Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-04-11
2002-08-06
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S497000
Reexamination Certificate
active
06429237
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the high-speed extrusion coating of wire conductors with pigmented fluoropolymers.
BACKGROUND OF THE INVENTION
Melt-processible fluoropolymers are widely used as insulation for conductors, i.e. wires. “Plenum cable” is one such use. Plenum cable is used for telephone, computer, and similar wiring in office buildings, schools, etc. Fluoropolymer coating on the wire makes a superior insulation because it is not flammable. A further advantage of fluoropolymers is their low dielectric constant, a desirable property in communications wire insulation.
Melt-processible fluoropolymers are applied to wire by melt extrusion on wire-coating equipment whose design is well-known to those skilled in the art. The wires are generally used in pairs, often called “twisted pairs”, and to distinguish the paired wires, the insulation is colored. One wire of the pair is white, and the other is blue or red or another non-white color, so that not only may the paired wires be distinguished from one another, but also the twisted pairs may be distinguished from one another by the various colors of the non-white insulated wire. U.S. Pat. No. 5,789,466 describes white pigmentation of fluoropolymers using titanium dioxide (TiO
2
) coated with silane.
Wire coating is typically done at about 1500 ft/minute (7.6 m/s). This is referred to as the “line speed”. The melt viscosity of the polymer is a factor that limits the line speed. As line speed is increased, a point is reached at which the appearance and quality of the coating begin to deteriorate. This deterioration shows up as surface roughness, variation in coating thickness, such as lumps of polymer at intervals along the wire, and defects in the insulating quality of the coating, known as “sparks”.
For more efficient use of the wire coating equipment and greater productivity, it is desirable that line speeds be increased without loss of coating quality. In fact, the standards of quality of the insulation are higher than in the past because the demand for faster and more nearly error-free transmission is increasing. Polymers have been developed recently that can be extruded on wire at speeds of 2500 feet/minute (12.7 m/s), preferably 3000 feet/minute (15 m/s). However, white pigment traditionally used in fluoropolymers for wire coating does not perform well in high-speed extrusion, but gives insulation having unacceptable levels of lumps and sparks.
There is a need for white pigmented fluoropolymer compositions that can be extruded at high speed onto wire to give insulation with few or no lumps or sparks.
SUMMARY OF THE INVENTION
In one embodiment, this invention is a process for the coating of a conductor comprising melt extruding onto said conductor a blend comprised of
(a) melt-processible fluoropolymer having a flex life of greater than about 1000 cycles, and capable of being extruded by itself at at least about 2500 ft/min (12.7 m/s) and
(b) a pigment comprising titanium dioxide coated with one or more layers comprising oxides, or mixtures of oxides, of at least one of silicon and aluminum, said extruding being at a rate of at least about 2000 ft/min (10 m/s) to give a conductor with a coating having no more than about 10 lumps/135,000 ft (41,000 m) or no more than about 10 sparks/135,000 ft (41,000 m).
In a second embodiment, this invention is a composition capable of being melt-extruded onto a conductor at a rate of at least about 2000 ft/min (10 m/s) comprised of (a) melt-processible fluoropolymer having a flex life greater than about 1000 cycles, and capable of being extruded by itself at at least about 2500 ft/min (12.7 m/s) and (b) pigment comprising titanium dioxide coated with one or more layers comprising oxides, or mixtures of oxides, of at least one of silicon and aluminum.
DETAILED DESCRIPTION
The melt-processible fluoropolymer used in the present invention is that special class that is not only by itself capable of high speed extrusion, but which also exhibits excellent physical properties, characterized by high flex life. Thus, the melt-processible fluoropolymers of this invention are preferably comprised of at least one fluoromonomer, have melting points below about 320° C., and have melt flow rates (MFR) of about 15 g/10 min to 50 g/10 min, more preferably of about 20 g/10 min to 40 g/10 min.
Fluoromonomers are monomers containing at least 35 wt % fluorine, preferably at least 50 wt % fluorine, that can be polymerized in the process of this invention include fluoroolefins having 2-10 carbon atoms, and fluorinated vinyl ethers of the formula CY
2
═CYOR or CY
2
═CYOR′OR wherein Y is H or F, and —R, and —R′— are independently completely-fluorinated or partially-fluorinated alkyl and alkylene groups containing 1-8 carbon atoms. Preferred —R groups contain 1-4 carbon atoms and are preferably perfluorinated. Preferred —R′— groups contain 2-4 carbon atoms and are preferably perfluorinated. Preferred perfluoro(alkyl vinyl ethers) (PAVE) are perfluoro(propyl vinyl ether) (PPVE) and perfluoro(ethyl vinyl ether) (PEVE). More preferred PAVE is PEVE. Preferred fluoroolefins have 2-6 carbon atoms and include TFE, hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), vinyl fluoride, vinylidene fluoride (VF
2
), trifluoroethylene, hexafluoroisobutylene, and perfluorobutyl ethylene (PFBE). More preferred fluoroolefins are TFE and HFP.
The fluoropolymers of this invention are melt-processible. By the term “melt-processible” it is meant that the copolymer can be processed (i.e., fabricated into shaped articles such as films, fibers, tubes, wire coatings and the like) by conventional melt extruding means. The fluoropolymers are preferably copolymers, more preferably copolymers of TFE and of CTFE, most preferably copolymers of TFE. These may be copolymers of TFE and of CTFE with other fluoromonomers. They may also be copolymers of TFE and of CTFE with nonfluoromonomers, such as hydrocarbon monomers. Hydrocarbon monomers that copolymerize with some combinations of fluoromonomers include propylene and ethylene. The preferred hydrocarbon monomer is ethylene. By “copolymer” is meant a polymer made by polymerizing two or more monomers.
Examples of useful copolymers include the copolymers of TFE with HFP and/or perfluoro(alkyl vinyl ethers) such as PPVE or PEVE, copolymers of TFE with PMVE, and copolymers of TFE or CTFE with ethylene. Further examples include the copolymers of vinylidene fluoride with HFP, or with HFP and TFE. As implied above, copolymers may contain additional monomers beyond the fluoromonomers named. TFE/ethylene copolymers, for example, are most useful if they include additional monomers that introduce bulky side groups such as PFBE, HFP, PPVE or 2-trifluoromethyl-3,3,3-trifluoro-1-propene.
Preferred copolymers of TFE are copolymers of TFE with HFP, and of TFE with fluorinated vinyl ethers. More preferred are copolymers of TFE, HFP, and PAVE. Most preferred are copolymers of TFE, HFP, and PEVE.
The composition and molecular weight of the fluoropolymer used in the present invention is selected from the foregoing so that the fluoropolymer is not only capable of being extruded at high speed, but also has a good flex life, as measured by ASTM D2176. Capability of extrusion at a rate of at least about 2500 ft/min (12.7 m/s), preferably about 3000 ft/min (15 m/s) is achieved by the fluoropolymer preferably having a melt flow rate of about 15 g/10 min to 50 g/10 min, as measured according to ASTM D-1238T as described in U.S. Pat. No. 4,380,618. The temperature and the weight used in the test depend upon the composition of the fluoropolymer.
Making such high melt flow rate fluoropolymers is not only a matter of reducing molecular weight. Because physical properties of polymers are strongly dependent upon molecular weight, simply reducing molecular weight (increasing melt flow rate) results in loss of properties such as flex life, which are important to applications such as wire insulation. To counteract this tendency, adjustments must be made to the composition of the
E. I. du Pont de Nemours & Company
Michl Paul R.
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