1. Field of Invention
The present invention relates to novel rheological modifiers and more particularly it relates to aqueous fluid polymer suspensions of hydrophobically modified polyacrylates, polyurethanes and poly(acetal- or ketal-polyethers).
2. Description of the Prior Art
It is desired by the latex paint industry to employ liquid rheology modifiers, rather than powders, for ease of incorporating these into paint formulations. A number of liquid thickeners are commercially available either in the form of solutions of these polymers in mixed solvents, or in the form of aqueous suspensions of these polymers as is described in the prior art references cited below.
In contrast to the prior art thickeners for paint containing volatile organic solvents it is preferred by the paint industry, as an environmental safeguard, to incorporate ingredients into latex paint that have little or no volatile organic compounds (VOCs) present. Thus, it is preferentially desired to employ water as a carrier medium with which to add these polymers to the paint.
It has been found in the prior art that water can be modified with various salts such as diammonium phosphate, diammonium sulfate or sodium formate salt to convert this medium to a non-solvent carrier for suspensions of specific water-soluble polymers. For example, U.S. Pat. No. 4,883,536 describes suspensions of hydroxyethylcellulose prepared in concentrated aqueous solutions of diammonium sulfate or diammonium phosphate, and that these suspensions in turn were useful for rheology modification of latex paint. U.S. Pat. No. 5,228,908 describes that concentrated aqueous sodium formate solution can be employed for preparation of fluid suspensions of the polymers such as hydroxyethylcellulose as well. In U.S. Pat. No. 5,578,168 the use of a number of salts, including sodium formate, were shown to be useful for preparing aqueous suspensions of poly(ethylene oxide). In U.S. Pat. No. 5,541,241 and U.S. Pat. No. 5,489,638 it was demonstrated that sodium formate and other salts were useful for preparing aqueous suspensions of polyvinyl alcohol.
None of the above polymers described in the prior art aqueous fluidized polymer suspensions, however, exhibit all of the desired features of latex paint thickeners. Specifically fluidized polymer suspensions of hydroxyethylcellulose or hydrophobically modified hydroxyethylcellulose, as described in U.S. Pat. No. 4,883,536 or U.S. Pat. No. 5,228,909, typically provide poor flow and leveling to the latex paint, along with an undesirably low high shear (ICI) viscosity. It was therefore desired to create a liquid thickener that would have improved performance in latex paint compared to these prior art thickeners. It was also desirable to combine, if possible, different latex paint rheological modifiers in one liquid carrier so that a combination of properties could be imparted to the latex paint.
According to the present invention there is provided an aqueous fluid polymer suspension comprising a water-soluble synthetic associative thickener, a water soluble carbon containing salt selected from the group consisting of sodium and potassium salts of aliphatic and aromatic carboxylic acids and sodium and potassium carbonate, and water. The polymer can be selected from the group consisting of hydrophobically modified polyurethanes, hydrophobically modified polyacrylates and hydrophobically modified poly(acetal- or ketal-polyethers) comprising a backbone of poly(acetal- or ketal-polyether) which has ends that are capped with hydrophobic groups independently selected from the group consisting of alky, aryl, arylalkyl, alkenyl, arylalkenyl, cycloaliphatic, perfluoroalkyl, carbosilyl, polycyclyl, and complex dendritic groups wherein the alkyl, alkenyl, perfluoroalkyl, and carbosilyl hydrophobic groups comprise 1 to 40 carbons, and the aryl, arylalkyl, arylalkenyl, cycloaliphatic and polycyclyl hydrophobic groups comprise 3 to 40 carbons.
In another aspect, the present invention provides a process for preparing an aqueous fluid polymer suspension of a water-soluble synthetic associative thickener polymer comprising dissolving the carbon containing salt in water and adding the polymer to and mixing it with the salt solution.
According to the present invention there are further provided processes for thickening aqueous systems by adding the aqueous suspension of the hydrophobically modified water-soluble polymers of the present invention thereto.
It has surprisingly been discovered that non-ionic associative thickener, such as hydrophobically modified poly(acetal-polyether) in which the polymer chain has been end capped with terminal cetyl hydrophobes, possesses enhanced thickening characteristics in latex paint. It has been discovered that such polymer can be suspended in aqueous carrier containing dissolved concentrated sodium formate. It has additionally been discovered that suspensions of the hydrophobically modified polymers of the present invention combined with other water-soluble polymers and associative thickeners, such as, hydrophobically modified hydroxyethylcellulose, could be used for thickening latex paints.
Although prior art patents have claimed aqueous sodium formate as a carrier medium for suspending various water-soluble polymers the suspension of the present polymer differs in kind from these prior art compositions with respect to the chemical nature of the suspended polymer species. Novelty of this approach becomes evident with the recognition that the prior art shows that the behavior of various water-soluble polymers, differing in chemical nature, exhibit unpredictable behavior in aqueous solutions containing various salts. For instance, high solids suspensions of water-soluble polymers such as hydroxyethylcellulose and sodium carboxymethyl cellulose can be prepared in concentrated diammonium sulfate, whereas the water-soluble polymers of the present invention, hydrophobically-modified poly(acetal- or ketal polyether), forms a useless agglomerate in that medium. Similarly, it was reported in the prior art that hydroxyethylcellulose can be suspended in an aqueous medium of concentrated sodium formate, whereas sodium carboxymethyl cellulose formed a paste in that medium. Based upon these observed idiosyncracies of water-soluble polymers in concentrated aqueous solutions of various salts it is clear that the prior art is of little utility in predicting in advance which water-soluble polymers may be amenable to preparation of fluid suspensions in a given type of aqueous medium. Accordingly, results obtained by the present invention are unexpected.
The aqueous fluid suspension of the present invention can be prepared from hydrophobically modified polyurethanes, hydrophobically modified polyacrylates and hydrophobically modified poly(acetal- or ketal-polyethers). The hydrophobically modified poly(acetal- or ketal-polyethers) are the subject of U.S. Pat. No. 5,574,127, the disclosure of which is hereby incorporated by reference. Generally, these water-soluble copolymers comprise a backbone of acetal- or ketal-linked polyether which has ends that are capped with hydrophobic groups. The hydrophobic groups can be independently selected from the group consisting of alkyl, aryl, arylalkyl, alkenyl, arylalkenyl, cycloaliphatic, perfluoralkyl, carbosilyl, polycyclyl, and complex dendritic groups, wherein the alkyl, alkenyl, perfluoralkyl, and carbosilyl hydrophobic groups comprise 1 to 40 carbons and the aryl, arylalkyl, arylalkenyl, cycloaliphatic and polycyclyl hydrophobic groups comprise 3 to 40 carbons. Generally the upper limit of the weight average molecular weight of the polymer can be 2,000,000, preferably 500,000 and most preferably 100,000. The lower limit can be about 500, preferably 15,000 and most preferably about 20,000.
Preferably the hydrophobically modified poly(acetal- or ketal-polyethers) used in the present invention are those wherein the hydrophobic groups comprise alkyl and alkenyl groups having 8 to 22 carbon atoms and aryl, arylalkyl, arylalkenyl, cycloaliphatic and polycyclyl groups having 6 to 29 carbon atoms and most preferably wherein such alkyl and alkenyl groups have 12 to 18 carbon atoms and the aryl, arylalkyl, arylalkenyl, cyloaliphatic and polycyclyl groups have 14 to 25 carbon atoms.
The water-soluble polymer to be used in the aqueous suspension of the present invention can be prepared, as disclosed in U.S. Pat. No. 5,574,127, by copolymerizing an alpha, omega-diol, -dithiol or -diamino polyether with a gem-dihalide compound in the presence of a base to from an alpha, omega-diol, -dithiol or diamino poly(acetal- or ketal-polyether) which in turn is reacted with hydrophobic reagents to form the final product. Other paint thickeners such as hydroxyethylcellulose or hydrophobically-modified hydroxyethycellulose can be co-suspended with the poly(acetal- or ketal-polyether)to form a multi-thickener system in a single liquid carrier useful as a rheological modifier additive for latex paint.
In addition to or instead of the hydrophobically modified poly(acetal- or ketal-polyethers) discussed above hydrophobically modified polyether-polyurethanes as described in U.S. Pat. Nos. 4,079,028, 4,155,892, 4,496,708, 4,426,485, 4,499,233, 5,023,309 and 5,281,654, and hydrophobically modified polyether-polyurethanes bearing terminal hydrophilic groups as described in PCT International WO 96/40820, and hydrophobically modified polyether-polyols as described in U.S. Pat. Nos. 4,288,639, 4,354,956, 4,904,466, and hydrophobically modified polyacrylates U.S. Pat. Nos. 4,514,552, 4,421,902, 4,423,199, 4,429,097, 4,663,385, 4,008,202, 4,384,096, and 5,342,883 and hydrophobically modified polyacrylamide as described in U.S. Pat. Nos.4,425,469, 4,432,881, 4,463,151, 4,463,152, and 4,722,962, and hydrophobically modified aminoplast-polyethers as described in PCT International WO 96/40625 and WO 96/40185), can also be used to make the aqueous suspensions of the present invention. The disclosure of these patents are hereby incorporated by reference. Hydrophobically modified polyurethane thickeners are low molecular weight polyether-polyurethane bearing hydrophobes. They are made by condensing relatively low molecular weight polyethylene glycol (molecular weight up to about 10,000) with hydrophobic diisocyanates and end-capping the resulting copolymers with hydrophobic alcohols or amines. They are characterized by having three or more hydrophobesxe2x80x94two of which are terminal and the remainder are internal. The hydrophobic groups are connected to the hydrophilic polyethylene oxide blocks through urethane linkages.
In another class of hydrophobically modified polyurethanes, disclosed in U.S. Pat. No 4,327,008, the hydrophobes have branched structure. They are made by reacting polyalkylene oxides with a polyfunctional material, a diisocyanate, and water and end-capping the resulting product with a hydrophobic monofunctional active hydrogen-containing compound or a monoisocyanate.
Hydrophobically modified polyacrylates are alkali-soluble hydrophobically modified polyacrylates. They are made by copolymerizing a mixture of acrylic monomers with a small amount of a hydrophobic co-monomer.
Salts suitable for use in the present invention are water-soluble, carbon containing salts selected from the group consisting of sodium and potassium salts of aliphatic and aromatic carboxylic acids and sodium and potassium carbonate. As used in the present application the term xe2x80x9cwater-solublexe2x80x9d regarding suitable carbon containing salts means that such salts are sufficiently soluble in water to result in a concentration of at least 10% of salt based on the weight of the solution. Such salts include, for example, sodium formate, sodium acetate, sodium benzoate, sodium carbonate as well as the potassium analogues thereof. In addition, polymeric species with carboxylic functionality, such as polyacrylate salts which are employed for pigment dispersion can also be used in the present invention. The preferred carboxylic salts are the sodium and potassium salts of carboxylic acids having from 1 to 6 carbon atoms and sodium and potassium carbonate. Most preferred salts are sodium and potassium formate, especially sodium formate.
The above carbon containing salts can also be used in conjunction with other water-soluble non-carbon containing electrolytes for preparing the aqueous suspensions of the present invention. Other water-soluble non-carbon containing electrolytes include, among others for example, sodium, potassium and ammonium chloride, bromide, sulfate, phosphate, borate, nitrate and hydroxide. When employed, generally the ratio of water-soluble non-carbon electrolytes to carbon containing salt is up to about 1:1, preferably, up to about 0.5:1 and most preferably up to about 0.25:1.
The lower limit of the amount of polymer in the aqueous suspension can be about 5% by weight, preferably about 15% and most preferably about 20%. The upper limit of the amount of polymer can be about 40% by weight, preferably about 30% and most preferably about 25%. The lower limit of the amount of carbon containing salt, such as sodium formate, in the aqueous suspension can generally be about 10% by weight, preferably 20% and most preferably 25%. The upper limit of the amount of carbon containing salt can be 45% by weight, preferably 40% and most preferably 35%. Particularly good results are obtained at about 30% by weight. The lower limit of the amount of water can be about 40% by weight, preferably 45% and most preferably 50%. The upper limit of the amount of water can be about 85% by weight, preferably 65% and most preferably 55%.
If desired, a stabilizer can also be used in the aqueous suspensions of the present invention. Examples of suitable stabilizers are xanthan gum, sodium carboxymethyl cellulose, bentonite clays and carrageenan. Preferred stabilizers are xanthan gum and carrageenan, and the most preferred, stabilizer is xanthan gum. The amount of stabilizer can be from 0 to about 1% based on the weight of the aqueous suspension, preferably from about 0.2 to about 0.4% and most preferably from about 0.2 to about 0.3%.
Optionally a preservative can be employed in the aqueous suspensions of the present invention. Suitable preservatives, for example, are Kathon LX, 5-chloro-2-methyl-4-isothiazoline-3-one, (Rohm and Haas); Merbac-35, benzyl bromoacetate, (Calgon); Nuosept 95, bicyclic oxazolidines, (Hxc3xcls); Nuosept 101, 4,4-dimethyloxazolidine, (Hxc3xcls) and Proxel GXL, 1,2-benzisothiazoline-3-one, (ICI Americas). The amount of preservative can be from 0 to about 0.5% based on the weight of the aqueous suspension, preferably from about 0.05 to about 0.2 and most preferably from about 0.1 to about 0.15%.
The aqueous fluid suspension of the present invention can be prepared by adding a blend of the carbon-containing salt and polymer to water and mixing the salt/polymer blend with the water. Alternatively the aqueous suspension can be made by adding a blend of carbon containing salt, polymer and a stabilizer to water and admixing the salt/polymer/stabilizer blend with the water. The aqueous suspension can also be made by dissolving a stabilizer in water and adding a blend of carbon-containing salt and polymer to and admixing it with the stabilizer solution.
The aqueous suspension of the present invention can also be prepared by simply dissolving the carbon containing salt, such as sodium formate, in water and adding the polymer to and mixing it with the salt solution. As mentioned, a stabilizer can advantageously be employed in the aqueous suspensions of the present invention. The stabilizer can be added anytime, i.e., before the carbon containing salt is dissolved or after the carbon containing salt is dissolved or even after the polymer has been added to the aqueous solution of the carbon containing salt. Preferably the stabilizer is added before the carbon containing salt is dissolved, especially when the carbon containing salt has a tendency to inhibit the dissolution of the stabilizer.
When it is desired to employ a preservative it can be added at any time during the process of preparing the aqueous suspensions of the present invention.
In one embodiment of the present invention the water-soluble polymer is added in fine particulate powder form.
The aqueous suspensions of the present invention can be used for thickening aqueous systems, such as latex paints, sizing systems, adhesives, cosmetics, pharmaceuticals, joint compounds, latices, oil well drilling muds, cementitious systems, paper coatings and mineral slurries. The aqueous suspensions of the present invention can be used by themselves for thickening or they can be used in combination with one or more other thickeners, such as hydroxyethlycellulose and ethylhydroxyethylcellulose, hydrophobically modified hydroxyethylcellulose, hydrophobically modified ethylhydroxyethylcellulose, methylhydroxypropyl cellulose, ethylhydroxyethyl cellulose, carboxymethylcellulose, polyvinyl alcohol, polyurethanes, polyacrylates, polyacrylamides, guar, guar derivatives, clays and alkali-soluble poly-acrylates.
The present invention is illustrated in the following examples, wherein all parts are by weight unless otherwise indicated. These examples are given merely by way of illustration and are not intended to limit the invention as set forth in the claims.