ANTI-CORROSION COATING

Abstract

The invention relates to the use of a powder composed of a mixture of zinc flakes and zinc oxide, Zn / ZnO, to increase the adhesion coefficient of an anti-corrosion coating, characterized in that the zinc flakes constitute between 60 and 99% of the zinc flakes and zinc oxide mixture, more particularly between 70 and 95% of the zinc flakes and zinc oxide mixture. The invention further relates to the methods for obtaining and applying said anti-corrosion coating, as well as the anti-corrosion coating itself and the substrates coated with the coating.

Description

Title of the invention: ANTICORROSION COATING

[0001] The invention relates to an anti-corrosion coating for metal parts having improved properties, in particular improved adhesion properties of the substrate once coated. TECHNOLOGICAL BACKGROUND

[0002] Various anti-corrosion coatings are known from the state of the art using active ingredients based, for example, on chromium, aluminum, zinc, silane or even molybdenum.

[0003] Such coatings are illustrated for example in patent documents CN111893468, CN112280040, WO0238686A2, EP3040445, CN105524505.

[0004] However, these different coatings have very different surface properties compared to each other.

[0005] In the automotive sector, the development of electric vehicles is booming. One difficulty encountered by car manufacturers is the increase in vehicle weight: a diesel engine weighs around 100 kg, while a standard battery for an electric vehicle weighs between 250 and 500 kg, with some models weighing over a ton. The energy consumption of a vehicle is linked to its weight: to travel an equivalent distance, a heavy vehicle will consume more energy than a light vehicle. There is therefore a need in this field for solutions to reduce the overall weight of a vehicle.

[0006] One possible solution is to reduce the size and weight of the screws and nuts used in vehicles. It can be estimated that on a vehicle, replacing all the screws of standard M12 sizes and all the nuts of standard M12 sizes with M8 references could reduce the overall weight of a vehicle by at least 1 kg. However, the use of screws and / or nuts of sizes smaller than standard sizes leads to a weakening of the structure, linked to a loss of adhesion in the assembly, and this is why this solution is not retained in the art.

[0007] There is therefore a need for a coating applicable to metal substrates in order to improve the adhesion between said metal substrates.

[0008] There is also a need for this coating to provide anti-corrosion properties to the metal substrate.

[0009] There is also a need for this coating to impart a black appearance to the coated metal substrates.

[0010] The object of the present invention proposes a solution having numerous advantages and improved technical characteristics compared to this known state of the art. Summary of the invention

[0011] The subject of the present invention thus relates to the use of a powder of a mixture of lamellar zinc and zinc oxide, also called "Zn / ZnO powder", to increase the value of the adhesion coefficient of an anti-corrosion coating, characterized in that the lamellar zinc represents between 60 and 99% of the mixture of lamellar zinc and zinc oxide, more particularly between 70 and 95% of the mixture of lamellar zinc and zinc oxide.

[0012] The subject of the present invention also relates to a liquid composition for anti-corrosion coating, preferably a suspension, characterized in that it comprises:

[0013] - between 15 and 30% by mass, preferably between 22 and 28% by mass, of Zn;

[0014] - between 5 and 15% by mass, preferably between 8 and 10% by mass, of ZnO;

[0015] - between 5 and 15% by mass, preferably between 10 and 11% by mass, of a binder silane;

[0016] - between 25 and 50% by mass, preferably between 30 and 40% by mass, of water;

[0017] - between 10 and 30% by mass, preferably 20% by mass, of at least one solvent organic; and

[0018] - optionally additives,

[0019] the percentages being expressed relative to the total mass of the liquid composition.

[0020] The subject of the present invention also relates to a method of manufacturing a composition according to the invention comprising the following successive steps:

[0021] (a) forming a silane binder in water, and

[0022] (b) adding and solubilizing the aqueous solution obtained in step (a) in a solvent solution containing Zn / ZnO powder.

[0023] The subject of the present invention further relates to a liquid composition for anti-corrosion coating capable of being obtained by the manufacturing process comprising the following successive steps:

[0024] (a) forming a silane binder in water and

[0025] (b) adding and solubilizing the aqueous solution obtained in step (a) in a solvent solution containing Zn / ZnO powder.

[0026] The subject of the present invention also relates to a method of protecting a metal substrate against corrosion by an anti-corrosion coating comprising the following successive steps:

[0027] (al) a step of applying said substrate by a liquid composition according to the invention;

[0028] (bl) a step of drying the coated substrate obtained in step (al); and

[0029] (cl) a step of baking the coated substrate obtained in step (bl).

[0030] The subject of the present invention thus relates to a substrate coated with at least one layer of composition capable of being obtained by the method of protecting a metal substrate against corrosion by an anti-corrosion coating comprising the following successive steps:

[0031] (al) a step of applying said substrate by a liquid composition according to the invention;

[0032] (bl) a step of drying the coated substrate obtained in step (al); and

[0033] (cl) a step of baking the coated substrate obtained in step (bl).

[0034] The subject of the present invention therefore relates to an anti-corrosion coating capable of being obtained by drying then baking a liquid composition according to the invention, characterized in that the thickness of the coating is between 5qm and 15qm, preferably 8qm plus or minus 3qm.

[0035] The subject of the present invention may more specifically relate to a vehicle comprising an anti-corrosion coating according to the invention, in particular at the level of the fixing means, such as bolts, screws, clips, crimps, clamps, rivets, etc., as well as the elements requiring fixing means, such as assembly plates of said vehicle. Indeed and preferably, the application to an assembly plate of a coating making it possible to increase the adhesion of said plate in contact with another plate, coated or not with a similar coating, makes it possible to reduce the risk of observing a displacement of said coated plate with respect to the other plate.

[0036] DEFINITIONS

[0037] By "anticorrosion coating" is understood in the context of the present invention either an anticorrosion coating method or an anticorrosion coating product, the product being derived from the method in this context. The coating aims to improve the surface anticorrosive properties of a treated object. Thus the coating obtained reduces the deterioration of the treated object by chemical reaction with an oxidant.

[0038] By "powder of a mixture of lamellar zinc and zinc oxide, also called Zn / ZnO powder", is understood in the context of the present invention particles of lamellar zinc reinforced by zinc oxides, in order to provide a dark tint to the zinc powder as well as to the liquid composition.

[0039] In the context of the present invention, the "coefficient of adhesion", also called "coefficient of friction at the interface" refers to a method of measuring a coefficient of friction between two coated metal plates. The coefficient of friction q characterizes the friction conditions according to T = q F, with T the translational force necessary to slide one part over another in Newton, and F the pressure between the parts in Newtons (see [Fig.3] for illustration). Thus, for a given pressure F between two parts, the greater the force T to be applied to observe a translation, the higher the coefficient of friction will be.

[0040] In the automotive and mechanical engineering fields, the coefficient of friction is a key parameter used in screwed assemblies, because it makes it possible to establish the link between the applied tightening torque and the resulting tension in the screw. In a screwed system, too high a coefficient of friction will lead to an under-tightening phenomenon between the screw and the nut. This phenomenon can be counterbalanced by a variation of the coefficient of friction adapted using lubricant on one or both of the fastening elements. However, excessive lubrication will lead to over-tightening, which may lead to a break in the torque during use.

[0041] In the context of this invention, the measurement of the coefficient of friction is determined at the interface between two coated metal plates, according to standard EN1090-2 “Executions of steel structures and aluminum structures - Part 2: Technical requirements for steel structures; Annex G”. The two coated plates are fixed against each other by means of several fixing elements and are subjected to a pressure F. One of the plates is designated “fixed plate” and the other plate is designated “moving plate”. A translational force T is applied to the moving plate in order to observe a defined displacement relative to the fixed plate, and thus determine the coefficient of adhesion q between the two plates (see [Fig.4]). A class is then assigned to the surface treatment according to the measured coefficient of friction value: Class A for q > 0.50; Class B for 0.40 < q <0.50; Class C for 0.30 < q <0.40 and Class D for 0.20 < q < 0.30.For comparison, the coefficient of friction of a steel surface with another steel surface is approximately 0.20, and the coefficient of friction of a greased steel surface with another greased steel surface is approximately 0.10. Furthermore, similar standards are being drafted in the automotive field and the subject of the present invention therefore makes it possible to anticipate these standards.

[0042] By "silane" is understood in the context of the present invention organic compounds comprising at least one silicon atom with at least one Si-C bond. In a silane, the bonds with the silicon atom, in addition to the Si-C bond, are generally Si-O, Si-Si or Si-H bonds, more advantageously Si-O. Advantageously, the silane contains at least one Si-O function, preferably at least two Si-O functions, more preferably at least three Si-O functions.

[0043] By "additives" is understood in the context of the present invention compounds allowing complementary technical effects depending on the application or the objective sought. Such additives can typically be rheology agents, more particularly wetting agents, surfactants, pH modifiers, salts, fluidifiers, thickeners, pigments, dyes, or even complementary antioxidants.

[0044] By "solvent solution" is understood in the context of the present invention a product whose formulation comprises a base of solvent(s).

[0045] By "obtainable" it is understood in the context of the present invention that the product obtained by the process of the invention can also be obtained by other process(es).

[0046] If this should not be specified, the percentages are expressed in relation to the total mass of the composition (or more generally of the product) considered. FIGURES

[0047] [Fig-1] represents the state of the art with a first plate 1, a second plate 2 connected to each other by a standard screw 3, a standard size nut 4A and an optional washer 4B.

[0048] [Fig.2] shows a first plate 5, a second plate 6, both coated with the coating 7 according to the present invention and connected to each other by a screw 8 of a size smaller than the standard size and a nut 9A of a size smaller than the standard size and an optional washer 9B.

[0049] [Fig.3] represents the implementation of the method for measuring a coefficient of friction. The coefficient of friction q characterizes the friction conditions according to T = q F, with T representing the translational force necessary to slide one part over another in Newton, and F representing the pressure between the parts in Newton.

[0050] [Fig.4] represents an implementation of the method for measuring a coefficient of friction comprising a plate 10, designated “fixed plate” and a plate 11, designated “moving plate”. The plates according to the implementation of the measurement method can also be designated by the term “test piece”. A translation force T is applied to the moving plate 11 in order to observe a defined displacement relative to the fixed plate 10, and thus determine the coefficient of adhesion q between the two plates. The fixed 10 and moving 11 plates are held together by fixing means 12 (which nevertheless allow the translation T).

[0051] [Fig.5] represents a top view of a steel test piece made of C45 E + N (yield strength >430 MPa) with an opening 13 with a diameter which may be 13.5 mm corresponding to an M12 fixing according to standard NF EN 20273. The test piece is of length A and width B. A and B may be equivalent, for example 100 mm. The test piece may comprise at least one opening 14 positioned close to a corner of the test piece. Preferably, the test piece comprises 4 openings 14 of diameter(s) smaller than that of opening 13. The test piece may further have bevelled angles, in which each bevel is formed by subtracting the values ​​C and D from lengths A and B, respectively. C and D may be equivalent, for example 6 mm.

[0052] [Fig.6] represents a side view of a steel test piece made of C45 E +N (yield strength >430 MPa) as represented in [Fig.5], said test piece has a thickness E.

[0053] [Fig.7] represents the principle of applying stress (traction / compression) to a pair of test pieces 15, 16, consisting of a static test piece 15 and a mobile test piece 16. Compressive forces F1, F2, called perpendicular compressive forces, are applied to this pair of test pieces perpendicular to the contact zone Z between the two test pieces, while a tensile or compressive force T is applied parallel to the plane constituted by this contact zone Z. A load cell 17 makes it possible to observe and / or record the compressive forces F1, F2. A support sleeve 18 may optionally be used to hold the two test pieces 15, 16. DETAILED DESCRIPTION

[0054] The use of zinc powder and zinc oxide in the context of the present invention, as well as the methods, compositions, coated substrates and coatings obtained according to the invention have several advantages.

[0055] On the one hand, the coating of the invention has the intrinsic characteristic of anti-corrosion, that is to say that it protects the surfaces to which it is applied from chemical reactions with an external oxidant.

[0056] On the other hand, the coating of the invention has excellent adhesion to the support (also called here substrate) while providing an adhesion coefficient greater than or equal to 0.5. For example, the coating of the invention has an adhesion coefficient greater than or equal to 0.6, greater than or equal to 0.7.

[0057] Thus, a technical advantage which results from this adhesion characteristic is a securing of the assemblies, and thus a reduction in the dimensioning of the fastening devices (for example screw / nut assemblies). In an assembly of two parts fixed to each other by one or more fastening means, a low coefficient of adhesion between the two parts will lead to displacements of the assembled parts, which can, for example, produce unscrewing in the context of screwing, or, more seriously, damage to the fastening system. Thus, a high coefficient of adhesion between the two assembly elements makes it possible to reduce the need for tension at the fastening zones to hold the assembly in position. This increased adhesion between the plates offers the opportunity to reduce the dimensions of the fastening means used while retaining the mechanical properties of said fastening means and maintaining the required assembly stability. It is therefore possible to use screws and nuts of smaller sizes and equivalent steel classes in an assembly compared to the standards, such as, for example, screws of size M12 replaced by screws of size M8 (see figures 1 and 2). The weight and / or the number of fasteners is thus reduced, and when such fasteners are used in a vehicle, the total weight of the vehicle is reduced. Thus, the reduction in weight implies a reduction in fuel consumption, a reduction in the emission of greenhouse gases resulting from the combustion of such a fuel (such as CO2), or an increase in the speed of the vehicle.However, conventional anti-corrosion protection techniques used in the automotive industry, such as cataphoresis, lead to coatings with an insufficient adhesion coefficient. The coating according to the invention makes it possible to resolve this drawback by giving the coated metal substrate resistance to corrosion as well as an increase in the adhesion coefficient.

[0058] Use of zinc powder to increase the coefficient of adhesion

[0059] The use according to the present invention involves a powder of lamellar zinc and zinc oxide also called "Zn / ZnO powder", said Zn / ZnO powder being able to be included in a liquid composition for the formation of an anti-corrosion coating, characterized in that the lamellar zinc represents between 60 and 99% of the mixture of lamellar zinc and zinc oxide, more precisely between 70 and 95% of the mixture. Liquid composition

[0060] Thus, one of the objects of the present invention relates to a liquid composition comprising particulate zinc with a geometry of between 1 pm and 40 pm for its use in the formulation of a liquid composition for anti-corrosion coating.

[0061] Preferably, the liquid composition for anti-corrosion coating according to the present invention comprises between 22 and 28% by mass of Zn, between 18 and 27% by mass of Zn, between 19 and 26% by mass of Zn, the percentages being expressed relative to the total mass of the composition.

[0062] More preferably, the liquid composition for anti-corrosion coating according to the present invention comprises 25% plus or minus 4% of Zn, the percentages being expressed relative to the total mass of the composition.

[0063] Preferably, the liquid composition for anti-corrosion coating according to the present invention comprises between 6 and 14% by mass of ZnO, between 7 and 13% by mass mass of ZnO, between 8 and 12% by mass of ZnO, between 9 and 11% by mass of ZnO, the percentages being expressed relative to the total mass of the composition.

[0064] Preferably, the liquid composition for anti-corrosion coating according to the present invention comprises 8% plus or minus 3% of ZnO, the percentages being expressed relative to the total mass of the composition.

[0065] In one embodiment, the liquid composition for anti-corrosion coating according to the present invention comprises:

[0066] - between 15 and 30% by mass of Zn, between 22 and 28% by mass of Zn, between 18 and 27% by mass of Zn, between 19 and 26% by mass of Zn, between 20 and 25% by mass of Zn, the percentages being expressed relative to the total mass of the composition; and

[0067] - between 5 and 15% by mass of ZnO, between 6 and 14% by mass of ZnO, between 7 and 13% by mass of ZnO, between 8 and 12% by mass of ZnO, between 8 and 10% by mass of ZnO, the percentages being expressed relative to the total mass of the composition.

[0068] Preferably, the liquid composition for anticorrosion coating according to the present invention comprises between 20 and 45% by mass of a Zn / ZnO mixture, between 23 and 42% by mass of a Zn / ZnO mixture, between 25 and 40% by mass of a Zn / ZnO mixture, between 27 and 38% by mass of a Zn / ZnO mixture, between 29 and 36% by mass of a Zn / ZnO mixture, the percentages being expressed relative to the total mass of the composition.

[0069] Preferably, the liquid composition for anti-corrosion coating according to the present invention comprises 10% plus or minus 3% of a silane binder (quantity introduced), the percentages being expressed relative to the total mass of the composition.

[0070] Advantageously, the silane binder is gamma-glycidoxypropyltrimethoxysilane or gamma-glycidoxypropyltriethoxysilane.

[0071] Preferably, the liquid composition for anti-corrosion coating according to the present invention comprises 31% plus or minus 5% of water, the percentages being expressed relative to the total mass of the composition.

[0072] Preferably, the type of composition according to the present invention is mainly aqueous in nature. The composition may nevertheless be enriched by the presence of an organic solvent, preferably water-soluble, which makes it possible to improve the solubility of the different components in the aqueous solution.

[0073] Preferably, the liquid composition for anti-corrosion coating according to the present invention comprises 20% plus or minus 5% of an organic solvent, the percentages being expressed relative to the total mass of the composition.

[0074] In an advantageous embodiment of the invention, the composition will use an organic solvent, for example consisting of an ether glycol, in particular monopropylene glycol, diethylene glycol, triethylene glycol and dipropylene glycol.

[0075] The subject of the present invention relates more particularly to a liquid composition for anti-corrosion coating, characterized in that it comprises:

[0076] - between 22 and 28% by mass, of Zn;

[0077] - between 7 and 9% by mass, of ZnO;

[0078] - between 5 and 15% by mass, preferably between 10 and 11% by mass, of a binder silane;

[0079] - between 25 and 50% by mass, preferably between 26 and 40% by mass, of water;

[0080] - between 10 and 30% by mass, preferably 20% by mass, of at least one solvent organic; and

[0081] - optionally one or more additives,

[0082] the percentages being expressed relative to the total mass of the composition.

[0083] Preferably, the additives in question here improve the rheological properties allowing easier formulation of the composition.

[0084] By way of non-limiting example, an additive may be chosen from:

[0085] - a wetting agent, such as fatty alcohol alcoholates;

[0086] - a pH modifier, such as selected from metal oxides and hydroxides alkali metals, advantageously lithium and sodium, oxides and hydroxides of metals belonging to groups IIA and IIB of the periodic table, such as compounds of strontium, calcium, barium, magnesium and zinc, or a carbonate or nitrate of the aforementioned metals;

[0087] - a phosphate, such as aluminum dihydrogen triphosphate;

[0088] - a salt, which may be organic or inorganic, such as alkali silicates

[0089] - a surfactant, such as acrylic copolymers or ethoxylated alcohols

[0090] - a thickener, in particular of a cellulose derivative, more particularly hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, xanthan gum, or an associative thickener of the polyurethane or acrylic type

[0091] In one embodiment, the composition according to the present invention may further comprise between 0.5 and 4% by mass of aluminum dihydrogen triphosphate, the percentages being expressed relative to the total mass of the composition.

[0092] Preferably, the composition according to the present invention may comprise 2% ± 1% by mass of aluminum dihydrogen triphosphate, the percentages being expressed relative to the total mass of the composition.

[0093] Aluminum dihydrogen triphosphate can thus act as an anti-corrosion agent.

[0094] In one embodiment, the composition according to the present invention may comprise between 0.5 and 4% by mass of a molybdenum salt, more particularly of molybdenum oxide MoO3, the percentages being expressed relative to the total mass of the composition.

[0095] Preferably, the composition according to the present invention may comprise 2% ± 1% by mass of a molybdenum salt, more particularly molybdenum oxide MoO3 (in particular, as introduced into the composition), the percentages being expressed relative to the total mass of the composition.

[0096] Molybdenum oxide MoO3 can thus act as an anti-corrosion agent. Manufacturing process of the liquid composition

[0097] The subject of the present invention further relates to a method of manufacturing a composition as described above comprising the following successive steps:

[0098] (a) forming a silane binder in water and

[0099] (b) adding and solubilizing the aqueous solution obtained in step (a) in a solvent solution containing a powder of lamellar zinc and zinc oxide also called “Zn / ZnO powder”.

[0100] In one embodiment, the method according to the invention can be characterized in that the powder-type zinc has a particle geometry of between 1 pm and 40 sq m.

[0101] Thus, the subject of the present invention relates to a liquid composition for anti-corrosion coating capable of being obtained by the manufacturing method as described in the embodiments above.

[0102] Method for protecting a metal substrate against corrosion

[0103] The subject of the present invention further relates to a method of protecting a metal substrate against corrosion by forming an anti-corrosion coating comprising the following successive steps:

[0104] (al) a step of applying said substrate by a liquid composition according to the invention;

[0105] (bl) a step of drying the coated substrate obtained in step (al) and

[0106] (cl) a step of baking the coated substrate obtained in step (bl).

[0107] The drying step (bl) can be carried out at temperatures between 60°C and 100°C.

[0108] The cooking step (cl) can be carried out at temperatures between 300°C and 350°C.

[0109] Preferably, step (al) may be preceded by a step of cleaning the metal substrate. The cleaning step consists of immersing the metal substrate in a cleaning solution, preferably a basic solution, removing the metal substrate from said cleaning solution, rinsing and drying said metal substrate.

[0110] Thus, the subject of the present invention relates to a substrate coated with at least one layer of composition capable of being obtained by the method of protecting a metal substrate against corrosion as described above.

[0111] Advantageously, the coated substrate according to the invention can be characterized in that said substrate is a mechanical part requiring an adhesion coefficient greater than or equal to 0.5, preferably greater than or equal to 0.6, or even greater than or equal to 0.7, such as an assembly plate.

[0112] In a particular embodiment, the coated substrate according to the invention is a fixing means, such as a bolt, a screw, a clip, a crimp, a clamp, a rivet, or a fixed element, such as a suspension arm etc.

[0113] Advantageously, the anti-corrosion coating according to the invention is applied to a portion of a fixing means as described above, for example, a portion intended for contact of the fixing means with another part. Such a contact portion may be, for example, the thread of a bolt or a screw. Anti-corrosion coating

[0114] The subject of the present invention also relates to an anti-corrosion coating capable of being obtained by drying then baking a liquid composition according to the invention, characterized in that the thickness of the coating is between 5qm and 15qm, preferably 1 μm plus or minus 3qm.

[0115] The drying step can be carried out at temperatures between 60°C and 100°C.

[0116] The cooking step can be carried out at temperatures between 300°C and 350°C.

[0117] Executing forms of the present invention will be described below, by way of non-limiting examples, with reference to the appended figures in which: EXAMPLES

[0118] Example 1: formula of the “liquid composition A” according to the invention

[0119] [Tables 1] Constituent Quantity (% by weight) Zinc powder “Zn / ZnO” 34-36% Deionized water 32-34% Dipropylene glycol 14-16% Silane 10-12% Additives 7-9%

[0120] Example 2: formula of “liquid composition B” according to the prior art

[0121] [Tables2] Constituent Quantity (% by weight) Zinc paste 31-33% Deionized water 37-39% Dipropylene glycol 10-11% Silane 8-9% Additives 11-13%

[0122] Example 3: Measurements of friction coefficient at the interface

[0123] Steel specimens are produced in C45 E+N (yield strength >430 MPa). The drilling diameter of 13.5 mm corresponds to an M12 fixing according to standard NF EN 20273 (see [Fig.5]). The minimum preload applied is 42,500 N.

[0124] Three types of test pieces are produced (see [Fig.5]):

[0125] - Test piece coated with a solid coating obtained from liquid composition B with a thickness of between 7 and 9 microns. Composition B and the method for obtaining a solid coating B obtained from liquid composition B are detailed in patent application WO02 / 38686, table 2.

[0126] - Test piece coated with a solid coating A obtained from liquid composition A with a thickness of between 7 and 9 microns

[0127] - Test piece coated by cataphoresis with a thickness between 15 and 20 microns

[0128] The specimens are pressed against each other with a regulated force maintained by means of a test bench. One of the specimens is static and the other specimen is mobile. A load is applied to the mobile specimen and the coefficient of friction at the interface between the two specimens is measured (see [Fig.6]).

[0129] The results obtained are illustrated in the following table:

[0130] [Tables3] Configuration Static specimen Mobile specimen q interface Free sliding 1 Cataphoresis Cataphoresis 0.064 ± 0.019 2 Coating B Coating B 0.647 ± 0.029 3 Coating A Coating A 0.766 ± 0.065 4 Coating B Cataphoresis 0.423 ± 0.045 5 Coating A Cataphoresis 0.630 + 0.051

[0131] The results show that configuration 1 has the worst results, with a coefficient of friction at the interface of approximately 0.064. As a reminder, the coefficient of friction of uncoated steel with uncoated steel is approximately 0.2 according to the literature. The application of a solid coating obtained according to liquid composition A or B on at least one of the two substrates makes it possible to increase this value beyond 0.4, as shown in configurations 2 to 5. The best results are obtained for a system of a mobile specimen coated with a solid coating obtained from liquid composition A associated with a fixed specimen coated with a solid coating obtained from liquid composition A.

[0132] These results show that the use of a solid coating according to the invention on assembly elements can lead to systems having high coefficients of friction.

Claims

Claims

1. Use of a powder of a mixture of flake zinc and zinc oxide, Zn / ZnO, for increasing the value of the adhesion coefficient of an anti-corrosion coating of a substrate, characterized in that the flake zinc represents between 60 and 99% of the mixture of flake zinc and zinc oxide, more particularly between 70 and 95% of the mixture of flake zinc and zinc oxide; and said substrate is a fixing means, such as a bolt, a screw, a clip, a crimp, a clamp, a rivet, or a fixed element, such as a suspension arm.

2. Liquid composition for anti-corrosion coating, characterized in that it comprises: - between 15 and 30% by mass of Zn; - between 8 and 10% by mass of ZnO; - between 5 and 15% by mass of a silane binder; - between 25 and 50% by mass of water; - between 10 and 30% by mass of at least one organic solvent; and - optionally additives; the percentages being expressed relative to the total mass of the liquid composition; said Zn and ZnO being derived from a solvent solution containing a Zn / ZnO powder of a mixture of lamellar zinc and zinc oxide.

3. Composition according to claim 2 characterized in that it further comprises between 0.5 and 4% by mass of aluminum dihydrogen triphosphate relative to the total mass of the composition.

4. A method of manufacturing a composition according to claim 2 or 3 comprising the following successive steps: (a) the formation of a silane binder in water and (b) the addition and solubilization of the aqueous solution obtained in step (a) in a solvent solution containing the Zn / ZnO powder.

5. Method according to claim 4, characterized in that the powder-type zinc has a particle geometry of between 1 pm and 40 pm.

6. Method for protecting a metal substrate against corrosion by an anti-corrosion coating comprising the following successive steps: (al) a step of applying said substrate with a liquid composition according to any one of claims 2 or 3; (bl) a step of drying the coated substrate obtained in step (al) and (cl) a step of baking the coated substrate obtained in step (bl).

7. Substrate coated with at least one layer of composition capable of being obtained by the method according to claim 6.

8. Substrate according to claim 7 characterized in that said substrate is a fixing means, such as a bolt, a screw, a clip, a crimp, a clamp, a rivet, or a fixed element, such as a suspension arm.

9. Anti-corrosion coating capable of being obtained by drying then baking a liquid composition according to any one of claims 2 or 3, characterized in that the thickness of the coating is between 5qm and 15qm, preferably 8qm plus or minus 3qm.

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