Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-08-12
2001-07-17
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S457000, C524S539000, C524S603000, C524S609000, C524S845000, C524S846000, C525S007000, C525S007100
Reexamination Certificate
active
06262149
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a water-based latex of an acrylic modified waterborne alkyd dispersion in water. Such acrylic modified waterborne alkyds are useful in a variety of coating compositions.
2. Description of Related Art
In recent years, considerable effort has been expended by the coatings industry to develop low or zero VOC containing coating formulations. Regulations to limit the amount of VOC content of industrial coatings have encouraged research and development to explore new technologies directed at reducing solvent emissions from industrial solvent-based coatings operations such as automotive, appliance, general metal, furniture, and the like. One technology involves the replacement of organic solvents with water and is of particular interest for the obvious reasons of availability, cost, and environmental acceptability. However, while the move from organic solvent-based compositions to aqueous compositions brings health and safety benefits, aqueous coating compositions must meet or exceed the performance standards expected from solvent-based compositions. The need to meet or exceed such performance standards places a premium on the characteristics and properties of waterborne polymer dispersions used in aqueous coating compositions.
Waterborne polymer dispersions have been prepared from each of the three primary industrial film-forming polymer types: polyesters, acrylics and alkyds. Of the three polymer types, waterborne alkyd resins exhibit significantly higher storage stability and coating stability than the waterborne polyester or acrylic resins. In addition, alkyd resins, due to their low molecular weight, exhibit exceptional film forming ability which translates into very high gloss in the final coating film. Resistance properties are developed, as with traditional solvent-borne alkyds, via autooxidative crosslinking of the alkyd film. However, while alkyd polymers have shown, and continue to show promise, they have relatively slow “dry” and/or cure times, particularly at ambient temperatures. In an attempt to address such concerns, hybrids of waterborne alkyds and relatively high molecular weight acrylic polymers have received considerable attention.
U.S. Pat. No. 4,413,073 describes the preparation of an aqueous dispersion of particles of a film-forming polymer comprising a pre-formed polymer and at least one polymer formed in situ (“multi-polymer particles”). The dispersion is prepared in the presence of an amphipathic stabilizing compound having an HLB of at least 8 and whose lipophilic portion comprises at least one ethylenic unsaturation. The aqueous dispersion is useful as a film-forming component of coating compositions.
U.S. Pat. No. 4,451,596 describes water-dilutable alkyd and acrylate resins for use in water-dilutable lacquer systems. A method for the preparation of water-dilutable resin preparations based upon alkyd and acrylate resins is also described.
European Patent Application 0 555 903 describes a water-dispersible hybrid polymer of an unsaturated fatty acid-functionalized polyester. In addition, aqueous dispersions of such a hybrid polymer for use in aqueous coating compositions with a high solids content and films produced by using such coating compositions are described.
PCT Application WO 95/02019 describes an emulsion of an air-drying resin dispersed in water and the preparation of such emulsions. Hybrid emulsions of an alkyd resin and an acrylate resin are also described.
Previous alkyd/acrylic hybrid latexes have been prepared using alkyds which do not contain metal sulfonate groups. Further, the acrylic polymers of these previous hybrids are either non-reactive or possess reactive groups (e.g. hydroxyl groups) which react, as do similar groups present in the alkyd resin, with aminoplasts such as melamine formaldehyde resins and only at elevated temperatures.
SUMMARY OF THE INVENTION
One aspect of the invention is a water-based latex of an acrylic-modified waterborne alkyd resin. The acrylic-modified waterborne alkyd resin is a hybrid resin resulting from the polymerization of at least one ethylenically unsaturated monomer in the presence of a waterborne alkyd having at least one pendant sulfonate functionality, i.e. a sulfonated waterborne alkyd. The invention also provides a method for preparing such water-based latexes by polymerizing a hybrid resin resulting from the polymerization of at least one ethylenically unsaturated monomer in the presence of a sulfonated waterborne alkyd. The invention further provides coating compositions containing the water-based latexes of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a water-based latex of an acrylic-modified waterborne alkyd resin. In one embodiment, the latex affords a stable, emulsion of a hybrid resin resulting from the polymerization of at least one ethylenically unsaturated monomer in the presence of a waterborne alkyd having at least one pendant sulfonate functionality, i.e. a sulfonated waterborne alkyd. In another embodiment, the latex affords a stable, emulsion of a hybrid resin resulting from the polymerization of at least one latent oxidatively-functional (LOF) acrylic monomer in the presence of a waterborne alkyd having at least one pendant sulfonate functionality such that the acrylic monomer retains a sufficient amount of LOF groups for further reaction with other LOF groups or alkyd functionality after or upon film formation. Latexes of the invention are stable when stored at temperatures at or moderately above room temperature. The latex of the invention is capable of affecting crosslinking upon film formation. Such latex films or coatings may be cured at ambient temperature, thermally or photochemically.
In the water-based latexes of the invention, the acrylic-modified waterborne alkyd resin generally exists as particles dispersed in water. The particles are generally spherical in shape. The particles may be structured or unstructured. Structured particles include, but are not limited to, core/shell particles and gradient particles. The core/shell polymer particles may also be prepared in a multilobe form, a peanut shell, an acorn form, or a raspberry form. It is further preferred in such particles that the core portion comprises about 20 to about 80 wt % of the total weight of said particle and the shell portion comprises about 80 to about 20 wt % of the total weight of the particle.
The average particle size of the hybrid latex may range from about 25 to about 500 nm. Preferred particle sizes range from about 50 to about 300 nm, more preferably from about 100 to 250 nm. The hybrid latex particles generally have a spherical shape.
The glass transition temperature (T
g
) of the acrylic portion of the hybrid resin in accordance with the invention, may be up to about 100° C. In a preferred embodiment of the invention, where film formation of the latex at ambient temperatures is desirable, that glass transition temperature may preferably be under about 70° C., and most preferably between about 0-60° C.
The acrylic-modified waterborne alkyd resins of the invention are prepared by polymerization of at least one ethylenically unsaturated monomer in the presence of a sulfonated waterborne alkyd. If at least one of the ethylenically unsaturated monomers is a latent oxidatively functional (LOF) acrylic monomer, as described below, the acrylic-modified waterborne alkyd resins of the invention will be prepared in the presence of a sulfonated waterborne alkyd such that sufficient latent oxidative functionality of the acrylic monomer survives the polymerization process to enhance crosslinking of the hybrid resin. Any polymerization process known in the art may be used. Preferably an emulsion polymerization process is used since emulsion polymerization allows for the preparation of high molecular weight polymers at low viscosity. The polymerization may take place as a single stage or multi-stage feed. If a multi-stage feed is used, one or more stages may contain an LOF acrylic monomer or mixtures
Clark Mark D.
Kuo Thauming
Shields Glen D.
Stockl Rebecca R.
Allen Rose M.
Eastman Chemical Company
Egwim Kelechi
Wu David W.
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