Non-stick coating with improved hydrophobic properties

Abstract

The present invention generally relates to anti-stick coatings for cooking utensils, which exhibit improved properties of hydrophobicity and resistance to high temperature. The present invention also relates to a culinary article comprising a support coated in said coating, and a process for applying on the support such a coating according to the invention.

Claims

1. An anti-stick top coating characterised in that it is in the form of a continuous film having an average thickness between 30 and 70 m and is constituted by a sol-gel material comprising: 30% to 50% by weight relative to the total weight of the coating of a matrix of at least one metallic polyalkoxylate forming a network; at least 5% by weight relative to the total weight of the coating of at least one colloidal metallic oxide dispersed in said matrix; and 0.1% to 6% by weight of at least one silicone oil, by total weight of the coating for the reconstitution, at temperature between 200 C. and 600 C., of hydrophobic groups of polyalkoxylate at the surface of said continuous film, wherein the silicone oil is selected from phenyl silicones, methylphenyl silicones, and methyl silicones with a molecular weight of at least 1000 g, which is non-reactive and has a viscosity of between 20 and 2000 mPa.Math.s.

2. The coating as claimed in claim 1, wherein the sol-gel material further comprises at least one filler and/or at least one pigment.

3. The coating as claimed in claim 2, wherein the pigment and/or the filler is in the form of flakes.

4. The coating as claimed in claim 2, wherein the pigment and/or the filler are of nanometric size.

5. The coating as claimed in claim 1, wherein the coating is free of PTFE.

6. The coating as claimed in claim 1, wherein the metallic polyalkoxylate is a polyalkoxysilane.

7. The coating as claimed in claim 6, wherein the polyalkoxysilane is amorphic.

8. The coating as claimed in claim 1, wherein metallic polyalkoxylate is an alum inate.

9. The coating as claimed in claim 1, wherein the sol-gel material comprises a mixed matrix of polyalkoxysilane and aluminate.

10. The coating as claimed in claim 1, wherein the matrix is grafted by at least one organic group selected from alkyl groups in C.sub.1-C.sub.4 and phenyl groups.

11. The coating as claimed in claim 10, wherein the organic group is a methyl group.

12. The coating as claimed in claim 1, wherein the colloidal metallic oxide is selected from the group consisting of silica, alumina, cerium oxide, zinc oxide, vanadium oxide and zirconium oxide.

13. The coating as claimed in claim 12, wherein the colloidal metallic oxide is colloidal silica.

14. The coating as claimed in claim 2, wherein the filler is selected from alumina, zirconium, mica, clays, and zirconium phosphate.

15. The coating as claimed in claim 2, wherein the pigment is selected from the group consisting of titanium dioxide, mixed oxides of copper-chrome-manganese, aluminosilicates, iron oxides, carbon black, pyralene red, metallic flakes and thermochromic pigments.

16. The coating as claimed in claim 1, wherein the silicone oil is a food-grade oil.

17. A culinary article having improved hydrophobic properties, comprising a support having an inner face capable of receiving foodstuffs and an outer face to be arranged towards a heat source, wherein the inner face is coated by an anti-stick top coating and the anti-stick top coating is a coating as defined by claim 16.

18. The culinary article as claimed in claim 17, wherein the support is a hollow cap having a base and a side wall rising from said base.

19. The culinary article as claimed in claim 17, wherein the support is made of a material selected from metals, wood, glass, ceramics, and plastics.

20. The culinary article as claimed in claim 19, wherein the support is a metallic support made of aluminium, anodised or not, or polished, brushed or beaded aluminium, or polished, brushed or beaded stainless steel, or cast, or hammered or polished copper.

21. The culinary article as claimed in claim 17, wherein the culinary article further comprises: a base anti-stick coating arranged on the inner face of the support, said base anti-stick coating being constituted by a sol-gel material comprising a matrix of at least one metallic polyalkoxylate and at least 5% by weight relative to the total weight of the base anti-stick coating of at least one colloidal metallic oxide a decor arranged on the base anti-stick coating, the decor being constituted by a sol-gel material comprising a matrix of at least one metallic polyalkoxylate and at least 5% by weight relative to the total weight of the decor of at least one colloidal metallic oxide, a decor arranged on the base anti-stick coating, the decor being constituted by a sol-gel material comprising a matrix of at least one metallic polyalkoxylate and at least 5% by weight relative to the total weight of the decor of at least one colloidal metallic oxide.

22. The culinary article as claimed in claim 21, wherein the sol-gel material of the decor further comprises at least one silicon oil.

23. The culinary article as claimed in claim 21, wherein the decor further comprises at least one reversible thermochromic chemical substance.

24. The culinary article as claimed in claim 21, wherein the decor comprises at least two patterns, one of the patterns including a thermochromic chemical substance that darkens with temperature and the other pattern including a chemical substance that lightens with temperature.

25. The culinary article as claimed in claim 24, wherein the chemical substance that darkens with temperature is ferric oxide Fe.sub.2O.sub.3 and the chemical substance that lightens with temperature is perlylene red associated with a black pigment.

26. The culinary article as claimed in claim 17, wherein the outer face of the support is coated with a base lacquer of one or more polyester silicon resins or a layer of enamel.

27. A process for coating the inner face of the support with the anti-stick top coating of claim 17, the process comprising: a) preparing an aqueous composition A comprising: i) 5 to 30% by weight relative to the total weight of the aqueous composition A of at least one colloidal metallic oxide, ii) 0 to 20% by weight relative to the weight of the composition A of a solvent comprising at least one alcohol, and iii) 0.05 to 3% by weight relative to the total weight of said aqueous composition A of at least one silicon oil; b) preparing a solution B comprising at least one precursor of metallic alkoxide type; c) mixing solution A and solution B to produce a sol-gel composition (A+B) with 40 to 75% by weight of aqueous composition relative to the weight of the sol-gel composition (A+B), such that the quantity of colloidal metallic oxide represents 5 to 30% weight of the sol-gel composition (A+B) in the dry state; d) applying to the support of at least one layer of the sol-gel composition (A+B) having a thickness between 30 and 70 m in the humid state; and e) cooking of said layer at a temperature of between 180 C. and 350 C. to obtain the anti-stick top coating having improved hydrophobic properties.

28. The process as claimed in claim 27, wherein the colloidal metallic oxide is selected from the group constituted by silica, alumina, cerium oxide, zinc oxide, vanadium oxide and zirconium oxide.

29. The process as claimed in claim 28, wherein the aqueous composition A comprises colloidal silica and/or colloidal alumina.

30. The process as claimed in claim 27, wherein the solvent of the composition A is an oxygen alcoholic solvent or an ether-alcohol.

31. The process as claimed in claim 27, wherein the precursor of metallic alkoxide type of the solution B is selected in the group constituted by: precursors corresponding to the general formula M.sub.1(OR.sub.1).sub.n, precursors corresponding to the general formula M.sub.2(OR.sub.2).sub.(n-1)R.sub.2, and precursors corresponding to the general formula M.sub.3(OR.sub.3).sub.(n-2)R.sub.3.sub.2, wherein R1, R2, R2, or R3 designating an alkyl group; R2 designating an alkyl or phenyl group; n is a whole number corresponding to the maximum valence of the metals M.sub.1, M.sub.2, or M.sub.3; and M.sub.1, M.sub.2, or M.sub.3 designating a metal selected from Si, Zr, Ti, Sn, Al, Ce, Nb, Hf, Mg, or Ln.

32. The process as claimed in claim 31, wherein the metallic alkoxide is an alkoxysilane.

33. The process as claimed in claim 32, wherein the alkoxysilane is methyltrimethoxysilane (MTMS) or tetraethoxysilane (TEOS).

34. The process as claimed in claim 32, wherein the solution B further comprises aluminium alkoxide.

35. The process as claimed in claim 27, wherein the acid of the solution B is formic acid or acetic acid.

36. The process as claimed in claim 27, wherein at least one layer of sol-gel composition (A+B) is applied during step d) to a structure having the form of a hollow cap of a culinary article and defining said support.

37. The process as claimed in claim 27, wherein the support is made of a material selected from metals, wood, glass, ceramics and plastics.

38. The process as claimed in claim 27, wherein the process further comprises: f) depositing a layer of enamel on the face opposite that coated with the base anti-stick coating, the step of depositing the layer of enamel being completed prior to that of anti-stick coating.

Description

DRAWINGS

(1) Other advantages and particular features of the present invention will emerge from the following description, given by way of non-limiting example and done in reference to the attached figures:

(2) FIG. 1 illustrates a schematic sectional view of a culinary article according to the invention according to a first variant embodiment,

(3) FIG. 2 illustrates a schematic sectional view of a culinary article support according to the invention according to a second variant embodiment,

(4) FIG. 3 illustrates a schematic sectional view of a culinary article support according to the invention according to a third variant embodiment,

(5) FIG. 4 illustrates a schematic sectional view of a culinary article support according to the invention according to a fourth variant embodiment,

(6) FIG. 5 illustrates a schematic sectional view of a culinary article support according to the invention according to a fifth variant embodiment,

(7) FIG. 6 illustrates a schematic sectional view of a culinary article support according to the invention according to a sixth variant embodiment.

DETAILED DESCRIPTION

(8) Identical elements represented in FIGS. 1 to 6 are identified by identical reference numerals.

(9) By way of example of a culinary article according to the invention, FIG. 1 illustrates a skillet 1 comprising a support 3 in the form of a hollow cap with a base 34 and a side wall 35 rising from the base 34, and a gripping handle 6. The support 3 comprises an inner face 31 capable of accommodating foodstuffs, and an outer face 32 intended to be arranged to the side of the heat source, such as a cooking plate or a burner.

(10) FIGS. 2 to 6 illustrate only the support 3 of the culinary article (or more exactly its base 34).

(11) In FIGS. 1 to 3, the inner face 31 of the support 3 is covered by an anti-stick coating according to the invention 2, called the base coating.

(12) In the variants illustrated in FIGS. 2 and 3, a layer of dcor 4 covers the base coating 2 and is constituted by a sol-gel material comprising a matrix of at least one metallic polyalkoxylate at least 5% by weight relative to the total weight of the decor of at least one colloidal metallic oxide and at least one silicon oil.

(13) More particularly, in the variant illustrated in FIG. 3 a second anti-stick coating 5, known as surface coating, covers the layer of dcor 4. This anti-stick surface coating 5 is an anti-stick coating 5 according to the invention.

(14) The variant illustrated in FIG. 4 differs from that illustrated in FIG. 3 in that the dcor 40 is constituted by a sol-gel material not comprising silicon oil. In fact, the dcor 40 is constituted by a sol-gel material comprising a matrix of at least one metallic polyalkoxylate and at least 5% by weight relative to the total weight of the decor of at least one colloidal metallic oxide.

(15) The variant illustrated in FIG. 5 differs from that illustrated in FIG. 4 in that the base anti-stick coating 20 covering the inner surface 31 of the support 3 does not comprise silicon oil either. In fact, this is a base coating 20 constituted by a sol-gel material comprising a matrix of at least one metallic polyalkoxylate and at least 5% by weight relative to the total weight of the anti-stick surface coating of at least one colloidal metallic oxide.

(16) The variant illustrated in FIG. 6 differs from that illustrated in FIG. 5, in that the dcor 4 is constituted by a sol-gel material comprising silicon oil, that is, a layer of dcor 4 according to that of the variant illustrated in FIG. 3.

(17) For the six variant embodiments, the layers of dcor 4, 40 can be continuous layers partially covering the base layer 2, 20, or discontinuous layers, for example in the form of points or elementary patterns.

(18) The dcor 4 preferably comprises a reversible thermochromic chemical substance, said decor partially covering said anti-stick coating 2.

(19) The chemical thermochromic substance mentioned hereinabove can be selected from those which lighten with a rise in temperature. This applies to perlylene red associated with a black pigment. The chemical substance can also be selected from those which darken with temperature. This applies to ferric oxide Fe.sub.2O.sub.3.

(20) Advantageously, the decor can comprise at least two patterns, one of the patterns including a chemical substance which lightens with temperature, such as for example perlylene red associated with a black pigment, and the other pattern including a chemical substance which darkens with a rise in temperature, for example ferric oxide Fe.sub.2O.sub.3.

(21) So, the contrast between the two pigments better distinguishes the change in temperature. If the chemical compounds hereinabove are used in each of the patterns of the decor (a pattern comprising ferric oxide Fe.sub.2O.sub.3 and the other pattern comprising perlylene red associated with a black pigment), a very marked contrast between the two patterns from 200 C. is observed, that is, the optimal temperature for frying or roasting.

(22) In a particularly advantageous version of this embodiment, the base anti-stick coating comprises fillers and/or pigments not optically transparent, and the anti-stick surface coating comprises neither fillers nor pigments or else comprises optically transparent fillers and/or pigments, and the decor comprises a thermostable binder resisting at least 200 C. and a reversible chemical thermochromic substance.

(23) The combined advantages of such an article are at the same time hydrophobic, even after contact with flame, and being able to inform a user of the temperature of the cooking surface of a culinary article.

(24) In fact, given that the upper layer of anti-stick coating according to the invention is transparent, the change in colour of the thermochromic substance of the decor is visible through the upper layer of anti-stick coating.

(25) The change in colour described hereinabove allows the user to be warned on the one hand that the culinary article is hot, and therefore presents the risk of burning, and on the other hand that the surface of the article has reached the right temperature for use.

(26) The outer face of the culinary article, opposite the inner face intended to receive the foodstuffs, can also be coated by an anti-stick coating according to the invention, pigmented or not, or by a lacquer base of one or more polyester silicon resins, or by enamel, or any other flame-resistant coating.

(27) The following examples illustrate the invention without limiting its scope.

(28) In the examples, unless indicated otherwise, all quantities are given in grams.

EXAMPLES

Products

(29) Aqueous Composition A

(30) Colloidal Metallic Oxide colloidal silica in the form of aqueous solution at 30% of silica, marketed by the company Clariant under the brand name Klebosol, colloidal silica in the form of aqueous solution at 30% silica, marketed by the company Grace Davison under the brand name Ludox, colloidal alumina in the form of aqueous solution at 5% marketed by the company DGTec.

(31) Solvent methanol, ethanol, Isopropanol, 2-(2-Butoxyethoxy)ethanol (Butylcarbitol).

(32) Silicon Oil Food-grade methyl silicon oil marketed by the company DOW CORNING under the brand name DOW CORNING 200 Fluid, and having a viscosity of 300 cSt, food-grade methyl silicon oil marketed by the company TEGO under the brand name TEGO ZV 9207.

(33) Pigments black pigment mineral marketed by the company Ferro under the brand name FA 1260, black pigment mineral marketed by the company Ferro under the brand name FA 1220, ultramarine pigment marketed by the company Holliday pigments, under the brand name CM13, red perlylene pigment marketed by BASF, titanium dioxide white pigment marketed by the company Kronos.

(34) Fillers Powdered alumina marketed by the company ALCAN under the brand name CAHPF 1000, Alumina in nanometric flakes dispersed in aqueous phase at 40% marketed by the company Baikowski, Powdered alumina is marketed by the company Baikowski under the brand name DF 1000, Zirconium phosphate (ZrP) marketed by the company Rhodia, Clay of BENTONITE SE3010 type marketed by the company Sd Chemie.

(35) Solution B

(36) Precursors methyltrimethoxysilane (MTMS) responding to the formula Si(OCH.sub.3).sub.3CH.sub.3, tetraethoxysilane (TEOS) responding to the formula Si(OC.sub.2H.sub.5).sub.4.

(37) Acid formic acid, acetic acid.

(38) Tests hardness evaluated with a Mohs scale: the coating is subjected to the action of materials of different hardness representing the levels of the Mohs hardness scale. The hardness of the coating is expressed by the highest value of the material not representing it. anti-adherence evaluated by means of the carbonised milk test according to the standard NF D 21-511. flame resistance: the coating is subjected to the action of a Bnsen burner flame for 30 seconds, cooled by soaking in cold water, then the contact angle is measured. hydrophobicity: measurement of the contact angle of a drop of water on the coating with a goniometer of Digidrop type by GBX.

Example 1

Preparation of an Aqueous Composition A1, According to the Invention

(39) A first aqueous composition A1 is made according to the invention, which is presented in Table 1:

(40) TABLE-US-00001 TABLE 1 Constituents of part A Quantity aqueous solution at 30% colloidal silica: 37 Ludox Water 14.1 Methanol 5.3 Butylcarbitol 1.8 Black pigment FA 1260 26.4 Alumina CAHPF 1000 13.2 Silicon oil TEGO ZV 9207 2.2 TOTAL 100

Example 2

Preparation of an Aqueous Composition A2 According to the Invention

(41) A second aqueous composition A2 is made according to the invention, which is presented in Table 2:

(42) TABLE-US-00002 TABLE 2 Constituents of part A Quantity aqueous solution at 30% colloidal silica: 48.5 Klebosol Water 6 Isopropanol 8 Black pigment FA 1220 35 Silicon oil Wacker 200 fluid 2.5 TOTAL 100

Example 3

Preparation of an Aqueous Control Composition A3 without Silicon Oil

(43) A first aqueous control composition A3 made without silicon oil. This composition is presented in Table 3:

(44) TABLE-US-00003 TABLE 3 Constituents of part A Quantity aqueous solution at 30% colloidal silica: 37.83 Ludox Water 14.42 Methanol 5.42 Butylcarbitol 1.84 Black pigment FA 1260 27 Alumina CAHPF 1000 13.49 TOTAL 100

Example 4

Preparation of an Aqueous Control Composition A4 without Silicon Oil

(45) A second aqueous control composition A4 without silicon oil is produced, presented in Table 4:

(46) TABLE-US-00004 TABLE 4 Constituents of part A Quantity aqueous solution at 30% colloidal silica: 49.74 Klebosol Water 6.16 Isopropanol 8.20 Black pigment FA 1220 35.9 TOTAL 100

Example 5

Preparation of an Aqueous Composition A5 Incorporating Colloidal Alumina

(47) An aqueous composition A5 is produced, which is presented in Table 5:

(48) TABLE-US-00005 TABLE 5 Constituents of part A Quantity aqueous solution at 38% colloidal alumina: 30 Baikowski Water 22.5 Isopropanol 17.1 Black pigment FA 1220 20 Alumina powder CAHPF 1000 9 Silicon oil DOW 200 fluid 1.4 TOTAL 100

Example 6

Preparation of a Solution B1 Based on MTMS

(49) A first solution B1 is made according to the invention by mixing 99.6 g of MTMS with 0.4 g of formic acid, giving a solution at 0.4% by weight of acid in the MTMS.

Example 7

Preparation of a Solution B2 Based on MTMS

(50) A second solution B2 is made according to the invention by mixing 59.7 g of MTMS with 0.3 g of acetic acid, giving a solution at 0.5% by weight of acid in the MTMS.

Example 8

Preparation of a Solution B3 Based on MTMS and TEOS

(51) A third solution B3 is made according to the invention by mixing 50 g of MTMS, 9.5 g of TEOS, and 0.5 g of acetic acid to produce a solution at 0.83% by weight of acid in the mixture of silanes.

Example 9

Preparation of a Sol-Gel Composition SG1 According to the Invention

(52) A sol-gel composition SG1 is made according to the invention by adding 100 g of aqueous composition A1 according to the invention to 100 g of solution B1. This is mixed in a planetary mixer for an hour by being kept at a temperature under 60 C., on completion of which a sol-gel composition according to the invention is obtained which is kept at ambient temperature. The composition SG1 is applied 48 hours after mixing.

Example 10

Preparation of a Sol-Gel Composition SG2 According to the Invention

(53) A sol-gel composition SG2 is made according to the invention by adding 100 g of aqueous composition A2 according to the invention to 60 g of solution B2. The A2 and B2 mixture is mixed in a planetary mixer for an hour at a temperature kept under 60 C., on completion of which a sol-gel composition according to the invention is obtained which is kept at ambient temperature. The composition SG2 is applied 48 hours after mixing.

Example 11

Preparation of a Sol-Gel Control Composition SG0I

(54) A sol-gel composition SG01 is made according to the invention by adding 100 g of aqueous composition A3 according to the invention to 100 g of solution B1. This is mixed in a planetary mixer for an hour by being kept at a temperature under 60 C., on completion of which a sol-gel composition according to the invention is obtained which is kept at ambient temperature. The composition SG0I is applied 48 hours after mixing.

Example 12

Preparation of a Sol-Gel Control Composition SG02

(55) A sol-gel composition SG02 is made according to the invention by adding 100 g of aqueous composition A4 according to the invention to 60 g of solution B2. This is mixed in a planetary mixer for an hour by being kept at a temperature under 60 C., on completion of which a sol-gel composition according to the invention is obtained which is kept at ambient temperature. The composition SG02 is applied 48 hours after mixing.

Example 13

Preparation of an Aqueous Composition SG3 According to the Invention

(56) A sol-gel composition SG3 is made according to the invention by adding 100 g of aqueous composition A2 according to the invention to 60 g of solution B3. This is mixed in a planetary mixer for an hour by being kept at a temperature under 60 C., on completion of which a sol-gel composition according to the invention is obtained which is kept at ambient temperature. The composition SG3 is applied 30 hours after mixing.

Example 14

Preparation of an Aqueous Composition SG4 According to the Invention

(57) A sol-gel composition SG4 is made according to the invention by adding 100 g of aqueous composition A5 according to the invention to 100 g of solution B2. This is mixed in a planetary mixer for an hour by being kept at a temperature under 60 C., on completion of which a sol-gel composition according to the invention is obtained which is kept at ambient temperature. The composition SG4 is applied 24 hours after mixing.

(58) The sol-gel compositions SG1 to SG4 of the invention, as well as the sol-gel control compositions SG01 and SG02 are listed in Table 6 hereinbelow.

(59) TABLE-US-00006 TABLE 6 Sol-gel compositions (A + B) Composition A Solution B SG01 (control) A3 B1 SG02 (control) A4 B2 SG1 A1 B1 SG2 A2 B2 SG3 A2 B3 SG4 A5 B2

Example 15

Producing Sol-Gel Coatings on an Aluminium Support

(60) It is applied by pistol to a blasted or sanded aluminium support to form the sol-gel compositions of examples 1 to 14, according to the following cycle: application to the support of a layer of sol-gel composition (A+B) with a humid thickness of 40 to 70 microns, drying for 3 minutes at 80 C., and cooling to ambient temperature.

(61) It is possible to apply this cycle a several times, the number of cycles being determined by the final preferred thickness.

(62) On completion of the application/drying cycle(s), there is baking for 18 minutes at 280 C. This produces a coating having a dry thickness of between 30 and 70 microns, which is smooth, black and shiny.

(63) The anti-stick coatings according to the invention R1 to R4 are the coatings obtained from sol-gel compositions according to the invention SG1 to SG4 respectively.

(64) The anti-stick control coatings R01 and R02 are coatings obtained from sol-gel control compositions SG01 and SG02 respectively.

(65) The properties of the different coatings obtained by application of each of the sol-gel compositions of examples 1 to 14 are listed in Table 7 hereinbelow.

(66) TABLE-US-00007 TABLE 7 Initial Contact Thickness contact angle after Antiadhesive Application (dry state) Hardness Antiadherence angle reconstitution coating cycles (m) (Moh) (points) () () R01 2 50 3-4 25 75 63 (control) R02 2 50 3-4 25 73 62 (control) R1 2 50 3-4 100 93 77 R2 2 50 3-4 100 96 79 R3 1 30 3 100 93 75 R4 2 70 4 100 94 76

(67) The coatings R1 to R4 according to the invention exhibit hardness of between 3 and 4 Mohs, excellent antiadherence (100 points on the carbonised milk test: standard NF D 21-511), and good flame resistance (no change in appearance after 30 seconds in direct contact with the flame of the Bnsen burner). The contact angle of a drop of water on the coatings R1 to R4 is respectively at 93 and 96 (before flame contact).

(68) A drop in hydrophobicity just after flame contact of the film (despite the unchanged appearance) is observed for the coatings R1 to R4: the contact angle becomes less than 30. But on completion of the reconstitution process (at least 5 minutes at 200 C.), angles greater than 75 for the coatings R1 to R4 are observed.

(69) Comparatively, the control coatings R01 and R02 exhibit, for equivalent hardness (between 3 and 4 Mohs), slight antiadherence (25 points on the carbonised milk test). Also, the static contact angle of a drop of water on these control coatings is of the order of 73-75 before flame contact. After flame contact, the angles of contact are slighter than those obtained with the coatings according to the invention (62-63 in place of 75-79).