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
2001-12-14
2003-12-02
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S185000, C525S187000, C525S190000, C525S131000, C525S312000, C526S217000, C526S236000, C526S301000, C526S302000, C526S312000, C526S320000
Reexamination Certificate
active
06657007
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns thermoset clearcoat compositions, especially for automotive vehicles.
BACKGROUND OF THE INVENTION
Clearcoat-basecoat composite coatings are widely used in the coatings art and are notable for desirable gloss, depth of color, distinctness of image and/or special metallic effects. Composite systems are particularly utilized by the automotive industry to achieve advantageous visual effects, especially a high degree of clarity. However, a high degree of clarity in the clearcoat makes it easier to observe defects. Defects resulting from environmental etch are particularly disadvantageous. Environmental etch is a phenomenon which manifests as spots or marks on or in the clearcoat which are removed only with loss of clearcoat.
Clearcoat compositions containing carbamate-functional acrylic polymers have been disclosed by the prior art as a solution to the problem of environmental etch. While such polymers and compositions containing them provide a significant improvement over the prior art, improvements in some areas are still desirable. In particular, it would be advantageous to provide polymers exhibiting improved adhesion while still possessing the positive environmental etch and performance characteristics of carbamate-functional acrylics. Improvements are particularly desired with respect to adhesion of the polymer-containing composition to one or more subsequently applied coatings that may be applied to correct minor defects or flaws. Adhesion failures resulting from a weak bond between the original clearcoat layer and a subsequently applied coating, also known as an intercoat adhesion failure, are undesirable, particularly for automotive OEM clearcoats.
U.S. Pat. No. 5,412,049 discloses acrylic copolymers of hydroxyalkyl (meth)acrylates and (meth)acrylate esters of hydroxyalkyl carbamates, optionally with other comonomers in amounts of up to 90 weight percent. The '049 patent does not disclose how to improve intercoat adhesion, however. U.S. Pat. No. 5,356,669 also describes carbamate-functional acrylic polymers. The acrylic polymers of the '669 patent may contain 10 to 90 weight percent of nonfunctional comonomers. This reference also does not discuss how to improve intercoat adhesion.
Flexibility is also an important property when the clearcoat is applied over a flexible substrate, such as a vehicle bumper. Coating compositions optimized for environmental etch resistance often do not provide the desired degree of flexibility, especially for acrylic polymers having carbamate functionality that are cured with aminoplast curing agents.
SUMMARY OF THE INVENTION
The clearcoat coating composition for automotive exterior coatings of the present invention provides intercoat adhesion to a subsequently applied coating layer and also provides improved flexibility over earlier environmental etch resistant clearcoats. The clearcoat composition of the invention contains a first vinyl copolymer prepared from a monomer mixture including no more than about 35% by weight of nonfunctional monomers. “Nonfunctional monomers” are monomers that do not have functional groups reactive with the crosslinker or curing agent component. The first vinyl copolymer has carbamate functionality and hydroxyl functionality. A carbamate group according to the invention may be represented by the 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 (a primary carbamate). At least a part, preferably all, of the monomer units bearing hydroxyl groups include an alkyl group, optionally branched, having at least about six carbon atoms.
The clearcoat composition further includes a second vinyl copolymer having hydroxyl functionality, preferably primary hydroxyl functionality. A primary hydroxyl group according to the invention is a hydroxyl group bound to a carbon that is bound to only one carbon atom.
The clearcoat composition also has a curing agent component that includes at least an aminoplast curing agent and optionally a polyisocyanate curing agent. The polyisocyanate curing agent is preferably blocked with a blocking agent that volatilizes during the cure reaction, regenerating a reactive isocyanate group.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
The clearcoat composition of the invention contains a first vinyl copolymer prepared from a monomer mixture including no more than about 35%, preferably no more than about 20%, and particularly preferably no more than about 10%, by weight of nonfunctional monomers. The first vinyl copolymer has carbamate functionality and hydroxyl functionality. A carbamate group according to the invention may be represented by the 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 (a primary carbamate). Preferably, from about 65% by weight to about 100% of the monomeric units of the polymer have at least one of the carbamate and hydroxyl groups.
In general, an acrylic polymer with carbamate or urea groups may be prepared in two ways. First, the acrylic polymer with carbamate or urea groups may be prepared by polymerization using a monomer having a carbamate or urea group. Secondly, the acrylic polymer may be prepared by polymerization of a monomer having functionality that can be converted to or adducted with carbamate or urea functionality after polymerization. Any of the methods described in U.S. Pat. No. 6,160,058, the disclosure of which is incorporated herein by reference, may be used.
In the first method, the acrylic polymer is prepared by polymerization of a monomer having carbamate or urea groups. For example, U.S. Pat. No. 5,412,049, incorporated herein by reference, discloses polymerization of the reaction product of an hydroxyl (meth)acrylate ester of an hydroxyalkyl carbamate compound.
In another embodiment of the first method, the acrylic polymer may be polymerized with a &bgr;-hydroxy carbamate monomer having the structure
in which either each R is hydrogen or one R is hydrogen and the other R is methyl; n is from 1 to about 4, preferably 1; and one of Y and Z is OH and the other of Y and Z is a carbamate or urea group as already defined. In a typical synthesis of such a monomer, the reaction kinetics produces a product that is a mixture of the compounds in which Y is hydroxyl and Z is hydroxyl. When Y is the hydroxyl group, the monomer also provides an hydroxyl group for the acrylic polymer.
One way of preparing a &bgr;-hydroxy carbamate monomer of this structure is by reacting a glycidyl-group containing polymerizable monomer first with carbon dioxide to convert the oxirane group to a cyclic carbonate group, and then with ammonia or a primary amine to convert the cyclic carbonate group to a &bgr;-hydroxy carbamate group. Examples of suitable oxirane group-containing polymerizable monomers include, without limitation, glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, and allyl glycidyl ether. Oxirane groups can be converted to carbamate groups by first converting to a cyclic carbonate group by reaction with CO
2
. This can be done at any pressure from atmospheric up to supercritical CO
2
pressures, but is preferably under elevated pressure (e.g., 60-150 psi). The temperature for this reaction is preferably 60-150° C. Useful catalysts include any that activate an oxirane ring, such as tertiary amine or quaternary salts (e.g., tetramethyl ammonium bromide), combinations of complex organotin halides and alkyl phosphonium halides (e.g., (CH
3
)
3
Snl, Bu
4
Snl, Bu
4
PI, and (CH
3
)
4
PI), potassium salts (e.g., K
2
CO
3
, KI) preferably in combination with crown ethers, tin octoate, calcium octoate, and the like. The cyclic carbonate group is reacted with ammonia or a primary amine. The primary amine preferably has up to four carbons, e.g. methyl am
Campbell Donald H.
Cook Vincent
Gilbert John A.
BASF Corporation
Pezzuto Helen L.
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