CA2116927C - Method for improving thickeners for aqueous systems - Google Patents
Method for improving thickeners for aqueous systems Download PDFInfo
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- CA2116927C CA2116927C CA002116927A CA2116927A CA2116927C CA 2116927 C CA2116927 C CA 2116927C CA 002116927 A CA002116927 A CA 002116927A CA 2116927 A CA2116927 A CA 2116927A CA 2116927 C CA2116927 C CA 2116927C
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- Prior art keywords
- cyclodextrin
- thickener
- beta
- methyl
- viscosity
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L5/00—Compositions of polysaccharides or of their derivatives not provided for in groups C08L1/00 or C08L3/00
- C08L5/16—Cyclodextrin; Derivatives thereof
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
- C09D7/40—Additives
- C09D7/43—Thickening agents
Abstract
An improved method is provided for reversibly suppressing the viscosity of an aqueous solution containing a hydrophobically-modified thickener by first complexing the hydrophobic moieties on the thickener with a methyl-.beta.-cyclodextrin and then decomplexing the methyl-.beta.-cyclodextrin from the thickener once the aqueous solution containing the thickener is added to the aqueous system which is intended to thicken.
Description
METHOD FOR IMPROVING THICKENERS FOR AQUEOUS
SYSTEMS
FIELD OF THE INVENTION
This invention relates to a method for improving thickeners for aqueous systems by eliminating the need for organic cosolvents. More particularly, the invention relates to a method of using a methyl-~i-cyclodextrin to reversibly complex the hydrophobic moieties on hydrophobically-modified thickener molecules to suppress the viscosity of the aqueous solutions containing such thickeners.
BACKGROUND OF THE INVENTION
Aqueous systems, such as for example coatings containing emulsion polymer binders, typically employ thickeners to obtain the desired degree of viscosity needed for the proper formulation and application of the aqueous system. One general type of thickener used in aqueous systems is referred to in the art by the term "associative."
Associative thickeners are so called because the mechanism by which they thicken is believed to involve hydrophobic associations between the hydrophobic moieties on the. thickener molecules themselves and/or with other hydrophobic surfaces. A number of different types of associative thickeners are known including, but not limited to hydrophobically-modified polyurethanes, hydrophobically-modified alkali soluble emulsions, hydrophobically-modified hydroxyethyl cellulose or other hydrophobically-modified natural products, and hydrophobically modified polyacrylamides.
211692'7 Certain of these associative thickeners, such as for example the hydrophobically-modified polyurethane thickeners, are sold as aqueous solutions containing organic cosolvents. The function of the organic cosolvent, such as for example propylene glycol and butyl carbital, is to suppress the viscosity of the aqueous solution containing the associative thickener to allow for ease in its handling before its use as a thickener. While these organic cosolvents perform their intended function, they possess potential environmental, safety and health disadvantages. Viscosity suppression may also be accomplished by the use of surfactants. While this presents no specific health/environmental hazard, it does degrade paint performance.
U.S. Patent 5,137,571 to Eisenhart et al. discloses a method for reversibly complexing a cyclodextrin compound with the hydrophobic moieties on a hydrophobically modified thickener to suppress the viscosity of the aqueous solution containing the thickener so that such solutions can be easily handled and then decomplexing the cyclodeXtrin compound from the thickener to permit the thickener to perform its intended function. Eisenhart et al. disclose that a, Vii, and 'y cyclodextrins can be used effectively to suppress the viscosity of the aqueous solutions of hydrophobically-modified thickeners. They also disclose that hydroxyethyl- and hydroxypropyl-cyclodextrins are preferred to the unmodified versions of cyclodextrin.
We unexpectedly have found the methyl-~3-cyclodextrin, a modified version of cyclodextrin which was not commericially available until about May 1992 gives superior viscosity suppression as compared to the preferred commericially-available hydroxyethyl 2Z169~'~
cyclodextrin and even as compared to the most preferred commericially-available hydroxypropyl cyclodextrin.
SUMMARY OF THE INVENTION
This invention is directed to an improved.method for reversibly suppressing the viscosity of an aqueous solution containing a hydrophobically-modified thickener by first complexing the hydrophobic moieties on the thickener with a methyl-(i-cyclodextrin and then decomplexing the methyl-~i-cyclodextrin from the thickener once the aqueous solution containing the thickener is added to the aqueous system which is intended to thicken.
DETAILED DESCRIPTION OF THE INVENTION
Cyclodextrin compounds are cyclically-closed oligosaccharides with 6, 7 or 8 a-D-glucoses per macrocycle. The six glucose ring cyclodextrin compound is referred to as an a-cyclodextrin; the 7 glucose ring cyclodextrin compound is referred to as a (3-cyclodextrin, and the 8 glucose ring cyclodextrin compound is referred to as a ~cyclodextrin.
Cyclodextrins are produced from starch of any selected plant variety, such as corn, potato, waxy maize, and the like. The starch may be modified or unmoc.'.ified, derived from cereal or tuber origin and the amylose or amylopectin fractions thereof. The selected starch in the form of an aqueous slurry, at concentrations up to about 35% by weight solids, is usually liquefied, by gelatination or by treatment with a liquefying enzyme such as bacterial a-amylase enzyme, and then subjected to treatment with a transglycosylate enzyme to form the 2~is~~7 cyclodextrins. The amount of individual a, (3 and y cyclodextrins will vary depending on the selected starch, selected transglycolase enzyme and processing conditions. Precipitation and separation of the individual cyclodextrins is described in the literature using solvent systems, inclusion compounds such as trichloroethylene and non-solvent systems utilizing selected ion exchange resins. ~i-cyclodextrin is the most widely used form and is known for use in the production of pharamaceuticals and foods.
The ability of cyclodextrins to form inclusion complexes with organic compounds and thereby increase the water solubility of the organic compound is known. In "Cyclodextrins ' Increase Surface Tension and Critical Micelle Concentrations of Detergent Solutions" by W. Saenger and A. Muller-Fahrnow, Agnew. Chem. Int. Ed. Egl 27 (1988) No. 3 at pages 393-394, the authors discuss the ability of the central hydrophobic cavity of the cyclodextrin compounds to accommodate the hydrophobic, aliphatic part of a detergent molecule having a diameter of about 5 Angstroms. Studies with such detergents showed that the cyclodextrins were capable of increasing the surface tension of the detergent molecule and shifting the critical micelle concentration of the detergent to a higher value, thus making the detergent more soluble in water. This was suggested as being beneficial in cases where micelles need to be destroyed or where surface tension needs to be increased, as for example to avoid foaming.
U.K. Patent Application 2,189,245A entitled "Producing Modified Cyclodextrins," published on October 21, 1987, and assigned to American Maize Products Company discloses a method for increasing the water solubility of cyclodextrins. This method involves modification with alkylene carbonates and preferably ethylene carbonate to form hydroxyethyl ethers on the ring structure.
Because cyctodextrin compounds absorb onto or form complexes with hydrophobic species, they can be 'absorbed onto the hydrophobic moieties of associative thickeners. The absorption of cyclodextrin compounds onto the hydrophobic moieties of associative thickeners causes a suppression of the viscosity of an aqueous solution containing the associative thickener. Cyclodextrin compounds can be readily desorbed or decomplexed from the associative thickener by the addition of another material which has an affinity for the cyclodextrin.
The water solubility limit of methyl-(i-cyclodextrin is about 80 grams per 100 grams of water. This limits the concentration of methyl-~-cyclodextrin which can be employed to suppress the viscosity of an aqueous solution containing an associative thickener. Since the viscosity of an aqueous solution containing an associative thickener increases with the concentration of the associative thickener solids, the solubility limit of the methyl-~i-cyclodextrin determines the maximum amount which can be added to the solution without resulting in the formation of undesirable solids. If the maximum concentration of the methyl-[3-cyclodextrin needed to reduce the viscosity of an aqueous solution containing an associative thickener to a handleable viscosity, such as for example a viscosity of about 2,000 centipoises, exceeds the solubility limit of the methyl-~3-cyclodextrin in water, then the methyl-~i-cyclodextrin is not effective as a viscosity suppressant additive. In other words, the effectiveness of the methyl-(3-cyclodextrin as a viscosity suppressing additive is a function of the solubility limit of the methyl-(3-cyclodextrin and the solids content of the associative thickener in the aqueous solution. The higher the solids content of the associative thickener the higher the viscosity of the aqueous solution containing it will be, and likewise the higher the concentration of the cyclodextrin which will be needed to be added to suppress the viscosity down to a level where it easily flows.
Applicants have found that the use of methyl-(i-cyclodextrin is useful in latex paint formulation for achieving a variety of effects, such as for example:
~ to permit the preparation and supply of a low viscosity, high solids solution of the thickener without the use of viscosity suppressing solvent;
~ to ease incorporating hydrophobically modified, associative thickeners, having marginal solubility in water, into aqueous systems;
~ to reduce the viscosity drop of assoaative thickener containing formulations upon the addition of colorants or surfactants to the formulation;
~ to improve the efficiency of the associative thickener itself, thus reducing the thickener required to reach a given paint viscosity;
~ to reduce foaming in a paint, with or without an associative thickener, which is especially desirable when the paint is to be applied by a roller; and ~ to reduce the color development problems caused by surfactants in some formulations.
The ability to decomplex the methyl-~i-cyclodextrin from the hydrophobic associative thickener is just as important as the ability of 211~'9?'~
the methyl-~i-cyclodextrin to absorb or complex with the associative thickener in the first instance. It is critical for the thickener to perform its intended viscosity increasing function in the aqueous system to which the associative thickener solution is added that the cyclodextrin becomes decomplexed or desorbed from the hydrophobic moieties on the associative thickener molecule. We have found that methyl-~i-cyclodextrin is readily desorbed or decomplexed from hydrophobic associative thickeners simply by the addition of a material which has an affinity for the cyclodextrin. In this regard, we have found that conventional surface active agents commonly present in aqueous coating systems including, anionic surfactants such as sodium lauryl sulfate, nonionic surfactants such as IGEPAL~ CO-660 (a 10 mole ethoxylate of nonyl phenol), and cationic surfactants, may be used to decomplex or desorb the cyclodextrin. Other water soluble organic solvents sueh as for example ethanol and TEXANOLc9 solvent may also be employed for this purpose but are not preferred. We have found that it is preferred to utilize about one mole of the decomplexing agent per mole of the methyl-~i-cyclodextrin added to the associative thickener solution to achieve complete desorption or decomplexation.
Both the complexation and decomplexation mechanisms are easily achieved by the addition of the reactants with mixing. No special purification or separation steps are required at room temperature. In our work, it was not necessary to add additional surfactant to cause this decomplexation process to occur; the formulation surfactants already present in the paint have been found to be sufficient.
The surfactant complexing effect of the cyclodextrins are also of benefit to the formulator far other properties than theological modification. Typically when formulating tinted paints, the composition of the formulation, specifically the surfactants, must be modified to maintain the stability of the colorant dispersion while not adversely affecting the dispersion of the other components. In some formulations, the paint components, such as the latex vehicle, bring an incompatible surfactant into the formulation. To correct for this, additional surfactants are added to the formulation to compatibilize the system. While effective in compatibilizing the system, these surfactants can contribute adverse water sensitivity and foaming characteristics to the formulation. Methyl-(i-cyclodextrin is useful in improving the compatibility of a colorant without adding additional surfactants.
The following examples are intended to illustrate the invention and are not intended nor should they be interpreted as limiting the scope of the invention since modifications to the process illustrated are considered to be obvious to one of ordinary skill in the art.
EXAMPLE 1. THICKENERS IN WATER
The methyl-~i-cyclodextrin was tested to demonstrate that it suppressed the viscosity of an hydrophobically modified thickener in water better than preferred commericially-available hydroxyethyI
cyclodextrin and most preferred commericially-available hydroxypropyl cyclodextrin.
4.9 grams of each cyclodextrin material were mixed with 77.6 grams of water and then I7.5 grams of ACRYSOL~ RM-8 solid grade hydrophobically modified polyurethane thickener was added and mixed. The low shear viscosity of the resultant mixture was measured using an Brookfield viscometer. The results are reported in Table 1.1 in centipoises.
Table 1.1 Viscosity (centipoises) Methyl-~i-ryclodextrin 802 (blacker) COMPAIZATI~JES
Hydroxypropyl-a-cydodextrin19,200 HP 0.6 (blacker) Hydroxypropyl-(i-cydodextrin5,240 HP 0.9 (blacker) Hydroxypropyl-(i-cydodextrin2,820 (American Maize) Hydroxypropyl-y-eyclodextrin> 100,000 HP 0.6 (blacker) EXAMPLE 2. THICKENERS IN PAINT FORMULATIONS
Paints with hydrophobically modified thickener complexed with cyclodextrin materials were formulated to demonstrate that the methyl-~i-cyclodextrin does not adversely affect the other properties of the paint formulation as compared to the other cyclodextrin materials.
The ingredients in Table 2.1 (in grams were used to formulate the paints. In a container, the grind ingredients were first mixed together at high speed with Cowles dissolver and then the letdown ingredients were added and mixed at a low speed. In a separate container, the cyclodextrin material and appropriate water portion were mixed together and then the thickener was added and mixed until homogeneous. The ~ complexed thickener mixture was then added to the grind and letdown mixture.
The anionic surfactant present in the paint formulations was sufficient to decomplex the cyclodextrin materials from the thickener.
Therefore, no additional surfactant needed to be added to the formulations.
z~~s~2~
Table 2.1 Iagredimt Paint PaintPaintPaint PaintPaint 6Y
I 2' 3' 4' 5' Water 45.00 45.0045.0045.00 45.0045.00 Cwlmoentt (propylene70.00 70.00T0.0070.00 ?0.0070.00 glycoU
fHaperaant (Tamol491235 12351235 12.35 1235 12.35 SG-1) (3594) AndformingagentL00 1.001.00 1.00 1.00 1.00 fFoattusoer VL) Tinnium dioxide209.99209.99209.99209.99209.99209.99 fTbPuram R-900) Factattda (A5PI70)88.02 88.0288.0288.02 88.0288.02 Water 116.70116.70116,70116.70116.70116.70 Acrylic latex 378.00378.00378.00378.00378.00378.00 mtubkm (Rhoplaxm AC-264) (60596 aolids>
Caahxmt Cfaxand)11A3 11.4311.4311A3 11.4311.43 (2.ZAtricrothyl-3hydtoxypetttyl acenn) Mti(oamlngagent3.00 3.003.00 3.00 3.00 3.00 (FoamaseerVL) HydeopirobinUy 1.67 1.711.66 13B 133 1.68 modified Pdyurethane Thickata (100% solids) Water 13258 132.2713233132.69132.7613152 ~l~lf~fEillO.(:<9~.r~
Mahyl-~.~ydodextrinOA1 - - - - -(Wscker) Hydmxyp~n-cydodaxtrin- OAB.. _ _ ( acka) Hydroxypropylp~yclodaxtrin - OA7 _ _ _ I Wackw) Hydroxyprapyl.p.cyelodexmn- _ _ p~
(Amnion Main HydroxypmpyI-ycydodaxmn_ _ _ _ p37 (Wacka) Butyl urbitol , - 1.26 'Compsrstives YContrd (no cydodextrm prewxad with dtiekenr) 1~
~1169~7 EXAMPLE 3. TESTING OF THICKENERS IN PAINT FORMULATIONS
Several tests were performed to demonstrate that while the method of the present invention gives superior viscosity suppression as compared to other cydodextrin materials, the method of the present invention does not detrimentally affect other properties of the paint formulation.
The efficiency of the thickener which had been complexed with a cyclodextrin material was measured by determining the amount of dry pounds of thickener that was required to thicken 100 gallons of the paint formulation to about a targeted 95 Krebs Uruts stormer viscosity.
The effiaency data are reported in Table 3.1 in dry pounds.
The high shear viscosity of the paints were measured using an ICI Viscometer. The viscosity measurements are reported in Table 3.1 in poise.
The flow and leveling of each paint were determined. Each paint was applied to a separate Leneta sealed 12H chart at 25°C and positioned horizontally to dry overnight. The dried charts were compared to reference standards in a Leneta Level-Luminator. The flow and leveling results are reported in Table 3.1 as the number of the 211692' reference standard which most nearly matched the appearance of each paint.
The sag of each paint was determined. Each paint was applied with a drawdown bar to a separate Leneta sealed 12H chart having a water-soluble ink line (drawn perpendicular to the length of the chart) at 25°C and hung vertically to dry overnight. The dried charts were rated by the highest thickeners (measured in mils) at which the paint sagged beyond the water-soluble ink line by less than 0.5 centimeter.
The sag results are reported in Table 3.1.
GLOSS (60 ° and 85 °l The gloss of each paint was measured. Each paint was drawndown on a Leneta 5C chart with a 3 mil Bird film applicator and dried at constant temperature and humidity for 7 days. The gloss of each paint was measured on a Hunter Glossmeter at 60° and B5°, according to ASTM D-523-89 Test Method. The gloss results are reported in Table 3.1.
The stability of each paint was measured before and after the addition of 2 ounces/gallon of Lamp Black colorant with a Krebs-stormer viscometer. The viscosity results and the delta values are reported in Table 3.1.
211fi92r~
The stability of each paint was measured before and after heat aging at 140°F for 10 days with a Krebs-stormer viscometer. The viscosity results and the delta values are reported in Table 3.1.
Table 3.1 PaW I Paint 2' Palst 3~ Paint 4~ Pdat 5~ Palst 41!
1.38 1.71 1.66 1.33 1.47 1.68 ~n P(i~~ P
SoeVLoo~IKIn 93 96 96 96 96 96 ICIVYooafl7(poiW0.6 0.6 0.7 0.6 0.6 0.6 Leseb flow 9 9 9 9 9 9 Lade San 8 8 B 8 8 8 es se e6 se a7 e6 ea Lw.ISto~vno~.it~.tKNIm Ion Ian Io6 w6 Io6 Pi..l Sar..r eo e3 s3 e3 e3 s3 vroo.ur tKLn DakaIKIJ) -21 -2.1 -i1 -Z3 -23 -23 btrtAitS11441IitiC
IddalSlomtarVbraalfrlKU1101 106 t06 106 106 106 Flttal Slotatrr109 110 109 110 114 118 Vltooaky DskatKUl +8 +4 +3 +4 +8 +12 'C;omParativea YControl ino ryelad~xerm Prawxed with thiekenr)
SYSTEMS
FIELD OF THE INVENTION
This invention relates to a method for improving thickeners for aqueous systems by eliminating the need for organic cosolvents. More particularly, the invention relates to a method of using a methyl-~i-cyclodextrin to reversibly complex the hydrophobic moieties on hydrophobically-modified thickener molecules to suppress the viscosity of the aqueous solutions containing such thickeners.
BACKGROUND OF THE INVENTION
Aqueous systems, such as for example coatings containing emulsion polymer binders, typically employ thickeners to obtain the desired degree of viscosity needed for the proper formulation and application of the aqueous system. One general type of thickener used in aqueous systems is referred to in the art by the term "associative."
Associative thickeners are so called because the mechanism by which they thicken is believed to involve hydrophobic associations between the hydrophobic moieties on the. thickener molecules themselves and/or with other hydrophobic surfaces. A number of different types of associative thickeners are known including, but not limited to hydrophobically-modified polyurethanes, hydrophobically-modified alkali soluble emulsions, hydrophobically-modified hydroxyethyl cellulose or other hydrophobically-modified natural products, and hydrophobically modified polyacrylamides.
211692'7 Certain of these associative thickeners, such as for example the hydrophobically-modified polyurethane thickeners, are sold as aqueous solutions containing organic cosolvents. The function of the organic cosolvent, such as for example propylene glycol and butyl carbital, is to suppress the viscosity of the aqueous solution containing the associative thickener to allow for ease in its handling before its use as a thickener. While these organic cosolvents perform their intended function, they possess potential environmental, safety and health disadvantages. Viscosity suppression may also be accomplished by the use of surfactants. While this presents no specific health/environmental hazard, it does degrade paint performance.
U.S. Patent 5,137,571 to Eisenhart et al. discloses a method for reversibly complexing a cyclodextrin compound with the hydrophobic moieties on a hydrophobically modified thickener to suppress the viscosity of the aqueous solution containing the thickener so that such solutions can be easily handled and then decomplexing the cyclodeXtrin compound from the thickener to permit the thickener to perform its intended function. Eisenhart et al. disclose that a, Vii, and 'y cyclodextrins can be used effectively to suppress the viscosity of the aqueous solutions of hydrophobically-modified thickeners. They also disclose that hydroxyethyl- and hydroxypropyl-cyclodextrins are preferred to the unmodified versions of cyclodextrin.
We unexpectedly have found the methyl-~3-cyclodextrin, a modified version of cyclodextrin which was not commericially available until about May 1992 gives superior viscosity suppression as compared to the preferred commericially-available hydroxyethyl 2Z169~'~
cyclodextrin and even as compared to the most preferred commericially-available hydroxypropyl cyclodextrin.
SUMMARY OF THE INVENTION
This invention is directed to an improved.method for reversibly suppressing the viscosity of an aqueous solution containing a hydrophobically-modified thickener by first complexing the hydrophobic moieties on the thickener with a methyl-(i-cyclodextrin and then decomplexing the methyl-~i-cyclodextrin from the thickener once the aqueous solution containing the thickener is added to the aqueous system which is intended to thicken.
DETAILED DESCRIPTION OF THE INVENTION
Cyclodextrin compounds are cyclically-closed oligosaccharides with 6, 7 or 8 a-D-glucoses per macrocycle. The six glucose ring cyclodextrin compound is referred to as an a-cyclodextrin; the 7 glucose ring cyclodextrin compound is referred to as a (3-cyclodextrin, and the 8 glucose ring cyclodextrin compound is referred to as a ~cyclodextrin.
Cyclodextrins are produced from starch of any selected plant variety, such as corn, potato, waxy maize, and the like. The starch may be modified or unmoc.'.ified, derived from cereal or tuber origin and the amylose or amylopectin fractions thereof. The selected starch in the form of an aqueous slurry, at concentrations up to about 35% by weight solids, is usually liquefied, by gelatination or by treatment with a liquefying enzyme such as bacterial a-amylase enzyme, and then subjected to treatment with a transglycosylate enzyme to form the 2~is~~7 cyclodextrins. The amount of individual a, (3 and y cyclodextrins will vary depending on the selected starch, selected transglycolase enzyme and processing conditions. Precipitation and separation of the individual cyclodextrins is described in the literature using solvent systems, inclusion compounds such as trichloroethylene and non-solvent systems utilizing selected ion exchange resins. ~i-cyclodextrin is the most widely used form and is known for use in the production of pharamaceuticals and foods.
The ability of cyclodextrins to form inclusion complexes with organic compounds and thereby increase the water solubility of the organic compound is known. In "Cyclodextrins ' Increase Surface Tension and Critical Micelle Concentrations of Detergent Solutions" by W. Saenger and A. Muller-Fahrnow, Agnew. Chem. Int. Ed. Egl 27 (1988) No. 3 at pages 393-394, the authors discuss the ability of the central hydrophobic cavity of the cyclodextrin compounds to accommodate the hydrophobic, aliphatic part of a detergent molecule having a diameter of about 5 Angstroms. Studies with such detergents showed that the cyclodextrins were capable of increasing the surface tension of the detergent molecule and shifting the critical micelle concentration of the detergent to a higher value, thus making the detergent more soluble in water. This was suggested as being beneficial in cases where micelles need to be destroyed or where surface tension needs to be increased, as for example to avoid foaming.
U.K. Patent Application 2,189,245A entitled "Producing Modified Cyclodextrins," published on October 21, 1987, and assigned to American Maize Products Company discloses a method for increasing the water solubility of cyclodextrins. This method involves modification with alkylene carbonates and preferably ethylene carbonate to form hydroxyethyl ethers on the ring structure.
Because cyctodextrin compounds absorb onto or form complexes with hydrophobic species, they can be 'absorbed onto the hydrophobic moieties of associative thickeners. The absorption of cyclodextrin compounds onto the hydrophobic moieties of associative thickeners causes a suppression of the viscosity of an aqueous solution containing the associative thickener. Cyclodextrin compounds can be readily desorbed or decomplexed from the associative thickener by the addition of another material which has an affinity for the cyclodextrin.
The water solubility limit of methyl-(i-cyclodextrin is about 80 grams per 100 grams of water. This limits the concentration of methyl-~-cyclodextrin which can be employed to suppress the viscosity of an aqueous solution containing an associative thickener. Since the viscosity of an aqueous solution containing an associative thickener increases with the concentration of the associative thickener solids, the solubility limit of the methyl-~i-cyclodextrin determines the maximum amount which can be added to the solution without resulting in the formation of undesirable solids. If the maximum concentration of the methyl-[3-cyclodextrin needed to reduce the viscosity of an aqueous solution containing an associative thickener to a handleable viscosity, such as for example a viscosity of about 2,000 centipoises, exceeds the solubility limit of the methyl-~3-cyclodextrin in water, then the methyl-~i-cyclodextrin is not effective as a viscosity suppressant additive. In other words, the effectiveness of the methyl-(3-cyclodextrin as a viscosity suppressing additive is a function of the solubility limit of the methyl-(3-cyclodextrin and the solids content of the associative thickener in the aqueous solution. The higher the solids content of the associative thickener the higher the viscosity of the aqueous solution containing it will be, and likewise the higher the concentration of the cyclodextrin which will be needed to be added to suppress the viscosity down to a level where it easily flows.
Applicants have found that the use of methyl-(i-cyclodextrin is useful in latex paint formulation for achieving a variety of effects, such as for example:
~ to permit the preparation and supply of a low viscosity, high solids solution of the thickener without the use of viscosity suppressing solvent;
~ to ease incorporating hydrophobically modified, associative thickeners, having marginal solubility in water, into aqueous systems;
~ to reduce the viscosity drop of assoaative thickener containing formulations upon the addition of colorants or surfactants to the formulation;
~ to improve the efficiency of the associative thickener itself, thus reducing the thickener required to reach a given paint viscosity;
~ to reduce foaming in a paint, with or without an associative thickener, which is especially desirable when the paint is to be applied by a roller; and ~ to reduce the color development problems caused by surfactants in some formulations.
The ability to decomplex the methyl-~i-cyclodextrin from the hydrophobic associative thickener is just as important as the ability of 211~'9?'~
the methyl-~i-cyclodextrin to absorb or complex with the associative thickener in the first instance. It is critical for the thickener to perform its intended viscosity increasing function in the aqueous system to which the associative thickener solution is added that the cyclodextrin becomes decomplexed or desorbed from the hydrophobic moieties on the associative thickener molecule. We have found that methyl-~i-cyclodextrin is readily desorbed or decomplexed from hydrophobic associative thickeners simply by the addition of a material which has an affinity for the cyclodextrin. In this regard, we have found that conventional surface active agents commonly present in aqueous coating systems including, anionic surfactants such as sodium lauryl sulfate, nonionic surfactants such as IGEPAL~ CO-660 (a 10 mole ethoxylate of nonyl phenol), and cationic surfactants, may be used to decomplex or desorb the cyclodextrin. Other water soluble organic solvents sueh as for example ethanol and TEXANOLc9 solvent may also be employed for this purpose but are not preferred. We have found that it is preferred to utilize about one mole of the decomplexing agent per mole of the methyl-~i-cyclodextrin added to the associative thickener solution to achieve complete desorption or decomplexation.
Both the complexation and decomplexation mechanisms are easily achieved by the addition of the reactants with mixing. No special purification or separation steps are required at room temperature. In our work, it was not necessary to add additional surfactant to cause this decomplexation process to occur; the formulation surfactants already present in the paint have been found to be sufficient.
The surfactant complexing effect of the cyclodextrins are also of benefit to the formulator far other properties than theological modification. Typically when formulating tinted paints, the composition of the formulation, specifically the surfactants, must be modified to maintain the stability of the colorant dispersion while not adversely affecting the dispersion of the other components. In some formulations, the paint components, such as the latex vehicle, bring an incompatible surfactant into the formulation. To correct for this, additional surfactants are added to the formulation to compatibilize the system. While effective in compatibilizing the system, these surfactants can contribute adverse water sensitivity and foaming characteristics to the formulation. Methyl-(i-cyclodextrin is useful in improving the compatibility of a colorant without adding additional surfactants.
The following examples are intended to illustrate the invention and are not intended nor should they be interpreted as limiting the scope of the invention since modifications to the process illustrated are considered to be obvious to one of ordinary skill in the art.
EXAMPLE 1. THICKENERS IN WATER
The methyl-~i-cyclodextrin was tested to demonstrate that it suppressed the viscosity of an hydrophobically modified thickener in water better than preferred commericially-available hydroxyethyI
cyclodextrin and most preferred commericially-available hydroxypropyl cyclodextrin.
4.9 grams of each cyclodextrin material were mixed with 77.6 grams of water and then I7.5 grams of ACRYSOL~ RM-8 solid grade hydrophobically modified polyurethane thickener was added and mixed. The low shear viscosity of the resultant mixture was measured using an Brookfield viscometer. The results are reported in Table 1.1 in centipoises.
Table 1.1 Viscosity (centipoises) Methyl-~i-ryclodextrin 802 (blacker) COMPAIZATI~JES
Hydroxypropyl-a-cydodextrin19,200 HP 0.6 (blacker) Hydroxypropyl-(i-cydodextrin5,240 HP 0.9 (blacker) Hydroxypropyl-(i-cydodextrin2,820 (American Maize) Hydroxypropyl-y-eyclodextrin> 100,000 HP 0.6 (blacker) EXAMPLE 2. THICKENERS IN PAINT FORMULATIONS
Paints with hydrophobically modified thickener complexed with cyclodextrin materials were formulated to demonstrate that the methyl-~i-cyclodextrin does not adversely affect the other properties of the paint formulation as compared to the other cyclodextrin materials.
The ingredients in Table 2.1 (in grams were used to formulate the paints. In a container, the grind ingredients were first mixed together at high speed with Cowles dissolver and then the letdown ingredients were added and mixed at a low speed. In a separate container, the cyclodextrin material and appropriate water portion were mixed together and then the thickener was added and mixed until homogeneous. The ~ complexed thickener mixture was then added to the grind and letdown mixture.
The anionic surfactant present in the paint formulations was sufficient to decomplex the cyclodextrin materials from the thickener.
Therefore, no additional surfactant needed to be added to the formulations.
z~~s~2~
Table 2.1 Iagredimt Paint PaintPaintPaint PaintPaint 6Y
I 2' 3' 4' 5' Water 45.00 45.0045.0045.00 45.0045.00 Cwlmoentt (propylene70.00 70.00T0.0070.00 ?0.0070.00 glycoU
fHaperaant (Tamol491235 12351235 12.35 1235 12.35 SG-1) (3594) AndformingagentL00 1.001.00 1.00 1.00 1.00 fFoattusoer VL) Tinnium dioxide209.99209.99209.99209.99209.99209.99 fTbPuram R-900) Factattda (A5PI70)88.02 88.0288.0288.02 88.0288.02 Water 116.70116.70116,70116.70116.70116.70 Acrylic latex 378.00378.00378.00378.00378.00378.00 mtubkm (Rhoplaxm AC-264) (60596 aolids>
Caahxmt Cfaxand)11A3 11.4311.4311A3 11.4311.43 (2.ZAtricrothyl-3hydtoxypetttyl acenn) Mti(oamlngagent3.00 3.003.00 3.00 3.00 3.00 (FoamaseerVL) HydeopirobinUy 1.67 1.711.66 13B 133 1.68 modified Pdyurethane Thickata (100% solids) Water 13258 132.2713233132.69132.7613152 ~l~lf~fEillO.(:<9~.r~
Mahyl-~.~ydodextrinOA1 - - - - -(Wscker) Hydmxyp~n-cydodaxtrin- OAB.. _ _ ( acka) Hydroxypropylp~yclodaxtrin - OA7 _ _ _ I Wackw) Hydroxyprapyl.p.cyelodexmn- _ _ p~
(Amnion Main HydroxypmpyI-ycydodaxmn_ _ _ _ p37 (Wacka) Butyl urbitol , - 1.26 'Compsrstives YContrd (no cydodextrm prewxad with dtiekenr) 1~
~1169~7 EXAMPLE 3. TESTING OF THICKENERS IN PAINT FORMULATIONS
Several tests were performed to demonstrate that while the method of the present invention gives superior viscosity suppression as compared to other cydodextrin materials, the method of the present invention does not detrimentally affect other properties of the paint formulation.
The efficiency of the thickener which had been complexed with a cyclodextrin material was measured by determining the amount of dry pounds of thickener that was required to thicken 100 gallons of the paint formulation to about a targeted 95 Krebs Uruts stormer viscosity.
The effiaency data are reported in Table 3.1 in dry pounds.
The high shear viscosity of the paints were measured using an ICI Viscometer. The viscosity measurements are reported in Table 3.1 in poise.
The flow and leveling of each paint were determined. Each paint was applied to a separate Leneta sealed 12H chart at 25°C and positioned horizontally to dry overnight. The dried charts were compared to reference standards in a Leneta Level-Luminator. The flow and leveling results are reported in Table 3.1 as the number of the 211692' reference standard which most nearly matched the appearance of each paint.
The sag of each paint was determined. Each paint was applied with a drawdown bar to a separate Leneta sealed 12H chart having a water-soluble ink line (drawn perpendicular to the length of the chart) at 25°C and hung vertically to dry overnight. The dried charts were rated by the highest thickeners (measured in mils) at which the paint sagged beyond the water-soluble ink line by less than 0.5 centimeter.
The sag results are reported in Table 3.1.
GLOSS (60 ° and 85 °l The gloss of each paint was measured. Each paint was drawndown on a Leneta 5C chart with a 3 mil Bird film applicator and dried at constant temperature and humidity for 7 days. The gloss of each paint was measured on a Hunter Glossmeter at 60° and B5°, according to ASTM D-523-89 Test Method. The gloss results are reported in Table 3.1.
The stability of each paint was measured before and after the addition of 2 ounces/gallon of Lamp Black colorant with a Krebs-stormer viscometer. The viscosity results and the delta values are reported in Table 3.1.
211fi92r~
The stability of each paint was measured before and after heat aging at 140°F for 10 days with a Krebs-stormer viscometer. The viscosity results and the delta values are reported in Table 3.1.
Table 3.1 PaW I Paint 2' Palst 3~ Paint 4~ Pdat 5~ Palst 41!
1.38 1.71 1.66 1.33 1.47 1.68 ~n P(i~~ P
SoeVLoo~IKIn 93 96 96 96 96 96 ICIVYooafl7(poiW0.6 0.6 0.7 0.6 0.6 0.6 Leseb flow 9 9 9 9 9 9 Lade San 8 8 B 8 8 8 es se e6 se a7 e6 ea Lw.ISto~vno~.it~.tKNIm Ion Ian Io6 w6 Io6 Pi..l Sar..r eo e3 s3 e3 e3 s3 vroo.ur tKLn DakaIKIJ) -21 -2.1 -i1 -Z3 -23 -23 btrtAitS11441IitiC
IddalSlomtarVbraalfrlKU1101 106 t06 106 106 106 Flttal Slotatrr109 110 109 110 114 118 Vltooaky DskatKUl +8 +4 +3 +4 +8 +12 'C;omParativea YControl ino ryelad~xerm Prawxed with thiekenr)
Claims (8)
1. Use of methyl-.beta.-cyclodextrin as a .beta.-cyclodextrin having hydrophobic groups for reversibly suppressing the viscosity of an aqueous system containing a hydrophobically-modified thickener.
2. Use as claimed in claim 1, wherein the aqueous system is a paint.
3. A method for reversibly suppressing the viscosity of an aqueous solution containing a hydrophobically-modified thickener, the method comprising the steps of:
i) complexing the hydrophobic moieties on the thickener with a pre-determined amount of a .beta.-cyclodextrin having hydrophobic groups;
ii) adding the complexed thickener and .beta.-cyclodextrin to an aqueous system which is to be thickened; and iii) decomplexing or desorbing the .beta.-cyclodextrin from the thickener;
characterized in that the .beta.-cyclodextrin is methyl-.beta.-cyclodextrin.
i) complexing the hydrophobic moieties on the thickener with a pre-determined amount of a .beta.-cyclodextrin having hydrophobic groups;
ii) adding the complexed thickener and .beta.-cyclodextrin to an aqueous system which is to be thickened; and iii) decomplexing or desorbing the .beta.-cyclodextrin from the thickener;
characterized in that the .beta.-cyclodextrin is methyl-.beta.-cyclodextrin.
4. The method of claim 3, wherein the hydrophobic thickener is selected from the group consisting of hydrophobically modified polyethoxylated urethanes, hydrophobically modified alkali soluble emulsions, hydrophobically modified hydroxyethyl cellulose and hydrophobically modified polyacrylamides.
5. The method of claims 3 or 4, wherein the methyl-.beta.-cyclodextrin is decomplexed or desorbed from the thickener by addition of a pre-determined amount of an anionic, nonionic or cationic surfactant.
6. The method of claim 5, wherein the surfactant is added to the aqueous system at a concentration of one mole per mole of methyl-.beta.-cyclodextrin.
7. The method as claimed in claims 3, 4, 5 or 6, wherein the aqueous system is a paint.
8. A paint or other thickened aqueous system comprising hydrophobically-modified thickener and methyl-(.beta.-cyclodextrin having hydrophobic groups as a .beta.-cyclodextrin viscosity suppressant.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/030,757 US5376709A (en) | 1993-03-12 | 1993-03-12 | Method for improving thickeners for aqueous systems |
| US08/030,757 | 1993-03-12 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2116927A1 CA2116927A1 (en) | 1994-09-13 |
| CA2116927C true CA2116927C (en) | 2006-10-31 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002116927A Expired - Fee Related CA2116927C (en) | 1993-03-12 | 1994-03-03 | Method for improving thickeners for aqueous systems |
Country Status (25)
| Country | Link |
|---|---|
| US (1) | US5376709A (en) |
| EP (1) | EP0614950B1 (en) |
| JP (1) | JP3545802B2 (en) |
| KR (1) | KR100291523B1 (en) |
| CN (1) | CN1047603C (en) |
| AT (1) | ATE145418T1 (en) |
| AU (1) | AU663245B2 (en) |
| BR (1) | BR9401128A (en) |
| CA (1) | CA2116927C (en) |
| DE (1) | DE69400928T2 (en) |
| DK (1) | DK0614950T3 (en) |
| ES (1) | ES2095128T3 (en) |
| FI (1) | FI103346B1 (en) |
| GR (1) | GR3021749T3 (en) |
| HK (1) | HK122297A (en) |
| IL (1) | IL108802A (en) |
| MX (1) | MXPA94001702A (en) |
| MY (1) | MY113825A (en) |
| NO (1) | NO940782L (en) |
| NZ (1) | NZ260009A (en) |
| PH (1) | PH30128A (en) |
| RU (1) | RU2132344C1 (en) |
| SG (1) | SG67893A1 (en) |
| TW (1) | TW237465B (en) |
| ZA (1) | ZA941665B (en) |
Families Citing this family (28)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0384167B1 (en) | 1989-01-31 | 1994-07-06 | Union Carbide Chemicals And Plastics Company, Inc. | Polysaccharides with alkaryl or aralkyl hydrophobes and latex compositions containing same |
| US5425806B1 (en) * | 1994-05-12 | 1997-07-01 | Rheox Inc | Pourable water dispersible thickening composition for aqueous systems and a method of thickening said aqueous systems |
| US5504123A (en) * | 1994-12-20 | 1996-04-02 | Union Carbide Chemicals & Plastics Technology Corporation | Dual functional cellulosic additives for latex compositions |
| US6020407A (en) * | 1995-11-07 | 2000-02-01 | Rheox, Inc. | Super dispersable thickening composition for aqueous systems and a method of thickening said aqueous systems |
| TW494125B (en) * | 1997-07-11 | 2002-07-11 | Rohm And Haas Compary | Preparation of fluorinated polymers |
| MX200986B (en) * | 1997-07-29 | 2001-03-07 | Rohm & Haas | Solubilized hydrophobically-modified alkali-soluble emulsion polymers |
| US6337366B1 (en) * | 1999-03-25 | 2002-01-08 | Rohm And Haas | Method of improving viscosity stability of aqueous compositions |
| KR100822674B1 (en) | 2000-09-21 | 2008-04-17 | 롬 앤드 하스 캄파니 | Aqueous nanocomposite dispersions: processes, compositions, and uses thereof |
| EP1236777B1 (en) * | 2001-02-28 | 2005-11-30 | Rohm And Haas Company | Method of improving viscosity stability upon addition of an aqueous tinting composition |
| US6887928B2 (en) * | 2001-02-28 | 2005-05-03 | Rohm And Haas Company | Method of improving viscosity stability upon addition of a colorant component |
| US6812278B2 (en) | 2001-02-28 | 2004-11-02 | Rohm And Haas Company | Method of improving viscosity stability upon addition of an aqueous tinting composition |
| DE60208098T3 (en) * | 2001-02-28 | 2010-05-20 | Rohm And Haas Co. | Process for improving the viscosity stability after addition of a colorant component |
| US6809132B2 (en) * | 2001-10-29 | 2004-10-26 | Hercules Incorporated | Suppression of aqueous viscosity of associating polyacetal-polyethers |
| US7378479B2 (en) * | 2002-09-13 | 2008-05-27 | Lubrizol Advanced Materials, Inc. | Multi-purpose polymers, methods and compositions |
| US20040241130A1 (en) * | 2002-09-13 | 2004-12-02 | Krishnan Tamareselvy | Multi-purpose polymers, methods and compositions |
| DE60315103T2 (en) * | 2002-10-11 | 2008-04-10 | Rohm And Haas Co. | Process for improving the viscosity of thickeners for aqueous systems |
| DE10310175A1 (en) * | 2003-03-08 | 2004-09-16 | Süd-Chemie AG | Associative thickener preparation |
| US6900255B2 (en) * | 2003-05-16 | 2005-05-31 | Hercules Incorporated | Suppression of aqueous viscosity of nonionic associative thickeners |
| US7741401B2 (en) * | 2007-03-21 | 2010-06-22 | Rohm And Haas Company | Thickener blend composition and method for thickening aqueous systems |
| JP5536314B2 (en) * | 2008-05-20 | 2014-07-02 | 株式会社Ａｄｅｋａ | Viscosity adjusting agent composition, aqueous solution viscosity adjusting method and gel adjusting method using the same |
| US7868122B2 (en) * | 2008-06-19 | 2011-01-11 | Southern Clay Products, Inc. | Tint-viscosity stabilization polymeric thickeners |
| FR2976579B1 (en) * | 2011-06-14 | 2013-07-05 | Coatex Sas | NONIONIC ASSOCIATIVE THICKENERS CONTAINING ALKYLS CYCLOHEXYLOLS, FORMULATIONS CONTAINING SAME AND USES THEREOF |
| PL2736946T3 (en) * | 2011-07-28 | 2019-03-29 | Hercules Llc | Readily dissolvable solid nonionic synthetic associative thickener with dissolution promotion water soluble additive |
| RU2633570C2 (en) | 2012-03-08 | 2017-10-13 | Геркулес Инкорпорейтед | Suppression of associative thickener viscosity by phosphororganic compounds |
| WO2014058438A1 (en) | 2012-10-12 | 2014-04-17 | Empire Technology Development Llc | Paints and coatings containing cyclodextrin additives |
| MX2018015283A (en) | 2016-06-10 | 2019-04-09 | Ecolab Usa Inc | Low molecular weight dry powder polymer for use as paper-making dry strength agent. |
| MX2020001349A (en) | 2017-07-31 | 2020-08-31 | Ecolab Usa Inc | Dry polymer application method. |
| EP3724265A1 (en) * | 2017-12-13 | 2020-10-21 | Ecolab USA Inc. | Solution comprising an associative polymer and a cyclodextrin polymer |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4079028A (en) * | 1975-10-03 | 1978-03-14 | Rohm And Haas Company | Polyurethane thickeners in latex compositions |
| US4155892A (en) * | 1975-10-03 | 1979-05-22 | Rohm And Haas Company | Polyurethane thickeners for aqueous compositions |
| US4180491A (en) * | 1976-12-01 | 1979-12-25 | Rohm And Haas Company | Nonionic polyurethane thickener with surfactant cothickener and organic diluent, clear concentrates, aqueous print pastes, coloring compositions, methods of making and printing |
| US4426485A (en) * | 1982-06-14 | 1984-01-17 | Union Carbide Corporation | Polymers with hydrophobe bunches |
| US4499233A (en) * | 1983-05-03 | 1985-02-12 | Nl Industries, Inc. | Water dispersible, modified polyurethane and a thickened aqueous composition containing it |
| JPS6049022A (en) * | 1983-08-29 | 1985-03-18 | Sannopuko Kk | Thickening composition giving excellent coloring property and leveling property |
| US4496708A (en) * | 1983-12-14 | 1985-01-29 | Union Carbide Corporation | Water-soluble polyurethane comb polymer production |
| US4920214A (en) * | 1986-04-16 | 1990-04-24 | American Maize-Products Company | Process for producing modified cyclodextrins |
| DE3828031A1 (en) * | 1988-08-18 | 1990-02-22 | Basf Ag | CYCLODEXTRINE AS A FOAM ABSORBER IN POLYMER DISPERSIONS |
| US5137571A (en) * | 1990-06-05 | 1992-08-11 | Rohm And Haas Company | Method for improving thickeners for aqueous systems |
-
1993
- 1993-03-12 US US08/030,757 patent/US5376709A/en not_active Expired - Lifetime
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1994
- 1994-03-01 DE DE69400928T patent/DE69400928T2/en not_active Expired - Lifetime
- 1994-03-01 EP EP94301448A patent/EP0614950B1/en not_active Expired - Lifetime
- 1994-03-01 AT AT94301448T patent/ATE145418T1/en not_active IP Right Cessation
- 1994-03-01 SG SG1996003553A patent/SG67893A1/en unknown
- 1994-03-01 ES ES94301448T patent/ES2095128T3/en not_active Expired - Lifetime
- 1994-03-01 IL IL10880294A patent/IL108802A/en not_active IP Right Cessation
- 1994-03-01 DK DK94301448.0T patent/DK0614950T3/en active
- 1994-03-02 AU AU56490/94A patent/AU663245B2/en not_active Expired
- 1994-03-02 NZ NZ260009A patent/NZ260009A/en unknown
- 1994-03-03 CA CA002116927A patent/CA2116927C/en not_active Expired - Fee Related
- 1994-03-04 MY MYPI94000514A patent/MY113825A/en unknown
- 1994-03-07 NO NO940782A patent/NO940782L/en unknown
- 1994-03-08 PH PH47895A patent/PH30128A/en unknown
- 1994-03-08 MX MXPA94001702A patent/MXPA94001702A/en active IP Right Grant
- 1994-03-09 KR KR1019940004573A patent/KR100291523B1/en active IP Right Grant
- 1994-03-10 ZA ZA941665A patent/ZA941665B/en unknown
- 1994-03-11 RU RU94007640A patent/RU2132344C1/en active
- 1994-03-11 BR BR9401128A patent/BR9401128A/en not_active IP Right Cessation
- 1994-03-11 FI FI941185A patent/FI103346B1/en active IP Right Grant
- 1994-03-12 CN CN94102889A patent/CN1047603C/en not_active Expired - Lifetime
- 1994-03-14 JP JP06906694A patent/JP3545802B2/en not_active Expired - Lifetime
- 1994-03-30 TW TW083102734A patent/TW237465B/zh active
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- 1996-11-21 GR GR960402893T patent/GR3021749T3/en unknown
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Also Published As
| Publication number | Publication date |
|---|---|
| SG67893A1 (en) | 1999-10-19 |
| DE69400928D1 (en) | 1997-01-02 |
| DE69400928T2 (en) | 1997-05-07 |
| EP0614950A1 (en) | 1994-09-14 |
| AU5649094A (en) | 1994-09-15 |
| FI103346B (en) | 1999-06-15 |
| MXPA94001702A (en) | 2005-01-10 |
| BR9401128A (en) | 1995-03-07 |
| GR3021749T3 (en) | 1997-02-28 |
| ATE145418T1 (en) | 1996-12-15 |
| ES2095128T3 (en) | 1997-02-01 |
| FI941185A (en) | 1994-09-13 |
| IL108802A0 (en) | 1994-06-24 |
| NZ260009A (en) | 1995-05-26 |
| IL108802A (en) | 1998-10-30 |
| CN1047603C (en) | 1999-12-22 |
| TW237465B (en) | 1995-01-01 |
| CN1095731A (en) | 1994-11-30 |
| FI103346B1 (en) | 1999-06-15 |
| US5376709A (en) | 1994-12-27 |
| KR100291523B1 (en) | 2001-10-22 |
| EP0614950B1 (en) | 1996-11-20 |
| JP3545802B2 (en) | 2004-07-21 |
| PH30128A (en) | 1996-12-27 |
| AU663245B2 (en) | 1995-09-28 |
| ZA941665B (en) | 1994-09-13 |
| HK122297A (en) | 1997-09-12 |
| FI941185A0 (en) | 1994-03-11 |
| CA2116927A1 (en) | 1994-09-13 |
| MY113825A (en) | 2002-06-29 |
| JPH073241A (en) | 1995-01-06 |
| RU2132344C1 (en) | 1999-06-27 |
| DK0614950T3 (en) | 1996-12-09 |
| NO940782L (en) | 1994-09-13 |
| NO940782D0 (en) | 1994-03-07 |
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