Patent Application
20230312969
The present invention relates to a composition which is an aqueous dispersion of polymer particles, polymeric organic crosslinked microspheres, and colloidal silica particles. The composition is useful as an exterior coating composition.
Exterior coatings require excellent durability, color retention, and dirt pickup resistance (DPUR). The addition of an aqueous dispersion of SiO2 nanoparticles (colloidal silica) to paint formulations has been shown to provide significant improvement in DPUR, but at the expense of chalking and color fading. Accordingly, it would be an advantage in the art of exterior coating formulations to achieve excellent durability and color retention in addition to DPUR.
The present invention addresses a need in the art by providing a composition comprising an aqueous dispersion of a) 10 to 60 weight percent, based on the weight of the composition, polymer particles having a z-average particle size in the range of from 70 nm to 550 nm and a calculated Tg in the range of from -10° C. to 50° C.; b) 10 to 40 weight percent, based on the dry weight percent of the composition, polymeric organic crosslinked microspheres having a median weight average (D50) particle size in the range of from 0.7 µm to 30 µm; and c) colloidal silica particles having a z-average particle size in the range of from 5 nm to 150 nm; wherein the weight-to-weight ratio of the colloidal silica particles to the polymer particles is in the range of from 5:95 to 35:65. The composition of the present invention is useful in the preparation of architectural coatings formulations with high dirt pick-up resistance and excellent durability.
The present invention is a composition comprising an aqueous dispersion of a) 10 to 60 weight percent, based on the weight of the composition, polymer particles having a z-average particle size in the range of from 70 nm to 550 nm and a calculated Tg by the Fox equation in the range of from -10° C. to 50° C.; b) 10 to 40 weight percent, based on the dry weight percent of the composition, polymeric organic crosslinked microspheres having a median weight average (D50) particle size in the range of from 0.7 µm to 30 µm; and c) colloidal silica particles having a z-average particle size in the range of from 5 nm to 150 nm; wherein the weight-to-weight ratio of the colloidal silica particles to the polymer particles is in the range of from 5:95 to 35:65.
The polymer particles may be acrylic, styrene acrylic, or vinyl ester polymer particles. Preferably the polymer particles are acrylic polymers having a z-average particle size in the range of from about 70 nm to 300 nm, as measured by dynamic light scattering. The acrylic polymer particles comprise at least 40, preferably at least 60, more preferably at least 80, and most preferably at least 90 weight percent structural units of one or more methacrylate monomers such as methyl methacrylate and ethyl methacrylate, and/or one or more acrylate monomers such as ethyl acrylate, butyl acrylate, 2-propylheptyl acrylate, and 2-ethylhexyl acrylate.
As used herein, the term “structural unit” of the named monomer refers to the remnant of the monomer after polymerization. For example, a structural unit of methyl methacrylate is as illustrated:
where the dotted lines represent the points of attachment of the structural unit to the polymer backbone.
The polymer particles, preferably the acrylic polymer particles, may also comprise from 0.1 to 10 weight percent structural units of ethylenically unsaturated carboxylic acid monomers such as methacrylic acid, acrylic acid, and itaconic acid, or salts thereof; or phosphorus acid monomers such as 2-phosphoethyl methacrylate (PEM).
The polymer particles, preferably the acrylic polymer particles, may also include structural units of ancillary monomers such as acrylamide and acrylonitrile, as well as structural units of multiethylenically unsaturated monomers such as allyl methacrylate, allyl acrylate, divinyl benzene, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, butylene glycol (1,3) dimethacrylate, butylene glycol (1,3) diacrylate, ethylene glycol dimethacrylate, and ethylene glycol diacrylate.
The polymeric organic crosslinked microspheres have a median weight average particle size (D50) in the range of from 0.7 µm, preferably from 1 µm, more preferably from 2 µm, and most preferably from 4 µm, to 30 µm, to preferably 20 µm, more preferably to 13 µm, and most preferably to 10 µm, as measured using a Disc Centrifuge Photosedimentometer (DCP). These organic polymeric microspheres are characterized by being non-film-forming and preferably having a low Tg crosslinked core, that is, a crosslinked core having a Tg, as calculated by the Fox equation, of not greater than 25° C., more preferably not greater than 15° C., and more preferably not greater than 10° C.
The crosslinked core of the polymeric organic crosslinked microspheres preferably comprises structural units of one or more monoethylenically unsaturated monomers whose homopolymers have a Tg of not greater than 20° C. (low Tg monomers) such as methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. Preferably, the crosslinked low Tg core comprises, based on the weight of the core, from 50, more preferably from 70, more preferably from 80, and most preferably from 90 weight percent, to preferably 99, and more preferably to 97.5 weight percent structural units of a low Tg monoethylenically unsaturated monomer. n-Butyl acrylate and 2-ethylhexyl acrylate are preferred low Tg monoethylenically unsaturated monomers used to prepare the low Tg core.
The crosslinked core further comprises structural units of a multiethylenically unsaturated monomer. The concentration of structural units of the multiethylenically unsaturated monomer in the crosslinked microspheres is preferably in the range of from 1, more preferably from 2 weight percent, to 9, more preferably to 8, and most preferably to 6 weight percent, based on the weight of the core.
The polymeric organic crosslinked microspheres are preferably multistage microspheres comprising a crosslinked core that is clad with high a Tg shell, that is, a shell having a Tg of at least 50° C., more preferably at least 70° C., and most preferably at least 90° C. The shell preferably comprises structural units of monomers whose homopolymers have a Tg greater than 70° C. (high Tg monomers), such as methyl methacrylate, styrene, isobornyl methacrylate, cyclohexyl methacrylate, and t-butyl methacrylate. The high Tg shell preferably comprises at least 90 weight percent structural units of methyl methacrylate.
The polymeric organic crosslinked microspheres, preferably multistage polymeric organic crosslinked microspheres, preferably further comprise, based on the weight of the microspheres, from 0.05 to 5 percent structural units of a polymerizable organic phosphate represented by the structure of Formula I:
or a salt thereof; wherein R is H or CH3, wherein R1 and R2 are each independently H or CH3, with the proviso that CR2CR1 is not C(CH3)C(CH3); each R3 is independently linear or branched C2-C6 alkylene; m is from 1 to 10; n is from 0 to 5; with the proviso that when m is 1, then n is from 1 to 5; x is 1 or 2; and y is 1 or 2; and x + y = 3.
When n is 0, x is 1, and y is 2, the polymerizable organic phosphate or salt thereof is represented by the structure of Formula II:
Preferably, each R1 is H, and each R2 is H or CH3; m is preferably from 3, and more preferably from 4; to preferably to 8, and more preferably to 7. Sipomer PAM-100, Sipomer PAM-200 and Sipomer PAM-600 phosphate esters are examples of commercially available compounds within the scope of the compound of Formula II.
Where n is 1; m is 1; R is CH3; R1 and R2 are each H; R3 is —(CH2)5—; x is 1 or 2; y is 1 or 2; and x + y = 3, the polymerizable organic phosphate or salt thereof is represented by the structure of Formula III:
A commercially available compound within the scope of Formula III is Kayamer PM-21 phosphate ester.
The polymeric organic crosslinked microspheres may also comprise 0.05 to 5 weight percent, based on the weight of the microspheres, structural units of an ethylene oxide salt of a distyryl or a tristyryl phenol represented by the structure of Formula IV:
where R1 is H, CH2CR═CH2, CH=CHCH3, or 1-phenethyl; R is C1-C4-alkyl; and n is 12 to 18. A commercial example of the structure of Formula IV is E-Sperse RS-1684 reactive surfactant.
The polymeric organic crosslinked microspheres are distinct from opaque polymers, which comprise water-containing cores that form voided polymer particles after application of the dispersion onto a substrate, followed by evaporation.
The composition of the present invention may comprise some level of inorganic extenders such as talc, clay, mica, sericite, CaCO3, nepheline, feldspar, wollastonite, kaolinite, dicalcium phosphate, and diatomaceous earth; however, it is not considered advantageous to include inorganic extenders; accordingly, the weight-to-weight ratio of inorganic extender to polymeric organic multistage crosslinked microspheres is not greater than 1:5, more preferably not greater than 1:10, more preferably not greater than 1:20, and most preferably not greater than 1:100.
The colloidal silica particles preferably have a z-average particle size in the range of from 10 nm to 100 nm, more preferably to 50 nm, and most preferably to 30 nm. The w/w ratio of the colloidal silica particles to polymer particles is preferably in the range of from 10:90, more preferably from 15:85, to preferably 30:70, more preferably to 25:75.
The composition further preferably comprises additional materials such as rheology modifiers, coalescents, surfactants, dispersants, defoamers, biocides, opacifying pigments such as TiO2 and organic opaque polymer particles, colorants, photoinitiators, and neutralizing agents.
The composition of the present invention is useful in coatings compositions for exterior applications. It has been discovered that coatings prepared from formulations containing the composition of the present invention exhibit excellent dirt pick-up resistance and durability.
DIRTSHIELD™ 12 M Acrylic Binder (199 g, methyl methacrylate/butyl acrylate/methacrylic acid, Tg = 27° C. as calculated by the Fox equation, 49 wt. % solids, a Trademark of The Dow Chemical Company or its Affiliates), Levasil CS40-113 colloidal silica (density = 1.3 g/cm3, specific surface area = 130 m2/g, 40 wt. % solids), and AMP-95 neutralizing agent (0.91 g) were mixed together to form Intermediate 1.
DIRTSHIELD™ 12 M Acrylic Binder (199 g, 49 wt. % solids), Bindzil CC-401 colloidal silica (density = 1.3 g/cm3, average particle size = 12 nm, 37 wt. % solids), and AMP-95 neutralizing agent (0.91 g) were combined to form Intermediate 2.
Table 1 illustrates the materials used to prepare paint formulations and their amounts. HEC refers to Natrosol 250HBR Hydroxyethylcellulose; Dispersant refers to OROTAN™ 731A Dispersant; Surfactant refers to TRITON™ DR-16 Surfactant; Defoamer refers to Tego Foamex Defoamer; TiO2 refers to Ti-Pure R-706 TiO2; CC-700 refers to CC-700 Calcium Carbonate Inorganic Extender; Microspheres refers to the aqueous dispersion of polymeric organic crosslinked microspheres prepared as described in US 2018/327,562, Example 1 (D50 particle size = 8.4 µm); Acrylic Binder refers to DIRTSHIELD™ 12 M Acrylic Binder; Opaque Polymer refers to ROPAQUE Ultra E Opaque Polymer; RM-2020 NPR refers to ACRYSOL™ RM-2020 NPR; RM-8W refers to ACRYSOL™ RM-8W; and Biocide refers to Rocima Biocide.
Blue paints tinted with phthlaocyanine colorant (3.1% v/v) were prepared and 150-µm wet films were drawn down onto aluminum panels using an applicator. The films were cured over 7 d, after which time initial L0*, a0*, b0* values were measured using a BYK Gardner Color-guide sphere spectrophotometer before the samples were placed in a QUV test instrument (Q-Lab Corp., 340 nm light source UVA with 0.77 w/m2 irradiance intensity) with the test area facing inward. Each QUV cycle consisted of an 8-h UV irradiation at 60° C. followed by a 4-h water spray at 50° C. L*, a*, b* measurement and surface changes were recorded every cycle for each panel. ΔE* was calculated by the following formula:
Table 2 illustrates the durability ranking for the various coatings, with 10 being the most durable. A durability ranking of 9 or 10 was considered a passing rating.
Table 3 illustrates the durability for each of the paints tested.
The durability tests indicated that Comparative Example 3 paint and Example paints 1 and 2 all passed, while Comparative Example paints 1 and 2 failed.
A primer was applied onto cement panels then allowed to cure for 2 h. Each paint was initially applied to the primed cement panels and allowed to cure for 2 h. Then the paints were applied again and allowed to cure overnight. Initial Y and L*, a*, b* values were recorded, after which time the panels were exposed outside with a southerly exposure and set at an angle of 45°. Y and L*, a*, b* values and changes in appearance were recorded every month. The dirt pickup resistance (Dc) value trend was recorded; Dc = L*/L*0. The higher the Dc the better the dirt pickup resistance. Table 4 illustrates the Dc trends at 1, 2, and 6 months. A Dc at 6 months of > 95% was considered acceptable.
Table 4 shows that Comparative Example 2 and Examples 1 and 2 showed acceptable dirt pickup resistance, while Comparative Examples 1 and 3 failed. The results show that only formulations that contained both polymeric organic crosslinked microspheres and colloidal silica particles exhibited acceptable durability and dirt pickup resistance.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2020/106102 | 7/31/2020 | WO |
