| Emulsion polymer blend coating compositions and methods for increasing chalky substrate adhesion -> Monitor Keywords |
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Emulsion polymer blend coating compositions and methods for increasing chalky substrate adhesionRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Involving Inert Gas, Steam, Nitrogen Gas, Or Carbon Dioxide, Processes Of Preparing A Desired Or Intentional Composition Of At Least One Nonreactant Material And At Least One Solid Polymer Or Specified Intermediate Condensation Product, Or Product Thereof, Adding A Nrm To A Preformed Solid Polymer Or Preformed Specified Intermediate Condensation Product, Composition Thereof; Or Process Of Treating Or Composition Thereof, Containing Two Or More Solid Polymers; Solid Polymer Or Sicp And A Sicp, Spfi, Or An Ethylenic Reactant Or Product Thereof, At Least One Solid Polymer Derived From Ethylenic Reactants Only, Two Or More Solid Polymers Derived From Ethylenic Reactants Only,Emulsion polymer blend coating compositions and methods for increasing chalky substrate adhesion description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070219307, Emulsion polymer blend coating compositions and methods for increasing chalky substrate adhesion. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a coating composition containing a polymer blend dispersion including a first polymer having a relatively low molecular weight and a relatively low glass transition temperature, and a second polymer having a relatively high molecular weight and a relatively high glass transition temperature. The emulsion coating composition according to the invention can advantageously be used in paint compositions and architectural coating applications. BACKGROUND OF THE INVENTION [0002] Good adhesion properties, particularly to chalky substrates, are important to coatings such as paints and architectural coatings. One conventional method for improving the chalk adhesion properties of a coating composition is to add an alkyd resin to the conventional coating composition. However, alkyd resins produce premature yellowing, rendering the coatings undesirable in certain circumstances. [0003] Another method for improving the chalk adhesion properties is to synthesize a polymer blend in a sequential polymerization. Examples of acrylic-based polymer blends made by sequential polymerization processes can be found in U.S. Pat. Nos. 5,990,228 and 6,710,112 B1. [0004] The '228 patent discloses aqueous coating compositions containing at least two polymer components which supposedly provide adhesion and improved durability, as measured in dried coatings made from the aqueous compositions by improved gloss retention or dirt pickup resistance. Specifically, in Comparative Example 1 of the '228 patent, this patent discloses the use of a pre-polymerized latex core of 60 nm particulate poly(butyl acrylate-co-methyl methacrylate-co-methacrylic acid), upon which was further polymerized two layers of poly(butyl acrylate-co-methyl methacrylate-co-acrylic acid) of the same composition. The at least two polymer components are synthesized as core-shell polymers by a sequential polymerization process. [0005] The '112 patent discloses aqueous polymer dispersions having two polymer phases that have different glass transition temperatures but that are formed by a sequential polymerization process. In addition, the molecular weights of the two polymer phases are different, due to the addition at some point during the sequential polymerization of a chain transfer reagent. [0006] Other publications disclose alternatives to alkyd resin modification in coating compositions. [0007] For example, U.S. Patent Application Publication No. 2004/0161542 A1 and U.S. Pat. No. 6,630,533 both disclose compositions containing at least one fatty acid ester. In the '542 publication, the fatty acid ester is unsaturated. In the '533 patent, the fatty acid ester comprises a C.sub.12 to C.sub.40 alkyl(meth)acrylate. [0008] U.S. Pat. No. 5,376,704 discloses aqueous coating compositions containing a neutralized half-ester product of an acrylic polymer containing at least two reactive anhydride groups that is crosslinked with an epoxy crosslinker. The molecular weights of both these components are less than 100,000 Daltons. [0009] U.S. Patent Application Publication No. 2004/0010091 A1 discloses two component coating compositions that cure under ambient conditions. The coating composition of the '091 publication contains crosslinkable and crosslinking components, with both components having molecular weights under 100,000 Daltons. [0010] U.S. Patent Application Publication No. 2004/0010071 A1 discloses an aqueous polymer blend composition containing soft and hard polymer particles. The hard polymer particles have a glass transition temperature greater than 25.degree. C., while the soft polymer particles have a glass transition temperature less than or equal to 25.degree. C. In addition, the hard polymer particles constitute from 2-30 wt % of the composition, while the soft polymer particles constitute from 70-98 wt % of the composition. [0011] U.S. Patent Application Publication No. 2005/0009954 A1 discloses aqueous polymer compositions containing hard polymers and soft polymers, with at least the hard polymers include phosphorus-containing and/or polyacid-containing pendant groups. The hard polymers have a glass transition temperature of at least 20.degree. C., while the soft polymers have a glass transition temperature of from -20.degree. C. to 5.degree. C. In addition, the hard polymers constitute from 2-40 wt % of the composition, while the soft polymer particles constitute from 60-98 wt % of the composition. [0012] There remains a need for other varied alternatives to alkyd resins and sequentially polymerized polymer blends for improving adhesion. BRIEF SUMMARY OF THE INVENTION [0013] The present invention involves a latex composition comprising a polymer blend of a first polymer and a second polymer, wherein: (a) the first polymer is made from first constituent monomers, has a number average molecular weight less than about 100,000 Daltons, has a glass transition temperature from about -20.degree. C. to about 60.degree. C., and comprises an amount of a self-crosslinking monomer; (b) the second polymer is made from second constituent monomers, has a number average molecular weight greater than about 150,000 Daltons, and has a glass transition temperature from about -20.degree. C. to about 60.degree. C.; (c) the glass transition temperature of the second polymer is at least 10.degree. C. higher than the glass transition temperature of the first polymer; and (d) the relative proportion of the first polymer to the second polymer is from about 1:4 to 4:3 by weight. [0014] The present invention also describes coating compositions containing the latex composition according to the invention, as well as coatings made therefrom and coated substrates on which the coating compositions containing the latex composition according to the invention are disposed. DETAILED DESCRIPTION OF THE INVENTION [0015] One aspect of the present invention relates to a latex emulsion composition containing a polymer blend of: (i) a first polymer having a relatively low molecular weight and a relatively low glass transition temperature; and (ii) a second polymer having a relatively high molecular weight and a relatively high glass transition temperature. Advantageously, the first polymer is polymerized from constituent monomers that include a self-crosslinking monomer. [0016] As used herein, the phrase "relatively low molecular weight" means a number average molecular weight of less than about 100,000 Daltons. Also as used herein, the phrase "relatively high molecular weight" means a number average molecular weight of greater than about 100,000 Daltons, preferably greater than about 200,000 Daltons. [0017] One of the benefits of relatively low molecular weight chains in coating compositions containing the latex polymer blends according to the invention can be improved substrate adhesion, whereas one of the benefits of relatively high molecular weight chains in the latex polymer blends according to the invention can be increased physical/mechanical strength. Combining these benefits by creating a coating composition containing a polymer blend having both relatively high molecular weight and relatively low molecular weight polymer chains is therefore desirable. [0018] When conventional paint compositions containing relatively high molecular weight acrylic-based latexes are applied to chalky substrates, for example, they can tend to exhibit poor adhesion to the chalky surface. In some cases, alkyd resins are combined with these poorly-adhering acrylic-based latex-containing paint compositions to improve the wet and/or dry adhesion properties. Alkyd resins, however, may negatively affect certain qualities of the paint compositions, including, but not limited to, causing loss of gloss, causing yellowing, causing color fading, causing chalkiness, causing brittleness, hindering clean-up, decreasing emulsion stability (thus increasing the need for added surfactant), increasing sensitivity to water, and the like, and combinations thereof. [0019] Another method for improving adhesion of paint compositions applied on chalky substrates and for reducing or eliminating the need for incorporating alkyd resins with relatively high molecular weight acrylic-based latexes includes the formation of polymers containing multimodal molecular weight distributions. Multimodal molecular weight distributions in polymer blends are typically attained by sequentially polymerizing monomers and by using a molecular weight control agent, such as a chain transfer agent, at some point during the polymerization process. See, e.g., commonly-owned, co-pending U.S. patent application Ser. No. 11/323,621, filed Dec. 30, 2005, and entitled "Emulsion Polymers Having Multimodal Molecular Weight Distributions". Such sequential polymerization processes have been described as forming core-shell type polymers, such as those disclosed in U.S. Pat. Nos. 5,990,228 and 6,710,112 B1, for example. However, because of the nature of the sequential polymerization process, the different molecular weights are typically attained for identical polymers (i.e., containing the same constituent monomer feeds), or for polymers that have relatively similar constituent monomer feeds. [0020] It is believed that the use of polymer blend compositions according to the invention containing both low molecular weight and high molecular weight chains in paint compositions applied on chalky substrates can advantageously reduce or eliminate the need for incorporating alkyd resins with high molecular weight latex polymers, and can be an alternative to sequentially polymerized and/or core-shell type polymers with multimodal molecular weight distributions. Without being bound by theory, it is believed that the presence of the first polymer in the blend having the lower molecular weight can sufficiently improve the adhesion of paint compositions containing them to chalky substrates. Nevertheless, because uniformly lower molecular weight polymer particles can tend to compromise the physical and mechanical properties of the paint compositions and/or the surfaces of the chalky substrates coated therewith, it is also believed that a combination of low and high molecular weight polymers can simultaneously result in acceptable adhesion and acceptable physical/mechanical properties. Continue reading about Emulsion polymer blend coating compositions and methods for increasing chalky substrate adhesion... Full patent description for Emulsion polymer blend coating compositions and methods for increasing chalky substrate adhesion Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Emulsion polymer blend coating compositions and methods for increasing chalky substrate adhesion patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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