Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-09-30
2001-02-06
Sanders, Kriellion (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C528S367000, C528S418000, C528S423000, C428S412000, C428S413000, C428S704000
Reexamination Certificate
active
06184273
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coating compositions having latent amine functional compounds, and particularly to such compositions having cyclic carbonate compounds.
BACKGROUND OF THE INVENTION
Thermosetting, or curable, coating compositions are widely used in coatings operations. In automotive coatings, in particular, thermoset coatings provide durable finishes. Automotive coatings include primers and topcoats, which may be single layer enamels or two layer basecoat/clearcoat systems. The primer may be applied either as a first coating layer or over another layer, for example over an electrocoat primer layer. The topcoat is then usually applied directly over the primer layer.
While thermosetting compositions provide desirable coating properties, there are a number of concerns that arise with thermosetting coating compositions. One consideration is the curing conditions needed to achieve sufficient crosslinking of the film. In general, higher temperatures and longer times at the curing temperature increase the manufacturing costs of the coated article. Another concern in some cases is that undesirable by-products of the curing reaction are generated. For example, blocked curing agents release the blocking agents as volatile organic compounds that constitute emissions regulated by various government rules. It is also important that the crosslinks that are formed are suitable for providing long life to the coating under the particular conditions to which the coated article will be exposed.
Different crosslinking mechanisms may be employed in thermosetting coatings. One curing mechanism utilizes a melamine formaldehyde resin curing agent in the coating composition to react with hydroxyl groups on the resin. This curing method provides good cure at relatively low temperatures (e.g., 250° F. with a blocked acid catalyst, or even lower with an unblocked acid catalyst), but the crosslink bonds contain undesirable ether linkages and the resulting coatings may provide poor overall durability under certain service conditions. In an alternative curing method, polyisocyanate curing agents may be reacted with amine or hydroxyl groups on the resin. This curing method provides desirable urea or urethane crosslink bonds, but it also has several disadvantages. In order to prevent premature gelation of the coating composition, the polyisocyanate must either be kept separate from the resin in what is known in the art as a two-package or two-pack coating system or else the highly reactive isocyanate groups on the curing agent must be blocked (e.g., with an oxime or alcohol). Blocked polyisocyanates, however, require high temperatures (e.g., 150° C. or more) to unblock and begin the curing reaction. The volatile blocking agents released during cure can adversely affect coating properties, as well as increasing the volatile organic content for the composition.
There is thus a need in the art for coating compositions that could provide desirable urethane crosslink linkages, but avoid the problems that accompany the use of polyisocyanate curing agents.
Coating compositions comprising carbonate curing agents and primary amine-functional crosslinkable resins have been proposed for electrocoat primers in December et al., U.S. Pat. No. 5,431,791. In the electrocoat bath, the primary amine groups are salted and rendered unreactive with the carbonate groups of the carbonate compound. When the coating is deposited onto the conductive substrate, the primary amine groups are regenerated from the salt and are once more reactive toward the carbonate curing agent. This method of achieving package stability, however, is unsuitable for solventborne and non-cathodic waterborne compositions.
SUMMARY OF THE INVENTION
We have now invented a coating composition capable of forming durable urethane linkages upon curing of the coating without the attendant problems of polyisocyanate curing agents. The compositions of the present invention comprise a compound having a plurality of latent primary amine groups and a compound having a plurality of cyclic carbonate groups. The present invention further provides a method of coating a substrate by applying a coating composition comprising a resin having latent primary amine functionality and a carbonate compound having a plurality of cyclic carbonate groups and then curing the applied composition. The present invention also provides a substrate having thereon a coating derived from a composition containing a compound having latent primary amine functionality and a carbonate compound having a plurality of cyclic carbonate groups.
DETAILED DESCRIPTION
The compositions of the invention include a compound having latent primary amine functionality and a compound with a plurality of cyclic carbonate groups. The compound having latent amine functionality may be formed by reacting two moles of a cyclic anhydride of a polycarboxylic acid with two moles of a compound having at least two primary amine groups. The compound having a plurality of cyclic carbonate groups has at least two carbonate groups, and preferably has more than two carbonate groups on average per molecule.
In the synthesis of the compound with latent primary amine functionality, an amine compound with preferably two primary amine groups is employed. The amine compound may optionally have additional functional groups that are not primary amine groups, so long as such groups do not interfere with the reaction between the primary amine groups of the amine compound and the cyclic anhydride. Suitable examples of the primary amine compounds include, without limitation, &agr;,&ohgr;-alkylenediamines and polyalkylene polyamines. Examples of suitable polyalkylene polyamines include, without limitation, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenetriamine, 1,6-diaminohexane, 1,3-diaminopropane, methyl imino-bis(propylamine), 1,4-diaminobutane, and mixtures of these. Particularly preferred among these are ethylenediamine, diethylenetriamine, dipropylenetriamine, and mixtures of these compounds. Preferred polyamines have molecular weights in the range of about 60 to about 400, more preferably from about 60 to about 250, and still more preferably from about 60 to about 160.
Suitable examples of cyclic anhydrides of polycarboxylic acids that may be used in the reaction with the primary amine compound include, without limitation, phthalic anhydride and substituted derivatives of phthalic anhydride such as 4-sulfophthalic anhydride, 4-methylphthalic anhydride, 3-hydroxyphthalic anhydride, nitrophthalic anhydride, and 4,4′-carbonyldiphthalic anhydride; hydrogenated derivatives of phthalic acid such as hexahydrophthalic anhydride, 1,2,3,6-tetrahydrophthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, hexahydro-4-methylphthalic anhydride, and methyltetrahydrophthalic anhydride; maleic anhydride and its derivatives, such as 2,3-dimethylmaleic anhydride, 2,3-diphenylmaleic anhydride, bromomaleic anhydride, and dichloromaleic anhydride; pyromellitic dianhydride; succinic anhydride and its derivatives, such as dodecenylsuccinic anhydride, and methylsuccinic anhydride; 1,2-cyclohexane dicarboxylic acid, nadic methyl anhydride (methyl-5-norborene-2,3-dicarboxylic anhydride), cis-5-norborene-endo-2,3-dicarboxylic anhydride, itaconic anhydride, 2,3-pyridinedicarboxylic anhydride, pyromellitic dianhydride, endo-bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylic anhydride, 1,2,3,4,-cyclobutanetetracarboxylic dianhydride, and 1-cyclopentene-1,2-dicarboxylic anhydride. Preferred among these are phthalic anhydride and substituted derivatives of phthalic anhydride and hydrogenated derivatives of phthalic acid.
The reaction between the cyclic anhydride and the amine compound is may be carried out with about a stoichiometric ratio of the reactants, but preferably is carried out using an excess of the amine compound. It is preferred to employ a ratio of at least about two moles, and preferably at least about three moles, of the primary amine compound per mole of the anh
December Timothy S.
Harris Paul J
BASF Corporation
Golota Mary E.
Sanders Kriellion
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