AQUEOUS POLYMER DISPERSION AND AQUEOUS COATING COMPOSITION COMPRISING THE SAME

Abstract

An aqueous polymer dispersion and an aqueous coating composition comprising the aqueous polymer dispersion, and the aqueous coating composition providing the resulting coatings with good anti-corrosion property.

Claims

1. An aqueous polymer dispersion, wherein the polymer comprises as polymerized units, based on the weight of the polymer, (a) from 0.5% to 3.2% by weight of a phosphorous-containing acid monomer, (b) from 10% to 50% by weight of a cycloalkyl (meth)acrylate, (c) from 0.3% to 1.2% by weight of a ureido monomer, (d) from 25% to 60% by weight of a soft monomer, and (e) a hard monomer; wherein the polymer has a weight average molecular weight of 110,000 or less.

2. The aqueous polymer dispersion of claim 1, wherein the polymer has a glass transition temperature of from 0 C. to 60 C.

3. The aqueous polymer dispersion of claim 1 wherein the polymer has a weight average molecular weight of from 20,000 to 80,000.

4. The aqueous polymer dispersion of claim 1, wherein the polymer comprises as polymerized units, based on the weight of the polymer, from 0.7% to 2.5% by weight of the phosphorous-containing acid monomer.

5. The aqueous polymer dispersion of claim 1, wherein the phosphorous-containing acid monomer is selected from phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, or mixtures thereof.

6. The aqueous polymer dispersion of claim 1, wherein the polymer comprises as polymerized units, based on the weight of the polymer, from 0.5% to 1.0% by weight of the ureido monomer.

7. The aqueous polymer dispersion of claim 1, wherein the ureido monomer is selected from ureido methyl acrylate, ureido acrylate, or mixtures thereof.

8. The aqueous polymer dispersion of claim wherein the polymer comprises as polymerized units, based on the weight of the polymer, from 20% to 40% by weight of the cycloalkyl (meth)acrylate.

9. The aqueous polymer dispersion of claim 1 wherein the cycloalkyl (meth)acrylate is cyclohexyl methacrylate.

10. The aqueous polymer dispersion of claim 1, wherein the hard monomer is selected from styrene, methacrylic acid, acrylic acid, or mixtures thereof.

11. The aqueous polymer dispersion of claim 1 wherein the soft monomer is selected from butyl acrylate, 2-ethylhexylacrylate, lauryl acrylate, n-decyl methacrylate, isobutyl acrylate, or mixtures thereof.

12. The aqueous polymer dispersion of claim 1, wherein the polymer comprises as polymerized units, based on the weight of the polymer, (a) from 1.0% to 1.5% by weight of a phosphorous-containing acid monomer; (b) from 20% to 30% by weight of a cycloalkyl (meth)acrylate; (c) from 0.5% to 0.9% by weight of a ureido monomer; (d) from 30% to 45% by weight of a soft monomer selected from butyl acrylate, 2-ethylhexylacrylate, lauryl acrylate, or mixtures thereof; and (e) a hard monomer selected from styrene, methacrylic acid, acrylic acid, or mixtures thereof.

13. A process of preparing an aqueous polymer dispersion of claim 1, comprising: preparing the polymer in an aqueous medium by a free-radical polymerization in the presence of a chain transfer agent to form the aqueous polymer dispersion, wherein the polymer comprises as polymerized units, based on the weight of the polymer, (a) from 0.5% to 3.0% by weight of a phosphorous-containing acid monomer, (b) from 10% to 50% by weight of a cycloalkyl (meth)acrylate, (c) from 0.3% to 1.2% by weight of a ureido monomer, (d) from 30% to 60% by weight of a soft monomer, and (e) a hard monomer.

14. An aqueous coating composition comprising an aqueous polymer dispersion of claim 1 and a pigment.

Description

EXAMPLES

[0058] Some embodiments of the invention will now be described in the following Examples, wherein all parts and percentages are by weight unless otherwise specified.

[0059] The following materials are used in preparing aqueous polymer dispersions in the examples:

[0060] Styrene (ST), 2-ethylhexyl acrylate (EHA), methacrylic acid (MAA), and methyl methacrylate (MMA) are all available from Huayi Chemicals.

[0061] Cyclohexy methacrylate (CHMA) is available from BASF.

[0062] Butyl acrylate (BA), phosphoethyl methacrylate (PEM), and methacrylo ethylethylene urea (MEU) are all available from The Dow Chemical Company.

[0063] n-Dodecyl mercaptan (nDDM) is used as a chain transfer agent.

[0064] RHODAFAC RS-610, available from Solvay, is used as a phosphate surfactant.

[0065] DISPONIL FES-32 is a surfactant available from BASF.

[0066] KATHON Preservatives, available from The Dow Chemical Company, is an isothiazolone and used as a biocide (KATHON is a trademark of The Dow Chemical Company).

[0067] NOPCO NDW, available from San Nopco, is a mineral oil and used as a defoamer.

[0068] The following standard analytical equipment and methods are used in the Examples.

[0069] Panels were prepared by drawing down coating compositions on a cold rolled steel substrate and dried for 7 days in a controlled temperature room at 23 C./50% relative humidity to give panels with a dry film thickness of 40-50 m. Properties (anti-corrosion, dry and wet adhesion, and water resistance properties) of the obtained panels were evaluated according to the following test methods.

Salt-Spray Test

[0070] Corrosion resistance was tested by exposure of the as prepared panels to a salt spray environment (5% sodium chloride fog) in accordance with the ASTM B-117-2011 method. Exposed metal was covered with tape (3M plastic tape #471) prior to exposure. A scribe mark made with a razor blade was scratched into the bottom half of the panels immediately before exposure. Panels were exposed to the salt spray environment for 240 hours, and then removed to rate blistering and rust. The results were presented as blister/rust ratings. Blister ratings were conducted in accordance with the ASTM D714-02(2009) method and comprised a number and one or more letters. The letter is a qualitative representation of the density of bubbles, whereby F refers to few, D refers to dense, MD refers to medium dense, and D refers to dense. The number refers to the size of the blister, whereby 0 is the largest size, 10 is no blister. The bigger the number, the smaller the size of blister. Rust ratings were shown as a percentage of rust on a panel as according to the ASTM D610-2001 test method. Therefore, a result of 8F/3% rust means that there was a few amount of small blisters with 3% of the panel covered by rust. The panels with blister rating being F or better and with less than 5% rust are acceptable.

Dry and Wet Adhesion

[0071] Dry adhesion of the as prepared panels was evaluated according to the ASTM D3359-2009 method.

[0072] Wet adhesion: The as prepared panels were dipped into water at 23 C. for 24 hours. Then, the panels were taken out of water and padded dry. The films on the panels were then cross-cut and tested according to the ASTM D3359-2009 method.

[0073] Ratings for both dry adhesion and wet adhesion were shown in Table 1 as a percentage of the paint film removed, whereby 5B is the best and 0B is the worst. The panels with rating being 4B or better are acceptable.

TABLE-US-00001 TABLE 1 Percent area removed Classification 0%, none 5B Less than 5% 4B 5~15% 3B 15~35% 2B 36~65% 1B Greater than 65% 0B

Water Resistance

[0074] The as prepared panels were dipped into water and the amount of rust and blister were observed at different time. Blister ratings and rust ratings were conducted substantially the same as those described above in the salt-spray test, e.g., blister ratings and rust ratings were conducted according to the ASTM D714-02(2009) method and the ASTM D610-2001 method, respectively. The panels with water resistant rating being F or better are acceptable.

Molecular Weight

[0075] Samples were dissolved in tetrahydrofuran/fluoroacetic acid (FA) (5%) and the concentration was 2 mg/mL and filtered through 0.45 m PTFE filter prior to GPC analysis. GPC experiments (Agilent 1200 with One Mixed B columns (7.8300 mm) in tandem. 65#) were undertaken to measure molecular weights. Data were acquired and processed using Agilent Refractive Index detector (40 C.) and Agilent GPC software. Data was collected from duplicate injections. Calibration curve were PL polystyrene 1 Narrow standards with molecular weights ranging from 2329,000 to 1480 g/mol using polynom 3.sup.rd fitness. Mobile phase solvent was tetrahydrofuran. Flow rate was 1.0 mL/min, and column temperature was 40 C.

Example (Ex) 1 Aqueous Polymer Dispersion

[0076] Preparation of Monomer EmulsionRHODAFAC RS-610 surfactant (35 g, 25% active) was dissolved in deionized water (1075 g), with stirring. An emulsified monomer mixture was prepared by adding the following monomers slowly to the agitated solution: 2-EHA, ST, CHMA, MAA, MEU, and PEM.

[0077] A solution containing DISPONIL FES-32 surfactant (16.5 g, 31% active) and deionized water (455 g) was placed in a 4-necked, 5 liter round bottom flask equipped with a thermocouple, a cooling condenser and an agitator, and heated to 85 C. under nitrogen. An aqueous sodium carbonate solution (1.4 g sodium carbonate in 38 g deionized water), aqueous ammonia persulfate (APS) initiator solution (1.4 g APS in 15 g deionized water), and 4.1% of Monomer Emulsion were added to the flask. Within about 5 minutes, initiation of polymerization was confirmed by the increase of temperature by 3 C. and a change of the external appearance of the reaction mixture. After generation of heat had ended, the remainder of the Monomer Emulsion was added gradually to the flask over a period of 90 minutes, with stirring. Polymerization reaction temperature was maintained at 87-89 C. After completing the addition, the vessel that contained Monomer Emulsion and feeding pipes leading into the flask were rinsed with 30 g deionized water, and the rinse was added back to the flask. The reaction mixture was held at 85 C. for 10 minutes, and then cooled to 80 C. Catalyst t-butylhydroperoxide (t-BHP) and reductant isoascorbic acid (IAA) were added together to chase the monomers over 30 minutes. After the chaser stage, the reaction was cooled to 50 C. and then neutralized to pH 7.0-8.0 by ammonia. The reaction mixture was held at 45-50 C. for 10 minutes, and then the biocide and the defoamer were added over 10 minutes. The reaction was cooled to room temperature to obtain the aqueous polymer dispersion.

Exs 2-8 Aqueous Polymer Dispersions

[0078] The aqueous polymer dispersions were prepared according the same procedure as described above for preparing the aqueous polymer dispersion of Ex 1, based on polymer compositions given in Table 2. Molecular weight of the polymers were measured according to the test method described above and given in Table 2.

TABLE-US-00002 TABLE 2 Polymer Sample Molecular Dispersion ID Polymer Composition (weight ratio*) Weight Ex 1 818 36.0EHA/36.7ST/22.6CHMA/2.0MAA/1.5PEM/ 63,723 0.7MEU/0.5n-DDM Ex 2 820 36.5EHA/36.7ST/22.6CHMA/2.0MAA/1.0PEM/ 67,534 0.7MEU/0.5n-DDM Ex 3 822 36.5EHA/37.2ST/22.6CHMA/2.00MAA/0.50PEM/ 68,322 0.7MEU/0.5n-DDM Ex 4 824 36.5EHA/18.8ST/40.00CHMA/2.00MAA/1.5PEM/ NA 0.7MEU/0.5n-DDM Ex 5 8390 36.5EHA/34.7ST/22.6CHMA/2.00MAA/3.0PEM/ NA 1.2MEU/0.5n-DDM Ex 6 8396 36.5EHA/9.1ST/50.00CHMA/2.00MAA/1.5PEM/ 97,600 0.7MEU/0.2n-DDM Ex 7 8391 36.5EHA/48.36ST/10.00CHMA/2.00MAA/1.5PEM/ 43,210 0.7MEU/1.0n-DDM Ex 8 8383 36.5EHA/36.3ST/22.6CHMA/2.00MAA/1.5PEM/ 54,313 0.3MEU/0.8n-DDM *Numbers separated by a single slash indicates weight ratio of polymerized units of monomers in polymer

Comparative (Comp) Exs A-K Aqueous Polymer Dispersions

[0079] The aqueous polymer dispersions were prepared according the same procedure as described above for preparing the aqueous polymer dispersion of Ex 1, based on polymer compositions given in Table 3. Molecular weight of the polymers were measured according to the test method described above and given in Table 3.

TABLE-US-00003 TABLE 3 Polymer Molecular Dispersion Polymer Composition (weight ratio*) weight Comp Ex A 36.5EHA/35.2ST/22.6MMA/3.5MAA/1.5PEM/0.7MEU 108,880 Comp Ex B 36.5EHA/34.7ST/22.6MMA/3.50MAA/1.5PEM/0.7MEU/0.5n- NA DDM Comp Ex C 36.5EHA/35.2ST/22.6CHMA/3.5MAA/1.5PEM/0.7MEU 112,310 Comp Ex D 36.5EHA/36.7ST/22.6MMA/3.5MAA/0.7MEU NA Comp Ex E 36.5EHA/36.2ST/22.6CHMA/3.5MAA/0.7MEU/0.5n-DDM 69,857 Comp Ex F 36.5EHA/36.2ST/22.6MMA/3.5MAA/0.7MEU/0.5n-DDM NA Comp Ex G 36.5EHA/36.9ST/22.6CHMA/2.0MAA/1.5PEM/0.5n-DDM NA Comp Ex H 35.6EHA/60.00CHMA/2.00MAA/3.5PEM/0.7MEU/0.2n-DDM NA Comp Ex I 36.5EHA/36.0ST/22.6CHMA/2.00MAA/1.5PEM/0.2MEU/1.2n- 20,141 DDM Comp Ex J 36.5EHA/35.8ST/22.6CHMA/2.00MAA/1.5PEM/1.5MEU/0.1n- 98,476 DDM Comp Ex K 36.5EHA/52.0ST/8.0CHMA/2.00MAA/0.3PEM/0.7MEU/0.5n- NA DDM *Numbers separated by a single slash indicates weight ratio of polymerized units of monomers in polymer

Coating Compositions P-1 to P-7 and P-A to P-K

[0080] The above obtained polymer dispersions were used as binders in preparing coating compositions of P-1 to P-7 and P-A to P-K, based formulations given in Tables 4 and 5. Water, the dispersant, wetting agent, neutralizer, defoamer and pigment were first mixed to allow the pigment to wet thoroughly using a conventional lab mixer, then water was further added to form the grind. The binder, water and the neutralizer were mixed to form the premix, and then the grind obtained above was added into the premix for 10 minutes. Then the flash rust inhibitor, rheology modifier and coalescent were added into the mixture obtained above to obtain the coating compositions. The obtained coating compositions all had a pigment volume concentration (PVC) of 20%, and volume solids of 40%. The coating compositions were evaluated according to the test methods described above. Properties of the obtained coatings are given in Tables 5 and 6.

TABLE-US-00004 TABLE 4 Raw Materials Kilogram Function Supplier Grind Water 42.00 OROTAN 681 7.80 Dispersant The Dow Chemical acrylic dispersant Company SURFYNOL TG 1.99 Wetting Air Products Nonylphenol ethoxylate agent Aqueous ammonia (28%) 1.99 Neutralizer TEGO Airex 902W 0.46 Defoamer Evonik Ti-Pure R-706 TiO.sub.2 209.24 Pigment DuPont Water 42.00 Subtotal 305.48 Letdown Aqueous polymer 604.60 Binder Self-prepared dispersion Water 27.00 Aqueous ammonia (28%) 4.00 Neutralizer Sodium nitrite (15%) 8.97 Flash Rust Inhibitor ACRYSOL RM-8W 2.00 Rheology The Dow Chemical HEUR modifier Company TEXANOL ester alcohol 30.00 Coalescent Eastman Total 982.05 *OROTAN and ACRYSOL are trademarks of The Dow Chemical Company.

[0081] Tables 5 and 6 give properties of coatings made from the coating compositions obtained above. As shown in Table 5, coatings made from coating compositions of P-1 to P-8 all demonstrated excellent corrosion resistance (rating F or above) and good adhesion. In contrast, as shown in Table 6, coatings made from comparative coating compositions (P-A to P-K) showed poorer corrosion resistance.

TABLE-US-00005 TABLE 5 Binder (Aqueous Salt spray Water Coating polymer Adhesion resistance resistance Composition dispersion) (dry/wet) (240 hours) (240 hours) P-1 Ex 1 5B/5B 10F/2% rust 10 P-2 Ex 2 5B/5B 10F/none rust 10 P-3 Ex 3 5B/5B 8F/2% rust 10 P-4 Ex 4 5B/5B 8F/3% rust 10 P-5 Ex 5 5B/5B 8F/3% rust 10 P-6 Ex 6 5B/5B 8F/3% rust 10 P-7 Ex 7 5B/5B 8F/3% rust 10 P-8 Ex 8 5B/5B 6F/2% rust 10

TABLE-US-00006 TABLE 6 Binder (Aqueous Salt spray Water Coating polymer Adhesion resistance resistance Composition dispersion) (dry/wet) (240 hours) (240 hours) P-A Comp Ex A 5B/4B 2D/10% rust 2MD P-B Comp Ex B 5B/5B 8M/5% rust 10 P-C Comp Ex C 5B/5B 8M/10% rust 10 P-D Comp Ex D 5B/5B 8M/15% rust 10 P-E Comp Ex E 5B/5B 8F/10% rust 10 P-F Comp Ex F 5B/5B 6M/5% rust 10 P-G Comp Ex G 5B/4B 6MD/3% rust 6F P-H Comp Ex H 5B/5B 8M/5% rust 10 P-I Comp Ex I 5B/5B 6M/5% rust 8F P-J Comp Ex J 5B/5B 6M/3% rust 6F P-K Comp Ex K 5B/4B 4D/50% Rust 6MD