The asphalt emulsions useful as components in the tiecoat of this invention are dispersions of asphalt in water. These asphalt emulsions may also contain emulsifiers and stabilizers, such as for example soap or surfactant, which are anionic, cationic or nonionic. A useful asphalt emulsion, for example, is SS-1 h grade asphalt, an anionically-stabilized asphalt emulsion. The asphalt emulsions contain from about 35% solids to about 75% solids, more preferably from about 55% solids to about 65% solids and most preferably about 60% solids. Asphalt emulsions with less than about 35% solids have been found to be detrimental to tack, lower the viscosity below a usable level and unduly prolong the application of the tiecoat. Asphalt emulsions with greater that about 75% solids have been found to be detrimental to stability and increase the viscosity above a usable level. The asphalt emulsions have hardness from about 20 pen hardness to about 100 pen hardness and more preferably from about 20 pen hardness to about 40 pen hardness. Pen hardness values greater than about 100 are too soft for man roofing applications and contribute significantly to surface tack.
The latices used in the tiecoat of this invention may be formed from any monomer or mixture of monomers which yields a water-insoluble latex polymer with a glass transition temperature of less than about 10° C. in the dried state. For example, acrylic ester monomers, including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, ethyl methacrylate, isodecyl methacrylate, butyl methacrylate; acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, styrene, substituted styrenes, butadiene, acrylonitrile, ethylene, vinyl acetate, and the like may be used. It is required that the glass transition temperature of resultant latex be less than about 10° C. so that the tiecoat composition, formed by admixture with the asphalt emulsion, is flexible enough to withstand the requirements of the mastic coating system which may experience exterior temperature extremes and concommitant substrate expansion and contraction. Some of the monomers may only be used with other monomers in a mixture because they alone would not give rise to a homopolymer whose glass transition temperature is less than about 10° C., such as for example methyl methacrylate, a monomer whose homopolymer has a Tg of 105° C.
Usage of mastic asphalt
In addition, conventional coating components such as, for example, pigments, dispersants, surfactants, coalescents, wetting agents, rheology modifiers, thickeners, drying retarders, biocides, antifoaming agents, colorants, waxes, and the like may be used in the latex of the tiecoat of this invention.
The latex polymer is incorporated into the asphalt emulsion at a level of from about 5% latex solids/95% asphalt emulsion solids to about 85% latex solids/15% asphalt emulsion solids, based on the % total solids of the admixture, more preferably from about 15% latex solids/85% asphalt emulsion solids to about 85% latex solids/15% asphalt emulsion solids and most preferably from about 15% latex solids/85% asphalt emulsion solids to about 50% latex solids/50% asphalt emulsion solids.
The overall level of solids in the tiecoat is from about 10% by weight to about 75% by weight of the weight of the tiecoat. We have found that if the total weight % solids is less than about 10% it is detrimental to tack, lowers the viscosity of the tiecoat below a usable level and unduly prolongs the application of the tiecoat. Total weight % solids greater than about 75% have been found to be detrimental to the stability of the tiecoat and increase the viscosity of the tiecoat above a usable level. The level of solids in the tiecoat is more preferably from about 40% by weight to about 60% by weight, based on the total weight %.
Applications of the tiecoat may be made to various substrates, such as for example asphalt-containing substrates, bitumen-containing substrates or modified bitumen, cement/asbestos shingles or roofing panels, urethane foam roofing panels, deteriorated concrete, and the like. The tiecoat may be applied by conventional techniques, such as for example by brush, roller, airless spray, and the like.
A tiecoat is applied to a substrate, such as for example a bituminous surface prone to releasing colored bodies which would otherwise migrate into and discolor a mastic topcoat if it were directly applied to the substrate or if it were applied to an non-latex modified asphalt emulsion tiecoat. The application of the tiecoat is an additional step in the application of the overall mastic coating system. It is essential that the tiecoat rapidly become low in tack so that the subsequent mastic topcoat can promptly be applied by operators walking on the tiecoat such that the overall application process is not unduly prolonged.