Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-12-19
2004-01-27
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S609000, C524S764000, C524S788000, C524S847000, C525S444500, C525S153000, C525S374000, C525S379000, C525S382000, C528S272000, C528S294000, C528S295500, C528S308000
Reexamination Certificate
active
06683132
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to self-crosslinking aqueous coating compositions, and more particularly, to coating compositions that contain an acetoacetate-functionalized sulfonated alkyd, a cross-linking agent that includes at least two primary amine functionalities, and a monofunctional primary or a monofunctional cycloaliphatic secondary amine. The compositions according to the invention crosslink via oxidative crosslinking, as do conventional alkyd compositions, as well as via reaction between the acetoacetate functionality of the alkyd and the primary amines of the cross-linking agent. The water-dispersible, self-crosslinking alkyds of the present invention are particularly useful in or as coatings, adhesives, inks, primers, and overprint varnishes.
2. Description of Related Art
In recent years, considerable effort has been expended by the coatings industry to develop low or zero VOC (volatile organic compound) 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 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 coating stability than do waterborne polyester resins and waterborne acrylic resins. In addition, alkyd resins, due to their relatively low molecular weight, exhibit exceptional film-forming ability that translates into very high gloss in the final coating film. Resistance properties are developed, as with traditional solvent-borne alkyds, via oxidative crosslinking of the alkyd film. However, while known 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. There remains a need, however, for a waterborne alkyd having improved crosslinking properties.
Also receiving much attention are amine-neutralized waterborne alkyds having free carboxyl groups, and thus a higher acid value. These alkyds unfortunately are susceptible to saponification from the neutralization used to disperse them in water, resulting in a loss of performance during storage. The pendant acid semiester moieties of these amine-neutralized waterborne alkyds are susceptible to hydrolysis as a result of the neutralization of the carboxyl groups necessary to effect dispersion of these alkyds in the aqueous carrier. The amine used to neutralize the waterborne alkyd tends to hydrolyze the ester bonds, as a result of the anchimeric effect. This results in a reduction in the pH of the system, with the potential for further loss of stability.
Scientists have attempted to eliminate this effect through careful raw material selection, in order to obtain more stable ester linkages.
Examples of such material selection are the inclusion of 1,4-cylcohexane dicarboxylic acid into the alkyd chain, in place of aromatic dicarboxylic acids, and the use of glycols having no hydrogen atoms bound to the carbon which is beta to the hydroxy group, and thus to the subsequent ester group. Such glycols include cyclohexane dimethanol, 2,2,4-trimethyl-1,3-pentane diol, trimethylolpropane, and neopentyl glycol. The use of polyethylene glycols as monomers in the alkyds to help disperse the polymer in water, thus lowering the level of carboxyl content necessary to produce a dispersion, has also been utilized. The hydrolysis exhibited has nonetheless ensured that, at best, amine-neutralized alkyds represent a short-term solution to the problem of providing waterborne coatings with the desired stability. There remains a need for waterborne alkyds that do not require neutralization for dispersion, and that exhibit improved crosslinking properties when compared to waterborne alkyds that cure solely via auto-oxidative crosslinking.
J. Stewart Witzeman et al., in an article entitled “Comparison of Methods for the Preparation of Acetoacetylated Coating Resins” in the October 1990 issue of
Journal of Coatings Technology
, outline various methods for the acetoacetylation of polyester and acrylic resins containing hydroxyl moieties. These examples are not directed toward alkyds or waterborne polyesters, nor indeed to any self-crosslinking systems.
F. Del Rector et al., in an article entitled “Applications for Acetoacetyl Chemistry in Thermoset Coatings” contained in the April 1989 issue of
Journal of Coatings Technology
, describe various means of crosslinking coatings containing acrylic or polyester resins having acetoacetyl moieties. Included in this discussion is the use of diamines as a crosslinker for such systems.
U.S. Pat. No. 5,288,804 (the '804 patent) discloses various types of polymers having at least two acetoacetate groups. The systems described require a crosslinking component having at least two groups which will react with an acetoacetate group, at least one of which is an aromatic aldimine group said to have a relatively low reactivity with water when compared with its reactivity with an acetoacetate group. Although an acetoacetate-functional alkyd is described in the '804 patent, the alkyd is solvent-based rather than water-dispersed, and does not appear to be suitable for dispersion into water, having an acid number prior to the acetoacetylation step of less than 10.
An alkyd that is otherwise similar to that described in the '804 patent, but having an acid number rendering it suitable for dispersion into water, would require a conventional neutralization step, in order to effect dissolution or dispersion. For example, the '804 patent teaches in Example 10 the use of a tertiary amine, triethylamine, to neutralize an acetoacetylated polyester having an acid value of 97.6. A major shortcoming of this neutralization technique is the saponification problems arising during storage from the carboxyl ions created during neutralization. The carboxyl ions, being in close proximity to the ester linkages of the alkyd backbone, accelerate the hydrolysis of the ester linkages, resulting in backbone cleavage via the anchimeric effect. The resulting carboxyl moieties released during hydrolysis decrease the pH of the system, thus resulting in an increased likelihood of further saponification. Clearly, a water-dispersible acetoacetate-functional alkyd not subject to such saponification problems would be a significant advance in the art.
U.S. Pat. No. 5,498,659 discloses a one-package aqueous polymeric formulation containing an aqueous carrier; a polymer having both acid-functional pendant moieties and acetoacetyl-functional pendant moieties; a “non-polymeric” (defined as less than about 2,000 g/mol) polyfunctional amine; and base. Alternatively, two or more separate polymers can be used, one of which has acid functionality, and one of which has acetoacetate functionality. The amount of base used is sufficient to inhibit the gellation which would otherwise occur as a result of crosslinking between the acetoacetate moieties of the polymer and the amine moieties of the polyfunctional amine. The polymers d
Bolton Amy Lee
Kuo Thauming
Schick Martin Frederick
Carrier Michael K.
Eastman Chemical Company
Graves, Jr. Bernard J.
Mulcahy Peter D.
Sastri Satya
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