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
2001-09-17
2004-07-20
Wyrozebski, Katarzyna (Department: 1714)
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...
C524S446000, C524S447000, C526S128000, C526S126000, C526S243000, C526S346000, C501S141000, C501S145000
Reexamination Certificate
active
06765049
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to polymer clay aqueous nanocomposite dispersions and methods for making and using the same. More particularly, the present invention relates to methods of making polymer clay nanocomposite dispersions derived from an acid containing monomer and clay that are used, for example, as alkali swellable and alkali soluble thickeners. This invention also relates to the use of these nanocomposite compositions such as, for example, dispersants, binders, coatings, print pastes, over print varnishes, dry powder cement modifiers, personal care products, household or industrial cleaners, or flexographic inks.
BACKGROUND OF THE INVENTION
Alkali swellable and alkali soluble thickening copolymers (“AST”) are generally carboxyl functional copolymers that are produced by the free-radical polymerization of ethylenically unsaturated monomers. The reference, Gregory D. Shaw, “Alkali-Swellable and Alkali-Soluble Thickener Technology”,
Polymers in Aqueous Media
, American Chemical Society (1989), pp. 457-494 provides a general overview of AST copolymers. These copolymers can be substantially water insoluble at low pH but may be completely soluble or swell substantially in water upon partial or complete neutralization. The term neutralization, as used herein, relates to raising the pH of the system via the addition of an appropriate base.
AST copolymers may be classified structurally as either conventional, i.e., lacking associative function, or associative. The structural distinctions between the two classes results in differences in rheological properties wherein the associative AST copolymers may provide higher degrees of thickening or a unique rheology to aqueous solutions. While either of these ASTs may be copolymerized from a variety of ethylenically unsaturated monomers, at least one of these monomers should have a carboxyl functional group, such as a carboxylic acid containing monomer, and be present in a sufficient amount to render the polymer water swellable or water soluble on partial or complete neutralization with an appropriate base. Conventional AST copolymers may generally contain one or more hydrophobic comonomers in addition to the hydrophilic carboxyl-containing acid monomer. Associative AST copolymers, by contrast, may generally contain a carboxylic monomer, such as a carboxylic acid containing monomer, a hydrophobic monomer, and an additional monomer that is associative. The hydrophobic monomer in the associative AST may be omitted if the associative monomer is able to impart the proper hydrophilic-hydrophobic balance for the desired pH-dependent solubility.
AST copolymers may further be classified by the polymerization techniques in which they are made. Non-aqueous, or non-emulsion polymerization techniques, may be used to produce conventional ASTs referred to as alkali-swellable or alkali-soluble non-emulsions (“ASNE”) or associative ASTs referred to as hydrophobically modified, alkali-swellable or alkali-soluble non-emulsions (“HASNE”). Aqueous based, emulsion polymerization techniques may be used to produce conventional ASTs referred to as alkali-swellable or alkali-soluble emulsions (“ASE”) or associative ASTs referred to as hydrophobically modified, alkali-swellable or alkali-soluble emulsions (“HASE”).
AST copolymers prepared by emulsion polymerization techniques, such as ASE or HASE copolymers, are typically prepared with about 10-80% by weight of carboxylic acid monomer and water-soluble persulfate initiators. Depending upon the application, it may be desirable that the AST copolymers exhibit high molecular weight, high viscosity, significant particle swelling, and are thus used at low percentage solids upon neutralization. Typically, high acid polymers are compounds or additives within formulations. Further, it may also be desirable that the AST copolymers impart improved physical properties such as strength, toughness, block, print and dirt pick-up resistance, enhanced barrier properties, and enhanced temperature and flame retardence. Certain properties, such as strength and toughness are advantageous, for example, in overprint varnish applications but disadvantageous in other applications such as thickening agents.
AST copolymers are oftentimes used in applications such as thickeners to enhance the viscosity within an aqueous system by, for example, reducing the flow of the system. The increased viscosity imparted by the thickener may range from slight thickening in moderately flowable systems to generally immobile systems such as gels. Many of the thickeners used in the art are synthesized or derived from natural products such as natural gums which may make them expensive to manufacture and impart variability from lot to lot. To remedy these problems, inorganic thickeners, such as clay-base minerals, were adopted. However, these inorganic thickeners suffer numerous difficulties such as the inability to provide high strength, self-supporting gels or the inability to withstand the stresses of handling and shipping. In this regard, aqueous gels based upon inorganic thickeners may crack or crumble as they begin to lose water.
U.S. Pat. No. 4,351,754 issued to Dupre (“Dupre”) discloses a HASE thickening agent for aqueous compositions comprising an admixture of a water swellable clay mineral and an acrylic or methacrylic acid emulsion copolymer that is characterized by the inclusion of a hydrophobe containing monomer. In Dupre, the clay material is blended or admixed with the copolymer either before or after neutralization. The amount of clay mineral and acrylic or methacrylic acid copolymer in the mixture varies depending upon the degree of thickening desired and other properties such as strength, elasticity, and plasticity of the gelatinous form of aqueous systems. Dupre, however, does not disclose the addition of the clay mineral prior to the polymerization of the acrylic or methacrylic acid emulsion copolymer. Further, Dupre does not disclose, inter alia, AST copolymers with phase separated morphologies produced by sequential emulsions polymerization techniques such as core shell or polymer latex seed copolymers.
Clays may not always provide a desirable improvement in the physical properties, particularly mechanical properties, of the AST copolymer. This may be due, for example, to the lack of affinity between the clay and the polymer at the interface, or the boundary, between the clay and polymer within the material. In this connection, affinity between the clay and the polymer may improve the physical properties of the resulting nanocomposite by allowing the clay material to uniformly disperse throughout the polymer. The relatively large surface area of the clay, if uniformly dispersed, may provide more interfaces between the clay and polymer, and may subsequently improve the physical properties, by reducing the mobility of the polymer chains at these interfaces. By contrast, a lack of affinity between the clay and polymer may adversely affect the strength of the composition by having pockets of clay concentrated, rather than uniformly dispersed, throughout the polymer. Affinity between clays and the polymers is related to the fact that clays, by nature, are generally hydrophilic whereas polymers, such as the polymers used in the aforementioned applications, are generally hydrophobic.
Nanocomposites are polymer clay compositions in which at least one of its constituents has one or more dimensions, such as length, width or thickness, in the nanometer size range. The term “nanocomposite”, as used herein, denotes the state of matter wherein polymer molecules exist among at least partially exfoliated clay layers. Recently, nanocomposites that contain layered clay materials such as montmorillonite having silicate layers of a thickness of 1 nanometer dispersed within a polymeric matrix, have been developed as a means to improve the physical properties of polymers. In order to effectively improve the physical or mechanical properties, the clay is typically uniformly dispersed throughout the polymer in order to
Lorah Dennis Paul
Slone Robert Victor
Rohm and Haas Company
Wyrozebski Katarzyna
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