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
2000-02-03
2001-10-23
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...
C524S502000, C524S513000, C524S514000
Reexamination Certificate
active
06306952
ABSTRACT:
FIELD OF INVENTION
This invention is concerned with coating compositions having a low VOC content and which are quick to dry but easy to apply, their preparation and use.
BACKGROUND OF THE INVENTION
It has long been desired to reduce both the drying time of coating compositions, especially for use as traffic paints, and, for environmental reasons, the content of volatile organic components (VOC) in them (The permissible amount of VOC that can be released in the air in the United States from traffic paints is expected to drop to less than 150 grams of VOC per liter of paint). However these two attributes are in conflict because replacing VOC with water generally increases drying time, especially under ambient high humid conditions, which typically vary in the range of from 65 percent to 90 percent.
Improving the drying speed of aqueous compositions has been attempted, e.g. in EP-A 7210003, by adopting a two-stage approach wherein a layer of aqueous polymer is first applied, followed immediately by the application of thickener to accelerate its drying. However this approach is cumbersome and the two-stage, twin pack approach it demands fails to meet the third desirable attribute of coating compositions, namely that they be easy to apply.
This invention addresses the problem of reducing the VOC content of coating compositions which remain quick to dry and easy to apply in a single step by conventional single stage application means, such as air-atomized spray, airless spray, air-assisted airless spray, and high volume low pressure spray.
STATEMENT OF THE INVENTION
The present invention is directed to a method of coating a substrate comprising:
applying under ambient conditions on the surface of said substrate a layer of a single pack fast dry paint containing a low VOC waterborne coating composition, said composition comprising a latex binder, an associative thickener and a water soluble organic volatile solvent, wherein the amounts said associative thickener and said solvent are such that said paint has an in-can viscosity under ambient conditions in the range of from 1,000 cps to 6,000 cps and a set-to-touch dry time rating under ASTM D-1640 of less than 10 minutes; and
evaporating said solvent from said layer to form said coating on said substrate.
The present invention is also directed to a method of improving drying time of a traffic marking on a road or pavement surface comprising:
applying said surface a layer of a single pack traffic paint containing a low VOC waterborne coating composition comprising a latex binder, an associative thickener in the range of from 0.01 percent to 10 percent, and a water soluble organic volatile solvent in the range of from 0.2 percent to 10 percent, all in volume percentages based on the total volume of the composition, wherein said traffic paint has an in-can viscosity under ambient conditions in the range of from 1,000 cps to 6,000 cps and a set-to-touch dry time rating under ASTM D-1640 of less than 10 minutes;
evaporating said solvent from said layer to form said traffic marking on said substrate.
The present invention is further directed to a fast dry low VOC single pack waterborne coating composition comprising:
a latex binder;
an associative thickener in the range of from 0.01 percent to 10 percent; and
a water soluble organic volatile solvent in the range of from 0.2 percent to 10 percent, all in volume percentages based on the total volume of the composition, wherein a traffic paint containing said composition has an in-can viscosity under ambient conditions in the range of from 1,000 cps to 6,000 cps and a set-to-touch dry time rating under ASTM D-1640 of less than 10 minutes.
One of the advantage of the present invention is that it provides a composition with sufficiently low in-can viscosity, so that a paint prepared therefrom can be easily sprayed by conventional single head traffic paint application devices.
Yet another advantage is that a layer of a paint containing the composition of the present invention dries at a faster rate than a layer conventional waterborne paints even under high humidity conditions.
DETAILED DESCRIPTION OF THE INVENTION
As used herein:
“GPC weight average molecular weight” means the molecular weight of a polymer determined by gel permeation chromatography (GPC), using a differential refractometer as a detector. A set of 3 GPC columns packed with styrene/divinyl benzene beads having pore sizes in the range 100 to 10,000 angstroms, are typically used during the analysis. Generally the solvent used is tetrahydrofuran (THF), flowing at a rate of 1.0 ml/min. through the GPC columns. The temperature of the columns is usually maintained at 40° C.
The instrument, such as the one supplied by Polymer Laboratories, Amherst, Mass. and American Polymer Standards Co., Mentor, Oh. is first calibrated for molecular weight using narrow distribution polystyrene or a polymethacrylate standards. The weight average molecular weight of the sample is then determined by using the following equation:
Weight average molecular weight (Mw)=&Sgr;(R×M)/&Sgr;H
where R is the detector response measured above baseline at a given time and M is the molecular weight at that time, as determined from the calibration logarithm. The summation is made for the elution time at peak start to the elution time at peak end. This summation is the number reported as the weight average molecular weight. Further details of gel permeation chromatography (GPC) are found at page 4, Chapter I of The Characterization of Polymers published by Rohm and Haas Company, Philadelphia, Pa. in 1976.
“Glass transition temperature (Tg)” is a narrow range of temperature, as measured by conventional differential scanning calorimetry (DSC), during which amorphous polymers change from relatively hard brittle glasses to relatively soft viscous rubbers. To measure the Tg by this method, the copolymer samples were dried, preheated to 120° C., rapidly cooled to −100° C., and then heated to 150° C. at a rate of 20° C./minute while data was being collected. The Tg was measured at the midpoint of the inflection using the half-height method.
“Latex binder” means “Dispersed polymer”, “Solubilized polymer” (both defined below), or a mixture thereof.
“Dispersed polymer” means particles of polymer, which are colloidally dispersed and stabilized in an aqueous medium.
“Solubilized polymer” includes “Water soluble polymer”, “Water reducible polymer” or a mixture thereof Water soluble polymer means a polymer dissolved in an aqueous medium. Water reducible polymer means a polymer dissolved in water and water miscible solvent. Solubilized polymer results in a polymer solution characterized by having the self-crowding constant (K) of the Money equation [1/ln
hrel
=1/BC−K/2.5] equal to zero. By contrast, dispersed polymer has (K) equal to 1.9. The details of Money equation are disclosed in an article entitled “Physical Characterization of Water Dispersed and Soluble Acrylic Polymers” by Brendley et al., in “Nonpolluting Coatings and Coating Processes” published by Plenum Press, 1973 and edited by Gordon and Prane.
“Polymer particle size” means the diameter of the polymer particles measured by using a Brookhaven Model BI-90 Particle Sizer supplied by Brookhaven Instruments Corporation, Holtsville, NY., which employs a quasi-elastic light scattering technique to measure the size of the polymer particles. The intensity of the scattering is a function of particle size. The diameter based on an intensity weighted average is used. This technique is described in Chapter 3, pages 48-61, entitled Uses and Abuses of Photon Correlation Spectroscopy in Particle Sizing by Weiner et al. in 1987 edition of American Chemical Society Symposium series.
“Polymer solids” means polymer in its dry state.
“(meth)acrylate” includes acrylate and methacrylate.
“In-can viscosity” is the viscosity of a paint at the moment of application, such as at the time of spraying of the paint on the surface of a substrate.
Normally, the presence of an associative thickener in a coating
Cain Edward J.
Rohm and Haas Company
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