Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-02-20
2004-11-23
Wyrozebski, Katarzyna (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S447000, C524S186000, C501S145000, C501S148000
Reexamination Certificate
active
06822035
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for preparing organoclays, including clays purified in the conventional manner. More particularly, the invention relates to methods for the surface modification of clays using polymeric hydrotropes to produce organoclays with improved efficiency and dispersability in nonpolar solvents and polymer systems.
BACKGROUND OF THE INVENTION
Organoclays with a wide range of surface wetting characteristics have been described in the literature. It is well known that surface treatment can be used to render hydrophilic clay surfaces compatible with solvents of decreasing polarity such as alcohols, ethers, aromatic and aliphatic hydrocarbons, and the like. Conventional hydrophilic organoclays have been prepared by onium ion exchange using polyethyer substituted quaternary ammonium compounds. These organoclays are dispersible in water-based systems and can be used for rheology control in products such as latex paints. Other methods for preparing organoclays displaying surface properties ranging from hydrophilic to hydrophobic have been produced by surface modification of the clay through polymer adsorption rather than onium ion exchange. For example, clay/polymer intercalates have been produced through direct intercalation of clays with either polymer melts, as described in U.S. Pat. No. 5,955,535, or by contacting a clay slurry with a polymer solution followed by drying. These organoclays can be used in forming composites with thermoplastic or thermosetting resins, however they suffer from the drawback that the efficiency of exfoliation can be low due to the potential for cross linking of the clay platelets by the surface-modifying polymer.
Traditionally, hydrophobic organoclays have been prepared through onium ion exchange from a smectite-type clay by surface exchange with high molecular weight quaternary ammonium salts, such as dimethyl dihydrogenated tallow ammonium chloride, dimethyl benzyl hydrogenated tallow ammonium chloride, and methyl benzyl dihydrogenated tallow ammonium chloride. Other onium ions that have been used include phosphonium and sulfonium ions. Another variation described in the literature for making organoclays involves the preparation of a hydrophobic organoclay by onium ion exchange followed by intercalation of a hydrophilic or hydrophobic polymer melt. However, this method of producing organoclays does not directly bind the organic polymers to the clay surface. Consequently, these organoclays cannot be dispersed in a solvent system without loss of the polymer from the clay surface which leads to uncontrolled changes in the surface wetting properties of the organoclay. Additionally, these types of organoclay intercalates do not completely exfoliate in the absence of specific chemical polymerization reactions. This method of producing organoclays is further limited to organoclays that have been surface treated with onium ions having carbon chain lengths equal to or greater than 12. Moreover, the amount of polymer required to modify the surface hydrophilic-lipophilic balance (HLB) value of the clays is typically from 30 to 100 weight percent, or more, relative to the weight of the organoclay, thereby making this approach both costly and inefficient.
In any organoclay application, and especially in the preparation of nanocomposites, obtaining a good dispersion of the clay has always been problematic. Smectite clays have extremely large surface areas and because of their nanoscale, their behavior is dominated by a complex balance of surface chemical forces. It is well known in the patent literature that maximum organoclay dispersion in organic solvents, and hence gelling efficiency, requires the addition of low-molecular-weight polar organic compounds. Various “polar activators” as they are called, have been recommended and include low-molecular-weight ketones and alcohols—with methanol and acetone being preferred. The polar activators are typically combined with small amounts of water and are used at levels ranging from 20 to 60 weight percent relative to the weight of the organoclay. Propylene carbonate has been recommended where the volatility of the activator is a concern. It is believed that the polar organic compounds encourage delamination and dispersion of the organoclay by solvating the high-molecular-weight ammonium ion at the basal surface of the organoclay which in turn affects the inter-platelet associations (i.e., basal spacing) resulting from the van der Waals attractions between surfactant chains and the clay surface. The small amount of water added with the polar activator promotes gellation via bridging between hydrophilic platelet edges. To this end, full rheological effectiveness requires unobstructed access to the hydrogen bonding sites on the clay edges.
The pioneering work in the 1940s showed that increasing chain length of the amine and increasing amine loading leads to more complete coverage of the basal clay surface. This work is discussed in J. W. Jordan, B. J. Hook, and C. M. Finlayson, J. Phys. Colloid Chem. 54, 1196-1208 (1950). For example, approximately 80 percent of the basal surface is covered by amine molecules lying flat at an octadecylamine loading of 100 milliequivalents per 100 g of clay. However, maximum solvation of the hydrocarbon chains of the amine would require the hydrocarbon chain to lift off from the clay surface thereby exposing a hydrophilic, silicate surface. Jordan postulated that the polar organic activators facilitated the solvation of the hydrocarbon chains by simultaneously lifting the hydrocarbon chains on end and shielding the exposed silicate surface.
Self-activating organoclays have also been described and represent an improvement in performance. Self-activation has been achieved through various approaches including manufacturing and compositional modifications. For example, a common approach is to overtreat a clay with a 10 to 25 percent excess of a quaternary amine above the ion exchange capacity of the clay. To maximize the self-activating characteristic, this treatment approach usually requires that amine exchange of the clay be carried out in the presence of low molecular weight polar activators such as alcohols, ketones, ethers, carboxylic acids, carboxylic esters, and amides, as described in U.S. Pat. No. 4,365,030. In a slight variation on his approach, higher molecular weight anionic compounds such as carboxylic acids having low water solubility (e.g., stearic acid) have been used as self-activating agents in conjunction with amine treatment. In this approach, the anionic carboxylic acid forms a water-insoluble complex which attaches to the basal surface of the clay leaving the edge unobstructed.
Analogous approaches have been used to enhance the exfoliation of organoclays during the preparation of a variety of clay/polymer nanocomposites wherein a high molecular weight polar compound is used to activate the organoclay. Examples of activators which also function to compatibilize the organoclay with the polymer matrix include, polyolefin oligomers with telechelic OH groups and maleic anhydride-modified polyolefin oligomers. Oligomeric activators have been used at levels comparable to those of the low molecular weight polar activators. Because of the higher molecular weight of the oligomeric activators, the total organic loading on the organoclay necessary to achieve the desired degree of exfoliation exceeds 70 to 75 weight percent making this approach both expensive and inefficient. In addition, organic solvents are often required to facilitate intercalation of the oligomer which increases cost and manufacturing difficulty. Additionally, the efficiency with which the high molecular weight compatabilizers increase the basal spacing of the organoclay is surprisingly low. For example, telechelic polyolefins reportedly increase the basal spacing of an amine-treated montmorillonite from 33 Å to only 38 Å at a mixture ratio of 1:1. These results are reported in U.S. Pat. No. 6,121,361. This small increase in basal spacing suggests
The University of Chicago
Wyrozebski Katarzyna
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