METHOD FOR SYNTHESISING A METAL-OXIDE NANOFILLER, AND USE THEREOF IN A FLUOROCARBON-RESIN NON-STICK COATING

Abstract

Provided is a metal-dioxide nanofiller including at least two graft chains, at least one of the chains being a hydrophilic and the other being a hydrophobic chain compatible with fluorinated polymers. The hydrophobic chain is an oligomer, the weight-average molar mass Mw of which is between 300 and 20, 000 g/mol-1 .Math. Also provided is a non-stick coating comprising such a filler, as well as to a culinary article provided with such a coating.

Claims

1. A dispersion in aqueous phase of at least a fluorocarbon resin including a nanofiller of a metal-oxide comprising at least two graft chains, at least one of the chains being hydrophilic and the other being a hydrophobic chain compatible with fluorinated polymers, wherein the hydrophobic chain is an oligomer, the weight-average molar mass Mw of which is between 300 and 20,000 g/mol.

2. The dispersion according to claim 1, wherein the fluorocarbon resin is selected among the polytetrafluoroethylene (PTFE), the copolymer of tetrafluoroethylene and perfluoro propylvinylether (PFA), and the copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), the polyvinylidene fluoride (PVDF), the MVA (copolymer of TFE/PMVE) , the terpolymer TFE/PMVE/FAVE, the ETFE and their mixtures.

3. The dispersion according to comprising pigments, and/or additives claim 1, further selected among the thickening agents, surfactants, stabilizers and cosolvents.

4. A method of synthesis of a silica nanofiller comprising a hydrophilic chain consisting in a derivative of polyalkylene glycol modified by an alkoxysilane and a hydrophobic chain consisting in a hydrophobic oligomer of HFPO, and/or a VDF and/or a TFE modified by an alkoxysilane, said method comprising the following steps: (a) providing a polyalkylene glycol modified by an alkoxysilane; (b) oligomerizing said hydrophobic oligomer, followed by its functionalization by an alkoxysilane; and (c) grafting on the silica nanofiller on the one hand of said hydrophobic oligomer functionalized by an alkoxysilane, and on the other hand of polyalkylene glycol modified by analkoxysilane.

5. The method according to claim 4 wherein the grafting is a two-step grafting, in which: first, the functionalized hydrophobic oligomer HFPO is grafted on the silica nanofiller; then second, the modified polyalkylene glycol is grafted on the silica nanofiller.

6. The method according to claim 4, wherein the grafting of the functionalized hydrophobic oligomer and the modified polyalkylene glycol is achieved simultaneously on the silica nanofiller.

7. A non-stick coating comprising at least a layer comprising at least a fluorocarbon resin alone or mixed with a thermally stable bonding resin and resistant to at least 200 C., this (these) resin(s) forming a continuous fritted lattice, wherein it comprises a nanofiller such as defined according to claim 1.

8. The non-stick coating according to claim 7 wherein the fluorocarbon resin is selected among the polytetrafluoroethylene (PTFE), the copolymer of tetrafluoroethylene and perfluoro propylvinylether (PFA), and the copolymer of tetrafluoroethylene and hexafluoropropene (FEP), the polyvinylidene fluoride (PVDF), the MVA (copolymer of TFE/PMVE), the terpolymer TFE/PMVE/FAVE, the ETFE and their mixtures.

9. The non-stick coating according to claim 7, wherein the bonding resin is selected among polyamides imids (PAI), polyether-imids (PEI), polyamids (PA), polyimids (PI), polyetherketones (PEK), polyetheretherketones (PEEK), polythersulfones (PES), polyphenylene sulfides (PPS), polybenzimidazoles (PBI).

10. The non-stick coating according to claim 7, wherein it comprises a bonding primer layer and at least a finishing layer.

11. A culinary article comprising a support exhibiting an inner side able to receive foods and an outer side intended to be disposed towards the source of heat, wherein the inner side is coated with a non-stick coating such as defined according to claim 7.

12. The culinary article according to claim 11, wherein the support is a hollow bowl having a base and a lateral wall rising from said base.

13. The culinary article according to claim 11, wherein the support is achieved in a material selected among the metals, wood, glass, ceramics and plastic material.

14. The culinary article according to claim 13, wherein the support is a metal support in anodized aluminum or unanodized aluminum, or in polished, brushed or microbeaded aluminum, or cast aluminum, or in beaten or polished copper.

15. A method for achieving a non-stick coating such as defined accordng to claim 7, wherein it comprises the following steps: (a) introducing a nanofiller in a dispersion in aqueous phase of at least a fluorinated polymer, then (b) step of applying on a substrate said dispersion comprising the fluorinated polymer and said nanofiller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Other advantages and features of the present invention will result from the following description, given by way of non limiting example and made with reference to the examples and accompanying figures:

[0053] FIG. 1 represents a schematic cross-sectional view of an example of culinary article in accordance with the invention, exhibiting a non-stick coating on its inner surface; and

[0054] FIG. 2 schematically represents the reaction scheme of the synthesis of the silica nanofiller of example 1A (route A) and 1B (route B).

[0055] FIG. 2 is commented in example 1.

DETAILED DESCRIPTION OF THE INVENTION

[0056] FIG. 1 particularly represents, by way of culinary article example a pan 1 with a grip handle 11, which comprises a hollow metal bowl 2 having a base 21 and a lateral wall 22 rising from the base 21.

[0057] The bowl 2 exhibits a concave inner side 201 intended to be disposed on the side of food liable to be introduced therein, and an outer side 202 intended to be arranged towards a source of heat (for example a cooking plate).

[0058] The inner side 201 is covered with a non-stick coating 3, which comprises a layer of primer base 31 covering the inner side 201, and a finishing layer 32 covering the layer of primer base 31. The prime 31, finishing 32 and decorative layers 33 are PTFE-based.

EXAMPLES

[0059] Products

[0060] Supports [0061] aluminum supports sanded on its two main sides (having a measured arithmetic mean roughness Ra comprised between 4 and 6 m); [0062] smooth, merely degreased aluminum supports.

[0063] Fillers [0064] colloidal silica commercialized under trade name LUDOX AM 30 by company GRACE DAVISON: it is an unmodified colloidal silica surface with a specific surface area of approximately 220 m.sup.2/g and presented in the form of an aqueous dispersion with 30% dry matter, the size of the particles is estimated at 50 nm; [0065] pyrogenic silica commercialized under trade name AEROSIL 150 by company EVONIK with a specific surface area of approximately 150 m.sup.2/g in solid form the size of the particles is estimated at 14 nm; [0066] monomer: HFPO (having a purity of 97%) under name commercialized by ABCR; [0067] vinylidene fluoride (VDF) ; [0068] polyethylene glycol ; [0069] polyethylene glycol amine commercialized under trade name Jeffamine 1000 by company HUNTSMAN; [0070] methoxy-PEG-triethoxysilane oligomer of formula CH.sub.30-(CH.sub.2CH.sub.20).sub.9-(CH.sub.2).sub.3Si (Oet).sub.3 commercialized by company SPECIFIC POLYMERS.

[0071] Pigments [0072] pigment flakes (mica and titanium oxide) commercialized by company MERCK under brand names Iriodin 153 and 225:

[0073] Tests

[0074] Evaluating the Stability of a PTFE Dispersion with a Silica-Based Filler

[0075] It consists in evaluating the stability of the viscosity of a primer formulation applied by spraying PTFE-based spray comprising a silica filler (colloidal silica or silica nanofiller according to the invention) by BYK-Gardner cup according to DIN EN ISO 2433/ASTM D5125 standard: [0076] use of a 2.5 cup for the primers applied by spraying and measurement of the dry flow time (which corresponds to a viscosity) of the liquid and at ambient temperature in the orifice of calibrated diameter. [0077] follow-up of the development of the viscosity by the measurement of the dry flow time and at ambient temperature straight after the formulation of the primer and follow up of the development of this viscosity over time at ambient temperature; [0078] follow-up of the development of the viscosity by measurement of the dry flow time and at ambient temperature straight after the formulation of the primer and stoving at 40%C of the formulated primers; [0079] then follow-up of the development time of the flow time hence of the viscosity, which is measured at ambient temperature.

[0080] Evaluating the Abrasion Resistance

[0081] The abrasion resistance of a non-stick coating on a sanded aluminum substrate is evaluated. This test realized in accordance with the AFNOR NF D21-511 $3.3.7 standard consists: [0082] on the one hand in evaluating the scratch resistance of the prime layer by subjecting it to a green abrasive pad of SCOTCH BRITE type (registered trademark), the scratch resistance being estimated quantitatively by the number of passages with the pad needed to create the first scratch mark (corresponding to the appearance of the support constitutive metal); and [0083] on the other hand in evaluating the loss of the non-stick property of the prime layer throughout the test, the latter being quantitatively estimated by the number of cycles carried out until the loss of the non-stick property of the prime layer (test using carbonized milkin accordance with the NF D 21-511 standard): the latter is measured according to the more or less easy cleaning of the carbonized milk. The notation is as follows:

[0084] 100: means that the film of carbonized milk is entirely removed by simple application of a water jet from a kitchen tap;

[0085] 50: means that circular movements need to be carried out on the object under the water jet in order to entirely unstick the carbonized film;

[0086] 25: means that a 10-minute soak is needed and possibly forcing the removal by wiping with a wet sponge to completely remove the film;

[0087] 0: means that after the previous process, all or part of the carbonized film remains stuck.

[0088] Evaluating the Adherence of a Non-Stick Coating on a Smooth Aluminum Substrate

[0089] This test is carried out by grid pattern in accordance with the ISO 2409 standard, followed by a 9 hour immersion of the article (by 3 cycles of 3 hours in boiling water).

[0090] Then, a check is carried out to see whether the non-stick coating exhibits a detachment or not. The notation is as follows: [0091] to obtain a notation of 100, no square should become unstuck (excellent adherence); [0092] in the event of un-sticking the value recorded is equal to 100 minus the number of unstuck squares.

[0093] Evaluating the Corrosion Resistance of the Prime Layer on a Smooth Aluminum Substrate

[0094] The corrosion resistance of a non-stick coating is evaluated deposited on an aluminum substrate, by evaluating its resistance to the diffusion of salt towards the metal substrate which corrodes. This evaluation is carried out in practice by immersion, during 20 hours, of the substrate coated with the prime layer, in a saline aqueous solution brought to a boil. This saline solution comprises 10% in weight of sodium chloride. The protocol of this test is that defined in the AFNOR NF D21-511 $3.3.5. standard.

[0095] Following each immersion, a visual check is carried out of the final aspect of the coating, consisting in marking the presence or absence of corrosion traces (by visual observation with the naked eye or with the binocular magnifier). It consists in practice to detect the possible presence of traces such as blisters with area extension, white traces under the coating. This observation is followed by a cross-cut test in accordance with the ISO 2409 standard.

Comparative Example 1A (With Colloidal Silica)

[0096] A primer base composition CPC1A is achieved including the following compounds, their respective quantities being indicated in g for 1000 g of composition:

TABLE-US-00001 PFA (50% dry matter) 92 g PTFE dispersion (60% dry matter) 226 g Carbon black dispersion (25% dry matter) 41 g PAI in aqueous phase + solvent (NMP) 434 g (9.5% dry matter) Alkylphenol ethoxyl-based non-ionic surfactant 21 g (13%) Colloidal silica (30% dry) 62 g NH.sub.4OH (d = 0.9) 2 g Water 123 g Total 1000 g

Comparative Example 1B (With Pyrogenic Silica)

[0097] A primer base composition CPC1B is achieved including the following compounds, their respective quantities being indicated in g for 1000 g of composition:

TABLE-US-00002 PFA (50% dry matter) 78 g PTFE dispersion (60% dry matter) 192 g Carbon black dispersion (25% dry matter) 39 g PAI in aqueous phase + solvent (NMP) 590 g (9.5% dry matter) Pyrogenic silica 24 g Alkylphenol ethoxyl-based non-ionic surfactant 70 g (3.7%) NH.sub.4OH (d = 0.9) 7 g Total 1000 g
A finishing composition CF1 (colorless and without silica) is further achieved comprising the following compounds, their respective quantities being indicated in g for 1000 g of composition:

TABLE-US-00003 PTFE dispersion (60% dry) 844 g PFA dispersion (50% dry) 5 g Carbon black (25% dry) 0.2 g Octylphenol 11 mole ethoxylate: 3.7 g Sodium lauryl sulfate: 3.2 g Water: 47.6 g Xylene: 38.7 g Acrylique copolymer >95%: 5.1 g Oleic acid: 1.1 g triethanolamine: 1.3 g Iriodin 153: 2 g Propylene Glycol: 12.1 g WATER 35.9 g Total 1000 g
One side of the aluminum substrates is typically coated (sanded or smooth depending on the tests to be carried out) by proceeding as follows: [0098] a finished layer of the CPC1A or CPC1B composition is sprayed onto this inner side ; [0099] the thus formed wet prime layer is then dried at a temperature of around 65% until it is no longer sticky; [0100] the finishing composition CF1 is then sprayed onto the primer layer; [0101] after drying, curing the assembly at a temperature of the order of 420 C.+/10 C.

[0102] It is obtained substrates coated with a non-stick coating, wherein the colloidal silica is found in the prime layer. The thus obtained pieces then undergo the set of previously mentioned tests in the present application.

[0103] The results obtained following these different tests are collected in table 1 of results hereinafter.

Comparative Example 2

[0104] It is sought to achieve a prime composition identical to the CPC1A composition, but by replacing the colloidal silica by a pyrogenic silica (CPC1B composition) comprising a hydrophobic chain constituted of an HFPO oligomer.

[0105] The grafting of the hexafluoropropene oxide (HEPO) on the silica is carried out by hydrolysis-condensation of hexafluoropropene oxide (HEPO) oligomers.

[0106] First, anionic addition polymerization is carried out by opening the hexafluoropropene oxide (HEPO) cycle as follows: [0107] the polymerization has been carried out in a Hastelloy reactor of 100 mL (HC-276) fitted with a mechanical agitator, a rupture disk, valves and a manometer; [0108] after heating the reactor while under vacuum at 50-70 C. during one hour and placed under argon (typically three cycles empty/argon have been carried out), the KF has been added under a flow of argon. The reactor is then closed then heated during one hour under inert atmosphere, then the tetraglyme and the C.sub.4F.sub.sH.sub.S are introduced in vacuo; [0109] when the liquid reagents have been introduced, the reactor is cooled by a methanol cooler thanks to its double envelope; [0110] the HFPO in gaseous form is added by double weighing; [0111] then the autoclave is connected with an outer bath and heated to 10 C. (before heating, the temperature of the reactor was of 20 C.); [0112] the polymerization is stopped at the end of 2-3 hours by adding 15-20 mL of methanol; [0113] the terminal groups are esterified in 1 h at 30 C.; [0114] after opening the reactor, the recovered product is washed in water in order to solubilize the excess Tetraglyme; [0115] the aqueous phase is then separated using a dropping funnel and the solvent (in the organic phase) is evaporated by rotating evaporator. The resulting product is colorless and viscous.

[0116] The quantitative values are as follows: the reactor is loaded with 0.41 g (7.1 mmol) of KF, 2.9 mL (13.2 mmol) of tetraglyme and 10 mL of C.sub.4F.sub.5H.sub.5. Then 45 g (0.27 mol) of hexafluoropropene oxide are transferred to the reactor. The polymerization starts when the temperature is close to 0 C. and is stopped after 2 h by adding 15 mL of methanol. The polymer is washed three times with distilled water in order to remove the tetraglyme, the methanol and the catalyst. The solvents are evaporated using a rotating evaporator at 40-50 C. In this case, the yield is of 56%, the molar masses are of 1290 g/mol by NMR and 1207 by CPV.

[0117] Second, at the surface of the pyrogenic silica a hydrolysis-condensation is carried out by grafting onto the oligomers of the hexafluoropropene oxide (HFPO) with an alkoxysilane;

[0118] The quantitative values are as follows: 1.0 g of pyrogenic silica, vacuum dried beforehand during 2 h at 200 C., is dispersed in a water/ethanol solution (10/90, 100 mL). This dispersion is then placed under argon with a vigorous agitation during 15 minutes.

[0119] Then 2.6 g (1.7 mmol) of functionalized oligo(HFPO) amido (propyl) trimethoxysilane (HFPO.sub.x-Si (OEt).sub.3) are added therein. The mixture is refluxed during 24 h at 80 C., then filtered and washed several times with distilled water. The white powder obtained (SiO.sub.2SiO.sub.y-HFPO.sub.x) is vacuum dried during 4 h at 80 C. until constant weight is reached.

[0120] By this method, it has been possible to prepare hydrophobic silica with a 130 contact angle.

[0121] In this case it is not possible to introduce this grafted silica in a PTFE-based dispersion (of CPC1A type where colloidal silica would have been replaced by this modified silica), the formulation precipitates and implementation in the form of a stable dispersion is not possible.

Example 1

[0122] It is sought to achieve a prime composition identical to the CPC1 composition, but by replacing the colloidal silica by a silica nanofiller according to the invention including a double coating composed of the HFPO oligomer and the polyethylene glycol (PEG) oligomer.

[0123] The grafting onto the pyrogenic silica of a double strand composed of a VDF oligomer functionalized by Si(OEt).sub.3 and a PEG oligomer functionalized by Si(OEt).sub.3 is carried out by hydrolysis-condensation. The purpose is to make compatible and thus increase the colloidal silica dispersion in PTFE coatings.

[0124] Synthesis of the VDF Oligomer

[0125] Use of a methoxy-PEG-triethoxysilane of Formula CH.sub.3O(CH.sub.2CH.sub.2O).sub.9(CH.sub.2).sub.3Si (Oet)3 Provided by Specific Polymers and a Pyrogenic Silica: AEROSIL 150 from EVONIK

Example 1A

A Grafting of the Double Strand is Achieved onto the Pyrogenic Silica by Method A (Illustrated on FIG. 2)

[0126] Silica is modified with fluorinated chains in a first step with the following conditions: 3.0 g of silica, vacuum dried beforehand during 2 h at 200 C., is dispersed in a water/ethanol solution (10-90, 150 mL). This dispersion is then placed under argon with a vigorous agitation during 15 minutes. Then, 1.26 g (1.8 mmol) of oligo(HEPO) functionalized amido(propyl) triethoxysilane (HFPO.sub.3-Si (OEt).sub.3) are added therein. The mixture is refluxed during 24 h at 80 C., then filtered and washed several times with distilled water. The white powder obtained (SiO.sub.2SiO.sub.y-HFPO.sub.3) is vacuum dried during 4 h at 80 C. 1 g (1.8 mmol) PEG.sub.9Si (OEt).sub.3) were then grafted at the surface of the silica by using the same method of synthesis. A white powder is also recovered (PEG.sub.9-SiO.sub.ySiO.sub.2SiO.sub.y-HFPO.sub.x) with x=3;

[0127] The HFPO/PEG ratio is such that the PEG.sub.5-SiO.sub.ySiO.sub.2SiO.sub.yHFPO.sub.3 has the following proportions:

[0128] [SiO.sub.2].sub.0:[HFPO].sub.0:[PEG].sub.0:100:5:5.

[0129] This rate is optimized: it makes it possible to reduce the hydrophobicity of the silica with respect to comparative example 2.

[0130] In this case, the contact angle is of 86 2: this makes it particularly possible to be able to consider an implementation of this silica in aqueous phase.

Example 1B

A Grafting on the Double Strand is Achieved onto the Pyrogenic Silica by Method B (Illustrated on FIG. 2)

[0131] The method is similar to the previous one, the only difference relates to the simultaneous addition of the two types of strands to modify 1.00 g of silica 0.08 g (0.114 mmol) of HFPO.sub.3Si (OEt).sub.3 and 0.58 g (1.06 mmol) of PEG.sub.5Si (OEt).sub.3. The white powder obtained (PEG.sub.5-SiO.sub.ySiO.sub.2SiO.sub.y-HFPO.sub.3)is vacuum dried during 4 h at 80 C.

[0132] Then a first prime composition is achieved according to the invention C1 by replacing the pyrogenic silica of CPC1B by this double grafted silica (according to example 1A or 1B), with the following quantity, replacing 1/1/p.

[0133] Then, typically one of the sides of the aluminum substrate is coated by composition C1, then the finishing composition CF1(identical to that used in comparative example 1).

[0134] Substrates coated with a non-stick coating are obtained, wherein the double grafted silica is found in the prime layer. The thus obtained pieces then undergo the series of aforementioned tests of the present application.

[0135] The results obtained following these different tests are collected in table of results 1 hereinafter.

Example 2

[0136] This example is different from example 1 by a decrease in the rate of silica added to the formulation of type CPC1B, such that the quantity of silica described in example 1 is in a ratio with respect to the pyrogenic silica of 2/1/p.

[0137] The obtained results following these different tests are collected in table of results 1 hereinafter.

Example 3

[0138] It is sought to achieve a prime composition identical to composition CPC1, but by replacing the colloidal silica by a silica nanofiller according to the invention comprising a dual coating composed of VDF oligomer and ethylene glycol oligomer (PEG).

[0139] This grafting onto the pyrogenic silica of a double strand composed of VDFSi(OEt).sub.3 and oligo(PEG) is carried out by hydrolysis-condensation.

[0140] The purpose is to make compatible and thus increase the dispersion of colloidal silica in PTFE coatings.

[0141] Synthesis of VDF Oligomer

[0142] The oligomerization of the VDF (vinylidene fluoride) has been achieved by a Hastelloy autoclave (HC 2/6) of 160 mL fitted with a manometer, a mechanical anchor in Hastelloy, a rupture disk (3000 PSI), and gas inlet and discharge valves. An electronic system has made it possible to regulate and control both the agitation and the temperature in the autoclave.

[0143] Before the reaction, the autoclave is pressurized at 30 nitrogen bars in order to check for the absence of leaks.

[0144] Then, the autoclave is conditioned based on various empty cycles (10.sup.2 mbar)/nitrogen in order to get rid of any traces of oxygen.

[0145] Then, liquid and solid reagents, dissolved in an appropriate solvent of polar type, not leading to any transfer reactions are introduced under vacuum into the autoclave (via a funnel): [0146] 2.00 g (or 0.005 mol) of di-tert-butyl peroxydicarbonate by way of initiator, for example the product commercialized under name Perkadox 16S by AKZO NOBEL, [0147] 3.34 g (or 0.0074 mol) of C.sub.6F.sub.13I by way of transfer agent, [0148] 80 mL of acetonitrile (solvent).

[0149] Then, the reactor is cooled and placed under vacuum before transferring therein, under vacuum, 20.2 g (or 0.316 mol) of gaseous vinylidene fluoride (VDF) by double weighting (that is to say by difference of masses of the autoclave before and after the introduction of VDF).

[0150] The reactor is gradually heated by stage up to the following temperatures 40 C. (around 10 minutes), 50 C. (around 20 minutes), and finally 60 C. (4 hours). At 60 C., the pressure is of 19 bars, then it drops to 1 bar after 4 hours of heating at this temperature.

[0151] After these 4 hours of heating at 60 C., the reactor is stopped, then cooled. It is immersed in ice during around 60 minutes then degassed and opened. A brown liquid mixture is obtained.

[0152] After evaporation of the solvent (here acetonitrile), the residue is dissolved in the acetone, then the oligomers thus produced are precipitated in methanol. They are filtered, dried then weighed: oligomers in the form of powder are obtained, whereas the filtrate (which contains telomeres of lesser molar masses) is evaporated then dried.

[0153] These two fractions are constituted of: [0154] (1) 13.2 g of a yellow powder corresponding to higher molar masses (oligomers), and [0155] (2) 16.6 g of a brown wax (telomeres of low molar masses).

[0156] These two fractions are characterized by NMR spectroscopy of .sup.19F and .sup.1H:

[0157] NMR of .sup.1H (acetone d6, ppm) : 3.75 (CF.sub.2CF.sub.2CH.sub.2I, 2H); 3.50 (CH.sub.2CF.sub.2I, 2H); 3.30 (CF.sub.2CF.sub.2CH.sub.2CF.sub.2CH.sub.2CF.sub.2, 2H); 2.80 ([CH.sub.2CF.sub.2]nI, 2nH); absence of the signal at 2.4 ppm.

[0158] Assigned to the inverse diades VDF-VDF tail-tail

[0159] NMR of .sup.19F (acetone d6, ppm) : 39 (CH.sub.2CF.sub.2I, 2F); 82 (CF.sub.3CF.sub.2, 3F); 92 ([CF.sub.2CH.sub.2]n, 2nF); normal additions head-tail; 109 (CF.sub.2CF.sub.2CH.sub.2I, 2F); 112 (CF.sub.2CF.sub.2(CF.sub.2) xCF.sub.2CH.sub.2) absence of signals at 113 and 116 ppm assigned to tail-tail inverse additions in the VDF-VDF diades; 122 to 124 (CF.sub.3CF.sub.2(CF.sub.2)xCF.sub.2, 2F); 126 (CF.sub.3CF.sub.2, 2F).

[0160] Functionalization of the VDF Oligomer

[0161] In a triple-neck flask provided with a cooler and a nitrogen inlet are successively introduced: 0.053 g (namely 0.00032 mol) of tert-butyl-peroxypivalate, 1.125 g (namely 0.0057 mole) of vinyltriethoxysilane, 10.02 g (namely 0.0029 mole) of aforementioned oligomer and 20 mL of dry acetonitrile.

[0162] The reactive mixture is heated during 4 hours at 74 C. After cooling, the triethoxysilane modified VDF oligomer is precipitated in dry pentane and filtered, then dried.

[0163] The NMR specter of .sup.1H and .sup.19F show the characteristic signals of VDF units and the end CH.sub.2CHISi (OEt).sub.3:

[0164] NMR of .sup.1H (acetone d6, ppm) disappearance of signals at 3.75 (CF.sub.2CF.sub.2CH.sub.2I) and at 3.50 (CH.sub.2CF.sub.2I, 2H); presence of a multiple peak with center at 4.5 ppm, assigned to CHI and quadruplet and triplet towards 3.8 ppm and 1.2 ppm (respectively assigned at OCH.sub.2 and CH.sub.3); of signal at 3.30 (CF.sub.2CF.sub.2CH.sub.2CF.sub.2CH.sub.2CF.sub.2, 2H); 2.80 ([CH.sub.2CF.sub.2]n and CHICH.sub.2VDF).

[0165] NMR of .sup.19F (acetone d6, ppm) disappearance of signal at 39 (assigned to group CH.sub.2CF.sub.2I, 2F); presence of groups at 82 (CF.sub.3CF.sub.2, 3F); 92 ([CF.sub.2CH.sub.2]n, 2nF); 112 (CF.sub.2CF.sub.2(CF.sub.2) xCF.sub.2CH.sub.2) and presence of signals between 122 and 124 (CF.sub.3CF.sub.2(CF.sub.2) xCF.sub.2, 2F); 126 (CF.sub.3CF.sub.2, 2F).

[0166] Use of a methoxy-PEG-triethoxysilane of Formula CH.sub.3O(CH.sub.2CH.sub.2O).sub.9(CH2).sub.3Si (Oet)3 Provided by Specific Polymers and a Pyrogenic Silica: AEROSIL 150 by EVONIK

Example 3A

A Grafting is Achieved of the Double Strand on the Pyrogenic Silica by Method A (Illustrated on FIG. 2).

[0167] Silica is modified by fluorinated chains in a first step with the following conditions: 3.0 g of silica, vacuum dried beforehand during 2 h at 200 C. is dispersed in a solution of water/ethanol (10/90, 150 mL).

[0168] This dispersion is then placed under argon with vigorous agitation during 15 minutes. Then 1.26 g (1.8 mmol) of (VDF) oligo functionalized by an amido(propyl) triethoxysilane (HFPO.sub.3-Si (OEt).sub.3) are added therein.

[0169] The mixture is refluxed during 24 hours at 80 C. then filtered and washed several times with distilled water. The white powder obtained (SiO.sub.2SiO.sub.y-VDFx) is vacuum dried during 4 h at 80 C. 1 g (1.8 mmol) of PEG.sub.9-Si (OEt).sub.3) are then grafted onto the surface of the silica by using the same method of synthesis. A white powder is also recovered (PEG.sub.9-SiO.sub.ySiO.sub.2SiO.sub.y-VDF.sub.x) with x=3;

[0170] The VDF/PEG ratio is such that the PEG.sub.5-SiO.sub.ySiO.sub.2SiO.sub.y-VDF.sub.3 is in the proportions:

[0171] [SiO2].sub.0:[VDF].sub.0:[PEG].sub.0:100:5:5

[0172] This rate is optimized: it makes it possible to reduce the hydrophobia of the silica with respect to the comparative example 2.

[0173] In this case, the contact angle is of 86 2: this particularly makes it possible to be able to consider implementing this silica in aqueous phase.

Example 3B

A Grafting of the Double Strand on the Pyrogenic Silica is Carried out by Method B (Illustrated on FIG. 2)

[0174] The method is similar to the previous one, the only difference relating to the simultaneous addition of the two types of strands to modify 1.00 g of silica 0.08 g (0.114 mmol) of PVDF-Si(OEt).sub.3 and 0.58 g (1.06 mmol) of PEG.sub.5-Si(OEt).sub.3. The white powder obtained (PEG.sub.5-SiO.sub.ySiO.sub.2SiO.sub.y-HFPO.sub.3) is vacuum dried during 4 h at 80 C.

[0175] Then is achieved a prime composition according to the invention C3 by replacing the pyrogenic silica of CPC1B by this double grafted silica (according to example 3A or 3B), with the following quantity, replacement 1/1/p.

[0176] Then, one of the sides of the aluminum substrate is typically coated one by the composition C1, then the finishing composition CF1 (identical to that used in comparative example 1).

[0177] It is obtained substrates coated with a non-stick coating, wherein the double grafted silica is found in the prime layer. The thus, obtained pieces then undergo the series of aforementioned tests of the present application.

[0178] The results obtained following these different tests are collected in the table of results 1 hereinafter.

Example 4

[0179] This example is different from example IA by an increase in the size of the nanoparticles, which is here of the order of 1200 nm.

[0180] The results obtained following these different tests are collected in the table of results 1 hereinafter.

TABLE-US-00004 TABLE 1 Comparative Comparative Comparative example 1A example 1B example 2 Example 1A Example 1B Example 2 Example 3A Example 3B Example 4 Feasibility of OK Not Ok Not ok ok ok ok ok ok ok the implementation in aqueous phase stability of <30 days >6 months >6 months >6 months >6 months >6 months >4 months the viscosity of a primer at ambient temperature stability of <10 days >30 days >30 days >30 days >30 days >30 days >15 days the viscosity of the primer at 40 C. Adherence Not ok Ok OK OK OK OK OK test on a smooth aluminum substrate Behavior Bad 100% Ok 100% Ok 100% Ok 100% Ok 100% Ok 100% Ok 100% under corrosion conform conform conform conform conform conform corrosion on points smooth aluminum substrate abrasion Appearance Appearance Appearance Appearance Appearance Appearance Appearance resistance on of scratches of scratches of scratches of scratches of scratches of scratches of scratches sanded on the on the on the on the on the on the on the aluminum metal:1000 metal:11000 metal:15000 metal:7000 metal:13000 metal:13000 metal:10000 substrate scrubbings scrubbings scrubbings scrubbings scrubbings scrubbings scrubbings Total loss of Total loss of Total loss of Total loss of Total loss of Total loss of Total loss of non-stick non-stick non-stick non-stick non-stick non-stick non-stick property property property property property property property 4000 20000 25000 16000 19000 19000 14000 scrubbings scrubbings scrubbings scrubbings scrubbings scrubbings scrubbings