Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-02-26
2002-10-08
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S450000, C525S440030, C525S460000, C525S445000, C528S069000, C528S085000, C428S413000, C428S423100
Reexamination Certificate
active
06462144
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to carbamate-functional resins and their use in high solids coating compositions. More specifically it relates to carbamate functionalized star or hyperbranched polyols as reactive resins in coatings.
BACKGROUND OF THE INVENTION
Coating compositions based on carbamate-functional acrylic polymers and aminoplast cross-linking agents are desirable as automotive topcoats because they have excellent durability, hardness, gloss, appearance, and resistance to environmental etch. As such, they are highly suitable for use as a clearcoat layer applied over a basecoat layer in a color plus clear composite coating.
A problem associated with curable coating compositions based on acrylic polymers containing pendant carbamate groups and aminoplast curing agents is that the compositions do not have particularly good intercoat adhesion. This problem presents itself when the compositions are used as clearcoats and composite color plus clear coatings, especially during repair procedures which involve applying the clear film forming composition to a flawed area of a previously applied color plus clear composite coating.
Another area for improvement in the use of carbamate-functional acrylic polymers with amino resins systems as cross-linkers is compatibility with waterborne basecoats. The waterborne basecoats contain amines used to salt the resin into water. During baking, the amine is released from the basecoat and travels through the clearcoat to the surface, where it is released into the atmosphere. The concentration of amine at the bottom of the clearcoat is greater than the concentration at the top, which sets up a pH gradient in the clearcoat. Because the cure rate is a function of the pH, a so called cure gradient forms in the clearcoat. This leads to an appearance defect known as wrinkling.
The curable carbamate-functional compositions are generally formulated with a low-imino amino resin so as to achieve high solids, which is desirable for economic and environmental reasons. If instead high-imino amino resins are used, the cure gradient is minimized along with the wrinkling. This is because the dependency on pH of the cure rate of a high-imino amino resin is not as great as that of a low-imino resin.
However, when high-imino resins are used, the solids content of the coating becomes unacceptably low. Thus, it would be desirable to provide a coating composition based on carbamate-functional resins and amino resin crosslinkers that have a combination of high solids and compatibility with waterborne basecoats. Preferably, such a composition would also exhibit improved intercoat adhesion.
U.S. Pat. No. 5,759,694 to Mayo has addressed the intercoat adhesion problem by providing a polyester made by copolymerizing a diol, optional triol, a hydroxyl functional and acidic functional material, and a polyacid, followed by reaction with a monoepoxide and carbamoylation. The polyester is combined with a carbamate-functional acrylic resin and an aminoplast to yield a film forming composition. Mayo does not directly address the problem of compatibility of the film forming composition with a waterborne basecoat.
U.S. Pat. No. 5,693,723 to Green describes a carbamate-functional resin prepared by reacting a compound having at least one hydroxyl group and one carboxyl group with an epoxy compound, and then carbamoylating the reaction product. High solids coating compositions are obtained, but there is no discussion of how to improve intercoat adhesion.
SUMMARY OF THE INVENTION
The present invention provides a coating composition containing
1) a carbamate-functional resin having in its structure a hyperbranched or star polyol core, a first chain extension based on a polycarboxylic acid or anhydride, a second chain extension based on an epoxy-containing compound, and having carbamate functional groups on the core, the second chain extension, or both; and
2) a second resin containing functional groups reactive with the carbamate groups on the carbamate-functional resin.
In one embodiment, the coating compositions are used as clearcoats applied over basecoats to form composite coatings. The compositions exhibit a combination of desirable properties, such as scratch and mar resistance, resistance to environmental etch, good intercoat adhesion, and high solids.
In another embodiment, the coating compositions also contain a carbamate-functional acrylic resin. In this embodiment, the carbamate-functional resin of the invention may act as a reactive diluent. Methods are also provided to synthesize the carbamate-functional resins of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The terms “carbamate group”, “carbamate-functional”, and the like, as used in connection with the present invention refer to a group having a structure:
in which R is H or alkyl, preferably R is H or alkyl of from 1 to about 8 carbon atoms, more preferably R is H or alkyl of from 1 to about 4 carbon atoms, and yet more preferably R is H. When R is H, the carbamate group is referred to herein as a primary carbamate group.
The carbamate-functional resin of the invention is based on a star or hyperbranched core and contains carbamate functionality. The carbamate functionality can be introduced onto the core by reacting the core with a compound containing a carbamate group and a functional group reactive with the hydroxyl groups on the core. Alternatively, it can be introduced by a series of extension steps with a polycarboxylic acid or anhydride and epoxy compound, followed by carbamoylation. The degree of carbamoylation and the number of extensions can be selected so as to obtain desirable properties of coatings prepared from the resin.
The carbamate-functional resins of the invention can be formulated with another resin having functional groups reactive with the carbamate groups to form curable coating compositions particularly useful as a topcoat or as a clearcoat component of a basecoat-clearcoat composite coating. The coating compositions of the invention can further contain a carbamate-functional acrylic resin.
The star core is a structure based on a star polyol. A star polyol is a monomeric polyol containing three or more primary or secondary hydroxyl groups. In a preferred embodiment, the star polyol has four or more hydroxyl groups. Examples of star polyols include, without limitation, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, ditrimethylolpropane, dipentaerythritol, tetrakis (2-hydroxyethyl)methane, diglycerol, trimethylolethane, xylitol, glucitol, dulcitol, and sucrose. Mixtures of star polyols may also form the star core of the carbamate-functional resin of the invention.
A hyperbranched core is a structure based on hyperbranched polyols. Hyperbranched polyols are prepared by the reaction of a first compound having two or more hydroxyl groups and a second compound having one carboxyl group and two or more hydroxyl groups. The first and second compounds can be reacted to form a first generation hyperbranched polyol. Alternatively, the second compound can be reacted with the first generation hyperbranched polyol to form a second generation and, if desired, subsequent generations. Preferably, a first generation or second generation hyperbranched polyol is used as the hyperbranched core of the carbamate-functional resin of the invention.
The first compound can suitably be an aliphatic, a cycloaliphatic, or an aromatic diol, triol, or tetrol, a sugar alcohol such as sorbitol and mannitol, dipentaerythritol, an &agr;-alkylglucoside such as &agr;-methylglucoside, or an alkoxylate polymer having a molecular weight of at most about 8,000 that is produced by a reaction between an alkylene oxide or a derivative thereof and one or more hydroxyl groups from any of the alcohols mentioned above. Mixtures of these can also be used as the first compound.
Diols suitable as the first compound include straight diols with 2-18 carbon atoms. Examples include, without limitation, 1,3-propanediol, 1,2-ethanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.
The dio
Campbell Donald H.
Green Marvin L.
Ohrbom Walter H.
Ramesh Swaminathan
BASF Corporation
Bissett Melanie
Frentrup Mark A.
Seidleck James J.
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