EP1419016B1 - Non-stick coating having improved scratch and abrasion resistance - Google Patents

Abstract

The non-stick coating of the invention comprises at least one primer layer comprising a fluorocarbon resin and inorganic particles, the primer layer being applied on a support and covered in one or more finishing layers based on fluorocarbon resin. The inorganic particles are ceramic particles having a mean diameter less than 4 mum. The coating is particularly suitable for cooking utensils.

Description

The present invention relates to a release liner having improved resistance to scratching and abrasion.

The invention also relates to articles, and in particular culinary utensils, comprising a coating according to the invention.

The release coatings commonly used for coating cookware are made of fluorocarbon resin, such as polytetrafluoroethylene (PTFE).

Conventionally, these coatings are formed by the application, directly on the support, of a first bonding layer based on fluorocarbon resin, commonly called "primary layer", this first layer being covered by one or more layers of finish, also based on fluorocarbon resin.

Such PTFE based coatings are known for their release properties but also for their chemical and thermal resistance.

However, they have the disadvantage of being sensitive to scratching and abrasion, this creating an early wear of this type of coatings.

To overcome this major disadvantage and obtain release coatings having improved resistance to scratching and abrasion, a first solution consists in forming a hard undercoat or a hard base between the support and the primary layer, said underlayer forming a barrier preventing scratches from reaching the surface of the support.

A hard underlayer may especially be formed by a polymer, such as polyamide-imide (PAI) and / or oxy-1,4-phenylene-oxy-1,4-phenylene-1,4-carbonyl-phenylene (PEEK), as taught by international applications WO 00/54895 and WO 00/54896 in the name of the Applicant.

A hard base may especially be enamel, stainless steel or alumina.

A hard base formed of alumina can be deposited on the support by thermal plasma spraying.

In the particular case of an aluminum support, this hard alumina base can also be formed directly from the support, by anodic oxidation thereof. A coating comprising such a hard base, and whose resistance to scratching and abrasion is particularly satisfactory, has been described by the Applicant in his application EP 0 902 105.

As an alternative to the introduction of a hard undercoat or a hard base, a second solution for reinforcing the PTFE-based coatings is to introduce reinforcing fillers into one of the layers forming said coatings, particularly in the primary layer.

Among the various reinforcing fillers commonly used, mention may be made of inorganic particles such as particles of mica (EP 0 389 966), silica, mullite (FR 2 756 875) or metal flakes or metal oxides, in particular aluminum alloy (EP 0 656 831). The average dimensions of the inorganic particles indicated by the two European documents are of the order of 5 to 200 microns.

These solutions to strengthen PTFE-based coatings with particles Inorganic materials have been criticized and found unsatisfactory in terms of scratch and abrasion resistance by EP 1 016 466.

To avoid having to reinforce this type of coatings, EP 1 016 466 describes a coating whose objective is to deflect the abrasive forces from the external surface of the coating: for this it comprises a fluorocarbon resin-based primer and which contains inorganic ceramic particles which extend beyond this primary layer, the primary layer being applied to the support and covered by one or two upper layers based on fluorocarbon resin, these upper layers covering all the ceramic particles being able to extend beyond the primary layer.

Indeed, the ceramic particles present in the primary layer taught by this prior art have dimensions such that they deform the surface of the upper layers and thus ensure the formation of deflection zones on the outer surface of the coating, these deflection zones allowing then to deflect the abrasion forces, thus reinforcing the abrasion resistance of the coating.

The average dimensions of the ceramic particles allowing the formation of these deflection zones, as taught by EP 1 016 466, are a function of the total thickness of the dry coating, according to the following relation: the ratio of this total thickness of dry coating the longest diameter of said ceramic particles is between 0.8 and 2.0. This document specifies that such particles have an average size of at least 14 microns (μm), advantageously at least 20 μm and preferably at least 25 μm.

This prior art tends to meet the problem of achieving a non-stick coating that resists scratching and abrasion but indirectly because it tends to protect the surface of the coating by deflecting the abrasion forces, and thus avoids the perforation of the coating itself.

However, it has the major disadvantage of linking the dimensioning of the ceramic particles to the thickness of the final coating that is desired: in fact, small particles do not allow to confer the desired technical effect, since n ' generate no point of deflection on the surface of the coating; on the other hand , too large particles can perforate the coating and alter its anti-adhesive and low friction properties.

In addition, the outer surface of the coating is then deformed by the presence of the deflection zones which, over time, will be eroded by the action of the friction forces, this may eventually cause the formation of bare areas, anti-adhesive properties of the coating decreasing in part.

The object of the present invention is therefore to provide a coating which, while retaining excellent anti-adhesive properties, presents in itself and not by a deflection effect, improved resistance to scratching and abrasion without deformation of its external surface and without necessarily resorting to the insertion of a hard undercoat or a specific hard base, in the particular application of cooking utensils.

The subject of the present invention is thus a coating comprising at least one primary layer containing a fluorocarbon resin and particles inorganic, the primary layer being applied to a support and covered by one or more fluorocarbon resin-based topcoats.

According to the invention, the inorganic particles are ceramic particles having a mean diameter of less than 4 microns (μm) and are entirely included in the primary layer, whose outer surface is not deformed by their presence.

Advantageously, the ceramic particles which meet the object of the present invention have a high hardness which is greater than about 1500 Vickers and a remarkable melt strength, with melting points above 2000 ° C.

Preferably, the mean diameter of the ceramic particles is between 0.01 and 3 μm, advantageously between 0.05 and 2 μm, more advantageously between 0.1 and 1 μm, preferably of the order of 0.5 μm.

The Applicant has found that, in spite of their small dimensions, the ceramic particles of the invention give the coating a much greater resistance to scratching and abrasion than the coatings comprising inorganic particles described by the prior art, such as the mica, mullite, metallic flakes, on the one hand and / or higher dimensions, or even much higher, recommended by the prior art, on the other hand.

This observation is all the more surprising and unexpected as the remarkable physical and chemical properties of the ceramic particles according to the invention, in particular an extreme hardness combined with a high melting point, are expressed, even for extremely small dimensions.

In addition, and contrary to the postulate of the document EP 1 016 466, this high-performance resistance to scratching and abrasion is obtained in the absence of any formation of deflection zones intended to deflect the abrasion forces; in this, the present invention overcomes the prejudice posed by this teaching.

Preferably, the ceramic particles used in the context of the present invention comprise at least one element selected from metal carbides, metal nitrides, metal borides, metal oxycarbides, metal oxynitrides, metal carbonitrides and metal oxides.

However, there is no reason to consider the use of a mixture comprising two or more of the ceramic particles mentioned above.

Preferably, the metal is a refractory metal, or even a mixture of refractory metals. In the latter case, there may be mentioned mixed carbides or mixed nitrides, which are respectively carbides and nitrides comprising at least two different refractory metals.

Preferably, the refractory metals are chosen from titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), niobium (Nb), tungsten (W), molybdenum (Mo ), boron (B), beryllium (Be), silicon (Si) and aluminum (Al).

Processes for obtaining carbides or nitrides, whether these carbides or nitrides are mixed or not, oxycarbides, oxynitrides and / or carbonitrides of refractory metals as envisaged above have been described in the documents FR 2,609,461, EP 0 543 753 and WO 99/47454.

Indeed, the implementation of the teaching of FR 2 609 461 makes it possible to obtain particles homogeneous ceramics, both in terms of chemical composition and physical properties, for reproducible particle sizes.

In particular, the ceramic particles described by EP 0 543 753 have a particularly high hardness, in this case greater than 2000 Vickers associated with an equally high density, which can be between 5 and 16 approximately.

In addition, thanks to their quasi-spherical shape, the ceramic particles as taught by EP 0 543 753 make it possible to better withstand the impact of "large" particles that would strike the multilayer coating according to the invention.

More preferably, the metal is at least one of the elements selected from Ti, Zr or Hf.

The ceramic particles TiC, ZrC, HfC, TiN, ZrN or HfN conjugate both the characteristics of hardness and high melting point recalled above with those of metals, especially in terms of thermal conductivity.

In an advantageous version of the invention, the weight proportion of ceramic particles in the primary layer is, after firing, between 1 and 40%, advantageously between 3 and 25%, preferably between 5 and 15%.

These relatively high weight ratios of ceramic fillers also give a surprising result to the coatings of the invention; indeed, and contrary to what is commonly admitted, namely that the addition of inorganic fillers, in proportions greater than 15%, impairs the cohesion of the layer enclosing them (appearance of cracks and cracks) and therefore has to reduce its resistance to scratching and its anti-adhesive properties, the Applicant has found that the cohesion of the primary layer was found to be reinforced.

• on incorpore, de manière homogène, des particules céramiques dont le diamètre moyen est inférieur à 4 microns à une composition comprenant une résine fluorocarbonée pour former une couche primaire,
• on applique, sur le support, au moins une couche primaire renfermant les particules céramiques, la couche primaire formant une surface lisse,
• on applique, sur cette couche de primaire, la ou les couches de finition à base de résine fluorocarbonée, puis
• on fritte l'ensemble des couches à 400-420°C.

The invention also relates to a method of producing a coating on a support, this method comprising the following steps:

• homogeneously incorporating ceramic particles having an average diameter of less than 4 microns to a composition comprising a fluorocarbon resin to form a primary layer,
• at least one primary layer containing the ceramic particles is applied to the support, the primary layer forming a smooth surface,
• the fluorocarbon resin-based top coat (s) is then applied to this layer of primer.
• the layers are sintered at 400-420 ° C.

The invention aims in particular, culinary utensils coated inside and / or outside by a release coating.

The support of these utensils can be aluminum, steel, enamelled steel, stainless steel, glass, ceramic.

This support may or may not undergo prior treatment, depending on whether it is desired to have a rough or smooth support: it can thus be treated chemically, for example by acid etching, or mechanically, particularly by sandblasting.

The primary and finishing layers contain a fluorocarbon resin.

This fluorocarbon resin may be PTFE, perfluoroalkoxy (PFA) or fluorinated ethylene-propylene (FEP), or a mixture of these compounds.

The primary and finishing layers are deposited on the support, previously treated or not, by spraying (spraying), by screen printing, for example according to the process described in document FR 2 689 037 in the name of the Applicant, by pad printing or by roll coating.

By way of illustration, three examples of embodiments of coatings according to the invention are given below.

Example 1

The coating of this Example 1 consists of a primary layer applied to the support, then covered by two topcoats, formed of an intermediate layer, itself covered by a topcoat.

The composition of each of the three layers, given in parts by weight, is given below, by way of example:

Primary layer

. aqueous dispersion of polyamide-imide (PAI) (from 10 to 15% solids) 18-35 . N-methylpyrrolidone 0-12 . spreading agent emulsion and film forming agent 4-10 . dispersion of fluorocarbon resin (s) (from 50 to 60% solids) 15-35 . colloidal silica (30% dry extract) 10-16 . TiC powder (0.1 to 1 μm) 1-10

Intermediate layer

. dispersion of fluorocarbon resin (s) (from 50 to 60% solids) 11-89 . spreading agent emulsion and film forming agent 10-20 . TiO ₂ coated mica flakes 0.1 to 1.6 . pigments (carbon black) 0.1 to 1.6

Topcoat

. PTFE dispersion (60% dry extract) 78-90 . spreading agent emulsion and film forming agent 10-20 . mica flakes coated with TiO ₂ 0.1 to 1.6

The primary layer is preferably formed by a homogeneous composition of the ceramic particles with the fluorocarbon resin.

In fact, a distribution of the ceramic particles which is homogeneous, that is to say uniform and therefore does not form an agglomerate, makes it possible to produce a coherent and homogeneous primary layer on the surface and throughout its thickness, and thus a layer primary free of defects, cracks, cracks, bubbles ...

In this example, the titanium carbide (TiC) incorporated in the primary layer consists of a mixture of ceramic particles whose average diameter is between 0.1 and 1 micron.

The primary layer is deposited on the support to form a smooth surface, that is to say a flat outer surface, devoid of any deflection zone.

The primary layer is then dried to obtain a primary layer whose thickness is between 4 and 16 microns; the intermediate layer and then the top topcoat are then applied, the assembly consisting of the intermediate and topcoat layers having a thickness of between 10 and 25 μm.

After drying all three layers, a sintering step is carried out at 400-420 ° C of the coating thus obtained for 3 to 7 minutes.

A coating is obtained, on the one hand adhering strongly to the support and, on the other hand, which has scratch resistance performance improved: tests have shown that intensive cooking of food by means of metal spatulas on a cooking utensil, in this case a pan, covered with a coating according to the first example above, these firings representing one to two years Conventional use of a kitchen utensil, practically scratched the coating, compared to identical intensive cooking carried out by means of plastic spatulas, on a utensil, whose primary layer did not contain particles TiC.

In an advantageous version of the invention, the coating may furthermore comprise, between the support and the primer layer, a hard underlayer.

The presence of a hard undercoat combines the effects of the present invention with those imparted by the hard sublayers described by the prior art, thereby enhancing the scratch and abrasion resistance.

In a preferred version, the coating may also comprise at least two primary layers, each of which contains ceramic particles having an average diameter of less than 4 microns.

A second embodiment of a coating combining these two variants of the invention is given below.

Example 2

• d'une sous-couche dure dépourvue de résine fluorocarbonée telle que décrite par WO 00/54896 ou par WO 00/54896, cette sous-couche étant directement appliquée sur le support,
• de deux couches primaires, de composition identique, appliquées successivement sur la sous-couche,
• une couche intermédiaire recouvrant la seconde couche primaire, puis
• une couche de finition supérieure recouvrant la couche intermédiaire.

This coating is produced by the deposit:

• a hard underlayer devoid of fluorocarbon resin as described by WO 00/54896 or WO 00/54896, this underlayer being directly applied to the support,
• two primary layers, of identical composition, applied successively on the underlayer,
• an intermediate layer covering the second primary layer, then
• an upper finish layer covering the intermediate layer.

The undercoat, devoid of fluorocarbon resin, is based on polyetheretherketone or oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene (PEEK).

The two primary layers have a composition identical to that of the primary layer of Example 1, and both contain TiC constituted by a mixture of particles whose mean diameter is between 0.1 and 1 micron.

The total thickness formed by the two primary layers is between 4 and 16 microns.

Similarly, the intermediate and topcoat layers have respective compositions identical to those described in Example 1 above.

Before the application of the PEEK-based underlayer, the support may or may not be chemically or mechanically treated to roughen its surface.

The underlayer may be applied to the support by spraying in the form of an aqueous dispersion.

Such an underlayer will, after firing, consist exclusively of PEEK, as taught in WO 00/54895, or by at least 50% of PEEK, the rest being composed of pure or mixed thermostable polymers (such as polyphenylene sulfide, polyetherimide). polyimide, polyetherketone, polyethersulfone, polyamide-imide) and inert fillers selected from metal oxides, silica, mica particles, or lamellar fillers, as taught in WO 00/54896.

The primary, intermediate and topcoat layers are then successively applied according to the procedure described above for Example 1.

The whole is then sintered at 400-420 ° C for 3 to 7 minutes.

In a variant of the invention, the coating may further comprise, between the support and the primer layer, a hard base.

A third embodiment of a coating combining a hard base and the application of two primary layers is given below.

Example 3

• une base dure,
• deux couches primaires, de composition identique, appliquées successivement sur la sous-couche,
• une couche intermédiaire recouvrant la seconde couche primaire, puis
• une couche de finition recouvrant la couche intermédiaire.

This coating consists of:

• a hard base,
• two primary layers, of identical composition, applied successively on the underlayer,
• an intermediate layer covering the second primary layer, then
• a topcoat covering the intermediate layer.

The hard base may be of the ceramic type and formed on the support, for example by plasma application of an Al ₂ O ₃ / TiO ₂ layer. It may also be of metal type, and carried on the support by plasma deposition of stainless steel powder.

This hard base can also be obtained directly from the support, and prior to the application of the primary layer (s), by carrying out a hard anodization or anodization by micro-arcs as described in EP 0 902 105 in the name of of the Applicant.

The presence of this hard base makes it possible to isolate the coating of the support, in the case of deep scratching.

The primary, intermediate and topcoat layers are then successively applied, according to the procedure described above for Examples 1 and 2, and then sintered at 400-420 ° C for 3 to 7 minutes.

It is obvious that in each of the three embodiments detailed above, it is possible to perform a chemical or physical treatment of the support, prior to the application of the hard sub-layer and / or the (first) primary layer.

Of course, the invention is not limited to the examples described above, and whose improved resistance properties to scratching and abrasion have been measured for culinary utensils having an inner surface intended to be in contact with the food, covered with a coating according to the invention.

Such a coating can of course be used more broadly in the culinary field, to coat the inside and / or outside of any type of cooking utensils, hotplates, grill plates, ...; it may also be intended to coat any sliding surface, and in particular those of iron for example.

Claims (15)

1. A non-stick coating presenting improved resistance to scratching and abrasion, the coating comprising at least a primer layer comprising a fluorocarbon resin and inorganic particles, the primer layer being applied to a support and itself being covered in one or more finishing layers based on fluorocarbon resin, the coating being characterized in that the inorganic particles are ceramic particles having a mean diameter of less than 4 µm, in that the ceramic particles comprise at least one element selected from metal carbides, metal nitrides, metal borides, metal oxicarbides, metal oxinitrides, metal carbonitrides, and in that the proportion by weight of the ceramic particles in the primer layer, after firing, lies in the range 1% to 40%, advantageously in the range 3% to 25%, and preferably in the range 5% to 15%.
2. A coating according to claim 1, characterized in that the mean diameter of the ceramic particles lies in the range 0.01 µm to 3 µm approximately, advantageously in the range 0.05 µm to 2 µm approximately, more advantageously in the range 0.1 µm to 1 µm approximately, and is preferably about 0.5 µm.
3. A coating according to claim 1 or claim 2, characterized in that the ceramic particles present high hardness, in excess of 1500 on the Vickers scale.
4. A coating according to any one of the preceding claims, characterized in that the metal is at least one of the elements selected from: titanium (Ti); zirconium (Zr); hafnium (Hf); tantalum (Ta); niobium (Nb); tungsten (W); molybdenum (Mo); boron (B); silicon (Si); beryllium (Be); and aluminium (Al).
5. A coating according to any one of the preceding claims 1 to 4, characterized in that it comprises at least two primer layers.
6. A coating according to any one of the preceding claims 1 to 5, characterized in that the total thickness of the primer layer(s) lies in the range 4 µm to 16 µm.
7. A coating according to any one of the preceding claims 1 to 6, characterized in that it further comprises a hard underlayer between the support and the primer layer(s).
8. A coating according to claim 7, characterized in that the hard underlayer does not contain any fluorocarbon resin.
9. A coating according to any one of the preceding claims 1 to 7, characterized in that it further comprises a hard base between the support and the primer layer(s).
10. A cooking utensil coated by a coating in accordance with any one of the preceding claims 1 to 9.
11. A method of making a coating according to any one of the preceding claims 1 to 9 on a support, the method comprising the following steps:

    - uniformly incorporating ceramic particles of mean diameter less than 4 µm in a composition comprising a fluorocarbon resin so as to form a primer layer, the ceramic particles comprising at least one element selected from metal carbides, metal nitrides, metal borides, metal oxicarbides, metal oxinitrides, metal carbonitrides, the proportion by weight of the ceramic particles in the primer layer, after firing, lying in the range 1% to 40%, advantageously in the range 3% to 25%, and preferably in the 5% to 15%;

    - applying at least one primer layer containing the ceramic particles on the support, the primer layer forming a smooth surface;

    - applying the finishing layer(s) based on fluorocarbon resin on the primer layer(s); and then

    - sintering all of the layers at 400°C to 420°C.
12. A method according to claim 11, characterized in that at least one second primer layer containing ceramic particles of mean diameter less than 4 µm is also deposited on the primer layer prior to applying the finishing layer(s).
13. A method according to claim 11 or claim 12, characterized in that a hard base or a hard underlayer having no fluorocarbon resin is also deposited directly on the support prior to applying the primer layer(s) thereto.
14. A method according to claim 11 or claim 12, characterized in that the support is subjected to anodizing prior to applying the primer layer(s).
15. A method according to any one of preceding claims 11 to 14, characterized in that chemical or physical treatment is applied to the support prior to applying the hard underlayer and/or the primer layer(s).