Induction-Compatible Sol-Gel Coating

Abstract

The present invention relates to a sol-gel coating composition comprising conductive fillers, intended to make a culinary article compatible with induction.

Claims

1. A sol-gel coating composition comprising conductive fillers, for making a culinary article induction-compatible.

2. The composition according to claim 1, wherein the conductive fillers are ferromagnetic, diamagnetic or paramagnetic.

3. The composition according to claim 1, wherein the conductive fillers are selected from silver, copper, aluminum, iron, nickel, cobalt, stainless steel, carbon black and mixtures thereof.

4. The composition according to claim 1, wherein it comprises from 40 to 90% conductive fillers, percentages expressed by mass based on the total mass of the sol-gel coating composition.

5. The composition according to claim 1, wherein it comprises at least one sol-gel precursor selected from metal or metalloid alkoxylate type precursors and metal or metalloid polyalkoxylate type sol-gel precursors.

6. The composition according to claim 5, wherein the sol-gel precursor is selected from tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), methyltrimethoxysilane (MTMS) and mixtures thereof.

7. A sol-gel coating comprising at least one layer of the sol-gel coating composition according to claim 1.

8. A culinary article comprising a support coated with the sol-gel coating according to claim 7.

9. The culinary article according to claim 8, wherein said support is of inorganic material or of organic material.

10. The culinary article according to claim 8, wherein an outer face of the support of the article is coated with the sol-gel coating.

11. A process for manufacturing an induction-compatible culinary article comprising the following successive steps: (i) provide a support; (ii) apply to the support the sol-gel coating composition according to claim 1; (iii) apply a heat treatment at a temperature of 200 to 500° C.; (iv) obtain an article whose support is coated with a sol-gel coating.

12. Use of conductive fillers to prepare a sol-gel coating in order to make a culinary article induction-compatible.

13. The composition according to claim 4, wherein it comprises from 50 to 85% conductive fillers, percentages expressed by mass based on the total mass of the sol-gel coating composition.

14. The culinary article according to claim 9, wherein inorganic material is glass or ceramic and organic material is plastic.

15. The composition according to claim 1, wherein the conductive fillers are ferromagnetic, diamagnetic or paramagnetic, it comprises from 40 to 90% conductive fillers, percentages expressed by mass based on the total mass of the sol-gel coating composition and it comprises at least one sol-gel precursor selected from metal or metalloid alkoxylate type precursors and metal or metalloid polyalkoxylate type sol-gel precursors.

Description

DESCRIPTION OF THE FIGURES

[0135] FIG. 1 is a schematic cross-sectional representation of an example of an induction heating system. A container 1 containing water to be heated is placed on an induction cooktop. This cooktop comprises a glass-ceramic plate 4, induction coils 5 forming an electromagnet and an electrical power supply 6. In operation, the coils generate a magnetic field 3 which passes through the plate 4 and the bottom of the container 1. Depending on the material of the container 1, the latter becomes the seat of induced currents 2 causing it to heat up, and thus causes the water contained in the container 1 to heat up by thermal conduction.

EXAMPLES

Laser Granulometry Method

[0136] In the present description, including the accompanying claims, granulometry and particle size are measured by laser particle size analysis, for example using a Malvern MS2000 laser particle size analyzer.

[0137] The measurement is carried out in a suitable medium, either via a wet process (for example in an aqueous or solvent medium) or via a dry process. The light source consists of a class 1 laser, with a red He—Ne light emission source and a blue diode. The optical model is the Mie model and the computational matrix is of Mie type.

[0138] The apparatus is regularly calibrated with a standard sample (several different powders of monodisperse latex) whose particle size curve is known. It is necessary to know the refractive index of each material used in order to make the necessary corrections during the laser diffraction analysis.

[0139] The alignment of the laser and the cleanliness of the analysis chambers are checked before the measurements.

[0140] A background noise measurement is first performed: [0141] in the presence of water or solvent liquid for the wet process with a pump speed of 2000 rpm, an agitator speed of 800 rpm and a noise measurement over 10 s and in the absence of ultrasound; or [0142] in the presence of air for the dry process with a noise measurement over 10 s.

[0143] It is then verified that the light intensity of the laser is at least equal to 80%, and that a decreasing exponential curve is obtained for the background noise. If this is not the case, the lenses of the cell must be cleaned.

[0144] Then a first measurement on the sample is performed with the following parameters: [0145] wet process: pump speed of 2000 rpm, agitator speed of 800 rpm, no ultrasound, obscuration limit between 10 and 20%; [0146] dry process: obscuration limit between 10 and 20%.

[0147] The sample is introduced to obtain an obscuration slightly higher than 10%. After stabilization of the obscuration, the measurement is carried out in the presence of ultrasound (to avoid agglomerates) with a duration of 10 s (acquisition time of 10 000 diffraction images analyzed). In the particle size distribution curve obtained, it must be taken into account that a part of the powder population could be agglomerated.

[0148] Without emptying the cell, the measurement is repeated at least twice to check the stability of the result and the evacuation of any bubbles.

[0149] All measurements presented in the description and the specified ranges correspond to the average values obtained with ultrasound.

Products:

[0150] Sol-gel precursors: [0151] methyltriethoxysilane (MTES); [0152] tetraethoxysilane (TEOS); [0153] trimethylborate; [0154] Colloidal oxide: colloidal silica as a 40% aqueous solution of silica; [0155] Solvents: [0156] propan-2-ol; [0157] terpinol; [0158] butyl glycol; [0159] Acid: hydrochloric acid; [0160] Bases: [0161] KOH; [0162] NaOH; [0163] NH.sub.4OH; [0164] Rheology agents: [0165] urea modified acrylic copolymer; [0166] ethyl cellulose with a viscosity of 18-22 mPa.Math.s, measured for a 5% solution at 25° C. with an Ubbelohde viscometer; [0167] acrylic polymer with a molar mass of 2500-5000 g.Math.mol.sup.−1; [0168] Wetting agent: diol functionalized fluorinated polyether polymer; [0169] Water: distilled water; [0170] Conductive fillers: [0171] silver powder no. 1 with D10 of 0.64 μm, D50 of 1.5 μm and D90 of 3.0 μm and D100 of 7.0 μm; and BET surface area >0.5 m.sup.2/g; [0172] silver powder no. 2 with D10 of 0.97 μm, D50 of 3.03 μm, D90 of 7.62 μm and D100 of 25.43 μm; and BET surface area >0.5 m.sup.2/g; [0173] ferromagnetic powder with D10 of 1-3 μm, D50 of 4-6 μm, D90 of 8.5-12 μm and D100 of 15 μm; and BET surface area >0.5 m.sup.2/g; [0174] encapsulated aluminum with D10 of 2.0-6.0 μm, D50 of 7.0-11.0 μm, D90 of 12.0-17.0 μm and D100 of 15 μm; and BET surface area >0.5 m.sup.2/g; [0175] Filler: alumina Al.sub.2O.sub.3; [0176] Support: ceramic pottery; [0177] Silicone oil: food grade reactive silicone oil.

Compositions:

Example 1: Sol-Gel Coating Composition in Accordance with the Invention Comprising a Silver Powder (Acid Route)

[0178] A sol-gel coating composition in accordance with the invention was made in the proportions described in the following Table 1.

TABLE-US-00001 TABLE 1 Compounds mass % MTES 15-20 TEOS  5-10 Trimethylborate 0.1-6.sup.  Propan-2-ol 1-2 Terpineol 5-7 40% colloidal silica  5-10 Hydrochloric acid 0.2-0.4 Wetting additive 0.1-0.3 Silver Powder no. 1 60-80 Urea modified acrylic copolymer    2.7 TOTAL 100

[0179] To make this composition, the silanes, trimethylborate with water, acid and colloidal silica were reacted to obtain the binder of the screen-printable sol-gel coating composition in accordance with the invention. The reaction was quite rapid (a few minutes to 1 hour) depending on the amounts to be produced. It is advisable to work under an extractor hood and to use a cooling system for the reactor walls, as the reaction is exothermic.

[0180] After stabilization and cooling of this mixture, the conductive fillers (silver powder) and/or pigments and/or reinforcing fillers were added progressively under dispersion.

[0181] Then the other components of the composition (solvents, additives and surfactants) were incorporated. After a few hours of rest, the paste was used to be screen printed.

[0182] The paste was stored in a refrigerator or at room temperature to ensure maximum rheological stability for several days to weeks.

[0183] A sol-gel coating composition in accordance with the invention was obtained.

Example 2: Sol-Gel Coating Composition in Accordance with the Invention Comprising a Ferromagnetic Powder (Acid Route)

[0184] A sol-gel coating composition in accordance with the invention was made in the proportions described in the following Table 2.

TABLE-US-00002 TABLE 2 Components mass % MTES 20-40 TEOS 10-15 Propan-2-ol 1-2 Terpineol 5-7 40% colloidal silica  5-10 Hydrochloric acid 0.2-0.4 Wetting additive 0.1-0.3 Ferromagnetic powder 50-70 Ethyl cellulose  5-10 TOTAL 100

[0185] This sol-gel coating composition in accordance with the invention was obtained according to the protocol described in Example 1.

Example 3: Sol-Gel Coating Composition in Accordance with the Invention Comprising an Aluminum Powder (Acid Route)

[0186] A sol-gel coating composition in accordance with the invention was made in the proportions described in the following Table 3.

TABLE-US-00003 TABLE 3 Components mass % MTES 20-40 TEOS 10-15 Trimethylborate 0.1-6.sup.  Propan-2-ol 1-3 Butyl glycol 6-8 40% colloidal silica 15-20 Hydrochloric acid 0.1-0.5 Wetting additive 0.1-1.sup.  Reactive silicone oil 0.1-0.5 Al.sub.2O.sub.3 1-3 Encapsulated aluminum 50-70 Urea modified acrylic copolymer 1-5 TOTAL 100

[0187] This sol-gel coating composition in accordance with the invention was obtained according to the protocol described in Example 1.

Example 4: Sol-Gel Coating Composition in Accordance with the Invention Comprising a Silver Powder (Basic Route)

[0188] A sol-gel coating composition in accordance with the invention was made in the proportions described in the following Table 4.

TABLE-US-00004 TABLE 4 Components mass % MTES 15-20 TEOS  5-10 Trimethylborate 0.1-6.sup.  Propan-2-ol 1-2 Butyl glycol 5-7 KOH 1-2 NaOH 1-2 NH.sub.4OH 1-2 Wetting additive 0.1-0.3 Silver powder no. 2 60-80 Acrylic polymer 2-4 TOTAL 100

[0189] To make this composition, the silanes, trimethylborate, soda, potash and ammonia were weighed in a glass flask. Then these components were stirred for 12 h in a 25° C. water bath. After 12 h, the solution was translucent yellowish, demineralized water was added dropwise very slowly because there was a risk of heating the solution and creating “flakes”. Then the solution was cooled to 25° C., before filtering it, first on 8-12 μm filter paper and under vacuum, then on 5-8 μm filter paper.

[0190] The conductive fillers (silver powder) were added gradually under dispersion. Then the other components of the composition (solvents, additives and surfactants) were incorporated. The paste was stored in a refrigerator or at room temperature in order to guarantee a maximum rheological stability of several days or weeks.

[0191] A sol-gel coating composition in accordance with the invention was obtained.

Supports Coated with a Coating

[0192] The sol-gel coating composition of Example 1 was applied to a ceramic pottery support (pan type container) in order to obtain a support coated with a sol-gel coating in accordance with the invention according to the following protocol: [0193] first the container was cleaned, then heated to a temperature of 40 to 80° C.; [0194] a decorative colored sol-gel coating composition was sprayed on the entire outer face of the container (outer skirt and bottom), followed by a drying time of a few seconds, at a temperature of 80 to 120° C. This composition did not comprise conductive fillers and was not in accordance with the invention. This decorative sol-gel coating composition was made according to the proportions described in the following Table 5; [0195] then, the sol-gel coating composition of Example 1 was applied by brush in one or more layers until a thickness of 30 μm was obtained, followed by slow drying at a temperature of 80 to 120° C.; [0196] the curing step was carried out at about 250° C. starting with a temperature rise to 250° C. in 5 minutes, followed by holding the temperature for 10 minutes at 250° C. and then cooling in 5 minutes.

TABLE-US-00005 TABLE 5 Components mass % 40% colloidal silica 20-30 Water  5-10 Isopropanol 1-5 Butyl glycol 0.2-4.sup.  MTES 25-45 Trimethylborate 0-5 Formic acid  0.34 Black pigment 14.14 Alumina 12.51 Silicone oil 0.1-2.sup.  TOTAL 100   

[0197] A ceramic pottery pan coated on its outer bottom with the induction-compatible coating obtained by the application of the composition of Example 1 was obtained.

[0198] The resistivity of the sol-gel coating composition applied to the support was measured with a SOLEMS SQOHM-1 4-point multimeter. The calculated resistivity is 5.Math.10.sup.−6.

Tests

[0199] The induction heating performance of the ceramic pottery article with the bottom coated with the silver sol-gel composition of Example 1 was tested. The container was filled with 1 L of water and heated on an induction heating system. The results are shown in Table 6 below.

TABLE-US-00006 TABLE 6 Temperature Boiling time of Induction cooktop reached in 13 1 L of water to brand tested Power minutes reach 100° C. Brandt TI 126B 600 W 60° C. 15 minutes Miele KM 6114 450 W 47° C. 17 minutes