Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2000-11-14
2003-08-05
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
Reexamination Certificate
active
06602552
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to coating compositions having a low curing temperature and short cure time.
BACKGROUND OF THE INVENTION
The present invention is directed to a method for decreasing the bake temperature and cure or dwell time of a coating process by utilizing a coating composition comprising a Lewis acid catalyst or a trifluoroacetic acid catalyst.
A method for coating over a cured coating with a coating containing Lewis acid catalysts is taught in U.S. Pat. No. 5,972,422 to Harmon et al., for a Method for Low Bake Repair of Composite Color Plus Clear Coatings and Compositions for Use Therein. These coatings however, are directed to low bake repair methods, where a coating comprising a carbamate functionality is applied over an area having a cured coating on it already. The repair coating requires a carbamate functional resin and is an automotive repair coating process for OEM.
Another references teaching the use of a Lewis Acid catalyst in a coating is U.S. Pat. NO. 6,045,872 to Harmon for a Method for Eliminating Wrinkling in Composite Color-Plus-Clear Coating and Compositions for Use Therein. This reference is also limited to a method using a coating containing a carbamate functional resin in a coating method for automotive coatings in an OEM coating process.
The coatings in both Harmon references are directed to carbamate coatings which cure for much longer times, and which provide a more brittle coating than those coatings contemplated by the present invention. Additionally, the coatings taught in Harmon are directed for use in processes for coating in OEM automotive applications.
The present invention is directed to industrial coating compositions that are used in a wide variety of coating applications, including application to primed metal and direct to metal coatings. These coatings include both liquid and powder coatings. The coatings are applied by a variety of methods including for liquids, electrodeposition, spraying, extruding, plate coating, dipping, and coil coating, and for powders, cloud chamber, plasma coating and electrostatic deposition. These coatings are applied to metal and plastic substrates.
Coatings applied by the above described methods employ forming a film of a liquid or powder coating composition at temperatures between about 280° F. and 450° F. (232° C.) at a thickness of between 0.01 and 5 mils, for a period of between about 10 minutes and about 40 minutes.
In the coil coating operation, a coil of sheet metal is uncoiled as it is pulled through a series of rollers, one or more of which is a paint applicator roller, at up to about 600 feet per minute. It is then passed through a curing oven and coiled again for the market. The paint is picked up by a roller rotating in the paint pan and transferred to a reverse or direct applicator roller. The cure temperature in a coil coating operation is typically measured as a peak metal temperature (PMT). The peak metal temperature is generally between 425° F. and 525° F. using a conventional acid catalyst such as aromatic sulfonic acid catalysts, including napthalene disulfonic acid, dinonyl napthalene sulfonic acid, para-toluene sulfonic acid, and dececylbenzene sulfonic acid, other acids such as phosphate acid catalysts including phosphoric acid, and mono- and dibutyl acid phophate may also be used. The curing times range generally from 14 to 40 seconds.
The present invention provides an improvement over the known methods of coil coating by providing a low temperature curing composition by use of the Lewis Acid or perfluoroacetic acid, or methane sulfonic acid catalyst, or any mixture of these catalysts in the present invention provides a curing at lower temperatures than those of a coating using other catalysts. This results in savings on energy costs to the coater and increased line speeds which result in larger volumes of coated product and higher productivity to the coater.
SUMMARY OF THE INVENTION
The present invention is directed to a method for coating a metallic substrate comprising the steps of applying to a substrate a low temperature cure coating composition consisting essentially of a non-carbamate polymeric film forming component selected from the group consisting of polyester, polyurethane, acrylic, alkyd, epoxy, polyamide, and polysilane polymers and mixtures thereof, a crosslinking component to crosslink the polymeric component, and a catalyst selected from the group consisting of Lewis acids, trifluoroacetic acid, methane sulfonic acid and mixtures thereof, wherein the coated substrate is subjected to a low cure temperature for a time sufficient to cure the coating composition.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a method for coating a metallic or plastic substrate to minimize the cure temperature and cure or dwell time used in the coating process. The process comprises the steps of applying to a substrate a low temperature curing coating composition consisting essentially of a non-carbamate polymeric film forming component, a crosslinking component to crosslink the polymeric component, and a catalyst selected from the group consisting of Lewis acids, trifluoroacetic acid, methane sulfonic acid and mixtures thereof. It is believed that the specific catalysts utilized in the present invention lower the cure temperature and cure time of the coating. The coating is applied to a substrate, either directly or to a coated or uncoated substrate. When the uncoated substrate is metal, it is referred to as “direct to metal”, or the coating may be applied to a substrate that has been coated with a first coating such as a primer or other coating. In processes such as spraying, electrodeposition, extruding, plate coating, dipping, powder coating, cloud chamber, plasma coating and electrostatic deposition, the typical,cure time ranges from 10 to 40 minutes, at temperatures between 250° F. and 450° F., contrasting with the method of the present invention, where the cure time is reduced to about 5 to 25 minutes, generally at reduced temperatures between 180° F. and 350° F. In coil coating, generally the cure time ranges from about 10 to about 60 seconds at temperatures between about 425° F. to 525° F., in contrast to the present invention, where the cure time ranges from about 5 to about 60 seconds and more preferably from about 7 to about 40 seconds and most preferably from about 7 to about 35 seconds, generally at a curing temperature of between about 300° F.(135°) and about 450° F.(232° C.). In coil coating the cure temperature is referred to as the peak metal temperature. It is desirable to minimize the cure temperature and cure or dwell time used in all coating processes. Using the specific catalysts described in the present invention enables cure times and temperatures to be reduced to levels below that in coating compositions utilizing catalysts other than those defined in the present invention.
The non-carbamate functional film forming polymer component useful in the coatings of the present invention consists essentially of polymers selected from the group consisting of polyester, polyurethane, acrylic, alkyd, epoxy, polyamide, and polysilane polymers and mixtures thereof. Most preferably, the coating is a polyester, acrylic or polyurethane polymer or any combination thereof. Polymers useful in the present invention are described as follows. The non-carbamate functional polymer is present in the coating composition in an amount between 10% and 90% by weight, based on total coating composition weight. More preferably, the polymer is present in amount between 20% and 80% by weight and most preferably between 25% and 65% by weight, based on total coating composition weight.
Polyester compositions useful for solvent borne coatings in accordance with the invention are formed by polyesterification of organic polycarboxylic acids and polyhydric alcohols. Suitable acids include but are not limited to, phthalic acid, isophthalic acid, hexahydrophthalic acid, adipic acid, succinic acid, fumaric acid , maleic acid, isophthalic acid, cyclo
Daraskevich Edward J.
Lewarchik Ronald J.
McCann Sebastian E.
Slawikowski Mark P.
BASF Corporation
Cameron Erma
Sabourin Anne
LandOfFree
Low temperature cure coating composition and method therefore does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low temperature cure coating composition and method therefore, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low temperature cure coating composition and method therefore will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3088172