Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2002-11-18
2004-11-09
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S038000, C525S186000, C525S221000, C525S222000
Reexamination Certificate
active
06815466
ABSTRACT:
The present invention relates to a colloidally and sedimentation stable coating composition containing ion exchange resins, and a method of using a colloidally and sedimentation stable coating composition containing ion exchange resins.
Coating compositions are routinely applied to the surfaces of substrates. Substrates frequently contain water soluble or extractable 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, tannins contained in woods such as redwoods, cedar, elm, and mahogany often leach from the substrate into the coating, causing tannin staining, which appears as discoloration on the surface of the coating; salts contained in cementitious substrates often cause efflorescence, which is a staining caused by the migration of the salt to the paint coating, where it appears as white deposits; when applied to asphalt substrates, solvents contained in some coatings can cause asphalt to bleed through the coating, causing asphalt staining. Discoloration of the coating can occur even when the coating is applied to a previously coated substrate, as the leaching agent can pass through the previously applied coat, and enter the subsequently applied coat. 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 is the change in color of a light colored substrate or substrate coating; and exposure to water can cause a discoloration of the substrate or substrate coating called water spotting. These stains can leach into subsequently applied water based coatings. Each of the abovementioned types of staining is highly undesirable in coatings. Attempts have been made to resolve this problem by adding ion exchange resins to the coating formulation. However, the ion exchange resin can settle in the formulation into a hard packed sediment that is difficult to redisperse. In addition, the presence of the ion exchange resin can cause colloidal instability, which is seen as the formation of grit (a suspended gum-like material) which undesirably makes the surface of the dried coating uneven, or in extreme cases, gelation of the formulation. Therefore, there is an ongoing need for coating compositions which prevent or mitigate staining such as nicotine staining, water spotting, efflorescence, asphalt staining, or tannin staining, while remaining sedimentation stable and colloidally stable upon addition of ion exchange resins.
For example, this has been addressed by U.S. Pat. No. 3,494,878, which discloses an aqueous coating composition comprising a mixture of a water-insoluble addition polymer and an anion exchange resin (having a diameter of about 0.5 to about 25 microns). By virtue of the ion exchange resin, which is made by suspension polymerization, the coating composition is resistant to staining when applied over substrates that would tend to stain the coating composition. The addition polymer aqueous dispersion is stabilized using one or more emulsifiers. If water soluble cellulose derivatives are added to the coating composition, such addition is done during formulation of the coating composition, for bodying purposes. However, the composition of the '878 patent is neither sedimentation stable nor colloidally stable, and even when the composition is thickened with a cellulose derivative, it may become sedimentation stable, but it is not colloidally stable.
Some have been able to accomplish the creation of a coating composition that is sedimentation stable, and resistant to staining. For example, U.S. Pat. No. 3,847,857 discloses a sedimentation stable aqueous coating composition comprising a mixture of a water-insoluble addition polymer and a stably dispersed water insoluble vinyl copolymer having a size of 0.05 to 0.3 microns, which is prepared by emulsion polymerization. However, the coating composition is not colloidally stable.
Others have been able to accomplish the creation of a coating composition that is colloidally stable, and resistant to staining. For example, U.S. Pat. No. 5,922,777 discloses a grit free coating composition comprising an emulsion polymer and an ion exchange resin (having a size of 0.1 to 50 microns). Prior to addition to the emulsion polymer, the ion exchange resin is pretreated with a water-soluble anionic polymer which acts to stabilize the composition. However, the composition is not sedimentation stable, particularly with larger particle size ion exchange material. In addition, extra undesirable water soluble polymer is introduced into the coating which can detract from water resistance of the coating and the stain blocking capacity of the ion exchange material.
Applicants have discovered that by blending anion exchange particles having a size of 0.5 to 50 microns, with a water-insoluble addition copolymer, one can produce a stain resistant water based coating composition that is both sedimentation stable, and colloidally stable.
In a first aspect of the present invention there is provided an aqueous dispersion comprising a blend of: (1) an anion exchange resin having a particle size of 0.5 to 50 microns, wherein said anion exchange resin is prepared by a process selected from the group consisting of suspension polymerization, phenol formulated condensation, and condensation polymerization of at least one polyamine and epichlorohydrin; with (2) a water-insoluble addition copolymer, wherein said copolymer is prepared by emulsion polymerization; wherein said emulsion polymerization occurs in the presence of a nonionic protective colloid; wherein said copolymer has a particle size of less than one micron; wherein said aqueous dispersion has a Brookfield viscosity, at 60 rpm of less than 2000 cps; wherein said aqueous dispersion is colloidally stable and sedimentation stable.
In a second aspect of the present invention there is provided a method of preparing a coating composition comprising, blending the above-described aqueous dispersion in combination with a binder.
In a third aspect of the present invention there is provided a method of inhibiting staining of a coated substrate, comprising the steps of: (a) applying to said substrate an aqueous dispersion comprising a blend of: (1) an anion exchange resin having a particle size of 0.5 to 50 microns, wherein said anion exchange resin is prepared by a process selected from the group consisting of suspension polymerization, phenol formulated condensation, and condensation polymerization of at least one polyamine and epichlorohydrin; with (2) a water-insoluble addition copolymer, wherein said copolymer is prepared by emulsion polymerization; wherein said emulsion polymerization occurs in the presence of a nonionic protective colloid; wherein said copolymer has a particle size of less than one micron; wherein said aqueous dispersion has a Brookfield viscosity, at 60 rpm of less than 2000 cps; wherein said aqueous dispersion is colloidally stable and sedimentation stable; and (b) drying, or allowing to dry, said aqueous dispersion.
The composition of the present invention is particularly useful as a stain blocking coating composition. By “stain blocking”, herein is meant preventing discoloration of the coating composition by minimizing or eliminating the tendency of stains to migrate from a substrate or a source external to the substrate, through the composition of the invention and any subsequently applied coating composition.
The composition, and methods of this invention relate to an aqueous dispersion which includes a blend of an anion exchange resin having a particle size of 0.5 to 50 microns, and which has been prepared by either suspension polymerization, phenol formulated condensation, or a condensation reaction between at least one polyamine and epichlorohydrin, with a water-insoluble addition copolymer, having a particle size of less that one micron, which has been prepared, in the presence of a nonionic protecti
Egwim Kelechi C.
Rohm and Haas Company
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