MXPA01006025A - Method of reducing syneresis in aqueous compositions - Google Patents

Abstract

A method for reducing or eliminating syneresis in an aqueous latex composition caused by the flocculation of the latex particles as a result of interaction with hydrophobically modified ethylene oxide based urethane rheology modifiers. The method of the invention involves adding to the aqueous latex composition a molecule containing a single hydrophobic moiety which has a poly-ethylene oxide backbone chain-length of greater than about 5000 Mn. The method of the present invention also increases the viscosity efficiency of the aqueous latex composition by combining a multiphobe with a monophobe.

Description

METHOD TO REDUCE THE SYNRRESIS IN COMPOSITIONS AQUEOUS The present invention relates to a method for reducing syneresis in certain aqueous compositions, while, at the same time, increasing the viscosity efficiency of the aqueous system. The method of this invention is particularly applicable to aqueous compositions containing latex polymers and thickening agents. Since water-based compositions were first introduced, additives have been sought to increase viscosity and maintain this viscosity at the desired levels under various process conditions and end-use situations. These additives are commonly referred to as "thickening agents" or "thickeners". The thickeners are used in latex paints to improve the control viscosity, as well as for the protective colloidal action and for the improvement of the pigment suspension, leveling and flow. In addition, the additives often emulsify, disperse, stabilize the latex ingredients. In latex paints and compositions for the treatment of textiles, thickeners often improve the "stickiness" or agglutination properties of the general composition. Thickeners are commonly used in the cosmetics industry as thixotropic agents and to improve the softening, sizing and handling properties. With additives for paper coating compositions, thickeners improve thickening under high cut conditions. Likewise thickeners are useful for the above properties and others in the drilling of oil wells and in flood fluids, foams and fluids that fight fire, detergents, leather pastes and finishes, adhesives, pharmaceuticals, formulations, emulsions of the agriculture of all types. Among the many well-known thickeners are natural products, such as alginates, casein, karaya gum, locust bean gum and tragacanth gum, and modified natural products, such as cellulosics, which include methyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose. Many synthetic thickeners are also available, such as carboxy and vinyl ether copolymers, acrylic polymers and copolymers of maleic anhydride and styrene. One of the most significant classes of synthetic thickeners available now, is comprised of urethane polymers. More specifically, these polymers contain hydrophobic moieties attached to a skeleton of ethylene polyoxide. The various polymer chains are joined together by urethane bonds. This class of thickeners is often referred to as HEUR modifier, which are "hydrophobically modified urethane and ethylene oxide bonds". The hydrophobic groups are placed at the ends of the polymer chain and contain together at least 20 carbon atoms. Since the end of the polymer chain contains a hydrophobic group, these modifiers are referred to as "dipopes". The polymer skeleton is comprised of hydrophilic polyether segments. Such HEUR modifiers are described in detail in U.S. Patent Nos. 4,079,028 4,426,485. HEUR thickeners are referred to as "associated thickeners" due to the mechanism by which they thicken the formation of hydrophobic associations between the hydrophobic parts in the thickener molecules and other hydrophobic surfaces, which include other thickener molecules, pigments or latex particles. It is this interaction with the latex particles to which this invention is focused. Certain formulations that contain the HEUR modifiers, can cause the formation of bridges between the latex particles, which, in turn, leads to the flocculation or "syneresis" of the aqueous latex system. Syneresis is the separation of a liquid from a gel, and manifests itself as an exudation or "squeezing" of the diluent from a separate phase. Obviously, such separation is not acceptable when it is found in aqueous formulations of latex paint. Nevertheless, attempts to solve this problem by removing or reducing the amount of HEUR modifiers results in an unacceptable drop in the viscosity of the formulation. Specifically, an unacceptable fall in the average cut viscosity (Krebs-Stormer) results, measured as a drop in KU, or "Krebs Units". The present invention solves the problem of l syneresis in aqueous latex formulations. Surprisingly, the method of the present invention also results in an increase in KU efficiency. This efficiency KU is defined as a measure of the amount of the thickener required to achieve a target viscosity. That is, the greater the amount of thickener required to reach a specified viscosity, the lower the KU efficiency. Achieving greater KU efficiency while, at the same time, reducing or eliminating syneresis, often involves using solutions of two diametrically opposed process parameters. To achieve both objectives through a single process step is both surprising and counter-indicated, based on the known technique.

EXHIBITION OF THE INVENTION The invention is directed towards a method for reducing syneresis and increasing the efficiency of the viscosity in aqueous compositions, which contains thickeners based on urethane, or "HEUR", adding a high molecular weight monopolar or a monophore in combination with a multiflow. This monophore contains at least one hydrophilic segment and only one hydrophobic segment. The hydrophobic segment will ideally have a carbon content greater than 12 and preferably in a range of 12 to 18. The monophobes of the invention may be nonionic, anionic, cationic or amphoteric. The M (number average molecular weight) of the hydrophobic monophobic segment is at least 2,000 and preferably greater than 5,000 to 10,000. The monophore may optionally contain multispindle molecules of various molecular weight chain lengths. A multiflow is a molecule that contains at least one hydrophilic segment and at least two hydrophobic segments. The multiflow is preferably a diphobe (2 hydrophobic segments). The Mn of the hydrophilic diphobic segment is less than twice the Mn of the monophobe. The hydrophobicity of the hydrophobic diphobic segment is sufficient to form non-specific hydrophobic associations. Preferably, the hydrophobic diphobic segments each contain a hydrocarbon portion having at least 8 carbon atoms or its equivalent. In order to achieve the dual objectives of increasing viscosity efficiency and reducing syneresis, it has been discovered that the multiflow can be combined with the mono-phobe. Up to 66% of the total weight of the monophobe plus the multi-buff can be of the multi-buff. If s add the multipurpose in excess of this amount, the KU efficiency increases, but the syneresis is very likely to result. The monophobic and the monophobic and multiphobic blends of the invention are added to the aqueous composition as a function of the amount of the HEUR thickener therein present. The mixtures of the invention are added in an amount of at least 1% by weight of the HEUR thickener. Preferably, this amount is from 2 to 50% and more preferably from 1 to 30%.

EXAMPLES Several paint formulations were prepared to verify the beneficial effects provided by the present invention. A standard paint without pigments was prepared as follows: MATERIAL AMOUNT (% in vol.) Tamol 681 4.13 Nuosept 95 (Creanova, Inc.) 0.22 Roamaster AP (Henkel Corp.) 0.55 Propylene glycol 4.34 Aqueous ammonia 0.14 Texanol (Texaco Corp.) 5.54 Triton GR-7M 0.25 Rhoplex HG- 74P (Rohm and Haas) 82.67 Water 2.17 100% The HEUR rheology modifier, RM2020NPR, available from Rohm and Haas Company, Philadelphia, PA, was also used. Preparation of the diphobe: Hydrophilic segment = pEO (average Mn = ~ 8,600) hydrophobic segment = part C18. Four hundred and fifty grams of toluene and 258 (0.03 moles) of poly (ethylene glycol) (mean Mn of ~8,600) were loaded into a flask, then stirred and heated to azeotropically remove the residual water by means of a Dean Stark trap. The temperature of the copper was reduced to 90 ° C and 17.73 g (0.06 moles) of isocyanate d octadecyl was added, followed by 0.2 g of dibutyl tin dilaurate catalyst. After stirring at 90 ° C for 1 hour, the reaction was complete.

Monophobic preparation: hydrophilic segment = pEO (mean Mn = -10,000) Three hundred grams of toluene and 300 g (0.03 moles) of poly (ethylene glycol) -monomethyl ether (mean Mn = -10,000) were charged to a flask, then it was stirred and heated to azeotropically remove the water by means of a Dean Stark trap. The temperature of the copper was reduced to 90 ° C and 8.02 g (0.03 mole) of hexadecyl isocyanate was added, followed by 0.2 g of dibutyltin dilaurate catalyst. After stirring at 90 ° C for 1 hour, the reaction was complete. The results of adding aqueous solutions at 20% of the monophobic and / or diphobic to 150 grams of the paint without pigment are shown in Table 1.

TABLE 1 Experiment Number RM2020 Monophobic Dífobo KU Inhibited Syneresis? Standard 5g og or g 93 No Control 6.! 5 g or g or g 100 No 1 5 g -1.5 g 0 g 102 Yes 2 5 g 0 g 1.5 g > 144 No * 3 5 g 1.2 g 0.3 g 114 Yes 4 5 g 1.0 g 0.5 g 120 Yes 5 5 g 0.75 g 0.75 g 135 Yes 6 5 g 0.5 g 1.0 g > 144 Yes 7 5 g 0.3 g 1.2 g > 144 No Comparative 5 g 1.5 g ** o g 82 No * The syneresis was worse than expected ** Commercial surfactant agent, Triton X-405 (hydrophobic octyl-phenol, and polyethylene oxide polymer backbone with a molecular weight, Mw, of 1800) The use of the common surfactant in the Comparative Example reflects the well-recognized practice of using such materials to counteract the undesired effects of syneresis. It is evident from the above results that the use of a surfactant in the same amount as the monophobic one, significantly decreases the efficiency of the thickener (lower KU) and also fails to inhibit the syneresis. However, since the monophore and the Tritó X-405 are considered as nonionic surfactants, it is surprising, in view of the failure of the commercial surfactant agent, that the monophore will increase both the efficiency of the thickener and also inhibit the syneresis.

Claims (10)

1. CLAIMS 1. In an aqueous composition, containing thickeners, a method to reduce syneresis and increase the efficiency of the viscosity in said composition, the cua comprises adding to this composition a monopop of molecular weight, said monophobic comprises at least one segment hydrophilic and only a hydrophobic segment.
2. 2. The method of claim 1, wherein thickeners are urethane rheology modifiers based on hydrophobically modified ethylene oxide.
3. 3. The method of claim 1, wherein the number average molecular weight (Mn) of the monophobic hydrophilic segment is at least 2,000.
4. 4. The method of claim 3, wherein the M of the monophobic hydrophilic segment is from 5,000 to 10,000.
5. 5. The method of claim 1, further comprising a multiflow.
6. 6. The method of claim 5, wherein the multiflow is a diphobe.
7. 7. The method of claim 6, wherein up to 66% of the weight of the monophobe and the diphobe comprises the diphobe.
8. 8. The method of claim 7, wherein the molecular weight, Mw, of the hydrophobic diphobic segment is less than twice the molecular weight in number, Mn of the hydrophilic segment of the mono- phobe.
9. 9. The method of claim 1, wherein the viscosity efficiency is defined by an increase in the KU units.
10. 10. The method of claim 1, wherein the composition contains a latex polymer.