COATING COMPOSITION COMPRISING A POLYELECTROLYTE COACERVATE AND CERAMIC PARTICLES

Abstract

The present invention relates to a coating composition comprising a coacervate including a cationic polyelectrolyte and an anionic polyelectrolyte, ceramic particles, and water. It also relates to a method for forming a coating using such a composition, and a coating obtained by such a method.

Description

Title of the invention: COATING COMPOSITION COMPRISING A POLYELECTROLYTE COACERVATE AND CERAMIC PARTICLES

[0001] The present invention relates to a coating composition comprising a coacervate including a cationic polyelectrolyte and an anionic polyelectrolyte, ceramic particles, and water. It also relates to a method for forming a coating using such a composition, and a coating obtained by such a method.

[0002] Coating compositions, such as paints, containing ceramic particles represent a significant advancement in the field of industrial and artistic coatings. These particles, often composed of materials such as alumina, zirconia, or silicon carbide, impart exceptional properties to the coatings, particularly in terms of abrasion resistance, durability, and resistance to high temperatures. The addition of ceramic particles to paints can also improve their mechanical performance, making these coatings ideal for demanding applications such as those found in the aerospace, automotive, and construction sectors.

[0003] However, incorporating ceramic particles into liquid compositions is not without its problems. One of the main issues encountered is particle sedimentation, particularly with high ceramic particle concentrations in the composition. Due to their high density relative to the liquid matrix, ceramic particles tend to settle to the bottom of the container over time. This sedimentation can lead to an uneven distribution of particles within the composition, affecting the consistency, appearance, and functional properties of the applied coating. Poor particle dispersion can also complicate the application process and necessitate additional mixing or stirring procedures before use.

[0004] To avoid sedimentation, various strategies can be implemented. The use of dispersants and stabilizing additives is common to improve the suspension of ceramic particles in the composition. In addition, optimizing particle size and viscosity can help maintain a homogeneous particle distribution.

[0005] However, these strategies have certain drawbacks. For example, the use of large quantities of dispersants and stabilizing additives increases the cost of the composition and requires good compatibility with the other components of the composition. Using particles of optimized size requires specialized equipment to produce them, which also increases the cost of the composition. Adjusting the viscosity results in coating compositions that are more difficult to apply and require longer drying times.

[0006] In this context, the inventors have now developed a coating composition in which ceramic particles can be added at high concentrations without sedimentation. Such a composition is based on the use of a coacervate of a cationic polyelectrolyte and an anionic polyelectrolyte in water.

[0007] SUMMARY

[0008] Thus, the present invention relates to a coating composition comprising:

[0009] - a coacervate comprising a cationic polyelectrolyte and a polyelectrolyte anionic,

[0010] - ceramic particles, and

[0011] - water,

[0012] in which the weight ratio of ceramic particles to cationic and anionic polyelectrolytes is at least 1 / 2.

[0013] In some embodiments, the cationic polyelectrolyte is a weak polyelectrolyte and the pH of the coating composition is preferably greater than the pi of the weak cationic polyelectrolyte.

[0014] In some embodiments, the anionic polyelectrolyte is a weak polyelectrolyte, and the pH of the coating composition is preferably lower than the pi of the weak anionic polyelectrolyte.

[0015] In some embodiments, the cationic polyelectrolyte and the anionic polyelectrolyte are both weak polyelectrolytes,

[0016] the pH of the coating composition preferably being such that:

[0017] -pH>pI+, or

[0018] -pH <pL,

[0019] in which pl+ refers to the pi of the weak cationic polyelectrolyte and pi refers to the pi of the weak anionic polyelectrolyte, with pl+ > pi.

[0020] In some embodiments, the coating composition further comprises a volatile pH buffer, such as 2-amino-2-methyl-l-propanol.

[0021] In some embodiments, the cationic polyelectrolyte is selected from polyethyleneimine, poly(allylamine hydrochloride), poly(aniline), poly(2-vinylpyridine), poly(2-(dimethylamino)ethyl methacrylate), poly(L-lysine), chitosan, and mixtures thereof.

[0022] In some embodiments, the anionic polyelectrolyte is selected from polyacrylic acid, poly(methacrylic acid), poly(glutamic acid), hyaluronic acid, alginic acid, salts thereof and mixtures thereof.

[0023] In certain embodiments, the ceramic particles are selected from particles of a metallic or metalloid element oxide, a metallic or metalloid element nitride, a metallic or metalloid element boride (preferably a metallic element boride), a metallic or metalloid element carbide, and a mixture thereof, preferably particles of boron nitride, montmorillonite, alumina, silica, zirconia, silicon carbide, glass-ceramic, or mixtures thereof.

[0024] In some embodiments, the weight ratio of ceramic particles to cationic and anionic polyelectrolytes ranges from 1 / 1 to 200 / 1, preferably from 2 / 1 to 150 / 1, for example from 4 / 1 to 100 / 1.

[0025] In some embodiments, the weight content of the ceramic particles ranges from 30 to 95% by weight, preferably from 40 to 85% by weight, more preferably from 50 to 80% by weight, relative to the dry weight of the coating composition.

[0026] In some embodiments, the cationic and anionic polyelectrolytes together represent from 1 to 45% by weight, preferably from 1 to 20% by weight, more preferably from 1 to 10% by weight, or even more preferably from 1 to 5% by weight, of the total weight of the composition.

[0027] In some embodiments, the coating composition further comprises a water-soluble polyphenol comprising at least one polyhydroxylated aromatic cyclic structure, and optionally a water-soluble polyvalent transition metal salt.

[0028] The present invention also relates to a method for forming a coating comprising the following steps:

[0029] a) the application of a coating composition as defined herein onto a substrate, to form a wet coating,

[0030] b) drying the wet coating, so as to obtain said coating,

[0031] wherein said coating preferably has a thickness ranging from 0.02 µm to 1000 pm, more preferably from 2 to 600 pm, even more preferably from 5 to 500 pm.

[0032] Another object of the present invention is a coating formed by a process as defined herein. FIGURES

[0033] [Fig. 1] photograph of a boron nitride-based composition of the invention, after 1 month.

[0034] [Fig.2] photograph of a silica-based composition of the invention, after 1 month. DETAILED DESCRIPTION

[0035] The composition of the invention is a coating composition. Such a composition comprises a coacervate comprising a cationic polyelectrolyte (hereinafter referred to as "polycation") and an anionic polyelectrolyte (hereinafter referred to as "polyanion").

[0036] It is known that when an aqueous solution of an anionic polyelectrolyte (hereafter referred to as the "polyanion") and an aqueous solution of a cationic polyelectrolyte (hereafter referred to as the "polycation") are mixed at a pH where the anionic polyelectrolyte has a net negative charge and the cationic polyelectrolyte has a net positive charge, the polyelectrolytes immediately associate and form a solid complex (polyelectrolyte complex) which separates from the aqueous phase. When the aqueous polymer solutions contain water-soluble mineral salts in sufficient quantity to at least partially occult the opposite charges of the polymers, the attraction between the polyanion and the polycation is reduced and the formation of a solid complex is prevented.When such solutions are mixed, a phase separation is observed, with, on the one hand, a concentrated, polymer-rich phase called the "coacervate," and, on the other hand, a polymer-depleted supernatant phase. A detailed description of this phenomenon can be found, for example, in Wang et al., "The Polyelectrolyte Complex / Coacervate Continuum," Macromolecules, 2014, 47, 3108-3116. Such a coacervate state can also be obtained when the pH of the mixture is such that at least one of the anionic and cationic polyelectrolytes has a net charge of zero. In such a case, it is therefore not necessary to add salts to partially occult the charges.

[0037] The term “cationic polyelectrolyte” encompasses a cationic polyelectrolyte, but also mixtures of two or more cationic polyelectrolytes. The term “anionic polyelectrolyte” encompasses an anionic polyelectrolyte, but also mixtures of two or more anionic polyelectrolytes.

[0038] The composition of the invention advantageously comprises similar amounts of a cationic polyelectrolyte and an anionic polyelectrolyte, "similar amounts" here meaning that these two types of polyelectrolytes of opposite charges are used in respective amounts such that the ratio of the number of positive charges of the polycation to the number of negative charges of the polyanion is between 0.5 and 2.0, preferably between 0.6 and 1.8, more preferably between 0.7 and 1.6 and even more preferably between 0.8 and 1.4, or even between 0.9 and 1.2.

[0039] Polyelectrolytes can be strong or weak. A strong polyelectrolyte is a polymer having a net positive or negative charge that is essentially independent of the pH of the composition. In particular, the zeta potential of a strong cationic polyelectrolyte is positive for any pH in the range of 1 to 14, and the zeta potential of a strong anionic polyelectrolyte is negative for any pH in the range of 1 to 14. The zeta potential can be measured using a zeta potential analyzer (e.g., a "Zetasizer" type device) at an appropriate concentration (generally greater than 0.01%, e.g., 1% by weight of polyelectrolyte relative to the volume of solution analyzed) and generally at 20 °C.

[0040] Conversely, a weak polyelectrolyte is a polymer having a net positive or negative charge that depends on the pH. Typically, the zeta potential of a weak polyelectrolyte measured at pH 1 and that measured at pH 14 are at least 10% different. In general, a weak polyelectrolyte has a pi value between 1 and 14. More specifically, a weak cationic polyelectrolyte generally has a pi value greater than 7, for example, between 7.5 and 14, and a weak anionic polyelectrolyte generally has a pi value less than 7, for example, between 1 and 6.5. In the present application, the pi values ​​are determined in water, at a temperature of 25 °C and in 0.01 M NaCl.

[0041] Strong cationic polyelectrolytes are, for example, polymers comprising a plurality of quaternized amine groups; strong anionic polyelectrolytes are, for example, polymers comprising a plurality of sulfonate (-SO3) groups. Poly(acrylic acid) is an example of a weak anionic polyelectrolyte, and non-quaternized polyamines are examples of weak cationic polyelectrolytes.

[0042] In the present invention, an anionic polyelectrolyte is a polymer having a net negative charge at pH 7, and a cationic polyelectrolyte is a polymer having a net positive charge at pH 7. This does not mean that an anionic polyelectrolyte comprises only negative charges and is devoid of positive charges. By analogy, cationic polyelectrolytes can comprise both cationic and anionic charges, provided that at pH 7, the overall net charge is positive.

[0043] Therefore, the definition of anionic polyelectrolytes encompasses zwitterionic polyelectrolytes having an isoelectric point (pi) < 7, preferably < 6, and the definition of cationic polyelectrolytes encompasses zwitterionic polyelectrolytes having an isoelectric point (pi) > 7, preferably > 8. The best-known zwitterionic polyelectrolytes are proteins or peptides comprising both carboxyl pendant groups (-COOH) and amino pendant groups (-NH2).

[0044] In a preferred embodiment, the anionic polyelectrolyte comprises only negative charges and is devoid of positive charges, and the cationic polyelectrolyte comprises only positive charges and is devoid of negative charges.

[0045] The anionic polyelectrolyte and the cationic polyelectrolyte can be linear or branched polymers.

[0046] The cationic groups of the cationic polyelectrolyte are, for example, primary, secondary, or tertiary amino groups or quaternized amine groups, located in the main chain of the polymer or on pendant groups.

[0047] The anionic groups of the anionic polyelectrolyte are, for example, chosen from the group consisting of carboxylate, sulfonate, phosphonate, boronate, sulfate, borate, and phosphate groups, located in the main chain of the polymer or on pendant groups thereof.

[0048] The cationic polyelectrolyte is preferably chosen from the group consisting of:

[0049] - poly(dialyldimethylammonium chloride) (PDADMAC),

[0050] - poly[(2-hydroxypropyl)dimethylammonium chloride],

[0051] - polyamidoamine-epichlorohydrin (PAAE),

[0052] - polyethylene imine,

[0053] - poly(acrylamide-diallyldimethylammonium co-chloride),

[0054] - poly(acrylic acid-dialyldimethylammonium co-chloride),

[0055] - copolymer of hydroxyethylcellulose and poly(chloride of diallyldimethylammonium) (Polyquatemium-4),

[0056] - copolymer of acrylamide and quaternized dimethylaminoethyl methacrylate with dimethyl sulfate (Polyquaternium-5, CAS 26006-22-4),

[0057] - copolymer of dimethylaminomethyl methacrylate and alkyl methacrylate,

[0058] - copolymer of methyl ester and dimethylaminoethyl stearyl acid methacrylic,

[0059] - homopolymer of N,N-(dimethylamino)ethyl ester of methacrylic acid quaternized with bromomethane or quaternized hydroxyethylcellulose,

[0060] - chitosan,

[0061] - quaternized N,N-(dimethylamino)ethyl poly(methacrylate),

[0062] - guar hydroxypropyltrimonium chloride,

[0063] - poly(2-(dimethylamino)ethyl methacrylate),

[0064] - poly(N,N-dimethyl-3,5-dimethylenepiperidinium chloride),

[0065] - poly(vinylbenzyltrimethylammonium chloride),

[0066] - poly[3-(methacryloylamino)propyl-trimethylammonium chloride],

[0067] - poly(chloride of [2-(methacryloloxy)ethyl]-trimethylammonium),

[0068] - polyvinylamine (PVA),

[0069] - poly(N,N-dimethyl-3,5-dimethylenepiperidinium chloride) (PDDPC),

[0070] - poly(vinylbenzyltrimethylammonium chloride) (PVBTAC),

[0071] - poly(allylamine hydrochloride) (PAH),

[0072] - poly[3-(methacryloylamino)propyltrimethylammonium chloride] (PMATPAC),

[0073] - cationic dextran,

[0074] - poly(aniline),

[0075] - poly(2-vinylpyridine),

[0076] - poly(L-lysine),

[0077] - type A gelatin, and

[0078] - mixtures of these.

[0079] More preferably, the cationic polyelectrolyte is chosen from polyethyleneimine, poly(allylamine hydrochloride), poly(aniline), poly(2-vinylpyridine), poly(2-(dimethylamino)ethyl methacrylate), poly(L-lysine), chitosan, and mixtures thereof.

[0080] The anionic polyelectrolyte is preferably selected from the group consisting of poly(acrylic acid), poly(acrylic-co-acrylamido acid), poly(4-styrene-sulfonic acid), lignosulfonic acid, humic acid, alginic acid, poly(2-acrylamido-2-methyl-l-propanesulfonic acid), hyaluronic acid, poly(vinylsulfonic acid), poly(glutamic acid), dextran sulfate, salts thereof (for example, sodium salts), type B gelatin, and mixtures thereof.

[0081] More preferably, the anionic polyelectrolyte is chosen from polyacrylic acid, poly(methacrylic acid), poly(glutamic acid), hyaluronic acid, alginic acid, salts thereof (for example, sodium salts), and mixtures thereof.

[0082] The average molecular mass by weight (determined by light scattering) of each of the anionic and cationic polyelectrolytes is generally between 5,000 and 2,000,000 Da, preferably between 10,000 and 1,500,000 Da, more preferably between 20,000 and 1,000,000 Da, even more preferably between 50,000 and 700,000 Da, for example between 100,000 and 500,000 Da. The anionic polyelectrolyte and the cationic polyelectrolyte preferably have similar molecular masses.

[0083] The ratio of the average molecular mass by weight of the anionic polyelectrolyte to the average molecular mass by weight of the cationic polyelectrolyte is preferably between 0.4 and 1.6, more preferably between 0.7 and 1.3 and even more preferably between 0.8 and 1.2.

[0084] In a preferred embodiment, at least one of the anionic polyelectrolyte and the cationic polyelectrolyte is a weak polyelectrolyte.

[0085] In one embodiment, the cationic polyelectrolyte is a weak polyelectrolyte (preferably branched). In such an embodiment, the anionic polyelectrolyte may be a strong or weak polyelectrolyte (for example, a polyelectrolyte strong). In such an embodiment, the pH of the composition of the invention is advantageously greater than the ρ of the weak cationic polyelectrolyte. The ρ of a weak cationic polyelectrolyte is generally greater than 7, for example between 7.5 and 14.

[0086] In another embodiment, the anionic polyelectrolyte is a weak polyelectrolyte. In such an embodiment, the cationic polyelectrolyte may be a strong or weak polyelectrolyte (for example, a strong polyelectrolyte). In such an embodiment, the pH of the composition of the invention is advantageously lower than the pI of the weak anionic polyelectrolyte. The pI of a weak anionic polyelectrolyte is generally less than 7, for example, between 1 and 6.5.

[0087] In a more preferred embodiment, the cationic polyelectrolyte and the anionic polyelectrolyte are both weak polyelectrolytes. In such an embodiment, the pH of the composition is advantageously such that:

[0088] - pH > pl+, or

[0089] - pH < π.,

[0090] in which pl+ refers to the pi of the weak cationic polyelectrolyte and pi refers to the pi of the weak anionic polyelectrolyte, with pl+ > pi.

[0091] Cationic polyelectrolytes and anionic polyelectrolytes together preferably represent 1 to 45% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight, or even more preferably 1 to 5% by weight, of the total weight of the composition. In some embodiments, cationic polyelectrolytes and anionic polyelectrolytes together preferably represent 2 to 40%, 3 to 40%, 4 to 40%, 5 to 35%, or 8 to 30% of the total weight of the composition.

[0092] For very high molecular masses, the lower limit may be about 1% by weight of the composition.

[0093] The composition may further comprise a water-soluble mineral salt. Such a water-soluble mineral salt is particularly useful for regulating the coacervate state of a strong cationic polyelectrolyte and a strong anionic polyelectrolyte.

[0094] As used here, "water soluble" means having a solubility in distilled water at 20 °C greater than 100 g / L, preferably greater than 200 g / L, even more preferably greater than 300 g / L.

[0095] Such a water-soluble mineral salt is preferably chosen from the group consisting of alkali metal halides or alkaline earth metal halides. The preferred alkali metals are lithium, sodium, and potassium. The preferred alkaline earth metals are calcium and magnesium. The preferred halides are chlorides and bromides. The function of the water-soluble mineral salt is to filter the opposite charges are used to reduce the ionic interaction between the polyelectrolytes, preventing the formation of a solid, insoluble polyelectrolyte complex and allowing the formation of a coacervate (a viscous solution rich in polyelectrolytes). The water-soluble mineral salt is preferably a monovalent metallic salt, i.e., an alkali metal halide. Alkaline earth metal salts, when present, preferably do not exceed 20 mol% of the total mineral salts.

[0096] The appropriate amount of water-soluble mineral salt (when present) depends on the total amount of polyelectrolyte charges, i.e., for a given molecular mass of polyelectrolytes, it is approximately proportional to the amount of polyelectrolytes in the composition.

[0097] When present, the amount of water-soluble mineral salt is generally between 40% and 95% by weight, preferably between 55% and 75% by weight, relative to the total dry weight of cationic polyelectrolyte, anionic electrolyte and water-soluble mineral salt.

[0098] The weight ratio of the total amount of cationic polyelectrolyte and anionic polyelectrolyte to the total amount of water-soluble mineral salt (when present) is preferably between 0.10 and 4.0, more between 0.50 and 2.50, and even more preferably between 0.80 and 1.50.

[0099] The aforementioned quantity and ratio may also depend, to some extent, on the molecular mass of the polyelectrolyte. The higher the average molecular mass by weight of the polyelectrolytes, the more water-soluble mineral salt will be required to obtain a sufficiently low viscosity of the aqueous composition.

[0100] Alternatively, or in addition, the composition may further comprise a pH buffer, which is advantageously volatile. Such a pH buffer is particularly useful for regulating the coacervate state of a cationic polyelectrolyte and an anionic polyelectrolyte, where at least one of the cationic and anionic polyelectrolytes is a weak polyelectrolyte.

[0101] As used here, a "volatile" pH buffer is a pH buffer having a boiling point below 400 °C, preferably below 260 °C, more preferably below 100 °C, even more preferably below 50 °C.

[0102] pH buffers (including volatile pH buffers) are well known to those skilled in the art and can be selected according to their pKa. The pKa(s) (measured at 25 °C in water) of the pH buffer used in the composition of the invention are advantageously between 1 and 14.

[0103] The pH buffer may in particular be ammonia, an ammonium salt, an amine, a carboxylic acid, an amino acid, an amino alcohol, or a combination thereof.

[0104] Examples of volatile pH buffers include, but are not limited to, 2-amino-2-methyl-l-propanol, formic acid, pyridine / formic acid, trimethylamine / formic acid, pyridine / acetic acid, trimethylamine / acetic acid, ammonia / formic acid, ammonia / acetic acid, trimethylamine / carbonate, ammonium bicarbonate, ammonium carbonate / ammonia, ammonium carbonate, ammonia, and N-ethylmorpholine / acetate.

[0105] A preferred volatile pH buffer is 2-amino-2-methyl-l-propanol.

[0106] The weight content of the pH buffer in the composition advantageously ranges from 0.1 to 5% by weight, preferably from 0.2 to 4% by weight, more preferably from 0.5 to 2.5% by weight, relative to the total weight of the composition.

[0107] The composition may further comprise a water-soluble polyphenol comprising at least one polyhydroxylated aromatic cyclic structure, optionally in combination with a water-soluble polyvalent transition metal salt. Such a polyphenol may have a beneficial effect on the physicochemical and / or mechanical properties of the final materials.

[0108] The amount of polyphenol, or polyphenols, should be between 0.02% and 1.0% by weight, preferably between 0.02% and 0.5%, more preferably between 0.03% and 0.5% by weight, even more preferably between 0.04% and 0.1% by weight, relative to the aqueous composition.

[0109] When expressed in relation to the dry weight of the composition, the total quantity of polyphenol(s) is between 0.001% and 0.5% by weight, preferably between 0.01% and 0.25% by weight, more preferably between 0.05% and 0.5% by weight or between 0.02% and 0.1% by weight.

[0110] The term “polyphenol” designates an organic compound comprising at least one polyhydroxylated aromatic cyclic structure, “polyhydroxylated” meaning that it comprises two hydroxyl groups on the same aromatic ring.

[0111] In a preferred embodiment, at least a portion of the polyphenols used in the composition comprise more than one polyhydroxylated aromatic cyclic structure, i.e. at least two, preferably at least three, and more preferably at least four polyhydroxylated aromatic cyclic structures.

[0112] Polyhydroxylated aromatic cyclic structures are preferably chosen from groups consisting of catechol groups, pyrogallol groups, tetrahydroxylated aromatic cyclic structures and pentahydroxylated aromatic cyclic structures.

[0113] In a particularly interesting embodiment, the polyphenol is tannic acid (CAS No. 1401-55-4).

[0114] Other examples of polyphenols include synthetic organic polymers comprising comonomers with polyhydroxylated cyclic structures (see, for example, the work of Cheng et al., in Nature Communications, 13, article number 1892 (2022)).

[0115] In another preferred embodiment of the present invention, the polyphenol is a synthetic copolymer comprising comonomers with polyhydroxylated cyclic structures, preferably a copolymer of styrene and a comonomer selected from dihydroxystyrene, trihydroxystyrene, tetrahydroxystyrene and pentahydroxystyrene.

[0116] The mechanical performance of the final material can be further improved by combining the polyphenol-reinforced polyelectrolyte coacervate with polyvalent transition metal ions. In another preferred embodiment, the composition further comprises a water-soluble polyvalent transition metal salt or a mixture of polyvalent transition metal salts, preferably in a total amount of between 0.001 and 0.1%, more preferably between 0.002% and 0.05%, and even more preferably between 0.005 and 0.05%, relative to the total weight of the composition.

[0117] When expressed in relation to the water-soluble polyphenol, the weight ratio of the transition metal salt to the dry weight of the polyphenol is generally between 0.1 and 0.2, preferably between 0.12 and 0.18.

[0118] Transition metals are preferably chosen from the group consisting of Fe, Zn, Co, Cu, and V. Halides, in particular chlorides and bromides, are preferred anions of the reinforcing transition metal salts used in the present invention.

[0119] The composition of the invention may also include an organic polymer. Such an organic polymer may be useful for giving flexibility to a coating formed from the composition.

[0120] Examples of organic polymers include, but are not limited to, acrylic polymers, methacrylic polymers, polyvinyl butyral, ethylene-vinyl acetate polymers, ethylene-vinyl chloride polymers, styrene-acrylic polymers, styrene-butadiene polymers, chloroprene, natural rubber.

[0121] More particularly, such organic polymers may be selected from polymers based on one or more of the following monomers: 2-ethylhexyl acrylate, butyl acrylate, ethyl acrylate, methyl acrylate, acrylic acid, hydroxyethyl methacrylate, styrene, cyclohexyl methacrylate, methacrylate butyl, isobornyl methacrylate, isobutyl methacrylate, ethyl methacrylate, isobornyl acrylate, methyl methacrylate, vinyl acetate, butadiene.

[0122] The weight content of said organic polymer advantageously ranges from 0.5 to 15%, preferably from 1 to 12%, more preferably from 2 to 9%, even more preferably from 3 to 7%, relative to the total weight of the composition.

[0123] The composition may further comprise a hydrophobic agent, generally added as an emulsion. The hydrophobic agent may be a wax, for example, paraffin wax, polyethylene wax, polypropylene wax, silicone wax, or poly(tetrafluoroethylene) wax. Hydrophobic resins, for example, hydrophobic silicone resins such as Variphob® AC 3030, may also be used effectively as hydrophobic agents. The hydrophobic agent is generally used in proportions of up to 15% by weight, preferably between 1% and 15% by weight, more preferably between 2% and 10% by weight, and even more preferably between 3% and 5% by weight, relative to the total dry weight of the composition.

[0124] The composition may further comprise up to about 20%, preferably from 0.1 to about 10% (by weight, based on the total weight of the composition), of one or more additives other than those mentioned above. These additives are chosen, for example, from the group consisting of co-solvents such as ethanol and polyethylene glycol, colorants, pigments, biocides, buffering agents, surfactants, dispersants, and thickening agents. Another additive is, for example, an antifoaming agent. The composition may further comprise one or more plasticizers, preferably in an amount of between 0.1 and 10% by weight, relative to the total dry weight of the composition.

[0125] The composition of the invention further comprises ceramic particles. As used herein, the term "ceramic" refers to a material that is neither metallic ("metallic" meaning "consisting solely of metal(s) or metalloid(s)") nor organic ("organic" meaning "consisting essentially of C-H bonds, and optionally also comprising heteroatoms such as O, N, and / or S atoms"). In particular, it consists of one or more oxides, nitrides, borides, or carbides of metallic or metalloid elements. Examples of such metallic or metalloid elements include, but are not limited to, boron (B), aluminum (Al), zirconium (Zr), titanium (Ti), magnesium (Mg), silicon (Si), or a combination thereof.

[0126] Examples of ceramic particles include, but are not limited to, boron nitride, montmorillonite, alumina, silica, titanium, zirconia, silicon carbide, glass-ceramic, and mixtures thereof.

[0127] Preferably, the ceramic particles are chosen from boron nitride, alumina, zirconia, silica, glass-ceramic, silicon carbide particles, and mixtures thereof.

[0128] More preferably, the ceramic particles are chosen from boron nitride, alumina, zirconia, glass-ceramic, silicon carbide particles, and mixtures thereof.

[0129] Preferably, the boron nitride is hexagonal boron nitride.

[0130] "Glass-ceramic" is well known to those skilled in the art. In certain embodiments, the glass-ceramic has a composition comprising the following components:

[0131] - SiO2: 60 to 70 molar %, preferably 61 to 64 molar %,

[0132] - BaO: 25 to 35 molar percent, preferably 30 to 33 molar percent,

[0133] - Al₂O₃: 0 to 15 molar %, preferably 0 to 10 molar %, and

[0134] - ZrO2: 0 to 5 molar %.

[0135] The d50 of the ceramic particles can range from 5 nm to 200 pm, typically from 10 nm to 200 pm, advantageously from 20 nm to 200 pm, preferably from 50 nm to 200 pm, more preferably from 0.1 pm to 200 pm, even more preferably from 0.2 pm to 100 pm (for example from 1 pm to 50 pm, from 1 pm to 30 pm, or from 2 pm to 20 pm).

[0136] The d50 designates the value for which 50% of the particles - by number - have a size less than or equal to this value, and 50% of the particles - by number - have a size greater than this value.

[0137] The d50 can be determined by laser diffraction.

[0138] The weight ratio of ceramic particles to cationic and anionic polyelectrolytes is at least 1 / 2. Preferably, the weight ratio of ceramic particles to cationic and anionic polyelectrolytes ranges from 1 / 1 to 200 / 1, more preferably from 2 / 1 to 150 / 1, even more preferably from 4 / 1 to 100 / 1, more particularly from 4 / 1 to 25 / 1.

[0139] The weight content of the ceramic particles advantageously ranges from 30 to 95% by weight, preferably from 40 to 85% by weight, more preferably from 50 to 80% by weight, relative to the dry weight of the coating composition.

[0140] Advantageously, the composition has a water content ranging from 15 to 80% by weight, preferably from 20 to 75% by weight, more preferably from 25 to 70% by weight.

[0141] The composition of the invention may be in the form of a liquid or a paste, depending on the intended use.

[0142] The coating composition of the invention is particularly suitable for use as a paint composition.

[0143] The present invention also relates to a method for forming a coating comprising the steps of:

[0144] - apply a composition as defined herein to a substrate, so as to form a wet coating, and

[0145] - dry the wet coating, so as to form said coating.

[0146] The composition can be applied by any suitable method, including using a roller, a brush, or even by spraying. The composition can be applied in several layers.

[0147] The substrate can be flexible or rigid. More particularly, the substrate can, for example, be a plastic film (e.g. polyolefin-based films, such as polyethylene and / or polypropylene-based films), a textile substrate, a paper substrate, a metallic substrate, a ceramic substrate, or a foam substrate (e.g. inorganic or organic foam).

[0148] The wet coating formed on the substrate is then dried. Drying can be done by air drying, without heating. Alternatively, the wet coating can be dried by heating at a suitable temperature, for example, between 50 °C and 180 °C, more particularly between 80 °C and 120 °C. The time required for drying can be adjusted according to the drying temperature. When no heating is applied, drying can take several hours, for example, from 4 to 24 hours. When heating is applied, drying can take a few minutes, for example, from 1 to 20 minutes.

[0149] The present invention also relates to a coating formed from a composition as defined herein.

[0150] More particularly, the present invention relates to a coating obtained by a process as defined above.

[0151] The coating of the invention generally comprises a complex of a cationic polyelectrolyte and an anionic polyelectrolyte, and ceramic particles (and optionally one or more other ingredients described above).

[0152] It is understood that the ratios described above for the composition (for example, the ratio of the weight of ceramic particles to the total dry weight of the cationic and anionic polyelectrolytes) apply to the coating (i.e. the dry coating).

[0153] The weight content of ceramic particles in the coating (i.e. the dry coating) ranges from 30 to 95% by weight, preferably from 40 to 90% by weight, more preferably from 50 to 85% by weight, relative to the weight of the coating.

[0154] The coating can have a thickness ranging from 0.02 pm to 1000 pm, preferably from 2 to 600 pm, more preferably from 5 to 500 pm.

[0155] The thickness can be measured by optical measurements using, for example, microscopy (for example, scanning electron microscopy “SEM”).

[0156] In this application, unless otherwise specified, a component weight content (or a component weight ratio) is based on the component weight itself, and therefore on its weight in dry extract, when used for example diluted in a dispersion or solution.

[0157] The present invention is illustrated by the following non-limiting examples. Examples

[0158] 1 - Composition comprising a coacervate based on strong polyelectrolytes and boron nitride particles

[0159] a. Preparation of the polycation salt solution:

[0160] A concentrated aqueous solution of tannic acid with a concentration of 0.14 g / mL was prepared. Using a pipette, 45 µL of the concentrated tannic acid solution was added to 15.9 mL of water, acidified by adding 1 M HCl to pH 1, and then 5.45 g of KBr were added. Next, 3.0 g of EVA 462 (PDADMAC) were added to the resulting aqueous composition and stirred until the polyelectrolyte was completely dissolved. After the polyelectrolyte had dissolved, 0.001 g of FeCl3 was added while stirring.

[0161] b. Preparation of the polyanion salt solution:

[0162] To 16.4 ml of water previously acidified to pH 1 with HCl, 5.45 g of KBr were added. To the resulting acidic saline solution, 2.65 g of Versai TL 130 having a poly(styrene sulfonate) content of approximately 30% were added.

[0163] c. Preparation of the coacervate:

[0164] After complete dissolution of the polyelectrolytes, the polyanion solution (PSS) was poured into the polycation solution (PDADMAC) under vigorous stirring. The mixture was allowed to stand for a few minutes until phase separation occurred.

[0165] The upper (supernatant) phase has been eliminated.

[0166] The lower phase (coacervate) was green and changes color (red) when neutralized by the addition of 0.3 ml of AMP 95 (2-amino-2-methyl-l-propanol) until a pH > 7.

[0167] The composition of the coacervate obtained is detailed in Table 1.

[0168] [Tables 1] Weight (g) Weight (% of total) Water 7.9 16.14% PDAMAC 17.2 35.14% PSS 15.2 31.07% KBr 8.6 17.57% Tannic acid 0.034 0.07% Ferrous chloride 0.00573 0.01% Total (g) 48.94 100%

[0169] d. Addition of boron nitride particles

[0170] To 10 g of a coacervate sample prepared as described above, an antifoaming agent, a stabilizing agent, and a dispersant were added under stirring. Once thoroughly mixed, hexagonal boron nitride was added under constant stirring. Then, all the components were mixed under high-shear stirring at 4,000 rpm for 15 minutes.

[0171] The coating composition consisted of approximately 58% by weight of poly electrolyte coacervate and 33% of boron nitride particles (Table 2).

[0172] The coating composition was applied to the surface of a polyethylene substrate and water was applied over it. Hardening occurred when the salt left the coacervate.

[0173] [Tables2] Component weight (g) Content (% by weight) Dry matter content (after removal of se 1) (% by weight) Composition of coacervate from Table 1 10 58.4 19.2 Boron nitride (d50 = 30 pm) 5.6 32.7 71.5 Stabilizing agent (solution of an alkyl ol ammonium salt of a high molecular weight acid polymer) (Solids content 70%) 0.51 3.0 4.5 Dispersant (Solids content 40%) 0.88 5.1 4.5 Antifoam (Solids content 17%) 0.14 0.8 0.3 Total sample (g) 17.13 100 100

[0174] 2 - Composition comprising a coacervate based on weak polyelectrolytes and boron nitride particles

[0175] Polyethyleneimine (25% by weight of solids in deionized water) and TAMP95 were mixed in deionized water to reach a pH of 10, then polyacrylic acid (12% by weight of solids in deionized water) was added. Next, the dispersant and antifoam were added with stirring. Then, the Boron nitride particles were added while stirring. Water was then added and the resulting mixture was stirred (4000 rpm) for 5 minutes (Table 3).

[0176] A film was formed by pouring the composition onto a polyethylene substrate and then drying it at 100 °C for 2 minutes. The dried films had a thickness of approximately 200 µm.

[0177] [Tables3] Component weight (g) Content (% by weight) Dry matter content (after drying) (% by weight) AMP 95 (pH buffer) 2 4.7 0 Polyacrylic acid (12% by weight of solids; 250 kg / mol) 10 23.5 6.2 Polyethyleneimine (25% by weight of solids; 25 kg / mol) 9.7 22.8 12.4 Water 3.3 7.8 0 Hexagonal boron nitride (d50 = 30 pm) 14.5 34.1 74.4 Stabilizer 0.8 1.9 2.9 Dispersant 1.9 4.5 3.9 Defoamer 0.3 0.7 0.2 Total sample (g) 42.5 100 100

[0178] 3 - Composition comprising a coacervate based on weak polyelectrolytes and silica particles

[0179] A composition was prepared by mixing the ingredients listed in Table 4 below, based on a protocol similar to that described in Example 2.

[0180] [Tables4] Component Weight (g) Content (% by weight) Dry matter content (after drying) (% by weight) Polyacrylic acid (20% solids; 250 kg / mol) 10 28.9% 10 Polyethyleneimine (67% by weight of solids; 25 kg / mol) 6 17.3% 20 AMP 95 (pH buffer) 0.1 0.3% 0 Silica 1 PYROGENATED SILICONE POWDER FMT-A07 (d50 = 1.3 pm) 10.9 31.4% 55 Silica 2 Colloidal silica L UDOX® AS-40 (d 50 = 15 nm) (solids content 40%) 5.9 17.0% 12 Dispersant 1.6 4.6% 3 Deaerators 0.16 0.5% 0 Total sample (g) 34.7 100% 100%

[0181] 4 - Composition comprising a coacervate based on weak polyelectrolytes, boron and alumina nitride particles

[0182] A composition was prepared by mixing the ingredients listed in Table 5 below, based on a protocol similar to that described in Example 2.

[0183] [Tables5] Wet Dry Component Weight (g) Content (% by weight) Weight (g) Content (% by weight) Water 30.0 65.4% 0 0.0% pH buffer: AMP 95 0.66 1.4% 0 0.0% Antifoam 0.25 0.5% 0.0425 0.34% Stabilizing additive 1 2.2% 0.35 2.79% Boron nitride (d50 = 5-6 pm) 8 17.4% 8.1 64.58% Colloidal alumina (d50 = 50 nm) 3 6.5% 3 23.92% Polyacrylic acid (35% by weight of solids; 250 kg / mol) 1 2.2% 0.35 2.79% Polyethyleneimine (25% by weight of solids; 25 kg / mol) 2.0 4.4% 0.7 5.58% Total sample (g) 45.91 100% 12.54 100%

[0184] 5 - Composition comprising a coacervate based on weak polyelectrolytes, boron nitride and montmorillonite particles

[0185] A composition was prepared by mixing the ingredients listed in Table 6 below, based on a protocol similar to that described in Example 2.

[0186] [Tableauxô] Wet Dry Component Weight (g) Content (% by weight) Weight (g) Content (% by weight) Water 30.0 45.5% 0 0.0% pH Buffer: AMP 95 0.66 1.0% 0 0.0% Antifoam 0.31 0.5% 0.0527 0.2% Stabilizing Additive 1 1.5% 0.35 1.1% Boron Nitride (d50 = 30 pm) 28.54 43.2% 28.5 87.8% Sodium Montmorillonite (Bentonite) 2.5 3.8% 2.5 7.7% Polyacrylic Acid (35% by weight of solids; 250 kg / mol) 1 1.5% 0.35 1.1% Polyethyleneimine (25% by weight solids ids; 25 kg / mol) 2.0 3.0% 0.7 2.1% Total sample (g) 66.0 100% 32.5 100%

[0187] The compositions in Tables 2, 3, 4, 5, and 6 were prepared with high contents of ceramic particles, and no sedimentation was observed after one month, as shown in [Fig.1] (composition of Table 3) and [Fig.2] (composition of Table 4).

Claims

Demands

1. Coating composition comprising: - a coacervate comprising a cationic polyelectrolyte and an anionic polyelectrolyte, - ceramic particles, and - water, wherein the weight ratio of the ceramic particles to the cationic and anionic polyelectrolytes is at least 1 / 2.

2. Coating composition according to claim 1, wherein the cationic polyelectrolyte is a weak polyelectrolyte.

3. Coating composition according to claim 2, wherein the pH of the coating composition is greater than the pi of the weak cationic polyelectrolyte.

4. Coating composition according to any one of claims 1 to 3, wherein the anionic polyelectrolyte is a weak polyelectrolyte.

5. Coating composition according to claim 4, wherein the pH of the coating composition is lower than the pi of the weak anionic polyelectrolyte.

6. Coating composition according to claim 1, wherein the cationic polyelectrolyte and the anionic polyelectrolyte are both weak polyelectrolytes, the pH of the coating composition preferably being such that: - pH > pl+, or - pH < pi, in which pl+ refers to the pi of the weak cationic polyelectrolyte and pi refers to the pi of the weak anionic polyelectrolyte, with pl+ > pi.

7. Coating composition according to any one of claims 1 to 6, wherein the coating composition further comprises a volatile pH buffer, such as 2-amino-2-methyl-1-propanol.

8. Coating composition according to any one of claims 1 to 7, wherein the cationic polyelectrolyte is selected from polyethyleneimine, poly(allylamine hydrochloride), poly(aniline), poly(2-vinylpyridine), the poly(2-(dimethylamino)ethyl methacrylate), poly(L-lysine), chitosan, and mixtures thereof.

9. Coating composition according to any one of claims 1 to 8, wherein the anionic polyelectrolyte is selected from polyacrylic acid, poly(methacrylic acid), poly(glutamic acid), hyaluronic acid, alginic acid, salts thereof and mixtures thereof.

10. 0 Coating composition according to any one of claims 1 to 9, wherein the ceramic particles are selected from particles of a metallic or metalloid element oxide, a metallic or metalloid element nitride, a metallic or metalloid element boride, a metallic or metalloid element carbide, and a mixture thereof, preferably particles of boron nitride, montmorillonite, alumina, silica, zirconia, silicon carbide, glass-ceramic, or mixtures thereof.

11. 1 Coating composition according to any one of claims 1 to 10, wherein the weight ratio of ceramic particles to cationic and anionic polyelectrolytes ranges from 1 / 1 to 200 / 1, preferably from 2 / 1 to 150 / 1, for example from 4 / 1 to 100 / 1.

12. 2 Coating composition according to any one of claims 1 to 11, wherein the weight content of ceramic particles ranges from 30 to 95% by weight, preferably from 40 to 85% by weight, more preferably from 50 to 80% by weight, relative to the dry weight of the coating composition.

13. 3 Coating composition according to any one of claims 1 to 12, wherein the cationic and anionic polyelectrolytes together represent from 1 to 45% by weight, preferably from 1 to 20% by weight, more preferably from 1 to 10% by weight, or even more preferably from 1 to 5% by weight, of the total weight of the composition.

14. 4 Coating composition according to any one of claims 1 to 13, wherein the coating composition further comprises a water-soluble polyphenol comprising at least one polyhydroxylated aromatic cyclic structure, and optionally a water-soluble polyvalent transition metal salt.

15. 5 A method for forming a coating comprising the following steps:

16. a) the application of a coating composition as defined in any one of claims 1 to 14 onto a substrate, to form a wet coating, b) drying the wet coating, so as to obtain said coating, in which said coating preferably has a thickness ranging from 0.02 pm to 1000 pm, more preferably from 2 to 600 pm, even more preferably from 5 to 500 pm. 6 Coating formed by a process as defined in claim 15.

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