Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-05-24
2003-11-11
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S421000
Reexamination Certificate
active
06645590
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of fluoropolymers having functional side groups, and is concerned with articles made from such fluoropolymers.
BACKGROUND OF THE INVENTION
Thermoplastic fluoropolymers are well known for outstanding combinations of properties including chemical resistance, unique surface characteristics, high service temperatures, and good dielectric characteristics. As a result, fluoropolymer resins are used in a wide variety of applications including wire insulation, cable jacket, hose, tubing, film, linings for chemical process equipment, articles for fluid handling in laboratory and manufacturing situations, and the like. The service temperature in some of these applications can be high. As is common for thermoplastics, some properties of fluoropolymers change as temperature increases. Modulus and tensile strength, for example, typically decrease with increasing temperature, and fabricated articles such as tubing and wire insulation typically have lower cut-through resistance at high temperature.
Fluoropolymer articles having improved properties, particularly at high temperature, are desired.
The use of functional groups in fluoropolymers has been aimed at modifying the surface characteristics of fluoropolymers. For example, Kerbow in U.S. Pat. No. 5,576,106 discloses a grafted fluoropolymer powder that is effective in such uses as an adhesive to join dissimilar materials, Iura et al. in European Patent Application Publication EP 0 761 757 disclose a fluorine-containing polymer alloy of a grafted fluorine-containing polymer and a polymer containing no fluorine, and Shimizu et al. in European Patent Application Publication 0 626 424 disclose a blend of a thermoplastic resin and a fluoropolymer having a functional group that improves interfacial affinity with the thermoplastic resin.
SUMMARY OF THE INVENTION
This invention provides articles made from melt-fabricable fluoropolymer resin and having improved mechanical properties. Preferred such articles include tubing and wire insulation, which exhibit improved cut-through resistance.
The fluoropolymer resin from which such articles are made has pendant functional groups. Such groups can be produced by grafting a polar-functional compound to the fluoropolymer.
DETAILED DESCRIPTION
It has been discovered that addition of functional groups to fluoropolymers can result in surprising improvement of bulk properties. Improved properties are evident at room temperature, but are accentuated at elevated temperatures.
The articles of this invention can be fabricated by conventional melt processing techniques. For example, articles can be formed by melt extrusion, using such techniques as pressure extrusion or extrusion accompanied by melt draw, or by injection molding. The processes of fabricating the articles of the present invention are new in that the melt-fabricable fluoropolymer resin used has pendant functional groups.
Generally, when articles of this invention are fabricated by melt extrusion, a cross-section of such articles normal to the extrusion direction is characterized by a perimeter that is a closed figure. Such figures include, for example, regular geometric shapes such as circles, ellipses, rectangles and the like, and also irregular shapes including shapes that are either minor or major departures from regular shapes. Preferably, extruded articles of the invention have general axial symmetry though not necessarily exact axial symmetry. For example, convoluted tubing having helical convolutions does not have exact axial symmetry, but is considered for purposes of the present invention to have general axial symmetry (or near axial symmetry). Preferred extruded articles include wire insulation, cable jacket, tubing including convoluted tubing, hose, and the like.
Articles of the present invention exhibit improved mechanical properties. Such improvements include increased stiffness and increased toughness, the latter indicated, e.g., by increased force required to cut through a thin section. Such improvement can be evident at room temperature, but may be more pronounced at elevated temperature. For wire insulation of the present invention, substantial increases in cut-through resistance have been observed at 150° C. See Example 1, which discloses an increase of about 100%. Such large increases are not required for articles of the invention. Cut-through resistance of wire insulation or tubing at 150° C., for example, is generally at least 25% greater than for such articles made from comparable fluoropolymer resin but not having pendant functional groups, and is preferably at least 50% greater. Stiffness (flex modulus) is also increased. For example, flex modulus at room temperature is generally increased by at least 10% relative to that of the same article made from similar fluoropolymer lacking pendant functional groups.
The fluoropolymer having pendant functional groups exhibits a reduction in melt flow rate (increase in melt viscosity) after being exposed to elevated temperature such as may be encountered during melt fabrication of the article. This reduction in melt flow indicates that cross-linking occurs, even in the absence of cross-linking promoter or catalytic agent.
Articles of the present invention are fabricated essentially from fluoropolymer resin having pendant functional groups. The articles consist essentially of such resin in the sense that other substance or material which may react with said pendant functional groups is not present. Thus, for example, no cross-linking promoter or co-agent or such material is present. Likewise, no fluorine-free polymer is present as a component of a blend or alloy, or as a reinforcing component. However, articles of the invention can contain inert additives present in minor amount, such as pigments, or present merely as filler, such as carbon. Additives such as thermal or oxidative stabilizers that are normally present in fluoropolymer resins can be present in usual amounts in articles of the invention.
As used herein, “functionalized fluoropolymer” means fluoropolymer having functional side groups or functional groups attached to side groups, i.e., pendant functional groups. Usually, but not necessarily, such functional units are at the ends of the pendant side groups. Fluoropolymer that does not have such pendant functional groups is sometimes described herein as “non-functional fluoropolymer”. Thus, non-functional fluoropolymer and functionalized fluoropolymer differ at least by the presence in the latter of pendant functional groups. Non-functional fluoropolymer can be a precursor to functionalized fluoropolymer, in which instance the process of functionalizing involves addition of functional groups to the non-functional polymer. However, “functionalizing” is also used in a broader sense herein to include preparation of functionalized fluoropolymer which would be non-functional if pendant functional groups were not present, even though non-functional fluoropolymer may not be the precursor.
Functional groups, in the context of the present invention, are groups capable of improving the mechanical properties of fluoropolymer articles when such functional groups are present in a fluoropolymer composition. Improvement of mechanical properties is indicated, for example, by an increase in cut-through resistance (e.g., as measured for wire insulation or for tubing) or by an increase in stiffness (flex modulus), as discussed above. Functional groups that can improve the properties of fluoropolymers when present include ester, alcohol, acid (including carbon-, sulfur-, and phosphorus-based acid) and salt and halide thereof. Other functionalities include anhydride and epoxide. Preferred functional groups include —CH
2
—OH and anhydride, especially maleic anhydride. As one skilled in the art will recognize, more than one type of functional group can be present. Normally, however, a single type of functional group is used.
Such functional groups can be introduced, for example, by incorporating into the fluoropolymer, during polymerization, mono
E. I. du Pont de Nemours and Company
Nolan Sandra M.
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