Composition with 2-octyl acrylate / methyl methacrylate based latex and photoinitiator

Abstract

The present invention relates to a composition comprising a) an aqueous dispersion of polymer particles comprising structural units of 2-octyl acrylate, methyl methacrylate, and an ethylenically unsaturated acid monomer; and b) a photoinitiator. The composition of the present invention is useful, for example, in architectural coating formulations, especially exterior architectural paint formulations.

Description

[0001] Composition with 2-Octyl Acrylate / Methyl Methacrylate Based Latex and Photoinitiator

[0002] Background of the Invention

[0003] The present invention relates to a composition comprising a 2-octyl acrylate / methyl methacrylate-based latex and a photoinitiator. Aqueous dispersions of polymer particles (latexes) found in waterborne exterior architectural coating formulations comprise polymers typically with structural units of butyl acrylate, methyl methacrylate, and methacrylic acid, as well as ancillary specialty acrylic monomers such as ureido methacrylate. It is desirable for coatings arising from these formulations to both withstand exposure to commonly occurring environmental stresses such as UV exposure from sunlight, seasonal temperature changes, precipitation, and pollutants, and to retain acceptable aesthetic appearance. One commonly used measure of aesthetics is dirt pickup resistance (DPUR) of a coating when exposed to pollutants. DPUR is largely impacted by the hardness of the surface of a coating; therefore, DPUR can be enhanced by increasing the measured glass transition temperature (Tg) of the latex to greater than 25 °C. Unfortunately, an increase in the latex Tgoften results in brittleness, swelling, and contraction of the coating arising from seasonal variations, particularly in wood substrates. The DPUR of a coated finished prepared from a formulation containing a latex having a Tgof less than 15 °C can be improved to acceptable levels with the inclusion of an effective amount of a UV-active photoinitiator such as benzophenone. Nevertheless, the amount of photoinitiator required to achieve acceptable DPUR often compromises the effective lifetime of the coating, as manifested by loss of gloss, loss of tint, and binder chalking, and surface cracking. Accordingly, it would be advantageous to develop a latex with a moderately low Tgthat provides the benefits of good DPUR performance without the detriments of premature coating degradation upon outdoor exposure.

[0004] Summary of the Invention

[0005] The present invention addresses a need in the art by providing a composition comprising a) an aqueous dispersion of polymer particles comprising structural units of 2-octyl acrylate, methyl methacrylate, and an ethylenically unsaturated acid monomer; and b) a photoinitiator, wherein the Tgof the polymer particles, as measured by differential scanning calorimetry, is in the range of from -20 °C to 20 °C, wherein the concentration of the photoinitiator, based on the weight of the polymer particles and the photoinitiator, is in the range of from 0.02 weight percent to 4 weight percent. The composition of the present invention is useful in paint compositions, especially exterior paint compositions that form coatings with high dirt pickup resistance and improved integrity over time.

[0006] Detailed Description of the Invention

[0007] The present invention is a composition comprising a) an aqueous dispersion of polymer particles comprising structural units of 2-octyl acrylate, methyl methacrylate, and an ethylenically unsaturated acid monomer; and b) a photoinitiator, wherein the Tgof the polymer particles as measured by differential scanning calorimetry is in the range of from -20 °C to 20 °C, wherein the concentration of the photoinitiator, based on the weight of the polymer particles and the photoinitiator, is in the range of from 0.02 weight percent to 4 weight percent.

[0008] The polymer particles typically have a z-average particle size as measured by dynamic light scattering in the range of from 50 nm to 300 nm. The glass transition temperature (Tg) of the polymer particles as measured by dynamic scanning calorimetry is in the range of from -20 °C, preferably from -10 °C to 20 °C, preferably to 10 °C. In a preferred embodiment, the polymer particles comprise at least 90, more preferably at least 95 weight percent structural units of 2-octyl acrylate and methyl methacrylate. In this embodiment, the polymer particles preferably comprise, based on the weight of the polymer particles, from 45, and more preferably from 50 weight percent, to 70, more preferably to 60 weight percent structural units of 2-octyl acrylate; and preferably from 29, and more preferably from 40 weight percent, to 54, and more preferably to 48 weight percent structural units of methyl methacrylate; and from 0.2, more preferably from 0.5, and most preferably from 1.0 weight percent, to 5 and more preferably from 3 weight percent of an ethylenically unsaturated acid monomer, preferably one or more ethylenically unsaturated acid monomers selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, and 2-phosphoethyl methacrylate (PEM).

[0009] In another embodiment, the polymer particles comprise from 25 to 42 weight percent structural units of ethyl acrylate; from 25 to 42 weight percent structural units of 2-octyl acrylate; from 16 to 40 weight percent structural units of methyl methacrylate; and from 0.2 to 5 weight percent structural units of an ethylenically unsaturated acid monomer.

[0010] The polymer particles may also comprise structural units of one or more ancillary monomers such as ureido methacrylate, acetoacetoxyethyl methacrylate (AAEM), diacetone acrylamide (DAAM), 2-(dimethylamino)ethyl methacrylate (DMAEMA), typically at a concentration not greater than 15 weight percent, based on the weight of the polymer particles. The term “structural unit” is used herein to describe the remnant of the recited monomer after polymerization. For example, a structural unit of methyl methacrylate is as illustrated: structural unit of methyl methacrylate where the dotted lines represent the points of attachment of the structural unit to the polymer backbone.

[0011] A photoinitiator refers to one or more compounds which, when exposed to wavelengths of light in the range of 100 nm to 400 nm, generates radicals by way of hydrogen atom abstraction (i.e., Norrish Type II chemistry) or a compound that undergoes homolytic cleavage when exposed to wavelengths in the range of 100 nm to 400 nm (i.e., Norrish Type I chemistry). Examples of photoinitiators include benzophenone, methyl-2-benzoyl benzoate, 4-methylbenzophenone, 2,2-dimethoxy-2-phenylacetophenone, 4-methoxybenzophenone, 3 ,4-dimethylbenzophenone, 4-hydroxybenzophenone, 2-ethylanthraquinone, 2-(p-toluoyl)benzoic acid, benzoin isobutyl ether, 4-benzoyl biphenyl, p-anisoin, 4-(4-methylphenylthio)benzophenone, 4,4'-dimethylbenzophenone, triphenylacetic acid, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl-2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzophenone, 4-phenyl benzophenone, isopropylthioxanthone, benzoin ethyl ether, benzophenone hydrazone, diphenylacetic acid, benzophenone methacrylate, vinylbenzyl methylbenzoylbenzoate, hydroxymethacryloxypropyl methylbenzoylbenzoate, hydroxymethacryloxypropyl benzophenone, benzophenones substituted with hydroxyl-terminated alkylene oxide groups as described in US 11,760,713 B2, and polymeric benzophenones commercially available examples of which include Omnipol 2702, Omnipol 910, and Omnipol BP photoinitiators.

[0012] The concentration of photoinitiator is preferably in the range of from 0.05, or from 0.1 weight percent, to 2, or to 1, or to 0.6, or to 0.4 weight percent, based on the weight of the polymer particles and the photoinitiator. The latex is advantageously prepared by emulsion polymerization that are well-known in the art. The latex may be prepared by a single stage, multi-stage, or a power-feed polymerization process, for example, and can have a variety of particle size distributions.

[0013] The composition of the present invention can be prepared in a variety of ways, including a) contacting the photoinitiator with a monomer emulsion prior to emulsion polymerization; b) contacting the photoinitiator to the aqueous dispersion of polymer particles; or c) contacting the photoinitiator with a paint or a pre-paint containing the polymer particles.

[0014] In another aspect, the present invention is a paint composition comprising water, the latex, the photoinitiator, a dispersant, a surfactant, and a rheology modifier, and optionally one or more of the following materials: an inorganic opacifying pigment such as TiOr, an organic pacifying pigment such as opaque polymers, a coalescent, an extender, and a light stabilizer such as a hindered amine light stabilizer. The paint composition may have any desired pigment volume concentration (PVC), including a PVC in the range of from 5 to 70. PVC is defined by the following formula: 100

[0015] The composition of the present invention may also be a caulk, a sealant, a roof coating, or a clear coat for wood or leather, for example. For paint compositions, volatile organic content (VOC) is preferably < 50 g / L, or < 10 g / L or zero g / L of paint, as determined by ASTM D3960-02.

[0016] An added advantage of 2-octyl acrylate is that is a base-cleavage product of ricinoleic acid, which is found in castor oil. There is a continuing demand for finding bio-based alternatives to supplant fossil fuels; 2-octyl acrylate offers one such alternative. Significantly, it has been surprisingly discovered that coatings prepared from paint formulations containing 2-octyl acrylate -based latexes show excellent DPUR at relatively low concentrations of the photoinitiator.

[0017] Examples

[0018] Differential Scanning Calorimetry Method for Determining Glass Transition Temperature

[0019] Differential Scanning Calorimetry (DSC) was used to calculate the Tgof the latexes. The latex samples were dried, placed in an aluminum pan, and crimped shut. The pan was placed in the DSC unit (TA Instruments Discovery 2500). The pan was then exposed to thermal cycling with the following programmed instructions: ramp at 20.00 C° / min to 150.00 °C, hold isothermal for 2.00 min, cool at 20.00 C7min to -90.00 °C, hold isothermal for 2.00 min, ramp at 20.00 C7min to 150.00 °C. Thermal data was collected on the second heating ramp. Tgwas measured at the inflection point (change in value of second derivative) of the heat flow curve. Table 1 illustrates the latexes used in the DPUR studies. BA refers n-butyl acrylate, 2-OA refers to 2-octyl acrylate, MMA refers to Methyl Methacrylate, MAA refers to methacrylic acid, UMA refers to ureido methacrylate, and n-DCC refers to / / -dodecyl mercaptan. Cl refers to Comparative Example 1 Latex; C2 refers to Comparative Example 2 Latex; Exl refers to Example 1 Latex; and Ex2 refers to Example 2 Latex.

[0020] Table 1 - Description of Latexes

[0021] Preparation of Paint Formulations

[0022] These Example and Comparative Example latexes were used to make paints suitable for use in exterior applications. Table 2 illustrates the Grind portion of each formulation; pbw refers to parts by weight of each ingredient. The components were added in the specified amounts to a steel grind pot and mixed at 2000 rpm for 25 min using a serrated mixing blade. The grind mixture was then aliquoted into four 1-L containers. Preparation of each individual paint was completed using an overhead mixer fitted with a 3-paddled blade. Table 2 - Grind Portion of the Paint Formulation

[0023] TAMOL, TRITON, and DOWSIL are all Trademarks of The Dow Chemical Company and Its Affiliates.

[0024] Table 3 illustrates the Letdown portion of the paint formulations. The components listed in the Letdown table were added sequentially in their specified amounts to the containers with mixing at 1000 rpm. A portion of each paint (50.0 g) of each paint was then apportioned into 9 plastic containers. ROPAQUE, TERGITOL, and ACRYSOL are all Trademarks of The Dow Chemical Company or Its Affiliates.

[0025] Table 3 - Letdown Portion of the Paint Formulation

[0026] Solutions of each photoinitiator were prepared by dissolving photoinitiator (6.0 g) in acetone (54.0 g). Each of Paints 1-4 were evaluated for DPUR with and without photoinitiator. The photoinitiators were benzophenone (BZ), methyl 2-benzoylbenzoate (M2B), 4-methylbenzophenone (MBP), and 2,2-dimethoxy-2-phenylacetophenone (DMP). Each paint that contained photoinitiator was evaluated at 2 concentrations of photoinitiator: 0.2 wt% and 0.6 wt% photoinitiator based on the weight of latex polymer particles. The 0.2 wt% samples were prepared by pipetting 0.24 g of photoinitiator solution to a first group of Paints 1-4 (50 g) with mixing at 500 rpm; the 0.6 wt% samples were prepared by pipetting 0.72 g of the photoinitiator solution to a second group of Paints 1-4. Each of these samples was applied to a chromated aluminum panel (AL36, provided by Q-Lab) using a Teflon drawdown bar with a 10-mil gap. Paint samples were allowed to dry for 24 h in a controlled temperature and humidity room (22 °C, 50% relative humidity). The panels were then placed in a Q-Lab QUV Accelerated Weathering Tester using 340-nm UVA bulbs with radiant flux density of 0.89 W / m2at 60 °C. Panels were exposed in the QUV for 72 h, after which time they were removed in preparation for DPUR testing. A dirt slurry was prepared by mixing Davis Colors 641 Brown Iron Oxide (125 g), water (250 g), and TAMOL™ 731 A Dispersant (2 mL). This slurry was dispersed using a benchtop mixer for 1 min until smooth. The dirt slurry was then applied to the bottom half of exposed painted panels, and allowed to dry for 4 h. The dirt was then washed off the panels by hand using running water and cheesecloth. The panels were then allowed to dry for 24 h, and the color difference (AE) between the cleaned bottom half of each panel and the top half of each panel (to which no dirt was applied, to serve as a benchmark) was measured.

[0027] AE was calculated using the CIELAB 1976 formula as shown below.

[0028] “L*” is a measure of lightness, indexed from 0 to 100, where 0 is dark (absence of color) and 100 is light (completely white). The “a*” represents a scale of red / green, and the “b*” represents a scale of blue / yellow. The sum of the difference of squares of these values as measured by a colorimeter (BYK Spec tro- Guide) give a holistic value of change of color, “AE”. Table 4 illustrates a summary of the AE values from DPUR results for the paints tested. The subscripts “0.2” and “0.6” refer to the wt% of the photoinitiator (PI) based on the weight of latex solids.

[0029] Table 4 - AE Results for DPUR Study

[0030] The table illustrates that with no photoinitiator, the paints containing 2-OA / MMA latexes exhibited comparable AE values in the DPUR study. However, the paints containing 2-OA / MMA latexes showed a dramatic reduction in AE with as little as 0.2 wt% of any of the photoinitiators tested. The low levels of photoinitiator required to achieve excellent DPUR resulted in a coating with more robust performance of the coating over time.

Claims

Claims:

1. A composition comprising a) an aqueous dispersion of polymer particles comprising structural units of 2-octyl acrylate, methyl methacrylate, and an ethylenically unsaturated acid monomer; and b) a photoinitiator, wherein the Tgof the polymer particles, as measured by dynamic scanning calorimetry, is in the range of from -20 °C to 20 °C, wherein the concentration of the photoinitiator, based on the weight of the polymer particles and the photoinitiator, is in the range of from 0.02 weight percent to 4 weight percent.

2. The composition of Claim 1 wherein the polymer particles comprise, based on the weight of the polymer particles, from 45 to 70 weight percent structural units of 2-octyl acrylate; from 29 to 54 weight percent structural units of methyl methacrylate; and from 0.2 to 5 weight percent structural units of the ethylenically unsaturated acid monomer.

3. The composition of Claim 2 wherein the ethylenically unsaturated acid monomer is one or monomers selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and 2-phosphoethyl methacrylate; wherein the Tgof the polymer particles is in the range of from about -10 °C to 10 °C.

4. The composition of Claim 3 wherein the ethylenically unsaturated acid monomer is methacrylic acid; and the photoinitiator is one or more compounds selected from the group consisting of benzophenone, methyl-2-benzoyl benzoate, 4-methylbenzophenone, 2,2- dimethoxy-2-phenylacetophenone, 4-methoxybenzophenone, 3,4-dimethylbenzophenone, 4-hydroxybenzophenone, 2-ethylanthraquinone, 2-(p-toluoyl)benzoic acid, benzoin isobutyl ether, 4-benzoyl biphenyl, p-anisoin, 4-(4-methylphenylthio)benzophenone, 4,4'- dimethylbenzophenone, triphenylacetic acid, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl-2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzophenone, 4-phenyl benzophenone, isopropylthioxanthone, benzoin ethyl ether, benzophenone hydrazone, diphenyl acetic acid, benzophenone methacrylate, vinylbenzyl methylbenzoylbenzoate, hydroxymethacryloxypropyl methylbenzoylbenzoate, hydroxymethacryloxypropyl benzophenone, benzophenones substituted with hydroxyl-terminated alkylene oxide groups, and polymeric benzophenones: wherein the concentration of the photoinitiator is in the range of from 0.05 weight percent to 1 weight percent.

5. The composition of Claim 3 wherein the ethylenically unsaturated acid monomer is methacrylic acid; and the photoinitiator is one or more compounds selected from the groupconsisting of benzophenone, methyl 2-benzoylbenzoate, 4-methylbenzophenone, and 2,2- dimethoxy-2-phenylacetophenone; wherein the concentration of the photoinitiator is in the range of from 0.05 weight percent to 0.6 weight percent.

6. The composition of Claim 5 wherein the photoinitiator is methyl 2-benzoylbenzoate.

7. The composition of Claim 5 wherein the photoinitiator is 4-methylbenzophenone.

8. The composition of Claim 1 wherein the polymer particles comprise from 25 to 42 weight percent structural units of ethyl acrylate: from 25 to 42 weight percent structural units of 2-octyl acrylate; from 16 to 40 weight percent structural units of methyl methacrylate; and from 0.2 to5 weight percent structural units of the ethylenically unsaturated acid monomer.

9. A paint composition comprising a) an aqueous dispersion of polymer particles comprising structural units of 2-octyl acrylate, methyl methacrylate, and an ethylenically unsaturated acid monomer; b) a photoinitiator; c) a dispersant; d) a surfactant; and a e) a rheology modifier: wherein the Tgof the polymer particles, as measured by dynamic scanning calorimetry, is in the range of from -20 °C to 20 °C, wherein the concentration of the photoinitiator, based on the weight of the polymer particles and the photoinitiator, is in the range of from 0.02 weight percent to 4 weight percent.

10. The paint composition of Claim 9 wherein the polymer particles comprise, based on the weight of the polymer particles, from 45 to 70 weight percent structural units of 2-octyl acrylate; from 29 to 54 weight percent structural units of methyl methacry late; and from 0.2 to 5 weight percent structural units of the ethylenically unsaturated acid monomer, wherein the ethylenically unsaturated acid monomer is one or more monomers selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, and 2-phosphoethyl methacrylate; and wherein the Tgof the polymer particles is in the range of from about -10 °C to 10 °C.

11. The paint composition of Claim 10 wherein the ethylenically unsaturated acid monomer is methacrylic acid; and the photoinitiator is one or more compounds selected from the group consisting of benzophenone, methyl-2-benzoyl benzoate, 4-methylbenzophenone, 2,2-dimethoxy-2-phenylacetophenone, 4-methoxybenzophenone, 3 ,4-dimethylbenzophenone, 4-hydroxybenzophenone, 2-ethylanthraquinone, 2-(p-toluoyl )benzoic acid, benzoin isobutyl ether, 4-benzoyl biphenyl, p- an isoin, 4-(4-methylphenylthio)benzophenone, 4,4'-dimethylbenzophenone, triphenylacetic acid, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl-2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, isopropylthioxanthone, benzoin ethyl ether, benzophenone hydrazone, diphenyl acetic acid, benzophenone methacrylate, vinylbenzyl methylbenzoylbenzoate, hydroxymethacryloxypropyl methylbenzoylbenzoate, hydroxymethacryloxypropyl benzophenone, benzophenones substituted with hydroxyl-terminated alkylene oxide groups, and polymeric benzophenones: wherein the concentration of the photoinitiator is in the range of from 0.05 weight percent to 1 weight percent; and wherein the composition further comprises TiCh.

12. The paint composition of Claim 10 wherein the ethylenically unsaturated acid monomer is methacrylic acid; and the photoinitiator is one or more compounds selected from the group consisting of benzophenone, methyl 2-benzoylbenzoate, 4-methylbenzophenone, and 2,2-dimethoxy-2-phenylacetophenone; wherein the concentration of the photoinitiator is in the range of from 0.05 weight percent to 0.6 weight percent; and wherein the composition further comprises TiCK13. The paint composition of Claim 12 wherein the photoinitiator is methyl 2-benzoylbenzoate.

14. The paint composition of Claim 12 wherein the photoinitiator is 4-methylbenzophenone.

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