Aqueous coating compositions for wood surfaces

#This invention is directed to aqueous coating compositions. More particularly, this invention is directed to aqueous coating compositions for wood surfaces which can be used to obtain clear open and/or closed pore coatings. The coating compositions are based on polymer dispersions containing N-methylol acrylamide units. Alternatively, the dispersions containing N-methylol acrylamide units can be processed together with a paint composition based on a water-soluble acrylic copolymer.

#The painting of wood with clear varnishes is described in detail in "Lehrbuch der Lacke und Beschichtungen," H. Kittel, Vol. V, pages 305-317, edition W. A. Colomb, 1977. As stated thereby, nitrocellulose lacquers (cellulose nitrate lacquers at times referred to as NC-lacquers) and acid curing alkyd-amine resin enamels, polyurethane paints and paints based on unsaturated polyesters are primarily used in varnishes for use on wood. All these coating compositions require a large amount of organic solvent for processing and application or of polymerizable monomers, which, at least in part, can have a narcotic effect. Accordingly, there is a concerned effort to obtain coating compositions based on water as a solvent, eliminating substantial environmental pollution, and where the paints correspond to nitrocellulose lacquers in performance.

#Polymer dispersions containing N-methylol acrylamide units are known in the literature and have been used for various purposes. U.S. Pat. No. 3,856,734 describes the preparation of dispersions from vinylacetate, N-methylol acrylamide, and acrylic acid. The dispersions are used as adhesive for plywood. Acrylic dispersions which, in addition to the acrylates or methacrylates, can also optionally contain N-methylol acrylamide are disclosed in U.S. Pat. No. 3,790,520. The dispersions are used in the textile industry, and for the surface protection of plastics, metals, and wood. Dispersions described in Deutsche Auslegeschrift No. 10 47 431 which contain methylol acrylamide units are used for crosslinking polymer particles during production of the dispersion. Deutsche Offenlegungsschrift No. 25 35 660 describes the preparation of auto-crosslinking polymer dispersions containing methylolated carboxylic acid amides and polymer solutions wherein emulsion polymers containing acrylamide are produced which are subsequently reacted with methylolated carboxylic acid amides. These known dispersions, when stoved at the conditions applicable to wood, give coatings which do not meet the requirements for practical use from the standpoint of mar resistance, hardness and flexibility, and pile strength.

#A polymerization reactor equipped with reflux condensor, thermometer, and inert gas supply is charged with 1322 parts of deionized water, 18 parts of the sodium salt of an octylphenol reacted with 2 moles of ethylene oxide and sulfated, 12 parts of an octylphenol reacted with 16 moles of ethylene oxide and 7.2 parts of sodium vinyl sulfonate. The charge is heated to 85.degree.-87.degree. C. While continuously stirring, the following ingredients are added simultaneously, from three separate addition funnels, within a period of 90 minutes:

#1. A monomer blend consisting of 645 parts of methylmethacrylate, 267 parts of n-butylmethacrylate, 180 parts of ethylacrylate, and 66 parts of styrene;

#2. 246 parts of a 36% aqueous solution of N-methylolmethacrylamide, and