Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1995-03-03
2001-10-16
Reddick, Judy M. (Department: 1713)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C524S386000, C524S388000, C524S501000, C524S457000, C524S507000
Reexamination Certificate
active
06303189
ABSTRACT:
The present invention relates to a method for increasing the open time of an aqueous coating and aqueous coating compositions providing useful open time. Open time is the time that an aqueous coating remains workable after it has been applied to a substrate. Open time is important in aqueous coatings, such as latex paints, to permit rebrushing over a freshly coated wet surface without causing defects such as brush marks or lap lines in the final dried coating.
One method for improving the open time of an aqueous coating is disclosed in U.S. Pat. No. 5,270,380. This method involves the reactive interaction between a latex polymer and a modifying compound in which the latex polymer and modifying compound become chemically bound.
The reactive interaction disclosed in the '380 patent is a useful method for increasing the open time of an aqueous coating, however, the choice of a modifying compound is limited to only those compounds capable of reacting with the particular latex polymer in the coating composition. The problem is that a given modifying compound will only work with a limited number of polymer chemistries, and therefore many different modifying compounds are required to effect an open time improvement across the wide range of possible latex polymers used in different coating compositions.
The present invention provides an alternate method for improving the open time of an aqueous coating, wherein one modifying compound may be used universally with all latex polymer chemistries and in all coating compositions since no interaction is required between the modifying compound and latex polymer.
In a first aspect of the present invention, there is provided a method for extending the open time of an aqueous coating composition comprising:
a) forming an aqueous coating composition comprising at least one film-forming latex polymer,
b) admixing with said coating composition at least one aqueous-based polyurethane dispersion having a glass transition temperature less than the glass transition temperature of the latex polymer;
c) applying said aqueous coating composition to a substrate; and
d) drying said aqueous coating composition.
In a second aspect of the present invention, there is provided an aqueous coating composition having extended open time comprising at least one film-forming latex polymer and at least one aqueous-based polyurethane dispersion having a glass transition temperature less than the glass transition temperature of the film-forming latex polymer.
Film forming polymers useful in this invention are those capable of forming a continuous film upon drying. Film forming polymers are those with a glass transition temperature (Tg) below the drying temperature or, in the alternative, are polymers with a higher Tg used in conjunction with levels of volatile coalescents effective to provide a film formation temperature sufficiently below the drying temperature, thereby effecting the formation of a continuous film on a substrate. Preferably, the latex polymer contains at least one polymeric component with a glass transition temperature between −15° C. and +50° C. as measured by differential scanning calorimetry (DSC). Most preferably the Tg of the film-forming polymer is in the range of from +10° C. to +35° C.
The latex polymer useful in this invention can be a homopolymer, a copolymer or a mixtures of such polymers. The latex polymer is film-forming and may be a single film-forming polymer or a mixture of different polymer compositions, provided the mixture contains at least one film-forming latex polymer and that the aqueous composition formed from the mixture is film-forming.
The film-forming latex polymer of this invention is a substantially thermoplastic, or substantially uncrosslinked, polymer when it is applied to a substrate. Low levels of deliberate or adventitious crosslinking may be present. It is important, however, that the quality of the film formation not be materially impaired by this crosslinking.
The film-forming latex polymer may be formed from at least one ethylenically-unsaturated monomer such as, for example, alkyl acrylates and methacrylates wherein the alkyl group contains from one to eighteen carbon atoms; acrylamide or substituted acrylamides; styrene or substituted styrenes; butadiene; vinyl acetate or other vinyl esters; vinyl monomers such as vinyl chloride, vinylidene chloride, N-vinyl pyrrolidone; acrylonitrile or methacrylonitrile and ethylene. Low levels of copolymerizable ethylenically-unsaturated acid monomers, in the range of 0.1% to 10% may also be used. Preferred monomers for use in this invention include methyl methacrylate, butyl acrylate, styrene, acrylonitrile, butyl methacrylate and methacrylic acid.
The latex polymers may be made by conventional polymerization techniques well known in the art. A preferred method of making the latex polymer is by conventional emulsion polymerization. The latex polymers useful in the present invention are not limited to any particular particle size, molecular weight, chemistry or physical shape.
While the particle size is not critical, a preferred particle size of the latex polymer is in the range from 50 nanometers to 300 nanometers in diameter. The morphology of the particles is not critical. The particles may be a single phase or be composed of two or more phases such as, for example, core/shell particles, core/shell particles with shell phases incompletely encapsulating the core, core/shell particles with a multiplicity of cores and interpenetrating networks of particles.
Polyurethane dispersions useful in the present invention are aqueous-based. “Aqueous-based” means that in the final form, regardless of the method of synthesis, the polyurethane particles are distributed as the dispersed phase in water and that water serves as the continuous medium. The polyurethane dispersion (PUD) is non-reactive with the polymer latex. The glass transition temperature of the polyurethane particles are in the range of from −50° C. to +10°C. , preferably in the range of from −50° C. to −10° C., as measured by differential scanning calorimetry. A critical element of the present invention is that the Tg of the polyurethane polymer must be less than the Tg the latex polymer.
Polyurethane dispersions useful in this invention have particle sizes in the range of from 10 nanometers to 100 nanometers. A preferred particle size is about 30 nanometers. A polyurethane dispersion found to be preferably useful in this invention is Sancure® 815 (BFGoodrich) having a particle size of 30 nanometers and a glass transition temperature of −40° C.
The polyurethane dispersion is present in the aqueous coating composition at from 10% to 50% by weight based on solids of the polyurethane to the total polymer solids. Preferably the polyurethane dispersion is present at about 20% by weight solids based on total polymer solids.
The aqueous coating composition may contain one or more water-soluble coalescents to aid in film formation. The coalescents may be separately added or may be present as a result of coalescent use in the manufacture of a component in the coating composition such as, for example, the polyurethane dispersion. Preferable water-soluble coalescents include, for example, alkylene glycols in the range of from 0% to 40%, by weight based on the weight of the dry latex polymer. Alkylene glycols include, for example, ethylene glycol, propylene glycol and mixtures thereof.
Aqueous coating composition is free from water-insoluble coalescents. “Water-insoluble coalescents” as used herein are defined as organic compounds having a boiling point at atmospheric pressure of less than about 250° C. and a water solubility in the range from 0.1% to 10%, by weight in water at 25° C. Water-insoluble coalescents include, for example, 2,2,4-trimethylpentane-1,3-diol monoisobutyrate (Texanol®, Eastman Chemical).
The aqueous coating composition is prepared by conventional paint making techniques which are well known in the coatings art. First, the pigment and other adjuvants are wel
Gray Richard Thomas
Lee Jungsik
Bakule Ronald D.
Reddick Judy M.
Rohm and Haas Company
LandOfFree
Method for increasing the open time of aqueous coatings does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for increasing the open time of aqueous coatings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for increasing the open time of aqueous coatings will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2600111