Sol-gel coating comprising anisotropic particles and culinary article provided with such a coating

Abstract

Provided is a vitreous coating comprising at least one layer embodied in the form of a continuous film of sol-gel material comprising a matrix formed from at least one metal polyalkoxylate and wherein anisotropically-shaped particles are dispersed, said layer comprising at least one area wherein the particles are particles predominantly inclined by an angle (α) of between 20° and 90° relative to the median plane of the film. The subject matter of the present invention also comprises a method of manufacturing such a coating, and a culinary article one of the surfaces of which is coated with such a coating.

Claims

1. Vitreous coating comprising at least one layer in the form of a continuous film of a sol-gel material comprising a matrix formed from at least one metallic polyalkoxylate and in which anisotropic shaped particles are dispersed, said layer comprising at least one first area in which said particles are particles which are inclined at an angle α between 20° and 90° with respect to the average plane of the film, wherein more than 66% of said anisotropic shaped particles are inclined at an angle α between 20° and 90° with respect to the average plane of the film, and wherein said coating further comprises, adjacent to the first area, at least one second area in which more than 66% of the particles are particles which are inclined at an angle β that is greater than 0° and less than 20° with respect to the average plane of the film.

2. Coating according to claim 1, wherein more than 80% of said anisotropic shaped particles are inclined at an angle α between 20° and 90° with respect to the average plane of the film.

3. Coating according to claim 1, wherein said particles comprise particles capable of being oriented by mechanical or physical means.

4. Coating according to claim 3, wherein said particles capable of being oriented are magnetisable particles.

5. Coating according to claim 4, wherein said magnetisable particles comprise at least one ferromagnetic metal.

6. Coating according to claim 5, wherein the magnetisable particles have a core-shell structure, in which the ferromagnetic metal is in the core and/or in the shell of said particles.

7. Coating according to claim 6, wherein the magnetisable particles are mica flakes encapsulated with iron oxide Fe.sub.2O.sub.3.

8. Coating according to claim 6, wherein the magnetisable particles are flakes whose core is made of a plastic material and the shell is made of iron oxide Fe.sub.2O.sub.3, or flakes or fibres whose core is made of ferromagnetic metal and the shell is made of a plastic material or of a sol-gel material.

9. Coating according to claim 4, wherein said vitreous coating layer further comprises non-magnetisable particles.

10. Coating according to claim 9, wherein the magnetisable particles, and the non-magnetisable particles, have a core-shell structure.

11. Coating according to claim 9, wherein the non-magnetisable particles are selected from the group comprising mica flakes, and titanium dioxide encapsulated mica or silica flakes.

12. Coating according to claim 4, wherein the magnetisable particles are ferritic stainless steel fibres.

13. Coating according to claim 1, wherein more than 80% of said particles are, in the second area, inclined at an angle β lower than 20° with respect to the average plane of the film.

14. Coating according to claim 1, said coating being non-opaque and further comprising, adjacent to the first area, at least one second area in which the particles are randomly arranged in the layer in the form of a film.

15. Coating according to claim 1, wherein the alternation of the first and second areas defines a decor.

16. Coating according to claim 1, said coating being a finish layer.

17. Coating according to claim 1, comprising: a base layer intended to be arranged on a support, and at least one finish layer covering said base layer and intended to be in contact with the outside environment, said finish layer being in the form of a continuous film of a sol-gel material comprising a matrix formed from at least one metallic polyalkoxylate in which said anisotropic particles are dispersed.

18. Coating according to claim 17, wherein said base layer is also in the form of a continuous film of a sol-gel material, the sol-gel material preferably comprising a matrix formed from at least one metallic polyalkoxylate.

19. Coating according to claim 17, wherein said base layer is a continuous or discontinuous hard base, said hard base being made of one of enamel, of ceramic, or of metal.

20. Coating according to claim 17, wherein the metallic polyalkoxylate of the finish layer, and of the base layer, is a polyalkoxysilane.

21. Coating according to claim 20, wherein the film of sol-gel material of the finish layer, and of the base layer, further comprises at least 5% by weight with respect to the total coating weight of at least one colloidal metallic oxide dispersed in said matrix, said oxide being selected from the group comprising silica, alumina, cerium oxide, zinc oxide, vanadium oxide and zirconium oxide.

22. Coating according to claim 1, wherein the sol-gel material forming said vitreous coating further comprises at least one silicone oil.

23. Coating according to claim 22, wherein the silicone oil is selected from methyl-phenyl silicone oils, methyl silicone oils and hydroxylated silicone oils.

24. Coating according to claim 1, wherein said vitreous coating comprises at least one pigment selected from the thermostable pigments, the metallic salts, the thermochromic semiconductor pigments, and mixtures thereof.

25. Article comprising a support having two opposite sides, at least one of which is covered with a coating as defined in claim 1.

26. Article according to claim 25, wherein the support is made of a material selected from metals, wood, glass, ceramics and plastic materials.

27. Article according to claim 26, wherein the support is a metallic support made of one of anodised or non-anodised aluminium, or of polished, brushed, or micro-shotpeened aluminium, or of polished, brushed or micro-shotpeened stainless steel, or of cast iron, or of hammered or polished copper.

28. Article according to claim 25, which is a culinary article, or a sole plate of an electric iron, or plates of hair straighteners, or a hood of a household appliance.

29. Method for manufacturing a vitreous coating according to claim 1 on a support in which anisotropic particles are dispersed, comprising a step of orienting said anisotropic particles by physical or mechanical means in at least one area of said vitreous coating according to claim 1.

30. Method according to claim 29, comprising the following steps: a) providing the support; b) preparing a hybrid composition comprising at least one metallic alkoxide type sol-gel precursor and anisotropic shaped particles; c) hydrolysing said sol-gel precursor by introduction of water and of an acid or basic catalyst, followed by a condensation reaction to obtain a sol-gel composition SG; (d) maintaining the support at a temperature lower than or equal to 100° C. followed by applying, directly or indirectly on all or part of the support, at least one layer of sol-gel composition SG; e) orienting said anisotropic particles by physical or mechanical means in at least one area of said SG composition layer; then f) firing.

31. Method according to claim 30, wherein said anisotropic shaped particles are magnetisable particles, and in step e) of orienting said magnetisable particles is a step of magnetisation by applying a magnetic field, said magnetisation e) being carried out either during the application d) of the sol-gel composition SG on the support, or after said application step d) and prior to the firing step f).

32. Method according to claim 31, wherein a sol-gel composition SG essentially free of opaque pigments is prepared, so that the SG composition layer (31) is essentially transparent, and wherein the magnetisation step e) comprises the application of a magnetic field in at least one specific first area of the SG composition layer, second area(s) immediately adjacent to said specific first area not being subjected to the effect of the magnetic field or being subjected to the effect of field lines substantially parallel to the layer being in the form of a film, so as to form a three-dimensional pattern.

33. Method according to claim 27, further comprises, prior to the application step d) of the SG composition layer, forming at least one base layer arranged between the support and said SG composition layer.

34. Method according to claim 33, wherein the base layer is a pigmented base layer obtained by preparing a colored composition comprising at least one metallic alkoxide type sol-gel precursor and at least one pigment selected from thermostable pigments, metallic salts, thermochromic semiconductor pigments and mixtures thereof; then hydrolysing said sol-gel precursor by introduction of water and of an acid or basic catalyst, and condensing to obtain a colored sol-gel composition SG0; and applying, directly on all or part of the support having a temperature lower than 100° C., the colored sol-gel composition to form the pigmented base layer.

35. Method according to claim 34, further comprising, after applying the colored sol-gel composition, drying at a temperature lower than or equal to 100° C.

36. Method according to claim 30, wherein the firing step f) is carried out at a temperature of 200° C. to 350° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages and features of the present invention will appear from the following description, given by way of non-limitative example and with reference to the accompanying figures:

(2) FIG. 1 shows a schematic sectional view of a first embodiment of a frying pan according to the invention provided with a single-layered vitreous coating film (comprising at least one area with anisotropic particles substantially perpendicular to the film);

(3) FIG. 2 shows a schematic sectional view of a second embodiment of a frying pan according to the invention provided with a double-layered vitreous coating comprising at least one area with anisotropic particles substantially perpendicular to the film;

(4) FIG. 3 shows a schematic sectional view of a third embodiment of a frying pan according to the invention provided with a double-layered vitreous coating comprising a three-dimensional pattern;

(5) FIG. 4 shows a series of five scanning electron microscope (SEM) images 4A to 4E of a cross section of the frying pan shown in FIG. 3 taken at the area with anisotropic particles substantially perpendicular to the film;

(6) FIG. 5 shows a series of four scanning electron microscope (SEM) images 5A to 5D of a cross section of the frying pan shown in FIG. 3 taken at the area with anisotropic particles substantially parallel to the film.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows, as an example of a culinary article according to the invention, a frying pan 1 before the magnetisation step, which comprises a support 2 in the form of a hollow bowl and a gripping handle 7. The support 2 comprises an inner side 21 which is the side oriented towards the food that may be received in the frying pan 1, and an outer side 22 which is intended to be arranged towards an external heat source.

(8) The support 2 comprises, on its inner side 21, a single layer of vitreous coating 3, which consists only of a finish layer 31 in the form of a continuous film. It is a continuous film 31 of a sol-gel material comprising a matrix formed from at least one metallic polyalkoxylate and in which anisotropic shaped particles 32 (for example flakes or microfibres, as shown in the illustrative examples of the present invention described below) are dispersed.

(9) FIG. 1 shows that the finish layer comprises at least one area 311 in which the particles are substantially perpendicular to the finish layer.

(10) This specific orientation of the anisotropic particles 32 in the first area 311 can be obtained for example by magnetisation if the anisotropic particles comprise magnetisable particles. This magnetisation of the specific first area 311 can be achieved for example by arranging underneath the support a permanent magnet, in particular of elastomeric type (which limits the magnetisation conditions to a temperature lower than 80° C.) or an electromagnet.

(11) It is also possible to use a ferrite or neodymium type permanent magnet. In this case, the maximum temperature value of the conditions under which magnetisation is carried out can then be greater than 80° C., but should remain below the Curie temperature of the magnets used.

(12) Preferably, a magnet is used that emits a magnetic field of intensity comprised between 40 and 100 mT, preferably around 70 mT.

(13) FIG. 1 clearly shows that the magnetisable particles of the finish layer 31 are oriented perpendicularly to this layer in this specific first area 311, according to the field lines generated by the permanent magnet located just underneath this area 311.

(14) FIG. 2 shows a schematic sectional view of a second embodiment of a frying pan according to the invention, which differs from that illustrated in FIG. 1 in that the vitreous coating 3 is double-layered. The double-layered coating 3 comprises a base layer 30 arranged on the inner side 21 of the support 2 and a finish layer 31 in the form of a continuous film of a sol-gel material covering the base layer 30, the anisotropic particles 32 being included in the finish layer. The sol-gel material of the finish layer may comprise in particular a matrix formed from at least one metallic polyalkoxylate in which the particles 32 are dispersed.

(15) FIG. 3 shows a schematic sectional view of a third embodiment of a frying pan 1 according to the invention provided with a vitreous double-layered coating comprising a three-dimensional pattern formed by the alternation of second areas 312 with anisotropic particles substantially parallel to the film and of first areas 311 with particles substantially perpendicular to the film.

(16) The specific orientation of the anisotropic particles 32 in the first areas 311 can be obtained for example by magnetisation if the anisotropic particles comprise magnetisable particles.

(17) This magnetisation can therefore be achieved for example by arranging underneath the support a plurality of concentric permanent magnets made of elastomer, which emit a magnetic field of the same intensity or of different intensities, for example of about 80 mT when measured independently. These concentric magnets may advantageously be in the form of a central disc of small diameter (for example lower than or equal to 15 mm) and of a plurality of concentric rings having a width of about 10 to 15 mm arranged around this central disc. These magnets may advantageously be arranged on a substrate (for example a stainless steel plate) which can move perpendicularly to the support of the article. This movement can be done by means of an actuator that brings the substrate (or plate) near the article to be magnetised, so as to define an air gap.

(18) The magnetisable anisotropic particles will then oriente themselves according to the field lines, in other words perpendicularly to the support 2 (or to the film 3) at the areas 311 underneath which a magnet was arranged (the field lines being perpendicular to the coating in the form of a film), and parallelly to the support 2 (and thus to the film 3) in the second areas 312 where the field lines are parallel to the support 2, with a progressive orientation continuum of the magnetisable anisotropic particles between these two areas.

(19) FIG. 4 shows a series of five scanning electron microscope (SEM) images 4A to 4E of a cross section of the frying pan 1 shown in FIG. 3 taken at the area 311 with anisotropic particles substantially perpendicular to the coating in the form of a film.

(20) FIG. 5 shows a series of four scanning electron microscope (SEM) images 5A to 5D of a cross section of the frying pan 1 shown in FIG. 3 taken at the area 312 with anisotropic particles substantially parallel to the coating.

(21) In the case of magnetisable anisotropic particles, first area 311 corresponds to an area underneath which a permanent magnet was arranged and at the perpendicular of which the field lines are perpendicular to the support. In second area 312 the field lines are oriented parallel to the support and movement from one to the next is via a progressive orientation continuum of the magnetisable particles.

EXAMPLES

(22) Products

(23) In the Pigmented Sol-Gel Base Layer

(24) Colloidal Metallic Oxide

(25) colloidal silica in the form of a 30% silica aqueous solution, sold by the Clariant company under the trade name Klebosol, colloidal silica in the form of a 40% silica aqueous solution, sold by the Grace Davison company under the trade name Ludox, colloidal alumina in the form of a 5% aqueous solution sold by the DGTec company.
Solvents isopropyl alcohol, 2-(2-Butoxyethoxy)-ethanol (trade name: Butyl CARBITOL™), demineralised water.
Silicone Oil methyl silicone oil sold by the DOW CORNING company under the trade name “DOW CORNING 200 Fluid”, and having a viscosity of 300 cSt, methyl silicone oil sold by the Bluestar company under the trade name “Rhodorsil 47V50”, hydroxylated methyl silicone oil sold by the Wacker company under the trade name “OEL CT101M”.
Pigments mineral black pigment sold by the Ferro company under the trade name “FA 1220”, ultramarine blue pigment sold by the Holliday pigments company, under the trade name “CM13”, perylene red pigment sold by BASF, titanium dioxide white pigment sold by the Kronos company, orange pigment “259150” sold by the BASF company.
Fillers alumina powder sold by the Alcan company under the trade name “CAHPF 1000”, alumina nanometric flakes dispersed in a 40% aqueous phase sold by the Baikowski company.
Sol-Gel Precursors methyltriethoxysilane (MTES) of formula Si(OC.sub.2H.sub.5).sub.3CH.sub.3, methyltrimethoxysilane (MTMS) of formula Si(OCH.sub.3).sub.3CH.sub.3, tetraethyl orthosilicate (TEOS) of formula Si(OC.sub.2H.sub.5).sub.4.
Acids formic acid, acetic acid.
In the Sol-Gel Finish Layer:
Colloidal Metallic Oxide colloidal silica in the form of a 30% silica aqueous solution, sold by the Clariant company under the trade name Klebosol, colloidal silica in the form of a 40% silica aqueous solution, sold by the Grace Davison company under the trade name Ludox, colloidal alumina in the form of a 5% aqueous solution sold by the DGTec company.
Solvents isopropyl alcohol, butyl glycol, demineralised water.
Silicone Oil methyl silicone oil sold by the Dow Corning company under the trade name “DOW CORNING 200 Fluid”, and having a viscosity of 300 cSt, methyl silicone oil sold by the BLUESTAR company under the trade name “Rhodorsil 47V50”, hydroxylated methyl silicone oil sold by the Wacker company under the trade name “OEL CT101M”.
Anisotropic Particles mica flakes encapsulated with iron oxide sold by the ECKART company under the name STAPA TA Ferricon 200 (magnetisable flakes), mica flakes encapsulated with iron oxide sold by the MERCK company under the name Colorona Blackstar blue or green (magnetisable flakes), unencapsulated mica flakes sold by the MERCK company under the name Iriodin 119 (non-magnetisable flakes), stainless steel microfibres.
Sol-Gel Precursors methyltriethoxysilane (MTES) of formula Si(OC.sub.2H.sub.5).sub.3CH.sub.3, methyltrimethoxysilane (MTMS) of formula Si(OCH.sub.3).sub.3CH.sub.3, tetraethyl orthosilicate (TEOS) of formula Si(OC.sub.2H.sub.5).sub.4.
Acids formic acid, acetic acid.
Tests
Chipping Resistance Test

(26) The ability of different vitreous coatings, of the same thickness and applied to the same metallic substrates, to withstand chipping is evaluated as follows.

(27) These coatings are given a 10 mm long scratch, made using a calibrated diamond stylus of 50 microns in diameter, which is applied with a force gradually increasing from 0 to 5 Newtons. To do that, a device sold under the name “Microscratch tester” of the CSM Instruments company is used.

(28) After forming the scratch, a microscope is used to determine the force from which chipping of the coating down to the metal is visible (see table 3 for results).

Comparative Example 1

(29) Formation of a Double-Layered Vitreous Coating According to the Method of International Application WO2010/123294, which is Incorporated by Reference its Entirety Herein.

(30) A first coloured sol-gel composition is prepared in the form of a bi-component comprising a part A and a part B: part A comprises a colloidal silica dispersion, demineralised water, the isopropyl alcohol, the butyl glycol, the silicone oil, the fillers and the pigments, part B comprises the sol-gel precursor (silane) as well as the organic acid.

(31) These two parts A and B can be stored for more than 6 months separately.

(32) Parts A and B are then combined in a mixer at room temperature (for example a reactor provided with a blade for stirring, or a container that will be rotated at 80 rpm. on a jar mill) in order to initiate the silane hydrolysis reaction. The mixture must then be allowed to mature for at least 24 hours before application of the mixture A+B on a support, so as to allow the hydrolysis/condensation reactions to progress sufficiently. Under the effect of these reactions an increase in temperature up to 55° C. is observed. This maturation time may however be reduced or increased depending on the stirring speed of the products and on the temperature reached or maintained during the stirring. The pot life of the mixture is at least 48 hours.

(33) The coloured sol-gel composition is shown in table 1:

(34) TABLE-US-00001 TABLE 1 Amounts in weight Amounts in weight percent percent Components (variation ranges) (preferred example) Klebosol 30% 25-35% 29% colloidal silica Demineralised water 10-15% 10% Isopropyl alcohol  1-5% 4.5% 47V50 silicone oil  0.1-1% 1% FA1220 black pigment 20-25% 20% MTES 30-35% 35% Formic acid  0.5-1% 0.5%

(35) The A+B mixture is then filtered on a stainless steel mesh having apertures of 40 microns in size, before being applied with a pneumatic spray gun in at least one layer of 35 microns in thickness to form a coloured base layer, on the inner surface of an aluminium support which has been sandblasted, degreased, and heated to a temperature of 55° C.

(36) The base layer thus formed is then dried at 100° C. for 30 minutes, as taught by WO 2010/123294.

(37) A colourless sol-gel composition is then prepared in the same way as for the pigmented base layer described above, but replacing the pigments with flakes encapsulated with iron oxide. This colourless sol-gel composition is filtered on a stainless steel mesh having apertures of 80 μm in size and applied using a pneumatic spray gun on the base layer, which is heated to a temperature of 55° C.

(38) The colourless sol-gel composition is shown in table 2:

(39) TABLE-US-00002 TABLE 2 Amounts in weight Amounts in weight percent percent Components (variation ranges) (preferred example) Ludox 40% colloidal 25-30% 30% silica Demineralised water 10-15% 10% Isopropyl alcohol  1-5% 5% Butyl glycol  5-15% 10% 47V50 silicone oil  0.1-1% 1% Colorona Blackstar 0.1-15%  2% flakes OR stainless steel microfibres MTES 35-45% 40% Acetic acid  1-2% 2%

(40) It proves impossible to form a continuous film with the colourless sol-gel composition layer. Indeed, the method as taught by WO 2010/123294 with a drying step at at least 100° C. leads to an excessive densification of the coloured base layer, which thus develops a hydrophobic nature such that a continuous layer can no longer be formed with the flaked colourless sol-gel composition: the latter retracts, when applied on the base layer, in the form of isolated droplets.

(41) Consequently, if the conditions of the method for manufacturing a sol-gel coating as taught by WO 2010/123294 are applied, it is not possible to form a homogeneous vitreous double-layered coating.

Comparative Example 2

(42) Formation of a Single-Layered Vitreous Coating Film Comprising Flakes Substantially Parallel to the Film.

(43) A colourless sol-gel composition is prepared in the form of a bi-component comprising a part A and a part B: part A comprises a colloidal silica dispersion, the demineralised water, the isopropyl alcohol, the butyl glycol, the silicone oil as well as mica flakes encapsulated with iron oxide, part B comprises a sol-gel type precursor (silane) as well as an organic acid.

(44) These two parts A and B can be stored for more than 6 months separately.

(45) Parts A and B are then combined in a mixer at room temperature (for example a reactor provided with a blade for stirring, or a container that will be rotated at 80 rpm on a jar mill) in order to initiate the silane hydrolysis reaction. The mixture must then be allowed to mature for at least 24 hours before application of the mixture A+B on a support, so as to allow the hydrolysis/condensation reactions to progress sufficiently. Under the effect of these reactions an increase in temperature up to 55° C. is observed. This maturation time may however be reduced or increased depending on the stirring speed of the products and on the temperature reached or maintained during the stirring. The pot life of the mixture is at least 48 hours.

(46) The colourless sol-gel composition is the same as that shown in table 2.

(47) The mixture is then filtered on a stainless steel mesh having apertures of 80 microns in size before being applied with a pneumatic spray gun in at least one continuous film of 20 microns in thickness, on an aluminium support which has been sandblasted, degreased, and heated to a temperature of about 60° C. to facilitate the application.

(48) During spraying the particles arrive randomly and, under the effect of gravity, they oriente themselves substantially parallelly to the support as long as they have sufficient mobility to do so.

(49) The coating thus formed is then fired, at a temperature comprised of 250° C. for at least 15 minutes.

(50) The final dry thickness of the coating thus obtained is 12 μm.

(51) The observations of this coating through scanning electron microscope (SEM) correspond to the SEM images shown in FIG. 5, which show that the flakes contained in the coating film are for the most part substantially parallel to the film, in other words at an angle lower than 20° with respect to the substrate.

Comparative Example 3

(52) Formation of a Double-Layered Vitreous Coating Film Comprising Flakes Substantially Parallel to the Film.

(53) A coloured sol-gel composition is prepared in the form of a bi-component comprising a part A and a part B: part A comprises a colloidal silica dispersion, demineralised water, the isopropyl alcohol, the butyl glycol, the silicone oil, the fillers and the pigments, part B comprises a sol-gel precursor (silane), as well as the organic acid.

(54) These two parts A and B can be stored for more than 6 months separately.

(55) Parts A and B are then combined in a mixer at room temperature (for example a reactor provided with a blade for stirring, or a container that will be rotated at 80 rpm on a jar mill) in order to initiate the silane hydrolysis reaction. The mixture must then be allowed to mature for at least 24 hours before application of the mixture A+B on a support, so as to allow the hydrolysis/condensation reactions to progress sufficiently. Under the effect of these reactions an increase in temperature up to 55° C. is observed. This maturation time may however be reduced or increased depending on the stirring speed of the products and on the temperature reached or maintained during the stirring. The pot life of the mixture is at least 48 hours.

(56) The coloured sol-gel composition is the same as that shown in table 1.

(57) The mixture is then filtered on a stainless steel mesh having apertures of 40 microns in size before being applied with a pneumatic spray gun in at least one layer of 55 microns in thickness, on the inner surface of an aluminium support which has been sandblasted, degreased, and heated to a temperature of 55° C. to facilitate application of the mixture on the substrate.

(58) A colourless sol-gel composition containing encapsulated mica flakes is then prepared in the same way as in comparative example 2, and then applied by spraying with a spray gun on the pigmented base layer to form a finish layer in the form of a film.

(59) This is followed by firing of the whole at a temperature of 250° C. for at least 15 minutes minimum.

(60) The colourless sol-gel composition is the same as that shown in table 2.

(61) The final dry thickness of the coating thus formed is 45 microns.

(62) The observations of this coating through scanning electron microscope (SEM) correspond to the SEM images shown in FIG. 5, which show that the flakes contained in the coating film are for the most part substantially parallel to the film, in other words at an angle lower than 20° with respect to the substrate.

Comparative Example 4

(63) Formation of a Double-Layered Vitreous Coating Film Comprising Microfibres Substantially Parallel to the Film.

(64) This example only differs from comparative example 3 by the particles in the finish layer: the encapsulated flakes are replaced by stainless steel microfibres.

(65) The final dry thickness of the coating thus formed is also 45 microns.

Example 1

(66) Formation of a Single-Layered Coating Film According to the Present Invention Comprising Flakes Substantially Perpendicular to the Film.

(67) A sol-gel composition in the form of a bi-component A+B is prepared in the same way as in comparative example 2. This composition is also applied, in the same way as in comparative example 2, on an aluminium support which has been sandblasted, degreased, and heated to a temperature of 60° C.

(68) However, immediately after the application by spraying of the sol-gel composition (but prior to firing), a magnetic field of 70 mT is applied using a permanent magnet arranged underneath the substrate. Under the action of the magnetic field, the mica flakes, due to their encapsulation with magnetic iron oxide, oriente themselves according to the field lines, in other words perpendicularly to the magnet. It is observed that the encapsulated mica flakes are mainly inclined at an angle α comprised between 20° and 90° with respect to the average plane of the film.

(69) The coating is then fired at 250° C. for at least 15 minutes minimum.

(70) The final dry thickness of the coating thus formed is 12 microns.

Example 2

(71) Formation of a Double-Layered Coating Film According to the Present Invention Comprising Flakes Substantially Perpendicular to the Film

(72) A coloured sol-gel composition and a colourless sol-gel composition containing encapsulated mica flakes are prepared in the same way as in comparative example 3. These compositions are applied in succession on an aluminium support which has been sandblasted, degreased and heated to a temperature of 55° C., also in the same way as in comparative example 3.

(73) However, immediately after the application by spraying of the colourless sol-gel composition (but prior to firing), a magnetic field of 70 mT is applied using a permanent magnet arranged underneath the substrate. Under the action of the magnetic field, the mica flakes, due to their encapsulation with magnetic iron oxide, oriente themselves according to the field lines, in other words perpendicularly to the magnet substantially vertically.

(74) The coating is then fired at 280° C. for at least 15 minutes.

(75) The observations of this coating through scanning electron microscope (SEM) correspond to the SEM images shown in FIG. 4, which show that the majority of the flakes tend to oriente themselves perpendicularly to the formed coating film, in other words most of them are at an angle of inclination comprised between 20° and 90° with respect to the substrate.

Example 3

(76) Formation of a Double-Layered Coating Film According to the Present Invention Comprising Microfibres Substantially Perpendicular to the Film

(77) This example only differs from example 2 by the shape of the particles in the finish layer: the encapsulated flakes are replaced by stainless steel microfibres.

Example 4

(78) Formation of a Double-Layered Coating Film According to the Present Invention Comprising Flakes Substantially Perpendicular to the Film

(79) This example only differs from example 2 in the nature of the silicone oil. The 47V50 silicone oil is replaced by the CT101M OEL hydroxylated silicone oil, in the same weight proportions (shown in table 2).

Example 5

(80) Evaluation of the Resistance to Chipping

(81) The ability to resist to chipping of the vitreous coatings formed in examples 1 to 4 and comparative examples 1 to 4 is evaluated according to the test described above. The results obtained are shown in table 3 below:

(82) TABLE-US-00003 TABLE 3 Coating thickness Delamination to (in μm) the metal (in N) Comparative example 1 NA Not measurable given (method according to WO2010- the discontinuity 123294) of the film Comparative example 2 12 1.31 +/− 0.09 (single-layered and non-oriented flakes) Example 1 12 1.57 +/− 0.10 (single-layered and oriented flakes) Comparative example 3 45 3.91 +/− 0.17 (double-layered and non-oriented flakes) Example 2 45 4.56 +/− 0.19 (double-layered and oriented flakes) Comparative example 4 45 3.98 +/− 0.16 (double-layered and non-oriented microfibres) Example 3 45 4.49 +/− 0.14 (double-layered and oriented microfibres) Example 4 45 4.52 +/− 0.13 (double-layered with hydroxylated oil, oriented flakes)

(83) The comparison of example 1 with comparative example 2 (single-layered coating) clearly shows that the force to be applied during the test to achieve a delamination to the metal is greater when the particles are, in the context of the invention, oriented substantially perpendicularly to the coating (in other words, that they are mainly inclined at an angle α comprised between 20° and 90° with respect to the average plane of the film), than when not (in other words, the particles are randomly oriented, or are mainly inclined at an angle α lower than 20° with respect to the average plane of the film). This means that the resistance to chipping is improved when the coating comprises oriented particles.

(84) The comparison of example 2 and comparative example 3 leads to the same conclusions for a double-layered coating.

(85) The comparison of example 3 and comparative example 4 shows that similar conclusions also apply when anisotropic particles of different shape (microfibres instead of flakes) are used.

(86) Finally, the comparison of example 4 and example 2 shows that when a hydroxylated silicone oil is used, the same results are achieved as with a non-hydroxylated silicone oil.