Method for improving Anti-blocking properties in a coating composition using a phosphate ester surfactant compound

Abstract

The invention relates to a method for imparting or improving block resistance, preferably early high-temperature blocking resistance of a waterborne coating composition comprising adding an effective amount of at least one anti-blocking compound comprising a phosphate ester surfactant in a corresponding waterborne monomer emulsion intended to be polymerized into a latex polymer used to prepare said coating composition, wherein the phosphate ester surfactant comprises an acid or a salt of alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units.

Description

METHOD FOR IMPROVING ANTI BLOCKING PROPERTIES IN A COATING COMPOSITION USING A PHOSPHATE ESTER SURFACTANT COMPOUND

[0001] This application claims priority filed on 2024-04-26 in UNITED STATES with Nr 63 / 639228, the whole content of this application being incorporated herein by reference for all purposes.FIELD OF THE INVENTION

[0002] This invention relates to a method and a use of phosphate ester surfactants for improving block resistance, specifically early high-temperature blocking resistance, of a coating composition, such as a paint or an adhesive for example. The invention also relates to such a coating composition showing improved block resistance compared to coating compositions of the prior art.PRIOR ART

[0003] In the field of composition coatings, such as paints for example, improved block resistance is attributed to increased bulk modulus or surface hardness of coating film, in particular paint film.

[0004] One of the challenges for low-VOC coatings is simultaneously attaining smooth film formation and acceptable block resistance and film hardness. Smooth film formation is obtained at the minimum film forming temperature (acronym MFFT), which is the minimum temperature at which a waterborne emulsion (latex) coalesces when laid on a substrate as a thin film.

[0005] Several approaches exist to address this challenge. First is a latex with core-shell morphology, which is a common approach. Another approach is the blending of a high MFFT latex with a low MFFT latex. Crosslinking of the paint film or latex particle to increase the film hardness has also been proposed, as well as anti-block additives that can quickly move to the air / paint film interface and lower the surface tension of the paint film. Alternatively, combinations of the above techniques may be employed to improve anti-blocking property of paints.

[0006] For example, document WO2022 / 150168 shows that neutralized Cs-Ci2 nonethoxylated phosphate esters are used as paint additives, that is, as an additive added directly into the final paint, in order to deliver early hot block performances in the paint. As a clarification, non-ethoxylated phosphate esters are phosphate esters that do not have ethyleneoxide (i.e. ethylene glycol) units, having the formula -O-CH2-CH2- and making the link between the alkyl group and the phosphate group in the formula.

[0007] Moreover, fluorocarbon surfactants (acronym FCS), such as Capstone FS-63, are currently being used in latex synthesis to improve early (1 day dry) oven / hot block resistance (also called high temperature block resistance) of architectural water based coatings, which is a desirable property for semigloss and gloss coatings.

[0008] While the manufacturing of fluorocarbon surfactants do not directly involve the use of perfluorooctanoic acid (acronym PFOA), PFOA is an unintended by-product that may be found in trace amounts in some products. As there is a much scrutiny regarding elimination of PFOA’s, especially due to do potential negative impact on the environment and human health, it is desirable to replace FCS in the coating formulations while delivering similarly good early hot block performance without the health issues associated with FCS.SUMMARY OF THE INVENTION

[0009] The present invention aims to overcome the aforementioned drawback. The invention especially aims to improve block resistance, also called “anti-blocking”, in various coating compositions, such as paints, adhesives, inks or varnishes for example, without using fluorocarbon surfactants.

[0010] To this end, the invention proposes to use a phosphate ester surfactant and to add it to the waterborne monomer emulsion or to the waterborne latex polymer from which the coating composition is prepared, to impart of improve the block resistance of said coating composition.

[0011] The blocking resistance is preferably early blocking resistance at high temperature (generally called “early high-temperature blocking resistance” or “early hot blocking resistance” or “early oven blocking resistance”). The coating composition may be, for example, a paint, a varnish, an ink, or an adhesive.

[0012] The early high-temperature blocking resistance is defined and measured according to the standard ASTM D4946-89 at 50°C.

[0013] For clarification, a coating composition such as a paint is prepared from a latex polymer, or just “latex” by adding pigments, liquid agents such as water, solvents, glycols, or coalescing agents, and additives such as defoamers, surfactants, dispersants, or additives having very specific properties such as those which improve open time, freeze thaw or resistance to corrosion. The latex itself is prepared from the polymerization of a corresponding monomer emulsion.

[0014] Hence, according to a general concept of the invention, the phosphate ester surfactant is not added as an additive in the coating composition, but in the corresponding waterborne composition from which the coating composition is prepared.

[0015] Now, according to a more specific concept of the invention, the phosphate ester surfactant may be added either in the monomer emulsion, that is, before polymerization of the monomers or in the latex itself, that is, after polymerization of the monomers. The latex is then further processed to obtain the final coating composition, for example the paint.

[0016] Latexes are products well known to those skilled in the art. They consist of aqueous dispersions of water-insoluble polymers. These fluid systems contain, as dispersed phase, particles of polymers consisting of several entangled polymer chains in an aqueous dispersion medium. The diameter of the polymer particles within the dispersion can range between 10 nm and 500 nm. In the present text, the terms “waterbased polymer emulsion”, water-based polymer dispersion” and “latex” refer to the same chemical object and are used indifferently.

[0017] On this basis, a first object of the invention is a method for imparting or improving block resistance, preferably early high-temperature blocking resistance, of a waterborne coating composition comprising adding an effective amount of at least one anti-blocking compound comprising a phosphate ester surfactant in a corresponding waterborne monomer emulsion intended to be polymerized into a latex polymer used to prepare said coating composition, wherein the phosphate ester surfactant comprises an acid or a salt of alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units.

[0018] In other terms, the invention proposes the use of an effective amount of at least one anti-blocking additive comprising a phosphate ester surfactant by adding it in a waterborne monomer emulsion intended to be polymerized into a latex polymer used to prepare a coating composition, to impart or improve block resistance, preferably early high-temperature blocking resistance, of said coating composition obtained therefrom, wherein the phosphate ester surfactant comprises an acid or a salt of alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units.

[0019] According to the first object of the invention, the phosphate ester surfactant is thus added in the monomer emulsion before polymerization to a latex.

[0020] A second object of the invention is a method for imparting or improving block resistance, preferably early high-temperature blocking resistance, of a waterborne coatingcomposition comprising adding an effective amount of at least one anti-blocking compound comprising a phosphate ester surfactant in a corresponding waterborne latex polymer used to prepare said coating composition, wherein the phosphate ester surfactant comprises an acid or a salt of alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units.

[0021] In other terms, the invention proposes the use of an effective amount of at least one anti-blocking additive comprising a phosphate ester surfactant by adding it in a waterborne latex polymer used to prepare a coating composition, to impart or improve block resistance, preferably early high-temperature blocking resistance, of said coating composition obtained therefrom, wherein the phosphate ester surfactant comprises an acid or a salt of alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units.

[0022] According to the second object of the invention, the phosphate ester surfactant is thus added in the latex, after polymerization of the monomer emulsion, but before preparation of the final coating composition obtained therefrom.

[0023] The invention is thus based on the use of a 0-3 EO phosphate ester surfactant in a waterborne (water-based) emulsion before or after polymerization, to improve antiblocking in the corresponding coating composition obtained therefrom.

[0024] The term “0-3” means between 0 and 3 ethylene oxide units, and may be any number, integer or decimal, between 0 and 3, including the lower and upper limits 0 and 3 themselves.

[0025] The number of EO is determined by Mass Spectrometry, and the weighted average of the molecules with different EO units in the product is calculated and used as the final EO unit number for the product. The number of EO thus may be decimal.

[0026] The term “EO” means ethylene oxide or oxyethylene, and refers to the number of ethoxylation (derived from ethylene glycol) of the surfactant, having the formula -O- CH2-CH2- and making the link between the alkyl group and the phosphate group of the surfactant.

[0027] In the following of the text, the terms “ethylene oxide”, “ethylene oxide unit(s)”,“ethylene glycol”, “ethylene glycol unit(s)”, “ethoxylation(s)”, and “EO” are used indifferently and all refer to the ethylene oxide groups having the formula -O-CH2-CH2-.

[0028] In the following of the text, the phosphate ester surfactant may be referred to as “surfactant” or “phosphate ester surfactant” to simplify the text.

[0029] According to other optional features of the method of the invention: the phosphate ester surfactant comprises between 0 and 2 ethylene oxide units;the alkyl group of the phosphate ester surfactant is a C4-C15 carbon chain, preferably a Cs-Cn carbon chain, optionally branched and / or substituted; the phosphate ester surfactant is a potassium salt, a sodium salt, an ammonium salt, or an organic amine salt; the phosphate ester surfactant comprises a Cs-Cn carbon chain, between 0 and 2 ethylene oxide units, and a potassium salt; the phosphate ester surfactant is a non-reactive phosphate ester surfactant. The term “non-reactive surfactant” means a surfactant that does not react with monomers or polymers during polymerization of the monomers into a latex, contrary to the reactive or polymerizable surfactants, and thus which does not contain a reactive group on the hydrophobic segment that is capable of covalently bonding to the latex surface; the effective amount of anti-blocking compound is greater or equal to 0.010% by weight, preferably greater or equal to 0.05% by weight, based on the total amount of the coating composition; the effective amount of anti-blocking compound is lower or equal to 1.0% by weight, preferably lower or equal to 0.5% by weight, based on the total amount of the coating composition; the anti-blocking additive is used in an amount between 0.5 BOTM% and 3 BOTM% in the latex polymer. The term “BOTM” is classic in the technical field of polymer chemistry and means “Based On Total Monomers”; the method further comprises the addition of at least one sulfate, sulfonate, and / or phosphate alkyl surfactant, ethoxylated or non ethoxylated; the anti -blocking compound comprises:• at least one phosphate ester surfactant comprising a C4-C20 carbon chain, preferably a Cs-Cn carbon chain, between 0 and 3 ethylene oxide units, preferably between 0 and 2 ethylene oxide units, and a potassium salt, a sodium salt, an ammonium salt, or an organic amine salt; and• at least one olefin sulfate, sulfonate, and / or phosphate alkyl surfactant, preferably a C10-C20 olefin sulfate, sulfonate, and / or phosphate alkyl surfactant. the anti -blocking compound comprises:• at least one phosphate ester surfactant comprising a C10-C12 carbon chain, between 0 and 2 ethylene oxide units, and a potassium salt; and• at least one Cie-Cis olefin sulfonate.the anti -blocking compound comprises:• at least one phosphate ester surfactant comprising a Cs-Cio carbon chain, between 0 and 1 ethylene oxide units, and a potassium salt; and• at least one Cie-Cis olefin sulfonate.

[0030] Another object of the invention is a coating composition presenting block resistance, preferably early high-temperature blocking resistance properties, comprising:- at least one latex polymer,- optionally, at least one pigment,- water,- an anti-blocking compound comprising a phosphate ester surfactant, wherein the phosphate ester surfactant comprises an acid or a salt of an alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units, wherein the latex polymer is prepared from a waterborne monomer emulsion containing said anti-blocking compound and intended to be polymerized into a latex polymer used to prepare said coating composition.

[0031] Another object of the invention is a coating composition presenting block resistance, preferably early high-temperature blocking resistance properties, comprising:- at least one latex polymer,- optionally, at least one pigment,- water,- an anti-blocking compound comprising a phosphate ester surfactant, wherein the phosphate ester surfactant comprises an acid or a salt of an alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units, wherein the latex polymer is prepared from a waterborne latex polymer containing said anti-blocking compound and used to prepare said coating composition.

[0032] According to other optional features of the coating composition of the invention: the coating composition presents a block resistance, preferably an early high- temperature blocking resistance improved by at least 2 units compared to the same coating composition lacking the anti-blocking additive; the coating composition presents a block resistance, preferably an early high- temperature blocking resistance between 5 and 10, preferably between 6 and 9; the coating composition is prepared from an (meth)acrylic or a styrene- (meth)acrylic latex polymer;the coating composition comprises 30% to 55% by weight of acrylic latex containing 0.5 BOTM% to 1 BOTM% of the anti-blocking compound, 25% to 45 % by weight of pigment, and 5% to 40% by weight of water; the coating composition further comprises one or more additional components selected from defoamers, rheology modifiers, solvents, biocides, neutralizing agents, and preservatives; the coating composition is a paint intended to be applied to a substrate, an adhesive optionally pressure-sensitive, a varnish, or an ink. The substrate may be for example wood, concrete, paper, metal, another paint, tiles, cement, etc.

[0033] In the present text, it should be noted that in specifying any range of concentration, weight ratio or amount, any particular upper concentration, weight ratio or amount can be associated with any particular lower concentration, weight ratio or amount, respectively.

[0034] As used herein, the term “alkyl” or "alkyl group" means a saturated hydrocarbon radical, which may be straight, branched or cyclic, such as, for example, methyl, ethyl, n- propyl, iso-propyl, n-butyl, sec-butyl, t-butyl, pentyl, n-hexyl, cyclohexyl.DETAILED DESCRIPTION OF THE INVENTION

[0035] The invention generally relates to the use of a 0-3 EO phosphate ester surfactant in a waterborne (water-based) emulsion before or after polymerization to impart or improve block resistance, preferably anti-blocking of the corresponding coating composition obtained therefrom.

[0036] This is contrary to a common practice in the field of coatings, whereby compounds designed to improve blocking resistance are used as additives added directly to the coating composition, such as the paint or the varnish for example.

[0037] A decisive advantage of the method of the invention is that the corresponding coating compositions show good early hot block resistance properties without using fluorocarbon surfactants.

[0038] According to a first aspect of the invention, the anti-blocking compound comprising the phosphate ester surfactant is added in the monomer emulsion, that is, before polymerization to a latex.

[0039] According to a second aspect of the invention, the anti-blocking compound comprising the phosphate ester surfactant is added in the latex, that is, after polymerization of the monomer emulsion.

[0040] The latex is then further processed to lead to the corresponding coating composition.

[0041] Of course, one or more of such phosphate ester surfactants may be added in the emulsion, before and / or after the polymerization.

[0042] Preferably, the phosphate ester surfactant is ethoxylated, and where applicable, contains between 1 and 3 ethoxylations, i.e. EO units.

[0043] Alternatively, the phosphate ester surfactant may be non-ethoxylated, thus containing no ethoxylation.

[0044] The phosphate ester surfactant may be a mono-ester phosphate, a di-ester phosphate, a tri-ester phosphate, or mixture thereof. Preferably, the phosphate ester surfactant is a mixture of the mono-ester phosphate and the di -ester phosphate.

[0045] Preferably, the phosphate ester surfactant has the following formula (I):R1-O-(CH2-CH2-O)„-X1(I) whereinR1is a C4-C20 substituted or an unsubstituted alkyl group, preferably a C4-C15 alkyl group, and more preferably a Cs-Cn alkyl group;-O-CH2-CH2- is a divalent oxyethylene (EO) group, n being an integer or a decimal between 0 and 3;X1is a phosphate group.

[0046] The salt is preferably a sodium, potassium, ammonium, or organic amine salt.

[0047] When the phosphate ester surfactant contains a di-ester, the latter preferably has the following formula (II):R2-O-(CH2-CH2-O)n-X2-(O-CH2-CH2)n-O-R2(II) whereinR2is a C4-C20 substituted or an unsubstituted alkyl group, preferably a C4-C15 alkyl group, and more preferably a Cs-Ci2alkyl group;-O-CH2-CH2- is a divalent oxyethylene (EO) group, n being an integer or a decimal between 0 and 3;X2is a phosphate group.

[0048] The salt is preferably a sodium, potassium, ammonium, or organic amine salt.

[0049] When the phosphate ester surfactant contains a tri-ester, the latter preferably has the following formula (III):whereinR3is a C4-C20 substituted or an unsubstituted alkyl group, preferably a C4-C20 alkyl group, more preferably a C4-C15 alkyl group, and more preferably a Cs-Ci2 alkyl group;-O-CH2-CH2- is a divalent oxyethylene (EO) group, n being an integer or a decimal between 0 and 3;X3is a phosphate group.

[0050] The salt is preferably a sodium, potassium, ammonium, or organic amine salt.

[0051] With respect to the effective amount of anti-blocking compound to be added, it is preferably greater or equal to 0.010% by weight based on the total amount of the coating composition.

[0052] Moreover, said effective amount of anti-blocking compound is preferably lower or equal to 1.0% by weight based on the total amount of the coating composition.

[0053] According to an embodiment of the invention, the anti-blocking compound further comprises at least one sulfate, sulfonate, and / or phosphate alkyl surfactant, ethoxylated or non ethoxylated. In other terms, the phosphate ester surfactant is added in combination with at least one sulfate, sulfonate, and / or phosphate alkyl surfactant, ethoxylated or non ethoxylated, in the waterborne emulsion. This additional compound may be for example SLS, Rhodacal® A246L, Rhodacal® DS4, Rhodafac® RS610 A25, Rhodapon® UB STD, Rhodapon® LX28AEP, all of those being commercially sold by Solvay.

[0054] Preferably, said coating composition is prepared from an (meth)acrylic or a styrene-(meth)acrylic latex polymer.

[0055] The method of the invention significantly increases the early high-temperature blocking resistance. Thanks to the addition of the anti -blocking compound, the coating composition presents an early high-temperature blocking resistance: improved by at least 2 units compared to the same coating composition lacking the anti-blocking additive. These units are those of the scale ranging from 1 to 10 as defined in the standard ASTM D4946-89; comprised between 5 and 10, preferably between 6 and 9.

[0056] The method of the invention also leads to great performance of early hot antiblocking after heat aging of the coating. In other words, the anti-blocking effect remains high even after the coating is heat-aged.

[0057] The coating composition of the invention presents great early high- temperature blocking resistance properties, and comprises:- at least one latex polymer,- optionally, at least one pigment,- water,- an anti-blocking compound comprising a phosphate ester surfactant, wherein the phosphate ester surfactant comprises an acid or a salt of an alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units

[0058] According to a first embodiment, the coating composition is prepared from a waterborne monomer emulsion containing the anti-blocking compound. The monomer emulsion is intended to be polymerized into a latex polymer used to prepare said coating composition. In other terms, the anti-blocking compound is added into the monomer emulsion.

[0059] According to a second embodiment, the coating composition is prepared from the waterborne latex polymer itself containing said anti-blocking compound and used to prepare said coating composition. In other terms, the anti-blocking compound is added into the latex.

[0060] The coating composition may be prepared from an (meth)acrylic or a styrene- (meth)acrylic latex polymer.

[0061] The coating composition may comprise further components selected from defoamers, rheology modifiers, solvents, biocides, neutralizing agents, and preservatives.

[0062] The coating composition may be a paint, an adhesive optionally pressuresensitive, a varnish, or an ink.

[0063] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.EXAMPLES OF EMBODIMENTS OF THE INVENTION

[0064] Preparation of phosphate ester surfactants

[0065] Phosphate ester surfactants are prepared by the reaction of an alcohol with polyphosphoric acid and / or phosphoric anhydride to give a phosphate ester composition having varying levels of phosphoric acid, monoalkyl phosphate, dialkyl phosphate, trialkyl phosphate, and residual starting alcohol. The ratio of the two phosphorylating reagents (polyphosphoric acid and phosphoric anhydride) to the alcohol, and to each other when used together, are varied to target a desirable phosphate ester composition.

[0066] For this work, two different sets of phosphation conditions were employed using either n-octanol or iso-octanol as the starting alcohols.

[0067] The phosphate esters products are then neutralized to a salt using KOH.

[0068] Preparation of several latex by emulsion polymerization using phosphate ester surfactants

[0069] Example 1 : n-octyl-phosphate ester.K

[0070] 1.46g of Rhodacal® A246L is mixed with 2.16g of n-octyl-phosphate, K in about 130 g of DI water. The mixture is heated to 82 °C in the kettle.

[0071] On the side, the monomer pre-emulsion is prepared by mixing 2.83 of Rhodacal® A46L with 4.33g of n-octyl-PO4,K in 96g of DI water. 110g of MMA, 106g of BA and 4.4g of MAA are slowly added under strong shear to the surfactant solution. 0.44g of sodium bicarbonate is added to the emulsion to adjust the pH close to 4. The monomer pre-emulsion is sheared for 15 min.

[0072] Add 16g of the monomer pre-emulsion to the kettle. Once the temperature is back to 82°C, add a solution of initiator (0.6g of ammonium persulfate dissolved in 5g of DI water).

[0073] Feed the rest of the monomer pre-emulsion over the course of 2.5-3h alongside with a second solution of initiator (0.3g of Ammonium persulfate dissolved in 30g of DI water).

[0074] Once the monomer emulsion is completely added to the kettle, flush the lines with 5 g water and hold the reaction at 82C for an extra 30 min.

[0075] Cool the reactor down to 65C and add a chaser solution. The chaser consists of two separate solutions (0.18g t-BHP diluted in 2.4g water and 0.18g of isoascorbic acid dissolved in 2.4g water). The reaction is then held at 65°C for another 30 min.

[0076] Finally the reactor is cooled down and the pH of the latex is adjusted to 8.5 with ammonia. The latex is subsequently fdtered over a 150-micron mesh filter to measure the coagulum formed during the reaction.

[0077] Example 2: Dermalcare® MAP L-213 / K

[0078] 3.15g of Dermalcare® MAP L-213 / K is mixed in about 129 g of DI water.The mixture is heated to 82 °C in the kettle.

[0079] On the side, the monomer pre-emulsion is prepared by mixing 6.3g of Dermalcare® MAP L-213 / K in 94g of DI water. 110g of MMA, 106g of BA and 4.4g of MAA are slowly added under strong shear to the surfactant solution. 0.44g of sodium bicarbonate is added to the emulsion to adjust the pH close to 4. The monomer pre- emulsion is sheared for 15 min.

[0080] Add 16g of the monomer pre-emulsion to the kettle. Once the temperature is back to 82°C, add a solution of initiator (0.6g of Ammonium persulfate dissolved in 5g of DI water).

[0081] Feed the rest of the monomer pre-emulsion over the course of 2.5-3h alongside with a second solution of initiator (0.3g of Ammonium persulfate dissolved in 30g of DI water).

[0082] Once the monomer emulsion is completely added to the kettle, flush the lines with 5 g water and hold the reaction at 82C for an extra 30 min.

[0083] Cool the reactor down to 65°C and add a chaser solution. The chaser consists of two separate solutions (0.18g t-BHP diluted in 2.4g water and 0.18g of isoascorbic acid dissolved in 2.4g water). The reaction is then held at 65°C for another 30 min.

[0084] Finally the reactor is cooled down and the pH of the latex is adjusted to 8.5 with ammonia. The latex is subsequently fdtered over a 150-micron mesh filter to measure the coagulum formed during the reaction.

[0085] Example 3: Ci2-phosphate ester.K

[0086] 3.66g of Ci2-phosphate,K in about 129 g of DI water. The mixture is heated to 82°C in the kettle.

[0087] On the side, the monomer pre-emulsion is prepared by mixing 7.31g of C12- PO4,K in 94g of DI water. 110g of MMA, 106g of BA and 4.4g of MAA are slowly added under strong shear to the surfactant solution. 0.44g of sodium bicarbonate is added to the emulsion to adjust the pH close to 4. The monomer pre-emulsion is sheared for 15 min.

[0088] Add 16g of the monomer pre-emulsion to the kettle. Once the temperature is back to 82°C, add a solution of initiator (0.6g of Ammonium persulfate dissolved in 5g of DI water).

[0089] Feed the rest of the monomer pre-emulsion over the course of 3h alongside with a second solution of initiator (0.3g of Ammonium persulfate dissolved in 30g of DI water).

[0090] Once the monomer emulsion is completely added to the kettle, flush the lines with 5 g water and hold the reaction at 82°C for an extra 30 min.

[0091] Cool the reactor down to 65°C and add a chaser solution. The chaser consists of two separate solutions (0.18g t-BHP diluted in 2.4g water and 0.18g of isoascorbic acid dissolved in 2.4g water). The reaction is then held at 65°C for another 30 min.

[0092] Finally the reactor is cooled down and the pH of the latex is adjusted to 8.5 with ammonia. The latex is subsequently fdtered over a 150-micron mesh filter to measure the coagulum formed during the reaction.

[0093] Example 4 Preparation of a latex using Rhodafac® RS610 / A25

[0094] 4.4g of Rhodafac® RS610 / A25 is mixed in about 128 g of DI water. The mixture is heated to 82°C in the kettle.

[0095] On the side, the monomer pre-emulsion is prepared by mixing 8.8g of Rhodafac® RS610 / A25 in 92g of DI water. 110g of MMA, 106g of BA and 4.4g of MAA are slowly added under strong shear to the surfactant solution. 0.44g of sodium bicarbonate is added to the emulsion to adjust the pH close to 4. The monomer pre-emulsion is sheared for 15 min.

[0096] Add 16g of the monomer pre-emulsion to the kettle. Once the temperature is back to 82°C, add a solution of initiator (0.6g of Ammonium persulfate dissolved in 5g of DI water).

[0097] Feed the rest of the monomer pre-emulsion over the course of 2.5-3h alongside with a second solution of initiator (0.3g of Ammonium persulfate dissolved in 30g of DI water).

[0098] Once the monomer emulsion is completely added to the kettle, flush the lines with 5 g water and hold the reaction at 82°C for an extra 30 min.

[0099] Cool the reactor down to 65°C and add a chaser solution. The chaser consists of two separate solutions (0.18g t-BHP diluted in 2.4g water and 0. 18g of isoascorbic acid dissolved in 2.4g water). The reaction is then held at 65°C for another 30 min.

[0100] Finally the reactor is cooled down and the pH of the latex is adjusted to 8.5 with ammonia. The latex is subsequently fdtered over a 150-micron mesh fdter to measure the coagulum formed during the reaction.

[0101] Example 5 : n-octyl-phosphate.K in styrene acrylic latex

[0102] 1.41g of Rhodacal A246L is mixed with 1.44g of n-octyl -phosphate, K in about 130 g of DI water. The mixture is heated to 82 °C in the kettle.

[0103] On the side, the monomer pre-emulsion is prepared by mixing 2.83 of Rhodacal A46L with 2.87g of n-octyl-PO4,k in 94g of DI water. 101g of styrene, 115g of BA and 4.4g of AA are slowly added under strong shear to the surfactant solution. 0.44g of sodium bicarbonate is added to the emulsion. The monomer pre-emulsion is sheared for 15 min.

[0104] add 16g of the monomer pre-emulsion to the kettle. Once the temperature is back to 82C, add a solution of initiator (0.6g of Ammonium persulfate dissolved in 5g of DI water).

[0105] feed the rest of the monomer pre-emulsion over the course of 3h alongside with a second solution of initiator (0.3g of Ammonium persulfate dissolved in 30g of DI water).

[0106] Once the monomer emulsion is completely added to the kettle, flush the lines with 5 g water and hold the reaction at 82C for an extra 30 min.

[0107] Cool the reactor down to 65C and add a chaser solution. The chaser consists of 2 separate solutions (0.18g t-BHP diluted in 2.4g water & 0.18g of isoascorbic acid dissolved in 2.4g water). The reaction is then held at 65C for another 30 min.

[0108] Finally the reactor is cooled down and the pH of the latex is adjusted to 8.5 with ammonia. The latex is subsequently fdtered over a 150-micron mesh filter to measure the coagulum formed during the reaction.

[0109] The latex obtained are presented in Table 1 below.Table 1 : latex prepared using phosphate esters neutralized with KOH

[0110] In Table 1:Dermalcare® MAP L-213 / K is a solution of the potassium salt of laureth phosphate ester, commercialized by Syensqo;Rhodafac® RS610A25 is a clear liquid anionic ammonium phosphate, polyoxyethylene tridecyl ether, commercialized by Syensqo;Rhodacal® A246L is an APE-free anionic surfactant, commercialized by Syensqo;Duraphos® 2EHA PO4 K is a phosphoric acid ethylhexyl ester, commercialized by Syensqo.

[0111] The latex containing the phosphate esters neutralized with KOH are directly formulated into paints.

[0112] Semigloss formulations used to Prepare Water-based Paints for Testing are shown in Table 2 below.Table 2: Semigloss formulations for water-based paints prepared with some of the latex of Table 1

[0113] Block resistance test (D 4946-89 (2017)) is performed on dry paint films. The results are shown in Table 3 below.

[0114] With respect to these results, paints B, C, D, E, H, J, M, Q, R show to good to excellent early 1-day oven (hot) block resistance, and the results are even better after 7 days, all showing very good hot block resistance. Paints F, K, L show good 7-day hot block resistance.

[0115] Paint A (counter-example) does not contain any phosphate ester but only Rhodacal® A246L as a surfactant, thus being used as a comparative.

[0116] The control, paint (column “none”) is made with a benchmark FluorocarbonSurfactant (FCS). The fail control (<4) and the pass control (FCS (>7) were included to show the overall good performance for early hot block of the run.Table 3: Block resistance test carried out with the paints of Table 2

[0117] The same paints were also heat aged (H / A) for 10 days in a 50°C oven, allowed to cool to room temperature for 24 hours and then check for viscosity stability.

[0118] Table 4 summarizes the results. It shows that paints B, C, D, and E of the invention were stable and that the early hot block resistance of these paints was retained.Table 4: Results after heat ageing of the paints

[0119] These results show that the method of the invention leads to great performance of early hot anti -blocking after heat aging of the coating. The anti -blocking effect remains high even after the coating is heat-aged.

[0120] The test procedure for Early (1 day dry) “hot” block Resistance is detailed in the following. This procedure is carried out as per ASTM Standard Test Method for Blocking Resistance of Architectural Paints, Designation D 4946-89 (2017); Resistance Test Method # 502: Peel Block Resistance.

[0121] Test Method Highlights:1) Cast the test paint on an all white sealed Leneta chart with a 3mil Bird applicator in the controlled temperature room. Allow test samples to dry.2) Cut out 1-1 / 2” by 1-1 / 2” sections (to run duplicates) from white area of each conditioned panel.3) Place the cut sections with the paint surfaces face-to-face.4) Place the face-to-face specimens in a 50oC (120oF) oven on a flat metal plate. Top each individual specimen with a heated, solid #8 rubber stopper and place a heated 1000 gram weight on each stopper.5) After exactly 30 minutes, remove the stoppers and weights and remove the test specimens from the oven. All to cool for 30 minutes at room temperature.6) After cooling, separate the sections with slow and steady force. Pull apart at an angle of approximately 180o and listen for tack. Rate the samples for block resistance on a scale of 0-10.SCALE (from ASTM):10: no tack perfect9: trace tack excellent8: slight tack very good7: good6: moderate tack good5: fair4: severe tack, no seal fair3: 5-25% seal poor2: 25-50% seal poor1: 50-75% seal very poor0: complete seal very poor

Claims

CLAIMS1. Method for imparting or improving block resistance, preferably early high-temperature blocking resistance, of a waterborne coating composition comprising adding an effective amount of at least one anti-blocking compound comprising a phosphate ester surfactant in a corresponding waterborne monomer emulsion intended to be polymerized into a latex polymer used to prepare said coating composition, wherein the phosphate ester surfactant comprises an acid or a salt of alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units.

2. Method for imparting or improving block resistance, preferably early high-temperature blocking resistance of a waterborne coating composition comprising adding an effective amount of at least one anti-blocking compound comprising a phosphate ester surfactant in a corresponding waterborne latex polymer used to prepare said coating composition, wherein the phosphate ester surfactant comprises an acid or a salt of alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units.

3. Method according to claim 1 or claim 2, wherein the phosphate ester surfactant comprises between 0 and 2 ethylene oxide units.

4. Method according to any of the preceding claims, wherein the alkyl group of the phosphate ester surfactant is a C4-C15 carbon chain, preferably a Cs-Ci2 carbon chain, optionally branched and / or substituted.

5. Method according to any of the preceding claims, wherein the phosphate ester surfactant is a potassium salt, a sodium salt, an ammonium salt, or an organic amine salt.

6. Method according to any of the preceding claims, wherein the effective amount of antiblocking compound is greater or equal to 0.010% by weight, preferably greater or equal to 0.05% by weight, based on the total amount of the coating composition.

7. Method according to any of the preceding claims, wherein the effective amount of antiblocking compound is lower or equal to 1.0% by weight, preferably lower or equal to 0.5% by weight, based on the total amount of the coating composition.

8. Method according to any of the preceding claims, wherein the anti-blocking additive is used in an amount between 0.5 BOTM% and 3 BOTM% in the latex polymer.

9. Method according to any of the preceding claims, said method further comprising the addition of at least one sulfate, sulfonate, and / or phosphate alkyl surfactant, ethoxylated or non ethoxylated.

10. Method according to any of the preceding claims, wherein the anti -blocking compound comprises:• at least one phosphate ester surfactant comprising a C4-C20 carbon chain, preferably a Cs-Cn carbon chain, between 0 and 3 ethylene oxide units, preferably between 0 and 2 ethylene oxide units, and a potassium salt, a sodium salt, an ammonium salt, or an organic amine salt; and• at least one olefin sulfate, sulfonate, and / or phosphate alkyl surfactant, preferably a C10-C20 olefin sulfate, sulfonate, and / or phosphate alkyl surfactant.

11. Coating composition presenting block resistance, preferably early high-temperature blocking resistance properties, comprising:- at least one latex polymer,- optionally, at least one pigment,- water,- an anti-blocking compound comprising a phosphate ester surfactant, wherein the phosphate ester surfactant comprises an acid or a salt of an alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units, wherein the latex polymer is prepared from a waterborne monomer emulsion containing said anti-blocking compound and intended to be polymerized into a latex polymer used to prepare said coating composition.

12. Coating composition presenting block resistance, preferably early high-temperature blocking resistance properties, comprising:- at least one latex polymer,- optionally, at least one pigment,- water,- an anti-blocking compound comprising a phosphate ester surfactant, wherein the phosphate ester surfactant comprises an acid or a salt of an alkyl phosphate ester, optionally ethoxylated, comprising a C4-C20 carbon chain and between 0 and 3 ethylene oxide units, wherein the latex polymer is prepared from a waterborne latex polymer containing said anti-blocking compound and used to prepare said coating composition.

13. Coating composition according to claim 11 or claim 12, said coating composition presenting a block resistance, preferably an early high-temperature blocking resistance improved by at least 2 units compared to the same coating composition lacking the antiblocking compound.

14. Coating composition according to any of claims 11 to 13, said coating composition presenting a block resistance, preferably an early high-temperature blocking resistance between 5 and 10, preferably between 6 and 9.

15. Coating composition according to any of claims 11 to 14, further comprising one or more additional components selected from defoamers, rheology modifiers, solvents, biocides, neutralizing agents, and preservatives.

16. Coating composition according to any of claims 11 to 15, said coating composition being a paint intended to be applied to a substrate, the substrate being preferably wood, concrete, paper, metal, another paint, tiles, or cement, or said coating composition being an adhesive optionally pressure-sensitive, a varnish, or an ink.

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