Latex containing phosphate ester

Abstract

The present invention is a composition comprising a waterborne dispersion of a) polymer particles functionalized with structural units of a phosphorus acid monomer; b) an orthophosphate n-butyl ester block additive. The composition of the present invention is useful in a paint formulation to provide block resistance and high tint strength.

Description

[0001] Phosphate Ester Functionalized Latex and Alkyl Phosphate Ester Blend

[0002] Background of the Invention

[0003] The present invention relates to a composition comprising a phosphate ester functionalized latex and an alkyl phosphate ester. Resistance to adhesion between two coated surfaces (block resistance) is an important property for architectural coatings. Block resistance is particularly challenging for waterborne coatings containing latexes with a low glass transition temperature (Tg). Perfluoralkyl substances (PFAS), which are currently being used in waterborne coating formulations to provide this critical property, are considered environmentally unfriendly due to their persistence; moreover, their prevalence worldwide has been linked to harmful effects to humans and animals. It would therefore be advantageous to discover an environmentally friendly alternative block additive in coatings formulation.

[0004] Latexes functionalized with structural units of a phosphorus acid monomer such as 2-phosphoethyl methacrylate (PEM) increase the tint strength of the consequent coating by making more efficient use of opacifying pigments, particularly titanium dioxide; nevertheless, tint strength may be compromised by the addition of a block additive. Accordingly, it would be further advantageous to find a block additive that does not adversely affect tint strength.

[0005] Summary of the Invention

[0006] The present invention addresses a need in the art by providing a composition comprising a waterborne dispersion of a) polymer particles functionalized with structural units of a phosphorus acid monomer; b) an orthophosphate / -butyl ester block additive.

[0007] The composition of the present invention is useful in a paint formulation to provide block resistance and high tint strength.

[0008] Detailed Description of the Invention of the Invention

[0009] The present invention is a composition comprising a waterborne dispersion of a) polymer particles functionalized with structural units of a phosphorus acid monomer; b) an orthophosphate / / -butyl ester block additive.

[0010] The polymer particles preferably have a particle size as measured by dynamic light scattering in the range of from 50 rnn to 400 or to 300 or to 200 nm, and constitute typically from 20 or from 30 to 60 or to 55 or to 45 weight percent of the waterborne composition. The polymer particles typically have a glass transition temperature (Tg) as calculated by the Fox equation in the range of from -20 °C or from -10 °C or from -5 °C, to 35 °C or to 25 °C or to 15 °C.

[0011] Examples of suitable polymer particle dispersions (latexes) include acrylic, styrene-acrylic, urethane, alkyd, vinyl ester (e.g., vinyl acetate and vinyl versatate), and vinyl acetate-ethylene (VAE) latexes, and combinations thereof.

[0012] Preferred latexes are acrylic latexes, which contain structural units of one or more methacrylate monomers such as methyl methacrylate and ethyl methacrylate, and structural units of one or more acrylate monomers such as n-butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, 2-propylheptyl acrylate, and 2-octyl acrylate. Especially preferred acrylic latexes are functionalized with monomers that can be biobased such as ethyl acrylate and 2-octyl acrylate. The concentration of structural units of ethyl acrylate or 2-octyl acrylate is preferably in the range of from 20 to 75 weight percent, based on the weight of the polymer particles.

[0013] The polymer particles are functionalized with preferably from 0.5 or from 1 weight percent, to 10 or to 5 weight percent structural units of a phosphorus acid monomer, which is a phosphonate or dihydrogen phosphate ester of an alcohol in which the alcohol contains or is substituted with a polymerizable vinyl or olefinic group. Preferred dihydrogen phosphate esters are phosphates of hydroxyalkyl(meth)acrylates, including phosphoethyl methacrylate and phosphopropyl methacrylates, with 2-phosphoethyl methacrylate (PEM) being especially preferred. The polymer particles may be functionalized with structural units of other acid monomers such as methacrylic acid, ac ylic acid, itaconic acid, and sodium styrene sulfonate.

[0014] The polymer particles may include structural units of ancillary monomers such as acetoacetoxy ethyl methacrylate, ureido methacrylate, and acetonitrile.

[0015] The orthophosphate n-butyl ester block additive is a monoester and / or diester having the following formulas:

[0016] In one aspect, the orthophosphate / / -butyl ester block additive is a mixture of the monoester and diester at a ratio in the range of from 35:65 monoester to diester, to 95:5 or to 75:25 or to 60:40 or to 50:50 monoester to diester. The concentration of the block additive is preferably in the range of from 50 ppm or from 100 ppm or from 200 ppm, to 20,000 ppm or to 5000 ppm or to 1000 ppm or to 750 ppm, based on the weight of the composition.

[0017] In another aspect, the present invention is a coating composition comprising a waterborne dispersion of a) polymer particles functionalized with structural units of a phosphorus acid monomer; b) an orthophosphate n-butyl ester block additive; c) opacifying pigment particles; d) a rheology modifier; and e) a surfactant.

[0018] Opacifying pigments include inorganic opacifying pigments having a refractive index of greater than 1.90. TiOy and ZnO are examples of inorganic opacifying pigments, with TiOy being preferred. Other opacifying pigments include organic opacifying pigments such as opaque polymers. Although an organic opacifying pigment may be used as a substitute for an inorganic opacifying pigment, it is more desirable to use the organic opacifying pigment as a supplement to augment the efficiency of the inorganic opacifying pigment. The organic opacifying pigment can be added to the mixing chamber from a separate additives tank. ROPAQUE™ ULTRA Opaque Polymers (A Trademark of The Dow Chemical Company or its Affiliates) and AQACell HIDE 6299 Opaque Polymers are commercial examples of opaque polymers.

[0019] The rheology modifier is used at a concentration sufficient to achieve the desired Brookfield, KU, and ICI viscosity of the final paint. Examples of suitable rheology modifiers include hydrophobically modified ethylene oxide urethane polymers (HEURs); hydrophobically modified alkali swellable emulsion (HASEs); alkali swellable emulsions (ASEs); hydroxyethyl cellulosics (HECs); hydrophobically-modified polyacetal-polyethers (HM-PAPEs); and hydrophobically modified hydroxyethyl cellulosic (HMHECs); and combinations thereof. Suitable surfactants include ionic surfactants and nonionic surfactants, especially secondary alcohol ethoxylate nonionic surfactants having a hydrophilic lipophilic balance (HLB) in the range of from 9 to 19.

[0020] HLB is determined by the equation:

[0021] MW of hydrophilic group HLB = 20 x -r, - - -

[0022] MW of molecule where MW is molecular weight.

[0023] An example of a preferred class of nonionic surfactants is a linear or branched alcohol ethoxylate having the following formula:

[0024] R*(CHR2CH2O)X-H where R1is a saturated or partially unsaturated linear or branched Ce-Cso-alkyl group; and each R2is independently H, methyl, or ethyl, and x is from 2 to 100. As used herein, “partially unsaturated” allows for the presence of one or more double bonds in R1group. R1is preferably a Cio-C24-alkyl group; each R2is preferably independently H or CHs; most preferably each R2is H; and x is preferably in the range of from 6 to 50. Examples of commercially available nonionic surfactants include TERGITOL™ 15-S-7 Surfactant (15-S-7, HLB = 12.1), TERGITOL™ 15-S-9 Surfactant (15-S-9, HLB = 13.3), TERGITOL™ 15-S-20 Surfactant (15-S-20, HLB = 16.3); TERGITOL™ 15-S-40 Surfactant (15-S-40, HLB = 18); and Ecosurf SA-7 Surfactant (SA-7, HLB = 9.7). (TERGITOL is a Trademark of The Dow Chemical Company or its Affiliates.)

[0025] The coating composition of the present invention advantageously includes one or more of the following materials: dispersants; defoamers; colorants; and fillers such as calcium carbonate, mica, clay, alumina silicate. The composition of the present invention has been found to form coatings with excellent block resistance and maintenance of tint strength.

[0026] Examples

[0027] In the following example, block additive refers to orthophosphate n-butyl ester and orthophosphate di-n-butyl ester at a w / w ratio of 43.3:56.7; or orthophosphate n-Cs-Cw-alkyl ester and orthophosphate di-n-Cs-Cio-alkyl ester at a w / w ratio of 40:54; or orthophosphate n -hexyl ester and orthophosphate di-n-hexyl ester at a w / w ratio of 41 :46.

[0028] Example 1 - Preparation of Blend of Phosphate Functionalized Ester and Block Additive

[0029] A latex containing 69 wt% structural units of ethyl acrylate, 25.5 wt% structural units of methyl methacrylate, and 2.2 wt% structural units of 2-phosphoethyl methacrylate (60 wt% active) based on the weight of latex solids was mixed in a first vessel with the block additive (500 ppm) for 10 min, then stored overnight.

[0030] The grind was prepared in a second vessel by combining Kronos 4311 TiCL , water, TAMOL™ 2011 Dispersant, KOH, TERGITOL™ 15-S-20 Surfactant, defoamer, and an HM-PAPE rheology modifier into a grind pot. This mixture was then allowed to mix on Cowles mixer for 3 min followed by addition of sodium hexametaphosphate (hexaphos). After mixing for 5 min, the Minex 3 extender, ASP 170 extender and Attagel 50 extender were sequentially added. The mixing speed was adjusted to ensure powder wetting and dispersion without splashing or air entrapment. The mixture was stirred for 20 to 30 min. (TAMOL is a trademark of The Dow Chemical Company or its Affiliates.)

[0031] Water, ROPAQUE Ultra EF Opaque Polymer, and defoamer were added with stirring to the first vessel to form the pre-mix. Then, the grind from the second vessel was then added to the first vessel and stirring continued for 5 to 10 minutes. Finally, the letdown ingredients - a high boiling point coalescent, an HM-PAPE rheology modifier, a HEUR rheology modifier, and water - were added sequentially to the first vessel with stirring.

[0032] Table 1 shows the ingredients and amounts from the pre-mix, the grind, and the letdown stages of the paint formulation. Table 1 - Paint Formulation Tint Strength Measurements

[0033] The paints were tinted with black colorant at 2 oz / gal. Tinted paints were drawn down on Penopac charts and were allowed to dry. Y reflectance from the paint film on the sealed portion of the chart was measured. Tint strength was calculated with respect to control paint using the formula below, where Ri is the reflectance from the paint and R is the reflectance from the control. Both Ri and R are in decimals in 0 - 1 scale. 100

[0034] Block Resistance Testing

[0035] Drawdowns of paints were prepared on Leneta WB charts using 3-mil bird applicators. The coating was allowed to dry in a controlled temperature room maintained at 22 °C and 50% relative humidity, and block resistance was measured at 1 and 7 days. The paint films were cut into 1.5” x 1.5” squares, and the coated faces were pressed together. A number 8 rubber stopper and 1 -kg weight were placed on top of the squares for 30 min in a 50 °C oven. The squares are allowed to cool, and were then pulled apart to determine hot block resistance in accordance with ASTM D4946. The ratings for block performance are illustrated in Table 2. Table 3 illustrates 1-d and 7-d hot block resistance, and tint strength for a coating sample containing no block additive (CE 1), a sample containing the orthophosphate n-Cs-Cio-alkyl ester and orthophosphate di-n-Cs-Cio-alkyl ester (CE 2), a sample containing the orthophosphate / / -hexyl ester and orthophosphate di-n-hexyl ester at a w / w ratio of 41:46 (CE 3), and a sample containing the orthophosphate n -butyl ester and orthophosphate di-n-butyl ester (IE1). A coating was considered to fail if its hot block value was 4 or less or its tint strength was 96 or less.

[0036] Table 3 - Hot Block Resistance and Tint Strength

[0037] The data illustrate that the only coating that passed both block and tint strength tests contained the orthophosphate n-butyl ester and orthophosphate di-n-butyl ester block additive.

Claims

Claims:

1. A composition comprising a waterborne dispersion of a) polymer particles functionalized with structural units of a phosphorus acid monomer; b) an orthophosphate n-butyl ester block additive.

2. The composition of Claim 1 wherein the polymer particles are acrylic polymers comprising structural units of methyl methacrylate and one or more acrylate monomers selected from the group consisting of / / -butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, 2-propylheptyl acrylate, and 2-octyl acrylate.

3. The composition of Claim 2 wherein the orthophosphate / / -butyl ester block additive is a mixture of orthophosphate / / -butyl monoester and orthophosphate / -butyl diester.

4. The composition of Claim 3 wherein the concentration of the block additive is in the range of from 50 ppm to 20000 ppm, based on the weight of the composition; and the polymer particles comprise from 20 to 60 weight percent of the waterborne composition.

5. The composition of Claim 4 wherein the polymer particles comprise structural units of ethyl acrylate and methyl methacrylate; and wherein the phosphorus acid monomer is 2-phosphoethyl methacrylate.

6. A coating composition comprising a waterborne dispersion of a) polymer particles functionalized with structural units of a phosphorus acid monomer; b) an orthophosphate n-butyl ester block additive; c) opacifying pigment particles; d) a rheology modifier; and e) a surfactant.

7. The coating composition of Claim 5 wherein the polymer particles are acrylic polymer polymers comprising structural units of methyl methacrylate and one or more acrylate monomers selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, 2-propylheptyl acrylate, and 2-octyl acrylate; wherein the phosphorus acid monomer is 2-phosphoethyl methacrylate; and wherein the opacifying pigment particles comprise TiO particles.

8. The coating composition of Claim 7 wherein the orthophosphate n-butyl ester block additive is a mixture of the monoester and diester; and wherein the polymer particles comprise structural units of ethyl acrylate and methyl methacrylate.

9. The coating composition of any of Claim 6 to 8 which further comprises one or more additives selected from the group consisting of dispersants, defoamers, colorants, and fillers.