Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
1998-11-18
2001-05-29
Wu, David W. (Department: 1713)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S316000, C524S047000, C524S052000, C524S056000, C524S058000
Reexamination Certificate
active
06238470
ABSTRACT:
This invention relates to an aqueous coating composition having improved block resistance. More particularly, this invention relates to an aqueous coating composition including an emulsion polymer, a nonionic or anionic surfactant, the surfactant having an HLB value less than 11.6 or greater than 14.6, and an alkyl polyglycoside. And the invention relates to a method for improving the block resistance of a dried aqueous coating composition by forming an aqueous coating composition including an emulsion polymer, a nonionic or anionic surfactant, the surfactant having an HLB value less than 11.6 or greater than 14.6, and an alkyl polyglycoside; applying the aqueous coating composition to a substrate; and drying, or allowing to dry, the aqueous coating composition.
The present invention serves to provide a dried, or partially dried, coating which has improved resistance to blocking, i.e., resistance to adhering or sticking to a like-coated surface, when partially or fully dried. Coatings frequently come in contact with like coatings in painted window frames or door jambs where it is desired that the coatings do not fuse together even under adverse conditions of elevated temperature, pressure, or humidity even to the extent of resisting separation or marring the surfaces of one or both coatings on separation.
U.S. Pat. No. 4,657,999 discloses the use of alkyl polyglycosides of C8-C22 alkanols and reducing sugars, in which one sugar chain containing on average from 1 to 10 sugar residues attached to one another by glycoside bonds is present for every alkyl group, as sole emulsifiers or as co-emulsifiers with other surfactants in the emulsion polymerization of ethylenically unsaturated monomers. The use of these emulsion polymers in coatings was not disclosed nor is there any recognition of the criticality of the HLB value of the co-surfactant on the block resistance of a dried coating derived therefrom.
U.S. Pat. No. 5,340,394 discloses a aqueous dispersed pigmented tinting concentrate useful for tinting aqueous latex paints which contains at least about 2% by weight non-ionic alkyl polyglycoside surfactant based on the total weight of pigment in the tinting composition, a polyethylene glycol polyether vehicle having a number average molecular weight between about 200 and 700, and, optionally, other cosurfactants such as nonionic surfactants or amphoteric surfactants. There is no recognition of the criticality of the HLB value of the cosurfactant on the block resistance of a dried coating derived therefrom.
The problem faced by the inventors is the provision of a suitable composition and a method for improving the block resistance of a coating so that surfaces bearing the composition would exhibit a lessened tendency to block than a surface containing the same emulsion polymer absent the alkylpolyglycoside and the selected surfactant components of the composition of this invention. We have now found that that certain surfactants having an HLB range outside that reported for the alkyl polyglycosides when used in conjunction with alkylpolyglycosides are benefical to improved block resistance
In a first aspect of the present invention there is provided an aqueous coating composition having improved block resistance including an emulsion polymer, a nonionic or anionic surfactant, the surfactant having an HLB value less than 11.6 or greater than 14.6, and an alkyl polyglycoside.
In a second aspect of the present invention there is provided a method for improving the block resistance of a dried aqueous coating composition by forming an aqueous coating composition including an emulsion polymer, a nonionic or anionic surfactant, the surfactant having an HLB value less than 11.6 or greater than 14.6, and an alkyl polyglycoside; applying the aqueous coating composition to a substrate; and drying, or allowing to dry, the aqueous coating composition.
The aqueous coating composition contains a waterborne emulsion polymer. The emulsion polymer contains at least one copolymerized ethylenically-unsaturated monomer, such as, for example, a (meth)acrylic ester monomer including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, aminoalkyl (meth)acrylate; styrene or substituted styrenes; butadiene; vinyl acetate or other vinyl esters; vinyl monomers such as vinyl chloride, vinylidene chloride, N-vinyl pyrollidone; (meth)acrylonitrile and (meth)acrylamide. The use of the term “(meth)” followed by another term such as acrylate or acrylamide, as used throughout the disclosure, refers to both acrylates and acrylamides and methacrylates and methacrylamides, respectively.
The emulsion polymer may also contain from 0% to 15%, preferably from 1% to 5%, of a copolymerized monoethylenically-unsaturated acid monomer, based on the dry weight of the polymer, such as, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, sulfoethyl methacrylate, phosphoroethyl methacrylate, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, and maleic anhydride.
The emulsion polymer used in this invention is substantially thermoplastic, or substantially uncrosslinked, when it is applied to the substrate, although low levels of deliberate or adventitious crosslinking may be present. When low levels of precrosslinking or gel content are desired low levels of multi-ethylenically unsaturated monomers such as, for example, 0.1%-5%, by weight based on the weight of the emulsion-polymerized polymer, allyl methacrylate, diallyl phthalate, 1,3-butylene glycol dimethacrylate, 1,6-hexanedioldiacrylate, and divinyl benzene may be used. It is important, however, that the quality of the film formation is not materially impaired. Chain transfer agents such as, for example, alkyl mercaptans may be used in order to moderate the molecular weight of the polymer.
The polymerization techniques used to prepare emulsion polymers are well known in the art. In the preparation of emulsion polymers conventional surfactants may be used such as, for example, anionic and/or nonionic emulsifiers such as alkali or ammonium alkyl sulfates, alkyl sulfonic acids, fatty acids, and oxyethylated alkyl phenols. The amount of surfactant used is usually up to 6% by weight, based on the weight of total monomer. Either thermal or redox initiation processes may be used. Conventional free radical initiators may be used such as, for example, hydrogen peroxide, t-butyl hydroperoxide, and ammonium and/or alkali persulfates, typically at a level of 0.05% to 3.0% by weight, based on the weight of total monomer. Redox systems using the same initiators coupled with a suitable reductant such as, for example, sodium bisulfite may be used at similar levels.
In another aspect of the present invention the emulsion polymer may be prepared by a multistage emulsion polymerization process, in which at least two stages differing in composition are polymerized in sequential fashion. Such a process usually results in the formation of at least two mutually incompatible polymer compositions, thereby resulting in the formation of at least two phases within the polymer particles. Such particles are composed of two or more phases of various geometries such as, for example, core/shell or core/sheath particles, core/shell particles with shell phases incompletely encapsulating the core, core/shell particles with a multiplicity of cores, and interpenetrating network particles. In all of these cases the majority of the surface area of the particle will be occupied by at least one outer phase and the interior of the particle will be occupied by at least one inner phase. Each of the stages of the multi-staged emulsion polymer may contain the same monomers, surfactant, chain transfer agents, etc. as disclosed herein-above for the emulsion polymer. The polymerization techniques used to prepare such multistage emulsion polymers are well known in the art such as, for example, U.S. Pat. Nos. 4,325,856; 4,654,397; and 4,
Krasnansky Robert
Maver Tammy Lynne
Bakule Ronald D.
Egwin K. C.
Rohm and Haas Company
Wu David W.
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