Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-02-01
2003-12-02
Short, Patricia A. (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S388200, C427S393500, C525S444500, C528S295500
Reexamination Certificate
active
06656530
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed generally to coating compositions and methods, particularly automotive refinish topcoat compositions and refinishing methods.
BACKGROUND OF THE INVENTION
Polyurethane systems have been widely used for refinish coatings. These systems contain hydroxyl-functional resins that react with polyisocyanate crosslinkers to form polyurethane coatings with excellent 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 only 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 be formulated as two-component compositions in each desired color, or may be prepared as an intermix system including separately stored color components, a crosslinker component, and possibly other components such as a reducer component or an unpigmented component containing resin or polymer reactive with the crosslinker. While two-component compositions avoid premature reactions, care must be taken by the end-user to combine the correct amounts of the two components in order to obtain the desired coating properties.
Another issue of concern to manufacturers of refinish coatings has been increasing the solids content of refinish coatings compositions in order to reduce regulated emissions during application of the coatings. While regulated emissions are of concern in applying other coatings as well, reducing such emissions with automotive refinish coatings is a particularly difficult problem. One of the ways in which the need for low emissions formulations has been addressed for coatings for original finish (“OEM” coatings) for industrial or automotive applications has been by using resins and polymers with lower molecular weights. The lower molecular weight resins generally have lower viscosities, and thus the compositions requires less solvent to achieve the desired application viscosity. Because of their low molecular weight, however, such resins must have higher functionality and be further reacted during cure in order to provide the desired performance in the applied coating. OEM coatings are typically baked at relatively high temperatures (typically about 200° F. (93° C.) and higher) to cure the compositions in a reasonably short time. Unlike OEM coatings, automotive refinish coatings must be formulated as either thermoplastic compositions or thermosetting compositions that cure at relatively low temperatures, both because the many plastic components of a finished vehicle cannot withstand high temperature bakes and because many of the collision shops using the paint could not afford equipment large enough for a baked finish on a vehicle. On the other hand, it is still desirable to have the applied refinish coating “dry to handle” in a short time.
Room temperature-curing coating compositions containing an acetoacetate-functional addition polymer and a blocked polyamine are disclosed in Noomen et al., U.S. Pat. No. 4,772,680. The addition polymer has a number average molecular weight of 1000 to 10,000 and 3.5 to 45% by weight acetoacetate groups. The blocked polyamines have number average molecular weights of 250 to 4000. The composition can be cured at room temperature. The acetoacetate-functional addition polymer, however, like the hydroxyl-functional addition polymer used with polyisocyanate curing agents, must have a low molecular weight if compositions with low organic solvent content are desired. Low molecular weight polymers, on the other hand, require a much higher functional group content and take longer to cure sufficiently to become dry to the touch.
EP 0 483 915 similarly discloses a binder composition in which an acrylate polymer is amine, ketimine, or aldimine-functional and a crosslinking agent has acetoacetate functionality. This composition is comparable to the Nooman composition in that it contains an acrylic polymer and a curing agent, although the functionalities of the polymer and curing agent have been reversed relative to the Nooman composition.
U.S. Pat. Nos. 5,344,897 and 5,332,785 to Brindoepke et al. disclose a two-component automotive refinish coating that contains an acetoacetate-functional polymer and an aldimine or ketimine. The acetoacetate-functional polymer is prepared by reacting an aromatic polyepoxide (bisphenol A or bisphenol F) with water, amine, or hydroxycarboxylic acid and then with acetoacetic acid to introduce the acetoacetate groups. The Brindoepke patent reports that its compositions harden rapidly and have shorter gelling time than does the composition with the acetoacetate-functional addition polymer. Aromatic epoxy-based resins, however, are sensitive to ultraviolet light and will chalk and lose gloss in outdoor exposure. Additionally, these are poor pigment dispersants. Finally, the Brindoepke patent compositions have undesirably high levels of volatile organic compounds.
Similarly to the Brindoepke patents, U.S. Pat. No. 5,288,802 to Walters et al. describes a curable refinish primer composition containing an amine-functional polyepoxide resin (which can be blocked to form a ketimine or aldimine), an acetoacetate-containing polyester, and a polyacrylate. The polyacrylate contains at least two acrylate groups. The Walters patent suggests that both the acetoacetate groups and the acrylate groups react with the ketimine-containing polyepoxide resin. The Walters patent composition, however, suffers from the same drawbacks as the Brindoepke patent compositions.
DE 196 20 351 A1 discloses a coating composition in which the acetoacetate functionality is on an unsaturated polyester and the coating composition contains, in addition, an acetoacetate-functional polyalcohol reactive diluent; a hardener selected from epoxide-amine adducts, polyfunctional amines, and ketimines; a radically or ionically polymerizable compound; and a photoinitiator.
It would be desirable to have a coating composition that offers high solids content along with being “dry to handle” a short time after application.
SUMMARY OF THE INVENTION
The ambient curing compositions of the invention contain an acetoacetate-functional compound having at least two acetoacetate groups and a molecular weight of up to about 1000; a blocked polyamine, particularly a polyketimine and/or polyaldimine; an alkyd; and pigment. The alkyd is not reactive toward the acetoacetate-functional compound or the blocked polyamine. The ambient curing compositions may be used for refinishing automotive vehicles, metal signs, and so on.
The compositions of the invention can be formulated with a low content of volatile organic solvents and provide coatings that are dry to the touch in a short time. A metal drier can be included in the composition to provide for further curing of the coating.
The invention also provides an intermix system that has a plurality of color bases and one or more clear components. The color bases each include the alkyd resin and at least one color and/or special effect pigment. One of the acetoacetate-functional compound and the blocked polyamine is in a clear component, and the other may be in the color bases or may be in a different clear component. In one embodiment, the intermix system has a plurality of color bases containing alkyd and pigment, a first clear component containing the acetoacetate-functional compound, and a second clear component containing blocked polyamine. If used, a drier can be included in the
Goan John C.
Thieben Lawrence E.
BASF Corporation
Short Patricia A.
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