Antimicrobial 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 50 nm to 500 nm and an antiseptic amount of an iodate salt, in particular potassium iodate. The composition of the present invention provides a means of preserving latex against microbial growth even in the absence of biocides.

Description

Background Technology

[0001] This invention relates to a latex that resists microbial formation without the use of biocides. More specifically, this invention relates to a latex composition containing a preservative amount of iodate.

[0002] In the coating industry, aqueous dispersions of polymer particles (i.e., latex) are stored with antimicrobial agents to inhibit the formation and growth of biological organisms such as bacteria, yeasts, and molds during storage. Inhibition of these organisms prevents product degradation and spoilage, as well as the venting of volatile products and subsequent pressure buildup in closed containers. Therefore, corrosion protection is essential for health, safety, and performance reasons.

[0003] Canned preservatives (such as isothiazolinones) are facing intense regulatory scrutiny due to their actual or perceived adverse effects on health, safety, and the environment; in fact, many parts of the world appear poised for a complete ban on these biocides. To some extent, developing new biocides is not feasible due to cost considerations and the widespread (whether justified) awareness of the inherent dangers of these biocides, thus necessitating the replacement of biocides with safer and more sustainable alternative non-biocidal preservatives.

[0004] A recent example of a non-biocidal method for preserving coatings to prevent microbial contamination can be found in EP 3 456 787 B1, which discloses aqueous coating formulations with pH adjusted to the range of 10 to 12.5. While seemingly effective, these very high pH formulations present additional safety and hygiene concerns, rendering the method impractical. Other non-traditional methods, such as adding silver or zinc ions, may adversely affect coating properties and are also subject to regulatory scrutiny. For these reasons, there is a need for safer and more sustainable methods for preserving coatings and the materials used in them. Summary of the Invention

[0005] This 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 50 nm to 500 nm and an iodate content suitable for preservation. The composition of this invention provides a method for preserving latex and preventing microbial growth even in the absence of biocides. Detailed Implementation

[0006] The present invention is a composition comprising an aqueous dispersion of polymer particles having a z-average particle size in the range of 50 nm to 500 nm and a corrosion-resistant amount of iodate.

[0007] There is no limitation on the type of aqueous dispersion (latex) of polymer particles suitable for the purposes of this invention. Particularly suitable latexes are those that can be used in paint formulations, including acrylic latexes, styrene-acrylic latexes, and vinyl ester latexes well known in the art. Acrylic latex refers to an aqueous dispersion of polymer particles containing at least 50% by weight, or at least 70% by weight, or at least 80% by weight, or at least 90% by weight of structural units of acrylates, methacrylates, and acid monomers. The term "structural unit" for the listed monomers refers to the monomer residue after polymerization. For example, the structural unit of methyl methacrylate is shown below:

[0008]

[0009] Structural units of methyl methacrylate

[0010] Styrene-acrylic latexes comprise structural units of acrylates, methacrylates, and acid monomers, and 10% to 70% by weight of one or more styrene monomers such as styrene and α-methylstyrene. Vinyl ester latexes include vinyl acetate latex and vinyl tert-carbonate latex.

[0011] As used in this article, z-average particle size refers to the particle size determined by dynamic light scattering.

[0012] The amount of iodate used for corrosion prevention refers to the amount required to pass at least two factory challenge tests as described below. Generally, based on the weight of the latex, the effective amount of iodate is preferably at least 200 ppm, and most preferably at least 400 ppm, up to 5000 ppm, more preferably up to 2500 ppm, and most preferably up to 1200 ppm.

[0013] Iodates include alkali metal salts and alkaline earth metal salts, including lithium iodate, sodium iodate, potassium iodate, calcium iodate, and magnesium iodate. Potassium iodate is the preferred iodate.

[0014] The compositions of the present invention are advantageously prepared by the following steps: preparing a latex by emulsion polymerization, and then adding iodates during the process, as described in the following Examples section.

[0015] It has been found that the compositions of the present invention are resistant to microbial growth in the absence of biocides. More specifically, the compositions contain less than 5 ppm, more preferably less than 1 ppm, and most preferably 0 ppm of any isothiazolinone, such as methylisothiazolinone, chloromethylisothiazolinone, benzisothiazolinone, octylisothiazolinone, dichlorooctylisothiazolinone, and butylbenzisothiazolinone.

[0016] The compositions of the present invention also contain less than 500 ppm, less than 100 ppm, less than 50 ppm, or less than 10 ppm of iodine.

[0017] Example

[0018] Example 1 - Preparation of acrylic latex containing 500 ppm potassium iodate

[0019] The first monomer emulsion (ME1) was prepared by mixing deionized water (160 g), sodium dodecylbenzenesulfonate (36.96 g, 23% active material), a blend of C1-C6-alkyl acrylate monomers (374 g), methyl methacrylate (303.28 g), and methacrylic acid (2.72 g).

[0020] A second monomer emulsion (ME2) was prepared by mixing deionized water (270 g), Disponil FES 993 surfactant (23.8 g, 30% active ingredient), a blend of C1-C6-alkyl acrylate monomers (561 g), methyl methacrylate (383.52 g), ethyl acetoacetate methacrylate (34 g, 95% active ingredient), ethyl phosphate methacrylate (30.6 g, 60% active ingredient), sodium 4-vinylbenzenesulfonate (11.33 g, 90% active ingredient), and methacrylic acid (2.38 g).

[0021] Deionized water (1000 g) and sodium dodecylbenzenesulfonate (14.79 g, 23% active material) were added to a 5 L four-necked round-bottom flask equipped with a paddle stirrer, thermometer, N2 inlet, and reflux condenser. The contents of the flask were heated to 85 °C under N2 and stirred. Then, a portion of ME1 (105 g) was added, followed by a rapid addition of an aqueous solution of ammonium persulfate (5.1 g) dissolved in deionized water (25 g), and then rinsed with deionized water (5 g). After stirring for 10 minutes, the remaining ME1 and a solution containing ammonium persulfate (0.67 g) dissolved in deionized water (30 g) were added linearly and separately to the flask over a total time period of 45 minutes. The contents of the flask were maintained at 85 °C during the addition of ME1. Once all additions are complete, rinse the flask containing ME1 with deionized water (25g), then add it to the flask and maintain the contents of the flask at 85°C for 15 minutes.

[0022] After holding for 15 minutes, ME2 and a solution containing ammonium persulfate (1.03 g) dissolved in deionized water (50 g) were added linearly and separately to the flasks over a total time period of 70 minutes. The contents of the flasks were maintained at 85°C during the ME2 addition. When all additions were complete, the flask containing ME2 was rinsed with deionized water (25 g) and then added to the flask, and the contents of the flask were maintained at 85°C for 10 minutes. After holding for 10 minutes, a solution containing ammonium hydroxide (10 g, 29% active material) and deionized water (20 g) was added to the flask over 5 minutes.

[0023] 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 tetrasodium EDTA (1.1 g, 1% solids) were added to the vessel. The catalyst / activator pair t-pentyl hydroperoxide (t-AHP, 3.4 g, 85% active material) and Disponil FES-993 surfactant (1.19 g, 30% active material), 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 20-minute period. The contents of the flask were cooled to 55°C during the addition of the catalyst / activator pair.

[0024] The contents of the flask were cooled to room temperature. The resulting dispersion of polymer particles was neutralized to approximately pH 7.5 with an aqueous solution of ammonium hydroxide (5 g, 29% active material) and Tergitol 15-S-40 surfactant (12.15 g, 70% active material) 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 determined to be 105 nm using a Malvern particle size analyzer; the solids content was 46.5%.

[0025] Example 2 - Preparation of acrylic latex with 1000 ppm potassium iodate

[0026] Example 2 was carried out essentially 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.

[0027] Example 3 - Preparation of styrene-acrylic latex with 500 ppm KIO3

[0028] A. Preform synthesis

[0029] Monomer emulsions were prepared by mixing deionized water (200 g), Disponil FES 993 surfactant (43 g, 30% active ingredient), butyl acrylate (371.2 g), methyl methacrylate (195.2 g), allyl methacrylate (9.6 g), ethyl methacrylate (51.2 g, 60% active ingredient), and methacrylic acid (12.8 g).

[0030] Deionized water (600 g) and Disponil FES 32 surfactant (43 g, 30% active ingredient) were added to a 5 L four-necked round-bottom flask equipped with a paddle stirrer, thermometer, N2 inlet, and reflux condenser. The contents of the flask were heated to 85 °C under N2 and stirred. A portion of the first monomer emulsion (70 g) was then added, followed by a rapid addition of a solution of sodium persulfate (2.56 g) dissolved in deionized water (30 g), and then rinsed with deionized water (5 g). After stirring for 10 minutes, the remaining first monomer emulsion was added linearly and separately over 40 minutes, followed by the rinse solution (25 g) and an initiator solution of sodium persulfate (0.64 g) dissolved in deionized water (50 g). After the monomer emulsion feeding was complete, the contents of the flask were held at 85 °C for 10 minutes, after which the feeding was complete; and then the contents of the flask were held at 85 °C for another 10 minutes. 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 nm to 75 nm, and the solids content was 40% to 41%.

[0031] B. Shell polymerization

[0032] Monomer emulsions were prepared by mixing deionized water (340 g), sodium dodecylbenzenesulfonate (66 g, 23% active ingredient), butyl acrylate (856.8 g), styrene (550.1 g), acrylic acid (28.8 g), and sodium 4-vinylbenzenesulfonate (4.8 g, 90% active ingredient).

[0033] The reactor is a 5-liter four-necked round-bottom flask equipped with a paddle stirrer, thermometer, nitrogen inlet, and reflux condenser. Add 950 g of deionized water to the flask. Heat the contents of the flask to 85°C under a nitrogen atmosphere and start stirring. Add a solution of sodium persulfate (4.8 g) dissolved in deionized water (20 g) and a rinsing solution of deionized water (5 g) to the reactor. Add a preform (approximately 400 g) equal to 10% of the total final polymer to the reactor. Once the reactor temperature has returned to >80°C, begin ME feeding.

[0034] The monomer emulsion and an oxidant solution containing sodium persulfate (2.4 g) and sodium hydroxide (2 g, 50% active substance) dissolved in deionized water (57 g) were linearly and separately added to the flask over a 120-minute period. The contents of the flask were maintained at 85°C during the addition of the monomer emulsion. Once 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 tetrasodium EDTA (1.1 g, 1% solids) were added to the vessel. The catalyst / activator pair t-pentyl hydroperoxide (t-AHP, 3.2 g, 85% active material) and sodium dodecylbenzenesulfonate (2.36 g, 23% active material) dispersed in 30 g of deionized water, along with isoascorbic acid (IAA, 1.8 g) dissolved in 30 g of deionized water, were added linearly and separately to the flask over a 20-minute period. 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 resulting dispersion of polymer particles was neutralized to approximately pH 9.0 with an aqueous solution of sodium hydroxide (20 g, 50% active ingredient) and Tergitol 15-S-40 surfactant (10.7 g, 70% active ingredient) in deionized water (150 g). An aqueous solution of Dequest 2016 (1.1 g, 33% active ingredient) 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-mean particle size was determined to be 129 nm using a Malvern particle size analyzer; the solids content was 45.0%.

[0037] Example 4 - Preparation of styrene-acrylic latex with 1000 ppm KIO3

[0038] Example 4 was carried out essentially 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.

[0039] Preparation of antimicrobial samples

[0040] The antimicrobial properties of samples were tested "as is" (out of the factory, without heat aging) and after being subjected to 50°C for four weeks (heat aging). 10g aliquots were taken from each sample and tested with 10... 6 One to 10 7A standard pool of bacteria, yeasts, and molds (obtained from the American Type Culture Collection (ATCC), representing common contaminants in coatings) was inoculated three times at 7-day intervals. After inoculation, samples were stored in an incubator at 25°C. Microbial contamination of test samples was monitored by agar plate inoculation using the standard streak plate method. Samples were inoculated onto trypsin-soybean agar (TSA) and potato dextrose agar (PDA) plates on days 1 and 7 after each microbial challenge. All agar plates were examined daily after inoculation until day 7 to determine the number of surviving microorganisms in the test samples. Between examinations, the agar plates were stored in incubators at 30°C for TSA plates and at 25°C for PDA plates. The degree of microbial contamination was determined by colony counting, where a rating score was determined based on the number of microbial colonies observed on the agar plates. Results were reported from day 7 readings and summarized for both “original” and heat-aged samples. The results are described by a score for each type of microorganism: B = bacteria, Y = yeast, and M = mold. For example, 3B describes a plate with a score of 3 for bacteria, or Tr Y(1) describes a plate with trace amounts of yeast (1 colony on the plate). Table 1 illustrates the rating system used to assess the level of microbial contamination on streak plates. A colony is the number of colonies on the plate.

[0041] Table 1 - Rating System for Assessing Microbial Contamination

[0042]

[0043] In Table 1, “Pass” means that fewer than ten colonies were detected on the plate on a specific day after inoculation (Day 1 (D1) or Day 7 (D7)). Samples are considered pass if they pass at least one factory challenge test. The most preferred samples are those that pass three challenge tests under heat aging conditions. “Fail” means that ten or more distinct colonies were detected on the plate on a specific day after inoculation.

[0044] Table 2 shows the results of thermal aging challenge tests for acrylic latexes and styrene-acrylic latexes with and without 1000 ppm of added KIO3.

[0045] Table 2 - Results of Thermal Aging Challenge Test

[0046]

[0047] Latex containing added KIO3 passed three heat aging challenge tests; conversely, samples without KIO3 failed even the first challenge test.

Claims

1. A composition comprising an aqueous dispersion of polymer particles having a z-average particle size in the range of 50 nm to 500 nm and a preservative content of iodate.

2. The composition of claim 1, wherein the aqueous dispersion of the polymer particles comprises 200 ppm to 5000 ppm of the iodate.

3. The composition of claim 1, wherein the aqueous dispersion of the polymer particles comprises 200 ppm to 2500 ppm of the iodate.

4. The composition of claim 1, wherein the aqueous dispersion of the polymer particles comprises 400 ppm to 1200 ppm of the iodate, wherein the iodate is potassium iodate; wherein the polymer particles are acrylic polymer particles or styrene-acrylic polymer particles.

5. The composition according to claim 1, wherein the composition contains less than 5 ppm of any isothiazolinone.

6. The composition according to claim 5, wherein the composition contains less than 500 ppm of iodine.

7. The composition according to claim 6, wherein the composition comprises less than 1 ppm of any isothiazolinone and less than 100 ppm of iodine.

8. The composition according to claim 7, wherein the composition comprises less than 50 ppm of iodine and 0 ppm of any isothiazolinone.

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