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
2001-07-09
2003-10-14
Mullis, Jeffrey (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...
C525S069000, C525S070000, C525S077000, C525S085000
Reexamination Certificate
active
06632880
ABSTRACT:
TECHNICAL FIELD
This invention relates to high solids solvent based coating compositions having a low VOC (volatile organic content) and in particular to a clear coating composition useful for refinishing clear coat/color coat finishes of a vehicle such as an automobile or a truck.
BACKGROUND OF THE INVENTION
Clear coat/color coat finishes for automobiles and trucks have been used in recent years and are very popular. Kurauchi et al U.S. Pat. No. 4,728,543 issued Mar. 1, 1988 and Benefiel et al U.S. Pat. No. 3,639,347 issued Feb. 1, 1972 show the application of a clear coat to a color coat or basecoat in a “wet on wet” application, i.e., the clear coat is applied before the color coat is completely cured.
There is a need for a clear coating composition that can be used to repair these clear coat/color coat finishes that has a low VOC to meet with pollution regulations for refinishing vehicles, that cures rapidly to a tack free coating at ambient temperatures, and that can be buffed in a relatively short period of time thereafter to a high gloss finish. Such a combination of properties is not provided by the prior art coatings, as for example, as shown in Lamb et al U.S. Pat. No. 5,286,782 issued Feb. 15, 1994 and Barsotti et al U.S. Pat. No. 5,763,528 issued Jun. 9, 1998.
The novel coating composition of this invention has the aforementioned desirable characteristics.
SUMMARY OF THE INVENTION
A coating composition containing about 40-90% by weight of film forming binder and 10-60% by weight of an organic liquid carrier;
wherein the binder contains about
(a) 10-70% by weight, based on the weight of the binder, of a dispersed gelled acrylic polymer having
(i) a core of gelled polymerized ethylenically unsaturated monomers which is not soluble in the organic liquid carrier and having chemically grafted thereto
(ii) substantially linear stabilizer polymeric components that are soluble in the organic liquid carrier and comprise polymerized ethylenically unsaturated monomers and have a weight average molecular weight of about 500-20,000 determined by GPC (gel permeation chromatography) using polystyrene as the standard;
wherein the core, the stabilizer polymeric component, or both contain at least 3% by weight of polymerized ethylenically unsaturated monomers having isocyanate groups attached thereto that are capable of reacting with component (b);
(b) 30-90% by weight, based on the weight of the binder, of an oligomer or polymer or both having functional groups capable of reacting with the isocyanate groups of component (a); and
(c) 0-60% by weight, based on the weight of the binder, of an organic polyisocyanate crosslinking agent.
Dispersed gelled acrylic polymers of the foregoing composition are also a part of this invention.
DETAILED DESCRIPTION OF THE INVENTION
In repairing a clear coat/color coat finish of an automobile or truck, generally the color coat is applied and dried for a short time but not cured and then the clear coat is applied and both coats are cured. If necessary, the cured clear coat is buffed to improve appearance and remove minor imperfections. The coating composition of this invention has a short drying time and thereby improves the rate of processing vehicles through a typical repair facility. In particular, the novel composition has a short tack and dust free time when used as a clear finish so that the vehicle can be moved out of the work area to provide room for another vehicle to be painted. The novel composition when used as a clear finish is buffable in a short period of time after application and initially drying and remains buffable for several days, preferably up to one week before it cures into a hard durable finish. For a finish to be buffable it must be hard but not tough.
Preferably, the coating composition of this invention when used as a clear coat dries to tack free state in about two hours of application and can be buffed in about three hours of application.
The novel coating composition is solvent based and contains about 10-60% by weight of an organic liquid carrier and correspondingly, about 90-40% by weight of film forming binder and preferably has a VOC of about 3.5-4.5 pounds of solvent per gallon of coating composition. The binder contains (a) about 10-70% by weight, preferably 20-60%, most preferably 30-50%, of a dispersed gelled acrylic polymer having isocyanate functionality, (b) about 30-90% by weight, preferably 40-80%, most preferably 50-70%, of an oligomer or polymer or a combination thereof having functional components that are reactive with the isocyanate groups on the dispersed gelled acrylic polymer, and (c) about 0-60% by weight, preferably 0-50%, most preferably 0-30%, of a polyisocyanate crosslinking agent capable of reacting with the functional components on the oligomer or polymer. Herein, binder components (a) plus (b) plus (c) are considered to equal 100 weight percent, and other components are calculated as parts (weight) relative to 100 parts of (a) plus (b) plus (c).
Generally, the novel coating composition is used as a clear coat but can be pigmented with conventional pigments and used as a monocoat or as basecoat.
The dispersed gelled acrylic polymer (also referred to herein as a non-aqueous dispersion or NAD polymer) used to formulate the coating composition of this invention is prepared from a macromonomer which forms the linear stabilizer polymeric components that are chemically grafted to a core.
Preferably, the polymer contains about 30-70% by weight of the core and 70-30% by weight of substantially linear stabilizer polymeric components. These linear stabilizer components are soluble in the organic carrier liquid used to form the coating composition and keep the acrylic polymer dispersed in the liquid while the core is insoluble in this liquid. These macromonomers which form the stabilizer polymeric components of the polymer comprise polymerized alpha-beta ethylenically unsaturated monomers and have one ethylenically unsaturated moiety preferably but not necessarily at the terminal end and have a weight average molecular weight (Mw) of 500-20,000, preferably 1,000 to 10,000. The core, conversely, is formed from a high molecular weight polymer having a weight average molecular weight (Mw) of 50,000 to 500,000, preferably 50,000 to 200,000. About 25-75% (by weight), preferably 40-60%, of the macromonomer is copolymerized with 75-25%, preferably 60-40%, of a blend of other alpha-beta ethylenically unsaturated monomers which form the core of the acrylic polymer.
In the present invention, the core, the stabilizer component, or both contain isocyanate groups that are capable of reacting with the other binder components present in the coating composition. More particularly, at least 3%, preferably 3-30% by weight, of the polymerized monomers in the core, stabilizer component or in both have isocyanate groups attached thereto. The isocyanate groups can be attached by post reaction of isocyanate reactive functional groups in the core, the macromonomer, or both with polyisocyanates, e.g., di- and triisocyanates. The isocyanate groups can also be attached to the dispersed acrylic gelled polymer by copolymerization of isocyanate functional monomers with the core, macromonomer, or both.
In the present composition, while both the stabilizer components and the core may contain isocyanate groups, it is generally preferred to have such reactive functionality only or essentially only or substantially only on the stabilizer components. It is to be understood that the core or macromonomers referred to as having isocyanate functionality may be part of a mixture of core polymers or macromonomers of which a portion do not have any functionality or variable amounts of functionality. It is also understood that, in preparing any core or macromonomers, there is a normal distribution of functionality.
The dispersed gelled acrylic polymer may be, and preferably is, prepared by polymerizing ethylenically unsaturated monomers that comprise the insoluble core in the presence of macromonomers, each macromonomer having at least one ethyl
Barsotti Robert J.
Lewin Laura Ann
Scopazzi Christopher
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Mullis Jeffrey
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