EP2492022B1 - Non-stick coating - Google Patents

Description

Technical area

The invention relates to a non-stick coating with significantly improved abrasion resistance.

State of the art

Organic fluoropolymer coatings show very good non-stick properties due to their low surface energy and high temperature and chemical resistance due to the high C-F bond energies. In particular, as non-stick coatings for kitchen appliances such coatings are widely used. The low hardness of the fluoropolymers used in these coatings, however, means that these coatings are not very resistant to damage.

In addition to the low hardness, such coatings usually show poor adhesion to the surface to be coated due to the low adhesion forces of the fluorine-containing organic polymers used.

In the literature it is therefore proposed to proceed to improve the adhesion of the non-stick coating on the surface to be coated a multilayer structure, wherein the fluoropolymers with one or more high temperature resistant binders such as Pofyphenylensuffiden (PPS), polyethersulfones (PES), polysulfones, Pofyaryletherketonen (PEEK or PEK), polyimides (PI) or polyamide-imides (PAI), which provide better adhesion to the substrate.

In addition, it is known that the adhesion of the layers following the base layer depends on the content of thermoplastic fluoropolymers present in the interface between the base layer and the subsequent layer. This is due to the fact that the adhesion between the base layer and subsequent layer is achieved by the fluoropolymers in the base layer during the firing process with the fluoropolymers of the next layer merge.

An advantage with respect to adhesion to the substrate is a gradient of fluoropolymers with as few fluoropolymers as possible in the interface between the substrate and the base layer and as many fluoropolymers as possible in the interface between the base layer and the subsequent layer.

For this reason, great efforts have been made in the past to achieve the highest possible degree of segregation between the binder and the fluoropolymer in the base layer so that the binder of the base layer is mainly at the interface between substrate and base layer and the fluoropolymer at the interface between base layer and subsequent layer is enriched there to increase the intermediate adhesion between base layer and subsequent layer (see, eg US 4,087,394 or US 5,240,775 ).

Polyamide-imides (PAI) have proven to be suitable, which can therefore also be regarded as adhesion promoter layers for fluoropolymer-containing non-stick coatings ( FIG. 1 ).

Out US 7,026,036 In particular, it is known that certain fluoropolymers containing CF ₂ -CH ₂ units containing binders containing amine or amide groups, particularly polyamide-imide (PAI), can undergo chemical crosslinking reactions that further improve adhesion between high temperature-resistant binder and fluoropolymers.

To improve the mechanical durability of non-stick coatings, hard inorganic fillers have been used in addition to the aforementioned improvement in adhesion to the substrate.

So describes eg US 5,250,356 a multi-layer system comprising a finely divided aluminum oxide reinforced adhesion promoter layer consisting of PTFE, PFA and PAI, an intermediate layer consisting of PTFE, PFA and finely divided aluminum oxide and a cover layer of pure PTFE.

EP 1016466 A2 describes a multi-layer ceramic reinforced non-stick coating in which the base layer contains ceramic particles, but which are so large that they protrude from the cover layer and thereby keep the abrasive stress of the cover layer. For the same purpose, a ceramic-reinforced non-stick coating in the WO 2007/070601 A2 described.

US 6,761,964 describes a multilayer non-stick coating comprising a base layer of fluoropolymers, primer polymers and large inorganic filler particles anchored in the base layer and projecting into the subsequent intermediate layer consisting of fluoropolymers and smaller ceramic filler particles and a cover layer consisting exclusively of fluoropolymers ,

A further possibility to improve the mechanical properties of non-stick coatings is the adhesion-promoting, relatively brittle polymer polyamide-imide (PAI) (elongation at break approx. 8%) at least partially against the more viscous, linear aromatic, partially crystalline polyetheretherketone (PEEK, FIG. 2 ) (Breaking elongation approx. 50%).

Due to the toughness of the polyetheretherketone (PEEK), the coatings are less brittle and a force on the coating leads less quickly to breakage.

US 6,596,380 describes, for example, a multilayer coating which has a base layer consisting of min. 50% PEEK adhesion promoting polymers selected from polyamideimide (PAI), polyphenylene sulphide (PPS), polyetherimide (PEI) or polyimide (PI) and inert inorganic fillers, followed by an intermediate layer consisting of organic fluoropolymers and a topcoat of organic fluoropolymers.

Further disclosed WO 00/54895 a non-stick coating with improved scratch resistance with a base layer applied to a substrate consisting exclusively of polyetheretherketone (PEEK), which is characterized by one or more several cover layers which includes a fluoroplastic is covered. The layer following the polyetheretherketone layer is an adhesion-promoting polyamideimide-containing layer.

The base layer is first melted at at least 340 ° C and cooled again, then the adhesion-promoting intermediate layer consisting of polyamide-imide (PAI) and PTFE and the possibly following outer layers is applied and baked the entire assembly at 400 to 420 ° C.

DE 10 2005 004828 A1 describes a multilayer coating whose base layer comprises one or more high-performance polymers selected from polyaryl ether ketones (PEEK or PEK), liquid crystal polymers (LCP), polyphenylene sulfide (PPS) or mixtures thereof and the final covering layer of a high-performance thermoplastic selected from polyaryl ether ketones (PEEK or PEK), liquid crystal polymers ( LCP), polyphenylene sulfide (PPS) and 20-30% thermoplastic fluoropolymers. In addition to the high-performance thermoplastics, hard inorganic fillers may be contained in the layers lying below the top layer whose d ₅₀ value of the particle size must be at most twice as large as the layer thickness of the finished baked layer.

US 5,536,583 describes an article comprising as a base layer a polyether resin layer and at least one cover layer consisting of a fluoropolymer resin and an additive such as polyphenylene sulfide (PPS) or inorganic crystalline powders.

As the fluoropolymers, there have been used tetrafluoroethylene-perfluoro (alkyloxyvinyl ether) copolymer (PFA), poly (vinylidene fluoride) (PVDF), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), ethylene-tetrafluoroethylene copolymer (E-TFE), perfluoroethylene-propylene copolymer (FEP) and poly (chlorotrifluoroethylene) (CTFE) or mixtures thereof, but not polytetrafluoroethylene (PTFE).

PTFE has the highest non-stick effect among fluoropolymers. Due to its high melt viscosity above the crystallite melting range, PTFE is not easy to melt but only sinters at the grain boundaries. This makes it difficult to formulate a cover layer for polyether resin layers with PTFE contents> 30%. Topcoats with high PTFE contents have so far shown no sufficient adhesion to the underlying layer without the use of adhesion promoter layers.

Presentation of the invention

An object of the present invention is to propose an improved non-stick coating for an article over the prior art. The object of the invention is achieved by the non-stick coating according to claim 1. This non-stick coating has at least three layers, with a cover layer having a dry film thickness of 10 to 50 .mu.m, preferably 20 and 30 .mu.m, an intermediate layer having a dry film thickness of 10 to 100 .mu.m, preferably 20 and 30 .mu.m, and a base layer with a Dry film thickness of 10 to 50 microns, preferably from 20 and 30 microns. The top layer contains 40% to 90% organic fluoropolymers, wherein 20% to 50%, based on the top layer, polytetrafluoroethylene (PTFE) and 20% to 70%, based on the top layer, copolymers of tetrafluoroethylene with perfluoroalkyl vinyl ether with 1-3 C atoms in the alkyl group, namely MFA or PFA, or copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) or mixtures thereof. Furthermore, the topcoat contains 10% to 60% poly (oxy-1,4, phenylenecarbonyl-1,4-phenylene) (PEK).

The intermediate layer contains 20-30% of organic thermoplastic fluoropolymers selected from copolymers of tetrafluoroethylene with perfluoroalkyl vinyl ether having 1-3 C atoms in the alkyl group, namely MFA or PFA, copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) or mixtures thereof, and poly ( oxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEK), as well as inorganic fillers. The fillers comprise particles with a size of 40 μm to 100 μm, preferably from 45 μm to 70 μm. The particle size is selected so that at least some of the particles protrude partially into the cover layer, but do not penetrate this cover layer. Here are the measures of the invention Copolymers of tetrafluoroethylene with perfluoroalkyl vinyl ether having 1-3 C atoms in the alkyl group (MFA or PFA), copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) or mixtures thereof) are possible in the cover layer and thereby an improved non-stick effect without the To lose adhesion to the underlying layer or to require an additional adhesion-promoting layer of polyamide-imide (PAI) or polyphenylene sulfide (PPS). This is achieved in that the inorganic filler particles embedded in the intermediate layer are so large that they can project into the cover layer and thus convey the adhesion to the cover layer.

Advantageous embodiments of the inventive non-stick layer are given in the dependent claims 2 to 5.

Advantageous is a base layer which has more than 98% poly (oxy-1,4-phenylenecahonyl-1,4-phenylene) (PEK).

It is furthermore advantageous if the inorganic fillers comprise ceramic hard materials from the series of oxides, carbides, nitrides, borides, in particular silicon carbide and / or aluminum oxide.

It is particularly advantageous if the particles of the inorganic fillers of the intermediate layer have at least partially penetrated into the base layer. This is a particular advantage of the invention.

The above-mentioned as well as the claimed and described in the following embodiments, according to the invention to be used elements are subject to their size, shape design, material usage and their technical conception no special conditions of exception, so that the well-known in the respective field of application selection criteria can apply without restriction.

Brief description of the figures

Figur 1

die chemische Formel eines Polyamidimids;

Figur 2

die chemische Formel eines Polyetheretherketons (PEEK);

Figur 3

die chemische Formel eines Polyetherketons (PEK); und

Figur 4

einen Schichtaufbau gemäss eines bevorzugten Ausführungsbeispiels der Erfindung.

Exemplary embodiments of the invention will be described in more detail below with reference to drawings, in which:

FIG. 1

the chemical formula of a polyamideimide;

FIG. 2

the chemical formula of a polyetheretherketone (PEEK);

FIG. 3

the chemical formula of a polyether ketone (PEK); and

FIG. 4

a layer structure according to a preferred embodiment of the invention.

Ways to carry out the invention

According to a preferred embodiment, as in FIG. 4 is shown, has a non-stick coating, in particular for a cookware three layers, namely a cover layer 6 with a dry film thickness of about 20 and 30 microns, an intermediate layer 4 with a dry film thickness of about 20 and 30 microns, and a base layer 2 with a Dry film thickness about 20 and 30 microns. The cover layer 6 in this embodiment contains about 55% of organic fluoropolymers. Of these, about 35%, based on the cover layer (6), polytetrafluoroethylene (PTFE) and about 20%, based on the cover layer, a copolymer of tetrafluoroethylene with are about 35wt%, based on the cover layer (6), polytetrafluoroethylene (PTFE) and about 20wt%, based on the cover layer, a copolymer of tetrafluoroethylene with perfluoroalkyl vinyl ether having 1-3 carbon atoms in the alkyl group, namely PFA , Furthermore, the cover layer 6 contains about 35% by weight of poly (oxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEK).

The intermediate layer 4 contains about 30% of a copolymer of tetrafluoroethylene with perfluoroalkyl vinyl ether having 1-3 C atoms in the alkyl group, namely PFA and about 70% poly (oxy-1,4-phenylenecabonyl-1,4-phenylene) (PEK), as well as inorganic fillers 8. In this embodiment, the fillers have particles with a size of up to 70 μm. In this case, the particle size is selected so that at least some of the particles protrude partially into the cover layer 6, but do not penetrate this cover layer 6.

The base layer 2 of this preferred embodiment has greater than 98% poly (oxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEK).

The inorganic filler particles used mainly consist of silicon carbide and aluminum oxide.

It has been found that it is precisely this non-stick coating containing inorganic fillers in the intermediate layer in the specified size, a particularly good adhesion of the cover layer on the underlying layer allows, wherein the content of polytetrafluoroethylene (PTFE) is higher than 30% and no must be applied to other adhesion-promoting layers.

Furthermore, polyetherketone (PEK, poly (oxy-1,4-phenylenecarbonyl-1,4-phenylene); for use as a non-stick coating for frying and cooking utensils; FIG. 3 ), better than polyetheretherketone (PEEK; poly (oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene; FIG. 2 ). Namely, PEK has a higher glass transition temperature and a higher melting point, as compared with polyether ether ketone (PEEK; poly (oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene), with comparable toughening elasticity.

The preferred method for applying the non-stick coating is such that the layers are applied by a wet-in-wet application, namely without intermediate drying, from aqueous dispersions and subsequent drying and melting. By this method, it is possible that the inorganic fillers 8 can even penetrate into the base layer and thus the specified particle sizes can be achieved without the particles protrude from the cover layer.

LIST OF REFERENCE NUMBERS

2

base layer

4

interlayer

6

topcoat

8th

inorganic filler particles

10

substratum

Claims (5)

1. Non-stick coating for an object, wherein the non-stick coating comprises at least three layers, comprising

   - a cover layer (6) with a dry film thickness of 10 to 50 µm, preferably of 20 and 30 µm,

   - an intermediate layer (4) with a dry film thickness of 10 to 100 µm, preferably of 20 and 30 µm, and

   - a base layer (2) with a dry film thickness of 10 to 50 µm, preferably of 20 and 30 µm,
   wherein the cover layer (6) contains 40% to 90% organic fluoropolymers, wherein 20% to 50% relating to the cover layer (6) are polytetrafluoroethylene (PTFE) and 20% to 70% relating to the cover layer are copolymers of tetrafluoroethylene with a perfluoroalkyl vinyl ether with 1 to 3 C atoms in the alkyl group, namely MFA or PFA, or copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) or mixtures thereof, and the cover layer (6) contains 10% to 60% poly(oxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEK),
   wherein the intermediate layer (4) contains 20 to 30% organic thermoplastic fluoropolymers selected from copolymers of tetrafluoroethylene with a perfluoroalkyl vinyl ether with 1 to 3 C atoms in the alkyl group, namely MFA or PFA, copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) or mixtures thereof, and poly(oxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEK), and inorganic filler materials (8), wherein the filler materials (8) comprise particles having a size of 40 µm to 100 µm, preferably of 45 µm to 70 µm, and wherein the particle size is selected so that at least some of the particles partly protrude into the cover layer (6) but do not traverse said cover layer (6).
2. Non-stick coating according to claim 1, characterized in that the base layer (2) comprises more than 98% poly(oxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEK).
3. Non-stick coating according to claim 1 or 2, characterized in that the inorganic filler materials (8) comprise ceramic hard materials selected from the group of oxides, carbides, nitrides, borides.
4. Non-stick coating according to claim 3, characterized in that the inorganic filler materials (8) comprise silicon carbide and/or aluminum oxide.
5. Non-stick coating according to one of claims 1 to 4, characterized in that particles of the inorganic filler materials (8) of the intermediate layer partly protrude into the base layer.

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