Microbe resistant latex

Abstract

The present invention is a composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with a phosphorus acid monomer and having a z-average particle size as measured using dynamic light scattering in the range of from 50 nm to 500 nm; b) a salt of iodic acid; c) a C8-C10-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with the phosphorus acid monomer, the composition further comprises d) a hydrotrope. The composition of the present invention provides a way of preserving a latex against microbial growth 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] Summarv of the Invention

[0008] The present invention addresses a need in the art by providing a composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with a phosphorus acid monomer and having a z-average particle size as measured using dynamic light scattering in the range of from 50 nm to 500 nm; b) a salt of iodic acid; and c) a Cs-Cio-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with the phosphorus acid monomer, the composition further comprises d) a hydrotrope. The composition of the present invention provides a way of preserving a latex against microbial growth in the absence of a biocide.

[0009] Detailed Description of the Invention

[0010] The present invention is a composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with a phosphorus acid monomer and having a z-average particle size as measured using dynamic light scattering in the range of from 50 nm to 500 nm; b) a salt of iodic acid; and c) a Cs-Cio-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with the phosphorus acid monomer, the composition further comprises d) a hydrotrope.

[0011] The aqueous dispersion of polymer particles (the latex) can be any of a variety of latexes including acrylic, styrene-acrylic, vinyl acetate, and ethylene-vinyl acetate latexes. The latex may be functionalized with a phosphorus acid monomer, which is a phosphonate or a dihydrogen phosphate ester of an alcohol in which the alcohol contains or is substituted with a polymerizable vinyl or olefinic group. Preferred dihydrogen phosphate esters are phosphates of hydroxyalkyl methacrylates, including phosphoethyl methacrylate and phosphopropyl methacrylates, with 2-phosphoethyl methacrylate (PEM) being especially preferred. The concentration of structural units of PEM is preferably in the range of from 0.1 or from 0.2 or from 0.3 weight percent, to 10 or to 5 or to 3 weight percent, based on the weight of the polymer particles.

[0012] The polymer particles may further be functionalized with a salt of a sulfonic acid monomer such as sodium styrene sulfonate, typically at a concentration in the range of from 0.05 or from 0.1 weight percent to 2 or to 1 weight percent based on the weight of the polymer particles.

[0013] The salt of the iodic acid is preferably used in preservative amount, in combination with the Cs-Cio-alkyl phosphate or sulfate and optionally the hydrotrope. The term “preservative amount” refers to that amount required for the latex to pass at least 2, preferably 3 heat-aged challenge tests. The concentration of the salt of iodic acid is preferably in the range of from 100 ppm or from 200 ppm or from 250 ppm, to 1000 ppm or to 600 ppm or to 400 ppm. A preferred salt of iodic acid is potassium iodate (KIO3). The Cs-Cio-alkyl phosphate is a mono- or a bis-Cs-Cio-alkyl phosphate or a mixture thereof; or a mono- or bis-Cs-Cio-alkyl sulfate, or a mixture thereof. A preferred Cs-Cio-alkyl phosphate or sulfate is a bis(Cs-Cio-alkyl) phosphate, more preferably a branched bis(Cs-Cio-alkyl) phosphate such as bis(2-ethylhexyl) phosphate. The concentration of the Cs-Cio-alkyl phosphate or Cs-Cio- alkyl sulfate is preferably in the range of from 0.4 or from 0.6 weight percent to 3 or to 2 or to 1 weight percent, based on the weight of the composition.

[0014] The term “hydrotrope” is used herein to refer to a Ci-C4-alkyl substituted-aryl alkali metal phosphate or sulfate that, unlike a surfactant, is incapable of self-assembling into micelles. Examples of hydrotropes include sodium and potassium salts of Ci-C4-alkylphenyl phosphates, sulfates, and sulfonates such as sodium and potassium xylene phosphates, sodium and potassium cumene phosphates, sodium and potassium xylene sulfonates, sodium and potassium cumene sulfonates, sodium and potassium xylene sulfates, and sodium and potassium cumene sulfates. Other suitable hydrotropes include aromatic phosphates, sulfates, or sulfonates of the following formula: where each R1is independently a Ci-C4-alkyl group; M is a sodium, potassium, or ammonium cation; X is S or P; m is 1, 2, or 3; n is 0 or 1; y is 1 to 8; and z is 1 or 2; with the proviso that when X is P, n is 1 and z is 2; and when X is S, z is 1.

[0015] The concentration of the hydrotrope is preferably in the range of from 0.05 or from 0.1 or from 0.2 or from 0.3 weight percent, to 1 or to 2 weight percent, based on the weight of the composition. When the latex is not functionalized with a phosphorus acid monomer, the hydrotrope is a required component of the composition; when the latex is functionalized with a phosphorus acid monomer such as PEM, the hydrotrope is an optional component.

[0016] The salt of iodic acid, the Cs-Cio-alkyl phosphate or Cs-Cio-alkyl sulfate, and the hydrotrope are advantageously post-added to the latex, although these materials may be added during the formation of the latexes. Preferably, the latex, the salt of iodic acid, the Cs-Cio-alkyl phosphate or sulfate, and the hydrotrope comprise at least 90 or at least 95 or at least 99 weight percent of the composition. It has been surprisingly discovered that the presence of the Cs-Cio-alkyl phosphate or sulfate and the hydrotrope in the composition reduces the demand for the salt of iodic acid required to achieve the most stringent of heat-age challenge tests.

[0017] Examples

[0018] Microbial Inhibition Screening Procedure

[0019] Samples were tested for microbial inhibition after being heat-aged at 50 °C for two weeks. A 10.0-g aliquot was taken from each sample and inoculated three times at 1-, 2-, and 5-d intervals with 108-l 09colony forming units per milliliter of sample (CFU / mL) of standard bacteria from American Type Culture Collection (ATCC) that are common contaminants in coatings. Once inoculated, the samples were stored in 25 °C incubators.

[0020] Inoculated test samples were monitored for resistance to microbial growth using a 96-well plate called Most Probable Number (MPN) screening method. The monitoring of inoculated samples is flexible. The Challenge number is depicted by CH and number. The number of days after inoculation is listed as D and number; CH3D7 refers to inoculation challenge 3, day 7 after inoculation.

[0021] Sterile tryptic soy media was added to the wells of a 96-well plate (180 pL per well). A 20-pL aliquot of sample was added into the first well in Row A / Column 1. This addition was repeated in Row A columns 2 and 3 for testing a sample in triplicate. Using a sterile 20-300-pL multichannel pipette, row A was mixed thoroughly. Then, 20 p L was transferred from Row A to Row B, thereby forming a 1 :10 serial dilution of 20 pL of sample into 180 pL fresh media. After thorough mixing, the transfer of 20 pL of sample to the next row (rows C-H) was repeated.

[0022] The 96-well plates were visually ready after 48-72 h of incubation at 30° C. Signs of bacterial growth were indicated by turbidity, media discoloration, and / or pellet observed at the bottom of the plate well. These events were considered failures. Every well of growth moving down the enumerated rows (A-H) is considered 1 log. Thus, if rows A, B and C showed bacterial growth after 48-72 h of incubation, the most probable growth rating is 103CFU / mL. Table 1 - Rating System for Estimating Microbial Contamination

[0023] KIO3 and bis(2-ethylhexyl) phosphate were post-added to a styrene-acrylic latex as shown in Table 2. Comparative Examples illustrate the significance of including both additives to achieve passing the most stringent challenge tests. 2-EHP refers to bis(2-ethylhexyl) phosphate. Table 2 - Challenge Test Results for PEM-Functionalized Latex with KIO3

[0024] The results show that the latex containing a combination of KIO3 and bis(2-ethylhexyl) phosphate passes the most stringent challenge tests at relatively low levels of KIO3.

Claims

Claims:

1. A composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with a phosphorus acid monomer and having a z-average particle size as measured using dynamic light scattering in the range of from 50 nm to 500 nm; b) a salt of iodic acid; and c) a Cs-Cw-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with the phosphorus acid monomer, the composition further comprises d) a hydrotrope.

2. The composition of Claim 1 wherein the latex is functionalized with a phosphorus acid monomer, the salt of iodic acid is used in a preservative amount, and the concentration of the Cs-Cw-alkyl phosphate or sulfate is in the range of from 0.2 to 4 weight percent, based on the weight of the composition; wherein the aqueous dispersion of polymer particles is an acrylic latex, a styrene-acrylic latex, a vinyl acetate latex, or an ethylene-vinyl acetate latex.

3. The composition of Claim 2 wherein concentration of the salt of iodic acid is in the range of from 100 ppm to 1000 ppm, based on the weight of the composition; and wherein the polymer particles are functionalized with a phosphorus acid monomer which is 2-phosphoethyl methacrylate.

4. The composition of Claim 3 wherein the Cs-Cio-alkyl phosphate or Cs-Cio-alkyl sulfate is a branched Cs-Cio-alkyl phosphate or branched Cs-Cio-alkvl sulfate; and the salt of iodic acid is potassium iodate.

5. The composition of Claim 4 wherein the branched Cs-Cio-alkyl phosphate or branched Cs-Cio-alkyl sulfate is bis(2-ethylhexyl) phosphate; and the concentration of potassium iodate is in the range of from 200 ppm to 600 ppm.

6. The composition of Claim 1 which comprises the hydrotrope at a concentration in the range of from 0.05 to 2 weight percent, based on the weight of the composition; wherein the hydrotrope is a sodium or potassium salt of a) a Ci -Chalky Iphenyl phosphate, b) a C1-C4- alkylphenyl sulfate, or c) a Ci -Ch-alky I phenyl sulfonate; or the hydrotrope is a compound of the following formula:where each R1is independently a Ci-C4-alkyl group; M is a sodium, potassium, or ammonium cation; X is S or P; m is 1, 2, or 3; n is 0 or 1; y is 1 to 8; and z is 1 or 2; with the proviso that when X is P, n is 1 and z is 2; and when X is S, z is 1 ; wherein the aqueous dispersion of polymer particles is an acrylic latex, a styrene-acrylic latex, a vinyl acetate latex, or an ethylene-vinyl acetate latex; wherein, based on the weight of the composition: the concentration Cs-Cw-alkyl phosphate or sulfate is in the range of from 0.2 to 4 weight percent; and the concentration of the salt of iodic acid is in the range of from 100 ppm to 1000 ppm.

7. The composition of Claim 6 wherein the hydrotrope is sodium or potassium xylene phosphate, sodium or potassium cumene phosphate, sodium or potassium xylene sulfonate, sodium or potassium cumene sulfonate, sodium or potassium xylene sulfate, or sodium or potassium cumene sulfate; where the salt of iodic acid is potassium iodate, and the Cs-Cw-alkyl phosphate or Cs-Cw-alkyl sulfate is a branched Cs-Cio-alkyl phosphate or a branched Cs-Cio- alkyl sulfate.

8. The composition of Claim 7 wherein the branched Cs-Cio-alkyl phosphate or Cs-Cio-alkyl sulfate is bis(2-ethylhexyl) phosphate; wherein the concentration of potassium iodate is in the range of from 250 ppm to 600 ppm, based on the weight of the composition.

9. The composition of Claim 8 wherein the hydrotrope is sodium or potassium cumene sulfonate.

10. The composition of Claim 1 wherein the aqueous dispersion of polymer particles, the salt of iodic acid, the Cs-Cio-alkyl phosphate or sulfate, and the hydrotrope comprise at least 90 weight percent of the composition.

Images