AQUEOUS MIXTURE OF RHEOLOGY MODIFIER AND AMINOSILANE

Abstract

The present invention is a composition comprising an aqueous mixture of a neutralized or partially neutralized aminosilane and an associative thickener, wherein the mixture has a pH less than 10.2. The mixture is beneficial as an easy-to-use paint additive that provides stain removal, stain blocking, and corrosion resistance for low-VOC paint coatings.

Description

AQUEOUS MIXTURE OF RHEOLOGY MODIFIER AND AMINOSILANE nofre Ln / zznz / E / YiAi BACKGROUND OF THE INVENTION The present invention provides an aqueous coating composition comprising an acid-modified mixture of a hydrophobically modified alkyleneurethane oxide rheology modifier and an aminosilane. The composition is useful for providing hydrophilic stain removal performance and maintaining film appearance in the final dry coating. Aminosilanes are a class of additives used in latex paints to improve adhesion, stain blocking, and corrosion resistance, among other properties. However, when exposed to water, aminosilanes hydrolyze and condense to form polymeric siloxane species within minutes. Furthermore, these reaction products are polycationic in the pH range of latex paints, thus causing flocculation of anionally stabilized latex. Flocculation can be mitigated by diluting the aminosilane in an organic solvent before addition; however, solvents are impractical for low-VOC aqueous systems. Alternatively, the paint must be carefully formulated to avoid flocculation, often at the expense of other properties. Therefore, it would be Ref. 339581 It is beneficial to have a simple and widely applicable method for adding an aminosilane to a low VOC latex paint to provide formulators with access to improved performance. BRIEF DESCRIPTION OF THE INVENTION In a first aspect, the present invention is a composition comprising an aqueous mixture of a) a neutralized or partially neutralized aminosilane and b) an associative thickener having a water-soluble polymeric backbone with terminal or internal hydrophobic groups or both; wherein the weight ratio of the neutralized or partially neutralized aminosilane to the associative thickener is in the range of 1:30 to 5:1, and wherein the composition has a pH less than 10.2. In a second aspect, the present invention is a method comprising the step of contacting an aqueous mixture of a neutralized or partially neutralized aminosilane and an associative thickener comprising a water-soluble polymer backbone with terminal or internal hydrophobic groups, or both, with a prepaint to produce a composition having a concentration of the neutralized or partially neutralized aminosilane in the range of 0.05 to 5 percent by weight, and a concentration of the associative thickener in the range of 0.2 to 10 percent by weight. The composition of the present invention is useful for imparting thickening to a coating composition and improving stain removal from coatings prepared from the composition. DETAILED DESCRIPTION OF THE INVENTION In a first aspect, the present invention is a composition comprising an aqueous mixture of a) a neutralized or partially neutralized aminosilane and b) an associative thickener having a water-soluble polymeric backbone with terminal or internal hydrophobic groups or both; wherein the weight ratio of the neutralized or partially neutralized aminosilane to the associative thickener is in the range of 1:30 to 5:1, and wherein the composition has a pH less than 10.2. Aminosilane is a compound containing a primary, secondary, or tertiary amino group, or a quaternary ammonium group, separated by 2 to 6 carbon atoms, preferably 3 carbon atoms, from a Si-O group or a group hydrolyzable to a Si-O group (such as a SiH₂O₅SiCl₂ group). Most preferably, aminosilane is illustrated by the following structure I: R1 R nofre Ln / zznz / E / YiAi where each R is independently H, C1-C3 alkyl, I phenyl, or 2-aminoethyl; R1 is C1-C3 alkyl or C(O)CH3,· and each R2 is independently H, C1-C3 alkyl, C1-C3 alkoxy or 0C(O)CH3. The aminosilane can also be a hydrolyzed product of the compound of structure I. Examples of suitable aminosilanes include N-methylaminopropyltrimethoxysilane, W-2-aminoethyl-3-aminopropylmethyldimethoxysilane, aminopropyldimethylethoxysilane, 2V-2-aminoethyl-3-aminopropyltrimethoxysilane, N-3-aminopropylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and N,V-dimethylaminopropyltrimethoxysilane, as well as hydrolyzed products of these. A preferred aminosilane is prehydrolyzed N-2-aminoethyl-1,3-aminopropyltrimethoxysilane, which is the reaction product of N-2-aminoethyl-3-aminopropyltrimethoxysilane and water. Examples of suitable backbones for associative thickeners include polyether, polymethacrylamide, polysaccharide, or polyvinyl backbones, preferably a polyether backbone. Most preferably, the associative thickener is a hydrophobically modified alkylene-urethane oxide polymer, most preferably a hydrophobically modified ethylene-urethane oxide polymer (a HEUR). The hydrophobically modified alkylene-urethane oxide polymer is advantageously prepared by contacting, under reactive conditions, a diisocyanate, a water-soluble polyalkylene glycol, and an amine or alcohol terminating agent. Water-soluble polyalkylene glycol refers to water-soluble polyethylene glycols, water-soluble polyethylene oxide / polypropylene glycol copolymers, and water-soluble polyethylene oxide / polybutylene glycol copolymers. The composition is advantageously prepared by first contacting an acid with an aqueous solution of the associative thickener, preferably HEUR, and then contacting the acidified associative thickener with the aminosilane to produce a mixture having a pH less than 10.2, preferably less than 10.0, and more preferably less than 9.7; and preferably greater than 6.0, more preferably greater than 7.0, and most preferably greater than 8.0. The concentration of the associative thickener in the aqueous solution is preferably in the range of 5, more preferably 10, and most preferably 15 percent by weight, to 35, more preferably 30, and most preferably 25 percent by weight, based on the weight of the associative thickener and water in the mixture. The concentration of the neutralized or partially neutralized aminosilane in the aqueous mixture is preferably in the range of 0.2, more preferably 0.5, with a higher preference of 1, and with a maximum preference of 2 percent by weight to 20, with a higher preference of 15, and with a maximum preference of 10 percent by weight, based on the weight of the neutralized or partially neutralized aminosilane and water in the mixture. The mixture of the associative thickener, preferably HEUR, and the neutralized or partially neutralized aminosilane is contacted with a prepaint comprising a stable aqueous dispersion of polymeric particles (a latex), a coalescing agent, a defoamer, and a surfactant. The prepaint may also comprise one or more additional components, including an opacifying pigment, an extender, a dispersant, a cosolvent, and another thickener. The polymeric particles of the latex preferably have an average particle size z measured by dynamic light scattering in the range of 50 nm, with a greater preference for 100 nm, to 500 nm, with a greater preference for 300 nm. A preferred opacifying pigment is TiO2, and extenders include inorganic extenders such as calcium carbonate and nepheline syenite, and organic opacifying pigment particles, such as the opaque polymer ROPAQUE™ Ultra E (a trademark of The Dow Chemical Company or its affiliates). In another aspect, the present invention is a method comprising the step of contacting an aqueous mixture of a neutralized or partially neutralized aminosilane and an associative thickener, preferably a hydrophobically modified alkylene-urethane oxide polymer, with a prepaint to produce a paint composition having a concentration of the neutralized or partially neutralized aminosilane in the range of 0.05 to 5 percent by weight, based on the weight of the paint, and a concentration of the associative thickener in the range of 0.5 to 10 percent by weight, based on the weight of the paint. The composition of the present invention is useful in paint compositions for improving the stain removal of coatings prepared from paints. Examples In the following Examples and Table, ACRYSOL, ACUMER, TAMOL, DOWSIL and RHOPLEX are trademarks of The Dow Chemical Company or its affiliates. Example 1: Preparation of HEUR-aminosilane mixture treated with acid ACRYSOL™ RM-3030 rheology modifier (76.0 g, 20.5% active in water) and ACUMER™ 9932 polyacrylic acid (5.0 g) were added to a container and mixed with a Flacktek mixer at 2900 rpm for 30 s. Pre-hydrolyzed N-2-aminoethyl-3-aminopropyltrimethoxysilane (19 g, 27% active in water) was added to the container, followed by further mixing at 2900 rpm for 30 s. The pH of the mixture was 9.5. nofre Ln / zznz / E / YiAi Example 2: Preparation of HEUR-aminosilane mixture treated with acid The acid-treated mixture was prepared substantially as described in Example 1, except that 7.6 g of ACUMER™ 9932 polyacrylic acid was used. The pH of the mixture was 8.8. Example 3: Preparation of HEUR-aminosilane mixture treated with acid The acid-treated mixture was prepared substantially as described in Example 1, except that 3.8 g of ACUMER™ 9932 polyacrylic acid was used. The pH of the mixture was 10.0. Comparative example 1: preparation of HEURaminosilane mixture To a container, ACRYSOL™ RM-3030 rheology modifier (76.0 g) and pre-hydrolyzed 2-aminoethyl-3-aminopropyltrimethoxysilane (19 g) were added and mixed at 2900 rpm for 30 s. The pH of the mixture was 10.8. Comparative example 2: preparation of HEURaminosilane mixture treated with acid The acid-treated mixture was prepared substantially as described in Example 1, except that 2.3 g of ACUMER™ 9932 polyacrylic acid was used. The pH of the mixture was 10.3. A pre-paint formulation was prepared as shown in Table 1: Table 1- Nofrr ίη / ζζηζ / Ε / γίΛΐ prepaint formulation Material Name Weight (g) Water 96.00 Propylene Glycol 5.30 Dispersant TAMOL™ 2011 4.00 Antifoam DOWSIL™ 8590 0.50 Acrylic Emulsion RHOPLEX VSR-1049LOE 608.00 Coalescing Agent Texanol 6.10 Surfactant DOWSIL™ 67 2.00 Water 140.70 In the first series of experiments, a visual cleanliness check was performed by adding mixtures of the sample and comparison samples to separate precoats (100 g), then preparing coatings of each sample using a 3-mil sweep applicator. Table 2 illustrates the results of a visual cleanliness check for each sample: Table 2 - Visual control of coating cleanliness of samples in a pH range Example No. pH Cleaning Check Result 1 9.5 Clean / Small amount of grit 2 8.8 Clean 3 10.0 Small amount of grit Comp. 1 10.8 Large amount of grit Comp. 2 10.3 Medium amount of grit The results illustrated in Table 2 show the great importance of acidifying the HEUR-aminosilane mixture to reduce or eliminate grit. In a separate set of experiments, the order of addition of the components was examined. Four paints were prepared as described below: Paint No. 1 was prepared by adding a portion of the mixture from Example 1 (4.60 g) to a container holding pre-paint (100 g) and mixing the contents with a laboratory top mixer at 500 rpm for 10 min. Paint No. 2 was prepared using the same procedure used to prepare Paint No. 1, except that a mixture from Comparative Example 1 (4.4 g) was used. Paint No. 3 was prepared by adding the rheology modifier (3.50 g) to a container holding the prepaint (100 g). The contents were mixed at 500 rpm for 5 min, after which polyacrylic acid (0.23 g) was added to the container and the contents were mixed for another 5 min. Then, aminosilane (0.88 g) was added to the container and the contents were mixed for another 5 min. Paint No. 4 was prepared by adding the rheology modifier (3.50 g) to a container containing the pre-paint (100 g). The contents were mixed at 500 rpm for 5 min, after which aminosilane (0.88 g) was added to the container and the contents were mixed for another 5 minutes. nofre Ln / zznz / E / YiAi The films were applied using a 3-mil sweep applicator. The film appearance (clarity and gloss) was recorded and measured after each coating had fully cured. Table 3 illustrates the gloss and film appearance for coatings prepared using Paints 1-4. nPfrP ίη / 77Π7 / E / YΙΛΙ Property Paint No. 1 Paint No. 2 Paint No. 3 Paint No. 4 pH 9.0 9.4 9.1 9.6 Gloss at 20° 47.5 7.5 4.1 3.7 Gloss at 60° 77.1 29.6 24.4 21.0 Gloss at 85° 92.4 32.9 37.0 28.2 Film Appearance Clear Abundant amount of grit Fine and dispersed grit Fine and dispersed grit The results demonstrate the significant benefit of adding a pre-neutralized HEUR-aminosilane blend. Adding the components separately resulted in an inferior film appearance and noticeably lower gloss at all measured angles. Adding a blend of unneutralized HEUR-aminosilane resulted in a coating with a film appearance containing a large amount of grit. The composition of the present invention provides a simple method for adding an aminosilane to a paint to provide stain removal, stain blocking, and corrosion resistance benefits without the use of organic solvents containing VOCs. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, the following claims are claimed as property:

1. A composition characterized in that it comprises an aqueous mixture of a) a neutralized or partially neutralized aminosilane and b) an associative thickener having a water-soluble polymeric backbone with terminal or internal hydrophobic groups or both; wherein the weight ratio of the neutralized or partially neutralized aminosilane to the associative thickener is in the range of 1:30 to 5:1, and wherein the composition has a pH less than 10.

2.

2. The composition according to claim 1, characterized in that the associative thickener is a hydrophobically modified alkylene-urethane oxide polymer, and the aminosilane is represented by the following structure I: R1 R nobr Ln / zznz / E / YiAi I wherein each R is independently H, C1-C3 alkyl, phenyl, or 2-aminoethyl; R1 is C1-C3 alkyl or C(O)CH3,· and each R2 is independently H, C1-C3 alkyl, C1-C3 alkoxy or OC(O)CH3, or a hydrolyzed product of the compound of structure I.

3. The composition according to claim 2, characterized in that the hydrophobically modified alkylene oxide-urethane polymer is a hydrophobically modified ethylene oxide-urethane (HEUR) polymer, and the concentration of the neutralized or partially neutralized aminosilane in the aqueous mixture is in the range of 0.5 to 20 percent by weight, based on the weight of the neutralized or partially neutralized aminosilane and water in the mixture, wherein the concentration of the HEUR in the aqueous mixture is in the range of 10 to 30 percent by weight, based on the weight of the HEUR and water in the mixture; and wherein the composition has a pH in the range of 6.0 to 10.

0.

4. The composition according to claim 3, characterized in that it has a pH in the range of 8.0 to 9.7, characterized in that the aminosilane is N-methylaminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropyldimethoxysilane, aminopropyldimethylethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-3-aminopropyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane or N,N-dimethylaminopropyltrimethoxysilane, or a non-hydrolyzed product thereof, wherein the aminosilane is neutralized or partially neutralized with polyacrylic acid.

5. The composition according to claim 4, characterized in that the aminosilane is a hydrolyzed N-2-aminoethyl-1-3-aminopropy-1-rimethoxy silane.

6. A method characterized in that it comprises the step of contacting with a prepaint an aqueous mixture of a neutralized or partially neutralized aminosilane and an associative thickener comprising a water-soluble polymer backbone with terminal or internal hydrophobic groups or both, characterized in that the mixture has a pH less than 10.2, and the prepaint comprises a stable aqueous dispersion of polymer particles, a coalescing agent, a defoamer and a surfactant.

7. The method according to claim 6, characterized in that the weight-to-weight ratio of the neutralized or partially neutralized aminosilane to the associative thickener is in the range of 1:30 to 5:1, wherein the associative thickener is a hydrophobically modified alkylene-urethane oxide polymer.

8. The method according to claim 7, characterized in that the mixture has a pH in the range of 6.0 to 10.0 and the aminosilane is represented by the following structure I: R1 R nobe I, wherein each R is independently H, C1C3 alkyl, phenyl, or 2-aminoethyl; R1 is C1-C3 alkyl or C(O)CH3; and each R2 is independently H, C1-C3 alkyl, C1-C3 alkoxy or OC(O)CH3, or a hydrolyzed product of the compound of structure I; wherein the hydrophobically modified alkylurea oxide polymer is a hydrophobically modified ethylene oxide-urethane polymer.

9. The method according to claim 8, characterized in that the aminosilane is a pre-hydrolyzed 2-aminoethyl-3-aminopropyltrimethoxysilane, and wherein the pre-paint further comprises one or more additional components selected from the group consisting of T1O2, an extender, a dispersant, and a co-solvent.

10. A method for preparing the composition according to claim 1, characterized in that it comprises the steps of contacting an acid with an aqueous solution of the associative thickener, then contacting the acidified associative thickener with the aminosilane to produce the mixture.