Coating composition comprising polyelectrolytes coacervate and ceramic particles

Abstract

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

Description

[0001] COATING COMPOSITION COMPRISING POLYELECTROLYTES COACERVATE AND CERAMIC PARTICLES

[0002] The present invention relates to a coating composition comprising a coacervate comprising a cationic polyelectrolyte and an anionic polyelectrolyte, ceramic particles, and water. It also relates to a process for forming a coating using such composition, and to a coating obtained by such process.

[0003] Coating compositions, such as paints, containing ceramic particles represent a significant advance in the field of industrial and artistic coatings. These particles, often composed of materials such as alumina, zirconia, or silicon carbide, provide exceptional properties to coatings, particularly in terms of abrasion resistance, durability and resistance to high temperatures. The addition of ceramic particles to paints may also improve their mechanical performance, making these coatings ideal for demanding applications such as those found in the aerospace, automotive and construction sectors.

[0004] However, incorporating ceramic particles into liquid compositions is not without challenges. One of the major problems encountered is particle settling, especially for high contents of ceramic particles in the composition. Due to their high density compared to the liquid matrix, ceramic particles tend to settle to the bottom of the container over time. This settling phenomenon can lead to uneven distribution of particles in the composition, thus affecting the consistency, appearance and functional properties of the applied coating. Poor particle dispersion can also complicate the application process and require additional mixing or agitation procedures before use.

[0005] To avoid settling, various strategies can be implemented. The use of dispersants and stabilizing additives is common to improve the suspension of ceramic particles in the composition. Additionally, optimizing particle size and viscosity may help maintain even particle distribution. However, such strategies have some drawbacks. For instance, the use of amounts of dispersants and stabilizing additives increases the cost of the composition and requires a good compatibility with the other components of the composition. The use of particles having an optimized size requires a particular equipment to produce such particles, which also increases the cost of the composition. Adjusting viscosity leads to coating compositions that are more difficult to apply and that require long drying times.

[0006] In this context, the inventors have now developed a coating composition in which ceramic particles can be added in high contents, without settling. Such 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 an anionic polyelectrolyte,

[0010] - ceramic particles, and

[0011] - water, wherein the weight ratio of the ceramic particles to the cationic and anionic polyelectrolytes is at least 1 / 2.

[0012] In some embodiments, the cationic polyelectrolyte is a weak polyelectrolyte and the pH of the coating composition is preferably higher than the pl of the weak cationic polyelectrolyte.

[0013] In some embodiments, the anionic polyelectrolyte is a weak polyelectrolyte, and the pH of the coating composition is preferably lower than the pl of the weak anionic polyelectrolyte.

[0014] In some embodiments, the cationic polyelectrolyte and the anionic polyelectrolytes are both weak polyelectrolytes, the pH of the coating composition being preferably such that:

[0015] - pH > pl+, or

[0016] - pH < pL, wherein pl+ refers to the pl of the weak cationic polyelectrolyte and pl- refers to the pl of the weak anionic polyelectrolyte, with pl+ > pl-.

[0017] In some embodiments, the coating composition further comprises a volatile pH buffer, such as 2-amino-2-methyl-l-propanol.

[0018] In some embodiments, the cationic polyelectrolyte is chosen from polyethylene imine, poly(allylamine hydrochloride), poly(aniline), poly(2-vinylpyridine), poly(2- (dimethylamino)ethyl methacrylate), poly(L-lysine), chitosan, and mixtures thereof. In some embodiments, the anionic polyelectrolyte is chosen from polyacrylic acid, poly(methacrylic acid), poly(glutamic acid), hyaluronic acid, alginic acid, salts thereof, and mixtures thereof.

[0019] In some embodiments, the ceramic particles are chosen from particles of an oxide of metal or metalloid element, a nitride of metal or metalloid element, a boride of metal or metalloid element (preferably a boride of a metal element), a carbide of metal or metalloid element, and a mixture thereof, preferably particles of boron nitride, montmorillonite, alumina, silica, zirconia, silicon carbide, glass-ceramic, or mixtures thereof, preferably particles of boron nitride, montmorillonite, alumina, silica, zirconia, silicon carbide, glass-ceramic, or mixtures thereof.

[0020] In some embodiments, the weight ratio of the ceramic particles to the cationic and anionic polyelectrolytes is at least 1 / 1, preferably from 1 / 1 to 200 / 1, more preferably from 2 / 1 to 150 / 1, for instance from 4 / 1 to 100 / 1.

[0021] In some embodiments, the weight content of ceramic particles is from 50 to 95 wt%, preferably from 55 to 95 wt%, relative to the dry weight of the coating composition.

[0022] In some embodiments, the weight content of ceramic particles is from 30 to 95 wt%, preferably from 40 to 85 wt%, more preferably from 50 to 80 wt%, relative to the dry weight of the coating composition.

[0023] In some embodiments, the cationic and anionic polyelectrolytes together represent from 1 to 45 wt%, preferably from 1 to 20 wt%, more preferably from 1 to 10 wt%, or even more preferably from 1 to 5 wt%, of the total weight of the composition.

[0024] In some embodiments, the coating composition further comprises a water-soluble polyphenol comprising at least one polyhydroxylated aromatic ring structure, and optionally a water- soluble polyvalent transition metal salt.

[0025] The present invention also relates to a process for forming a coating comprising the following steps: a) applying a coating composition as defined herein on a substrate, to form a wet coating, b) drying the wet coating, so as to obtain said coating, wherein said coating preferably has a thickness from 0.02 pm to 1000 pm, more preferably from 2 to 600 pm, even more preferably from 5 to 500 pm. Another object of the present invention is a coating formed by a process as defined herein.

[0026] FIGURES

[0027] [Fig 1] photograph of a boron nitride-based composition of the invention, after 1 month. [Fig 2] photograph of a silica-based composition of the invention, after 1 month.

[0028] DETAILED DESCRIPTION

[0029] The composition of the invention is a coating composition. Such composition comprises a coacervate comprising a cationic polyelectrolyte (which may be called hereinafter "polycation") and an anionic polyelectrolyte (which may be called hereinafter "polyanion").

[0030] It is known that when an aqueous solution of an anionic polyelectrolyte (also called hereafter "polyanion") and an aqueous solution of a cationic polyelectrolyte (also called hereafter "polycation") are mixed together at a pH where the anionic polyelectrolyte has a negative net charge and the cationic polyelectrolyte has a positive net charge, the polyelectrolytes will immediately associate and form a solid complex (polyelectrolyte complex) that will separate from the aqueous phase. When the aqueous polymer solutions contain water-soluble mineral salts in a sufficient amount to at least partially screen the opposite charges of the polymers, the attraction between the polyanion and polycation will be reduced and formation of a solid complex be prevented. Upon mixing of such solutions, one will observe phase separation with, on the one hand, a concentrated polymer-rich phase, called "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 coacervate state can alternatively be obtained when the pH of the mixture is such that at least one of the anionic polyelectrolyte and the cationic polyelectrolyte has a zero net charge. In such case, there is thus no need to add salts to partially screen the charges.

[0031] The term "a cationic polyelectrolyte" encompasses one cationic polyelectrolyte but also mixtures of two or more cationic polyelectrolytes. The term "an anionic polyelectrolyte" encompasses one anionic polyelectrolyte, but also mixtures of two or more anionic polyelectrolytes.

[0032] The composition of the invention comprises advantageously similar amounts of a cationic polyelectrolyte and an anionic polyelectrolyte, "similar amounts" meaning here 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 on the polyanion is comprised between 0.5 and 2.0, preferably between 0.6 and 1.8, more preferably between 0.7 and 1.6 and still more preferably between 0.8 and 1.4, or even between 0.9 and 1.2.

[0033] The polyelectrolytes may be strong or weak polyelectrolytes. A strong polyelectrolyte is a polymer having a positive or negative net 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 from 1 to 14 and the zeta potential of a strong anionic polyelectrolyte is negative for any pH in the range from 1 to 14. The zeta potential can be measured using a zeta potential analyzer (e.g. "zetasizer" device) at a suitable concentration (generally greater than 0.01%, for example 1% by weight of polyelectrolyte relative to the volume of solution analyzed) and generally at 20°C.

[0034] On the contrary, a weak polyelectrolyte is a polymer having a positive or negative net charge which is dependent on the pH. Typically, the zeta potential of a weak polyelectrolyte measured at pH 1 and the one measured at pH 14 are different by at least 10%. Usually, a weak polyelectrolyte has a pl between 1 and 14. More particularly, a weak cationic polyelectrolyte usually has a pl higher than 7, for instance between 7.5 and 14, and a weak anionic polyelectrolyte usually has a pl lower than 7, for instance between 1 and 6.5. In the present application, pl's are determined in water, at a temperature of 25°C and at 0.01 M of NaCI.

[0035] 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 (-SOs- groups). Poly(acrylic acid) is an example of a weak anionic polyelectrolyte and non-quaternized polyamines are examples of weak cationic polyelectrolytes. In the present invention, an anionic polyelectrolyte is a polymer with a negative net charge at pH 7 and a cationic polyelectrolyte is a polymer with a positive net charge at pH 7. This does not mean that an anionic polyelectrolyte comprises only negative charges and is free of positive charges. By analogy, cationic polyelectrolytes may comprise both cationic and anionic charges as long as, at pH 7, the overall net charge is positive.

[0036] Consequently, the definition of anionic polyelectrolytes encompasses zwitterionic polyelectrolytes having an isoelectric point (pl) < 7, preferably < 6, and the definition of cationic polyelectrolytes encompasses zwitterionic polyelectrolytes having an isoelectric point (pl) > 7, preferably > 8. The most commonly known zwitterionic polyelectrolytes are proteins or peptides comprising both pending carboxyl groups (-COOH) and pending amino groups (- NH2).

[0037] In a preferred embodiment, the anionic polyelectrolyte comprises only negative charges and is free of positive charges, and the cationic polyelectrolyte comprises only positive charges and is free of negative charges.

[0038] The anionic polyelectrolyte and the cationic polyelectrolyte may be linear or branched polymers.

[0039] 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 pending groups.

[0040] The anionic groups of the anionic polyelectrolyte are for example selected from the group consisting of carboxylate, sulphonate, phosphonate, boronate, sulphate, borate, and phosphate groups, located in the main chain of the polymer or on pending groups thereof.

[0041] The cationic polyelectrolyte is preferably selected from the group consisting of:

[0042] - poly(diallyldimethylammonium chloride) (PDADMAC),

[0043] - poly[ (2-hydroxypropyl)dimethylammonium chloride],

[0044] - polyamidoamine-epichlorhydrine (PAAE),

[0045] - polyethylene imine,

[0046] - poly(acrylamide-co-diallyldimethylammonium chloride),

[0047] - poly(acrylic acid-co-diallyldimethylammonium chloride), - copolymer of hydroxyethylcellulose and poly(diallyldimethylammonium chloride) (Polyquaternium-4),

[0048] - copolymer of acrylamide and dimethylaminoethylmethacrylate quaternized with dimethyl sulphate (Polyquaternium-5, CAS 26006-22-4),

[0049] - copolymer of dimethylaminomethyl methacrylate and alkyl methacrylate,

[0050] - copolymer of methyl and stearyl dimethylaminoethyl ester of methacrylic acid,

[0051] - homopolymer of N,N-(dimethylamino)ethyl ester of methacrylic acid quaternized with bromomethane or quaternized hydroxyethyl cellulose,

[0052] - chitosan,

[0053] - poly(quaternized N,N-(dimethylamino)ethyle methacrylate),

[0054] - guar hydroxypropyltrimonium chloride,

[0055] - poly(2-(dimethylamino)ethyl methacrylate,

[0056] - poly(N,N-dimethyl-3,5-dimethylene piperidinium chloride),

[0057] - poly(vinylbenzyltrimethylammonium chloride),

[0058] - poly[3-(methacryloylamino)propyl-trimethylammonium chloride],

[0059] - poly([2-(methacryloloxy)ethyl]-trimethylammonium chloride),

[0060] - polyvinylamine (PVA),

[0061] - poly(N,N-dimethyl-3,5-dimethylene piperidinium chloride) (PDDPC),

[0062] - poly(vinylbenzyltrimethylammonium chloride) (PVBTAC),

[0063] - poly(allylamine hydrochloride) (PAH),

[0064] - poly[3-(methacryloylamino)propyltrimethylammonium chloride] (PMAPTAC),

[0065] - cationic dextran,

[0066] - poly(aniline),

[0067] - poly(2-vinylpyridine),

[0068] - poly(L-lysine),

[0069] - gelatin type A, and

[0070] - mixtures thereof.

[0071] More preferably, the cationic polyelectrolyte is selected from polyethylene imine, poly(allylamine hydrochloride), poly(aniline), poly(2-vinylpyridine), poly(2- (dimethylamino)ethyl methacrylate), poly(L-lysine), chitosan, and mixtures thereof. The anionic polyelectrolyte preferably is selected from the group consisting of poly(acrylic acid), poly(acrylic acid-co-acrylamido), 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 (e.g. sodium salts), gelatin type B, and mixtures thereof.

[0072] More preferably, the anionic polyelectrolyte is selected from polyacrylic acid, poly(methacrylic acid), poly(glutamic acid), hyaluronic acid, alginic acid, salts thereof (e.g. sodium salts), and mixtures thereof.

[0073] The weight average molecular weight (determined by light scattering) of each of the anionic and cationic polyelectrolytes is typically comprised between 5000 and 2 000 000 Da, preferably between 10 000 and 1 500 000 Da, more preferably between 20 000 and 1000000 Da, even more preferably between 50 000 and 700 000 Da, for instance between 100 000 and 500000 Da. The anionic polyelectrolyte and cationic polyelectrolyte preferably have similar molecular weights.

[0074] The ratio of the weight average molecular weight of the anionic polyelectrolyte to the weight average molecular weight of the cationic polyelectrolyte is preferably comprised between 0.4 and 1.6, more preferably between 0.7 and 1.3 and still more preferably between 0.8 and 1.2.

[0075] In a preferred embodiment, at least one of the anionic polyelectrolyte and the cationic polyelectrolyte is a weak polyelectrolyte.

[0076] In one embodiment, the cationic polyelectrolyte is a weak polyelectrolyte (preferably branched). In such embodiment, the anionic polyelectrolyte may be a strong or weak polyelectrolyte (for instance, a strong polyelectrolyte).

[0077] In such embodiment, the pH of the composition of the invention is advantageously higherthan the pl of the weak cationic polyelectrolyte. The pl of a weak cationic polyelectrolyte is usually higher than 7, for instance between 7.5 and 14.

[0078] In another one embodiment, the anionic polyelectrolyte is a weak polyelectrolyte. In such embodiment, the cationic polyelectrolyte may be a strong or weak polyelectrolyte (for instance, a strong polyelectrolyte). In such embodiment, the pH of the composition of the invention is advantageously lower than the pl of the weak anionic polyelectrolyte. The pl of a weak anionic polyelectrolyte is usually lower than 7, for instance between 1 and 6.5.

[0079] In a more preferred embodiment, the cationic polyelectrolyte and the anionic polyelectrolyte are both weak polyelectrolytes.

[0080] In such embodiment, the pH of the composition is advantageously such that:

[0081] - pH > pl+, or

[0082] - pH < pL, wherein pl+ refers to the pl of the weak cationic polyelectrolyte and pl- refers to the pl of the weak anionic polyelectrolyte, with pl+ > pl-.

[0083] The cationic polyelectrolytes and anionic polyelectrolytes together preferably represent from 1 to 45 % wt%, preferably from 1 to 20 wt%, more preferably from 1 to 10 wt%, or even more preferably from 1 to 5 wt%, of the total weight of the composition. In some embodiments, the cationic polyelectrolytes and anionic polyelectrolytes together preferably represent from 2 to 40 %, from 3 to 40 %, from 4 to 40 %, from 5 to 35 %, or from 8 to 30 % of the total weight of the composition.

[0084] For very high molecular weight molecular weights the lower limit may be about 1 % by weight of the composition.

[0085] The composition may further comprise a water-soluble mineral salt. Such water-soluble mineral salt is particularly useful to control the coacervate state of a strong cationic polyelectrolyte and strong anionic polyelectrolyte.

[0086] As used herein, "water-soluble" means having a solubility in distilled water at 20°C of more than 100 g / L, preferably more than 200 g / L, even more preferably more than 300 g / L.

[0087] Such water-soluble mineral salt is preferably selected from the group consisting of alkaline metal or alkaline earth metal halogenides. Preferred alkaline metal are lithium, sodium and potassium. Preferred alkaline earth metal are calcium and magnesium. Preferred halogenides are chlorides and bromides. The function of the water-soluble mineral salt is to screen the opposite charges and to thereby reduce the ionic interaction between the polyelectrolytes, to prevent the formation of a solid insoluble polyelectrolyte complex and to allow the formation of a coacervate (a viscous polyelectrolyte-rich solution). The water-soluble mineral salt preferably is a monovalent metal salt, i.e. an alkaline metal halogenide. Alkaline earth metal salts, when present, preferably do not represent more than 20 mol % of the total mineral salts.

[0088] The suitable amount of water-soluble mineral salt (when present) depends on the total amount of polyelectrolyte charges, i.e. for a given molecular weight of the polyelectrolytes, it is roughly proportional to the amount of polyelectrolytes in the composition.

[0089] When present, the amount of water-soluble mineral salt is typically comprised between 40% and 95 % by weight, preferably between 55 % and 75 % by weight, with respect to the total dry weight of cationic polyelectrolyte, anionic polyelectrolyte and water-soluble mineral salt. 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 comprised between 0.10 and 4.0, more between 0.50 and 2.50, and still more preferably between 0.80 and 1.50.

[0090] The above amount and ratio may also depend to a certain extent on the molecular weight of the polyelectrolyte. The higher the weight average molecular weight of the polyelectrolytes, the more water-soluble mineral salt will be necessary to achieve a suitably low viscosity of the aqueous composition.

[0091] Alternatively, or in addition, the composition may further comprise a pH buffer, which is advantageously volatile. Such pH buffer is particularly useful to control the coacervate state of a cationic polyelectrolyte and an anionic polyelectrolyte, wherein at least one of the cationic polyelectrolyte and the anionic polyelectrolyte is a weak polyelectrolyte.

[0092] As used herein, a "volatile" pH buffer refers to 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. pH buffers (including volatile pH buffers) are well-known to the skilled artisan and can be selected according to their pKa('s). The pKa('s) (measured at 25°C in water) of the pH buffer used in the composition of the invention is(are) advantageously between 1 and 14.

[0093] The pH buffer may be in particular be ammonia, an ammonium salt, an amine, a carboxylic acid, an aminoacid, aminoalcool, or a combination thereof. 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.

[0094] A preferred volatile pH buffer is 2-amino-2-methyl-l-propanol.

[0095] The weight content of the pH buffer in the composition is advantageously from 0.1 to 5 wt%, preferably from 0.2 to 4 wt%, more preferably from 0.5 to 2.5 wt%, relative to the total weight of the composition.

[0096] The composition may further comprise a water-soluble polyphenol comprising at least one polyhydroxylated aromatic ring structure, optionally in combination with a water-soluble polyvalent transition metal salt. Such polyphenol can have beneficial effect on the physicochemical and / or mechanical properties of the final materials.

[0097] The amount of polyphenol, or polyphenols, should be comprised 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, with respect to the aqueous composition.

[0098] When expressed with respect to the dry weight of the composition, the total amount of polyphenol(s) is comprised 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.

[0099] The term "polyphenol" refers to an organic compound comprising at least one polyhydroxylated aromatic ring structure, "polyhydroxylated" meaning comprising two hydroxyls on the same aromatic ring.

[0100] In a preferred embodiment, at least part of the polyphenols used in the composition comprise more than one polyhydroxylated aromatic ring structure, i.e. at least two, preferably at least three, and more preferably at least four polyhydroxylated aromatic ring structures.

[0101] The polyhydroxylated aromatic ring structures are preferably selected from the groups consisting of catechol groups, pyrogallol groups, tetrahydroxylated aromatic ring structures and pentahydroxylated aromatic ring structures. In a particularly interesting embodiment, the polyphenol is tannic acid (CAS n°1401-55-4).

[0102] Other examples of polyphenols include synthetic organic polymers comprising comonomers with polyhydroxylated ring structures (see for example the work of Cheng et al., in Nature Communications, 13, article number 1892 (2022)).

[0103] In another preferred embodiment of the present invention, the polyphenol is a synthetic copolymer comprising comonomers with polyhydroxylated ring structures, preferably a copolymer of styrene and of a comonomer selected from di hydroxystyrene, trihydroxystyrene, tetrahydroxystyrene and penta hydroxystyrene.

[0104] The mechanical performances of the final material may be still more improved by associating the polyphenol-reinforced polyelectrolyte coacervate with polyvalent transition metal ions. In another preferred embodiment, the composition therefore further comprises a water-soluble polyvalent transition metal salt or a mixture of polyvalent transition metal salts, preferably in a total amount comprised between 0.001 and 0,1 %, more preferably between 0.002% and 0.05%, even more preferably between 0.005 and 0.05%, with respect to the total weight of the composition.

[0105] When expressed with respect to the water-soluble polyphenol, the weight ratio of the transition metal salt to the dry weight of the polyphenol is typically comprised between 0.1 and 0.2, preferably between 0.12 and 0.18.

[0106] The transition metals are preferably selected from the group consisting of Fe, Zn, Co, Cu, and V. Halogenides, in particular chlorides and bromides, are preferred anions of the reinforcing transition metal salts used in the present invention.

[0107] The composition of the invention may further comprise an organic polymer. Such organic polymer may be useful to provide flexibility to a coating formed from the composition.

[0108] 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. More particularly, such organic polymers may be chosen from polymers based on one or more of the following monomers: 2-ethyl hexyl acrylate, butyl acrylate, ethyl acrylate, methyl acrylate, acrylic acid, hydroxyethyl methacrylate, styrene, cyclohexyl methacrylate, butyl methacrylate, isobornyl methacrylate, isobutyl methacrylate, ethyl methacrylate, isobornyl acrylate, methyl methacrylate, vinyl acetate, butadiene. The weight content of said organic polymer is advantageously 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.

[0109] The composition may further comprise a hydrophobic agent, typically added as an emulsion. The hydrophobic agent may be a wax, for example paraffin wax, polyethylene wax, polypropylene wax, silicone wax and poly(tetrafluoroethylene) wax. Hydrophobic resins, for example hydrophobic silicone resins such as Variphob® AC 3030, may also efficiently be used as hydrophobic agents. The hydrophobic agent is typically used in amounts up to 15 % by weight, preferably comprised between 1 % and 15 % by weight, more preferably between 2 and 10 % by weight, and still more preferably between 3 and 5 % by weight, with respect to the total dry weight of the composition.

[0110] 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 different from the ones mentioned above. Those additives are selected for examples from the group consisting of cosolvents such as ethanol and polyethyleneglycol, dyes, pigments, biocides, buffer agents, surfactants, dispersants and thickening agents. Another additive is for instance an antifoaming agent. The composition may further comprise one or more plasticizers, preferably in an amount comprised between 0.1 and 10 % by weight, with respect to the total dry weight of the composition.

[0111] The composition of the invention further comprises ceramic particles. As used herein, "ceramic" refers to a material that is not metallic ("metallic" meaning "made of metal(s) or metalloid(s) only") and not organic ("organic" meaning "essentially consists of C-H bonds, and optionally further comprising heteroatoms such as O, N, and / or S atoms). In particular, it refers to one or several oxide, nitride, boride, or carbide of a metal or metalloid elements. Examples of such metal or metalloid elements include, but are not limited to, boron (B), aluminum (Al), zirconium (Zr), titanium (Ti), magnesium (Mg), silicon (Si) or combination thereof. Examples of ceramic particles includes, but are not limited to, particles of boron nitride, montmorillonite, alumina, silica, titania, zirconia, silicon carbide, glass-ceramic, and mixtures thereof.

[0112] Preferably, the ceramic particles are selected from particles of boron nitride, alumina, zirconia, silica, glass-ceramic, silicon carbide, and mixtures thereof.

[0113] More preferably, the ceramic particles are selected from particles of boron nitride, alumina, zirconia, glass-ceramic, silicon carbide, and mixtures thereof.

[0114] Preferably, boron nitride is hexagonal boron nitride.

[0115] "Glass-ceramic" are well known to the skilled artisan. In some embodiments, glass-ceramic has a composition comprising the following components:

[0116] - SiO2 : 60-70 mol%, preferably 61-64 mol%,

[0117] - BaO : 25-35 mol%, preferably 30-33 mol%,

[0118] - AI2O3 : 0-15 mol%, preferably 0-10 mol%, and

[0119] - ZrO2 : 0-5 mol%.

[0120] The d50 of the ceramic particles may be 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 instance from 1 pm to 50 pm, from 1 pm to 30 pm, or from 2 pm to 20 pm).

[0121] The d50 refers to 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.

[0122] The d50 can be determined by laser diffraction.

[0123] The weight ratio of the ceramic particles to the cationic and anionic polyelectrolytes is at least 1 / 2, preferably at least 1 / 1 (more preferably at least 2 / 1).

[0124] Preferably, the weight ratio of the ceramic particles to the cationic and anionic polyelectrolytes is 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. The weight content of ceramic particles is advantageously from 30 to 95 wt%, preferably from 50 to 95 wt%, more preferably from 55 to 95 wt%, even more preferably from 60 to 95 wt%, relative to the dry weight of the coating composition.

[0125] In some embodiments, the weight content of ceramic particles is from 40 to 85 wt%, for instance from 50 to 80 wt%, relative to the dry weight of the coating composition.

[0126] Advantageously, the composition has a water content of from 15 to 80 % by weight, preferably of from 20 to 75 % by weight, more preferably of from 25 to 70 % by weight.

[0127] The composition of the invention may be in the form of a liquid or a past, depending on the intended use.

[0128] The coating composition of the invention is particularly suitable for use as a paint composition.

[0129] The present invention also relates to a process for forming a coating comprising the steps of:

[0130] - applying a composition as defined herein onto a substrate, so as to form a wet coating, and

[0131] - drying the wet coating, so as to form said coating.

[0132] Applying the composition can be carried out by any suitable method, in particular by using a roller, a brush or even by spraying. Applying the composition can be carried out in several layers.

[0133] The substrate may be flexible or rigid. More particularly, the substrate may for instance be a plastic film (e.g. polyolefin-based films, such as polyethylene- and / or polypropylene- based films), a textile substrate, a paper substrate, a metal substrate, a ceramic substrate, or a foam (e.g. inorganic or organic foam) substrate.

[0134] Typically, the substrate is water-insoluble. As used herein, "water-insoluble" means a solubility lower than 10% (preferably less than 5%, or even less than 2%), as measured in distilled water at 25°C.

[0135] The wet coating formed on the substrate is then dried. The drying may be an air-drying, with no heating. Alternatively, the wet coating may be dried by heating at a suitable temperature, for instance a temperature between 50°C and 180°C, more particularly between 80°C and 120°C. The duration needed for the drying may be adapted depending on the temperature of the drying. When no heating is applied, the drying may take several hours, for instance 4 hours to 24 hours. When heating is applied, the drying may take a few minutes, for instance 1 min to 20 min.

[0136] The present invention also relates to a coating formed from a composition as defined herein. More particularly, the present invention relates to a coating obtained by a process as defined above.

[0137] The coating of the invention typically comprises a complex of a cationic polyelectrolyte and an anionic polyelectrolyte, and ceramic particles (and optionally further ingredient(s) as described above).

[0138] It is understood that the ratios described above for the composition (e.g. the weight ratio of ceramic particles to cationic and anionic polyelectrolytes) applies to the coating (i.e. dry coating).

[0139] The weight content of ceramic particles in the coating (i.e. dry coating) is from 30 to 95 wt%, preferably from 40 to 90 wt%, more preferably from 50 to 85 wt%, relative to the weight of the coating.

[0140] The coating may have a thickness from 0.02 pm to 1000 pm, preferably from 2 to 600 pm, more preferably from 5 to 500 pm.

[0141] The thickness can be measured by optical measurements using for instance microscopy (e.g. scanning-electron microscopy "SEM").

[0142] The coating of the invention can be analyzed by the following techniques:

[0143] - Thermogravimetric analysis (TGA) on a coating sample (typically 10 mg) to determine the organic and inorganic content of the dry sample.

[0144] - Due to the reversibility of the polyelectrolytes complex, it is possible to use of a base, an acid, or a highly concentrated mineral salt solution on the coating (typically, from 1 to 10 cm2of coating) to recover a liquid solution comprising the polyelectrolytes. Charge measurements as a function of pH can be performed. Pyrolysis GC-MS (Gas-Chromatography Mass Spectrometry) to identify the nature of the polyelectrolytes.

[0145] - For the ceramic particles of the coating: Scanning Electron Microscopy (SEM) can be used for the morphology; Energy-Dispersive X-ray spectroscopy (EDX), micro-probe, or Inductively Coupled Plasma (ICP) can be used for the chemical composition; X-ray diffraction (XRD) can be used for the crystal structure (for SEM, microprobe, EDX : analysis scale is typically 10 pm; for ICP or XRD: few grams (e.g. 1-5 g) of samples are usually used for such techniques).

[0146] In the present application, unless otherwise mentioned, a weight content of a component (or a weight ratio of components) is based on the weight of the component itself, and therefore, to its weight in dry extract, when used for instance diluted in a dispersion or solution.

[0147] The present invention is illustrated by the following non-limiting examples.

[0148] EXAMPLES

[0149] 1 - Composition comprising strong polyelectrolytes-based coacervate and boron nitride particles a. Preparation of the polycation salt solution:

[0150] A concentrated aqueous tannic acid solution with a concentration of 0.14 g / mL was prepared. Using a pipette, 45 pL of the concentrated tannic acid solution was added to 15.9 mL of water, acidified by adding HCI (1 M) to pH = 1, then 5.45 g of KBr was added. Then 3.0 g of EVA 462 (PDADMAC) was added to the resulting aqueous composition and stirred until the polyelectrolyte was completely dissolved. After dissolution of the polyelectrolyte, 0.001 g FeCI3 was added with stirring. b. Preparation of the polyanion salt solution:

[0151] To 16.4 ml of water previously acidified to pH 1 with HCI, 5.45 g of KBr was added. To the acidic saline solution obtained, 2.65 g of Versal TL 130 having a polystyrene sulfonate) content of about 30%, was added. c. Preparation of the coacervate:

[0152] After complete dissolution of the polyelectrolytes, the polyanion solution (PSS) was poured into the polycation solution (PDADMAC) under strong agitation. The mixture was left to stand for a few minutes until phase separation occurs.

[0153] The upper phase (supernatant) was removed.

[0154] The lower phase (coacervate) was green and changed color (red) when neutralized by adding 0.3 mL AMP 95 (2-amino-2-methyl-l-propanol) to pH > 7. The composition of the resulting coacervate is detailed in Table 1.

[0155] [Tableau 1] d. Addition of boron nitride particles

[0156] To a 10g of coacervate sample prepared as described above, were added antifoam, antisettling agent and dispersant under stirring. Once well mixed, hexagonal Boron Nitride was added under constant mixing. Afterwards, all components are mixed under high shear stirring at 4000 rpm for 15 minutes.

[0157] The coating composition was composed of around 58wt% polyelectrolytes coacervate and 33% of Boron nitride particles (Table 2).

[0158] The coating composition was applied on a surface of a polyethylene substrate and water was applied on top. Curing took place as salt left the coacervate.

[0159] [Tableau 2] 2 - Composition comprising weak polyelectrolytes-based coacervate and boron nitride particles

[0160] Polyethyleneimine (25 wt% solids in deionized water) and AMP95 were mixed in deionized water to reach pH 10, and then polyacrylic acid (12% solids in deionized water) was added. Then, the dispersant and the antifoam were added under 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).

[0161] A film was formed by casting the composition on a polyethylene substrate, and then drying at 100°C for 2 min. The dried films had a thickness of ca. 200 pm.

[0162] [Tableau 3]

[0163] 3 - Composition comprising weak polyelectrolytes-based coacervate and silica particles

[0164] A composition was prepared by mixing the ingredients listed in the following table 4, based on a similar protocol as described in Example 2.

[0165] [Tableau 4]

[0166] 4 - Composition comprising weak polyelectrolytes-based coacervate, boron nitride and alumina particles

[0167] A composition was prepared by mixing the ingredients listed in the following table 5, based on a similar protocol as described in Example 2.

[0168] [Tableau 5]

[0169] 5 - Composition comprising weak polyelectrolytes-based coacervate, boron nitride and montmorillonite particles A composition was prepared by mixing the ingredients listed in the following table 6, based on a similar protocol as described in Example 2. [Tableau 6]

[0170] The compositions of Tables 2, 3, 4, 5, and 6 were prepared with high contents of ceramic particles, and no settling was observed after one month, as shown in Figure 1 (composition of Table 3) and Figure 2 (composition of Table 4).

Claims

CLAIMS1. A 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. The coating composition according to claim 1, wherein the cationic polyelectrolyte is a weak polyelectrolyte.

3. The coating composition according to claim 1 or 2, wherein the pH of the coating composition is higher than the pl of the weak cationic polyelectrolyte.

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

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

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

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

8. The coating composition of any one of claims 1 to 7, wherein the cationic polyelectrolyte is chosen from polyethylene imine, poly(allylamine hydrochloride), poly(aniline), poly(2- vinylpyridine), poly(2-(dimethylamino)ethyl methacrylate), poly(L-lysine), chitosan, and mixtures thereof.

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

10. The coating composition of any one of claims 1 to 9, wherein the ceramic particles are chosen from particles of an oxide of metal or metalloid element, a nitride of metal or metalloid element, a boride of metal or metalloid element, a carbide of metal or metalloid element, and a mixture thereof, preferably particles of boron nitride, montmorillonite, alumina, silica, zirconia, silicon carbide, glass-ceramic, or mixtures thereof.

11. The coating composition of any one of claims 1 to 10, wherein the weight ratio of the ceramic particles to the cationic and anionic polyelectrolytes is at least 1 / 1, preferably from 1 / 1 to 200 / 1, more preferably from 2 / 1 to 150 / 1, for instance from 4 / 1 to 100 / 1.

12. The coating composition of any one of claims 1 to 11, wherein the weight content of ceramic particles is from 50 to 95 wt%, preferably from 55 to 95 wt%, relative to the dry weight of the coating composition.

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

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

15. A process for forming a coating comprising the following steps: a) applying a coating composition as defined in any one of claims 1 to 14 on a substrate, to form a wet coating, b) drying the wet coating, so as to obtain said coating, wherein said coating preferably has a thickness from 0.02 pm to 1000 pm, more preferably from 2 to 600 pm, even more preferably from 5 to 500 pm.

16. A coating formed by a process as defined in claim 15.

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