Aqueous acrylic emulsion polymer composition

An aqueous acrylic emulsion polymer including, as copolymerized units, 70 to 99.5% by weight, based on dry polymer weight, monoethylenically unsaturated nonionic (meth)acrylic monomer and from 0.3 to 10% by weight, based on dry polymer weight, monoethylenically unsaturated acid monomer, wherein at least 40% by weight, based on dry polymer weight, of the emulsion polymer is formed by redox polymerization in the presence of 0.001 to 0.05 moles chain transfer agent per kg dry polymer weight is provided. An aqueous coating composition including the acrylic emulsion polymer and a method for improving the scrub resistance of a dry coating including applying the aqueous coating composition to a substrate; and drying, or allowing to dry, the aqueous coating composition are also provided.

COMPARATIVE EXAMPLES A-D 
 Preparation of Emulsion Polymers The monomers for each example (Table CE-1) were combined with 455 g DI water, 6.9 g sodium carbonate and 30.5 g SLS and emulsified with stirring. 5.2 g SLS and 400 g DI water were charged to a 3 L multi-neck flask fitted with mechanical stirring. The flask contents were heated to 85° C. under nitrogen. To the stirred kettle contents were added 35 g monomer emulsion followed by 3.5 g APS in 10 g DI water. 30 g of a 50% solution of ureido methacrylate was added to the remainder of the monomer emulsion and gradual addition of the monomer emulsion was subsequently initiated. Total addition time for monomer emulsion was 90-100 minutes. Reactor temperature was maintained at 83° C. throughout the polymerization. 20 g DI water was used to rinse the emulsion feed line to the reactor. After completion of the monomer emulsion addition the reactor was cooled to 60° C. 10 ppm ferrous sulfate, 1 g t-butyl hydroperoxide and 0.5 g D-Isoascorbic acid in aqueous solutions were added. The polymer emulsion was neutralized to pH 9-10 with ammonium hydroxide. 3 TABLE CE-1 Monomer Charges for Comparative Examples A-D. EXAMPLE BA MAA MMA n-DDM Comp. A 480 g 20 g 485 g 0 Comp. B 480 g 20 g 485 g 1.25 g Comp. C 480 g 20 g 485 g 2.5 g Comp. D 480 g 20 g 485 g 5 g 4 TABLE CE-2 Physical Properties for Comparative Examples A-D. SOLIDS PARTICLE VISCOSITY EXAMPLE (%) SIZE (nm) pH (cps) Comp. A 50.1 127 9.7 1284 Comp. B 50.4 119 10.0 1464 Comp. C 50.3 128 9.7 1440 Comp. D 49.2 129 9.8 1308 Notes: Particle Size determined by Brookhaven Instruments BI-90 Particle Sizer Total Solids determined by weight loss after 30-45 minutes at 150° C. Viscosity determined using Brookfield LVTD Viscometer &commat; 60 rpm 
 EXAMPLES 1-3 AND COMPARATIVE EXAMPLE E 
 Preparation of Acrylic Emulsion Polymers The monomers for each example (Table 1-1) were combined with 400 g DI water, 6.9 g sodium carbonate and 30.5 g SLS and emulsified with stirring. 5.2 g SLS and 380 g DI water were charged to a 3 L multi-neck flask fitted with mechanical stirring. The flask contents were heated to 65° C. under nitrogen. To the stirred kettle contents were added 35 g monomer emulsion followed by 0.02 g ferrous sulfate heptahydrate and 0.02 g tetrasodium salt of ethylenediamine-tetraacetic acid in 15.6 g DI water. Polymerization was initiated by the addition of 0.54 g APS in 8 g DI water followed by 0.27 g sodium hydrosulfite in 8 g DI water. 30 grams of a 50% solution of ureido methacrylate was added to the remainder of the monomer emulsion and gradual addition of the monomer emulsion was subsequently initiated. Separate solutions of 2.9 g APS in 50 g DI water and 1 g of D-Isoascorbic acid in 50 g DI water were fed concurrently with the monomer emulsion. Total addition time for the three feeds was 90-100 minutes. Reactor temperature was maintained at 65° C. throughout the polymerization. 20 g DI water was used to rinse the emulsion feed line to the reactor. After completion of the monomer emulsion addition the reactor was cooled to 60° C. 10 ppm ferrous sulfate, 1 g t-butyl hydroperoxide and 0.5 g D-Isoascorbic acid in aqueous solutions were added. The polymer emulsion was neutralized to pH 9-10 with ammonium hydroxide. 5 TABLE 1-1 Monomer Charges for Examples 1-3 and Comp. E EXAMPLE BA MAA MMA n-DDM Comp. E 480 g 20 g 485 g 0 1 480 g 20 g 485 g 1.25 g 2 480 g 20 g 485 g 2.5 g 3 480 g 20 g 485 g 5 g 6 TABLE 1-2 Physical Properties for Examples 1-3 and Comp. E SOLIDS PARTICLE VISCOSITY EXAMPLE (%) SIZE (nm) pH (cps) Comp. E 49.6 164 9.3 314 1 49.4 145 9.9 207 2 49.8 162 9.5 390 3 49.5 158 9.6 428 Notes: Particle Size determined by Brookhaven Instruments BI-90 Particle Sizer Total Solids determined by weight loss after 30-45 minutes at 150° C. Viscosity determined using Brookfield LVTD Viscometer &commat; 60 rpm 
 EXAMPLE 4 
 Formation of Aqueous Coating Compositions All aqueous coating compositions were made using the following formulation: 7 Material Grams Propylene Glycol 18.2 Pigment Dispersant (TAMOL ™ 731) 6.45 Defoamer (FOAMASTER ™ VL) 0.5 Titanium dioxide (TI-PURE ™ R-900) 126.50 Water 31.0 The preceding ingredients were mixed in a high shear Cowles mixer and then the following ingredients were added with low shear mixing. 8 Emulsion Polymer 232.29 Opaque Polymer (ROPAQUE ™ ULTRA) 14.40 Coalescent (TEXANOL ™) 4.83 Defoamer (FOAMASTER ™ VL) 0.5 Rheology modifier (ACRYSOL ™ RM-1020) 14.2 Rheology modifier (ACRYSOL ™ RM-825) 0.25 Water 77.79 Note: TAMOL, ROPAQUE and ACRYSOL are trademarks of Rohm and Haas Company. FOAMASTER is a trademark of Henkel Corp. TI-PURE is a trademark of EI DuPont de Nemours. Co. TEXANOL is a trade mark of Eastman Chemical Co. These aqueous coating compositions contain 4.4% VOC by weight based on the total weight of the coating composition. 
 EXAMPLE 5 
 Evaluation of Scrub Resistance of Dry Coatings Aqueous coating compositions according to Example 4 were prepared as with the emulsion polymers of Examples 1-3 and Comparative Examples A-E. The dry film of each aqueous coating composition was evaluated for scrub resistance; results are presented in Table 5-1. 9 TABLE 5.1 Scrub resistance results Emulsion Comp. Comp. Comp. Comp. Comp. Sample A B C D E 1 2 3 Polymer thermal thermal thermal thermal redox redox redox redox Process CTA Level 0.00% 0.125% 0.25% 0.50% 0.00% 0.125% 0.25% 0.50% Scrub 100 123 94 95 123 155 167 117 Resistance (as % of Comp. A) The dry film of the aqueous coating composition containing the emulsion polymer of Example 1 of this invention provides scrub resistance superior to that of the corresponding composition containing the emulsion polymer of Comparative Example B. The dry film of the aqueous coating composition containing the emulsion polymer of Example 2 of this invention provides scrub resistance superior to that of the corresponding composition of Comparative Example C. The dry film of aqueous coating composition containing the emulsion polymer of Example 3 of this invention provides scrub resistance superior to that of the corresponding composition of Comparative Example D. Dry films of preferred aqueous coating compositions containing the emulsion polymer of Examples 1 and 2 of this invention provide scrub resistance substantially superior to that of compositions of Comparative Examples A-E. 
 EXAMPLE 6 
 Evaluation of Alkali Resistance-Gloss Loss Aqueous coating compositions were prepared according to Example 4 incorporating the aqueous emulsion polymers of Examples 1 and 2, and Comparative Example F, a p(74.8 VA/24.8 BA/0.4 acid) emulsion polymer. A dry film of the three compositions was prepared on a single black vinyl chart and the Alkali Resistance-Gloss Loss of the film was determined. Results are presented in Table 6-1. 10 TABLE 6.1 Evaluation of alkali resistance 20° Gloss 60° Gloss Before After Tide Gloss Before After Tide Gloss Tide Treatment Treatment Change (%) Tide Treatment Treatment Change (%) Comp. Ex. F 29.6 25.5 −13.9 68.5 64.0 −6.6 Example 1 28.0 28.9 3.2 66.1 67.7 2.4 Example 2 27.9 29.3 5.0 66.4 68.1 2.6 The dry films of aqueous coating compositions containing aqueous acrylic emulsion polymers of Examples 1 and 2 of this invention exhibit no gloss loss and thereby pass the test. 
 EXAMPLE 7 
 Evaluation of Hydrolytic Stability Aqueous coating compositions were prepared according to Example 4 incorporating the aqueous emulsion polymers of Examples 1 and 2, and Comparative Example F, a p(74.8 VA/24.8 BA/0.4 acid) emulsion polymer. A dry film of the three compositions was prepared on a single black vinyl chart and the Hydrolytic Stability was determined. Results are presented in Table 7-1. 11 TABLE 7.1 Evaluation of hydrolytic stability Weight Loss of Whole Sample Strip Before After NaOH NaOH Weight Visual Assessment of Treatment Treatment Loss the Coating Immersed Sample (g) (g) (%) in NaOH Comp. Ex. F 0.61 0.51 16% Completely Dissolved Example 1 0.63 0.63 0% Unchanged Example 2 0.58 0.58 0% Unchanged The dry films of aqueous coating compositions containing aqueous acrylic emulsion polymers of Examples 1 and 2 of this invention exhibit no dissolution and thereby pass the test. 
 EXAMPLE 8 AND COMPARATIVE EXAMPLE G 
 Preparation of Acrylic Emulsion Polymers The monomers for Comp. Ex. G (Table 8-1 ) were combined with 455 g DI water, 6.9 g sodium carbonate and 30.5 g SLS and emulsified with stirring. 5.2 g SLS and 400 g DI water were charged to a 3 L multi-neck flask fitted with mechanical stirring. The flask contents were heated to 85° C. under nitrogen. To the stirred kettle contents were added 35 g monomer emulsion followed by 3.5 g APS in 10 g DI water. 30 g of a 50% solution of ureido methacrylate was added to the remainder of the monomer emulsion and gradual addition of the monomer emulsion was subsequently initiated. Total addition time for monomer emulsion was 90-100 minutes. Reactor temperature was maintained at 83° C. throughout the polymerization. 20 g DI water was used to rinse the emulsion feed line to the reactor. After completion of the monomer emulsion addition the reactor was cooled to 60° C. 10 ppm ferrous sulfate, 1 g t-butyl hydroperoxide and 0.5 g D-Isoascorbic acid in aqueous solutions were added. The polymer emulsion was neutralized to pH 9-10 with ammonium hydroxide. The monomers for Example 8 (Table 8-1 ) were combined with 400 g DI water, 6.9 g sodium carbonate and 30.5 g SLS and emulsified with stirring. 5.2 g SLS and 380 g DI water were charged to a 3 L multi-neck flask fitted with mechanical stirring. The flask contents were heated to 65° C. under nitrogen. To the stirred kettle contents were added 35 g monomer emulsion followed by 0.02 g ferrous sulfate heptahydrate and 0.02 g tetrasodium salt of ethylenediamine-tetraacetic acid in 15.6 g DI water. Polymerization was initiated by the addition of 0.54 g APS in 8 g DI water followed by 0.27 g sodium hydrosulfite in 8 g DI water. 30 g of a 50% solution of ureido methacrylate was added to the remainder of the monomer emulsion and gradual addition of the monomer emulsion was subsequently initiated. Separate solutions of 2.9 g APS in 50 g DI water and 1 g of D-Isoascorbic acid in 50 g DI water were fed concurrently with the monomer emulsion. Total addition time for the three feeds was 90-100 minutes. Reactor temperature was maintained at 65° C. throughout the polymerization. 20 g DI water was used to rinse the emulsion feed line to the reactor. After completion of the monomer emulsion addition the reactor was cooled to 60° C. 10 ppm ferrous sulfate, 1 g t-butyl hydroperoxide and 0.5 g D-Isoascorbic acid in aqueous solutions were added. The polymer emulsion was neutralized to pH 9-10 with ammonium hydroxide. 12 TABLE 8-1 Monomer Charges Emulsion Polymer BA MMA MAA n-DDM Comp. Ex. G 600 g 365 g 20 g 0 Example 8 600 g 365 g 20 g 1.25 
 EXAMPLE 9 
 Formation of Aqueous Coating Compositions The Grind Premix was made using ingredients in the ratios in Table 9.1 and mixed on a high speed Cowles disperser for 20 minutes. A portion of the Grind Premix that contained the ingredients in the amounts listed in Table 1 was transferred to another container for each paint and the Let Down ingredients were added under low speed mixing in the order given. The final pigment volume concentration for each paint was 19% and the volume solids was 36%. The VOC of the aqueous coating compositions is 0.1% by weight based on the total weight of the coating composition. 13 TABLE 9.1. Aqueous coating composition Comp. Example H Example 9 Material Weight (g) Weight (g) Grind Premix TAMOL ™ 731A 6.04 6.04 TEGO ™ Foamex 810 0.49 0.49 SURFYNOL ™ CT-111 0.97 0.97 TI-PURE ™ R-706 114.19 114.19 Water 26.89 26.89 Let Down Water 10 10 Emul. Pol. Comp. G (50.2% Solids) 269.03 0 Emul. Pol. Ex. 8 (49.5% Solids) 0 275.57 SURFYNOL ™ CT-111 .5 .5 ACRYSOL ™ RM-2020NPR 14.2 11.5 ACRYSOL ™ RM-8W 1.9 2.70 Water 73.11 68.18 Note: SURFYNOL is a trademark of Air Products and Chemicals Inc; TEGO is a trademark of Tego Chemie Service. A scrub test was run on two specimens of each example following the procedure outlined in ASTM test method D2486-00 with the following exceptions: a Bird 3 mil film applicator was used to draw down the paints, and the test specimens were held down on each side of the shim midway between the shim and the end of the specimen directly by clamping rather than by means of a gasketed frame as outlined in ASTM D2486. Method A of the test method was otherwise followed. The data obtained is given in Table 9.2. 14 TABLE 9.2 Scrub Resistance Test Results, Cycles to Fail Coating Average of 2 Specimens Comparative Example H 474 Example 9 1860 The dry film of the aqueous coating composition containing the emulsion polymer of Example 8 of this invention provides scrub resistance superior to that of the corresponding composition containing the emulsion polymer of Comparative Example H.