METHOD FOR ASSEMBLING A RELEASE FILM ON A METAL SUBSTRATE BY HOT STAMPING

Abstract

The invention relates to a method for manufacturing a coated cooking element (1) comprising the following steps: i. Providing a metal substrate (2) having a face (2a), intended to be coated with a film (3); ii. Providing said film (3), said film (3) comprising a layer (3a) intended to be brought into contact with said face (2a) of said metal substrate (2), said layer (3a) comprising: 50-100% by weight of polytetrafluoroethylene (PTFE) 0-50% by weight of one or more thermoplastic polymers other than PTFE, the percentages being expressed relative to the total weight of PTFE and said thermoplastic polymer(s); iii. Heating said metal substrate (2); iv. Positioning said film (3) so that the layer (3a) faces said face (2a) of the metal substrate (2) heated during step iii.; v.Production of the assembly of said metal substrate (2) and said film (3) by hot stamping, said metal substrate (2) being at a temperature between 350°C and 550°C, preferably at a temperature between 400°C and 450°C at the time of assembly. Figure for abstract: Figure 1.

Description

Title of the invention: METHOD FOR ASSEMBLING A NON-STICK FILM ON A METAL SUBSTRATE BY HOT STAMPING FIELD OF THE INVENTION

[0001] The present invention relates to the field of methods for obtaining cooking elements coated with a non-stick polymeric film. STATE OF THE ART

[0002] In the industry of cookware having a non-stick cooking surface, the performance of non-stick coatings as well as the development of processes for obtaining such coatings constitute important concerns.

[0003] Conventionally, a metal substrate is first shaped to form a cooking utensil, and then the inner surface of the cooking utensil is coated with a fluororesin having excellent heat resistance such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) by means of a liquid spray coating process or a powder coating process. An alternative is to coat the substrate and then shape the coated substrate.

[0004] The liquid spray coating process has a number of disadvantages. When the metal substrate has a curved shape, it is difficult to obtain a coating of uniform thickness. The liquid spray coating process also involves the use of solvents or volatile organic compounds that evaporate during the process and must be recovered and recycled. From an environmental point of view, a solvent-free and volatile organic compound-free process is preferred. On the other hand, the coating thickness is limited. Cracks are likely to appear when the coating thickness is too great.

[0005] The powder coating process also has disadvantages. The coating obtained has defects, such as pinheads, which can lead to a reduction in the non-stick character.

[0006] The coatings obtained using these two processes may have significant surface roughness which can cause cleaning problems, as certain cooking residues may persist on the surface of the coating even after several washes.

[0007] In order to overcome the drawbacks mentioned above, the state of the art describes metal substrates coated with fluorinated films by rolling.

[0008] Patent application KR20150030719 describes a kitchen utensil comprising a body including a metal substrate on which a film of a fluororesin is laminated. A method for obtaining a kitchen utensil is also described. In Example 1, a PTFE multilayer film is used without information on the nature of the layers. The operation of laminating the film onto the substrate is not described.

[0009] Application KR20160099388 describes the method for obtaining a metal substrate coated with a fluorinated film (devoid of a primer layer comprising an organic compound or an adhesive). The fluorinated film is a multilayer film obtained by successive deposition on a support of an aqueous dispersion of the constituents of the layer (fluorinated resin and possibly an inorganic filler) which is dried and sintered. The multilayer film is then removed from its support and positioned on the metal substrate before assembly. The layer of the fluorinated film in contact with the metal is made of PTFE and a resin chosen from FEP, PFA, TFM, MFA (or their mixture) which has good flow properties, thus allowing good adhesion, which PTFE does not allow. The metal substrate / fluorinated film assembly is carried out by thermal compression, in a static press or between rollers (roll-to-roll process).In the static joining process, both the substrate and the film are heated to a temperature between 300°C and 410°C with an applied pressure of 100 to 800 psi (0.7 MPa and 5.6 MPa). In the roll-to-roll joining process (which is difficult to implement when the metal substrate is thick), both the substrate and the film are heated to a temperature between 330°C and 420°C with an applied pressure between 2 and 15 MPa.

[0010] In both process variants, the pressure applied during assembly is a few MPa and the processing temperature is limited by the degradation temperature of the fluorinated film (in particular of PTFE which begins at 420°C). The assembly rates of the polymer film and the metal substrate are therefore limited by the parameters of the assembly process. Statement of the invention

[0011] From an industrial point of view, there remains the need to develop methods for assembling a polymeric film on a metal substrate which are more advantageous in terms of assembly time without causing a reduction in the quality of adhesion of said film to said substrate and without causing degradation of said film.

[0012] The applicant has thus developed a method for manufacturing a coated cooking element by assembling by hot stamping a metal substrate and a polymeric film. Summary of the invention

[0013] The inventors have discovered that the method according to the invention makes it possible to achieve rapid assembly between a metal substrate and a polymer film comprising mainly PTFE in the layer in contact with the metal substrate while ensuring good adhesion of the polymer film to said substrate.

[0014] Unlike the usual method of assembling fluoropolymer films on metal such as hot pressing, only the substrate is heated prior to assembly according to the method of the present invention. The polymeric film is heated essentially by conduction when it is brought into contact with the substrate at the time of assembly, then is cooled due to the thermal inertia of the assembly tools which remain at a temperature lower than the heating temperature of the metal substrate.

[0015] During assembly, it is thus possible to heat very locally, in particular at the substrate-film interface, the film comprising mainly PTFE in its layer in contact with the substrate at a temperature above its melting temperature and this for a very short time, which does not cause degradation of the film.

[0016] The implementation of this high temperature combined with the pressure applied during the stamping makes it possible to carry out the assembly of the polymer film and the metal substrate in a much shorter time than according to conventional methods of assembling polymer films on metal substrates such as hot pressing.

[0017] The invention thus relates to a method of manufacturing a coated cooking element (1) comprising the following steps:

[0018] i. Provision of a metal substrate (2) having a face (2a), intended to be coated with a film (3);

[0019] ii. Providing said film (3), said film (3) comprising a layer (3a) intended to be brought into contact with said face (2a) of said metal substrate (2), said layer (3a) comprising: - 50-100% by weight of polytetrafluoroethylene (PTFE) - 0-50% by weight of one or more thermoplastic polymers different from the PTFE

[0020] the percentages being expressed relative to the total weight of PTFE and said thermoplastic polymer(s);

[0021] iii. Heating said metal substrate (2);

[0022] iv. Positioning said film (3) so that the layer (3a) is opposite said face (2a) of the metal substrate (2) heated during step iii.;

[0023] v. Production of the assembly of said metal substrate (2) and said film (3) by hot stamping, said metal substrate (2) being at a temperature between 350°C and 550°C, preferably at a temperature between 400°C and 450°C. time of assembly.

[0024] The invention also relates to a method for shaping a coated cooking element (1) as described above comprising a step (a) of stamping the coated cooking element (1) obtained at the end of step (v).

[0025] Other aspects of the invention are as described below and in the claims.

[0026] Definitions

[0027] The term "film" is understood to mean, within the meaning of the present invention, an assembly consisting of one or more superimposed layers intended to be assembled with the metal substrate. The term "film" also corresponds to said assembly once assembled with the metal substrate.

[0028] The term "layer" is understood to mean, within the meaning of the present invention, a continuous layer. A continuous layer (or also called a monolithic layer) is a single whole forming a total flat area completely covering the surface on which it is placed or is going to be placed.

[0029] For the purposes of the present invention, the term "hot stamping" means the method of assembling the previously heated metal substrate (2) and the film (3) between a lower tool and an upper tool.

[0030] For the purposes of the present invention, the term "aluminum alloy" means an aluminum alloy of series 1000, 2000, 3000, 4000, 5000, 6000, 7000 and 8000. DESCRIPTION OF FIGURES

[0031] [Fig-1] represents a sectional view of an exemplary embodiment of an element of coated baking (1), comprising a film (3) and a metal substrate (2), before assembly according to the method of the invention.

[0032] [Fig.2] represents a sectional view of an exemplary embodiment of a coated cooking element (1) according to the method of the invention, comprising a film (3) and a metal substrate (2).

[0033] [Fig.3] represents a coated cooking element (1), comprising a film (3) and a metal substrate (2), obtained according to the method of the invention and shaped by stamping.

[0034] [Fig.4] represents a metallic substrate (2) made of hydrated brushed aluminum coated with the PTFE 0167 film according to example 1 and having undergone a stamping operation according to example 3.

[0035] [Fig.5] represents a metallic substrate (2) made of hydrated brushed aluminum coated with the PTFE 0167 film according to example 1 and having undergone a stamping-drawing operation according to example 4. DETAILED DESCRIPTION OF THE INVENTION

[0036] The inventors have developed a manufacturing process meeting the expressed needs.

[0037] The invention relates to a method for manufacturing a coated cooking element (1) comprising the following steps:

[0038] i. Provision of a metal substrate (2) having a face (2a), intended to be coated with a film (3);

[0039] ii. Providing said film (3), said film (3) comprising a layer (3a) intended to be brought into contact with said face (2a) of said metal substrate (2), said layer (3a) comprising: - 50-100% by weight of polytetrafluoroethylene (PTFE) - 0-50% by weight of one or more thermoplastic polymers different from the PTFE

[0040] the percentages being expressed relative to the total weight of PTFE and said thermoplastic polymer(s);

[0041] iii. Heating said metal substrate (2);

[0042] iv. Positioning said film (3) so that the layer (3a) is opposite said face (2a) of the metal substrate (2) heated during step iii.;

[0043] v. Carrying out the assembly of said metal substrate (2) and said film (3) by hot stamping, said metal substrate (2) being at a temperature between 350°C and 550°C, preferably at a temperature between 400°C and 450°C at the time of assembly.

[0044] Metal substrate (2) used in step i of the process

[0045] As metallic substrates (2) which can be used in the context of the invention, mention may advantageously be made of substrates made of aluminum, stainless steel, cast iron or aluminum, or titanium or copper.

[0046] For the purposes of the present invention, aluminum means a metal consisting of 100% aluminum or an aluminum alloy.

[0047] Advantageously, the metal substrate (2) is an aluminum substrate, a stainless steel substrate or a multi-layer metal substrate, in particular two-layer or three-layer, these multi-layers being able to be obtained for example by co-lamination, by hot diffusion under load (solid State bonding) or by hot or cold impact bonding.

[0048] Preferably, the metal substrate (2) comprises an alternation of layers of metal and / or metal alloy.

[0049] According to one embodiment, the metal substrate (2) is a substrate made of aluminum alloy, stainless steel or a multilayer metal substrate whose face (2a) is made of aluminum alloy or stainless steel.

[0050] Preferably, the metal substrate (2) is an aluminum substrate.

[0051] Advantageously, the thickness of the metal substrate (2) is between 0.5 mm and 10 mm.

[0052] Advantageously, the face (2a) of the metal substrate (2) has undergone a surface treatment prior to assembly with the film (3) making it possible to improve the adhesion of said film to said substrate.

[0053] According to one embodiment, the surface of the face (2a) of the metal substrate (2) has undergone a surface treatment, said surface treatment being a chemical attack, brushing, hydration, sandblasting, shot blasting, a physicochemical treatment of the plasma or corona or laser type, a chemical activation or a combination of these different techniques.

[0054] Advantageously, the average arithmetic roughness Ra of the surface of the face (2a) of the metal substrate (2) is greater than or equal to Ipm.

[0055] The arithmetic mean roughness Ra is measured using a roughness meter according to ISO 4287. Ra represents the arithmetic mean of the deviations from the mean. The surface topography can be studied in particular with a profilometer with a probe equipped with a fine stylus fitted with a diamond tip, or with an optical metrology device such as Altisurf®, in which a chromatic confocal sensor allows a contactless measurement. The study of this surface topography makes it possible to define the arithmetic mean roughness Ra. Film (3) used in step ii of the process

[0056] The adhesion of a fluorinated film to a metal substrate presents technical difficulties due to the intrinsic non-stick nature of fluorinated polymers: one of the solutions consists of using a fluorinated underlayer of copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA) or of copolymers of tetrafluoroethylene and hexafluoropropene (FEP) which acts as a hot-melt adhesive, thus allowing the adhesion of the fluorinated film to the metal substrate.

[0057] Direct adhesion of PTFE to a metal substrate is limited by the poor flow properties of PTFE when hot but also by its thermal degradation which occurs from 420°C.

[0058] The method according to the invention makes it possible to overcome these difficulties and to carry out the assembly of a metal substrate (2) and a film (3) comprising mainly PTFE as polymer in the layer (3a) in contact with the metal substrate (2).

[0059] The film (3) used in the method according to the invention comprises a layer (3a) intended to be brought into contact with said face (2a) of said metal substrate (2), said layer (3a) comprising mainly PTFE as polymer.

[0060] Layer (3a) thus comprises: - 50-100% by weight of polytetrafluoroethylene (PTFE) - 0-50% by weight of one or more thermoplastic polymers different from the PTFE

[0061] the percentages being expressed relative to the total weight of PTFE and said thermoplastic polymer(s).

[0062] According to one embodiment, the PTFE polymer is the only polymer of the layer (3a).

[0063] When the layer (3a) comprises one or more thermoplastic polymers other than PTFE, this or these polymers are chosen from: - copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethylvinylether (MVA), terpolymers of tetrafluoroethylene, polymethylvinylether and fluoroalkylvinylether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), - polyarylether ketones (PAEK), including polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), preferably polyether ether ketone (PEEK) - polyamideimide (PAI), polyimide (PI), polyetherimide (PEI), polybenzy-midazole (PBI) - and their mixtures

[0064] The film (3) may consist of a single layer (3a) also forming a cooking face (4).

[0065] According to another configuration, the film (3) may also comprise an additional layer positioned above the layer (3a) as described above. In this case, the film (3) thus further comprises another layer (3b) forming a cooking face (4), said other layer (3b) comprising one or more polymers chosen from: - polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethylvinylether (MVA), terpolymers of tetrafluoroethylene, polymethylvinylether and fluoroalkylvinylether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), and mixtures thereof; preferably PTFE - polyarylether ketones (PAEK), including polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), preferably primarily polyether ether ketone (PEEK) - polyamideimide (PAI), polyimide (PI), polyetherimide (PEI), polybenzy-midazole (PBI) - silicone resins - and their mixtures, preferably mixtures of PTFE and PEEK.

[0066] According to one embodiment, the film (3) further comprises at least one intermediate layer (3c) positioned between the layer (3a) and the other layer (3b), said intermediate layer (3c) comprising one or more polymers chosen from:

[0067] - polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and per- fluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethylvinylether (MVA), terpolymers of tetrafluoroethylene, polymethylvinylether and fluoroalkylvinylether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), and mixtures thereof; preferably copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA) and PTFE; preferably PTFE

[0068] - polyarylether ketones (PAEK), including polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), preferably polyether ether ketone (PEEK)

[0069] - polyamideimide (PAI), polyimide (PI), polyetherimide (PEI), polybenzymidazole (PBI)

[0070] - silicone resins

[0071] - and their mixtures, preferably mixtures of polyarylether ketones (PAEK) and PTFE, preferably mixtures of PEEK and PTFE;

[0072] PTFE being particularly preferred.

[0073] Advantageously, the silicone resin(s) of the layer (3b) and, where appropriate, of the layer (3c), is / are chosen from the group consisting of methyl silicone and / or phenyl silicone and / or methyl-phenyl-silicone resins, silicone-polyester resin (copolymers), methyl-phenyl-silicone-polyester resin (copolymers), silicone-alkyd resin (copolymers), modified silicone resin.

[0074] The silicone resins can be obtained from precursors, notably chosen from: a silicone hydride, a silicone resin comprising at least one vinyl group (-CH=CH2), a silicone-polyester resin (copolymer) comprising at least one methoxy group, and / or a silicone-polyester resin (copolymer) comprising at least one ethoxy group, and mixtures thereof.

[0075] The film (3) may also further comprise at least one filler and / or at least one reinforcement.

[0076] As fillers which can be used in the present invention, mention may in particular be made of metal oxides, metal carbides, metal oxynitrides, metal nitrides, silicas and their mixtures.

[0077] These fillers may be present in one or more layers of the film (3) or in each of the layers of the film (3).

[0078] As reinforcements that can be used under the present invention, mention may be made of a mineral or metallic reinforcement of the fiber type, metal mesh, fiberglass material or fabric. The reinforcement may also consist of a non-fluorinated polymer with high thermomechanical properties of the polyaryletherketone (PEAK) type, such as for example polyetheretherketone (PEEK), or polyamide-imide (PAI). The reinforcement may be in the form of a layer of the film (3) positioned between the layer (3a) and the layer (3b) forming the cooking face.

[0079] In order to improve the adhesion of the film (3) and the metal substrate (2), the layer (3a) of the film (3) coming into contact with the face (2a) of the metal substrate (2) during step (v) may have undergone a mechanical or chemical surface treatment. This prior surface treatment may be a chemical attack, brushing, hydration, sandblasting, shot blasting, a physicochemical treatment of the plasma or corona or laser type, a chemical activation or a combination of these different techniques.

[0080] According to one embodiment, the thickness of said film (3) is between 5 μm and 500 μm, preferably between 25 μm and 150 μm.

[0081] The measurement of the thickness of the layer(s) of the film (3) is carried out at 20 random points on the section of the film. The average thickness of said film (3) is obtained by taking the average of these 20 measurements.

[0082] The total thickness of the film (3) of the coated cooking element (1) according to the invention, i.e. measured on the cooking element once it has been coated with the film (3), is between 5 μm and 500 μm, preferably between 25 μm and 150 μm.

[0083] The measurement of the thickness of the film (3) of the coated cooking element (1) according to the invention is carried out at 20 random points on the section of the coated substrate. The average thickness of said film (3) is obtained by averaging these 20 measurements.

[0084] The film (3), before assembly with the metal substrate (2), can be obtained by depositing a first layer on a support, then possibly by the successive deposition of the other layers, then by exfoliation of said film to separate it from the support. The layers of the film (3) can also be assembled together by any other assembly method, such as by rolling for example.

[0085] Generally, the film (3) of the coated cooking element (1) completely covers the face (2a) of the metal substrate (2), but it can be envisaged that only a part of the metal substrate (2) is covered.

[0086] In the embodiment illustrated in Figures 1 and 2, the film (3) comprises 3 layers (3a, 3b, 3c). Step iii

[0087] The metal substrate (2) is heated during step iii prior to steps iv and v of the method. The metal substrate can be heated using any suitable equipment, in a furnace or by induction for example. Step iv

[0088] Before assembly during step v, the film (3) is positioned above the metal substrate (2) so that its layer (3a) is opposite the face (2a) of the metal substrate (2) previously heated during step iii.

[0089] The film (3) is positioned so that the entire surface of the layer (3a) comes into contact simultaneously with the surface of the face (2a) of the metal substrate (2) during the assembly step v.

[0090] In order to ensure this contact of the layer (3a) of the film (3) with the face (2a) of the metal substrate (2), the film (3) can be fixed on the upper tool or be stretched between 2 rollers. Step v

[0091] When assembling the metal substrate (2) and the film (3) by hot stamping, said metal substrate (2) is at a temperature between 350°C and 550°C, preferably at a temperature between 400°C and 450°C at the time of assembly.

[0092] When the temperature is lower than 350°C, the adhesion of the film (3) to the metal substrate (2) is not sufficient.

[0093] When the temperature is higher than 550°C, degradation of the film (3) is observed.

[0094] The temperature of the metal substrate (2) at the time of assembly corresponds to the temperature of the metal substrate (2) when striking begins, i.e. when pressurization of the metal substrate (2) / film (3) assembly begins.

[0095] According to one embodiment, the assembly by hot stamping during step v. is carried out by means of a hydraulic or mechanical press comprising a lower tool and an upper tool between which the metal substrate (2) and the film (3) are assembled, said metal substrate (2) being preferentially in contact with the lower tool and said film (3) being preferentially in contact with the upper tool.

[0096] The surface of the lower tool, advantageously flat, can undergo a surface treatment

[0097] so as to avoid any sticking of the metal substrate on said tool.

[0098] Advantageously, the plane of the surface of the upper tool, relative to the plane of the surface of the lower tool, has an angle between 0.01° and 0.5°, preferably between 0.15° and 0.25°. This angle helps limit air entrapment during the assembly stage.

[0099] Optionally, the lower tool may be heated. Optionally, the upper tool may be cooled.

[0100] According to one embodiment, the lower tool is heated to a temperature between 25°C and the temperature of the metal substrate (2) at the time of assembly and / or the upper tool is brought to a temperature between 15°C and 120°C during step v.

[0101] Unless otherwise indicated, the temperature values ​​indicated in the present application correspond to measured temperature values ​​and are not set temperatures.

[0102] The temperature values ​​are measured by any suitable means, for example by means of a temperature probe positioned on the surface or in the mass of the heated or cooled element.

[0103] The temperature of the metal substrate (2), at the time of assembly (step v), is between 350°C and 550°C, preferably between 350°C and 500°C, particularly preferably between 400°C and 450°C. The temperature of the metal substrate (2) at the time of assembly corresponds to the temperature of the surface (2a) of the metal substrate (2) when striking begins, i.e. when pressurizing the metal substrate (2) / film (3) assembly begins.

[0104] The temperature of the metal substrate (2) may then drop during the striking operation, in particular when the lower tool is not heated prior to the assembly step.

[0105] During the striking operation of step v, a pressure of several hundred MPa is implemented.

[0106] According to one embodiment, the metal substrate (2) and the film (3) are maintained under a pressure of between 100 MPa and 800 MPa, preferably between 350 MPa and 500 MPa during step v.

[0107] The pressure applied during the coining operation is considerably higher than that applied in conventional metal substrate / polymer film assembly processes such as hot pressing which is only a few MPa.

[0108] According to one embodiment, the duration of maintaining the metal substrate (2) and the film (3) under pressure is less than or equal to 1 minute, preferably less than or equal to 15 seconds during step v.

[0109] The strike can be carried out by applying a sharp blow, for a duration of less than 5 seconds.

[0110] According to another embodiment, the duration of maintaining the substrate under pressure metallic (2) and film (3) is between 1 second and 1 minute, preferably between 2 seconds and 15 seconds during step v.

[0111] The film (3) is essentially heated by conduction when it is brought into contact with the heated substrate at the time of assembly. It is then cooled during the striking due to the thermal inertia of the assembly tools whose temperature is lower than the heating temperature of the metal substrate (2). The temperature of the film (3) can thus drop rapidly during the striking operation, in particular when the lower tool is not heated prior to the assembly step.

[0112] According to the method of the invention, it is thus possible to heat the film (3) very locally, in particular at the metal substrate (2) - film (3) interface, to a temperature above its melting temperature and this for a very short time, which does not cause degradation of the film.

[0113] Advantageously, the temperature of the film (3) at the end of step v. of assembling said film (3) and the metal substrate (2), i.e. when the assembly of the film (3) and the metal substrate (2) is no longer maintained under pressure, is lower than the melting temperature of the PTFE.

[0114] The combination, at the time of assembly by striking, of a temperature and a pressure such as described above, makes it possible to ensure the adhesion of the film (3) to the metal substrate (2) in very short times.

[0115] After assembly, the metal substrate (2) coated with the film (3) is left to cool to room temperature in order to obtain maximum adhesion between the film (3) and the metal substrate (2).

[0116] The metal substrate (2) coated with the film (3) can then be shaped at the end of step (v).

[0117] A second object of the invention thus relates to a method of shaping a coated cooking element as described above comprising a step (a) of stamping the coated cooking element (1) obtained at the end of step (v).

[0118] The shaping method may further comprise a step (b) of stretching the coated cooking element (1) obtained at the end of step (a).

[0119] The adhesion of the film (3) to the metal substrate (2) before shaping must be sufficiently good to avoid any loss of adhesion during and after the shaping operation.

[0120] The coated cooking element (1) according to the method of the invention can form a cooking container in a culinary article chosen from the group consisting of saucepan, frying pan, skillets or caquelons for fondue or raclette, stewpot, wok, sauté pan, crepe pan, grill, griddle, pot, casserole, culinary mold.

[0121] The coated cooking element (1) according to the method of the invention can form a cooking container in an electrical cooking appliance chosen from the group consisting of Electric crepe maker, electric raclette machine, electric fondue machine, electric grill, electric griddle, electric cooker, food processor, bread maker. Thus, the cookware can form a cooking accessory for an electric cooking appliance.

[0122] The following examples are given for illustrative purposes, but should in no case be considered as limiting the present invention. Examples

[0123] Equipment used: - for assembly tests: SGM 160 T hydraulic press equipped with a flat upper punch and a flat lower punch. The surface plane of the upper punch has an angle of 0.15° relative to the surface plane of the lower punch so as not to trap air during the assembly step - for Swift stamping tests: Zwick BPU 400 stamping machine

[0124] Metal substrates used:

[0125] A metal substrate (2) made of 1200 state 0 aluminum is used for the tests. The metal substrate (2) is used as is or after having undergone a surface treatment.

[0126] The following 3 configurations are tested: - metallic substrate (2) made of raw aluminum having an average arithmetic roughness Ra less than 1 pm; - metallic substrate (2) in hydrated brushed aluminum having an average arithmetic roughness Ra of between 2 pm and 3 pm; - chemically stripped metal substrate (2) having an average arithmetic roughness Ra between 3 pm and 4 pm.

[0127] The average arithmetic roughness Ra is measured using an optical metrology device such as Altisurf®.

[0128] Polymeric films used:

[0129] The following films (3), supplied by the company Saint-Gobain, were used: - Film (3) Chemfilm® skived PTFE 0001: colorless PTFE film with a thickness of 100 pm; - Film (3) Chemfilm® black skived PTFE 0167: black PTFE film with a thickness of 100 pm. Example 1: Assembly test

[0130] Experimental conditions:

[0131] The metal substrates (2) are cut into discs of 340 mm diameter.

[0132] The metal substrate (2) is heated in a furnace having a heating set temperature of 550°C.

[0133] After 15 minutes of heating, the temperature of the metal substrate (2) measured using a contact probe is 520°C.

[0134] After 15 minutes of heating, the metal substrate (2) is positioned on the unheated lower punch of the hydraulic press.

[0135] The unheated film (3) is brought into contact with the metal substrate (2) just before assembly.

[0136] The metal substrate (2) and the film (3) are assembled by sharp striking with a striking force of 3000 T (i.e. 33 kg / mm2 corresponding to a pressure of 330 Mpa), the temperature of the metal substrate (2) at the time of striking being 420°C.

[0137] Results:

[0138] After cooling, the quality of the adhesion of the film (3) to the metal substrate (2) is evaluated.

[0139] The PTFE film (3) adheres strongly to the hydrated brushed aluminum metal substrate (2), and to the chemically etched aluminum metal substrate (2).

[0140] The adhesion is not satisfactory on the raw aluminum metal substrate (2). Example 2: Swift stamping test

[0141] The hydrated brushed aluminum discs, and pickled and coated according to example 1 are subjected to a Swift stamping test.

[0142] Experimental conditions: - cutting discs to a diameter of 64 mm - 33 mm punch (Limiting Drawing Ratio = 1.9) - stamping die: 40 mm

[0143] Results:

[0144] [Fig.3] represents the metallic substrate (2) made of hydrated brushed aluminum coated with the PTFE 0167 film (3) according to example 1 and having undergone a stamping operation.

[0145] No detachment of the film (3) is observed after shaping while the film (3) is outside the substrate.

[0146] A similar result is obtained with the PTFE 0001 film (3) and for the pickled aluminum metal substrate (2) coated with the PTFE 0167 or PTFE 0001 film (3). Example 3: stamping a pan

[0147] The hydrated brushed aluminum discs, pickled and coated according to example 1, are shaped by stamping into a pan with a diameter of 26 cm.

[0148] Results:

[0149] [Fig.4] represents the metallic substrate (2) in coated hydrated brushed aluminum of PTFE film 0167 according to example 1 and having undergone a stamping operation.

[0150] The pan was then subjected to a thermal shock test. The cap was heated to 300°C on a gas hob and then the pan was immersed in water at room temperature, this step being repeated 25 times.

[0151] No problem of detachment of the film (3) on the metal substrate (2) made of aluminum was observed.

[0152] A similar result is obtained with the PTFE 0001 film (3) and for the pickled aluminum metal substrate (2) coated with the PTFE 0167 or PTFE 0001 film (3). Example 4: stamping a saucepan

[0153] The hydrated brushed aluminum discs, pickled and coated according to example 1, are shaped by stamping-drawing into a 20 cm diameter pan.

[0154] Results:

[0155] [Fig.5] represents the metallic substrate (2) in hydrated brushed aluminum coated with the PTFE 0167 film (3) according to example 1 and having undergone a stamping-drawing operation.

[0156] The pan was then subjected to a thermal shock test. The cap was heated to 300°C on a gas hob and then the pan was immersed in water at room temperature, this step being repeated 25 times.

[0157] No problem of detachment of the film (3) on the metal substrate (2) made of aluminum was observed.

[0158] A similar result is obtained with the PTFE 0001 film (3) and for the pickled aluminum metal substrate (2) coated with the PTFE 0167 or PTFE 0001 film (3).

[0159] These examples illustrate the excellent adhesion between the film (3) and the metal substrate (2) after assembly, as well as the suitability for stamping of the coated metal substrates (2) obtained according to the invention.

Claims

1.

2.

3. Claims A method of manufacturing a coated cooking element (1) comprising the following steps: i. Provision of a metal substrate (2) having a face (2a), intended to be coated with a film (3); ii. Providing said film (3), said film (3) comprising a layer (3a) intended to be brought into contact with said face (2a) of said metal substrate (2), said layer (3a) comprising: - 50-100% by weight of polytetrafluoroethylene (PTFE) - 0-50% by weight of one or more thermoplastic polymers different from PTFE the percentages being expressed relative to the total weight of PTFE and said thermoplastic polymer(s); iii. Heating said metal substrate (2); iv. Positioning said film (3) so that the layer (3a) is opposite said face (2a) of the metal substrate (2) heated during step iii.; v. Carrying out the assembly of said metal substrate (2) and said film (3) by hot stamping, said metal substrate (2) being at a temperature between 350°C and 550°C, preferably at a temperature between 400°C and 450°C at the time of assembly and the film (3) being heated essentially by conduction when brought into contact with the metal substrate (2) at the time of assembly. Method for manufacturing a coated cooking element (1) according to claim 1, characterized in that the assembly by hot stamping during step v. is carried out by means of a hydraulic or mechanical press comprising a lower tool and an upper tool between which the metal substrate (2) and the film (3) are assembled, said metal substrate (2) being preferentially in contact with the lower tool and said film (3) being preferentially in contact with the upper tool. A method of manufacturing a coated cooking element (1) according to claim 2, characterized in that the metal substrate (2) and the film (3) are maintained under a pressure of between 100 MPa and 800 MPa, preferably between 350 MPa and 500 MPa during step v.

4. Method for manufacturing a coated cooking element (1) according to claim 2 or claim 3 characterized in that the duration of holding under pressure of the metal substrate (2) and the film (3) is less than or equal to 1 minute, preferably less than or equal to 15 seconds during step v.

5. Method for manufacturing a coated cooking element according to one of claims 2 to 4, characterized in that the duration of holding the metal substrate (2) and the film (3) under pressure is between 1 second and 1 minute, preferably between 2 seconds and 15 seconds during step v.

6. Method of manufacturing a coated cooking element (1) according to any one of claims 2 to 5, characterized in that the plane of the surface of the upper tool, relative to the plane of the surface of the lower tool, has an angle of between 0.01° and 0.5°, preferably between 0.15° and 0.25°.

7. A method of manufacturing a coated cooking element (1) according to any one of claims 2 to 6, characterized in that the lower tool is heated to a temperature between 25°C and the temperature of the metal substrate (2) at the time of assembly and / or the upper tool is brought to a temperature between 15°C and 120°C during step v.

8. A method of manufacturing a coated cooking element (1) according to any one of the preceding claims, characterized in that said metal substrate (2) is an aluminum alloy substrate, a stainless steel substrate or a multi-layer metal substrate whose face (2a) is an aluminum alloy or a stainless steel substrate.

9. Method of manufacturing a coated cooking element (1) according to any one of the preceding claims, characterized in that the surface of the face (2a) of the metal substrate (2) has undergone a surface treatment, said surface treatment being a chemical attack, brushing, hydration, sandblasting, shot blasting, a physicochemical treatment of the plasma or corona or laser type, a chemical activation or a combination of these different techniques.

10. A method of manufacturing a coated cooking element (1) according to any one of the preceding claims, characterized in that the PTFE polymer is the only polymer in the layer (3a).

11. A method of manufacturing a coated cooking element (1) according to one of any of claims 1 to 9 characterized in that said thermoplastic polymer(s) other than PTFE of the layer (3a) are chosen from: - copolymers of tetrafluoroethylene and perfluoropropyl vinyl ether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethyl vinyl ether (MVA), terpolymers of tetrafluoroethylene, polymethyl vinyl ether and fluoroalkyl vinyl ether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), - polyarylether ketones (PAEK), including polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), preferably polyether ether ketone (PEEK) - polyamideimide (PAI), polyimide (PI), polyetherimide (PEI), polybenzymidazole (PBI) - and their mixtures

12. Method of manufacturing a coated cooking element (1) according to any one of the preceding claims, characterized in that said film (3) consists of a single layer (3a) also forming a cooking face (4).

13. Method of manufacturing a coated cooking element (1) according to any one of claims 1 to 11 characterized in that said film (3) further comprises another layer (3b) forming a cooking face (4), said other layer (3b) comprising one or more polymers chosen from: - polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethylvinylether (MVA), terpolymers of tetrafluoroethylene, polymethylvinylether and fluoroalkylvinylether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), and mixtures thereof; preferably PTFE - polyarylether ketones (PAEK), including polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), preferably polyether ether ketone (PEEK) - polyamideimide (PAI), polyimide (PI), polyetherimide (PEI), polybenzymidazole (PBI) - silicone resins - and their mixtures, preferably mixtures of PTFE and PEEK.

14. A method of manufacturing a coated cooking element (1) according to claim 13 characterized in that the film (3) further comprises at least one intermediate layer (3c) positioned between the layer (3a) and the other layer (3b), said intermediate layer (3c) comprising one or more polymers chosen from: - polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethylvinylether (MVA), terpolymers of tetrafluoroethylene, polymethylvinylether and fluoroalkylvinylether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), and mixtures thereof; preferably copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA) and PTFE; preferably PTFE - polyarylether ketones (PAEK), including polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), preferably polyether ether ketone (PEEK) - polyamideimide (PAI), polyimide (PI), polyetherimide (PEI), polybenzymidazole (PBI) - silicone resins - and their mixtures, preferably mixtures of polyarylether ketones (PAEK) and PTFE, preferably mixtures of PEEK and PTFE; PTFE being particularly preferred.

15. A method of manufacturing a coated cooking element (1) according to one of any of the preceding claims, characterized in that the film (3) further comprises at least one filler and / or at least one reinforcement.

16. Method of manufacturing a coated cooking element (1) according to any one of the preceding claims, characterized in that the face of the layer (3a) of the film (3) coming into contact with the face (2a) of the metal substrate (2) during step (v) has undergone a mechanical or chemical surface treatment.

17. Method of manufacturing a coated cooking element (1) according to any one of the preceding claims, characterized in that the thickness of said film (3) is between 5 pm and 500 pm, preferably between 25 pm and 150 pm.

18. A method of shaping a coated cooking element (1) according to any one of the preceding claims comprising a step (a) of stamping the coated cooking element (1) obtained at the end of step (v).

19. A method of shaping according to claim 18 a coated cooking element (1) further comprising a step (b) of stretching the coated cooking element (1) obtained at the end of step (a).

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