Antimicrobial coating composition

Abstract

The present invention relates to formulated coating compositions containing a preservative amount of a C4-C10-alkyl hydroperoxide and a process for preparing the coating.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a coating composition that is resistant to microbial growth even in the absence of biocides.

[0002] Coatings are preserved with antimicrobial agents to inhibit the formation and growth of living 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 build-up in closed containers. Thus, preservation is necessary for health, safety, and performance reasons.

[0003] Canned preservatives, such as isothiazolinones, are facing severe regulatory scrutiny due to their actual or perceived adverse effects on health, safety, and the environment; indeed, a complete ban on these biocides seems likely in many parts of the world. To some extent, due to cost reasons and the widespread perception (whether reasonable or not) of the inherent dangers of these biocides, the development of new biocides is not possible, and thus there is a need to replace biocides with safer and more sustainable alternative non-biocidal preservatives.

[0004] A recent example of a non-biocidal method for preserving coatings against microbial contamination can be found in EP 3 456 787 B1, which discloses an aqueous coating formulation with a pH adjusted to the range of 10 to 12.5. While seemingly effective, these very high pH formulations create additional safety and hygiene issues, making this method impractical. Other non-conventional methods, such as the addition of silver or zinc ions, may adversely affect the properties of the coating and also face regulatory scrutiny. For these reasons, there is a need for other safer and more sustainable methods for preserving coatings and the materials used in coatings. SUMMARY OF THE INVENTION

[0005] The present invention addresses the need in the art by providing a composition comprising a formulated coating and a mixture of C4-C 10 -alkyl hydroperoxides in the range of 40 ppm to 1000 ppm.

[0006] The composition of the present invention provides a coating that is resistant to microbial growth even in the absence of biocides. DETAILED DESCRIPTION

[0007] The present invention is a coating composition comprising a formulated coating and a mixture of C4-C 10 -alkyl hydroperoxides in the range of 40 ppm to 1000 ppm.

[0008] The formulated coating can be conveniently prepared by combining a paint - adjusting part, which is a mixture of an aqueous dispersion of polymer particles (i.e., latex), a thickener, an antifoaming agent, a surfactant, a neutralizing agent, and water, and a grinding part, which is a blend of an opaque pigment such as TiO2, an extender pigment, an antifoaming agent, a neutralizing agent, a dispersing agent, and water. In one aspect of the present invention, the latex preferably contains 100 ppm - 2500 ppm of C4 - C 10 -alkyl hydroperoxide, and the concentration of C4 - C 10 -alkyl hydroperoxide in the finally formulated coating is solely generated by the amount of this additive in the latex. Alternatively, the desired concentration of C4 - C 10 -alkyl hydroperoxide can be achieved by adding this additive to both the latex and the finally formulated coating.

[0009] C4 - C 10 The concentration of alkyl hydroperoxide in the latex is preferably in the range from 60 or 100 ppm or 125 ppm or 150 ppm or 175 ppm or 225 ppm or 275 ppm or 350 ppm to preferably 900 ppm or 750 ppm or 600 ppm or 500 ppm. Preferably, the tert - C4 - C 10 -alkyl hydroperoxide is tert - butyl hydroperoxide (t - BHP) or tert - amyl hydroperoxide (t - AHP), and the concentration of tert - C4 - C 10 -alkyl hydroperoxide in the latex is determined using NMR spectroscopy as detailed in the experimental section.

[0010] The formulated coating also preferably contains a biocide in an amount less than the amount of the preservative, which means that the amount of biocide contained in the coating is less than the amount of biocide required by the challenge test as defined herein. Preferably, the formulated coating does not contain a biocide.

[0011] Surprisingly, it has been found that the coating can be preserved by including only the amount of the preservative of tert - C4 - C 10 -alkyl hydroperoxide in the latex used for formulating the coating.

[0012] Example

[0013] NMR spectroscopic determination of t-AHP or t-BHP in the serum phase

[0014] 3.0 mL of the latex sample and 3.0 mL of Milli-Q water were charged into a 10-mL polycarbonate tube and centrifuged at 100,000 rpm for 15 minutes. The resulting clear supernatant was decanted and transferred to a 5-mm NMR tube. A flame-sealed capillary filled with an external standard (D2O containing 5.00 wt% sodium 3-trimethylsilylpropionate-d4) was added to the NMR tube. Care was taken to ensure the correct alignment of the external standard within the NMR tube. NMR spectra were 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 were kept constant for the series of samples. The concentration of free tert-amyl hydroperoxide was measured by using the zg pulse sequence with the following parameters: acquisition time (aq) = 2.5 s, recycle delay (d1) = 30 s, number of transients (ns) = 1024, receiver gain (rg) = 32, and pulse width (p1) = 11 ms. All other parameters (time domain size, sweep width, dwell time, prescan delay, and carrier frequency) were kept at their default values. The concentration of free hydrogen peroxide was calculated by comparing the integrals of the peaks resonating near 1.2 ppm and the peak of the external standard at 0.0 ppm. The spectra were referenced to the external standard at 0.0 ppm on the trimethylsilyl chemical shift scale. The 1 H- 13 C heteronuclear multiple bond coherence (HMBC) experiment clearly confirmed the purity of the hydrogen peroxide resonance. The integral normalization was estimated by using diffusion-ordered spectroscopy (DOSY) experiments to determine the weight-average mass of the SSS oligomers using the ledbpgp2s pulse sequence.

[0015] Preparation of samples for antimicrobial properties

[0016] The antimicrobial properties of the samples were tested “as received” (not thermally aged) and after being subjected to 50 °C for four weeks (thermally aged). 10-g aliquots were taken from each sample and diluted with 10 6 -10 7A standard pool of bacteria, yeast, and mold (obtained from the American Type Culture Collection (ATCC), common contaminants in coatings) at a concentration of colony forming units per milliliter of sample (CFU / mL) was inoculated into the samples three times at 7-day intervals. After inoculation, the samples were stored in an incubator at 25 °C. Microbial contamination of the test samples was monitored by agar plate inoculation using the standard streak plate method. The samples were inoculated onto tryptic soy agar (TSA) and potato dextrose agar (PDA) plates on Day 1 and Day 7 after each microbial challenge. All agar plates were examined daily after inoculation until Day 7 to determine the number of microorganisms surviving in the test samples. Between examinations, the agar plates were stored in the incubator, at 30 °C for TSA plates and at 25 °C for PDA plates. The degree of microbial contamination was determined by counting the colonies, where the rating score was based on the number of microbial colonies observed on the agar plates. The results reported were from the Day 7 readings and were summarized for both "as received" and heat-aged samples. The results were described by scoring 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 streak plates. Colony refers to the number of colonies on the plate.

[0017] Table 1 - Rating system for assessing microbial contamination

[0018] Colony Rating score Contamination Result None 0 None Pass 1 to 9 Tr Trace Pass 10 to 99 1 Very slight Fail 100 to about 1000 2 Slight Fail About 1000 to 10,000 3 Moderate Fail >10,000 4 Severe Fail

[0019] In Table 1, "Pass" means fewer 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 distinct colonies were detected on the plate on a specific day after inoculation.

[0020] Table 2 illustrates the components used to prepare the formulated coatings. Latex 1 refers to an ethyl methacrylate phosphate (PEM) functionalized acrylic latex (47.2% solids) containing 466 ppm of t-AHP and no biocide; Latex 2 refers to a PEM functionalized acrylic latex (50 wt% solids) containing <100 ppm of t-AHP and 220 ppm of Kordek MLX can preservative. Latex 3 refers to a styrene-acrylic latex (50.1 wt% solids) containing 536 ppm of t-AHP and no biocide; and Latex 4 refers to a styrene-acrylic latex (41.5 wt% solids) containing <100 ppm of t-AHP and 48 ppm of Kathon LX biocide.

[0021] Table 2 - Coating formulations

[0022] Ingredient (pbw) Comparative Example 1 Example 1 Comparative Example 2 Example 2 Water 200.0 197.4 200.0 198.0 Tamol 1124 dispersant 5.7 <![CDATA[OROTAN TM Dispersant CA-2500]]> 10.6 21.1 21.0 Potassium hydroxide (10%) 4.0 3.9 AMP-95 neutralizer 2.5 2.5 <![CDATA[DOWSIL TM 71 Defoamer]]> 1.0 1.0 1.0 1.0 <![CDATA[TRITON TM DF-16 surfactant]]> 2.0 2.0 2.0 2.0 Ti-Pure R-706 titanium dioxide 150.2 148.3 200.3 198.3 <![CDATA[Omycarb 3CaCO3]]> 135.2 133.4 90.1 89.2 <![CDATA[Omyacarb 8CaCO3]]> 270.4 267.7 Latex 1 389.1 Latex 2 385.6 Latex 3 322.3 Latex 4 387.8 <![CDATA[TERGITOL TM 15-S-40 surfactant]]> 2.0 2.0 2.0 2.0 <![CDATA[DOWSIL TM 71 Defoamer]]> 1.0 1.0 1.0 1.0 Water 113.2 123.5 22.3 94.0 <![CDATA[ACRYSOL TM TT-935 Rheology Modifier]]> 10.5 <![CDATA[CELLOSIZE TM QP-4400 Rheological Modifier]]> 2.5 4.5 <![CDATA[ACRYSOL TM RM-2020E rheology modifier]]> 20.0 19.7 20.0 19.8 <![CDATA[ACRYSOL TM RM-725 rheology modifier]]> 10.7 Potassium hydroxide (10%) (neutralizer) 59.2 4.3 Potassium tripolyphosphate 2.0 2.0 2.0 2.0

[0023] OROTAN, DOWSIL, TRITON, TERGITOL, DOWSIL, ACRYSOL, and CELLOSIZE are trademarks of The Dow Chemical Company or its affiliated companies.

[0024] Table 3 - As-received excitation test results

[0025] Example number C1 Example 1 Pass Comparative Example 1 Fail Example 2 Pass Comparative Example 2 Fail

[0026] The comparative coatings, which contain biocides at the preservative level in the latex used to prepare these coatings, did not pass the first excitation test. In contrast, the coatings containing t-AHP at the preservative level in the latex used to prepare the example coatings passed the first excitation test. In addition, the coatings of Example 1 passed both excitation tests, while the coatings of Example 2 passed all three excitation tests.

Claims

1. A composition, the composition comprising a formulated coating and a mixture of C4-C 10 -alkyl hydroperoxides in an amount from 40 ppm to 1000 ppm.

2. The composition according to claim 1, wherein the composition comprises 60 ppm to 900 ppm of C4-C 10 -alkyl hydroperoxide.

3. The composition according to claim 1, the composition comprising from 100 ppm to 750 ppm of a C4-C 10 -alkyl hydroperoxide, wherein the C4-C 10 -alkyl hydroperoxide is tert-butyl hydroperoxide or tert-amyl hydroperoxide.

4. The composition according to claim 3, wherein the composition comprises 100 ppm to 500 ppm of tert-butyl hydroperoxide or tert-amyl hydroperoxide.

5. The composition according to any one of claims 1 to 4, wherein the composition comprises a biocide in an amount less than the preservation dose.

6. A method for preparing a coating, the method comprising the step of mixing an acrylic or styrene-acrylic latex with water, an opaque pigment, a rheology modifier, a surfactant, an antifoaming agent, a neutralizing agent, an optional dispersant, and an optional extender, wherein the acrylic or styrene-acrylic latex contains 100 ppm to 2500 ppm of a C4-C 10 -alkyl hydroperoxide, and the amount of the latex mixed with the other components is in the range of 10% to 25% by weight based on the weight of all components used to prepare the coating.

7. The method according to claim 6, wherein the C4-C 10 -alkyl hydroperoxide is tert-butyl hydroperoxide or tert-amyl hydroperoxide, and the coating is prepared by mixing the acrylic or styrene-acrylic latex with water, an opaque pigment, a rheology modifier, a surfactant, an antifoaming agent, a neutralizing agent, a dispersant, and an extender.

8. The method according to claim 7, wherein the components other than the latex do not contain any C4-C 10 -alkyl hydroperoxides.

9. The method according to any one of claims 6 to 8, wherein a biocide in an amount less than the preservation dose is used to prepare the coating.