Process for preparing antimicrobial styrene latex

Abstract

The present invention relates to a process comprising the steps of: a) contacting styrene and ethylenically unsaturated monomers under emulsion polymerization conditions to form an aqueous dispersion of styrene copolymer particles and residual monomers; and b) contacting the dispersion of styrenic copolymer 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; wherein the molar ratio of the t-C4-C10-alkyl hydrogen peroxide to the reducing agent is in the range of from 3: 1 to 50: 1. The method of the present invention provides a method for preserving styrene latex even in the absence of a biocide.

Description

Background Art

[0001] The present invention relates to a process for preparing aqueous dispersions of styrene 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 styrene and an ethylenically unsaturated monomer under emulsion polymerization conditions to form an aqueous dispersion of styrene copolymer particles and residual monomer; and

[0007] b) mixing the dispersion of the styrene copolymer 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;

[0008] Among them, the t-C4-C 10The 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 can be used to prepare latexes that are resistant to attack by microorganisms even in the absence of biocides. DETAILED DESCRIPTION

[0010] The present invention is a method comprising the following steps:

[0011] a) contacting styrene and an ethylenically unsaturated monomer under emulsion polymerization conditions to form an aqueous dispersion of styrene copolymer particles and residual monomer; and

[0012] b) mixing the dispersion of the styrene copolymer 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;

[0013] Among them, the t-C4-C 10 The molar ratio of the alkyl hydroperoxide to the reducing agent is in the range of 3:1 to 50:1.

[0014] In the first step, styrene is contacted with ethylenically unsaturated monomers under emulsion polymerization conditions to form an aqueous dispersion of polymer particles. Examples of suitable ethylenically unsaturated monomers include acrylates such as ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, 2-propylheptyl acrylate, and ureido acrylate; methacrylates such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, isobornyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate; acid monomers, including carboxylic acid monomers and salts thereof, such as acrylic acid, methacrylic acid, and itaconic acid and salts thereof; phosphoric acid monomers and salts thereof, such as ethyl methacrylate phosphate and salts thereof; and sulfonic acid monomers and salts thereof, such as 2-acrylamido-2-methyl-1-propanesulfonic acid, salts of 2-acrylamido-2-methyl-1-propanesulfonic acid, vinyl sulfonic acid, salts of vinyl sulfonic acid, sodium 4-vinylbenzenesulfonate, 2-propylene-1-sulfonic acid, and salts of 2-propylene-1-sulfonic acid, and combinations thereof and salts thereof. Sodium 4-vinylbenzene sulfonate (also known as sodium styrene sulfonate or SSS) is a preferred ethylenically unsaturated sulfonate.The one or more acid monomers preferably comprise from 0.1 wt% to 10 wt% of the ethylenically unsaturated monomers used to prepare the polymer particles.

[0015] Other examples of ethylenically unsaturated monomers include acrylamide or C1-C6-alkylacrylamide, acrylonitrile, vinyl monomers such as vinyltrimethoxysilane; and polyethylenically unsaturated monomers such as divinylbenzene and allyl methacrylate.

[0016] As used herein, the term "styrene copolymer particles" refers to copolymer particles comprising 10 to 90 wt% styrene structural units and 10 to 90 wt% one or more ethylenically unsaturated monomer structural units. Thus, the term "ethylenically unsaturated monomer" refers to one or more ethylenically unsaturated monomers.

[0017] As used herein, the term "structural unit" refers to the residue of the monomer after polymerization. For example, the structural unit of styrene is illustrated as follows:

[0018]

[0019] The dotted lines indicate the points of attachment to the polymer backbone.

[0020] Examples of preferred ethylenically unsaturated monomers are acrylate monomers. Preferably, the weight ratio of styrene to acrylate monomers is in the range of 60:40 or 50:50 or 45:55 to 20:80 or to 30:70 or to 35:65. n-Butyl acrylate and 2-ethylhexyl acrylate are preferred acrylate monomers.

[0021] The resulting dispersion contains residual monomers, which are reacted with a reducing agent such as isoascorbic acid or disodium 2-hydroxy-2-sulfinatoacetic acid and t-C4-C 10 -alkyl hydroperoxide to track residual monomers. Preferably, t-C4-C 10 The -alkyl hydroperoxide is tert-butyl hydroperoxide (t-BHP) or tert-amyl hydroperoxide (t-AHP) or a combination thereof.

[0022] t-C4C 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):

[0023] a) adding a catalytic amount of a redox reaction catalytic metal salt, for example a salt of iron (II) such as FeSO4, copper, manganese, vanadium, silver, platinum, nickel, chromium, palladium or cobalt or a combination thereof; b) adding a chelating agent for the metal salt; c) adjusting the temperature; and d) adjusting the pH.

[0024] Therefore, t-C4-C10 -alkyl hydroperoxide and reducing agent, optionally in the presence of catalytic metal salt and 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 t-C4-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. 10 -Alkyl hydroperoxide and reducing agent can be in the range of 1:1 to 3:1 t-C4-C 10 -alkyl hydroperoxide and reducing agent are added in a molar ratio, followed by the addition of t-C4-C 10 -alkyl hydroperoxide to convert t-C4-C 10 - The molar ratio of alkyl hydroperoxide to reducing agent is increased to a range of greater than 3:1 to 50:1.

[0025] 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.

[0026] The resulting composition comprises from 250 ppm or 300 ppm or 350 ppm or 450 ppm or 550 ppm or 700 ppm to 5000 ppm or to 2500 ppm or to 1500 ppm of t-C4-C 10 -alkyl hydroperoxide and preferably less than 1000 ppm, more preferably less than 500 ppm of residual monomers. 10 The concentration of -alkyl hydroperoxides was determined using NMR spectroscopy as detailed in the experimental part.

[0027] In another aspect, the invention is a composition comprising: a) an aqueous dispersion of styrene 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) a C4-C50 polymer in a concentration in the range of 250 ppm to 5000 ppm based on the weight of the composition. 10 -Alkyl hydroperoxides.

[0028] The process of the present invention provides a method for preparing an acrylic-based latex having antiseptic properties against molds, bacteria and yeasts.

[0029] Example

[0030] NMR spectroscopy determination of t-AHP or t-BHP in serum phase

[0031] 3.0mL latex sample, 3.0mL Milli-Q water were loaded into a 10-mL polycarbonate tube and centrifuged at 100,000rpm for 15 minutes. The resulting clarified supernatant was decanted and transferred to a 5-mm NMR tube. A flame-sealed capillary filled with an external standard (D2O containing 5.00wt% d4-trimethylsilyl propionate) was added to the NMR tube. Careful attention was paid to the correct alignment of the external standard in the NMR tube. The NMR spectrum was obtained using a Bruker AVANCEIII 600 spectrometer equipped with a 5-mm BroadBand CryoProbe. Each sample was individually tuned and shimmed, but the pulse width and receiver gain remained constant for the sample series. The concentration of free tert-amyl hydroperoxide was measured by using a zg pulse sequence with the following parameters: acquisition time (aq) = 2.5 seconds, recycle delay (d1) = 30 seconds, number of transients (ns) = 1024, receiver gain (rg) = 32, and pulse width (p1) = 11 milliseconds. All other parameters (time domain size, scan width, dwell time, prescan delay, and carrier frequency) were kept at default values. The concentration of free hydrogen peroxide was calculated by comparing the peak resonating around 1.2 ppm with the integral of the peak of an external standard at 0.0 ppm. The spectra were referenced to an external standard at 0.0 ppm on the trimethylsilyl chemical shift scale. The hmbcgplpndqf pulse sequence was used for the 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.

[0032] Preparation of samples for antimicrobial resistance

[0033] 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.

[0034] Table 1 - Rating system for assessing microbial contamination

[0035] 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

[0036] 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.

[0037] Comparative Example 1 - Preparation of Styrene-Acrylic Latex

[0038] A monomer emulsion was prepared by mixing deionized water (445 g), sodium lauryl sulfate (42.25 g, 28% active), Disponil FES-993 surfactant (12.09 g, 30% active), butyl acrylate (1143.54 g), styrene (782.73 g), vinyltrimethoxysilane (5.92 g), sodium 4-vinylbenzenesulfonate (6.57 g, 90% active), and acrylic acid (33.52 g).

[0039] To a 5-L four-necked round bottom flask equipped with a paddle stirrer, thermometer, N2 inlet, and reflux condenser was added deionized water (770 g) and sodium lauryl sulfate (1.5 g, 28% active). The contents of the flask were heated to 87° C. under N2 and stirring was initiated.

[0040] A portion of the monomer emulsion (86 g) was then added, followed by the rapid addition of an aqueous sodium persulfate solution (2.35 g) dissolved in deionized water (47 g), followed by a rinse with deionized water (5 g). After stirring for 5 minutes, the remaining monomer emulsion and a solution containing sodium persulfate (7.05 g) and sodium hydroxide (3 g, 50% active) dissolved in deionized water (197 g) were each added to the flask separately over a total period of 150 minutes. During the addition of the monomer emulsion, the contents of the flask were maintained at a temperature of 87° C. 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.

[0041] The contents of the flask were cooled to 75°C and aqueous FeSO4 solution (21.0 g, 0.1% solids), aqueous EDTA tetrasodium salt solution (1.2 g, 1% solids) were added to the kettle. The first catalyst / activator pair tert-amyl hydroperoxide (t-AHP, 1 g, 85% active) dispersed in 15 g of deionized water and isoascorbic acid (0.5 g) dissolved in 15 g of deionized water were then added to the flask to reduce residual monomers. After addition, the contents of the flask were held at 75°C for 10 minutes. After holding for 10 minutes, the second catalyst / activator pair t-AHP (2 g, 1x, 85% active) and Disponil FES-993 surfactant (1.7 g, 30% active) dispersed in 30 g of deionized water and isoascorbic acid (1.9 g) dissolved in 35 g of deionized water were added to the flask linearly and separately over a 20 minute period. During the addition of the second catalyst / activator pair, the contents of the flask were cooled to 55° C. The pH was adjusted to 8.9.

[0042] Example 1 - Preparation of Styrene-Acrylic Latex with Excess-t-AHP

[0043] The method of Comparative Example 1 was repeated except that the amount of t-AHP added in the second catalyst pair was 5 g (2x) instead of 2 g. The pH was adjusted to 9.0.

[0044] Example 2 - Preparation of Styrene-Acrylic Latex with Excess-t-AHP

[0045] The method of Comparative Example 1 was repeated except that the amount of t-AHP added in the second catalyst pair was 8 g (3x) instead of 2 g. The pH was adjusted to 9.0.

[0046] 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.

[0047] Table 2 - Relative concentration of t-AHP

[0048] Added t-AHP Measured t-AHP (ppm) Measured t-AmOH (ppm) Comparative Example 1 1x 105 119 Example 1 2x 345 140 Example 2 3x 542 144

[0049] Table 3 shows the thermal aging challenge test results of the samples.

[0050] Table 3 - Thermal aging stimulation test results

[0051] C1 C2 C3 Comparative Example 1 Failure Failure Failure Example 1 qualified qualified Failure Example 2 qualified qualified qualified

[0052] 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 styrene and an ethylenically unsaturated monomer under emulsion polymerization conditions to form an aqueous dispersion of styrene copolymer particles and residual monomer; and b) mixing the dispersion of the styrene copolymer 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; wherein the t-C4-C 10 The molar ratio of the alkyl hydroperoxide to the 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 the dispersion of the styrene copolymer particles with an alkyl hydroperoxide and the reducing agent in a molar ratio ranging from 4.5:1 to 30:1; wherein during or after step b), 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 styrene copolymer 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 the dispersion of the styrene copolymer particles with an alkyl hydroperoxide and the reducing agent 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 the dispersion of the styrene copolymer particles with an alkyl hydroperoxide and the reducing agent in a molar ratio in the range of 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 ethylenically unsaturated monomer is an acrylate monomer; and a weight ratio of the acrylate monomer to the styrene is in the range of 60:40 to 30:

70. 7 . The method according to claim 6 , wherein the acrylate monomer is n-butyl acrylate, and a weight ratio of n-butyl acrylate to styrene is in the range of 50:50 to 35:

65.

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 acrylic acid-based polymer particles is further contacted with a catalytic amount of FeSO4 and optionally a chelating agent.

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