Anti-Adhesive Coating

Abstract

The present invention relates to a non-stick coating comprising a transparent finishing coat, said finishing coat comprising at least one thermostable resin and fillers whose d50 is greater than the average thickness of said finishing coat.

Claims

1. A non-stick coating comprising a transparent finishing coat, said finishing coat comprising at least one thermostable resin and fillers whose d50 is at least 1.4 times greater than the average thickness of said finishing coat and at most 3 times greater than the average thickness of said finishing coat, and wherein the fillers are metal oxides.

2. The coating according to claim 1, wherein the fillers have a d50 greater than 20 μm.

3. The coating according to claim 1, wherein the fillers have a d50 less than 60 μm.

4. The coating according to claim 1, wherein the finishing coat comprises from 0.5 to 20% fillers, percentages expressed by mass with respect to the total mass of the finishing coat.

5. The coating according to claim 1, wherein characterized in that the fillers are mineral fillers with a Mohs hardness greater than or equal to 7.

6. The coating according to claim 1, wherein the metal oxides are selected from alumina, zirconia, quartz, or mixtures thereof.

7. The coating according to claim 6, wherein the metal oxides are alumina.

8. The coating according to claim 1, wherein the finishing coat has an average thickness of 2 to 40 μm.

9. The coating according to claim 1, wherein the thermostable resin is a fluorocarbon resin.

10. An article comprising a support provided with the non-stick coating according to claim 1.

11. The coating according to claim 8, wherein the finishing coat has an average thickness of 10 to 30 μm.

12. The coating according to claim 9, wherein the thermostable resin is selected from polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoromethylvinylether (such as MFA), copolymers of tetrafluoroethylene and perfluoropropylvinylether (such as PFA), copolymers of tetrafluoroethylene and hexafluoropropylene (such as FEP) or mixtures thereof.

13. The coating according to claim 1, wherein the fillers have a d50 greater than 20 μm and less than 60 μm, the finishing coat comprises from 0.5 to 20% fillers, percentages expressed by mass with respect to the total mass of the finishing coat and the metal oxides are selected from alumina, zirconia, quartz, or mixtures thereof.

Description

EXAMPLES

[0032] In the following examples and counterexamples, the average thickness of the finishing coats was assessed by scanning electron microscope (SEM) cross-sectional observations. The finishing coat thickness measurement was performed at 20 random points on the cross-sections of the coatings. The average finishing coat thickness was obtained by averaging these 20 measurements.

Example 1: Coating in Accordance with the Invention Comprising a Finishing Coat Containing Alumina Fillers

[0033] A finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. 2.5% by mass of angular alumina fillers with a d50 of 44 μm in powder form were added to the dispersion. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0034] This finish formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator). The amount of finish formulation applied was adjusted to obtain an average measured thickness of 20±1 μm of the finishing coat after the article was fired for 11 min at 430° C.

[0035] After firing, a filler concentration of 5% by mass was obtained in relation to the total mass of the finishing coat (calculation made in relation to the theoretical dry extract of the finishing coat).

Example 2: Coating in Accordance with the Invention Comprising a Finishing Coat Containing Alumina Fillers

[0036] A first finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. 2.5% by mass of angular alumina fillers with a d50 of 44 μm in powder form were added to the dispersion. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0037] This first finish formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator).

[0038] A second non-filled clear finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted. This second finish formulation was then sprayed onto the first finish formulation.

[0039] The amount of formulation deposited was adjusted so as to obtain a measured average total thickness of 25±1 μm after the article was fired for 11 min at 430° C. and so that the first formulation represents 40% of the finishing coat and the second formulation represents 60% of the finishing coat.

[0040] After firing, a filler concentration of 2% by mass was obtained in relation to the total mass of the finishing coat (calculation made in relation to the theoretical dry extract of the finishing coat).

Counter Example 1: Coating Comprising a Non-Filled Finishing Coat

[0041] A non-filled finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0042] This finishing coat formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator). The amount of finishing coat formulation applied was adjusted to obtain an average measured thickness of 10±1 μm of the finishing coat after the article was fired for 11 min at 430° C.

Counter Example 2: Coating Comprising a Finishing Coat Containing Alumina Fillers

[0043] A finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. 1% by mass of colloidal alumina fillers with a d50 of 200 nm were added to the dispersion. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0044] This finish formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator).

[0045] The amount of finish formulation applied was adjusted to obtain an average measured thickness of 20±1 μm of the finishing coat after the article was fired for 11 min at 430° C. After firing, a filler concentration of 2% by mass was obtained in relation to the total mass of the finishing coat (calculation made in relation to the theoretical dry extract of the finishing coat).

Counter Example 3: Coating Comprising a Finishing Coat Containing Alumina Fillers

[0046] A finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. 2.5% by mass of angular alumina fillers with a d50 of 1 μm in powder form were added to the dispersion. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0047] This finish formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator). The amount of finish formulation applied was adjusted to obtain an average measured thickness of 20±1 μm of the finishing coat after the article was fired for 11 min at 430° C.

[0048] After firing, a filler concentration of 5% by mass was obtained in relation to the total mass of the finishing coat (calculation made in relation to the theoretical dry extract of the finishing coat).

Counter Example 3a: Coating Comprising a Finishing Coat Containing Alumina Fillers Whose d50 is 1.3 Times Greater than the Thickness of the Finishing Coat

[0049] A finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. 2.5% by mass of angular alumina fillers with a d50 of 26 μm in powder form were added to the dispersion. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0050] This finish formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator). The amount of finish formulation applied was adjusted to obtain an average measured thickness of 20±1 μm of the finishing coat after the article was fired for 11 min at 430° C.

[0051] The d50 of the alumina filler is therefore 1.3 times the thickness of the finishing coat.

[0052] After firing, a filler concentration of 5% by mass was obtained in relation to the total mass of the finishing coat (calculation made in relation to the theoretical dry extract of the finishing coat).

Counter Example 5: Coating Comprising a Finishing Coat Containing Alumina Fillers

[0053] A finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. 2.5% by mass of angular alumina fillers with a d50 of 44 μm in powder form were added to the dispersion. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0054] This finish formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator). The amount of finish formulation applied was adjusted to obtain an average measured thickness of 40±1 μm of the finishing coat after the article was fired for 11 min at 430° C.

[0055] The d50 of the alumina filler is therefore 1.1 times the thickness of the finishing coat. After firing, a filler concentration of 5% by mass was obtained in relation to the total mass of the finishing coat (calculation made in relation to the theoretical dry extract of the finishing coat).

Counter Example 6: Coating Comprising a Finishing Coat Containing Alumina Fillers Whose d50 is 3.2 Times the Thickness of the Finishing Coat

[0056] A finish formulation was prepared from a dispersion of PTFE particles of about 200 nm in diameter. 2.5% by mass of angular alumina fillers with a d50 of 64 μm in powder form were added to the dispersion. The dry extract of the dispersion was fixed at 50% by mass. In order to keep this parameter fixed, the amount of water was adjusted.

[0057] This finish formulation was sprayed onto a shaped article (a pan) previously coated with two other coats, all of which were predominantly composed of PTFE: a black primer, an intermediate coat, and decorative and functional attributes (decoration and optimal cooking temperature indicator). The amount of finish formulation applied was adjusted to obtain an average measured thickness of 20±1 μm of the finishing coat after the article was fired for 11 min at 430° C.

[0058] The d50 of the alumina filler is therefore 3.2 times the thickness of the finishing coat.

[0059] After firing, a filler concentration of 5% by mass was obtained in relation to the total mass of the finishing coat (calculation made in relation to the theoretical dry extract of the finishing coat).

[0060] Results

[0061] Scratch Test, Non-Stick Test and Wear Coefficient

[0062] This test assesses the resistance of the coating to the action of an abrasive pad applied to its surface and the non-stick drop of this coating by a milk carbonization test after it has been subjected to the abrasion cycle. It is based on a normative test: NF D 21-511 with adapted particularities.

[0063] The apparatus used is an abrasion tester with a horizontal movement. A fixed arm supports a rectangular pad of dimensions 70±5 mm×30±5 mm, on which is placed an abrasive pad of the same size, and includes a tare allowing the application of a load of 21 N (including the weight of the lever arm). The abrasive moves at a speed of 33 back and forth movements per minute. The abraded surface is 70 mm×130 mm, i.e., a stroke of 100 mm. After 1000 abrasion cycles (i.e., 1000 back and forth movements of the abrasive), change in the non-stick properties is assessed after carbonization of a film of milk.

[0064] The test is stopped at the appearance of a scratch or a loss of non-stick properties (milk irreversibly stuck even after cleaning).

[0065] The effect of the fillers in the coatings on their mechanical performance was also assessed by determining the coating thickness removed per abrasion cycle. This is expressed as an abrasion rate v (or damaged volume) described by the formula Math 1 in which (t.sup.0) and (t.sup.abr) represent respectively the coating thickness before and after abrasion, Sab the abraded surface and A the number of abrasion cycles undergone (here 1000 cycles). The operation is repeated 3 times per configuration.

[00001]$\begin{array}{cc}v=\frac{\left(t^0-t^{\mathrm{abr}}\right).Math.S_{\mathrm{ab}}}{A}& \left[\mathrm{Math}1\right]\end{array}$

[0066] Then, the Schimtz relation is used to find the wear coefficient K (mm.sup.3/N.Math.m) and is described by the formula Math 2 in which the damaged volume v is proportional to K, to the modulus of the normal force ∥{right arrow over (F.sub.N)}∥ (21 N) and to the distance traveled d (i.e., 200 m).

v=K.Math.∥F.sub.N∥.Math.d  [Math 2]

[0067] Visual Observation

[0068] A visual observation was conducted of each article in Examples 1 and 2 and Counterexamples 1 through 6. The visual observation was rated as “good” in cases where the decorative and functional attributes were not obscured by the finishing coat (no loss of detail, no loss of color) and “poor” in cases where they were not.

[0069] Transmittance and Total Haze Value

[0070] To evaluate the optical properties of the finishing coats, measurements were made using a Haze-gard i with standard ASTM D1003.

[0071] In order to make these measurements, the finish formulations in the above examples and counterexamples were each applied directly to a smooth enameled plate. The amount of finish formulation applied was adjusted to obtain the same average finishing coat thicknesses as the examples and counterexamples, after firing the plate for 11 min at 430° C. The resulting films were peeled off the plates and analyzed.

[0072] To be aesthetically appealing and to be compatible with the presence of decorative and functional attributes (such as decoration and/or an optimal cooking temperature indicator), a coating must contain a finishing coat with a direct transmittance greater than 90% and a total haze value less than 40%.

TABLE-US-00001 TABLE 1 Wear Non- Visual Direct Examples mm.sup.3/ Scratch stick obser- transmittance Haze Unit N .Math. m cycles test vation % % 1 1 .Math. 10.sup.−4 80000 ok good 96 29 2 1 .Math. 10.sup.−4 100000 ok good 96 24

TABLE-US-00002 TABLE 2 Counter- Wear Non- Visual Direct examples mm3/ Scratch stick obser- transmittance Haze Unit N .Math. m cycles test vation % % 1 6 .Math. 10.sup.−3 1500 ok good 96 21 2 5 .Math. 10.sup.−3 3000 ok bad 80 60 3 3 .Math. 10.sup.−3 3000 ok bad 88 52  3a 3 .Math. 10.sup.−3 3000 ok bad 88 52 5 — — ok bad 80 60 6 1 .Math. 10.sup.−4 >100000 bad good 94 28