Microbe resistant latex

Abstract

The present invention is a composition comprising an aqueous dispersion of polymer particles having a z-average particle size in the range of from 50 nm to 500 nm and a preservative amount of a salt of iodic acid, especially potassium iodate. The composition of the present invention provides a way of preserving a latex against microbial growth even in the absence of a biocide.

Description

[0001] Microbe Resistant Latex

[0002] Background of the Invention

[0003] The present invention relates to a latex that is resistant to microbe formation without the use of a biocide. More particularly, the invention relates to a latex composition comprising a preservative amount of an iodate salt.

[0004] Aqueous dispersions of polymer particles (i.e., latexes) used in the coatings industry are preserved with antimicrobial agents to inhibit the formation and growth of biological organisms such as bacteria, yeast, and mold while in storage. Inhibition of these organisms prevents product degradation and spoilage, as well as off-gassing of volatile products and consequent pressure build-up in closed containment. Preservation is therefore essential for reasons of health, safety, and performance.

[0005] In-can preservatives such as isothiazolinones are facing intense regulatory scrutiny for their real or perceived adverse impact on health, safety, and the environment; in fact, an outright ban of these biocides in many parts of the world appears in the offing. Inasmuch as the development of new biocides is unlikely for reasons of cost and a widespread perception, justified or not, of their inherent dangers, a need exists to supplant biocides with alternative non-biocidal preservatives that are safer and more sustainable.

[0006] A recent example of a non-biocidal approach for preserving paints against microbial contamination can be found in EP 3 456 787 Bl, which discloses a water-borne coating formulation adjusted to a pH in the range of 10 to 12.5. While ostensibly effective, these very high pH formulations create additional safety and health concerns that render this approach impractical. Other non-traditional approaches such as the addition of silver or zinc ions may adversely affect the properties of the paint and face regulatory scrutiny as well. For these reasons, other safer and more sustainable approaches for preserving paints, and materials that are used in paints, are needed.

[0007] Summary of the Invention

[0008] The present invention addresses a need in the art by providing a composition comprising an aqueous dispersion of polymer particles having a z-average particle size in the range of from 50 nm to 500 nm and a preservative amount of a salt of iodic acid. The composition of the present invention provides a way of preserving a latex against microbial growth even in the absence of a biocide.

[0009] Detailed Description of the Invention

[0010] The present invention is a composition comprising an aqueous dispersion of polymer particles having a z-average particle size in the range of from 50 nm to 500 nm and a preservative amount of a salt of iodic acid.

[0011] The class of aqueous dispersions of polymer particles (latexes) suitable for the purposes of the present invention is unlimited. Particularly suitable latexes are those useful in paint formulations, including acrylic latexes, styrene-acrylic latexes, and vinyl-ester latexes, which are well known in the art. An acrylic latex refers to an aqueous dispersion of polymer particles that comprise at least 50, or at least 70, or at least 80, or at least 90 weight percent structural units of acrylate, methacrylate, and acid monomers. The term “structural units” of the recited monomer refers to the remnant of the monomer after polymerization. For example, a structural unit of methyl methacrylate is as follows: structural unit of methyl methacrylate

[0012] A styrene-acrylic latex comprises structural units of acrylate, methacrylate, and acid monomers and from 10 to 70 weight percent structural units of one or more styrenic monomers such as styrene and a-methylstyrene. Vinyl ester latexes include vinyl acetate and vinyl versatate latexes.

[0013] As used herein, z-average particle size refers to particle size as determined by dynamic light scattering.

[0014] A preservative amount of a salt of iodic acid salt refers to an amount required to pass at least two off the mill challenge tests as described hereinbelow. In general, the effective amount of the salt of iodic acid is preferably at least 200 ppm, and most preferably at least 400 ppm, to 5000 ppm, more preferably to 2500 ppm, and most preferably to 1200 ppm, based on the weight of the latex. Salts of iodic acid include alkali metal and alkaline earth metal salts including lithium iodate, sodium iodate, potassium iodate, calcium iodate, and magnesium iodate. Potassium iodate is a preferred salt of iodic acid.

[0015] The composition of the present invention is advantageously prepared by the steps of preparing the latex by emulsion polymerization, followed by in-process addition of salt of iodic acid, as described in the example section below.

[0016] The composition of the present invention has been found to be resistant to microbial growth without the presence of a biocide. More particularly, the composition contains less than 5 ppm, more preferably less than 1 ppm, most preferably 0 ppm of any isothiazolinones such as methylisothiazolinone, chloromethylisothiazolinone, benzoisothiazolinone, octylisothiazolinone, dichlorooctylisothiazolinone, and butylbenzisothiazolinone.

[0017] The composition of the present invention further comprises less than 500 ppm or less than 100 ppm or less than 50 ppm or less than 10 ppm of iodine.

[0018] Examples

[0019] Example 1 - Preparation of an Acrylic Latex with 500 ppm Potassium Iodate

[0020] A first monomer emulsion (MEI) was prepared by mixing deionized water (160 g), sodium dodecylbenzene sulfonate (36.96 g, 23% active), a blend of Ci-Ce-alkyl acrylate monomers (374 g), methyl methacrylate (303.28 g), and methacrylic acid (2.72 g).

[0021] A second monomer emulsion (ME2) was prepared by mixing deionized water (270 g), Disponil FES 993 surfactant (23.8 g, 30% active), a blend of Ci-Ce-alkyl acrylate monomers (561 g), methyl methacrylate (383.52 g), acetoacetoxy ethyl methacrylate (34 g, 95% active), phosphoethyl methacrylate (30.6 g, 60% active), sodium 4-vinylbenzenesulfonate (11.33 g, 90% active), and methacrylic acid (2.38 g).

[0022] Deionized water (1000 g) and sodium dodecylbenzene sulfonate (14.79 g, 23% active) were added to a 5-L, four necked round bottom flask equipped with a paddle stirrer, a thermometer, N2 inlet, and a reflux condenser. The contents of the flask were heated to 85 °C under N2 and stirring was initiated. A portion of MEI (105 g) was then added, quickly followed by addition of an aqueous solution of ammonium persulfate (5.1 g) dissolved in deionized water (25 g) followed by a rinse of deionized water (5 g). After stirring for 10 min, the remainder of MEI and a solution containing ammonium persulfate (0.67 g) dissolved in deionized water (30 g), were each added linearly and separately to the flask over a total period of 45 min. The contents of the flask were maintained at a temperature of 85 °C during the addition of MEI. When all additions were complete, the flask containing MEI was rinsed with deionized water (25 g), which was then added to the flask, and the contents of the flask were maintained at 85 °C for 15 min.

[0023] After the 15-min hold, ME2 and a solution containing ammonium persulfate (1.03 g) dissolved in deionized water (50 g) were each added linearly and separately to the flask over a total period of 70 min. The contents of the flask were maintained at a temperature of 85 °C during the addition of ME2. When all additions were complete, the flask containing ME2 was rinsed with deionized water (25 g), which was then added to the flask, and the contents of the flask were maintained at 85 °C for 10 min. After the 10-min hold, a solution containing ammonium hydroxide (10 g, 29% active) and deionized water (20 g) was added to the flask over 5 min.

[0024] The contents of the flask were cooled to 75 °C and an aqueous solution of FeSO4 (15.1 g, 0.1% solids) and an aqueous solution of the tetrasodium salt of EDTA (1.1 g, 1 % solids) were added to the kettle. A catalyst / activator pair of / -amyl hydroperoxide (t-AHP, 3.4 g, 85% active) and Disponil FES-993 surfactant (1.19 g, 30% active) dispersed in 30 g of deionized water and isoascorbic acid (IAA, 1.2 g) dissolved in 30 g of deionized water were added linearly and separately to the flask over a period of 20 minutes. The contents of the flask were cooled to 55 °C during the addition of the catalyst / activator pair.

[0025] The contents of the flask were cooled to room temperature. The resultant dispersion of polymer particles was neutralized to pH ~ 7.5 with an aqueous solution of ammonium hydroxide (5 g, 29% active) and Tergitol 15-S-40 surfactant (12.15 g, 70% active) in deionized water (40 g). An aqueous solution of potassium iodate (1.85 g, 500 ppm) in deionized water (20 g) was then added to the dispersion. The z-average particle size was found to be 105 nm using a Malvern Particle Size Analyzer; the measured solids was 46.5%.

[0026] Example 2 - Preparation of an Acrylic Latex with 1000 ppm Potassium Iodate

[0027] Example 2 was carried out substantially as described in Example 1, except that 3.7 g (1000 ppm) of KIO3 in deionized water (20 g) was added to the dispersion in the final step. Example 3 - Preparation of a Styrene- Acrylic Latex with 500 ppm KIO3

[0028] A. Preform Synthesis

[0029] A monomer emulsion was prepared by mixing deionized water (200 g), Disponil FES 993 surfactant (43 g, 30% active), butyl acrylate (371.2 g), methyl methacrylate (195.2 g), allyl methacrylate (9.6 g), phosphoethyl methacrylate (51.2 g, 60% active), and methacrylic acid (12-8 g).

[0030] Deionized water (600 g) and Disponil FES 32 surfactant (43 g, 30% active) were added to a 5-L, four necked round bottom flask equipped with a paddle stirrer, a thermometer, N2 inlet, and a reflux condenser was added. The contents of the flask were heated to 85 °C under N2 and stirring was initiated. A portion of the first monomer emulsion (70 g) was then added, quickly followed by a solution of sodium persulfate (2.56 g) dissolved in deionized water (30 g) followed by a rinse of deionized water (5 g). After stirring for 10 min, the remainder of the first monomer emulsion, followed by a rinse (25 g), and an initiator solution of sodium persulfate (0.64 g) dissolved in deionized water (50 g) were added linearly and separately over 40 min. After the monomer emulsion feed was complete, the contents of the flask were held at 85 °C for 10 min, after which time the co-feed was complete; and the contents of the flask were then held at 85 °C for an additional 10 min. The contents of the flask were cooled to room temperature and neutralized to pH 3 with a dilute solution of ammonium hydroxide. The measured particle size was 60 - 75 nm and the solids were 40 - 41 %.

[0031] B. Shell Polymerization

[0032] A monomer emulsion was prepared by mixing deionized water (340 g), sodium dodecylbenzene sulfonate (66 g, 23% active), butyl acrylate (856.8 g), styrene (550.1 g), acrylic acid (28.8 g), and sodium 4-vinylbenzenesulfonate (4.8 g, 90% active).

[0033] The reactor was a 5-liter, four necked round bottom flask equipped with a paddle stirrer, a thermometer, nitrogen inlet, and a reflux condenser. To the flask was added 950 g of deionized water. The contents of the flask were heated to 85 °C under a nitrogen atmosphere and stirring initiated. A solution of sodium persulfate (4.8 g) dissolved in deionized water (20 g), and a rinse of deionized water (5 g) was added to the kettle. An amount of the preform equal to 10% of the total final polymer (~400g) was added to the kettle. Once the kettle temperature had returned to > 80 °C, the ME feed was started.

[0034] The monomer emulsion and an oxidant solution containing sodium persulfate (2.4 g) and sodium hydroxide (2 g, 50% active) dissolved in deionized water (57 g) were added linearly and separately to the flask over a period of 120 minutes. The contents of the flask were maintained at a temperature of 85 °C during the addition of the monomer emulsion. When all additions were complete, the container containing the monomer emulsion was rinsed with deionized water (25 g), which was then added to the flask.

[0035] The contents of the flask were cooled to 75 °C and an aqueous solution of FeSO4 (15.9 g, 0.1% solids) and an aqueous solution of the tetrasodium salt of EDTA (1.1 g, 1 % solids) were added to the kettle. A catalyst / activator pair of t-amyl hydroperoxide (t-AHP, 3.2 g, 85% active) and sodium dodecylbenzene sulfonate (2.36 g, 23% active) dispersed in 30 g of deionized water and isoascorbic acid (IAA, 1.8 g) dissolved in 30 g of deionized water were added linearly and separately to the flask over a period of 20 minutes. The contents of the flask were cooled to 55 °C during the addition of the catalyst / activator pair.

[0036] The contents of the flask were cooled to room temperature. The resultant dispersion of polymer particles was neutralized to pH ~ 9.0 with an aqueous solution of sodium hydroxide (20 g, 50% active) and Tergitol 15-S-40 surfactant (10.7 g, 70% active) in deionized water (150 g). An aqueous solution of Dequest 2016 (1.1 g, 33% active) in deionized water (10 g) was then added to the dispersion. An aqueous solution of potassium iodate (1.85 g, 500 ppm) in deionized water (20 g) was then added to the dispersion. The z-average particle size was found to be 129 nm using a Malvern Particle Size Analyzer; the measured solids was 45.0%. Example 4 - Preparation of a Styrene- Acrylic Latex with 1000 ppm KIO3

[0037] Example 4 was carried out substantially as described in Example 3, except that 3.7 g (1000 ppm) of KIO3 in deionized water (20 g) was added to the dispersion in the final step.

[0038] Preparation of Samples for Microbial Resistance

[0039] Samples were tested for microbial resistance “as-is” (off the mill, not heat-aged) as well as after being subjected to 50 °C for four- weeks (heat-aged). A 10-g aliquot was taken from each sample and inoculated three times at 7-d intervals with 106- 107colony forming units per milliliter of sample (CFU / mL) of a standard pool of bacteria, yeasts, and molds obtained from American Type Culture Collection (ATCC) that are common contaminants in coatings. Once inoculated, the samples were stored in 25 °C incubators. Test samples were monitored for microbial contamination by agar plating using a standard streak plate method. Samples were plated 1 day and 7 days after each microbial challenge onto trypticase soy agar (TSA) and potato dextrose agar (PDA) plates. All agar plates were checked daily up to 7 days after plating to determine the number of microorganisms surviving in the test samples. Between checks, the agar plates were stored in incubators at 30 °C for TSA plates and at 25 °C for PDA plates. The extent of microbial contamination was established by counting the colonies, where the rating score was determined from the number of microbial colonies observed on the agar plates. Reported results come from day 7 readings, and are summarized for both the “as-is” and heat-aged samples. Results are described by the rating score for each type of microorganism: B = bacteria, Y = yeast, and M = mold. For example, a 3B describes a plate with 3 rating score for bacteria, or a Tr Y(l) describes a plate with trace yeast (1 colony on plate). Table 1 illustrates the rating system used to estimate the level of microbial contamination on streak plates. Colonies refers to the number of colonies on the plate.

[0040] Table 1 - Rating system for Estimating Microbial Contamination

[0041] In Table 1, “Pass” means fewer than ten colonies were detected on plates on the specified day (Day 1 (DI) or Day 7 (D7)) after inoculation. Samples passed if they passed at least one off-the- mill challenge tests. Most preferred samples were those that passed three challenge tests under heat aged conditions. “Fail means that ten or more distinct colonies were detected on plates on the specified day after inoculation.

[0042] Table 2 illustrates heat-aged challenge test results for acrylic and styrene-acrylic latexes with and without 1000 ppm of post-added KIO3.

[0043] Table 2 - Heat- Aged Challenge Test Results The latexes containing post-added KIO3 passed three heat-aged challenge tests; in contrast, the samples that did not contain KIO3 did not even pass the first challenge test.

Claims

Claims:

1. A composition comprising an aqueous dispersion of polymer particles having a z-average particle size in the range of from 50 nm to 500 nm and a preservative amount of a salt of iodic acid.

2. The composition of Claim 1 where the aqueous dispersion of polymer particles comprises from 200 ppm to 5000 ppm of the salt of iodic acid.

3. The composition of Claim 1 wherein the aqueous dispersion of polymer particles comprises from 200 ppm to 2500 ppm of the salt of iodic acid.

4. The composition of Claim 1 wherein the aqueous dispersion of polymer particles comprises from 400 ppm to 1200 ppm of the salt of iodic acid, wherein the salt of iodic acid is potassium iodate; wherein the polymer particles are acrylic are styrene-acrylic polymer particles.

5. The composition of Claim 1 which comprises less than 5 ppm of any isothiazolinones.

6. The composition of Claim 5 which comprises less than 500 ppm of iodine.

7. The composition of Claim 6 which comprises less than 1 ppm of any isothiazolinones and less than 100 ppm of iodine.

8. The composition of Claim 7 which comprises less than 50 ppm of iodine and 0 ppm of any isothiazolinones.

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