Organophosphorus acid functionalized latex and an aminosilane

The present invention provides a composition comprising an organophosphorus acid functionalized latex and an aminosilane; the composition is useful for delivering stain blocking performance.

Historically, reactive pigments such as ZnO or barium metaborate, or other cationic additives have been used to improve stain blocking in films prepared from waterborne coating compositions. It is believed that these pigments bind stain molecules, which are typically anionic, thereby preventing stains from leeching through the film; however, according to U.S. Pat. No. 5,527,619 (Rokowski) reactive pigments “can cause stability problems, such as viscosity increase and polymer gelation, and are known to be environmentally unfriendly.”

Other efforts directed toward improving stain blocking have focused on improving the barrier properties of the coating through the use of hydrophobic and low molecular weight emulsion polymers. These attempts have been only partially successful; achieving stain block performance equivalent to solvent-based alkyd resins has remained elusive.

Rokowski further discloses aqueous coating compositions comprising an aminosilane and an emulsion polymer to deliver improved stain blocking performance in a primer; however, as will be demonstrated in the present application, these coating compositions are not effective at blocking stains when used in a paint and primer in one formulation. It would therefore be advantageous to discover a waterborne coating composition that is effective for improving block resistance in such a formulation.

The present invention addresses a need in the art by providing a composition comprising a) an aqueous dispersion of polymer particles comprising, based on the weight of the polymer particles from 0.2 to 5 weight percent structural units of a phosphorus acid monomer or a salt thereof; and b) from 0.05 to 5 weight percent, based on the weight of the polymer particles, of an aminosilane, which is a compound that contains a primary, a secondary, or a tertiary amino group, or a quaternary ammonium group separated by 2 to 6 carbon atoms, from an Si—O group or a group that is hydrolyzable to an Si—O group. The composition of the present invention provides effective stain blocking without the use environmentally unfriendly reactive pigments.

The present invention is a composition comprising a) an aqueous dispersion of polymer particles comprising, based on the weight of the polymer particles from 0.2 to 5 weight percent structural units of a phosphorus acid monomer or a salt thereof; and b) from 0.05 to 5 weight percent, based on the weight of the polymer particles, of an aminosilane, which is a compound that contains a primary, a secondary, or a tertiary amino group, or a quaternary ammonium group separated by 2 to 6 carbon atoms, from an Si—O group or a group that is hydrolyzable to an Si—O group.

The polymer particles can be acrylic, styrene-acrylic, vinyl acetate-ethylene, or vinyl acetate-acrylic polymers. Preferably, the polymer particles are acrylic based polymer particles comprising, based on the weight of the polymer particles, at least 30 weight percent structural units of methacrylate monomers such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate; and/or acrylate monomers such as methyl acrylate, ethyl acrylate, n-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:

Structural Unit of Methyl Methacrylate

where the dotted lines represent the points of attachment of the structural unit to the polymer backbone.

The polymer particles preferably have a z-average particle size, as measured by a Brookhaven BI 90 Particle Size Analyzer, in the range of from 50 nm, more preferably from 70 nm, and most preferably from 80 nm to 500 nm, more preferably to 400 nm, and most preferably to 300 nm.

Suitable phosphorus acid monomers include phosphonates and dihydrogen phosphate esters 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 hydroxyalkylacrylates and hydroxyalkylmethacrylates, including phosphoethyl methacrylate and phosphopropyl methacrylate, with phosphoethyl methacrylate being especially preferred. Phosphoethyl methacrylate (PEM) is used herein to refer to the following structure:

where R is H or

Another class of suitable phosphorus acid monomer is an allyl ethylene oxide phosphate of the following formula:

where y is from 3 to 5 and X is Li, Na, K, or NH 4 + . A commercially available example of an allyl ethylene oxide phosphate is Sipomer PAM-5000 monomer.

Polymer particles that comprise structural units of a phosphorus acid monomer or a salt thereof are said to be polymer particles polymers functionalized with organophosphorus acid groups.

The aminosilane is a compound that contains a primary, a secondary, or a tertiary amino group, or a quaternary ammonium group separated by 2 to 6 carbon atoms, preferably 3 carbon atoms, from an Si—O group or a group that is hydrolyzable to an Si—O group (such as an SiH or SiCl group). More preferably, the aminosilane is illustrated by the following structure:

where each R is independently H, C 1 -C 3 -alkyl, phenyl, or 2-aminoethyl; R 1 is C 1 -C 3 -alkyl or C(O)CH 3 ; and each R 2 is independently H, C 1 -C 3 -alkyl, C 1 -C 3 -alkoxy, or O—C(O)CH 3 .

Examples of suitable aminosilanes include N-methylaminopropyltrimethoxysilane, 2-aminoethyl-3-aminopropylmethyldimethoxysilane, aminopropyldimethylethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and N,N-dimethylaminopropyltrimethoxysilane.

The composition of the present invention is especially useful in providing stain blocking in pigmented coating compositions, for example, latex compositions that further comprise TiO 2 . The composition advantageously further comprises a pigment, a rheology modifier and one or more additives selected from the group consisting of dispersants, surfactants, neutralizing agents, defoamers, extenders, opaque polymers, and coalescents.

It has been surprisingly been discovered that an aqueous composition comprising the combination of an aminosilane and a dispersion of polymer particles functionalized with organophosphorus acid groups shows significant improvement in stain blocking over compositions that comprise polymer particles functionalized with organophosphorus acid groups but no aminosilane, or a composition comprising an aminosilane and polymer particles not functionalized with organophosphorus acid groups.

Comparative Example 1—Preparation of a Latex

A monomer emulsion (ME1) was prepared from deionized water (670 g), Disponil FES 993 emulsifier (FES 993, 22.5 g), butyl acrylate (BA, 825 g), methyl methacrylate (MMA, 645 g), and glacial methacrylic acid (MAA, 30 g). To a 5-L 4-neck flask equipped with a mechanical stirrer, a reflux condenser, a thermocouple, and inlets for monomer emulsion and initiator solution was added deionized water (750 g) and FES 993 (5.77 g). The contents of the flask were stirred and heated to 82° C. A seed charge consisting of a portion of ME1 (76.3 g) was added to the flask followed by an initiator solution consisting of deionized water (10 g) and sodium persulfate (3.75 g). The seed charge and the initiator solution were rinsed to the flask with deionized water. Polymerization of the seed charge was monitored by a thermocouple and when the temperature of the reaction mixture peaked, the remainder of ME1 as well as a second initiator solution consisting of deionized water (200 g), sodium persulfate (0.75 g), and sodium carbonate (10.5 g) were fed into the reactor monotonically over 150 min, while the reactor temperature was controlled at 85° C. After completion of the feeds, the ME1 and initiator solution were rinsed into the flask using deionized water and the reactor was held at 85° C. for 10 min. The reactor was cooled to 80° C., then a solution of ferrous sulfate heptahydrate (0.02 g) and ethylenediaminetetraacetic acid tetrasodium salt (0.02 g) in deionized water (5 g) was added to the flask and rinsed with deionized water. Residual monomer in the reaction mixture was polymerized by feeding a solution of t-butyl hydroperoxide (4 g) in deionized water (20 g); a separate solution of isoascorbic acid (2.2 g) in deionized water (20 g) was added to the flask over 20 min while cooling the reaction mixture to 55° C. After the feeds were complete the reaction mixture was cooled to 30° C. and neutralized to pH 8 using ammonium hydroxide solution. Once neutralized, a solution consisting of KATHON™ LX 1400 Preservative (0.36 g), FES 993 (21.73 g), and deionized water (8.19 g) was added to the flask. The resulting latex was filtered to remove coagulum. The measured solids of the resulting latex was 45.7%.

Comparative Example 2—Preparation of a Latex with an Aminosilane

The procedure of Comparative Example 1 was followed except that 1 weight % 2-aminoethyl-3-aminopropyltrimethoxysilane (2.29 g, 1 weight percent based on latex solids) was added to a portion of the final latex (500 g).

2-Aminoethyl-3-aminopropyltrimethoxysilane

Comparative Example 3—Preparation of a PEM-Functionalized Latex

The procedure was carried out as described for Comparative Example 1 except that the monomers composing ME1 were butyl acrylate (BA, 825 g), methyl methacrylate (MMA, 637.5 g), and phosphoethyl methacrylate (PEM, 22.5 g, 60% active); and the second initiator solution was composed of sodium persulfate (0.75 g) and sodium carbonate (2.5 g) in deionized water (200 g). The measured solids of the resulting latex was 45.6%.

Example 1—Preparation of a PEM-Functionalized Latex with 1% 2-Aminoethyl-3-aminopropyltrimethoxysilane

The procedure of Comparative Example 3 was followed except that 1 weight % 2-aminoethyl-3-aminopropyltrimethoxysilane, based on latex solids, was added to the latex.

Example 2—Preparation of a PEM-Functionalized Latex with 1% 2-Aminoethyl-3-aminopropylmethyldimethoxysilane

The procedure of Comparative Example 3 was followed except that 1 weight % 2-aminoethyl-3-aminopropylmethyl dimethoxysilane, based on latex solids, was added to the final latex.

2-Aminoethyl-3-aminopropylmethyldimethoxysilane