Latex composition with non-biocidal preservative

Abstract

The present invention is a composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with structural units of 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 C4-C10-alkyl hydroperoxide; c) a C8-C10-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with structural units of the phosphorus acid monomer, the composition further comprises d) a hydrotrope. The composition of the present invention provides a biocide-free latex with relatively low concentrations of a hydroperoxide.

Description

[0001] Latex Composition with non-Biocidal Preservative

[0002] of the Invention

[0003] The present invention relates to a composition containing a non-biocidal preservative. Aqueous dispersions of polymer particles (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.

[0004] In-can preservatives such as isothiazolinones are facing intense regulatory scrutiny for their real or perceived adverse impact on health, safety7, 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.

[0005] An example of a non-biocidal approach for preserving paints against microbial contamination can be found in EP 3 456787 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.

[0006] More recently, WO 2024 / 064581 Al discloses that an acrylic latex composition t-amyl hydroperoxide passes two heat-age challenge tests at fairly low concentrations: unfortunately, unacceptably high concentrations (from the viewpoint of strict EU regulation standards) are required to pass more stringent heat age tests. It would therefore be desirable to find an alternative biocide free latex that would meet the most stringent regulatory requirements. Summary of the Invention

[0007] The present invention relates to a composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with structural units of 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 Ca-Cio-alkyl hydroperoxide; c) a Cs-Cw-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with structural units of the phosphorus acid monomer, the composition further comprises d) a hydrotrope. The composition of the present invention provides a biocide-free latex with relatively low concentrations of a hydroperoxide.

[0008] Detailed Description of the Invention

[0009] The present invention is a composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with structural units of 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 C4-Cio-alkyl hydroperoxide; c) a Cs-Cio-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with structural units of the phosphorus acid monomer, the composition further comprises d) a hydrotrope.

[0010] 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 structural units of 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.

[0011] The polymer particles may further be functionalized with structural units of 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 or weight percent to 2 or to 1 weight percent based on the weight of the polymer particles. The C4-Cw-alkyl hydroperoxide is preferably used in a 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, and preferably 3 heat-age challenge tests. The concentration of the C4-Cio-alkyl hydroperoxide is preferably in the range of from 100 ppm or from 150 ppm or from 200 ppm, to 1000 ppm or to 800 ppm or to 600 ppm or to 400 ppm. Preferred C -Cio-alkyl hydroperoxides include t-amyl hydroperoxide (7- A HP) and Abutyl hydroperoxide (t-BHP).

[0012] The Cs-Cio-alkyl phosphate or Cs-Cio-alkyl sulfate 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 0.2 or from 0.4 or from 0.6 weight percent to 4 or to 3 or to 2 or to 1 weight percent, based on the weight of the composition.

[0013] 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:

[0014]

[0015] where each R1is independently a Ci-C-4-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.

[0016] 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 structural units of a phosphorus acid monomer, the hydrotrope is a required component of the composition; when the latex is functionalized with structural units of a phosphorus acid monomer such as PEM, the hydrotrope is an optional component.

[0017] The C4-Cio-alkyl hydroperoxide, the Cs-Cw-alkyl phosphate or 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 C4-Cio-alkyl hydroperoxide, 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

[0018] Cs-Cw-alkyl phosphate or sulfate and the hydrotrope in the composition reduces the demand for the C4-Cio-alkyl hydroperoxide required to achieve the most stringent of heat-age challenge tests.

[0019] Examples

[0020] Microbial Inhibition Screening Procedure

[0021] Samples were tested for microbial inhibition after being heat-aged at 50 °C for 14 d. A 10.0-g aliquot was taken from each sample and inoculated three times at 1-, 2-, and 5-d intervals with 108-109colony 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.

[0022] 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; thus, CH3D7 refers to the third inoculation challenge, seven days after inoculation.

[0023] 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 pL 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. 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 illustrates the rating system for estimating microbial contamination.

[0024] Table 1 - Rating System for Estimating Microbial Contamination

[0025] > <

[0026] >

[0027]

[0028] NMR Spectroscopic Detenuination of / -AHP in Serum Phase

[0029] A 10-mL polycarbonate tube was charged with 3.0 mL of a latex sample, 3.0 mL of Milli-Q water, and centrifuged at 100,000 rpm for 15 min. The resulting clear supernatant was decanted and transferred into a 5-mm NMR tube. A flame-sealed capillary tube filled with an external standard (5.00 wt% d4-sodium trimethylsilylpropionate in D2O) was added to the NMR tube. Careful attention was paid to proper alignment of the external standard within the NMR tube. NMR spectra were obtained using the Bruker AVANCE III 600 spectrometer equipped with a 5-mm BroadBand CryoProbe. Each sample was tuned and shimmed individually but pulse widths and receiver gain were held constant for a sample series. Concentration of free / -amyl hydroperoxide was measured by using the zg pulse sequence with the following parameters: acquisition time (aq) = 2.5 s, recycle delay (dl) = 30 s, number of transients (ns) = 1024, receiver gain (rg) = 32, and pulsewidth (pl) = 11 ms. All other parameters (time domain size, sweep width, dwell time, pre-scan delay, and carrier frequency) were left at the default values. Concentration of free hydroperoxide was calculated by comparing the integrations of peaks resonating around 1.2 ppm and the peak for the external standard at 0.0 ppm. Spectra were referenced to the external standard at 0.0 ppm on the trimethylsilyl chemical shift scale. The purity of the resonances ascribed to hydroperoxides were unambiguously confirmed with a ^-^C heteronuclear multiple bond coherence (HMBC) experiment using the hmbcgplpndqf pulse sequence. The / -AHP, bis(2-ethylhexyl) phosphate, and sodium cumene sulfonate were post-added to a non-PEM functionalized styrene-acrylic latex. As illustrated in Table 1, Comparative Examples illustrate the significance of including all three additives to achieve passing the most stringent challenge test (CH3D7). / -AHP refers to / -amyl hydroperoxide, 2-EHP refers to a mixture of mono- and bis(2-ethylhexyl) phosphate, and SCS refers to sodium cumene sulfonate.

[0030] Table 1 - Challenge Tests for non-PEM Functionalized Styrene- Acrylic Latex with r-AHP

[0031]

[0032] The data show the criticality of the Cs-Cio-alkyl phosphate and the hydrotrope to reducing the loading of r-amyl hydroperoxide required to pass the most stringent challenge tests.

[0033] The / -AHP, bis(2-ethylhexyl) phosphate, and sodium cumene sulfonate were post-added to a PEM-functionalized (0.5 wt% PEM, based on the weight of polymer particles) styrene-acrylic latex. The results of the challenge tests are illustrated in Table 2. Table 2 - Challenge Tests for PEM Functionalized Styrene-Acrylic Latex with t-AHP

[0034]

[0035] The data show that low microbial growth in the PEM-functionalized latex can be achieved without presence of a hydrotrope.

Claims

Claims:

1. A composition comprising a) an aqueous dispersion of polymer particles optionally functionalized with structural units of 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 C4-Cio-alkyl hydroperoxide; c) a Cs-Cio-alkyl phosphate or sulfate; with the proviso that when the polymer particles are not functionalized with structural units of the phosphorus acid monomer, the composition further comprises d) a hydrotrope.

2. The composition of Claim 1 wherein the polymer particles are functionalized with structural units of a phosphorus acid monomer, the C4-C10- alkyl hydroperoxide is used in a preservative amount, and the concentration Cs-Cio-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 ethylenevinyl acetate latex.

3. The composition of Claim 2 wherein the C4-Cio-alkyl hydroperoxide is / -amyl hydroperoxide or / -butyl hydroperoxide at a concentration in the range of from 100 ppm to 1000 ppm, based on the weight of the composition; wherein the phosphorus acid monomer 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 Cs-Cio-alkyl sulfate; and the C4-Cw-alkyl hydroperoxide is / -amyl hydroperoxide; wherein the polymer particles are further functionalized with structural units of sodium styrene sulfonate.

5. The composition of Claim 4 wherein the branched Cs-Cio-alkyl phosphate or Cs-Cio-alkyl sulfate is bis(2-ethylhexyl) phosphate; wherein the concentration of / -amyl hydroperoxide is in the range of from 200 ppm to 600 ppm, based on the weight of the composition.

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-C4-alkylphenyl phosphate, b) a C1-C4-alkylphenyl sulfate, or c) a Ci-C4-alkylphenyl 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 of the C4-Cio-alkyl hydroperoxide is in the range of from 100 ppm to 1000 ppm; andthe concentration of the Cs-Cio-alkyl phosphate or Cs-Cw-alkyl sulfate is in the range of from 0.2 to 4 weight percent.

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 C4-Cio-alkyl hydroperoxide is / -amyl hydroperoxide, and the Cs-Cio-alkyl phosphate or Cs-Cio-alkyl sulfate is a branched Cs-Cw-alkyl phosphate or a branched Cs-Cw-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 / -amyl hydroperoxide is in the range of from 150 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 where the aqueous dispersion of polymer particles, the C4-C10-alkyl hydroperoxide, the Cs-Cw-alkyl phosphate or sulfate, and the hydrotrope comprise at least 90 weight percent of the composition.

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