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
2000-04-20
2003-04-01
Wu, David W. (Department: 1713)
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...
C524S567000, C524S577000, C524S578000, C524S582000, C526S348000, C526S329700, C526S344000, C526S346000, C526S347200, C526S242000
Reexamination Certificate
active
06541558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thermoplastic polymers modified with certain fluorocarbon additives.
2. Description of the Prior Art
It has recently been proposed to modify thermoplastic polymers by incorporating therein various oils, gums, etc.
U.S. Pat. No. 3,485,787 discloses that certain block copolymers may be extended by incorporating mineral oil therein.
U.S. Pat. No. 3,830,767 teaches that bleeding of the extending oil from the block copolymer may be prevented by incorporating a petroleum hydrocarbon wax therein.
U.S. Pat. No. 4,123,409 relates to block copolymers having thermoplastic terminal blocks and an elastomeric intermediate block. The patent discloses blending with the copolymer a high molecular weight oil which is compatible with the elastomeric block portion of the copolymer. Where the elastomeric portion is a hydrocarbon, the oil employed is a mineral oil. Where the elastomeric block is a polysiloxane, a silicone oil is blended therewith.
U.S. Pat. No. 3,034,509 discloses the addition of silicone oil to polyethylene for use as surgical tubing.
SUMMARY OF THE INVENTION
These and other objects are realized by the present invention which provides compositions of matter formed by melt-blending certain thermoplastic polymers and from about 1.0% to about 7.5% by weight of a fluorocarbon additive selected from the group consisting of a fluorocarbon oil, a fluorocarbon gum, a fluorocarbon grease and mixtures thereof, the fluorocarbon additive having a lower surface energy than that of the polymer and the melt-blending resulting in an initially substantially homogeneous admixture of the polymer and the fluorocarbon additive. The admixture, upon cooling, results in a solid composition wherein the concentration of fluorocarbon additive becomes lower in the bulk polymer and higher at the surfaces thereof, i.e., is a gradient through a cross-section of the solid composition from a lower value in the interior or bulk thereof to a higher value at the surfaces thereof.
Another embodiment of the invention comprises a method of forming compositions of matter comprising certain thermoplastic polymers and from about 1.0% to about 7.5% by weight of a fluorocarbon additive selected from the group consisting of a fluorocarbon oil, a fluorocarbon gum and mixtures thereof, the fluorocarbon additive having a lower surface energy than that of the polymer. The method comprises melt-blending, preferably in an efficient compounding blender, the polymer and the fluorocarbon additive at a temperature above the glass transition temperature or softening point of the polymer, but below that having a deleterious effect on the polymer and the fluorocarbon additive and for a time sufficient to initially produce a substantially homogeneous admixture of polymer and fluorocarbon additive, followed by cooling the admixture to produce a solid composition wherein the concentration of fluorocarbon additive through a cross-section of solid composition becomes lower in the polymer bulk thereof and higher at the surfaces thereof, i.e., is a gradient through a cross-section of the solid composition from a lower value in the interior or bulk thereof to a higher value at the surfaces thereof.
DETAILED DESCRIPTION OF THE INVENTION
Although most non-fluorinated polymers are not compatible with fluorocarbon oils and gums and are also not readily blended therewith because of the high specific gravity of the fluorocarbons, the present invention is predicated on the discovery that certain thermoplastic polymers, when efficiently melt-blended with from about 1.0% to about 7.5% by weight of a fluorocarbon oil, gum or mixture thereof such that the fluorocarbon additive is homogeneously distributed throughout the melt, yield, upon cooling, solid compositions which, because of the differences in thermodynamic compatibility and surface energy between the fluorocarbon additive and the polymer, develop higher concentrations of the additive at the surface than throughout the interior thereof.
In the phrase “concentration of fluorocarbon additive in a gradient through a cross-section from a lower value at the center thereof to a higher value at the surfaces,” the term “gradient” is not intended to suggest that the concentration varies uniformly from the center of the composition to the surface. Although this may be the case with respect to some combination of polymers and additive, typically a much higher concentration of the additive is at the surfaces of the composition with a much smaller amount in the interior or bulk of the polymer.
This higher concentration of fluorocarbon additive at the surface of the polymer enables the provision of a polymer composition having heretofore unattainable properties. Thus, using very low concentrations of fluorocarbon additive, i.e., from about 1.0% to about 7.5% by weight, relatively high concentrations are attainable at the surface.
The high concentrations of fluorocarbon additive at the surfaces provide compositions having the advantages of fluorocarbon-like surface properties, i.e., greater hydrophobicity, lower surface energy, non-adherent surface characteristics, more chemically inert, lower friction, smoother, etc. In addition, the presence of the fluorocarbon additive enhances molding operations since it reduces “sticking” of the composition to the mold surfaces and enhances mold release. Also, the additive will, because of the lubricant properties thereof, permit higher speed processing of extruded objects, i.e., films, fibers and other objects formed therefrom and with smoother surfaces, with the added benefits of shorter injection molding cycles and higher extrusion rates.
For biological or biomedical applications of the polymer compositions, the fluorocarbon surfaces are especially advantageous since they exhibit superior biocompatibility in contact with tissue surfaces, cells, physiological fluids and blood as compared with most thermoplastic polymers.
The compositions of this invention are, therefore, particularly advantageous for such applications as blood and fluid handling, medical tubing, vascular grafts, mammary implants, orthopedic joint and tendon prostheses, ocular implants, and the like.
Fibers prepared from compositions of the invention possess superior surface smoothness and uniformity and handling properties for weaving, as well as different textures and “feel” because of the surface properties imparted by the fluorocarbon additives. In addition, the compositions and methods of the invention are advantageous and more economical in the manufacture of fibers since the higher concentration of fluorocarbon additive at the surfaces of the fiber facilitates high-speed processing with less damage to dies, shuttles and weaving equipment to produce more uniform, smooth, melt-spun fibers.
For the most part, the basic bulk mechanical, physical and chemical properties of the thermoplastic polymer employed are retained or even enhanced for the compositions of the present invention, but acquire the fluorocarbon surface properties of the additive due to the above-noted gradient concentration of the fluorocarbon additive through a cross-section of the composition from a lower value in the bulk to a higher value at the surface. This makes the compositions of this invention also advantageous for molds such as those used for optical and electronic parts, i.e., contact lenses, and for electro-optical or electromechanical devices which require lower surface energy and low friction surfaces, i.e., video tapes, compact discs for audio or video recording, electromechanical switches, and the like.
The lower concentrations of fluorocarbon additive in the interior portion of the thermoplastic can also advantageously modify the bulk mechanical, physical and chemical properties of the polymer, however, particularly with respect to the classes of thermoplastic polymers discussed hereinbelow.
A unique advantage associated with the compositions of the invention is that if cut into plural sections, the fluorocarbon additive in the interi
Goldberg Eugene P.
Sterling Robert E.
Choi Ling-Siu
Clarke Dennis P.
Miles & Stockbridge PC
RES Development Corporation
Wu David W.
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