0126] In FIG. 1, there is a depiction, as an example, of a cooking tool according to the invention, a frying pan (1) that comprises a medium (3) in the form of a shallow dome and a gripping handle (4). The medium (3) comprises an interior surface (31) that is the surface oriented on the side where food can be placed in the frying pan (1), and an exterior surface (32), which is designed to be placed toward an external heat source. The medium (3) comprises, on its interior surface (31), a non-stick coating (2) according to the invention.

[0127] FIG. 2 depicts a schematic cross-section view of the frying pan in FIG. 1, provided with a single-layer non-stick coating (2) according to the invention. The non-stick coating (2) comprises a decorative layer (20) comprising at least one compound of formula (I).

[0128] FIG. 3 depicts a schematic cross-section view of the frying pan in FIG. 1, provided with a single-layer non-stick coating (2) according to the invention. The non-stick coating (2) comprises a sub-layer (22), a finishing layer (21) and a decorative layer (20) comprising at least one compound of formula (I).

[0129] The invention is illustrated in greater detail in the following examples.

EXAMPLES

Example 1: Preparation, Through a Solid Process, of Pigment Compositions According to the Invention (PG1 to PG16)

[0130] The oxides are placed into a mechanical grinder in the proportions indicated in Table 1 in powder form (in keeping with the stoichiometry of the compound of formula (I) sought) in the presence of ethanol.

[0131] The grinding is performed for a duration that depends on the particle size of the oxide powders used and long enough to obtain a dispersion with an average aggregate particle size of approximately 2 m.

[0132] The dispersion is poured into a crucible, dried to remove the ethanol and then brought to 1350 C. by heating at a speed of approximately 2 C./minute.

[0133] Each of the powders obtained (PG1 to PG16) is maintained at 1350 C. for six hours so as to produce the compound of formula (I) by interdiffusion of the oxides through a solid process.

[0134] Each of the powders (PG1 to PG16) obtained has an average particle size of around 2 m.

[0135] The composition of each of the powders obtained (PG1 to PG16) is then analyzed by means of an X-ray diffraction (XRD) measurement and reported in Table 1.

[0136] The content by mass of the compound of formula (I) in each of the powders obtained (PG1 to PG16) is greater than or equal to 95%.

[0137] These powders (PG1 to PG16) each display a reversible change in colorimetric properties indicated in Table 1.

TABLE-US-00001 TABLE 1 PG1 PG2 PG3 PG4 PG5 PG6 PG7 PG8 Y.sub.2O.sub.3 (g) 5.7 5.7 5.42 5.23 5.51 5.23 5.51 5.51 Fe.sub.2O.sub.3 (g) 4 3.8 4 3.8 3.92 3.8 3.92 3.92 Al.sub.2O.sub.3 (g) Ga.sub.2O.sub.3 (g) 0.45 La.sub.2O.sub.3 (g) 0.25 SrCO.sub.3 (g) 0.37 0.15 0.37 0.15 0.15 GeO.sub.2 (g) 0.24 0.1 SiO.sub.2 (g) 0.26 0.1 TiO.sub.2 (g) 0.15 CaCO.sub.3 (g) Cr.sub.2O.sub.3 (g) Ethanol (g) 13 13 13 13 13 13 13 13 Composition Y.sub.3 Y.sub.3 Y.sub.2.85 Y.sub.2.75 Y.sub.2.9 Y.sub.2.75 Y.sub.2.9 Y.sub.2.9 obtained by Fe.sub.5 Fe.sub.4.75 La.sub.0.15 Sr.sub.0.25 Sr.sub.0.1 Sr.sub.0.25 Sr.sub.0.1 Sr.sub.0.1 spectroscopy O.sub.12 Ga.sub.0.25 Fe.sub.5 Fe.sub.4.75 Fe.sub.4.9 Fe.sub.4.75 Fe.sub.4.9 Fe.sub.4.9 O.sub.12 O.sub.12 Ge.sub.0.25 Ge.sub.0.1 Si.sub.0.25 Si.sub.0.1 Ti.sub.0.1 O.sub.12 O.sub.12 O.sub.12 O.sub.12 O.sub.12 Color at 20 C. Green Green Green Green Green Green Green Green Color at 220 C. Red Red Red Red Red Red Red Red PG9 PG10 PG11 PG12 PG13 PG14 PG15 PG16 Y.sub.2O.sub.3 (g) 5.42 5.23 5.23 5.7 5.7 5.7 5.7 5.7 Fe.sub.2O.sub.3 (g) 3.88 3.8 3.8 3.8 3.8 3.8 2.4 1.6 Al.sub.2O.sub.3 (g) 1.02 1.53 Ga.sub.2O.sub.3 (g) La.sub.2O.sub.3 (g) SrCO.sub.3 (g) 0.22 GeO.sub.2 (g) 0.24 0.24 SiO.sub.2 (g) 0.26 0.25 TiO.sub.2 (g) 0.22 CaCO.sub.3 (g) 0.25 0.25 Cr.sub.2O.sub.3 (g) 0.11 Ethanol (g) 13 13 13 13 13 13 13 13 Composition Y.sub.2.85 Y.sub.2.75 Y.sub.2.75 Y.sub.3 Y.sub.3 Y.sub.3 Y.sub.3 Y.sub.3 obtained by Sr.sub.0.15 Ca.sub.0.25 Ca.sub.0.25 Fe.sub.4.75 Fe.sub.4.75 Fe.sub.4.85 Fe.sub.3 Al.sub.3 spectroscopy Fe.sub.4.85 Fe.sub.4.75 Fe.sub.4.75 Ge.sub.0.25 Si.sub.0.25 Cr.sub.0.15 Al.sub.2 Fe.sub.2 Ti.sub.0.15 Ge.sub.0.25 Si.sub.0.25 O.sub.12 O.sub.12 O.sub.12 O.sub.12 O.sub.12 O.sub.12 O.sub.12 O.sub.12 Color at 20 C. Green Green Green Green Green Brown- Green Light Green Green Color at 220 C. Red Red Red Red Red Dark Brown- Dark Red Green Green

Example 2: Preparation Through a Sol-Gel Process of Pigment Compositions According to the Invention (PG17 to PG20)

[0138] An aqueous solution is prepared by mixing together nitrates, demineralized water and citric acid, in the proportions indicated in Table 2 (for the nitrates: in keeping with the stoichiometry of the compound of formula (I) sought).

[0139] The pH of the solution is adjusted to 2 by adding a 25% ammonia solution.

[0140] The solution is gradually heated to 120 C. to remove the water and obtain a gel.

[0141] Drying is done for 30 minutes in order to ensure that nearly all of the water is removed.

[0142] The gel is calcinated at 550 C. for one hour, and then re-baked at 900 C. for 6 hours.

[0143] Each of the powders obtained (PG17 to PG20) has an average particle size of about 2 m.

[0144] The composition of each of the powders obtained (PG17 to PG20) is analyzed using an X-ray Diffraction (XRD) measurement and is reported in Table 2 below.

[0145] The content by mass of the compound of formula (I) in each of the powders obtained is greater than or equal to 95%.

[0146] These powders (PG17 to PG20) each have a reversible colorimetric change indicated in Table 2 below.

TABLE-US-00002 TABLE 2 PG17 PG18 PG19 PG20 Fe(NO.sub.3).sub.9H.sub.2O (g) 12.6 13.3 12.32 13.02 Y(NO.sub.3).sub.6H.sub.2O (g) 7.8 7.8 7.8 7.8 Al(NO.sub.3).sub.9H.sub.2O (g) 1.26 0.63 1.26 0.63 Cr(NO.sub.3).sub.9H.sub.2O (g) 0.28 0.28 Demineralized water (g) 216.6 223.6 216.6 217.3 Citric acid (g) 61.4 62 60 60 Composition obtained Y.sub.3Fe.sub.4.5Al.sub.0.5O.sub.12 Y.sub.3Fe.sub.4.75Al.sub.0.25O.sub.12 Y.sub.3Fe.sub.4.4Al.sub..5Cr.sub.0.1O.sub.12 Y.sub.3Fe.sub.4.65Al.sub.0.25Cr.sub.0.1O.sub.12 by spectroscopy Color at 20 C. Green Green Green Green Color at 220 C. Red Red Red Red

Example 3: Preparation of Decorative Layer Compositions without Binder (SGD1)

[0147] The following components are added to a grinder and then ground and stirred to produce a decorative layer composition.

TABLE-US-00003 Compound Percentage by mass Pigment composition from 67.70 Example 1 or 2 Terpineol 6.05 Propylene glycol 6.05 Isopropanol 20.20

Example 4: Preparation of Decorative Layer Sol-Gel Compositions (SGD2)

[0148] The compounds of Part A are added to a grinder, and then ground and stirred to produce a paste.

[0149] The compounds of Part B are simply mixed together to combine.

[0150] In separated form, Parts A and B can be stored for several weeks.

[0151] Prior to use, Parts A and B are combined.

[0152] The mixture is allowed to stand for at least 6 hours to produce a decorative layer sol-gel composition. In this form, the sol-gel composition can be stored for several days.

TABLE-US-00004 Percentage by Part Compound mass A 30% colloidal silica 27.41 A Demineralized water 7.13 A Isopropanol 2.74 A Butyl glycol 0.88 A Pigment composition from 13.00 Example 1 or 2 A Alumina 11.51 B Methyl triethoxy ethanol 36.16 B Formic acid 0.36 B Silicone oil 47V50 0.81

Example 5: Preparation of a Surface Layer Sol-Gel Composition (SGS)

[0153] The compounds of Part A are added to a mixer and stirred.

[0154] The same procedure is followed for each of Parts B and C.

[0155] In separated form, Parts A, B and C can be stored for several months.

[0156] Prior to use, Parts A, B and C are combined.

[0157] The mixture is allowed to stand for at least 6 hours to produce a surface layer sol-gel composition. In this form, the sol-gel composition can be stored for several days.

TABLE-US-00005 Percentage by Part Compound mass A 30% colloidal silica 31.79 B Water 8.26 B Acetic acid 1.53 B Isopropanol 3.18 B Butyl glycol 3.05 B Silicone oil 47V50 0.87 B Methyl triethoxysilane 41.96 C Butyl glycol 9.08 C Metal flakes 0.18 C Spreading agent 0.10

Example 6: Preparation of a Bottom Layer Sol-Gel Composition (SGF)

[0158] The compounds of Part A are added to a grinder and then ground and stirred to produce a paste.

[0159] The compounds of Part B are simply mixed together to combine. In separated form, Parts A and B can be stored for several weeks.

[0160] Prior to use, Parts A and B are combined.

[0161] The mixture is allowed to stand for at least 6 hours to produce a bottom layer sol-gel composition. In this form, the sol-gel composition can be stored for several days.

TABLE-US-00006 Percentage by Part Compound mass A 30% colloidal silica 27.41 A Demineralized water 7.13 A Isopropanol 2.74 A Butyl glycol 0.88 A Spinel black (CuCoMn) 0.37 A Titanium dioxide 12.63 A Alumina 11.51 B Methyl triethoxy ethanol 36.16 B Formic acid 0.36 B Silicone oil 47V50 0.81

Example 7: Preparation of Decorative Layer Compositions without Binder (FFD1)

[0162] The following compounds are added to a grinder and then ground and stirred to produce a decorative layer composition. This decorative layer can be used as-is and can be stored for a few hours.

TABLE-US-00007 Percentage by Compound mass Pigment composition from 10.94 Example 1 or 2 Demineralized water 24.80 Monopropylene glycol 64.26

Example 8: Preparation of Decorative Layer Fluorinated Compositions (FFD2)

[0163] The composition is obtained by simply mixing together the different compounds. As-is, the composition can be stored for several days.

TABLE-US-00008 Percentage by Compound mass Aqueous PTFE dispersion 70.18 FFD1 composition 26.49 Anti-foaming agent 2.22 10.25% ammonia solution 1.11

Example 9: Preparation of Decorative Layer Fluorinated Compositions (FFD3)

[0164] The composition is obtained by simply mixing together the different compounds. As-is, the composition can be stored for several days.

TABLE-US-00009 Compound Percentage by mass Aqueous PTFE dispersion 52.7 Metal flakes 0.2 FFD1 composition 17.2 30% colloidal silica 4.3 PAI adhesive resin 12.9 Aqueous acrylic polymer 8.6 dispersion Demineralized water 4.1

Example 10: Preparation of a Bottom Layer Fluorinated Composition (FFF)

[0165] The composition is obtained by simply mixing together the different compounds. As-is, the composition can be stored for several days.

TABLE-US-00010 Compound Percentage by mass Aqueous PTFE dispersion 61.0 Metal flakes 0.2 25% carbon black solution 4.0 30% colloidal silica 5.0 PAI adhesive resin 15.0 Aqueous acrylic polymer 10.0 dispersion Demineralized water 4.8

Example 11: Preparation of a Surface Layer Fluorinated Composition (FFS)

[0166] The composition is obtained by simply mixing together the different compounds. As-is, the composition can be stored for several days.

TABLE-US-00011 Compound Percentage by mass Aqueous PTFE dispersion 85.0 Metal flakes 0.2 Aqueous acrylic polymer 10.0 dispersion Demineralized water 4.8

Example 12: Preparation of an Item Incorporating a Decorative Layer According to the Invention

[0167] An aluminum alloy disc is degreased and brushed in order to remove any greasy surface substances and oxides from the surfaces of the disc.

[0168] The decorative layer fluorinated composition (FFD3), prepared using pigment composition PG1, is applied to one of the surfaces of the disc by serigraphy.

[0169] After drying, the coated disc is baked at 415 C. for 7 minutes to obtain a disc comprising a single-layer fluorinated non-stick coating.

[0170] The disc is then stamped to produce a dome that is coated on its interior surface.

[0171] The coating obtained is green in color at room temperature (20 C.).

[0172] The coated dome is heated to 220 C.; a gradual color change of the coating, from the initial green color to a red color, is observed during heating.

[0173] The dome is allowed to cool to room temperature; a gradual color change of the coating, from the red color to the initial green color, is observed during cooling.

[0174] A series of 10 heating and cooling cycles is performed as described above; the coating displays the same changes in colorimetric properties each time.

Example 13: Preparation of an Item Incorporating a Decorative Layer According to the Invention

[0175] An aluminum alloy disc is degreased and brushed so as to remove any greasy surface substances and oxides from the surfaces of the disc.

[0176] The bottom layer fluorinated composition (FFF) is applied to one of the surfaces of the disc by serigraphy and then dried.

[0177] The decorative layer fluorinated composition (FFD1), prepared from pigment composition PG15, is applied by tampography to one part (circular imprint measuring 50 mm in diameter) of the surface of the disc coated with the bottom layer. The decorative layer is then dried.

[0178] The surface layer fluorinated composition (FFS) is then applied by serigraphy to the surface of the disc coated with the bottom layer and the decorative layer, and then dried.

[0179] The coated disc is baked at 415 C. for 7 minutes to obtain a disc comprising a multi-layer fluorinated non-stick coating. The disc is then stamped to produce a dome coated on its interior surface.

[0180] The coating obtained displays a decoration that is green in color at room temperature (20 C.) on a black background (corresponding to the bottom layer).

[0181] The coated dome is heated to 220 C.; a gradual color change of the decorative layer, from the initial green to a brown-green color, is observed during heating, while the colorimetric properties of the black background do not change.

[0182] The dome is allowed to cool to room temperature; a gradual color change of the decoration, from the brown-green color to the initial green color, is observed during cooling, while the colorimetric properties of the black background do not change.

[0183] A series of 10 heating and cooling cycles are performed as described above; the decoration displays the same changes in colorimetric properties each time.

Example 14: Preparation of an Item Incorporating a Decorative Layer According to the Invention

[0184] An aluminum alloy disc is degreased and brushed in order to remove any greasy surface substances and oxides from the surfaces of the disc.

[0185] The bottom layer fluorinated composition (FFF) is applied to one of the surfaces of the disc by serigraphy, and then dried.

[0186] The decorative layer fluorinated composition (FFD1), prepared from pigment composition PG16, is applied by tampography to one part (circular imprint measuring 50 mm in diameter) of the surface of the disc coated with the bottom layer. The decorative layer is then dried.

[0187] The surface layer fluorinated composition (FFS) is then applied by serigraphy to the surface of the disc coated with the bottom layer and the decorative layer, and then dried.

[0188] The coated disc is baked at 415 C. for 7 minutes to obtain a disc comprising a multi-layer fluorinated non-stick coating. The disc is then stamped to produce a dome that is coated on its interior surface.

[0189] The coating obtained displays a light-green-colored decoration at room temperature (20 C.) on a black background (corresponding to the bottom layer).

[0190] The coated dome is heated to 220 C.; a gradual color change of the decoration, from the initial light green color to a dark green color, is observed during heating, while the colorimetric properties of the black background do not change.

[0191] The dome is allowed to cool to room temperature; a gradual color change of the decoration, from the dark green color to the initial light green color, is observed during cooling, while the colorimetric properties of the black background do not change.

[0192] A series of 10 heating and cooling cycles is performed as described above; the decoration displays the same changes in colorimetric properties each time.

Example 15: Preparation of an Item Incorporating a Decoration Layer According to the Invention

[0193] An aluminum alloy disc is degreased and brushed so as to remove any greasy surface substances and oxides from the surfaces of the disc.

[0194] The bottom layer fluorinated composition (FFF) is applied to one of the surfaces of the disc by serigraphy, and then dried.

[0195] The decorative layer fluorinated composition (FFD2), prepared from pigment composition PG18, is applied by serigraphy to the surface of the disc coated with the bottom layer, to produce a checkerboard pattern of squares measuring 4 mm on a side. The decorative layer is then dried.

[0196] The surface layer fluorinated composition (FFS) is then applied by serigraphy to the surface of the disc coated with the bottom layer and the decorative layer, and then dried.

[0197] The coated disc is baked at 415 C. for 7 minutes to obtain a disc comprising a multi-layer fluorinated non-stick coating.

[0198] The disc is then stamped to produce a dome coated on its interior surface.

[0199] The coating obtained displays a decoration that is green in color at room temperature (20 C.) on a black background (corresponding to the bottom layer).

[0200] The coated dome is heated to 220 C.; a gradual color change of the decoration, from the initial green color to a red color, is observed during heating, while the colorimetric properties of the black background do not change.

[0201] The dome is allowed to cool to room temperature; a gradual color change of the decoration, from the red color to the initial green color, is observed during cooling, while the colorimetric properties of the black background do not change.

[0202] A series of 10 heating and cooling cycles is performed as described above; the decoration displays the same changes in colorimetric properties each time.

Example 16: Preparation of an Item Incorporating a Decorative Layer According to the Invention

[0203] A stainless steel dome is degreased and brushed so as to remove any greasy surface substances and oxides from the surfaces of the dome.

[0204] The decorative layer sol-gel composition (SGD2), prepared using pigment composition PG1, is applied by spray to the interior surface of the dome.

[0205] The decorative layer is then dried and baked for 15 minutes at 280 C.

[0206] The coating obtained is green in color at room temperature (20 C.). The coated come is heated to 220 C.; a gradual color change in the coating, from the initial green color to a red color, is observed during heating.

[0207] The dome is allowed to cool to room temperature; a gradual color change in the coating, from the red color to the initial green color, is observed during cooling.

[0208] A series of 10 heating and cooling cycles is performed as described above; the coating displays the same changes in colorimetric properties each time.

Example 17: Preparation of an Item Incorporating a Decorative Layer According to the Invention

[0209] An aluminum dome is degreased and brushed so as to remove any greasy surface substances or oxides from the surfaces of the dome.

[0210] The bottom layer sol-gel composition (SGF) is applied to the interior surface of the dome by spray, and then dried.

[0211] The decorative layer sol-gel composition (SGD1), prepared using pigment composition PG19, is applied by tampography to one part (circular imprint measuring 50 mm in diameter) of the surface of the disc coated with the bottom layer.

[0212] The surface layer sol-gel composition (SGS) is then applied by spray to the surface of the disc coated with the bottom layer and the decorative layer, and then dried and finally baked for 20 minutes at 280 C.

[0213] The coating obtained has a green-colored decoration at room temperature (20 C.) on a gray background (corresponding to the bottom layer).

[0214] The coated dome is heated to 220 C.; a gradual color change in the decoration, from the initial green color to a red color, is observed during heating, while the colorimetric properties of the gray background do not change.

[0215] The dome is allowed to cool to room temperature; a gradual color change of the decoration, from the red color to the initial green color, is observed during cooling, while the colorimetric properties of the gray background do not change.

[0216] A series of 10 heating and cooling cycles is performed as described above; the decoration displays the same changes in colorimetric properties each time.

Example 18: Preparation of an Item Incorporating a Decorative Layer According to the Prior Art

[0217] An aluminum alloy disc is degreased and brushed so as to remove any greasy surface substances and oxides from the surfaces of the disc.

[0218] The bottom layer fluorinated composition (FFF) is applied to one of the surfaces of the disc by serigraphy, and then dried.

[0219] A decorative layer composition is prepared by adding the compounds listed below to a grinder, and then grinding and stirring them.

TABLE-US-00012 Compound Percentage by mass Fe.sub.2O.sub.3 (hematite) 10.94 Demineralized water 24.80 Monopropylene glycol 64.26

[0220] The decorative layer composition is applied by tampography to one part (circular imprint measuring 50 mm in diameter) of the surface of the disc coated with the bottom layer. The decorative layer is then dried.

[0221] The surface layer fluorinated composition (FFS) is then applied by serigraphy to the surface of the disc coated with the bottom layer and the decorative layer, and then dried.

[0222] The coated disc is baked at 415 C. for 7 minutes to obtain a disc comprising a multi-layer fluorinated non-stick coating.

[0223] The disc is then stamped to produce a dome that is coated on its interior surface.

[0224] The coating obtained displays a decoration that is brown-red in color at room temperature (20 C.) on a black background (corresponding to the bottom layer).

[0225] The coated dome is heated to 220 C.; a gradual color change in the decoration, from the initial brown-red color to a slightly darker brown-red color, is observed during heating, while the colorimetric properties of the black background do not change.

[0226] The dome is allowed to cool to room temperature; a gradual color change in the decoration, from the slightly darker brown-red color to the initial brown-red color, is observed during cooling, while the colorimetric properties of the black background do not change.

[0227] Without a reference color, it is not possible to see that the hot temperature has been reached. It is therefore impossible to distinguish, at first glance, whether the frying pan is hot or cold, thus creating a safety problem.