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
2002-03-18
2004-09-14
Wyrozebski, Kat (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, C524S449000, C524S451000
Reexamination Certificate
active
06790896
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to phyllosilicates which have been modified to increase their dispersibility in polymers and methods for producing the same. More particularly, the present invention relates to mineral fillers which have been edge modified to improve their dispersibility in polymer matrices and methods for making composite materials using the mineral fillers.
BACKGROUND OF THE INVENTION
Mineral fillers are used extensively to enhance the performance of a wide range of thermoplastic and thermosetting polymers. Physical properties which are improved by fillers include stiffness, strength, impact and temperature resistance, improved dimensional stability, surface hardness and scratch resistance. Other properties improved with fillers include improved chemical resistance, electrical resistance, and flame retardancy. Mineral fillers can also be used to reduce the thermal expansion coefficient of thermoplastics and permeability to gases and liquids. The most commonly used mineral fillers in plastics are calcium carbonate, wollastonite, silica, and the phyllosilicates such as kaolin, talc, and mica. Talc is unique in that its surface is naturally hydrophobic and therefore compatible with olefinic polymers. On the other hand, calcium carbonate, silica, wollastonite and the other phyllosilicates are hydrophilic and must be surface treated in order to improve their dispersion and interaction with the polymer matrix. The surface treatment of hydrophilic phyllosilicates includes reaction of the basal surface of the mineral with organosilanes, modified oligomers and polymers containing anhydride functional groups, and a wide variety of surfactants. Maximum improvement in mechanical and barrier properties of polymers occurs with the use of well-dispersed platy minerals possessing high aspect ratios. and small particle sizes. The aspect ratios of platy minerals such as mica, talc and kaolin are typically in the range of 30 to 100.
Since the late 1980's the focus of much research around the world has shifted from the traditional mineral fillers to the incorporation of fully exfoliated smectite clays, primarily montmorillonite with its extremely high aspect ratio, into a variety of thermoset and thermoplastic polymers. The aspect ratios of exfoliated smectite clays can range from 100 to 1,000 or more. The exfoliation and nanoscale dispersion of small amounts of smectite clays into polymers leads to composite materials with enhanced physical features, but with significant reductions in weight as compared to traditional mineral-filled polymers. Like the other hydrophilic phyllosilicates, the smectite clays must be surface-treated to render them compatible with olefinic polymers. The approach that has been most often used is based on the technology utilized for the last fifty years to make organoclays as Theological control agents in paints, inks, greases, etc. This approach utilizes quaternary amine-based surfactants to render the basal surface of the clay compatible with the polymer matrix. Various high-molecular-weight quaternary ammonium salts have been used 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 the phosphonium and sulfonium groups. Surprisingly, this approach has not been very successful in promoting clay exfoliation in olefinic polymers such as polyethylene and polypropylene and their copolymers.
In any organoclay application, and especially in the preparation of composite materials, 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 to those skilled in the art that maximum organoclay dispersion in organic solvents 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. In rheological applications, a small amount of water is added with the polar activator to promote gellation via hydrogen-bond bridging between hydrophilic platelet edges. To this end, full rheological effectiveness requires unobstructed access to the hydrogen bonding sites on the clay edges. In composite material applications, the organoclay designs traditionally left the platelet edges untreated with the belief that the edge contribution to the hydrophilic lipophilic balance (HLB) of the organoclay is insignificant.
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 been described in the patent literature 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 the clay with a 10 to 25 percent excess of the 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. In a slight variation on his approach, higher molecular weight anionic compounds such as carboxylic acids having low water solubility have been used as self-activating agents in conjunction with amine treatment. In this approach, the anionic carboxylic acid forms a water-insoluble complex with the ammonium ion which then 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 composite materials 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, i.e., 30 to 100 weight percent relative to the weight of the organoclay. 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 relative to the weight of the
The University of Chicago
Wyrozebski Kat
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