Coating processes – Coating pavement or the earth – Striping – marking – or increasing reflectivity
Reexamination Certificate
2000-11-27
2003-11-11
Beck, Shrive P. (Department: 1762)
Coating processes
Coating pavement or the earth
Striping, marking, or increasing reflectivity
C427S136000, C427S202000, C427S203000, C427S385500, C427S393600, C427S407100
Reexamination Certificate
active
06645552
ABSTRACT:
This invention relates to a method of improving the drying time of a thick, aqueous coating. More particularly, this invention relates to a method of improving the drying time of a thick, aqueous coating containing a quick-setting binder by applying the coating as at least two separate layers.
Coatings may be applied as a thick layer (i.e., a wet thickness of at least 0.4 mm) to improve durability and to improve certain properties including sound dampening, insulating, and hiding and protecting the underlying substrate. Typically, applications where thick coatings may be needed include roof coatings and road-marking or traffic paints. One of the drawbacks of applying a thick coating is that the drying time is too long. This is particularly problematic for exterior coating applications where temperature and humidity are variable and the weather is unpredictable. Further exacerbating this problem is the need in such applications as road-marking paints to permit traffic to pass over the freshly-painted marking in as short a period of time as practicable.
The coating industry is replete with chemistries and methods for accelerating the drying time of products used in such exterior, thick coatings. A number of products utilize solvent-based fast-drying coatings. Low-boiling volatile organic solvents evaporate rapidly after application of the coating on the road to provide the desired fast drying characteristics of a freshly applied road marking. However, in addition to releasing volatile organic solvents into the environment, this type of paint formulation tends to expose the workers to the vapors of the organic solvents. Because of these shortcomings and increasingly stringent environmental mandates from governments and communities, it is highly desirable to develop more environmentally-friendly coatings while retaining fast drying properties and/or characteristics.
Much effort has been directed to developing aqueous or waterborne coating systems. Primarily due to a combination of high boiling point, high latent heat of vaporization, high polarity, and strong hydrogen bonding of water, drying times of waterborne coatings are generally longer than those exhibited by the organic solvent-based coatings. The drying time strongly depends on the relative humidity of the atmosphere in which the coatings are applied. An aqueous paint may take several hours or more to dry in high humidity. The problem of retarded drying rate is especially aggravated for more thickly applied traffic paint. Long drying times severely limit the desirability of using aqueous paints, particularly traffic paints and road marking paints because of longer traffic disruptions.
In an attempt to produce aqueous coatings with shorter drying times, i.e., fast or quick drying or setting coatings, methods utilizing salt, or acid, or combinations thereof to induce coagulation have been devised, as have pH sensitive binder systems. Such coatings include those disclosed in the following published patent applications and granted patents:
(a) EP-A-0,066,108 discloses an aqueous road marking composition in which the binder is a mixture of a pure acrylic resin, a carboxylated styrene/dibutyl fumarate copolymer and a polymeric, polyfunctional amine such as polypropylene imine.
(b) EP-B-0,322,188 discloses aqueous coating compositions containing film forming latex polymer, weak base-functional synthetic latex polymer and volatile base.
(c) EP-B-0,409,459 discloses an aqueous coating composition including an anionically stabilized emulsion polymer having Tg no lower than 0° C., a polyamine functional polymer, and a volatile base in an amount such that the composition has a pH where substantially all of the polyamine functional polymer is in a non-ionic state, and wherein more than 50% by weight of the polyamine functional polymer will be soluble at pH values of 5 to 7 on evaporation of the volatile base. In the non-ionic state (i.e., deprotonated), polyamine interaction with the anionically stabilized emulsion and any other anionic ingredients which may be present in the composition is eliminated. The volatile base must be volatile enough to be released under air drying conditions. In the absence of the volatile base, the protonated amine moieties interact with the anionic ingredients to destabilize the coating composition.
(d) U.S. Pat. No. 5,804,627 discloses methods of producing fast drying coatings on exterior surfaces that include applying on those surfaces an aqueous composition including an anionically stabilized emulsion polymer having a Tg greater than about 0° C., a polyamine functional polymer having from about 20% to about 100% of the monomer units by weight containing an amine group, and an amount of volatile base sufficient to raise the pH of the composition to a point where essentially all of the polyamine functional polymer is in a non-ionic state, and evaporating the volatile base to produce the coating.
(e) U.S. Pat. No. 5, 922,398 discloses waterborne coating compositions containing latex particles having pendant amine-functional groups. The latex particles have Tg greater than about 0° C. and are capable of film formation at application temperatures. An amount of base (e.g., ammonia) is added to raise the pH of the composition to a point where essentially all of the amine functional groups are in a non-ionic state. Upon formation of a film, the base evaporates, allowing the pendant amine moieties to become protonated. The resultant pendant ammonium moieties then interact with anionic surfactants to destabilize the aqueous system and, thereby, speed drying.
(f) U.S. Pat. No. 5,824,734 discloses a waterborne coating composition including an amine functional latex polymer having 0.1 to 5% by weight, based on solid weight of polymer, of a secondary or tertiary amino acrylate, a crosslinking monomer, and less than 5% by weight of hydrophilic monomers. The composition also includes mineral pigments. The amine functional latex polymer is prepared at pH of at least 7. Following polymerization, the pH is adjusted upward, preferably to between 8 and 9.5, to maintain the stability of the system. Upon reducing the pH, the stability of the dispersion of polymer particles and mineral pigment particles is decreased, leading to precipitation of the polymer and mineral particles and drying.
(g) U.S. Pat. No. 5,947,632 discloses waterborne coating compositions including a number of general categories of materials including talc, hollow sphere polymer, a solid polymer (e.g., ion exchange resin beads in acid, sodium or potassium form) and inorganic compounds (e.g., inorganic superabsorbent gel, Sumica gel). These materials share the characteristic that they speed the drying of coatings when applied either in the same first step with the waterborne binder, or in a subsequent step.
There is, however, a continuing need for improved methods, particularly those at minimal expense which accelerate the drying time of thick, exterior, aqueous coatings.
Statement of the Invention
This invention is directed to a method of improving the drying time of a coating, including the steps of:
(a) preparing an aqueous coating formulation containing a quick setting binder;
(b) applying a first portion of the coating formulation to a substrate to form a first wet coating;
(c) applying at least one second portion of the coating formulation to the first wet coating before the first wet coating has dried to form at least one second wet coating; and
(d) permitting the first wet coating and the at least one second coating to dry;
wherein the total thickness of the first wet coating and the at least one second coating is 0.4 mm to 5.0 mm, preferably 0.5 mm to 2.5 mm and most preferably 0.6 mm to 1.5 mm.
In one embodiment of the invention, the method employs a first portion at a level of 25% to 75% by weight, based on the weight of the total coating formulation.
In another embodiment of the invention, the method employs at least one second portion that is a single application and is 25% to 75% by weight, based on the weight of the total coating formulation.
Schall Donald Craig
Sobczak Jeffrey Joseph
Beck Shrive P.
Jolley Kirsten Crockford
Rohm and Haas Company
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