Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-01-26
2002-08-20
Niland, Patrick D. (Department: 1714)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S385500, C524S589000, C524S590000, C525S123000, C525S127000, C528S044000
Reexamination Certificate
active
06436477
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed generally to refinish coating compositions and methods. More specifically, the invention concerns refinish coating compositions and methods for colder temperatures, such as below about 20° C.
BACKGROUND OF THE INVENTION
Polyurethane systems have been widely used for many years for refinish coatings. These systems contain hydroxyl-functional resins that react with polyisocyanates to form polyurethanes with excellent film properties including durability, toughness, and solvent resistance. In automotive refinish coating compositions, the polyisocyanates are not blocked so that the reaction with the hydroxyl groups will take place within a reasonable amount of time without heating or with heating at low temperatures of perhaps up to 150° F. Given the reactivity between the unblocked polyisocyanate and the hydroxyl-functional polyol at typical storage temperatures, these materials are segregated into separately stored components until just shortly before application of the coating composition to the substrate to be coated. This type of coating composition, in which the materials that react to cure the coating are segregated in two separately stored components, is referred to in the art as a “two-component” or “two-package” or “2K” coating composition. Automotive refinish coatings may include other separately stored components, such as color components.
While it is advantageous for the reaction between the hydroxyl-functional resin and the polyisocyanate crosslinker to take place slowly enough to provide a usably long pot life (typically a pot life on the order of one to two hours is desirable), polyurethane coatings with long pot lives can take a long time to dry and cure, especially at low temperatures. The pot life test is intended to describe the time after a catalyzed paint sample is mixed when it is still low enough in viscosity that it may still be sprayed. The pot life is the time elapsed until the initial viscosity doubles. The dry time at low temperatures can be shortened by increasing the rate of reaction between polyol and isocyanate with a catalyst, for example by adding an organotin catalyst, but addition of the catalysts known in the art decreases the pot life as well. Further, when the temperature is below about 20° C., a great deal of catalyst is typically added to a coating composition to obtain the desired dry time, which results in a very short pot life. Large amounts of tin catalysts are also undesirable because the catalysts remain in the coating and can also catalyze degradation of the polyurethanes. For example, see Hansen et al., U.S. Pat. No. 6,005,062, column 3. Large amounts of catalyst may also result in “die-back,” or loss of gloss, in the cured coating. Further, if the coating cures too quickly, it may have poor adhesion, thought to be an artifact of the rapid shrinkage of the coating during fast curing.
Low molecular weight primary amines have been used in roof coatings to obtain fast cure. The components of these coatings are mixed at the head of the spray gun because, once combined, the coating has no useable pot life. In addition, low molecular weight, primary amine-functional materials are especially not ideal for topcoat coating systems because coatings prepared with them tend to yellow.
Another issue of concern to manufacturers of refinish coatings has been increasing the solids content of refinish coatings compositions to reduce regulated emissions during application of the coatings. Zwiener et al., U.S. Pat. Nos. 5,126,170, 5,236,741, 5,412,056, and 5,623,045, each of which is incorporated herein by reference, disclose two-component coating compositions having a first component containing an isocyanate-functional polyisocyanate and a second component containing a specified secondary amine-functional material referred to as a “polyaspartic acid derivative.” The polyaspartic acid derivative is prepared by reacting a compound having two or more primary amines with optionally substituted maleic or fumaric acid esters. The component containing the secondary amine-functional material can optionally include other isocyanate-reactive compounds, such as hydroxy-functional polyacrylates. Coating compositions prepared by combining these two components are said to cure at temperatures of from −20° C. to 100° C., preferably 10° C. to 80° C. Zwiener et al., U.S. Pat. No 5,623,045, describes a two-component coating composition in which the polyaspartic acid derivative component further includes a polyketimine material and not does include any hydroxyl-functional materials.
The mixed material of the Zwiener et al. patents, however, has inadequate pot life, as is discussed in Wicks et al, U.S. Pat. No. 5,243,012, incorporated herein by reference. The Wicks et al, U.S. Pat. No. 5,243,012 discloses that the pot life of a two-component system according to the Zwiener et al., U.S. Pat. No. 5,126,170 can be extended by addition of a tin (IV) compound. The Wicks patent describes the increase in the pot life as surprising because the tin compound is generally considered a catalyst and thus would be expected to shorten the pot life. The tin compound may likewise increase the dry time of the coating composition, however. The Wicks patent describes that all three components of polyisocyanate, polyaspartic acid derivative, and tin (IV) compound may be mixed together to prepare the composition for application, or the tin (IV) compound may be combined first with one of the other components.
Fenn, U.S. Pat. No. 5,977,246, incorporated herein by reference, also describes the compositions with aspartic esters replacing part of the polyol as having very short pot lives and hypothesizes that the diluent aspartic ester may catalyze the reaction between the polyol and the polyisocyanate. The Fenn patent discusses replacement of all of the polyol by the aspartic ester as a way to solve the pot life problem, but states that such compositions produce films that are too brittle, have poor adhesion, and are expensive because of the high cost of the aspartic ester. The Fenn patent resolves the problem of obtaining the desirable high solids available with the aspartic acid, the desirable properties provided by a polymeric polyol, and good pot life by employing a polyester having secondary hydroxyl groups.
Gras et al., U.S. Pat. No. 5,852,154, incorporated herein by reference, describes a cold-curing composition for preparing a polyurea coatings including a polyester- or polyether-based isocyanate-functional prepolymer and a diamine having two secondary amine groups having tert-butyl or 1,1,3,3-tetramethyl isopropyl N-alkyl groups. Curing temperatures are not discussed, but the coatings of the examples are cured “at room temperature for 7 days” in one test and for 14 days in a second test. In the second test, it appears that in some cases half of the secondary amine equivalents was replaced by hydroxyl equivalents. Pot lives of up to about two hours are shown.
Hansen et al., U.S. Pat. No. 6,005,062, incorporated herein by reference, discloses that the reaction products of the Zwiener et al. patents may be subject to hydantoin formation through reaction of the urea hydrogen with an ester group from the aspartic acid derivative moiety, eliminating an alcohol molecule and altering the dimension of the polymer. Shrinkage and cracking of the curing coating is attributed to the hydantoin formation. The Hansen patent proposes preparing the secondary amine compounds with maleic or fumaric acid half-esters, half-amides. The applied coating is said to cure at temperatures from 10° C. to 80° C. The tack-free time is less than five minutes and the pot life appears to be very short, as evidenced by the need in Example 5 to combine the components and apply the coating as quickly as possible.
While most automotive refinish coatings are applied at a facility designed for such work, in which the applications conditions may be controlled to provide moderate temperatures, some refinish customers would prefer to have refinish work done at a loc
Laginess Thomas J.
Mormile Patrick J.
Thieben Lawrence E.
BASF Corporation
Budde Anna M.
Niland Patrick D.
LandOfFree
Method and system for low temperature cure of automotive... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for low temperature cure of automotive..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for low temperature cure of automotive... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2936876