Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-10-01
2004-11-16
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S609000, C524S817000, C524S515000, C524S431000, C524S523000, C523S201000, C523S220000, C523S215000, C523S215000
Reexamination Certificate
active
06818697
ABSTRACT:
The present invention relates to an aqueous coating composition which includes a bimodal copolymer, and which provides an improvement in at least one of the following properties: stain blocking, block resistance, hiding, and shear stability.
Coating compositions are routinely applied to the surfaces of substrates, including the surfaces of previously coated substrates. Substrates frequently contain water soluble staining agents. When a water based coating is applied to the substrate, these staining agents often leach from the substrate into the coating, causing discoloration of the coating. For example, tennins contained in woods such as redwood, cedar, elm, and mahogany can leach from the substrate into the coating, causing tannin staining, which appears as discoloration on the surface of the coating; and salts contained in cementitious substrates often cause efflorescence, which is a staining caused by the migration of the salt from the substrate to the paint coating, where it appears as white deposits. Staining of the substrate, and of coatings previously applied to the substrate, can also be caused by sources external to the substrate. For example, cigarette smoke causes nicotine staining, which discolors light colored coatings; and inks from pens cause marker stains on the substrate. Each of the abovementioned typos of staining is highly undesirable in coatings. Attempts have been made to resolve this problem by incorporating strong acids into a polymer backbone. While the addition of strong acid can achieve the reduction, or elimination of stain bleeding, stain blocking generally requires the use of emulsion polymers having a small particle size, which limits the solid content of the polymer emulsion used to make the coating composition. For performance reasons, such as shear stability, open time, and formulation latitude, it is desirable to have a high solids content in the coating composition. Therefore, there is a need for a coating composition which is capable of stain blocking, and contains a high solids content.
U.S. Pat. No. 4,812,510, discloses colloid-free vinyl acetate latexes which include up to 15 weight parts of an ionic comonomer such as sodium styrene sulfonate, sodium vinyl sulfonate, and mono- and di-phosphated hydroxyethyl methacrylate and which are prepared with up to 20 weight parts of certain anionic surfactants including phosphates and sulfonates, for use in a variety of adhesives and coatings. However the use of the latexes in stain-blocking coating compositions is not disclosed. Furthermore, the use of bimodal polymers is not disclosed.
U.S. Pat. No. 5,922,410 discloses a clear (unpigmented) wood coating composition which includes a copolymer containing from 0.1 to 50 wt. % of a copolymerizable monomer containing a conjugate base of an acid, the acid having a pKa of less than 4 for use in clear coatings to enhance the yellowness (warmth) of the wood to which it is applied. However the use of the copolymers in stain-blocking coating compositions is not disclosed. Furthermore, the use of bimodal polymers is not disclosed.
Applicants have discovered that a water-based coating composition that is useful as stain blocker, and has a high solids content, can be made by incorporating a strong acid into the polymer backbone of a bimodal emulsion copolymer, while maintaining, or improving the stain blocking performance of a unimodal stain blocking coating composition. Unexpectedly, applicants also found that coating compositions of the invention may have improvements over a unimodal coating composition in one or more of the following properties: stain blocking, block resistance and shear stability.
A first aspect of the present invention provides a coating composition comprising a bimodal aqueous emulsion copolymer, wherein said copolymer comprises as polymerized units from 0.1% to 10% by weight, based on the dry weight of said copolymer, of a compound selected from the group consisting of at least one strong acid monomer, and salts thereof; wherein said copolymer contains small mode particles having a diameter of from 50 to 150 nm; wherein said copolymer contains large mode particles having a diameter of less than 400 nm, and said large mode particles are larger in diameter than said small mode particles; and wherein the ratio of said small mode particles to said large mode particles is from 10:90 to 90:10 by weight.
A second aspect of the present invention provides a method for blocking stains on a substrate comprising: (a) forming a coating composition comprising a bimodal aqueous emulsion copolymer, wherein said copolymer comprises as polymerized units from 0.1% to 10% by weight, based on the dry weight of said copolymer, of a compound selected from the group consisting of at least one strong acid monomer, and salts thereof; wherein said copolymer contains small mode particles having a diameter of from 50 to 150 nm; wherein said copolymer contains large mode particles having a diameter of less than 400 nm, and said large mode particles are larger in diameter than said small mode particles; wherein the ratio of said small mode particles to said large mode particles is from 10:90 to 90:10; (b) applying said coating composition to a substrate bearing a stain; and (c) drying, or allowing to dry said coating composition.
A third aspect of the present invention provides a method for improved hiding comprising: (a) forming a coating composition comprising a bimodal aqueous emulsion copolymer, wherein said copolymer comprises as polymerized units from 0.1% to 10% by weight, based on the dry weight of said copolymer, of a compound selected from the group consisting of at least one strong acid monomer, and salts thereof; wherein said copolymer contains small mode particles having a diameter of from 50 to 150 nm; wherein said copolymer contains large mode particles having a diameter of less than 400 nm, and said large mode particles are larger in diameter than said small mode particles; wherein the ratio of said small mode particles to said large mode particles is from 10:90 to 90:10; (b) applying said coating composition to a substrate bearing a stain; and (c) drying, or allowing to dry said coating composition.
A fourth aspect of the present invention provides a method for improved block resistance comprising: (a) forming a coating composition comprising a bimodal aqueous emulsion copolymer, wherein said copolymer comprises as polymerized units from 0.1% to 10% by weight, based on the dry weight of said copolymer, of a compound selected from the group consisting of at least one strong acid monomer, and salts thereof; wherein said copolymer contains small mode particles having a diameter of from 50 to 150 nm; wherein said copolymer contains large mode particles having a diameter of less than 400 nm, and said large mode particles are larger in diameter than said small mode particles; wherein the ratio of said small mode particles to said large mode particles is from 10:90 to 90:10; (b) applying said coating composition to a substrate bearing a stain; and (c) drying, or allowing to dry said coating composition.
A fifth aspect of the present invention provides a method for improved shear stability comprising: forming a coating composition comprising a bimodal aqueous emulsion copolymer, wherein said copolymer comprises as polymerized units from 0.1% to 10% by weight, based on the dry weight of said copolymer, of a strong acid monomer, or salts thereof; wherein said copolymer contains small mode particles having a diameter of from 50 to 150 nm; wherein said copolymer contains large mode particles having a diameter of less than 400 nm, and said large mode particles are larger in diameter than said small mode particles; wherein the ratio of said small mode particles to said large mode particles is from 10:90 to 90:10.
The composition of this invention is a coating composition containing a bimodal aqueous emulsion copolymer whose polymerized units include from 0.1% to 10% by weight (based on the dry weight of the copolymer), preferably from 1% to 10%, more preferably f
Pressley Ozzie Moore
Zhang Wei
Joliboi Chipo M.
Rohm and Haas Company
Sastri Satya
Wu David W.
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