Method of manufacturing a heating article provided with a sol-gel coating

Abstract

A method of manufacturing an item, notably a culinary item, includes: providing a support in the form of a preform; preparing a sol-gel composition; hydrolyzing the sol-gel precursor, followed by a condensation reaction; applying onto at least one support surface of the preform at least one layer of the sol-gel composition to form a sol-gel coating layer; and thermally treating the sol-gel coating layer to solidify the coating layer. Further, before thermally treating the sol-gel coating, the method includes pre-densifying the coated preform and stamping the preform to produce a final form of the culinary item.

Claims

1. Method of producing a heating item, comprising the following steps: a) providing a support in the form of a preform with at least two opposite surfaces; b) preparing a sol-gel composition comprising at least one metal-alkoxide sol-gel precursor; c) hydrolyzing said sol-gel precursor in the presence of water and an acid or base catalyst, followed by a condensation reaction; d) applying onto at least one support surface of the preform at least one layer of said sol-gel composition of a thickness ranging from 5 to 120 m, to form a sol-gel coating layer; followed by e) thermally treating to solidify said sol-gel coating layer to provide a coated preform; wherein, between step d) of applying the sol-gel composition onto at least one of the preform surfaces and step e) for thermally treating for solidification, the method includes two successive steps of: d) pre-densifying the coated preform to produce a sol-gel coating layer with a pencil hardness ranging from 4B to 4H; followed by d) stamping of said preform to produce a final form of a culinary item, with an interior surface intended to receive food and an exterior surface intended to come into contact with a heat source.

2. Method as in claim 1, in which the pre-densifying step comprises drying at a temperature ranging between 20 C. and 150 C.

3. Method as in claim 1, in which the sol-gel precursor of the sol-gel composition takes the general formula (1):
RnM(OR)(4n),(1) where: R represents an alkyl or phenyl group, R represents an alkyl group, M represents a metal or non-metal selected from Si, Zr, Ti, Al, V, Ce, or La, and n is between 0 and 3.

4. Method as in claim 3, in which the sol-gel precursor of general formula (1) is an alkoxysilane.

5. Method as in claim 3, in which the sol-gel composition further comprises at least one metal alkoxide with a non-hydrolyzable function.

6. Method as in claim 5, in which the non-hydrolyzable function is an alkyl or phenyl group.

7. Method as in claim 6, in which the alkyl group of the non-hydrolyzable function or the alkyl group R of Formula (1) consists of one of an ethylenic double bond, amine function or epoxide function.

8. Method as in claim 7, in which the alkyl group is one of a group selected from aminopropyl, methacryloxypropyl, or glycidoxypropyl.

9. Method as in claim 6, in which the alkyl group is a methyl group.

10. Method as in claim 1, in which the sol-gel composition further comprises at least one organic or inorganic load.

11. Method as in claim 10, in which said load is an organic polymer load, selected from powdered PTFE, silicone beads, silicone resin, linear or tri-dimensional polysilsesquioxanes, powdered polyethylene sulfide (PES), powdered poly ether ketone (PEEK), powdered polyphenylene sulfide (PPS), or perfluoro(propyl vinyl ether) (PFA), powdered fluorinated ethylene propylene (FEP), powdered polyurethane and mixtures thereof.

12. Method as in claim 10, in which said load is a lubricating inorganic charge.

13. Method as in claim 12, in which said inorganic load is one of boron nitride, molybdenum sulfide, or graphite.

14. Method as in claim 1, in which the support is a metal support selected from aluminum, steel, stainless steel, copper, titanium, or multiple layers of said metals.

15. Method as in claim 1, in which the preform is a flat support.

16. Method as in claim 15, in which the step of applying the sol-gel composition to one of the preform surfaces is carried out by one of screen printing, roller, ink jet, powder coating or curtain coating.

17. Method as in claim 1, wherein the thermally treating step e) is a cooking treatment conducted at a temperature ranging between 150 C. and 350 C.

18. Method according claim 1, which furthermore comprises, prior to step d) of applying the sol-gel composition onto at least one of the preform surfaces, a step a) of treating a surface destined to be coated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages and particularities of the present invention will emerge from the following description, provided by way of example and therefore non-limiting, and referencing the examples in the annexed corresponding figures, where:

(2) FIG. 1 is a schematic cross-sectional view of a standard hydraulic press in various stages of stamping a preform;

(3) FIG. 2 is an illustration of the Erichsen test used in the examples;

(4) FIG. 3 is an illustration of the Swift test used in the examples; and

(5) FIG. 4 is an illustration of the pencil hardness test used in the examples.

DETAILED DESCRIPTION OF THE INVENTION

(6) Identical elements represented in FIGS. 1 through 3 are identified by the same reference numbers.

(7) The invention is illustrated in detail in the following examples.

(8) In these examples, except as indicated, all percentages and proportions are expressed by weight.

EXAMPLES

(9) Products

(10) Supports: Flat Aluminum supports

(11) Compositions:

(12) SG1 black sol-gel composition (for screen printing) using MTES and TEOS.

(13) The composition of SG1 is provided in Table 1 below:

(14) TABLE-US-00001 Components Mass fraction MTES 38.5 TEOS 13.3 Propan-2-ol 1.9 Terpineol 8.5 Colloidal silica 40% 22.2 Hydrochloric acid 0.4 Wetting agent 0.9 Reactive silicone oil 0.9 Black pigment (iron oxide) 7.7 Inorganic load: aluminum 0.9 Stainless steel beads 2.1 Cellulosic rheology additive (Dow 2.7 Ethocel STD 20) TOTAL 100

(15) Copper-colored sol-gel composition SG2 using MTES and TEOS and a phenyl silane (for screen printing application)

(16) The composition of SG2 is provided in Table 2 below:

(17) TABLE-US-00002 Components Mass fraction MTES 35.5 TEOS 10.3 Phenylsilane 5 Propan-2-ol 1.9 Terpineol 8.5 Colloidal silica 40% 22.2 Hydrochloric acid 0.4 Wetting agent 0.9 Reactive silicone oil 0.9 Copper-plated mica-titanium flakes 4.5 Inorganic load: alumina 0.4 Stainless steel beads 4.4 Cellulosic rheology additive (Dow 2.6 Ethocel STD 20) TOTAL 100

(18) Copper-colored sol-gel composition SG3 using MTES and TEOS and spherical loads (for physical reinforcement) (for screen printing application)

(19) The composition of SG3 is provided in Table 3 below:

(20) TABLE-US-00003 Components Mass fraction MTES 38.5 TEOS 13.3 Propan-2-ol 1.9 Terpineol 8.5 Colloidal silica 40% 22.2 Hydrochloric acid 0.4 Wetting agent 0.9 Reactive silicone oil 0.9 Black pigment (iron oxide) 7.7 Organic load: polysilsesquioxanes 0.5 Inorganic load: alumina 0.4 Stainless steel beads 2.1 Cellulosic rheology additive (Dow 2.7 Ethocel STD 20) TOTAL 100

(21) Colorless finishing sol-gel composition SF1 using MTES and TEOS (for screen printing application)

(22) The composition of SF1 is provided in Table 4 below:

(23) TABLE-US-00004 Components Mass fraction MTES 45.5 TEOS 17.1 Propan-2-ol 1.9 Terpineol 8.5 Colloidal silica 40% 22.2 Hydrochloric acid 0.4 Wetting agent 0.9 Reactive silicone oil 0.9 Cellulosic rheology additive (Dow 2.6 Ethocel STD 20) TOTAL 100

(24) Sol-gel composition SG4 using MTES only (for powder coating application)

(25) The composition of SG4 is provided in Table 5 below:

(26) TABLE-US-00005 Components Solution Mass fraction 30% Colloidal silica in water A 27 Distilled water A 7 Isopropyl alcohol A 5 Butyl glycol A 3 Black pigment FA1220 A 12 Alumina A 8.3 Fluorosurfactant A 2 Powdered PTFE A 3 MTES B 32.2 Formic acid B 0.5 TOTAL 100

(27) Colorless finishing sol-gel composition SF2 using MTES only (for powder coating application)

(28) The composition of SF2 is provided in Table 6 below:

(29) TABLE-US-00006 Components Solution Mass fraction 30% Colloidal silica in water A 27.5 Distilled water A 10 Isopropyl alcohol A 5 Butyl glycol A 9 MTES B 35.1 TEOS B 13 Formic acid B 0.4 TOTAL 100

(30) Tests

(31) Erichsen Test:

(32) This test consists of stamping aluminum blanks (2) clamped between a sheet holder (12) and a die (11) onto a punch (10) with a spherical cap, as illustrated in FIG. 2.

(33) In the context of the present invention, the Erichsen test consists of conducting tests at varying depths (H) of the punch (10). At the conclusion of each test, the behavior of the sol-gel coating is evaluated.

(34) The maximum penetration depth varies in relation to the thickness (a) of the aluminum blank as there should be no necking of the metal.

(35) For our tests, we will evaluate the sol-gel coatings at the following Erichsen depths: 3, 5, 7 and 9 mm, always using the same aluminum blanks (Nuance 3003 alloy, 2.4 mm thickness) sandblasted and degreased.

(36) Swift Test:

(37) This test consists of stamping a cylindrical well in a single pass. Typically, the punch (10) has a diameter of 33 mm and the pressure applied by the sheet holder (12) is adjusted to prevent creasing when the blank (2) is held in place as shown in FIG. 3.

(38) The diameter of the die (11) varies in relation to the sheet thickness (a) and the desired draw ratio, as shown in Table 7 below.

(39) TABLE-US-00007 % Draw Die diameter in mm 0 33 + 2a 5 33 + 2 0.95a 10 33 + 2 0.90a 15 33 + 2 0.85a

(40) The Swift test consists of evaluating the behavior of the sol-gel coating after aluminum plates are stamped using the device illustrated in FIG. 3 under the following conditions: 0%, 5% et 10% drawing. The aluminum plates used are the same as those used for the Erichsen test.

(41) Pencil Hardness According to ISO Standard 15184 (Wolf Wilburn):

(42) The intended objective of this destructive standardized hardness test is to determine the resistance of the sol-gel coating to superficial scratching. The test provides a quick measurement that makes it possible to verify that the underlying conditions (time-temperature parameters) are suitable.

(43) In the context of the present invention, this test was adapted and used to quantify the surface hardness of the sol-gel coating layer just after the pre-densification step d) and before the stamping operation d).

(44) The quantification of hardness is correlated to the physical condition of the coating after densification (macro and microscopic observation). The quantification of hardness after pre-densification makes it possible to rule out many of the pre-densification techniques that could be used in the context of the present invention (drying in a heat chamber, with UV, IR, plasma or even prolonged drying at ambient temperature)

(45) The principle of the test is to apply, using a pencil of a given hardness (cf. table below) positioned inside a mobile device (as illustrated in FIG. 4), a fixed pressure of 7.5N at a fixed angle of 45 degrees, to the surface to be tested.

(46) The surface of the coating to be tested must be smooth. The first test is performed with a pencil of average hardness, 2H for example, and the coating is then examined (for penetration and damage). If the tested coating is intact after the initial test, the test must be conducted again using a pencil with a greater hardness value following the scale shown below.

(47) The test must be repeated with different leads, until the two pencils with successive hardness values on either side of the threshold are identified: the one that damages the coating and the other that does not damage the coating.

(48) The value recorded in the following table of results is that which produced a scratch on the tested surface. Pencil hardness was evaluated against the following scale:

(49) TABLE-US-00008 9H very hard (or dry) lead 8H 7H 6H 5H hard lead 4H 3H 2H H F HB lead of average hardness B 2B 3B 4B 5B 6B 7B 8B 9B very soft (or greasy) lead

Example 1

(50) Preparation and Application by Screen Printing of One Layer of the Sol-Gel Composition SG1, SG2 or SG3, onto which may Optionally be Applied a Colorless Finishing Layer SF1.

(51) The sol-gel compositions SG1, SG2, SG3 and SF1 are prepared as follows: reaction of silanes with water, acid, and colloidal silica, to obtain the bonding agent of the screen printable sol-gel coating according to the invention (the reaction is quite rapid, taking as little as several minutes up to one hour according to the quantity of the composition being produced) after the stabilization and cooling of the resulting sol-gel bonding agent, pigments and loads are progressively added under dispersion conditions; then, the various additives and surfactants are incorporated; after a few hours of maturing, the paste is ready to be screen printed; the paste may be stored in a refrigerator or at ambient temperature to preserve maximal rheological stability for several days to weeks.

(52) The coating is applied by screen printing in at least one layer of a thickness ranging from 2 to 40 microns. Multiple layers may be applied in succession onto one of the surfaces of the aluminum plate, with an optional drying between each layer.

(53) Optionally, a layer of the translucent sol-gel finishing composition SF1 may be applied onto the one or more layers of the pigmented sol-gel coating composition SG1, SG2 or SG3 described above.

(54) Optionally, a functional or non-functional decoration may also be incorporated between the pigmented sol-gel SG1, SG2 or SG3 layer and the finishing layer SF1.

(55) To add the decoration between these layers, a decoration in the form of at least one discontinuous layer consisting of at least one optically opaque chemical substance onto the first pigmented sol-gel coating layer.

(56) Among the optically opaque chemical substances that may be used for the decoration layer according to the invention, are notably thermostable pigments, thermochromatic pigments, flakes and mixtures thereof. Decoration pastes may be formulated with alkoxysilane binders (referred to as decorative sol-gel pastes), or binders such as silicone resins, polyesters, silicone-polyesters, acrylics, or even with no particular binders.

(57) The one or more decoration layers may, for example, be applied by pad printing, powder coating, screen printing, roller printing or ink jet.

Example 2

(58) Preparation and Screen-Printing of One Layer of the Sol-Gel Composition SG4, onto which may be Optionally Applied a Colorless Finishing Layer SF2.

(59) Sol-gel compositions SG4 and SF2 are prepared as follows: Solution A is prepared by successively introducing the colloidal load (alumina or silica), water, an alcohol (to improve compatibility between parts A and B) and the one or more pigments or loads into a planetary mixer to disperse the pigment and obtain a homogenous paste; Solution B is separately prepared by mixing the one or more silanes with an organic acid (acetic acid, formic acid, etc.) or base (soda, potash, etc.) to reduce the reactivity of the silane. The content in acid or base ranges from 0.1 to 10% of the mixture by weight. Higher levels are advantageous for extending the pot life of the mixture. Solutions A and B may be stored separately in this form for more than six months; Solutions A and B are then combined in a mixer to produce an intimate mixture and a hydrolysis reaction. While the mixing process itself may be completed quickly, the mixture must be left to mature for at least 12 hours before being applied onto the support. The pot life of the mixture is at least 48 hours.

(60) The coating is applied in at least one layer of a thickness ranging from 2 to 40 microns by powder coating onto one of the surfaces of the aluminum plate. Multiple layers may be applied in succession, with an optional drying between each layer.

(61) Optionally, a layer of the translucent sol-gel finishing composition SF2 may be applied onto the one or more layers of the pigmented sol-gel coating composition SG4 described above. Optionally, a functional or non-functional decoration may also be incorporated between the pigmented sol-gel SG4 layer and the finishing layer SF2, in the same manner described in Example 1.

Example 3

(62) Testing of the Sol-Gel Coatings in Examples 1 and 2

(63) The properties of the various coatings obtained through tests of each sol-gel coating from Examples 1 (screen printing) and 2 (powder coating) are summarized in Table 8 below.

(64) According to our tests, the approximate range of pencil hardness for a stamping operation falls between 4B to 4H, and preferably between 2B to 2H.

(65) These results show that by controlling the pre-densification conditions of the sol-gel coating (prior to stamping), encouraging results can be achieved in terms of stampability. Furthermore, it is even possible to improve the formability of our system by adding flexible loads to serve as stress buffers. It is therefore possible to obtain stampable sol-gel coatings, with all of the aforementioned industrial and decorative advantages.

(66) TABLE-US-00009 Drying Pencil Erichsen Erichsen Erichsen Erichsen Swift 0% Swift 5% Swift 10% Swift 15% Formulation conditions hardness 3 mm 5 mm 7 mm 9 mm drawing drawing drawing drawing SG1 None (a few 8B Macro Macro Macro Macro Macro Macro Macro Macro seconds at chipping chipping chipping chipping chipping chipping chipping chipping ambient temp.) SG1 160 C. 6H Macro Macro Macro Macro Macro Macro Macro Macro 3 minutes chipping chipping chipping chipping chipping chipping chipping chipping SG1 120 C. 5H Macro Macro Macro Macro Macro Macro Macro Macro 10 minutes chipping chipping chipping chipping chipping chipping chipping chipping SG1 120 C. 4H OK OK Micro Macro Micro Micro Macro Macro 2 minutes cracking chipping cracking cracking chipping chipping SG2 120 C. 2H OK OK OK Micro OK Micro Micro Macro 2 minutes cracking cracking cracking chipping SG3 30 min. at 3B OK OK OK OK OK OK Micro Micro ambient temp cracking cracking SG3 120 C. 2B OK OK OK OK OK OK Micro Micro 2 minutes cracking cracking SG3 + SF1 120 C. HB OK OK OK Micro OK Micro Micro Macro 2 minutes cracking cracking cracking chipping SG4 120 C. H OK OK OK OK OK Coating Micro Micro 2 minutes OK cracking cracking SG4 + SF2 120 C. 4B OK OK OK Micro OK Micro Micro Macro 2 minutes cracking cracking cracking chipping