Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2002-04-12
2004-08-24
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of polyester
C428S480000, C524S601000, C524S604000, C525S447000, C528S295500
Reexamination Certificate
active
06780523
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to waterborne coating compositions, and more particularly, to waterborne coating compositions having acetoacetate-functionalized alkyd resins.
BACKGROUND OF THE INVENTION
In recent years, considerable efforts have been made by the coatings industry to develop coating formulations containing little or no volatile organic compound (VOC) content. Regulations to limit the amount of VOCs in industrial coatings have encouraged research and development to explore new technologies directed at reducing solvent emissions from industrial solvent-based coatings operations in such products as automobiles, appliances, general metal products, furniture, and the like. However, while the move to reduced organic solvent-based compositions brings health and safety benefits, these lower VOC content coating compositions must still meet or exceed the performance standards expected from solvent-based compositions.
Alkyd resins are one of the most common binders used for ambient-cure, solvent-based coatings. The resistance properties of traditional solvent-borne alkyd resins are developed via autooxidative crosslinking of the alkyd film. Crosslinking occurs when the activated methylene groups in the unsaturated fatty acids or oils of the alkyd are oxidized in air to give hydroperoxides which subsequently decompose to generate free radicals, causing oxidative crosslinking. This oxidative crosslinking process is commonly accelerated by adding driers, such as, for example, various salts of cobalt, zirconium, calcium, and manganese. However, while alkyd resins have shown, and continue to show, promise, they have relatively slow “dry” and/or cure times, particularly at ambient temperatures. Various modifications have been made to alkyd resins to address such concerns.
One such attempt includes polymerization of an alkyd resin with a vinyl compound, such as styrene or methyl methacrylate, via a free-radical reaction, to produce a vinyl-alkyd copolymer or a vinyl alkyd. Vinyl alkyd resins generally have a higher molecular weight and a higher Tg, producing coatings with reduced tack-free time (solvent evaporation). However, the through-dry time (oxidation of the film) of such coatings takes longer due to the decreased degree of unsaturation in the alkyd as a result of copolymerization with the vinyl compound. This problem is described in further detail in Resins for Surface Coatings, Vol. 1, p. 181, ed. by P. K. T. Oldring and G. Hayward, SITA Technology, London, UK, 1987, which is incorporated herein by reference. An additional drawback is that paint formulations containing vinyl alkyd resins require greater amounts of solvent, due to the increased molecular weight and Tg of the vinyl alkyd.
Various methods for the preparation of acetoacetylated coating resins have been described by J. S. Witzeman et al. in the Journal of Coatings Technology, Vol. 62, No. 789, pp. 101-112 (1990). This document discloses acetoacetylation of polyester resins, and the application of such resins for baking enamels having a melamine crosslinker.
U.S. Pat. No. 5,484,849 discloses vinyl polymer compositions containing pendant acetoacetate functionality, which are curable in air in the presence of a source of free radicals. The vinyl polymers are prepared by free radical polymerization (i.e. emulsion polymerization) of an acetoacetate-functional monomer (e.g., acetoacetoxyethyl methacrylate) and other acrylic monomers. The patent also discloses that an autooxidizable compound is required to provide a source of free radicals to cure and to crosslink the acetoacetate functionality. As a result, a portion of the acetoacetate groups could be consumed during the free radical polymerization due to the reaction between the acetoacetate functionality and the free radicals. This could, in turn, lead to insufficient curing upon film formation. It is therefore desirable to provide an air-dry coating system based on acetoacetyl-functional polymers, prepared via a non-free radical reaction.
Thus, there still exists a need in the art for a modified or functionalized alkyd resin capable of undergoing crosslinking upon film formation, which can be used to prepare ambient oxidative cure, fast-dry, and waterborne coatings having low VOC content. Such coatings would exhibit the properties and advantages of high VOC coatings.
SUMMARY OF THE INVENTION
The invention provides a waterborne acetoacetate-functionalized alkyd coating composition comprising an acetoacetate-functionalized alkyd resin, at least one drier, and water. The acetoacetate-functionalized alkyd resin comprises the reaction product of (a) an alkyd resin, and (b) an alkyl acetoacetate.
The invention also relates to a method of preparing a waterborne acetoacetate-functionalized alkyd coating composition comprising the step of contacting an acetoacetate-functionalized alkyd resin with at least one drier in the presence of water.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a waterborne acetoacetate-functionalized alkyd coating composition comprising an acetoacetate-functionalized alkyd resin, at least one drier, and water. The acetoacetate-functionalized alkyd resin comprises the reaction product of (a) an alkyd resin, and (b) an alkyl acetoacetate as shown in FIG. (
1
).
Any of a number of alkyl acetoacetates may be effectively used as acetoacetylating agents in the transesterification reaction to generate the acetoacetate-functionalized alkyd resin. Typically, the reaction is driven by the removal of the alcohol by-product as it is formed. Although halides are traditionally utilized as leaving groups, the various acetoacetate esters are easier to handle and to store.
In a preferred embodiment of the invention, a waterborne acetoacetate-functionalized alkyd coating composition contains from about 30 to about 60 wt %, based on the total weight of the composition, of an acetoacetate-functionalized alkyd resin, from about 40 to about 70 wt %, based on the total weight of the composition, of water, from 0 to about 30 wt %, based on the total weight of the composition, of an organic solvent, and from about 0.01-1.0 wt %, based on the total weight of the composition, of at least one drier.
Such an acetoacetate-functionalized alkyd resin exhibits superior tack-free time and through-dry time properties. Furthermore, the acetoacetate-functionalized alkyd of the invention exhibits superior tack-free time properties, which previously could only be improved by increasing the molecular weight and Tg of the alkyd resin. Because the amount of VOC generally added to alkyd resin compositions and/or formulations is directly related to the molecular weight and Tg of the alkyd resin, compositions or formulations containing an acetoacetate-functionalized resin of the invention would require less VOC.
In one embodiment of the invention, the acetoacetate-functionalized alkyd resin comprises the reaction product of: (a) from about 70 to about 97 wt % of an alkyd resin, and (b) from about 3 to about 30 wt % of an alkyl acetoacetate, each as described herein, wherein the weight percents are based on the total weight of (a) and (b).
Any alkyd resin may be used as an alkyd resin in a coating composition of the invention. An alkyd may be prepared by reacting a diol, a polyol, a polyacid, a monofunctional acid, and a fatty acid, fatty ester or naturally occurring, partially-saponified oil, optionally in the presence of a catalyst. More particularly, an alkyd resin is the reaction product of (i) from 0 to about 30 mol % of a diol, (ii) from about 10 to about 40 mol % of a polyol, (iii) from about 20 to about 40 mol % of a polyacid, (iv) from 0 to about 10 mol % of a monofunctional acid, (v) from about 10 to about 50 mol % of a fatty acid, fatty ester or naturally occurring oil, and, optionally (vi) a catalyst, wherein the mole percents are based on the total moles of (i), (ii), (iii), (iv), (v), and (vi), if present. Suitable examples of each of the components of the alkyd resin include those known in the art including, but not limited to, those discussed b
Clark Mark Dwight
Grosso Paul Vincent
Kuo Thauming
Spilman Gary Eugene
Carrier Michael K.
Eastman Chemical Company
Graves, Jr. Bernard J.
Short Patricia A.
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