Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1999-10-28
2001-09-18
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C525S411000, C525S414000, C525S519000, C528S260000, C528S262000, C528S354000, C528S045000, C528S084000
Reexamination Certificate
active
06291073
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns curable coating compositions, especially compositions for high-gloss topcoats, particularly for clearcoats of color-plus-clear composite coatings.
BACKGROUND OF THE INVENTION
Curable, or thermosettable, coating compositions are widely used in the coatings art, particularly for topcoats in the automotive and industrial coatings industry. Color-plus-clear composite coatings are particularly useful as topcoats for which exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The automotive industry has made extensive use of these coatings for automotive body panels.
Single-layer topcoats and the clearcoats of color-plus-clear composite coatings, however, require an extremely high degree of clarity and gloss to achieve the desired visual effect. Such coatings also require a low degree of visual aberrations at the surface of the coating in order to achieve the desired visual effect such as high distinctness of image (DOI). As such, these coatings are especially susceptible to a phenomenon known as environmental etch. Environmental etch manifests itself as spots or marks on or in the finish of the coating that often cannot be rubbed out. It is often difficult to predict the degree of resistance to environmental etch that a high gloss topcoat or color-plus-clear composite coating will exhibit. Many coating compositions known for their durability and/or weatherability when used in exterior paints, such as known high-solids enamels, do not provide the desired level of resistance to environmental etch when used in high gloss coatings such as the clearcoat of a color-plus-clear composite coating.
Curable coating compositions utilizing carbamate- or urea-functional materials are described, for example, in U.S. Pat. Nos. 5,756,213; 5,760,127; 5,770,650, 5,792,810; and 5,827,930, each of which is incorporated herein by reference. These patents describe coating compositions including a carbamate-functional or urea-functional compound prepared by a ring-opening reaction with a lactone. While such compounds have proven useful in coatings, particularly coatings for flexible substrates, it has been found that even a modest number of lactone units in the compounds give rise to problems of solidification during storage at room temperature and the need to employ higher amounts of solvent than desired in order to obtain suitable viscosities. On the other hand, decreasing the average number of lactone units per compound leads to less than optimum properties in the cured coating, such as poorer durability, less resistance to environmental etch, and less resistance to scratching and marring.
SUMMARY OF THE INVENTION
The present invention provides a curable coating composition that includes at least three components: a component (a), a component (b), and a component (c). The present invention also provides a composition comprising component (a) and component (b) that has improved stability against crystallization or solidification as compared to compositions without the component (b).
The component (a) has at least one carbamate group or urea group and has a lactone or hydroxy carboxylic acid moiety. When used in connection with the invention, the term “carbamate group” refers to a group having a structure
in which R is H or alkyl. Preferably, R is H or alkyl of from 1 to about 4 carbon atoms, and more preferably R is H. When used in connection with the invention, terminal urea group refers to a group having a structure
in which R′ and R″ are each independently H or alkyl, or R′ and R″ together form a heterocyclic ring structure. Preferably, R′ and R″ are each independently H or alkyl of from 1 to about 4 carbon atoms or together form an ethylene bridge, and more preferably R′ and R″ are each independently H. The terminal urea group of the invention is distinguished from urea linking groups for which R″ would be other than alkyl.
Preferred compounds (a) may be represented by the structures
in which R, R′, and R″ are as previously defined; R
1
is alkylene or arylalkylene, preferably alkylene, and particularly preferably alkylene of 5 to 10 carbon atoms; R
2
is alkylene or arylalkylene, preferably alkylene and particular preferably alkylene of about 5 to about 10 carbon atoms; R
3
is alkylene (including cycloalkylene), alkylarylene, arylene, or a structure that includes a cyanuric ring, a urethane group, a urea group, a carbodiimide group, a biuret structure, or an allophonate group, preferably alkylene (including cycloalkylene) or a structure that includes a cyanuric ring; n is from 1 to about 10, preferably from 1 to about 5; m is from 2 to about 6, preferably 2 or 3; and L is O, NH, or NR
4
, where R
4
is an alkyl, preferably an alkyl of 1 to about 6 carbon atoms.
The compound (a) may be prepared by a process that involves a step of reacting together a lactone or a hydroxy carboxylic acid and a compound comprising a carbamate or urea group or a group that can be converted to a carbamate or urea group and a group that is reactive with the lactone or hydroxy carboxylic acid. In the case of a group that can be converted to a carbamate or urea group, the group is converted to the carbamate or urea group either during or after the reaction with the lactone or hydroxy carboxylic acid. The process for preparing compound (a) may include a further step in which a hydroxyl-functional product of the first step is reacted with a compound having at least two isocyanate groups.
The second component (b) is a branched polyol having a lactone or hydroxy carboxylic acid moiety. The branched polyol has at least two hydroxyl groups and at least one branch point. By “branch point” we mean a carbon atom having carbon-carbon bonds with at least three other carbon atoms. Preferred compounds of the second component (b) may be represented by the structure
in which R
1
, n, and m are as previously defined, R
5
is an m-valent moiety having at least one branch point, and X is a moiety having an active hydrogen group. Preferably, R
5
is alkylene, more preferably with one branch point, and particularly preferably R
5
has from 2 to about 12 carbon atoms. Preferably, X is OH or X is a moiety having a carbamate or terminal urea group, more preferably X is OH.
The third component (c) of the coating composition is a curing agent that is reactive with the first two components.
Additionally, the invention provides a process for increasing the solids content of a coating composition that includes a component (a) as described above having at least one carbamate group or urea group and having a lactone or hydroxy carboxylic acid moiety. In the process of the invention, a small amount of a polyol (b)(1) having at least one branch point, preferably from about 0.2 to about 10% by weight based on the total weight of the components (a) and (b), is incorporated into the composition, preferably during a step in which a compound (a)(1) is reacted with a lactone or hydroxy carboxylic acid to form the component (a). Preferred polyols (b)(1) may be represented by the structure R
5
(OH)
m
, where R
5
and m are as defined previously.
The invention further provides an article having a substrate, in particular a flexible substrate, upon which substrate is a cured coating derived from a coating composition according to the invention and a method of producing such a coating on a substrate.
DETAILED DESCRIPTION
The composition according to the present invention includes as a first component a compound (a) having at least one carbamate group or terminal urea group and having a lactone or hydroxy acid moiety. By “lactone or hydroxy acid moiety” it is meant a structure resulting from incorporation of a lactone or hydroxy acid into the compound. For example, a lactone or hydroxy acid could be incorporated into compound (a) as an ester or polyester segment by reaction with a hydroxyl or a primary or secondary amine group on a precursor to compound (a). Preferred compounds (a) may be represented by t
Harris Paul J.
Ohrbom Walter H
BASF Corporation
Budde Anna M.
Short Patricia A.
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