Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-05-01
2004-11-09
Reddick, Judy M. (Department: 1713)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S331000, C427S372200, C427S393500, C427S393600, C523S135000
Reexamination Certificate
active
06815010
ABSTRACT:
The present invention relates to improved elastomeric, exterior coating compositions, more specifically, elastomeric, exterior coating compositions having improved long term solar reflectance.
There is a growing awareness and concern over the “urban heat island” effect that is being created in cities. One of the major contributors to this effect is black roofs which strongly absorb solar energy from the sun. By putting a white coating on a roof, it is possible to significantly reduce the temperature of the roof and to greatly reduce the cooling requirements of the building. Obviously, the better the solar reflectivity and the longer the reflective life of the roof, the greater the benefit to the owner of the building and the community.
Many roofs are made of asphalt-based or rubber-based materials and these materials degrade with time (i.e. chalk, embrittle, etc.). By decreasing the amount of solar energy that is absorbed and the temperature of the roof, it is possible to slow the degradation rate and thereby extend the life of the roof.
By using a highly reflective roof coating, it is possible for architects and contractors to reduce the amount of insulation required under the roof of the building. This could represent a substantial cost savings and has already been incorporated into the Georgia Building Code. However, the solar reflectivity of conventional roof coating compositions degrades over time and the benefits of an initially high solar reflectivity are diminished.
U.S. Pat. No. 5,688,853 discloses water-borne soil-resistant coatings. In particular, there is provided an aqueous coating composition comprising a blend of a low Tg aqueous polymeric dispersion and a high Tg aqueous polymeric dispersion characterized in that: the PVC of the coating composition as measured by opacity is less than the critical PVC, the polymeric dispersion with a low Tg has a Tg of less than 0° C., the polymeric dispersion with a high Tg is not film forming and has a Tg of at least 35° C. and the volume ratio of low Tg polymer dispersion to high Tg polymer dispersion is from 0.4:1 to 1.4:1. As noted at col. 6, lines 50-64: “The relative proportion of the low and high Tg dispersions is most important to the working of the present invention and we require that the volume ratio of low Tg polymeric dispersion to high Tg polymeric dispersion to be from 0.4:1 to 1.4:1. This is of course calculated on a non-volatile basis. In practice there is usually little difference between the weight and volume ratios. If the particles are based on the same monomers it is convenient to use the weight ratios as the densities of the particles are essentially the same. At ratios above the 1.4:1 upper limit the soil resistance of paint films becomes unacceptably poor. As is demonstrated in later comparative examples soil resistance at a ratio of 1.5:1 is very poor. At ratios below 0.4:1 film properties such as ability to coalesce satisfactorily at low temperatures is adversely affected.”
U.S. Pat. No. 5,731,377 discloses a polymer blend of at least two emulsion polymers useful as a binder in an aqueous coating composition containing no coalescent, where the polymer blend comprises from about 20 to about 60 weight percent of a hard emulsion polymer, having a glass transition temperature (Tg) greater than about room temperature, and from about 80 to about 40 weight percent of a soft emulsion polymer, having a glass transition temperature (Tg) less than about 15° C. The polymer blend is particularly useful in preparing an aqueous coating composition which can be applied at low temperatures while providing good block resistance, as for example in the preparation of interior semi-gloss paints. As noted at col.4, line 66, to col. 5, line 14: “The soft polymer must have a Tg such that the polymer will form a film when applied to a substrate. The soft polymer should have a Tg as low as about minus 20 degrees Centigrade to about room temperature, about plus 20 degrees Centigrade. Preferably the soft polymer should have Tg in the range of from about minus 5 degrees Centigrade to about plus 10 degrees Centigrade, and most preferably from about 0 degrees Centigrade to about plus 5 degrees Centigrade. The hard polymer is required to be present in the blend to provide the film with the desired physical properties, such as for example hardness and block resistance. The Tg of the hard polymer should be greater than room temperature, preferably greater than about 25 degrees Centigrade, and most preferably in the range of from about 25 to about 65 degrees Centigrade.”
U.S. Pat. No. 5,990,228 discloses aqueous coating compositions containing at least two polymer components which provide adhesion and improved durability as measured by improved gloss retention or dirt pick up resistance in dried coatings made from the coating compositions. In particular, the aqueous coating compositions comprise an emulsion polymer prepared from at least one ethylenically unsaturated monomer, provided that the monomer is not an alkene or a diene, the emulsion polymer having: from 40% to 90% by weight of a first polymer having a Tg of from 0° C. to 60° C.; and from 10% to 60% by weight of a second polymer having a Tg of from 10° C. to 100° C., provided that the Tg of the second polymer is at least 10° C. higher than the Tg of the first polymer, and provided that the first polymer is higher in molecular weight than the second polymer, such that when both polymers are combined, from 5% to 40% by weight of the total polymer has a molecular weight greater than 225,000 and greater than 30% by weight of the total polymer has a molecular weight below 52,000.
U.S. Pat. No. 6,020,416 discloses aqueous blends of colloidally dispersed polymers for use in making organic coatings which are hard and ductile at ambient temperature, and which remain stiff and elastic at temperatures well above their film-formation or drying temperature. In particular, there are disclosed blends of high-molecular-weight, thermoplastic polymers which are capable of developing these mechanical properties without conventional amounts of volatile organic coalescing aids and without the need for chemical cure. More particularly, there is disclosed an aqueous dispersion comprising a blend of polymer components each in the form of colloidal particles having average hydrodynamic diameters less than about 1000 nm and preferably less than about 200 nm, the polymer components comprising: a first polymer component comprising about 20% to about 50% by volume of the total polymeric content and exhibiting a measured Tg of greater than or equal to 49° C.; a second polymer component comprising about 20% to about 50% by volume of the total polymeric content and exhibiting a measured Tg less than 49° C. and greater than 24° C.; and a third polymer component comprising 0% to about 35% by volume of the total polymeric content and exhibiting a measured Tg less than 24° C.; the sum of all three polymers being 100% by volume; wherein the first, second and third polymer components each have a molecular weight greater than about 80,000 Daltons and are mutually adherent; and wherein the aqueous dispersion has a volatile organic content of less than about 20% by weight of the total polymeric content.
European Published Patent Application No. 0 761 778 A1 discloses a method for providing gloss control in a dried film from an aqueous coating. A specified level of gloss is affected by the addition of hard latex polymer particles to soft film-forming polymer latex particles. By adjusting the hard particle parameters of amount and relative particle size, the desired film gloss can be achieved. Moreover, there is disclosed an aqueous coating composition comprising hard polymer particles and soft polymer particles, where the hard and soft polymer particles are in the range of from 30 nm to 1,000 nm in size; wherein the hard particles are present in an amount of from 1% to 60% by weight of polymer solids, are non-film-forming and have a Tg of from 35° C. to 160° C.; and wherein the soft particles are present in an amount
Elfring William Henry
Winey Donald Alfred
Reddick Judy M.
Rohm and Naas Company
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