Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-08-08
2003-07-15
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C525S456000, C525S509000, C528S045000, C528S058000, C528S073000, C528S080000
Reexamination Certificate
active
06592944
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to high solids, low VOC (volatile organic component) coating compositions and more particularly to low VOC clear coating compositions suited for multi-layered coatings used in automotive OEM and refinish applications.
Basecoat-clearcoat systems have found wide acceptance in the automotive finishes market. Continuing effort has been directed to improve the overall appearance, the clarity of the topcoat, and the resistance to deterioration of these coating systems at ever-higher application solids levels. Further effort has also been directed to the development of coating compositions having low VOC. A continuing need still exists for clear coating formulations having an outstanding balance of performance characteristics after application, particularly etch and mar resistance at high solids levels and low coating application viscosity. Melamine/acrylic polyol crosslinked or melamine self-condensed coatings for example, may provide coatings having acceptable mar but such coatings have poor acid etch resistance and decreased appearance at higher solids level. On the other hand, isocyanate/acrylic polyol based 2 K urethane coatings generally provide acceptable acid-etch resistance but such coatings have poor mar resistance. Therefore, a need still exists for coatings that not only provide acceptable mar and acid-etch resistance but also high gloss and DOI at the lowest VOC possible.
One approach described by Ntsihlele and Pizzi in an article titled “Cross-Linked Coatings by Co-Reaction of Isocyanate-Methoxymethyl Melamine Systems” (Journal of Applied Polymer Science, Volume 55, Pages 153-161-1995) provides for reacting aromatic diisocyanate with methoxymethyl melamine. However, a need still exists for a high solids clear coating composition, which upon a long-term exposure to sunlight does not yellow or become brittle and provides low coating application viscosities.
Another approach is disclosed in FR-A-2 265 828 provides for heat hardenable compositions suitable for coating metal objects. The composition includes a finely divided solid isocyanated polyester resin having masked isocyanate groups dispersed in a reactive liquid of highly etherized metylolated aminotriazine.
STATEMENT OF THE INVENTION
The present invention is directed to a clear coating composition comprising a polyester polyol a polyisocyanate and a melamine component wherein the total amount of said polyisocyanate and melamine components range from 50 percent to 90 percent, said percentages being in weight percentage based on the total weight of composition solids and wherein said polyisocyanate component comprises an aliphatic polyisocyanate having on an average 2 to 6 isocyanate functionalities.
The present invention is also directed to a method of producing a clear coating on a substrate comprising:
applying a layer of a clear coating composition comprising a polyester polyol, a polyisocyanate and a melamine component wherein the total amount of said polyisocyanate and melamine components range from 50 percent to 90 percent, said percentages being in weight percentage based on the total weight of composition solids and wherein said polyisocyanate component comprises an aliphatic polyisocyanate having on an average 2 to 6 isocyanate functionalities; and
curing said layer into said clear coating.
One of the advantages of the present invention is its low VOC, which is below the current guidelines of Environment Protection Agency (EPA) of the United States.
Another advantage is the mar and etch resistance and hardness of the coating resulting from the coating composition of the present invention.
Yet another advantage is the clarity and high gloss of the coating resulting from the coating composition of the present invention.
As Used Herein:
“Two-pack coating composition” means a thermoset coating composition comprising two components stored in separate containers. These containers are typically sealed to increase the shelf life of the components of the coating composition. The components are mixed prior to use to form a pot mix. The pot mix has a limited pot life typically of minutes (15 minutes to 45 minutes) to a few hours (4 hours to 6 hours). The pot mix is applied as a layer of desired thickness on a substrate surface, such as an autobody. After application, the layer is cured under ambient conditions or bake cured at elevated temperatures to form a coating on the substrate surface having desired coating properties, such as high gloss, mar-resistance and resistance to environmental etching. “One-pack coating composition” means a thermoset coating composition comprising two components that are stored in the same container. However, one component is blocked to prevent premature crosslinking. After the application of the one-pack coating composition on a substrate, the layer is typically exposed to elevated temperatures to unmask the blocked component. Thereafter, the layer is bake-cured at elevated temperatures to form a coating on the substrate surface having desired coating properties, such as high gloss, mar-resistance and resistance to environmental etching.
“Low VOC coating composition” means a coating composition that includes in the range of from 0 to 0.472 kilogram of organic solvent per liter (4 pounds per gallon), preferable in the range of from 0.118 (1 pound per gallon) to 0.295 kilogram of organic solvent per liter (2.5 pounds per gallon) of the composition, as determined under the procedure provided in ASTM D3960.
“High solids composition” means a coating composition having a solid component in the range of from 65 to 100 percent and preferably greater than 70 percent, all in weight percentages based on the total weight of the composition.
“Clear coating composition” means a clear coating composition that produces upon cure, a clear coating having DOI (distinctness of image) rating of more than 80 and 20° gloss rating of more than 80.
“GPC weight average molecular weight” and “GPC number average molecular weight” means a weight average molecular weight and a weight average molecular weight, respectively measured by utilizing gel permeation chromatography. A high performance liquid chromatograph (HPLC) supplied by Hewlett-Packard; Palo Alto, Calif. was used. Unless stated otherwise, the liquid phase used was tetrahydrofuran and the standard was polystyrene.
“Polymer particle size” means the diameter of the polymer particles measured by using a Brookhaven Model BI-90 Particle Sizer supplied by Brookhaven Instruments Corporation, Holtsville, N.Y. The sizer employs a quasi-elastic light scattering technique to measure the size of the polymer particles. The intensity of the scattering is a function of particle size. The diameter based on an intensity weighted average is used. This technique is described in Chapter 3, pages 48-61, entitled Uses and Abuses of Photon Correlation Spectroscopy in Particle Sizing by Weiner et al. 1987 edition of American Chemical Society Symposium series.
“Polymer solids” or “composition solids” means a polymer or composition in its dry state.
“Aliphatic” as employed herein includes aliphatic and cycloaliphatic materials.
“Crosslinkable” means that the individual components of a composition contain functionalities, which react within the composition of the invention to give a coating of good appearance, durability, hardness and mar resistance.
“Acid etch resistance” refers to the resistance provided by a coated surface against chemical etching action by the environment, such as for example acid rain.
“Mar resistance” refers to the resistance provided by coating to mechanical abrasions, such as, for example, the abrasion of a coated surface, such as an automotive body, that typically occurs during washing and cleaning of the coated surface.
Applicants have unexpectedly discovered that contrary to conventional approaches used in typical thermoset coating compositions, i.e., those involving polymers and crosslinking components, a very viable route lies in a combination of what would traditionally be considered
Nordstrom John David
Uhlianuk Peter William
Cameron Erma
Deshmukh Sudhir G.
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