Process for preparing antimicrobial acrylic latex

Abstract

The present invention relates to a process comprising the steps of: a) contacting monomers comprising an acrylate monomer, a methacrylate monomer and an acid monomer under emulsion polymerization conditions to form an aqueous dispersion of acrylic acid-based polymer particles and residual monomers; b) contacting the dispersion of acrylic polymer particles with a reducing agent and t-C4-C10-alkyl hydrogen peroxide to reduce the concentration of residual monomer in the aqueous dispersion to less than 1000 ppm of residual monomer. The method of the present invention provides a method that can preserve acrylic acid-based latexes even in the absence of biocides.

Description

Background Art

[0001] The present invention relates to a process for preparing aqueous dispersions of polymer particles which exhibit resistance to microbial growth even in the absence of a biocide.

[0002] Aqueous dispersions of polymer particles (i.e., latex) used in the coating industry are preserved 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 outgassing of volatile products and subsequent pressure buildup in closed containers. Therefore, preservation is necessary for health, safety, and performance reasons.

[0003] Can preservatives such as isothiazolinones are facing intense regulatory scrutiny for their real or perceived adverse effects on health, safety and the environment; in fact, a total ban on these biocides appears imminent in many parts of the world. To the extent that the development of new biocides is not possible due to cost reasons and the widespread perception (whether justified or not) of the inherent dangers of these biocides, there is a need to replace biocides with alternative non-biocidal preservatives that are safer and more sustainable.

[0004] In EP 3 456 787 B1, can be found for the preservation of coatings to prevent the recent example of non-biocidal methods of microbial contamination, the document discloses pH adjustment to the aqueous coating formulations in the range of 10 to 12.5. Although effective on the surface, these formulations of very high pH have produced other safety and sanitation issues, making this method impractical. Other non-traditional methods such as adding silver or zinc ions may adversely affect the characteristics of coatings, and also face regulatory review. Due to these reasons, it is necessary to be used to preserve other safer and more sustainable methods of the materials used in coatings and coatings. Summary of the invention

[0005] The present invention solves the need in the art by providing a method on the one hand, the method comprising the following steps:

[0006] a) contacting acrylate monomers, methacrylate monomers, and acid monomers under emulsion polymerization conditions to form an aqueous dispersion of acrylic-based polymer particles and residual monomers; and

[0007] b) mixing the dispersion of the acrylic acid-based polymer particles with a reducing agent and tC 4 -C 10 - contacting with an alkyl hydroperoxide to reduce the concentration of residual monomers in the aqueous dispersion to less than 1000 ppm of residual monomers;

[0008] Among them, tC 4-C 10 The molar ratio of the alkyl hydroperoxide to the reducing agent is in the range of 3:1 to 50:1.

[0009] The process of the present invention provides a method for preparing latexes that are resistant to attack by microorganisms even in the absence of biocides. DETAILED DESCRIPTION

[0010] In a first aspect, the present invention is a method comprising the steps of:

[0011] a) contacting acrylate monomers, methacrylate monomers, and acid monomers under emulsion polymerization conditions to form an aqueous dispersion of acrylic-based polymer particles and residual monomers; and

[0012] b) mixing the dispersion of the acrylic acid-based polymer particles with a reducing agent and tC 4 -C 10 - contacting with an alkyl hydroperoxide to reduce the concentration of residual monomers in the aqueous dispersion to less than 1000 ppm of residual monomers;

[0013] Among them, tC 4 -C 10 The molar ratio of the alkyl hydroperoxide to the reducing agent is in the range of 3:1 to 50:1.

[0014] As used herein, the terms "acrylate monomers," "methacrylate monomers," and "acid monomers" refer to one or more of the monomers. As used herein, "acrylic-based" means that at least 50 wt. %, more preferably at least 70 wt. %, more preferably at least 80 wt. %, and most preferably at least 90 wt. % of the monomers used to prepare the aqueous dispersion of acrylic-based polymer particles are acrylate, methacrylate, and acid monomers.

[0015] Examples of suitable acrylate monomers include C 1 -C 10 - Acrylates, such as ethyl acrylate, n-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate and 2-propylheptyl acrylate. Examples of suitable methacrylate monomers include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate and ureido methacrylate. Methyl methacrylate is the preferred methacrylate monomer; ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate are preferred acrylate monomers. The combination of acrylate and methacrylate monomers preferably accounts for 70 wt%, or 80 wt%, or 90 wt% to 99 wt% of the total monomers used to prepare the polymer particles.

[0016] Examples of suitable acid monomers include carboxylic acid monomers and salts thereof, such as acrylic acid, methacrylic acid and itaconic acid and their salts; phosphoric acid monomers and their salts, such as methyl methacrylate phosphoethyl ester and its salts; and sulfonic acid monomers and their salts, such as 2-acrylamido-2-methyl-1-propanesulfonic acid, salts of 2-acrylamido-2-methyl-1-propanesulfonic acid, vinylsulfonic acid, salts of vinylsulfonic acid, sodium 4-vinylbenzenesulfonate, 2-propylene-1-sulfonic acid and salts of 2-propylene-1-sulfonic acid, and combinations thereof and their salts. Sodium 4-vinylbenzenesulfonate (also known as sodium styrenesulfonate or SSS) is a preferred sulfonate. One or more acid monomers preferably account for 0.1 wt % to 10 wt % of the monomers used to prepare the polymer particles.

[0017] Other monomers such as acrylonitrile, acrylamide or C 1 -C 6 - alkyl acrylamides, and polyethylenically unsaturated monomers such as divinylbenzene and allyl methacrylate.

[0018] Aqueous dispersions of acrylate-based polymer particles are advantageously prepared by contacting the monomers under emulsion polymerization conditions well known in the art. The resulting dispersion contains residual monomers which are reacted with a reducing agent such as isoascorbic acid or 2-hydroxy-2-sulfinatoacetic acid disodium salt and tC 4 -C 10 -alkyl hydroperoxide to track residual monomers. Preferably, tC 4 -C 10 The -alkyl hydroperoxide is tert-butyl hydroperoxide (t-BHP) or tert-amyl hydroperoxide (t-AHP) or a combination thereof.

[0019] tC 4 -C 10 The molar ratio of alkyl hydroperoxide to reducing agent is preferably in the range of 1:1 or 3:1 or 3.5:1 or 4.5:1 or 5.5:1 or 6.5:1 or 7.0:1 to 50:1 or to 30:1 or to 20:1 or to 15:1 or to 10:1. The efficiency of this redox system can be controlled by a number of factors, including the optional addition during or after step a): a) a catalytic amount of a redox reaction catalytic metal salt, for example a salt of iron (II), such as FeSO 4 , copper, manganese, vanadium, silver, platinum, nickel, chromium, palladium or cobalt or a combination thereof; b) adding a chelating agent of a metal salt; c) adjusting the temperature; and d) adjusting the pH.

[0020] Therefore, tC 4 -C 10-alkyl hydroperoxide and reducing agent, optionally in the presence of a catalytic metal salt and a chelating agent, can be contacted with the aqueous dispersion of polymer particles in a single stage or in multiple stages, using the same or different molar ratios in each stage, provided that the added tC 4 -C 10 -The molar ratio of the total amount of alkyl hydroperoxide to the total amount of reducing agent added in multiple steps is within the specified range. For example, tC 4 -C 10 - The alkyl hydroperoxide and the reducing agent can be mixed in a ratio ranging from 1:1 to 3:1. 4 -C 10 - alkyl hydroperoxide and reducing agent in a molar ratio, followed by post addition of tC 4 -C 10 -Alkyl hydroperoxide to convert tC 4 -C 10 - The molar ratio of alkyl hydroperoxide to reducing agent is increased to a range of greater than 3:1 to 50:1.

[0021] The resulting aqueous dispersion of polymer particles is preferably neutralized in or after step a), more preferably in or after step b), to a pH in the range of 7.5 or 8.0 or 8.5 or 8.8 to 10.0 or to 9.5 or to 9.2.

[0022] The resulting composition comprises from 125 ppm or 250 ppm or 175 ppm or 225 ppm or 275 ppm or 350 ppm to 2500 ppm or to 1250 ppm or to 750 ppm of tC 4 -C 10 -alkyl hydroperoxide and preferably less than 1000 ppm, more preferably less than 500 ppm of residual monomers. 4 -C 10 The concentration of -alkyl hydroperoxides was determined using NMR spectroscopy as detailed in the experimental part.

[0023] In another aspect, the invention is a composition comprising: a) an aqueous dispersion of acrylic-based polymer particles having a z-average particle size in the range of 50 nm or 80 nm to 500 nm or to 300 nm or to 200 nm as measured using dynamic light scattering; and b) C in a concentration in the range of 125 ppm to 2500 ppm based on the weight of the composition. 4 -C 10 -Alkyl hydroperoxides.

[0024] The process of the present invention provides a method for preparing acrylic-based latexes having antiseptic properties against molds, bacteria and yeasts.

[0025] Example

[0026] NMR spectroscopy determination of t-AHP or t-BHP in serum phase

[0027] A 10-mL polycarbonate tube was charged with 3.0 mL of latex sample, 3.0 mL of Milli-Q water, and centrifuged at 100,000 rpm for 15 minutes. The resulting clear supernatant was decanted and transferred to a 5-mm NMR tube. A 10-mL polycarbonate tube filled with an external standard (containing 5.00 wt % d 4 -Sodium trimethylsilyl propionate D 2 0) is added to the NMR tube. Carefully note the correct alignment of the external standard in the NMR tube. Use the Bruker AVANCEIII 600 spectrometer equipped with a 5-mm BroadBand CryoProbe to obtain NMR spectra. Each sample is tuned and shimmed individually, but the pulse width and receiver gain remain constant for the sample series. The concentration of free tert-amyl hydroperoxide is measured by using a zg pulse sequence with the following parameters: acquisition time (aq) = 2.5 seconds, recycle delay (d1) = 30 seconds, transient number (ns) = 1024, receiver gain (rg) = 32, and pulse width (p1) = 11 milliseconds. All other parameters (time domain size, scan width, dwell time, pre-scan delay and carrier frequency) remain as default values. The concentration of free hydrogen peroxide is calculated by comparing the peak of the resonance near 1.2ppm and the integration of the peak of the external standard at 0.0ppm. The spectrum is referenced to the external standard at 0.0ppm on the trimethylsilyl chemical shift scale. The HMBCGPLPLDQF pulse sequence was used to 1 H- 13 The purity of the hydrogen peroxide resonances was unambiguously confirmed by C heteronuclear multiple bond coherence (HMBC) experiments. The SSS oligomer content was calculated by comparing the normalized integral of the peak resonating around 7 ppm with the peak of an external standard at 0.0 ppm. The integral normalization was estimated by determining the weight-average mass of the SSS oligomers using a diffusion ordered spectroscopy (DOSY) experiment using an LEDBPGP2S pulse sequence.

[0028] Preparation of samples for antimicrobial resistance

[0029] The samples were tested for antimicrobial properties "as is" (not heat aged) and after being subjected to 50°C for four weeks (heat aged). A 10-g aliquot was taken from each sample and heated to 10 6 -10 7The samples were inoculated three times with a pool of standard bacteria, yeasts and molds (obtained from the American Type Culture Collection (ATCC) for common contaminants in coatings) with 7-day intervals. After inoculation, the samples were stored in a 25°C incubator. The microbial contamination of the test samples was monitored by agar plate inoculation using the standard streak plate method. The samples were inoculated on tryptic soy agar (TSA) and potato dextrose agar (PDA) plates on the 1st and 7th days after each microbial attack. All agar plates were checked daily until the 7th day after inoculation to determine the number of microorganisms that survived in the test samples. Between inspections, agar plates were stored in an incubator, at 30°C for TSA plates, and at 25°C for PDA plates. The degree of microbial contamination was determined by counting colonies, where the rating score was determined according to the number of microbial colonies observed on agar plates. The reported results are from the 7th day readings, and are summarized for both "as is" and heat aging samples. 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 yeast (1 colony on the plate). Table 1 illustrates the rating system used to estimate the level of microbial contamination on the planned plate. Colony refers to the number of colonies on the plate.

[0030] Table 1 - Rating system for assessing microbial contamination

[0031] Colony Rating score pollute result none 0 none qualified 1-9 Tr Trace qualified 10 to 99 1 Very slight Failure 100 to about 1000 2 slight Failure Approximately 1000 to 10,000 3 Moderate Failure >10,000 4 Severe Failure

[0032] In Table 1, "pass" means less than ten colonies were detected on the plate on a specific day after inoculation (Day 1 (D1) or Day 7 (D7)). "Fail" means ten or more different colonies were detected on the plate on a specific day after inoculation.

[0033] Comparative Example 1 - Method for preparing acrylic latex

[0034] A monomer emulsion was prepared by mixing deionized water (800 g), sodium lauryl sulfate (16.59 g, 28% active), n-butyl acrylate (1016.58 g), methyl methacrylate (889.53 g), ureido methacrylate (39.1 g, 50% active), methacrylic acid (19.55 g), and sodium 4-vinylbenzene sulfonate (10.87 g, 90% active).

[0035] The mixture was equipped with a paddle stirrer, a thermometer, and N 2 A 5-L four-necked round-bottom flask with an inlet and reflux condenser was charged with deionized water (730 g), sodium lauryl sulfate (19.73 g, 28% active), and an aqueous solution of sodium carbonate (6.84 g) dissolved in deionized water (70 g).2 The contents of the flask were heated to 87° C. and stirring was initiated.

[0036] A portion of the monomer emulsion (58.8 g) was then added to the flask, followed by the rapid addition of an aqueous solution of ammonium persulfate (6.8 g) dissolved in deionized water (20 g), followed by a rinse with deionized water (5 g). After stirring for 5 minutes, the remaining monomer emulsion and a solution containing ammonium persulfate (1.04 g) dissolved in deionized water (92 g) were each added to the flask over a total period of 65 minutes. During the addition of the monomer emulsion, the contents of the flask were maintained at 87° C. When all additions were complete, the container containing the residual monomer emulsion was rinsed with deionized water (25 g), which was then added to the flask. The contents of the flask were cooled to 75° C., and the FeSO 4 An aqueous solution (20.1 g, 0.1% solids) and an aqueous solution of tetrasodium EDTA (2 g, 1% solids) were added to the kettle. A catalyst / activator pair of a) tert-amyl hydroperoxide (t-AHP, 1.27 g, 85% active) dispersed in 40 g of deionized water and b) isoascorbic acid (IAA, 0.75 g) dissolved in 40 g of deionized water were then added linearly and separately to the flask over 20 minutes. The contents of the flask were maintained at 75° C. during the addition of the catalyst / activator pair.

[0037] The polymer was then neutralized to pH ˜9.0 with aqueous ammonium hydroxide and deionized water. The z-average particle size was measured to be 116 nm using a Brookhaven BI-90 Plus particle size analyzer; the solids were measured to be 50.3%.

[0038] Example 1-4 - Method for preparing acrylic latex with excess t-AHP

[0039] The method of Comparative Example 1 was repeated except that the amount by weight of t-AHP added after the flask was cooled to 75° C. was increased by 2 times (Example 1), 3 times (Example 2), 4 times (Example 2), and 5 times (Example 4).

[0040] Table 2 shows the relative concentration of t-AHP added relative to Comparative Example 1, as well as the concentrations of t-AHP and tert-amyl hydroperoxide (t-AmOH) measured in the final neutralized dispersion.

[0041] Table 2 - Relative concentration of t-AHP

[0042] Added t-AHP Measured t-AHP (ppm) Measured t-AmOH (ppm) Comparative Example 1 1x 71 55 Example 1 2x 148 10552 Example 2 3x 188 54 Example 3 4x 298 60 Example 4 5x 395 62

[0043] Table 3 shows the thermal aging challenge test results of the samples.

[0044] Table 3 - Thermal aging stimulation test results

[0045] C1 C2 Comparative Example 1 Failure Failure Example 1 qualified qualified Example 2 qualified qualified Example 3 qualified qualified Example 4 qualified qualified

[0046] The data demonstrate that increasing t-AHP levels is effective in preserving acrylic-based latexes against microbial growth.

Claims

1. A method comprising the following steps: a) contacting acrylate monomers, methacrylate monomers, and acid monomers under emulsion polymerization conditions to form an aqueous dispersion of acrylic-based polymer particles and residual monomers; as well as b) mixing the dispersion of the acrylic acid-based polymer particles with a reducing agent and t-C4-C 10 - contacting with an alkyl hydroperoxide to reduce the concentration of residual monomers in the aqueous dispersion to less than 1000 ppm of residual monomers; Among them, t-C4-C 10 - The molar ratio of alkyl hydroperoxide to reducing agent is in the range of 3:1 to 50:

1.

2. The method according to claim 1, wherein the C4-C 10 - contacting an alkyl hydroperoxide and the reducing agent with the dispersion of the acrylic-based polymer particles in a molar ratio ranging from 4.5:1 to 30:1; wherein during or after step a), the pH is adjusted to a range of 7.5 to 10.

3. The method according to claim 1, wherein the C4-C 10 - alkyl hydroperoxide and the reducing agent are contacted with the dispersion of the acrylic acid-based polymer particles in a molar ratio ranging from 5.5:1 to 30:1; and wherein the C4-C 10 - the alkyl hydroperoxide is tert-amyl hydroperoxide or tert-butyl hydroperoxide or a combination thereof; wherein during or after step b), the pH is adjusted to a range of 8.0 to 9.

5.

4. The method according to claim 1, wherein the C4-C 10 - contacting an alkyl hydroperoxide and the reducing agent with the dispersion of the acrylic-based polymer particles in a molar ratio ranging from 6.5:1 to 20:1; wherein during or after step b), the pH is adjusted to a range of 8.0 to 9.

5.

5. The method according to claim 1, wherein the C4-C 10 - contacting an alkyl hydroperoxide and the reducing agent with the dispersion of the acrylic-based polymer particles in a molar ratio ranging from 7.0:1 to 15:1; wherein during or after step b), the pH is adjusted to a range of 8.0 to 9.

5.

6. The method according to any one of claims 1 to 5, wherein the concentration of acrylate and methacrylate monomers is in the range of 60 wt% to 99.9 wt% based on the weight of the monomers.

7. The method of claim 6, wherein the concentration of acrylate and methacrylate monomers is in the range of 80 wt% to 99.9 wt% based on the weight of the monomers.

8. The method of claim 7, wherein the monomer further comprises 0.1 wt% to 10 wt% of sodium styrene sulfonate.

9. The method according to claim 2, wherein in or after step a), the dispersion of the acrylic-based polymer particles is further contacted with a catalytic amount of FeSO4 and optionally a chelating agent.