BACKGROUND OF THE INVENTION
The present invention relates to a wet emulsion finish composition useful for providing a coating or film to a substrate surface such as a floor. More particularly, it relates to an emulsion finish composition incorporating surface modified inorganic particles providing enhanced shelf stability and film performance, and methods of preparing the same.
Polymer compositions are used in the formulation of various coating compositions such as floor finishes or polishes, for example. Commercially available floor finish compositions typically are aqueous emulsion-based polymer compositions comprising one or more organic solvents, plasticizers, coating aides, anti-foaming agents, polymer emulsions, metal complexing agents, waxes, and the like. The polymer composition is applied to a floor surface and then allowed to dry in air, normally at ambient temperature and humidity. A film is formed that serves as a protective barrier against soil deposited on the floor by pedestrian traffic, for example. These same polymer compositions can be applied to other substrate surfaces for which protection is desired, such as tile floors, walls, furniture, windows, counter tops, and bathroom surfaces, to name but a few.
Although many of the commercially available aqueous floor finishes have performed well and have experienced at least some commercial success, opportunities for improvement remain. In particular, it is highly desirable that the resultant floor finish film exhibits certain physical and performance characteristics including hardness, scratch resistance, soil resistance, black marks/scuff resistance, and abrasion resistance. Unfortunately, for applications in which an enhanced floor finish film hardness or resistance to deterioration is of great importance, currently available aqueous floor finish compositions may be less than satisfactory.
A primary factor in finish film hardness is the emulsion polymer formulation. A metal complexing agent included in the floor finish composition ionically bonds to the polymers when the composition is dried, resulting in the protective film. This reaction is reversible and the film is easily removed by a stripper solution when desired. In this regard, most aqueous floor finish polymer emulsions are polyacrylate-based. While other polymers (e.g., styrene) substituted for, or combined with, the acrylic polymer and/or additives such as coalescing agents or plasticizers can affect the resultant film hardness, only marginal improvements are typically achieved. Because resultant film hardness and deterioration resistance are a function of the types of solids within the formed film, a more viable approach may be to add hard, inorganic particles to the emulsion polymer matrix. In theory, these inorganic particles would increase the resulting film hardness, making the finish harder and improving properties such as scratch resistance and soil resistance. While promising, simply adding these particles does not result in a commercially viable product. In particular, the inorganic particles will not remain dispersed in the wet polymer composition, but instead readily precipitate (see Comparative Example 1 below).
Floor finish manufacturers continually strive to provide improved hardness, abrasion resistance, and soil resistance properties. To this end, the addition of inorganic, hard particles appears promising. Unfortunately, current efforts have not produced a shelf stable product. Thus, a need exists for a surface finish composition exhibiting enhanced bulk properties via inorganic nanoparticles that will not precipitate over extended periods of time.
SUMMARY OF THE INVENTION
One aspect of the present invention provides an aqueous surface finish composition comprising a film-forming, reversibly crosslinked, emulsion-based polymer composition, and a surface modified inorganic particle material. The surface modified inorganic particle material is dispersed within the polymer matrix, and enhances performance characteristics of a film produced by the composition following application to a surface, including hardness, modulus, and scratch and soil resistance. The composition is particularly well suited for application to floor surfaces, but also to other substrate surfaces such as walls, counter tops, furniture, windows, and bathroom surfaces.
Typically, the surface modified inorganic particle material consists of particles surface modified by a coupling agent. In general terms, the coupling agent stabilizes the inorganic particles within the aqueous polymer composition, and renders the inorganic particles compatible with the polymer composition once dried. Preferably, the surface modified inorganic particle material comprises silica nanoparticles surface modified by a silane coupling agent. The ratio (by weight) of emulsion polymer composition solids to surface modified inorganic particle material solids is preferably in the range of 1:1-10:1, more preferably 3:1-5:1.
Polymers of the polymer composition are preferably acrylic polymers, acrylic copolymers, styrene-acrylic copolymers, or blends thereof. In one preferred embodiment, the polymer component is a blend of an acrylic polymer and a urethane polymer, or alternatively, acrylic urethane copolymers, with the urethane enhancing the toughness of the resultant film. The finish composition can also contain certain alkali soluble resins, waxes, permanent and fugitive plasticizers, defoamers, wetting agents, metal complexing agents and biocides.
Another aspect of the present invention provides a process for improving the performance of an emulsion-based polymer surface finish composition by dispersing a surface modified inorganic particle material within the polymer matrix. Another aspect of the present invention relates to a method of preparing the surface finish composition of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides an aqueous surface finish composition comprising a film-forming emulsion based polymer composition and a surface modified inorganic particle material dispersed within the polymer composition. The finish composition can be applied to a variety of substrates such as, for example, floor, wall, counter top, furniture, window, and bathroom surfaces. Preferably, the substrate is a floor, but can be any surface upon which the coatable compositions of the present invention can be applied such as vinyl, ceramic, wood, marble, and the like. The resultant coatings are smooth, exhibit increased hardness and modulus, and are highly resistant to scratches and soil. The inorganic particles provide for these performance enhancements, with the surface modification thereof ensuring long-term shelf stability of the finish composition.
Individual components of the emulsion-based polymer composition are described in greater detail below. In general terms, however, the polymer composition preferably includes an acrylic polymer and a metal complexing agent suspended in water. With this in mind, the inorganic particles are surface modified to ensure long-term suspension within the polymer composition. In a preferred embodiment, the surface modified inorganic particle material consists of a plurality of ceramic-type particles modified by a coupling agent. More preferably, the inorganic particles are metal oxide particles in any oxidation state. Examples of preferred metal oxides include silica, alumina, zirconia, vanadia, titania, ceria, iron oxide, antimony oxide, tin oxide, alumina/silica and combinations thereof, with silica being the most preferred. Regardless of the exact material employed, the inorganic particles are preferably nanoparticles having an average particle size (diameter) of 5-150 nm. Nanoparticles maintain transparency of the floor finish coating.
“Surface modification” of the inorganic particles is characterized by the provision of a coupling agent that modifies at least a portion of a surface of each particle. The term “surface modified particle” refers to a particle that includes surface groups attached to the surface of the particle. The surface groups modify the character of the particle. By way of background, a non-surface modified colloidal dispersion (such as inorganic particles dispersed in an aqueous medium) typically relies upon ionic stabilization to keep particles from aggregating within the medium. With respect to aqueous floor finish polymer compositions, inorganic particle ionic stabilization is difficult to achieve due to the different pHs, ionic strengths, chemical additives, cosolvents, and the like associated with these polymer compositions. Thus, inorganic particles in an aqueous floor finish polymer composition can readily aggregate with themselves and/or with the polymer emulsion particles, resulting in particle precipitation. The present invention overcomes this marked stability concern via stearic stabilization or additional ionic character provided by the coupling agent.
The coupling agent chain effectively has two ends, with the first end adhering to the outer surface of each inorganic particle, and the other end (or “tail”) freely extending from the particle. The term “adhering” includes, for example, covalent bonding, hydrogen bonding, electrostatic attraction, London forces, and hydrophobic interactions. The coupling agent may be chemisorbed or physisorbed. The coupling agent may comprise organic acids, organic bases, silanes and combinations thereof. The type of coupling agent preferred will depend on the type of inorganic particle and the chemistry of the floor finish composition. The coupling agent preferably has a hydrophilic property, thus providing surface modified particle stability in the aqueous polymer composition. Further, the coupling agent is selected so as to not promote particle aggregation or aggregation with the polymer emulsion particles. Thus, the surface modified inorganic particle material will not precipitate. Further, the tail of the coupling agent chain can, depending upon formulation, interact with the polymer matrix once dried, providing a compatibilizing and/or ionic bonding effect. Similarly, with certain preferred coupling agents (for example ionically charged silane coupling agents), the tail may allow the surface modified inorganic particle material to bond to the dried polymer composition. In either case, the surface modified inorganic particle material is more compatible with the polymer composition, providing enhanced film performance.
In a preferred embodiment utilizing silica particles (more preferably silica nanoparticles), the coupling agent is a silane coupling agent. Silane coupling agents are bifunctional organosilanes, and a number of acceptable silane coupling agents are available. Acceptable silane coupling agent tails are preferably hydrophilic and may be nonionic or ionic. Nonionic silanes may include those having alcohol, amine, urea, or polyether functionality.
Acceptable nonionic coupling agents can provide the dried polymer matrix compatibility described above and include, for example, methoxyethoxyethoxyethoxyureidopropyltriethoxysilane (CH3CH2O)3Si(CH2)3NHC(O)OCH2CH2OCH2CH2OCH2CH2OCH3, 1-[3-(trimethoxysilyl)propyl]urea, and other polyethylene glycol based silanes. Preferred silanes are those with polyethylene glycol tails, represented by the following structure:
where X is a hydrolysable moity such as alkoxy, acyloxy or halogen; m is 1-3; Y is a bifunctional organic radical; n is 1-100; and R is an organic radical that does not impart hydrophobic character.
In a more preferred embodiment, ionic silane coupling agents are employed with either anionic or cationic functional groups. Anionic functional group types may include the salts of carboxylic acids, sulfonic acids, and phosphoric acids. Cationic types may include quaternary amines and protonated amines. The silane may contain one or more ionic groups per molecule. Silanes containing carboxylic acid salts are particularly advantageous for silica particle surface modification. These include carboxyethylsilanetriol, sodium salt, as well as the salts of other acid-based silane coupling agents such as 4-carboxybutyltriethoxysilane (CH3CH2O)3Si(CH2)4CO2H, 10-carboxydecyltriethoxysilane (CH3CH2O)3Si(CH2)10CO2H, etc. Similarly, a variety of diacid-based silane coupling agents are available, with the hydrolysis product of 3-(3-trimethysilylpropylthio)succinic anhydride, aqueous ammonia providing one acceptable formulation.
The surface modified inorganic particle material is preferably characterized by the coupling agent covering 5-100 percent of the surface area of each inorganic particle; more preferably 15-100 percent; most preferably 20-50 percent. In this regard, 100 percent surface area coverage best promotes composition stability; however from a cost standpoint, a lesser surface area coverage is preferably employed, yet still provides highly acceptable results.
The surface modification can be accomplished by any suitable means. The coupling agents are added to the suspension and allowed time to adhere to the inorganic particle surfaces. The time can range from minutes to many hours. In the case of silane coupling agents, suitable catalysis and elevated temperature may be required to complete the surface modification. In the case of ionic coupling agents, additional base may be added to neutralize the free acid or facilitate other reactions such as hydrolysis of anhydride functionality.
With the above-described surface modified inorganic particle material constraints in mind, and as previously described, the film-forming emulsion-based polymer composition can assume a wide variety of forms. In this regard, the polymer composition incorporates polymer(s) that are typically acrylic polymers, acrylic copolymers, styrene-acrylic copolymers, or blends thereof. Acrylic polymers contain only one type of acrylate monomer, whereas the acrylic copolymers comprise two or more different types of acrylate monomers. Styrene-acrylic copolymers comprise at least one type of styrene monomer and one type of acrylate monomer. The acrylate monomers include acrylic acid, butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethyl hexyl acrylate, acrylonitrile, acrylimide, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylamide, and the like. Styrene monomers include styrene, alpha-methyl styrene, and the like.
Commercially available acrylic copolymers suitable for finishing compositions include, but are not limited to, methyl methacrylate/butyl acrylate/methacrylic acid (MMA/BA/MAA) copolymers, methyl methacrylate/butyl acrylate/acrylic acid (MMA/BA/AA) copolymers, and the like.
Suitable commercially available styrene-acrylic copolymers include, but are not limited to, styrene/methyl methacrylate/butyl acrylate/methacrylic acid (S/MMA/BA/MMA) copolymers, styrene/methyl methacrylate/butyl acrylate/acrylic acid (S/MMA/BA/AA) copolymers, and the like.
Commercially available acrylic polymers suitable for floor finish composition include, for example, Morglo II Latex from Omnova Solutions, Inc., of Chester S.C.
In a preferred embodiment, the film-forming polymer matrix incorporates accepted acrylic chemistry in combination with polyurethane. Polyurethanes and polyacrylates can be used together to achieve coatings that are both harder and tougher. In one more preferred embodiment, the film-forming polymer matrix includes a hybrid copolymer consisting of urethane and acrylic polymer chains. In an even more preferred embodiment, the acrylic urethane hybrid polymer is added to commercially available acrylic-based surface finish compositions.
The finish composition typically contains between about 5 and 50 weight percent and preferably between about 10 and 35 weight percent emulsion-based polymers based on the weight of the finish composition. Further, a weight ratio of emulsion polymer composition solids to surface modified inorganic particle material solids is preferably in the range of 1:1-10:1; more preferably 3:1-5:1.
The surface finish compositions can also contain other components such as polyvalent metal compounds, alkali soluble resins, waxes, permanent and fugitive plasticizers, defoamers, wetting agents, and biocides. The polyvalent metal compound provides crosslinking of the polymers in the film and increases the detergent resistance of the finish. Plasticizers or coalescing agents can be added to lower the temperature of film formation. Alkali soluble resins improve the ability of the finish to be stripped from the substrate before reapplication of a fresh coating. Waxes improve the gloss of the finish and allow the finish to be buffed. Biocides help minimize the formation of molds or mildew in the coating. Antifoamers and defoamers minimize the formation of bubbles in the coating.
Suitable polyvalent metals include beryllium, cadmium, copper, calcium, magnesium, zinc, zirconium, barium, strontium, aluminum, bismuth, antimony, lead, cobalt, iron, nickel, and the like. Although the polyvalent metal compound can be added to the finish composition in dry form such as powder, it is preferably added as a solution. The polyvalent metal compound is typically a metal complex, a metal salt of an organic acid, or a metal chelate. The ammonia and amine complexes of these metals are particularly useful because of their high solubility. Amines capable of complexing many metals include, for example, monoethanol amine, diethylaminoethanol, and ethylenediamine. Polyvalent metal complexes and salts of organic acids are typically soluble in an alkaline pH range. Anions of organic acids include acetate, formate, carbonate, glycolate, octanoate, benzoate, bluconate, oxalate, lactate, and the like. Polyvalent metal chelates where the ligand is a bidentate amino acid such as glycine or alanine can also be used.
Zinc and cadmium are preferred polyvalent metal ions. Preferred polyvalent metal compounds include zinc acetate, cadmium acetate, zinc glycinate, cadmium glycinate, zinc carbonate, cadmium carbonate, zinc benzoate, zinc salicylate, zinc glycolate, and cadmium glycolate. In some applications, a fugitive ligand such as ammonia is preferred. A ligand is considered fugitive if at least a portion of the ligand tends to volatilize as the finish dries to form a film on the substrate.
The alkali-soluble resins include copolymers of styrene or vinyl toluene with at least one α-β-monoethylenically unsaturated acid or anhydride such as styrene-maleic anhydride resins, rosin/maleic anhydride adducts which are condensed with polyols, and the like. The alkali-soluble resins typically have a weight average molecular weight from about 500 to 10,000 and preferably from about 1000 to 5000. The resins are often used as a conventional resin cut, which is an aqueous solution of the resin with an alkaline substance having a fugitive cation such as ammonium hydroxide. The alkali soluble resin is typically employed in amounts from 0 to about 20 weight percent and preferably in amounts from 0 to about 15 weight percent based on the weight of the finish composition.
The waxes or mixtures of waxes that can be used include waxes of a vegetable, animal, synthetic, and/or mineral origin. Representative waxes include, for example, camuba, candelilla, lanolin, stearin, beeswax, oxidized polyethylene wax, polyethylene emulsions, polypropylene, copolymers of ethylene and acrylic esters, hydrogenerated coconut oil or soybean oil, and the mineral waxes such as paraffin or ceresin. The waxes typically range from 0 to about 15 weight percent and preferably from about 2 to about 10 weight percent based on the weight of the finish composition.
The aqueous finishing composition typically contains from about 1 to about 10 weight percent plasticizer based on the weight of the finish composition. The plasticizer facilitates film formation at ambient temperatures when the coating is applied to a substrate. A fugitive or semi-fugitive plasticizer is preferred over a permanent plasticizer for many applications. A fugitive or semi-fugitive plasticizer is a plasticizer that at least partially evaporates as the coating dries. Permanent plasticizers do not evaporate. Mixtures of fugitive and permanent plasticizers can be used. The particular plasticizer and the amount used are chosen in accordance with the demand for compatibility with the formulation, efficiency in lowering the film-forming temperature, and clarity of the coating.
Fugitive plasticizers or coalescents include, for example, the monobutyl, monoethyl, monomethyl or other monoalkyl ethers of diethylene glycol or diproplyleneglycol, isophorone, benzyl alcohol, butyl cellosolve, and 3-methoxybutanol-1. Permanent plasticizers include, for example, benzyl butyl phthalate, dibutyl phthalate, dimethyl phthalate, triphenyl phosphate, 2-ethyl hexyl benzylphthalate, fatty oil acid esters of caprolactam, acetyl tributyl citrate, toluene ethyl sulfonamide, tributoxyethyl phosphate, and tributyl phosphate.
The finish compositions of the invention typically have a solids content from about 10 to about 50 weight percent. In one embodiment, the solids range from about 10 to about 30 weight percent and preferably from about 15 to about 25 weight percent based on the weight of the finish composition. In another embodiment of the invention, a concentrated finish composition is provided containing up to about 35 to about 50 weight percent solids based on the weight of the finish composition. Such concentrated compositions are diluted prior to use by either mixing the concentrate with water or by applying the finish with a wet mop or applicator.
The pH of the finish composition is typically in the range of about 6 to about 10.5. Preferably, the pH is between about 7.5 and about 9.9. The pH can be adjusted using various bases or buffering agents. Suitable bases or buffering agents include, for example, borax, sodium hydroxide, alkali phosphates, alkali silicates, alkali carbonates, ammonia, and amines such as diethanolamine or triethanolamine.
Another aspect of the invention provides a method for applying the finish compositions of this invention. The finish can be applied to a variety of substrates including floor, wall, furniture, window, counter top and bathroom surfaces. The substrates can be fibers, metal, plastic, wood, stone, brick, glass, cement, concrete, ceramic masonite, dry wall, plaster, plastic, and the like. Bathroom surfaces can be countertops, shower stalls, toilets, and urinals. In one preferred embodiment, the substrate is a floor surface. The floor surface can be wood, composite vinyl tile, vinyl linoleum, asphalt, asbestos, concrete, ceramic, and the like.
The following examples and comparative examples further describe the finish compositions of the invention, methods of using the finish compositions, and the tests performed to determine the various characteristics of the finish composition. The examples are provided for exemplary purposes to facilitate an understanding of the invention, and should not be construed to limit the invention to the examples.