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
2000-03-21
2002-07-23
Yoon, Tae H. (Department: 1714)
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...
C524S602000, C524S603000, C524S901000, C528S287000, C528S294000, C427S058000, C427S096400, C205S317000
Reexamination Certificate
active
06423774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to electrocoating compositions containing a resinous phase dispersed in an aqueous medium, the resinous phase including an ionic electrodepositable resin with improved corrosion resistance formed from a hydrolytically stable ionic polyester polymer.
2. Description of the Related Art
Electrodeposition as a coating application method involves deposition of a film-forming composition onto a conductive substrate under the influence of an applied electrical potential. Electrodeposition has become increasingly important in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers increased paint utilization, improved corrosion protection and low environmental contamination.
U.S. Pat. No. 5,739,213 and U.S. Pat. No. 5,811,198, both to Freriks et al. disclose certain polyester compositions and glycidyl esters thereof, which are suitable for use in powder coatings. The compositions are resins obtainable by reaction of: an aromatic and/or cycloaliphatic carboxylic acid compound (a), comprising two aromatic and/or secondary aliphatic carboxyl groups or the anhydride thereof; a hydroxyl compound (b) comprising two primary or secondary aliphatic hydroxyl groups; at least one hydroxyl substituted carboxylic acid compound (c) comprising at least one tertiary aliphatic carboxyl group and two primary or secondary aliphatic hydroxyl groups; and optionally, one carboxylic acid compound (d) comprising one carboxyl group. The molar ratio of compounds a:b:c:d is (X+Y−1):X:Y:Z, wherein X ranges from 2 to 8, Y ranges from 2 to 8, and Z ranges from 0 to 2. While these compositions are known for their use in powder coatings, the applicability of their use in eletrocoating resins as a main vehicle has not been explored.
Certain polyesters have previously found use in electrodeposition applications as chain extenders and crosslinking agents. For instance, U.S. Pat. No. 4,148,772 discloses chain extension of polyepoxides with polyester polyols. The polyester polyols are formed from a variety of dicarboxylic acids and diols which were known in the art to be suitable chain extenders. However, use of the disclosed higher molecular weight polyester polyols in chain extension is hindered by the overall hydrolytic instability of the ester bonds in aqueous solutions.
It, therefore, would be advantageous to provide an electrocoating composition that combines the superior coating ability, flexibility, durability and corrosion resistance of polyesters with the hydrolytic stability of traditional electrodepositable compositions.
SUMMARY OF THE INVENTION
In accordance with the present invention, an electrodepositable coating composition comprising a resinous phase dispersed in an aqueous medium is provided. The resinous phase comprises an ionic polyester polymer. The ionic polyester polymer comprises the reaction products of a) an aromatic and/or cycloaliphatic carboxylic acid compound comprising at least two aromatic and/or secondary aliphatic carboxyl groups, or an anhydride thereof, b) a branched aliphatic, cycloaliphatic or araliphatic compound containing at least two aliphatic hydroxyl groups, the aliphatic hydroxyl groups being either secondary or tertiary hydroxyl groups or primary hydroxyl groups attached to a carbon adjacent to a tertiary or quaternary carbon; c) a compound comprising an ionic salt group or a group which is converted to an ionic salt group; and d) optionally, at least one hydroxyl substituted carboxylic compound comprising at least one tertiary aliphatic carboxyl group and at least two aliphatic hydroxyl groups. The ionic polyester polymer preferably has an ionic salt group equivalent weight of 1,000 to 10,000. Preferably, the carboxyl:hydroxyl equivalent ratio of a to b or of a to (b+d) is greater than 1:1.
Also provided in accordance with the present invention is a method for electrocoating a conductive substrate which serves as an electrode in an electrical circuit the conductive substrate and a counter-electrode. The method comprises the steps of: i) immersing the conductive substrate and the counter-electrode into an aqueous electrocoating composition comprising the resinous phase described above, the ionic polyester polymer of the resinous phase having functional groups which are reactive with a curing agent. The electrocoating composition further includes a curing agent having functional groups reactive with the reactive functional groups of the ionic polyester polymer; and ii) applying a direct current between the conductive substrate and the counter-electrode so as to deposit a film derived from the resinous phase.
Provided, also, is a substrate prepared according to the above-described method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The electrodepositable coating composition of the present invention includes a resinous phase dispersed in an aqueous medium, the resinous phase includes an ionic polyester polymer comprising the reaction product of the following reactants:
a. an aromatic and/or cycloaliphatic carboxylic acid compound comprising at least two aromatic and/or secondary aliphatic carboxyl groups, or an anhydride thereof;
b. a branched aliphatic, cycloaliphatic or araliphatic compound containing at least two aliphatic hydroxyl groups, said aliphatic hydroxyl groups being either secondary or tertiary hydroxyl groups or primary hydroxyl groups attached to a carbon adjacent to a tertiary or quaternary carbon;
c. a compound comprising an ionic salt group or a group which is converted to an ionic salt group; and
d. optionally, at least one hydroxyl substituted carboxylic compound comprising at least one tertiary aliphatic carboxyl group and at least two aliphatic hydroxyl groups.
The density of ionic groups on the polyester polymer will affect the ability of the polyester polymer to coat the substrate. Depending upon the final structure of the polyester polymer, the compounds included in the resinous phase and in the aqueous medium and the size, shape and metallic composition of the conductive substrate to be coated, the ionic salt group equivalent weight of the ionic polyester polymer will vary. Preferably, the ionic salt group equivalent weight of the polyester polymer is between 1,000 and 10,000.
As described above, the polyester polymer includes compounds (a)-(c), and optionally, (d). Compound (a) is an aromatic and/or cycloaliphatic carboxylic acid compound comprising at least two aromatic and/or secondary aliphatic carboxyl groups, or an anhydride thereof. Compound (a) is, for example, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid methylhexahydrophthalic acid, terephthalic acid, isophthatic acid, decahydronaphthalene dicarboxylic acid, endomethylene tetrahydrophthalic acid, methylendomethylene tetrahydrophthalic acid, or anhydrides thereof, or combinations thereof.
The polyester polymer is also derived from compound (b), a branched aliphatic, cycloaliphatic or aralaphatic compound containing at least two aliphatic hydroxyl groups. The aliphatic hydroxyl groups are either secondary or tertiary hydroxyl groups or primary hydroxyl groups attached to a carbon adjacent to a tertiary or quaternary carbon. A typical class of branched aliphatic compounds having primary hydroxyl groups attached to a carbon adjacent to a tertiary or quaternary carbon are 2,2-dialkyl-propane-1,3-diols. The two 2-alkyl groups can be the same or different and are typically branched or unbranched C
1
-C
6
alkanes. Compound (b) can also be a cycloalphatic or araliphatic compound, such as, for example, hydrogenated bisphenol A, dihydroxyl cyclohexane, dimethylol cyclohexane, dihydroxybenzene or combinations thereof.
Compound (c) is a compound comprising an ionic salt group or a group that is converted to an ionic salt group. The salt group can confer either an overall positive or negative charge to the ionic polyester polymer. A compound which is “a compound comprising an ionic salt group” is a compound which includes the ioni
Anderson Linda K.
Eswarakrishnan Venkatachalam
Kollah Raphael O.
McCollum Gregory J.
Peffer Robin M.
Meyers Diane R.
PPG Industries Ohio Inc.
Uhl William J.
Yoon Tae H.
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