Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-12-06
2003-06-17
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S507000
Reexamination Certificate
active
06579928
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to aqueous crosslinkable primer coating compositions and particularly such primer compositions that combine aqueous polyurethane dispersions and aqueous acrylic dispersions. The present invention further relates to composite coating finishes having one or more primer layers and one or more topcoat layers.
BACKGROUND OF THE INVENTION
Coating finishes, particularly exterior coating finishes in the automotive industry, are generally applied in two or more distinct layers. One or more layers of primer coating composition may be applied to the unpainted substrate first, followed by one or more topcoat layers. Each of the layers supplies important properties toward the durability and appearance of the composite coating finish. The primer coating layers may serve a number of purposes. First, the primer coating may be applied in order to promote adhesion between the substrate and the coating. Secondly, the primer coating may be applied in order to improve physical properties of the coating system, such as corrosion resistance or impact strength, especially for improving resistance to gravel chipping. Third, the primer coating may be applied in order to improve the appearance of the coating by providing a smooth layer upon which the topcoat layers may be applied. The topcoat layer or layers contribute other properties, such as color, appearance, and light stabilization.
In the process of finishing the exterior of automobiles today, metal substrates are usually first coated with an electrocoat primer. While the electrocoat primer provides excellent surface adhesion and corrosion protection, it is often desirable to apply a second primer layer. The second primer layer provides additional properties not available from the electrocoat primer. Resistance to gravel chipping is one of the critical properties provided by the second primer layer. The second primer layer may also enhance the corrosion protection of the finish and provide a smoother surface than the electrocoat primer. The second primer also serves to provide a barrier layer between the electrocoat primer layer, which usually contains aromatic moieties and other materials that can cause yellowing on exposure to sunlight, and the topcoat.
Several references disclose generally a process in which one or more ethylenically unsaturated monomers are emulsion polymerized in the presence of a dispersed polyurethane resin. Examples are Guagliardo, U.S. Pat. No. 4,318,833, which teaches that a coating composition using a polyurethane/acrylic emulsion so prepared provides a coating with better gloss, with preference given to aliphatic diisocyanates for better color stability; Kaizerman et al., U.S. Pat. No. 4,198,330, which teaches that vinyl polymer-modified polyurethane dispersion provides improved strength to a coating, compared to the polyurethane dispersion alone; Swarup et al., U.S. Pat. No. 5,854,332, which teaches using a branched polyurethane polymer for improved metallic pigment orientation and for good adhesion following humidity exposure in a basecoat coating; and Natesh et al., U.S. Pat. No. 5,739,194, which teaches preparing the polyurethane polymer with a particular combination of polyisocyanates to provide good adhesion of a coating following humidity exposure in a basecoat coating. These patents are incorporated herein in their entirety by reference. These patents do not discuss primer compositions or compositions that would provide resistance to stone chipping and other important properties for primers.
Hatch et al., U.S. Pat. No. 5,817,735, incorporated herein by reference, discloses an aqueous primer composition for golf balls that includes a polyurethane dispersion and an acrylic dispersion. The primer has a very low content of volatile organic solvent, which is important for minimizing regulated emissions from the coating process. The Hatch patent, however, does not disclose a curable (thermosetting) composition and does not disclose preparing a dispersion in which the acrylic polymer is associated with the polyurethane polymer. More importantly, the golf ball primers of the Hatch patent do not provide the properties, such as resistance to stone chipping and corrosion protection, that are required of an automotive primer.
It would be desirable, therefore, to have a primer composition that provides improved resistance to stone chipping and other properties that are important for an automotive primer, which additionally can be formulated with a very low content of volatile organic solvent.
SUMMARY OF THE INVENTION
The present invention provides a thermosetting primer composition that includes a polyurethane polymer, an acrylic polymer that is polymerized in the presence of at least a part of the polyurethane polymer, and a crosslinking component that is reactive with at least one of the polyurethane polymer and the acrylic polymer. The polyurethane polymer has a glass transition temperature of 0° C. or less. The acrylic polymer has a glass transition temperature that is at least about 20° C. higher than the glass transition temperature of polyurethane resin. The polyurethane and acrylic polymers are preferably dispersed or emulsified in an aqueous medium. As used herein, “emulsion” or “dispersion” will each be used to refer both to dispersions and emulsions.
The invention further provides a composite coating having as a primer layer a cured layer of the primer composition of the invention and having at least one topcoat layer.
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane polymer of the invention has a glass transition temperature of about 0° C. or less, preferably about −20° C. or less, and more preferably about −30° C. or less. The glass transition temperature of the polyurethane of the invention is in the range of from about −80° C. to about 0° C., more preferably from about −65° C. to about −10° C., still more preferably from about −65° C. to about −30° C., and even still more preferably from about −60° C. to about −35° C.
The weight average molecular weight of the polyurethane is preferably from about 15,000 to about 60,000, more preferably from about 15,000 to about 60,000, and even more preferably from about 20,000 to about 35,000.
Polyurethanes are prepared by reaction of at least one polyisocyanate and at least one polyol. The reactants used to prepare the polyurethane are selected and apportioned to provide the desired glass transition temperature. Suitable polyisocyanates include, without limitation, aliphatic linear and cyclic polyisocyanates, preferably having up to 18 carbon atoms, and substituted and unsubstituted aromatic polyisocyanates. Illustrative examples include, without limitation, ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 1,4-butylene diisocyanate, lysine diisocyanate, 1,4-methylene bis(cyclohexyl isocyanate), isophorone diisocyanate, toluene diisocyanates (e.g., 2,4-toluene diisocyanate and 2,6-toluene diisocyanate) diphenylmethane 4,4′-diisocyanate, methylenebis-4,4′-isocyanatocyclohexane, 1,6-hexamethylene diisocyanate, p-phenylene diisocyanate, tetramethyl xylene diisocyanate, meta-xylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, and combinations of two or more of these. Biurets, allophonates, isocyanurates, carbodiimides, and other such modifications of these isocyanates can also be used as the polyisocyanates. In a preferred embodiment, the polyisocyanates include methylenebis-4,4′-isocyanatocyclohexane, 1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, and combinations thereof. It is particularly preferred to use at least one &agr;,&ohgr;-alkylene diisocyanate having four or more carbons, preferably 6 or more carbons, in the alkylene group. Combinations of two or more polyisocyanates in which one of the polyisocyanates is 1,6-hexamethylene diisocyanate are especially prefe
BASF Corporation
Budde Anna M.
Cain Edward J.
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