Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Having discontinuous gas or vapor phase – e.g. – foam:
Reexamination Certificate
2002-04-17
2003-01-28
Foelak, Morton (Department: 1711)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Having discontinuous gas or vapor phase, e.g., foam:
C516S011000, C521S079000, C521S081000, C521S089000, C521S092000, C521S095000, C521S145000
Reexamination Certificate
active
06512013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates nucleating agent systems for foamable polymer compositions, preferably fluoropolymer resins, having foam cell nucleation sites using titanium dioxide (“TiO
2
”) based nucleating agents. The nucleating agent systems comprise synergistic amounts TiO
2
, certain inorganic salts, and optionally, sulfonic acid salts and/or phosphonic acid salts. The fluoropolymers useful for making the foamable compositions described herein are organic polymeric materials comprising at least about 35 weight percent fluorine and having a melt flow rate (“MFR”) of about 1 g/10 min. to about 100 g/10 min. as measured according to ASTM Standard D1238. The nucleating agents comprise TiO
2
in amounts from about 50 parts per million (“ppm”) to about 2,000 ppm by weight based on the total weight of the composition, inorganic salt in amounts from about 25 ppm to about 3,000 ppm by weight based on the total weight of the composition and, optionally, sulfonic acid salts and/or phosphonic acid salts in amounts of from 0 to about 3,000 ppm by weight based on the total weight of the composition. The foamed fluoropolymer compositions comprising the nucleating agents addressed herein have good structure and cell size, smaller than can be achieved with other systems, and have exemplary performance characteristics particularly for thin walled foamed insulation for conductive materials.
2. The Related Art
Foamed polymer compositions generally comprise nucleating agents to form a cell structure during processing. Conventional nucleating agents are boron nitride (“BN”), calcium carbonate, magnesium dioxide, lead oxide, barium oxide, antimony oxide, magnesium carbonate, zinc carbonate, barium carbonate, carbon black, graphite, alumina, calcium silicate, calcium metasilicate and calcium sulfate. Polytetrafluoroethylene (“PTFE”) is described in U.S. Pat. No. 4,304,713 as a nucleating agent for making dielectric compositions for use in coaxial cables, and U.S. Pat. No. 5,314,925 discusses fluoropolyolefin nucleating agents for molded thermoplastics. U.S. Pat. No. 5,716,665 addresses the use of PTFE, as well as BN, silicon nitride, alumina, talc and zinc sulfide, as nucleating agents for foamable solid compositions based on thermoprocessible perfluoropolymers.
Despite the number of nucleating agents disclosed in the art, BN has traditionally been the most preferred, particularly for making foamed insulation for conductive wire or other materials. BN, however, must generally be used in amounts from 0.5% to 2.0% by weight of total composition (5,000 ppm to 20,000 ppm) for effective nucleation of fluoropolymers. BN is a rather expensive, ranging in price from about $60 per pound to about $90 per pound. The price of BN is a significant drawback to the use of BN in all applications, and, accordingly, the art of nucleating agents for foamed polymer compositions is evolving to obtain nucleating agent systems which eliminate or reduce the quantity of BN while maintaining or improving on the performance characteristics needed for many applications.
Conductive wire is often used to transmit electronic signals. The conductor or conductive material must be protected, or insulated, and thermoplastic coatings in a molten state foamed and formed onto and around the conductor or conductive material are used for this purpose. The thermoplastic materials are selected on the basis of several criteria including high dielectric strength, low dielectric constant, and low dissipation factor. It has previously been found that if the thermoplastic material is foamed as it is applied to wire, the dielectric constant is desirably reduced due to the formation of numerous small non-interconnected cells in the foam. U.S. Pat. No. 3,072,583 discloses a nucleated foaming process for extruding perfluorinated polymer foam around transmission wire with a gas blowing agent. Foamed insulation using other thermoplastic materials, especially polyolefins, is also known in the art.
In general, after a conductor or conductive material is insulated with a foamed polymer, it is twisted into pairs (twinning), then four pairs are typically twisted together, and a polymer jacket is added to make the final cable. Adequate crush force of the insulation material is necessary so that the insulation material will maintain its structural integrity, e.g. foamed cell structure, during twinning and consumer use. Structural integrity can be achieved by minimizing or eliminating the amount of elongated cells in the foamed polymer structure and maximizing the amount of smaller sized cells. Elongated cells are elliptically shaped and are merely voids filled with gas, such as nitrogen, and provide poor mechanical strength to the foamed polymer. As such, during twinning, insulation material with a significant number of elongated cells has a tendency to crush which results in a final cable with poor electrical properties. Nucleating agents must be selected to obtain spherical shaped cells which provide the mechanical strength for durability, particularly during twinning operations, to obtain a final cable with good mechanical strength and good electrical properties. Thus, foamed polymer compositions require effective nucleating agent systems in effective amounts to make a foamed polymer with the appropriate structural integrity and performance properties, particularly for use as insulation for conductive materials.
In general, reduction in foam cell size is desired for thermoplastic resins. In particular, for thin wall foams (e.g. 5-10 mils) small voids to maximize the number of bubbles are desired for mechanical and electrical properties. This is especially so for smaller wire constructions of interest in the electronics field, so that, for example, foam cell dimensions will be small with respect to the radial dimension of the thin insulation.
Void space of foamed polymers is also important with regard to the capacitance of the foamed insulation material. It is important that the conductor with foamed insulation (primary) have a capacitance with low standard deviation. If the voids in the foamed insulation are not uniform, then capacitance variation can arise along a coated wire. Accordingly, small uniform bubbled distribution within the insulation material, which arises by creation of spherical shaped cells, will result in uniform capacitance. Thus, the nucleating agents are selected to obtain the uniform cell distribution within the foamed insulation material for stable capacitance.
Foamed fluoropolymers are also useful in applications other than wire insulation. Examples of foam structures include foamed sheet for electrical insulation, thermal insulation and cushioning, foamed pipe and tubing and injection molded pieces. Structural integrity and the minimization or elimination of elongated cells are also important for these applications.
A 0.5 to 2.0 weight percent loading of BN alone (5,000 ppm to 20,000 ppm) is typically used to provide foam cell nucleation in fluoropolymer resins having uniform, small cell structure. U.S. Pat. No. 4,764,538 discusses the use of synergistic combinations of BN in amounts of 0.02 to 2.0% by weight, and certain inorganic salts in amounts of 25 ppm to 3,000 ppm. The preferred range for BN in this system is 500 ppm to 10,000 ppm, and the minimum BN concentration exemplified in the patent is 2,500 ppm.
U.S. Pat. No. 4,877,815 describes a class of sulfonic and phosphonic acids, and salts of the acids, which are said to be effective nucleating agents for a wide variety of thermoplastic materials. The patent discusses the combination of certain sulfonic and phosphonic acids with BN, alone or combined with calcium tetraborate for foaming tetrafluoroethylene/hexafluoropropylene copolymers. U.S. Pat. No. 5,610,203 concerns the combination of BN crystals grown to final size, inorganic salt and/or sulfonic or phosphonic acids as nucleating agents.
TiO
2
is a white inorganic material and has a current market price of about $1 to about $2 per pound. TiO
2
is described in the art as
Ausimont USA, Inc.
Foelak Morton
Norris & McLaughlin & Marcus
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