Weatherable coating and stain system for thermoset or thermoplastic composite surfaces

#The present invention pertains to weatherable coating systems suitable for application to thermoset or thermoplastic composite surfaces having minimal surface porosity. More particularly, the present invention pertains to a topcoat, and to a stain and topcoat system which can be easily applied by the consumer to produce an aesthetic, weatherable surface, particularly on exterior doors and door entry components.

#Conventional finishing methods for exterior doors and door system components, where a traditional finely finished wood grain appearance is desired, have involved staining a bare wood surface with dye and/or pigment-bearing stains followed by application of one or more coats of exterior varnish. A seal coat is sometimes applied prior to the stain and topcoat to seal the pores of the wood and to promote a more adherent and uniform stain and topcoat. The stain is virtually always solvent borne, as water based stains have the effect of raising the grain, thus requiring an intermediate sanding step which is labor and time intensive. In addition to the solvent contained in the stain, stains contain drying oils as carriers, for example heat-bodied linseed oil. Generally, several different oils are provided to promote penetration of the stain into the wood surface.

#After the stain has dried, one or more transparent topcoats are applied. Traditional topcoats are varnishes containing dissolved resins such as copal, often in conjunction with a drying oil. More recently, chemically modified natural resins and synthetic polymers have replaced all or part of natural resins, especially for outdoor use. In addition, to provide superior weatherability, ultraviolet absorbers have been added. Despite the advances made in such finishes, varnishes still generally require light sanding or abrading with steel wool or the like between coats, or necessitate the addition of the second coat prior to the full drying of the previous coat. Otherwise, delamination between varnish coats may occur. Sanding and similar treatments are time consuming, and judging the proper time to apply a second coat onto a not fully-cured prior coat requires some skill and experience. Despite these drawbacks, stain/varnish systems continue to be used on exterior door systems.

#A preferred inventive topcoat formulation is as follows:

#A mill base is prepared in a small container in a high shear mixer set at 2000 rpm using a high speed dispersant blade such as a Cowles blade. Add 750 g of about 20 nm particle size translucent rutile titanium dioxide such a TITAN® L181; and 750 g of passivating coating, such as 5 weight percent calcium mixed neopentyl C9-C13 fatty acid carboxylate, preferably OM GROUP® 5 percent Calcium Hydro-Cem in approximately 8 L of clean water. The mixture is sheared for 30 minutes. After shearing, a flatting agent such as LOVEL® 27 is added, the quantity of which is dependent on the finish desired: flat, satin, semi-gloss, or glossy. Other adjuvants include Theological aids, such as synthetic clays for consistency, preferably 800 g of LAPONITE® clay; surfactants such as 1625 g of BYK® 024 defoamer, and/or 425 g of BYK® 181; and anti-marring waxes such as SHAMROCK® S-381, the amount which is determined by the product performance requirement, preferably 650 g.

#The mill base is transferred to a larger tank and the remaining non-polysiloxane materials are blended in under high shear conditions. Approximate additions are as follows: 160 kg of non-siloxane film-forming polymer latexes, such as urethane-acrylic hybrid polymer resin latex FLEXTHANE® 620; surfactants such as 1.1 kg of BYK® 321, and 2.8 kg of BYK® 346; hindered amine stabilized ultraviolet light stabilizers such as 725 g of TINUVIN® 292; anti-fungal and anti-microbial adjuvants such as 500 g of POLYPHASE® P-20-T and 380 g of PROXEL® GXL; as well as 1.4 kg co-solvent such as tridecyl alcohol.