CARBONI STEFANO (IT)
COGET KARINE (IT)
VETRI DOMENICO (IT)
| WO2013091209A1 | 2013-06-27 | |||
| WO2005058995A1 | 2005-06-30 | |||
| WO2016102596A1 | 2016-06-30 | |||
| WO2018172526A1 | 2018-09-27 | |||
| WO2010015494A2 | 2010-02-11 | |||
| WO2016102596A1 | 2016-06-30 |
| CLAIMS 1. An aqueous self-crosslinking coating composition comprising dispersed polymer particles, wherein: i) the dispersed polymer particles are polyurethane-vinyl polymer hybrid particles obtained by free-radical polymerization of at least one vinyl monomer and at least one ketone group containing vinyl monomer in the presence of a polyurethane, ii) the polyurethane and the vinyl polymer in the hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 1:4 to 20:1, iii) the polyurethane is obtained by the reaction of at least the following components: a) from 5 to 40 % by weight (wt%) of at least one aliphatic or cycloaliphatic diisocyanate, b) from 0.5 to 5 wt% of at least one diol having at least one carboxylic or carboxylate group, c) from 40 to 90 wt% of at least one diol with molecular weight between 500 and 5,000 g/mol, d) from 0.1 to 10 wt% of at least one chain extender having at least 2 active hydrogens toward the isocyanate (NCO) group, e) from 0 to 10 wt% of at least one diol or at least one polyol different from diols b) and c), f) from 0 to 20 wt% of an aliphatic or cycloaliphatic polyisocyanate having average functionality above 2, wherein the percentage amounts of a), b), c), d), e) and f) are referred to the sum of a)+b)+c)+d)+e)+f). The aqueous self-crosslinking coating composition according to Claim 1, wherein the aqueous self-crosslinking coating composition comprises: A) from 74 to 99.8 wt% of dispersed polymer particles; B) from. 0.2 to 15 wt% of a thickener; C) from 0 to 10 wt% of a surfactant; D) from 0.001% to 1 wt% of a dihydrazide functional compound, wherein the amounts of A), B), C) and D) are given relative to the total amount of dispersed polymer particles, thickener, surfactant and dihydrazide functional compound. The aqueous self-crosslinking coating composition according to Claim 2, wherein the dihydrazide functional compound is adipic acid dihydrazide. The aqueous self-crosslinking coating composition according to Claim 1, wherein the dispersed polymer particles have a mean particle size (D[0.5]) greater than 0.5 micron and a mean particle size (D[0.9]) less than 25 micron. The aqueous self-crosslinking coating composition according to Claim 1, wherein the at least one ketone group containing vinyl monomer is diacetone acrylamide. The aqueous self-crosslinking coating composition according to Claim 1, wherein the at least one diol having at least one carboxylic or carboxylate group is dimethylolpropionic acid (DMPA), dimethylolbutanoic acid (DM BA) or mixtures thereof. The aqueous self-crosslinking coating composition according to Claim 1, wherein the at least one diol having at least one carboxylic or carboxylate group is dimethylolbutanoic acid (DMBA). The aqueous self-crosslinking coating composition according to Claim 1, wherein the polyurethane is obtained by the reaction of b) from 1 to 3 wt% of at least one diol having at least one carboxylic or carboxylate group. A method for coating leather or artificial leather comprising: providing an aqueous self-crosslinking coating composition comprising dispersed polymer particles according to any of the Claims from 1 to 8, applying it to their upper (finished and exposed to sight) surface and drying. A method for coating woven fabrics, paper, cardboard, plastic, wood or metals comprising: providing an aqueous self-crosslinking coating composition comprising dispersed polymer particles according to any of the Claims from 1 to 8, applying it to their upper surface and drying. |
MECHANICAL PROPERTIES
TECHNICAL FIELD
The present invention relates to a low gloss aqueous coating composition with improved mechanical properties, such as resistance to liquids. This composition is particularly useful for the finishing of leather and artificial leather, but also for the superficial treatment of fabrics, paper, cardboard, plastic, wood and metals.
STATE OF THE ART
The surface of many manufactured articles, by way of example made from woven fabrics, leather, paper, plastic, wood and metal, is treated with the purpose of making it more homogeneous, or of protecting it from the wear of the time or the atmosphere and/or in order to improve certain aesthetic properties, such as high or low gloss, soft or rough touch, different colours, and so on.
Traditionally, low gloss coating compositions are obtained by addition of inorganic matting agents, such as amorphous or crystalline silica. However, due their extreme fineness and volatility, siliceous particles poses serious health risks and therefore their use should be avoided.
Aqueous polyurethane dispersions represent a safe valid alternative to the traditional inorganic matting agents.
For example, WO 2010/015494 discloses anionic polyurethane dispersions based on a polyglycol ether, poly(tetramethyleneglycol), that provide films having low gloss and soft touch atthe same time; soft touch effect or velvet effect is another superficial characteristic which is more and more appreciated by the market. However, films obtained from the anionic polyurethane dispersions described WO 2010/015494 show limited mechanical properties; particularly, they result impaired or damaged when contacted with organic solvents.
In order to improve the mechanical properties of the aqueous polyurethane dispersions described in WO 2010/015494, WO2016/102596 suggests an aqueous coating composition comprising dispersed polymer particles, wherein the dispersed polymer particles are polyurethane-vinyl polymer hybrid particles obtained by free- radical polymerization of at least one vinyl monomer in the presence of a polyurethane.
However, a need still exists in the art to provide low gloss aqueous coating compositions with improved mechanical properties.
It has now been found low gloss aqueous self-crosslinking coating compositions with improved mechanical properties can be obtained by using polyurethane-vinyl hybrid polymers and a dihydrazide functional compound.
SUM MARY OF THE INVENTION
Therefore, the present invention relates to an aqueous self-crosslinking coating composition comprising dispersed polymer particles, wherein: i) the dispersed polymer particles are polyurethane-vinyl polymer hybrid particles obtained by free-radical polymerization of at least one vinyl monomer and at least one ketone group containing vinyl monomer in the presence of a polyurethane, ii) the polyurethane and the vinyl polymer in the hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 1:4 to 20:1, iii) the polyurethane is obtained by the reaction of at least the fol lowing components: a) from 5 to 40 % by weight (wt%) of at least one aliphatic or cycloaliphatic diisocyanate, b) from 0.5 to 5 wt% of at least one diol having at least one carboxylic or carboxylate group, c) from 40 to 90 wt% of at least one diol with molecular weight between 500 and 5,000 g/mol, d) from 0.1 to 10 wt% of at least one chain extender having at least 2 active hydrogens toward the isocyanate (NCO) group, e) from 0 to 10 wt% of at least one diol or at least one polyol different from diols b) and c), f) from 0 to 20 wt% of at least one aliphatic or cycloaliphatic polyisocyanate having average functionality above 2, wherein the percentage amounts of a), b), c), d), e) and f) are referred to the sum of a)+b)+c)+d)+e)+f).
According to another aspect, the present invention relates to a method for coating leather or artificial leather comprising: providing an aqueous self-crosslinking coating composition comprising dispersed polymer particles as described above, applying it to their upper (finished and exposed to sight) surface and drying.
According to yet another aspect, the present the invention relates to a method for coating woven fabrics, paper, cardboard, plastic, wood or metals comprising: providing an aqueous self-crosslinking coating composition comprising dispersed polymer particles as described above, applying it to their upper surface and drying. According to the present invention, "self-crosslinking" means that a chemical crosslinking reaction takes place after having applied the aqueous coating composition on the substrate without the addition of other components to the coating composition. The aqueous coating composition according to the present invention allows toobtain a coating solely by drying the aqueous coating composition by evaporation of volatiles.
DETAILED DESCRIPTION OF THE INVENTION
The molar ratio between the sum of the NCO groups and the sum of the NCO reactive groups of the components used to prepare the polyurethane is from 1.05: 1 to 5:1, preferably from 1.2:1 to 3.2:1.
The polyurethane and the vinyl polymer in the self-crosslinking hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 1:4 to 20:1, preferably from 1:1 to 20:1, more preferably from 3:1 to 15:1.
The process for preparing the aqueous self-crosslinking coating composition of the present invention comprises the following steps: i) reaction of components a) to e) and optionally e) and f) to form a polyurethane prepolymer, ii) forming an aqueous dispersion of the polyurethane prepolymer in water, iii) chain extending the prepolymer with component d) to obtain a polyurethane dispersion, iv) polymerizing at least one vinyl monomer and at least one ketone group containing vinyl monomer in the polyurethane dispersion in the presence of a radical initiator to obtain a dispersion of polyurethane-vinyl polymer hybrid particles, v) adding a thickener and, optionally, a surfactant in water before forming the aqueous dispersion of the polyurethane prepolymer in water, or after any of the steps ii) to iv), vi) adding a dihydrazide functional compound in the dispersion between step iii) and iv) or after step iv).
The polyurethane present in the aqueous self-crosslinking coating composition of the present invention is obtained by reacting at least components a), b), c), d) and optionally e) and f).
Component a) is at least one aliphatic or cycloaliphatic diisocyanate. The amount of component a) relative to the total amount of components used to prepare the polyurethane is from 5 to 40 wt%, preferably from 10 to 35 wt%.
Examples of diisocyanates useful for the preparation of the polyurethane of the present invention are 1-isocyanate-3-isocyanate-methyl-3,5,5-trimethylcyclohexane (or isophorone diisocyanate), 4,4'-dicyclohexyl-methane-diisocyanate, hexamethylene diisocyanate, and mixtures thereof; most preferably the diisocyanate is isophorone diisocyanate. Mixtures of aliphatic and cycloaliphatic diisocyanates may be used.
Component b) is at least one diol having at least one carboxylic or carboxylate group. The amount of component b) relative to the total amount of components used to prepare the polyurethane is from 0.5 to 5 wt%, preferably from 1 to 3 wt%. Preferably component b) is a carboxylic acid or salt thereof which is substituted in the position 2 by two hydroxymethyl groups; more preferably component b) is dimethylolpropionic acid (DM PA), dimethylolbutanoic acid (DM BA) or mixtures thereof; most preferably component b) is dimethylolbutanoic acid.
The carboxylic water dispersing groups of component b) are preferably fully or partially in the form of a salt. Conversion to the salt form is effected by neutralisation with a base, preferably after the preparation of the prepolymer and before its dispersion in water. The base is preferably ammonia, an amine or an inorganic base. Suitable amines include tertiary amines, for example triethylamine or N,N- dimethylethanolamine. Suitable inorganic bases include alkali hydroxides and carbonates, for example lithium hydroxide, sodium hydroxide, or potassium hydroxide.
Component c) is at least one diol with molecular weight between 500 and 5,000 g/mol. The amount of component c) relative to the total amount of components used to prepare the polyurethane is from 40 to 90 wt%, preferably from 50 to 70 wt%.
As component c), nonionic polyether diols, polyester diols and polycarbonate diols, or mixtures thereof, may be used.
Among the utilizable polyester diols are those obtained, for example, by reacting dicarboxylic acids, or possibly the corresponding anhydrides or methyl esters, with diols, optionally in the presence of known esterification catalysts.
Examples of suitable acids or anhydrides include adipic acid, succinic acid, maleic acid, sebacic acid, azelaic acids, the various commercially available dimeric fatty acids in saturated (hydrogenated) or unsaturated form, phthalic acid, isophthalic acid, tetrahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid and hexahydrophthalic acid; adipic acid, succinic acid, maleic acid, sebacic acid and azelaic acids are preferred.
Suitable diols for the preparation of the polyester diols are, for example, ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, 1,6-hexanediol, 3- methyl-1, 5-pentanediol, 1,5-pentanediol, cyclohexanedimethanol, diethylene glycol, dipropylene glycol, neopentyl glycol and mixtures thereof, such as mixtures of 1,6- hexanediol and 1,5-pentanediol or of 1,6-hexanediol and neopentyl glycol. Other useful polyester diols are those obtainable from diol-initiated polymerization of hydroxy carboxylic acids containing from 2 to 26, and preferably from 4 to 12 carbon atoms, or a lactone thereof. The hydroxy carboxylic acids may be saturated or unsaturated, linear or branched.
Examples of suitable hydroxy carboxylic acids are glycolic acid, lactic acid, 5- hydroxy valeric acid, 6-hydroxy caproic acid, ricinoleic acid, 12-hydroxy stearic acid, 12- hydroxydodecanoic acid, 5-hydroxydodecanoic acid, 5-hydroxydecanoic acid and 4- hydroxydecanoic acid.
Examples of suitable lactones are p-propiolactone and, optionally C Cd-alkyl substituted, 8-valerolactone and s-caprolactone, such as p-methyl-8-valerolactone. Polyester diols obtained from s-caprolactone are especially preferred.
Useful polyether diols include products obtained by the polymerization of cyclic oxides, for example ethylene oxide, propylene oxide, butylene oxide, tetra hydrofuran, ethoxylated polyether-1,3-diols, and mixture thereof. Especially useful polyether diols include polyoxypropylene diol, poly(oxyethylene-oxypropylene) diol and poly(tetramethylene glycol)diol.
The preferred polyether diol is poly(tetramethylene glycol)diol.
The polycarbonate diols are those obtained, for example, by reacting carbonic acid derivatives, such as diphenyl carbonate or phosgene, and diols. Suitable diols include those mentioned above for the preparation of the polyester diols. The preferred polycarbonate diol is 1,6-hexanediol polycarbonate.
Mixtures of different diols may be used as components c). Polyether diols and polycarbonate diols, and especially polyether diols, are preferred.
The molecular weight of the polymeric diols c) is calculated from the hydroxyl number.
Component d) is at least one chain extender having at least 2 active hydrogens toward the isocyanate (NCO) group. The amount of component d) relative to the total amount of components used to prepare the polyurethane is from 0.1 to 10 wt%, preferably from 1 to 6 wt%.
Specific examples of chain extenders that can be used are ethylene diamine, diethylene triamine, triethylene tetramine, propylene diamine, butylene diamine, hexamethylene diamine, cyclohexylene diamine, piperazine, 2-methyl piperazine, phenylene diamine, toluylene diamine, xylylene diamine, tri(2-aminoethyl) amine, methane diamine, m-xylene diamine, isophorone diamines. Also suitable are hydrazine (e.g. in the form of its mono-hydrate), azines such as acetone azine, substituted hydrazines such as, for example, dimethyl hydrazine, 1,6-hexamethylene- bis-hydrazine, carbodihydrazine. Another suitable class of chain extenders is the so- called Jeffamine® compounds with a functionality of 2 or 3 (available from
Huntsman). These are polypropylene oxide (PPO) or polyethylene oxide (PEO)- based di- or triamines, e.g. Jeffamine® T403 and Jeffamine® D-400.
Anionic chain extenders, such as the sodium salt of 2-[(2- aminoethyl)amino]ethanesulfonic acid may also be used.
Component e) is at least one diol or at least one polyol different from diols b) and c). The amount of component e) relative to the total amount of components used to prepare the polyurethane is from 0 to 10 wt%, preferably from 0 to 5 wt%.
For the component e), suitable diols are propylene glycol, 1,4-butanediol, 1,6- hexanediol, neopentylglycol, cyclohexane dimethanol or mixtures thereof. Suitable polyols include glycerin, pentaerythritol, trimethylolpropane and its derivatives, such as a functional polypropylene glycol started on trimethylolpropane.
Componentf) is at least one aliphatic or cycloaliphatic polyisocyanate having average functionality above 2.
The amount of component f) relative to the total amount of components used to prepare the polyurethane is from 0 to 20 wt%, preferably from 0 to 10 wt%.
Component f) is an organic polyisocyanate having average functionality above 2, preferably from 2.3 and 4. Examples of suitable polyisocyanate are hexamethylene diisocyanate isocyanurate, hexamethylene diisocyanate biuret, isophoronediisocyanate isocyanurate and isophoronediisocyanate biuret.
The dispersed polyurethane-vinyl polymer hybrid particles present in the aqueous self-crosslinking coating composition of the present invention is obtained by free- radical polymerization of at least one vinyl monomer and at least one ketone group containing vinyl monomer in the presence of the polyurethane.
Said at least one vinyl monomer does not contain ketone groups and is selected among methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, styrene or mixtures thereof. Methyl methacrylate is preferred. Said at least one vinyl monomer represents at least 50 wt%, preferably at least 70 wt% of the total amount of the other vinyl monomer(s) used to prepare the vinyl polymer.
The at least one ketone group containing vinyl monomer is selected from the group consisting of diacetone acrylamide, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone, diacetone acrylate, acetonitrile acrylate or mixtures thereof. Diacetone acrylamide is preferred.
According to a preferred embodiment, the ketone groups are introduced in the vinyl polymer by copolymerizing of diacetone acrylamide with at least one other vinyl monomer.
The vinyl monomer(s) are polymerized using a conventional free radical yielding initiator system. Suitable free radical yielding initiators include mixtures partitioning between the aqueous and organic phases. Suitable free-radical-yielding initiators include inorganic peroxides such as ammonium persulphate, hydrogen peroxide, organic peroxides, such as benzoyl peroxide, alkyl hydroperoxides such as t- butyl hydroperoxide and cumene hydroperoxide; dialkyl peroxides such as di-t-butyl peroxide; peroxy esters such as t-butyl perbenzoate and the like; mixtures may also be used. The peroxy compounds are in some cases advantageously used in combination with suitable reducing agents (redox systems) such as iso-ascorbic acid. Azo compounds such as azobisisobutyronitrile may also be used. Metal compounds such as Fe- EDTA (EDTA is ethylene diamine tetracetic acid) may also be usefully employed as part of the redox initiator system. The amount of initiator or initiator system to use is conventional, e.g. within the range of 0.05 to 6 wt% based on the weight of vinyl monomer used.
The films obtained from the aqueous self-crosslinking coating composition of the present invention have improved mechanical properties and show low gloss and excellent soft touch, without using solid external matting agents.
Preferably, the aqueous self-crosslinking coating composition of the present invention contains less than 3% by weight of organic solvent, more preferably no organic solvent at all.
The aqueous self-crosslinking coating composition of the present invention comprises:
A) from 74 to 99.8 wt% of dispersed polymer particles;
B) from. 0.2 to 15 wt% of a thickener;
C) from 0 to 10 wt% of a surfactant;
D) from 0.001% to 1 wt% of a dihydrazide functional compound, wherein the amounts of A), B), C) and D) are given relative to the total amount of dispersed polymer particles, thickener, surfactant and dihydrazide functional compound. The mean particle size (D[0.5]) of the dispersed polymer particles is greater than 0.5 micron, preferably greater than 2 micron. D[0.5] means that the first 50 volume % of the particle size distribution has a mean particle size X.
The mean particle size (D[0.9]) of the dispersed polymer particles is less than 25 micron, preferably less than 15 micron. D[0.9] means that the first 90 volume % of the particle size distribution has a mean particle size Y. In the context of the present invention, the particle size and particle size distribution are measured by laser diffraction using a Mastersizer 3000 from Malvern.
The aqueous self-crosslinking coating composition of the present invention comprises from 0.1 to 15 wt%, preferably from 0.2 to 5.0 wt% of a thickener.
Preferably the thickener is an acrylic thickener, prepared by any known radical polymerization process, such as emulsion, inverse emulsion, suspension, solution and bulk polymerization of acrylic monomers.
The expression "acrylic monomers" refers to monomers derived from acrylic acid, methacrylic acid and mixtures thereof.
The expression "acrylic thickeners" refers to thickeners synthesized from acrylic monomers, that is monomers derived from acrylic acid, methacrylic acid and mixtures thereof.
Preferably, the acrylic thickener useful for the realization of the present invention are prepared by emulsion polymerization.
Suitable acrylic emulsion thickeners based on methacrylic acid and ethyl acrylate are alkali swellable acrylic emulsion thickeners (ASE), possibly including hydrophobic polyethoxylated monomers (such as (meth)acrylic esters of ethoxylated C1-C22 fatty alcohols) (HASE) and/or polyethylenically unsaturated monomers (crosslinkers)
(CHASE/CASE).
Preferably the thickener is an acrylic emulsion thickener based on methacrylic acid (25-50% by weight of the monomers), ethyl acrylate (40-70% by weight of the monomers), polyethylenically unsaturated monomer (0-1% by weight), (meth)acrylic esters of ethoxylated C1-C22 fatty alcohols (0-20% by weight).
In another preferred embodiment, the thickener is a polyurethane thickener such as a HEUR (associative ethoxylated polyurethane) thickener.
The aqueous self-crosslinking coating composition of the present invention comprises from 0 to 10 wt%, preferably from 0.2 to 3 wt% of a surfactant.
The surfactant can be chosen between non-ionic and anionic surfactants, but is preferably a non-ionic surfactant, more preferably a linear or branched aliphatic ethoxylated alcohol.
The aqueous self-crosslinking coating composition of the present invention comprises from 0.001 to 1 wt% of a dihydrazide functional compound with a molar mass below 500 g/mol that reacts with the keto functional group present on the vinyl polymer when the coating composition is applied and dried onto the substrate.
Suitable dihydrazide functional compounds include adipic acid dihydrazide, oxalic acid dihydrazide, isophthalic acid dihydrazide, polyacrylic acid polyhydrazide, or mixtures thereof.
Preferably, the dihydrazide functional compound is adipic acid dihydrazide.
The aqueous self-crosslinking coating composition of the present invention can be advantageously used in the finishing of leather and artificial leather, in the superficial coating of woven fabrics, paper, plastics, such as polycarbonates and PVC, wood and metals.
Non-matting additives may be present in the aqueous self-crosslinking coating composition in order to otherwise improve its performance, such as, by way of example, heat stabilizers, coalescing agents, plasticizers, levelling agents, anti-slip agents, anti-cratering agents, and the like.
The aqueous self-crosslinking coating composition of the invention allow to obtain durable films having high opacity, soft touch and improved mechanical properties. The content of the present invention is further illustrated by the following examples. EXAMPLES
Gloss measurements
The gloss has been determined by means of application of the polyurethane dispersion on a black card (Leneta FORM 2-A) and measured at 60° or 85°, following the ISO standard method 2813-2014.
The 60° gloss of the aqueous coating composition after drying is < 10, preferably < 2. The 85° gloss of the aqueous coating composition after drying is < 60, preferably < 20. Koniq hardness
The hardness of the final coating is measured according to the method ASTM D4366- 95.
Staining resistance
The resistance to various liquids (ethanol, coffee, water, ammonia and methyl ethyl ketone (M EK) was tested according to the standard method UNI EN 12720:2013. The test duration was 1 hour or 16 hours. For each sample a score from 1 (=fi I m completely damaged) to 5 (=no visible damage) is assigned.
The following examples and comparative experiments were prepared and coatings were obtained and tested. Example 1
Comparative example 1 is an aqueous polyurethane dispersion.
220 g (0.22 mol) of pTHFIOOO (polytetrahydrofuran having a molecular weight of 1000 g/mol) and 10.8 g of DM BA (0.0728 mol) are charged in a reactor vessel equipped with thermometer, stirrer and condenser, under nitrogen atmosphere at room temperature. 117.17 g of IPDI (0.527 mol) are added under stirring and the mixture is stirred for 10 minutes at 40°C. The reaction mixture is then heated up at 70°C and the reaction is carried out at 70°C until the residual content of NCO group in the prepolymer is 5.94%. The titration of the residual isocyanate group has been determined in this and in all the other examples according to the method ASTM D2572.
Once reached the required value of NCO groups, the prepolymer is cooled down at 65°C and triethylamine (TEA) is added under stirring to partially or fully neutralize the carboxylic groups present in the prepolymer backbone.
300 g of the neutralised prepolymer are dispersed in 490 g of demineralised water under vigorous stirring in presence of 5 g of a surfactant (ethoxylated linear alcohol C10-C16, 8 moles of ethoxy groups). After prepolymer is dispersed, stirring is continued for 5 minutes, after which 33.11 g of a 15.4% hydrazine solution and 9.94 g of 2-[(2- aminoethyl)amino]ethanesulfonic acid are added to provide the chain extended polyurethane dispersion at a temperature below 35°C.
The dispersion is thickened with 35 g of SIPACRIL 2723 OF (acrylic thickener commercially available from Lamberti spa) previously diluted in water 1:4 and filtered with a 150 pm canvas and brought to a dry content of 32%. The final pH is around 7.8 and the viscosity is 958 cps. The dispersion has a D (0.5) mean particle size of 4.9 pm and D (0.9) mean particle size of 11.6 pm. Example 2
Comparative example 2 is an 80/20 urethane/vinyl modification of Comparative example 1. A methylmethacrylate monomer is polymerised in the presence of the polyurethane dispersion prepared in the Comparative Example 1.
390 g of the polyurethane dispersion prepared in the Comparative Example 1 are charged in a reactor vessel equipped with thermometer, stirrer and condenser, at room temperature and 49 g of demineralized water are added. 32 g of methylmethacrylate are added dropwise to the mixture under stirring and the temperature is increased till 50°C, under nitrogen atmosphere.
The radical polymerization is initiated by the addition of 0.350 g of tert-butyl hydroperoxide and 0.350 g of Bruggolite® E28 (formaldehyde free sodium salt of an organic sulfinic acid derivative, commercially available from L. Bruggemann GmbH & Co. KG) simultaneously. Then 20 g of demineralized water are added.
The resulting urethane/acrylic hybrid dispersion is filtered with a 150 pm canvas and brought to a dry content of 31 % and has a pH around 8.2 and a viscosity of 472 cps. The dispersion has a D (0.5) mean particle size of 5.1 pm and D (0.9) mean particle size of 13.0 pm. Example 3
Comparative example 3 is an 80/20 urethane/vinyl modification of Comparative Example 1, with an internal crosslinking of the vinyl polymer. Methylmethacrylate and trimethylolpropane triacrylate monomers are polymerised in the presence of the polyurethane dispersion prepared in the Comparative Example 1.
390 g of the polyurethane dispersion prepared in the Comparative Example 1 are charged in a reactor vessel equipped with thermometer, stirrer and condenser, at room temperature and 49 g of demineralized water are added. 24 g of methylmethacrylate and 8 g of trimethylolpropane triacrylate are added dropwise to the mixture under stirring and the temperature is increased till 50°C, under nitrogen atmosphere.
The radical polymerization is initiated by the addition of 0.350 g of tert-butyl hydroperoxide and 0.350 g of Bruggolite® E28 (formaldehyde free sodium salt of an organic sulfinic acid derivative, commercially available from L. Bruggemann GmbH & Co. KG) simultaneously. Then 20 g of demineralized water are added.
The resulting urethane/acrylic Hybrid dispersion is filtered with a 150 pm canvas and brought to a dry content of 31.3% and has a pH around 7.9 and a viscosity of 343 cps. The dispersion has a D (0.5) mean particle size of 6.0 pm and D (0.9) mean particle size of 16.3 pm.
Example 4 (inve Example 4 is an 80/20 urethane/vinyl self-crosslinking modification of Comparative Example 1. Methylmethacrylate and diacetonacrylamide monomers are polymerised in the presence of the polyurethane dispersion prepared in the Comparative Example 1.
250 g of the polyurethane dispersion prepared in the Comparative Example 1 are charged in a reactor vessel equipped with thermometer, stirrer and condenser, at room temperature and 31 g of demineralized water are added. Then 2.5 g of diacetonacrylamide are added and the mixture is left stirring at room temperature for 10 minutes. 18 g of methylmethacrylate are added dropwise to the mixture under stirring and the temperature is increased till 50°C, under nitrogen atmosphere.
The radical polymerization is initiated by the addition of 0.245 g of tert-butyl hydroperoxide and 0.230 g of Bruggolite® E28 (formaldehyde free sodium salt of an organic sulfinic acid derivative, commercially available from L. Bruggemann GmbH & Co. KG) simultaneously. Than 0.643 g of adipic acid dihydrazide in 13 g of demineralized water are added.
The resulting self-crosslinking urethane/acrylic hybrid dispersion is filtered with a 150 pm canvas and brought to a dry content of 31.3% and has a pH around 7.9 and a viscosity of 343 cps. The dispersion has a D (0.5) mean particle size of 4.5 pm and D (0.9) mean particle size of 14.2 pm.
Performance tests
The results of the performance tests for Comparative Examples 1, 2, 3 and Example 4 are reported in Table 1. Table 1
*Comparative
The results reported in Table 1 show that the aqueous self-crosslinking coating composition from Example 4 has both excellent low gloss properties and overall improved mechanical properties respect to the aqueous coating compositions from
Comparative Examples 1, 2 and 3. In addition, for the aqueous self-crosslinking coating composition from Example 4 the improvement of the mechanical properties is achieved without increasing the hardness of the film obtained, as it can be observed from the Kbnig hardness values reported in Table 1.