Fluorine free anti-stick coating and method for its production

Abstract

Disclosed is a non-stick coating for an article, particularly for a baking pan or other household and utility item, comprises at least a base layer (G) burnt onto a surface (O) of the article and a covering layer (D) burnt above the base layer. The base layer and the covering layer each have a dry film thickness of 1 to 25 μm, wherein the base layer contains 10 to 100 wt.-%, related to the weight of the burnt base layer, of a thermoplastic resin having a temperature resistance exceeding 200° C., and wherein the covering layer contains a thermoplastic resin having a temperature resistance exceeding 200° C. and optionally a silicone resin. Both the base layer and also the covering layer are free of perfluorinated and polyfluorinated alkyl compounds. Due to the fact that the covering layer comprises a content of thermoplastic resin of at least 30 wt.-%, related to the weight of the burnt covering layer, and of at least 2.5 wt.-%, related to the weight of the burnt covering layer, of a silicone oil, novel fluorine-free non-stick coatings with good substrate adhesion and very good deep-drawing properties are obtained. In a process for applying the non-stick coating, the base layer to be formed is applied as a liquid varnish onto the surface of the article and subsequently dried at 250 to 440° C., subsequently the covering layer is applied as liquid varnish onto the predried base layer, and finally the layers are bonded to each other and to the surface of the article by means of heat treatment at 250 to 440° C.

Claims

1. A non-stick coating for an article, wherein the non-stick coating comprises; at least a base layer burnt onto a surface of the article resulting in a burnt base layer, and a covering layer burnt above the base layer resulting in a burnt covering layer, wherein the base layer having a weight, has a dry film thickness of 1 to 25 μm, wherein the covering layer having a weight, has a dry film thickness of 1 to 25 μm, wherein the base layer comprises: 10 to 100 wt.-% of a thermoplastic resin relative to the weight of the burnt base layer, the thermoplastic resin of the base layer having a temperature resistance exceeding 200° C., wherein the covering layer comprises: at least 30 wt.-% of a thermoplastic resin relative to the weight of the burnt covering layer, the thermoplastic resin of the covering layer having a temperature resistance exceeding 200° C., at least 2.5 wt.-% of a silicone oil relative to the weight of the burnt covering layer, and optionally, a silicone resin, wherein the base layer and the covering layer are free of perfluorinated and polyfluorinated alkyl compounds.

2. The non-stick coating according to claim 1, wherein the silicone oil has a kinematic viscosity at 20° C. of at least 100 mm.sup.2s.sup.−1.

3. The non-stick coating according to claim 1, wherein the covering layer contains the silicone resin, wherein the silicone resin constitutes 1 to 67.5 wt.-% relative to the weight of the burnt covering layer.

4. The non-stick coating according to claim 3, wherein the silicone resin is a methyl silicone resin, a phenyl silicone resin and/or a methyl phenyl silicone resin.

5. The non-stick coating according to claim 1, wherein the thermoplastic resin of the base layer and of the covering layer, respectively, is independently selected from the group consisting of polyethersulfone (PES), polyphenylene ether sulfone (PPSU), liquid crystalline polymer (LCP), polyarylether ketone, polyether ketone (PEK), polyether ether ketone (PEEK), polyether clay ketone (PEKK), polyphenylene sulfide (PPS) and mixtures thereof.

6. The non-stick coating according to claim 1, wherein the base layer and/or the covering layer comprise(s) at least one additive selected from the group consisting of pigments, fillers and metallic particles

7. The non-stick coating according to claim 1, wherein the dry film thickness of the base layer is 3 to 4 μm and the dry film thickness of the covering layer is 3 to 4 μm.

8. The non-stick coating according to claim 1, wherein the covering layer comprises a different thermoplastic resin than the base layer.

9. A method for applying the non-stick coating of claim 1, wherein the base layer to be formed is applied as a liquid varnish onto the surface of the article and subsequently dried at 250 to 440° C. resulting in a predried base layer, and subsequently, the covering layer is applied as liquid varnish onto the predried base layer and the base layer and covering layer are bonded to each other and to the surface of the article via a subsequent heat treatment at 250 to 440° C.

10. The method according to claim 9, wherein the varnish used to form the base layer or the covering layer comprises the thermoplastic resin in the form of a dispersion.

11. The method according to claim 9, wherein the varnish used to form the base layer or the covering layer comprises the thermoplastic resin in dissolved form.

12. The method according to claim 9, wherein the surface of the article is metallic.

13. The method according to claim 9, wherein the varnish used to form the base layer and the varnish used to form the covering layer are applied via a coil coating process.

14. The method according to claim 9, wherein the non-stick coating is subjected to a forming process after the heat treatment.

15. A coated article comprising the surface provided with the non-stick coating according to claim 1.

16. The coated article according to claim 15, wherein the article is a baking pan.

17. The coated article according to claim 15, wherein the article is a household or utility item.

18. The non-stick coating according to claim 2, wherein the covering layer contains the silicone resin, wherein the silicone resin constitutes 1 to 67.5 wt.-% relative to the weight of the burnt covering layer.

19. The non-stick coating according to claim 18, wherein the silicone resin is a methyl silicone resin, a phenyl silicone resin and/or a methyl phenyl silicone resin.

20. The non-stick coating according to claim 18, wherein the thermoplastic resin of the base layer and of the covering layer, respectively, is independently selected from the group consisting of polyethersulfone (PES), polyphenylene ether sulfone (PPSU), liquid crystalline polymer (LCP), polyarylether ketone, polyether ketone (PEK), polyether ether ketone (PEEK), polyether clay ketone (PEKK), polyphenylene sulfide (PPS) and mixtures thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Examples of the invention will henceforth be described in more detail by reference to the drawings, wherein are shown:

[0038] FIG. 1 a layer structure of a non-stick coating according to the present invention, as a schematic sectional view:

[0039] FIG. 2 round shapes of the exemplary embodiments 1-4 and of the comparative examples 1 and 2, each after a certain number of baking cycles (cleaning in dishwasher after cycle 1, 3, 5, 7 and 9).

MODES FOR CARRYING OUT THE INVENTION AND DESCRIPTION OF VARIOUS AND PREFERRED EMBODIMENTS

[0040] The non-stick coating shown in FIG. 1 for the surface O of an article, which is for example a baking pan, comprises a base layer G burnt onto a surface O and a covering layer (D) burnt above the base layer G.

Examples

[0041] According to a particularly preferred exemplary embodiment 1, a non-stick coating, in particular for bakeware, comprises two layers, namely a covering layer having a dry film thickness of 3 to 4 μm and a base layer having a dry film thickness of 3 to 4 μm.

[0042] The base layer in this particularly preferred exemplary embodiment 1 contains 85.1 wt.-% polyethersulfone, 8 wt.-% aluminum flakes, 4.3 wt.-% mica and 2.6 wt.-% carbon black.

[0043] The covering layer in this particularly preferred exemplary embodiment 1 contains 72.5 wt. % polyethersulfone, 10.4 wt.-% of a methyl phenyl silicone resin, 1.3 wt.-% of a methyl silicone resin, 3.1 wt.-% of a silicone oil consisting of an α,ω-hydroxy terminated polydimethylsiloxane, 6.9 wt.-% aluminum flakes, 3.6 wt.-% mica and 2.2 wt.-% carbon black.

[0044] The base layer is applied in liquid form onto a grease-free ECCS sheet with a thickness of 0.29 mm by means of a spreading knife and burned in for 30 seconds at 150° C. and subsequently burned in for 1 minute at 420° C. and then cooled to room temperature. The covering layer is applied onto the dried base layer by means of a spreading knife and burned in for 30 seconds at 150° C. and subsequently burned in for 1 minute at 320° C.

[0045] According to another exemplary embodiment 2, a non-stick coating, in particular for bakeware, comprises two layers, namely a non-pigmented covering layer having a dry film thickness of 3 to 4 μm and a base layer having a dry film thickness of 3 to 4 μm.

[0046] The base layer in this exemplary embodiment 2 contains 85.1 wt.-% polyethersulfone, 8 wt.-% aluminum flakes, 4.3 wt.-% mica and 2.6 wt.-% carbon black.

[0047] The covering layer in this exemplary embodiment 2 contains 85 wt.-% polyethersulfone, 11.5 wt.-% of a methyl phenyl silicone resin and 3.5 wt.-% of a silicone oil consisting of an α,ω-hydroxy terminated polydimethylsiloxane.

[0048] The base layer is applied in liquid form onto a grease-free ECCS sheet with a thickness of 0.29 mm by means of a spreading knife and burned in for 30 seconds at 150° C. and subsequently burned in for 1 minute at 420° C. and cooled to room temperature. The covering layer is applied onto the dried base layer by means of a spreading knife and burned in for seconds at 150° C. and subsequently burned in for 1 minute at 320° C.

[0049] According to a further exemplary embodiment 3, a non-stick coating, in particular for bakeware, comprises two layers, namely a covering layer having a dry film thickness of 3 to 4 μm and a base layer having a dry film thickness of 3 to 4 μm.

[0050] The base layer in this exemplary embodiment 3 contains 85.1 wt.-% polyethersulfone, 8 wt.-% aluminum flakes, 4.3 wt.-% mica and 2.6 wt.-% carbon black.

[0051] The non-pigmented covering layer in this exemplary embodiment 3 contains 96.1 wt.-% polyethersulfone and 3.9 wt.-% of a silicone oil consisting of an α,ω-hydroxy terminated polydimethylsiloxane.

[0052] The base layer is applied in liquid form onto a grease-free ECCS sheet with a thickness of 0.29 mm by means of a spreading knife and burned in for 30 seconds at 150° C. and subsequently burned in for 1 minute at 420° C. and cooled to room temperature. The covering layer is applied onto the dried base layer by means of a spreading knife and burned in for seconds at 150° C. and subsequently burned in for 1 minute at 320° C.

[0053] According to a further exemplary embodiment 4, a non-stick coating, in particular for bakeware, comprises two layers, namely a covering layer having a dry film thickness of 3 to 4 μm and a base layer having a dry film thickness of 3 to 4 μm.

[0054] The base layer in this exemplary embodiment 4 contains 85.1 wt.-% polyethersulfone, 8 wt.-% aluminum flakes, 4.3 wt.-% mica and 2.6 wt.-% carbon black.

[0055] The covering layer in this exemplary embodiment 4 contains 80.9 wt.-% polyethersulfone, 7.7 wt.-% aluminum flakes, 4.1 wt.-% mica, 2.5 wt.-% carbon black, 1.4 wt.-% of a methyl silicone resin and 3.5 wt.-% of a silicone oil consisting of an α,ω-hydroxy terminated polydimethylsiloxane.

[0056] The base layer is applied in liquid form onto a grease-free ECCS sheet with a thickness of 0.29 mm by means of a spreading knife and burned in for 30 seconds at 150° C. and subsequently burned in for 1 minute at 420° C. and cooled to room temperature. The covering layer is applied onto the dried base layer by means of a spreading knife and burned in for 30 seconds at 150° C. and subsequently burned in for 1 minute at 320° C.

[0057] The comparative example 1 is a single-layer fluoropolymer-containing non-stick coating having the following composition: 77.8 wt.-% polyethersulfone, 3.9 wt.-% mica, 2.3 wt.-% carbon black, 8.6 wt.-% PTFE, 7.4 wt.-% aluminum flakes.

[0058] The layer is applied in liquid form onto a grease-free ECCS sheet with a thickness of 0.29 mm by means of a spreading knife and burned in for 30 seconds at 150° C. and subsequently burned in for 1 minute at 420° C.

[0059] The comparative example 2 is a single-layer non-stick coating of a modified silicone polyester having the following composition: 70.6 wt.-% of a silicone-modified polyester, 2 wt.-% of a pyrogenic silica, 2 wt.-% of a rheology additive made from organically modified bentonite clay, 0.1 wt.-% carbon black, 1.5 wt.-% of an ultramarine pigment, 16.1 wt.-% barium sulfate filler, 4.1 wt.-% v and 3.9 wt.-% of an unreactive silicone oil.

[0060] For the combined baking and dishwashing test of comparative example 2 described below a round shape made of grease-free ECCS sheet with a thickness of 0.29 mm was first pressed and subsequently varnished by a spraying process for 30 seconds at 150° C. and subsequently burned in for 1 minute at 420° C., since this coating is not deep-drawable.

[0061] Properties of the Coatings:

[0062] Square molds with a size of 26×26 mm were drawn to approximately 60 mm (#05030132) from the burnt non-stick coatings according to the present invention with the help of an Erichsen thermoforming testing machine model 212 (sheet holding force 8-9 kN, drawing speed 4-5, drawing punch travel approximately 60 mm, drawing force maximum 11 kN), in order to evaluate the deep-drawing suitability. The surfaces of the deep drawing testing machine that come into contact with the sheet during deep drawing were previously degreased with ethyl acetate.

[0063] No delamination or loss of adhesion were found with any of the non-stick coatings according to the present invention. Moreover, no superficial color changes or abrasions were observed on any of the non-stick coatings of the present invention. Therefore, all non-stick coatings of the present invention have very good thermoforming properties.

[0064] Combined Baking and Dishwashing Test:

[0065] In addition, round molds with a diameter of 22.5 cm and a depth of 4 cm were pressed from the embodiments according to the present invention and the comparison examples, in order to be able to perform a baking test in combination with dishwashing.

[0066] The Following Dough Recipe was Used for the Test Cake:

[0067] 200 g butter, 200 g sugar, 1 pinch of vanilla sugar and 1 pinch of salt are stirred to a creamy blend. Gradually, 4 eggs, 300 g of flour and 3 teaspoons of baking powder are added while stirring. All the ingredients are stirred together to form a uniform dough mixture.

[0068] A convection oven is preheated to 180° C. 200 g of cake batter are poured into the ungreased round pan and spread evenly in the pan. The batter is baked for 20 minutes. The baking pan is removed from the oven and cooled for 8 minutes. The baking pan is inverted and the cake is unmolded. For this purpose, it may be necessary to drop the pan upside down onto the table. It is noted how easily the cake can be demolded. The amount of residue remaining is also noted. Subsequently, the baking pan is washed by hand with dishwashing detergent and dried thoroughly. The cleanability is assessed and noted.

[0069] A total of 10 cycles are baked, with cleaning in the dishwasher after the 1st, 3rd, 5th, 7th and 9th cycle. After each cycle, a picture is taken of the round mold after the cake is demolded.

[0070] When evaluating the demolding of the cake and the cleanability of the round mold after each cycle, a maximum of 10 points can be awarded per cycle, resulting in a maximum of 100 points after 10 cycles. Thereby, the demolding of the cake is weighted by a factor of 0.6 and the cleanability of the round mold by a factor of 0.4.

[0071] The Demolding of the Cake is Rated as Follows:

[0072] no sticking, the cake demolds very easily, 0-5% residue, is scored as 10 points

[0073] sporadic sticking, the cake demolds easily, 5-20% residue, is scored as 7.5 points

[0074] strong sticking, the cake can be demolded, 20-40% residue, is scored as 5.0 points

[0075] strong sticking, cake can only be demolded with a dough scraper, is scored as 2.5 points

[0076] The Cleanability of the Round Mold is Rated as Follows:

[0077] no residues is scored as 10 points

[0078] light (light pressure) is scored as 7.5 points

[0079] moderate (medium pressure) is scored as 5.0 points

[0080] cleaning sponge necessary is scored as 2.5 points

[0081] Table 1 shows the evaluation of the individual cycles of the combined baking and dishwashing test of the investigated embodiments according to the present invention and the comparative examples.

[0082] As shown in further tests, the presence of at least 2.5 wt.-% of a silicone oil related to the weight of the burnt covering layer is necessary to ensure the deep-drawing suitability of the non-stick coatings according to the present invention.

[0083] Moreover, Table 1 shows that even without the additional presence of a silicone resin in the covering layer (exemplary embodiment 3 and 4) good average results can be achieved in the combined baking and dishwashing test, which are quite comparable with the two comparative examples 1 and 2 according to prior art.

[0084] The addition of silicone resins in the covering layer according to the present invention can considerably improve the results of the combined baking and dishwashing tests.

TABLE-US-00001 TABLE 1 Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Sum of 1 2 3 4 5 6 7 8 9 10 Subtotal Weight Total totals Ex. 1 demolding 10 7.5 10 5 7.5 5 10 7.5 10 5 77.5 0.6 46.5 cleaning 10 7.5 10 7.5 7.5 7.5 7.5 7.5 7.5 7.5 80.0 0.4 32.0 78.5 Ex. 2 demolding 10 5 10 7.5 10 5 5 5 7.5 5 70.0 0.6 42.00 cleaning 10 7.5 10 7.5 7.5 7.5 7.5 5 5 7.5 75.0 0.4 30.00 72 Ex. 3 demolding 2.5 7.5 2.5 2.5 5 2.5 2.5 2.5 5 2.5 35.0 0.6 21.00 cleaning 5 5 5 5 5 5 2.5 5 5 5 47.5 0.4 19.00 40 Ex. 4 demolding 10 7.5 2.5 2.5 5 2.5 2.5 2.5 5 2.5 42.5 0.6 25.50 cleaning 10 5 5 5 5 5 2.5 2.5 5 5 50.0 0.4 20.00 45.5 Comparative demolding 10 5 7.5 2.5 5 2.5 2.5 2.5 5 5 47.5 0.6 10 Ex. 1 cleaning 10 7.5 5 5 5 5 2.5 5 5 7.5 57.5 0.4 10 51.5 Comparative demolding 10 5 5 2.5 2.5 2.5 2.5 2.5 5 2.5 40.0 0.6 10 Ex. 2 cleaning 10 5 5 5 2.5 2.5 2.5 2.5 5 5 45.0 0.4 10 42