Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/002—Inhomogeneous material in general
  • H01B3/006—Other inhomogeneous material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/441—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from alkenes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
  • H01B7/282—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable
  • H01B7/285—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable by completely or partially filling interstices in the cable

Definitions

• the present invention relates to filling materials for use in communication cables, such as electrical and optical cables, hi particular, the filling material exhibits a low dielectric constant and can be processed at elevated temperatures.
• Another, more widely practiced solution involves filing the interior interstitial space of a cable with a water insoluble filling material, such as a sealant, that would plug the cable and stop the migration of water.
• a filling material such as a sealant
• factors are usually taken into consideration, such as, e.g., its dielectric constant, density, aging and temperature stability, hydrophobic nature of the composition, processing and handling characteristics, shrinkage of the filling material upon cooling, toxicity, and cost.
• the filler material comprises (a) from about 50 to 95 percent by weight mineral oil; (b) less than about 10 percent by weight block copolymer selected from the group consisting of styrene-ethylene/butylene, styrene-ethylene/propylene, styrene-butadiene-styrene, styrene- isoprene-styrene, styrene-ethylene/butylene-styrene, styrene-ethylene/propylene-styrene, and combinations thereof; (c) less than about 25 percent by weight petroleum wax; (d) less than about 20 percent by weight hollow glass microspheres; and (e) less than about 10 percent by weight thixotropic agent selected from the group consisting of clay, colloidal metal oxide, fumed metal oxide, and combinations thereof.
• block copolymer selected from the group consisting of styrene-ethylene/butylene, styrene-ethylene/propylene
• the filler material comprises (a) from about 70.0 to 75.0 percent by weight mineral oil; (b) about 2.5 percent by weight styrene- ethylene/butylene-styrene block copolymer; (c) about 10.0 percent by weight petroleum wax; (d) from about 5.0 to 13.0 percent by weight hollow glass microsphere; (e) about 2.0 percent by weight surface modified fumed silica; and (f) about 0.2 percent by weight antioxidant or stabilizer.
• fumed silica is made by hydrolyzing silicon tetrachloride in vapor phase above 1000°C, giving very fine, nonporous, amorphous silica of high purity. See, e.g., Encyclopedia of Polymer Science and Engineering, Nolume 7, John Wiley and Sons, 1987, p. 57.
• surface modified fumed silica means generally that the fumed silica has been altered either by chemical reactions or through other mechanisms. It is within the scope of the present invention for the fumed silica to be altered in situ, as during the manufacturing of the filler material as described below in detail.
• One advantage of an exemplary embodiment of the present invention is that because the filler material has a low dielectric constant, that is a dielectric constant of less than or equal to 1.85, the thickness of the conductor insulation for an electrical cable can be reduced while maintaining the required mutual capacitance. With less insulation being used, the resulting cable would be smaller and weigh less. This advantage enables a lower cost electrical cable while not compromising its performance.
• hollow glass microspheres help lower the dielectric constant of the filler material.
• the microspheres can present a challenge.
• the density of the hollow glass microspheres is lower than the density of the other components used in the filler material, the hollow glass microspheres can phase separate, particularly at high temperature conditions.
• the phrase "high temperature” is used to mean when the filler material is exposed to a temperature in excess of 90°C, typically around 110°C.
• a thixotropic agent such clay, colloidal metal oxide, fumed metal oxide, and combinations thereof.
• the filler material When used in a cable, the filler material should have a sufficiently high melt drop temperature in order to prevent it from flowing out of the cable.
• An advantage of one embodiment of the present invention is that it exhibits high melt drop temperature.
• a high melt drop temperature is one that is typically above 90°C, as measured according to ASTM D-127.
• Another advantage of one embodiment of the present invention is that it exhibits low viscosity at high temperature conditions.
• a low viscosity is one that is less than 200 cP (0.2 Pa-s) at 110°C and a shear rate of 40 sec "1 , as measured according to ASTM D-3236.
• a low viscosity filler material is desirable in that it allows for ease of handling and processing.
• a filler material with low viscosity can more easily fill the interstitial space present in the cable.
• a low viscosity also allows the filler material to be processed at high temperature.
• the filler material of the present invention can but need not be cooled during the manufacture of the electrical cable.
• the filler material has a low density.
• a low density is one that is less than 0.8 g/cm 3 and in some applications can be less than 0.5 g/cm 3 .
• the variation in the density depends on the content of the hollow glass microsphere.
• a low density filler material is desirable because when used in a cable, the filler material will not contribute as much weight to the cable thus yielding a lighter weight cable.
• the filler material of the present invention can be used in various electrical, opto-electrical (i.e., a combination of optical and electronic components), and optical applications.
• Illustrative examples of such applications include cables, connectors, and closures.
• Illustrative connectors include, but are not limited to, discrete connectors, modular connectors, connector boxes and grease boxes.
• Illustrative closures include, but are not limited to drop wire closures, filled closures, buried closures, and terminal blocks.
• Figure 1 is a schematic cross-sectional view of an exemplary electrical cable of the present invention
• Figure 2 is a graph showing the interaction between solution viscosity and shear rate for a generic thixotropic material.
• Figure 1 shows an exemplary electrical cable using the filler material of the present invention.
• Electrical cable 10 comprises two electrical conductors 12, such as copper wires, typically twisted together to form a pair. Surrounding each electrical conductor is polymeric insulator 14, such as polyethylene. Exterior cable structure 18 encloses the twisted pair of electrical conductors and filler material 16.
• Figure 1 shows a pair of electrical conductors, one skilled in the art will understand that any number of electrical conductors can be used.
• the focus of the present invention lies in the filler material, which comprises or consists essentially of (i) mineral oil, (ii) block copolymer selected from the group consisting of diblock copolymer, triblock copolymer, and combinations thereof, (iii) petroleum wax, (iv) hollow glass microspheres, and (v) thixotropic agent.
• antioxidants or stabilizers or functionalized polymers can be added to the filler material.
• the filler material can be described as having a bulk phase and a discontinuous phase.
• the bulk phase is present up to 50 volume percent of the total volume and includes mineral oil, block copolymer, petroleum wax, and thixotropic agent.
• the discontinuous phase is present up to 50 volume percent of the total volume and includes the hollow glass microspheres.
• Mineral oil is the largest constituent and is present at a minimum of 50% by weight.
• the mineral oil is present at a maximum of 95% by weight.
• the mineral oil can be either a paraffinic mineral oil or a naphthenic mineral oil.
• the mmeral oil has less than 15% aromatic content.
• a naphthenic mineral is one that contains a naphthene group (more appropriately termed as a cycloparaffin) and is greater than 35% naphthenic and less than 65% paraffinic, according to ASTM D-2501.
• a suitable, commercially available mineral oil that can be used in the present invention is KAYDOL ® White Mineral Oil from Crompton Corp., Middleburg, Connecticut. According to the Crompton web site at www. cromptoncorp .
• KAYDOL ® White Mineral Oil is highly refined oil that consists of saturated aliphatic and alicyclic non-polar hydrocarbons, is hydrophobic, colorless, tasteless, odorless, and is chemically inert.
• SEMTOL ® 40 White Mineral Oil is Another useful commercially available mineral oil, also from Crompton Corporation.
• the filler material contains block copolymer selected from the group consisting of diblock copolymer, triblock copolymer, and combinations thereof.
• the block copolymer is present at a maximum of 10% by weight.
• Suitable diblock copolymers include, but are not limited to, styrene-ethylene/butylene and styrene-ethylene/propylene.
• Suitable triblock copolymers include, but are not limited to, styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene (SEBS), and styrene-ethylene/propylene-styrene (SEPS).
• SBS styrene-butadiene-styrene
• SIS styrene-isoprene-styrene
• SEBS styrene-ethylene/butylene-styrene
• SEPS styrene-ethylene/propylene-styrene
• Suitable, commercially available SEBS block copolymers that can be used in the present invention include KRATON TM G-1650 Block Copolymer and KRATON TM G-1652 Block Copolymer, both available from Kraton Polymers, Houston, Texas
• both polymers are linear SEBS block copolymers having a block styrene content of 30% in mass spectroscopy.
• the web site reported a solution viscosity of 8 Pa-s at 25% mass in toluene at 25°C and a melt flow rate of less than 1 g/10 minute for KRATON TM G-1650 Block Copolymer.
• the web site reported a solution viscosity of 1.35 Pa-s at 25% mass in toluene at 25°C and a melt flow rate of 5 g/10 minute for the KRATON TM G-1652 Block Copolymer.
• Another useful commercially available block copolymers is KRATON TM G- 1726 Block Copolymer.
• the filler material contains petroleum wax present at a maximum of 25% by weight.
• One function of the petroleum wax is to improve, i.e., to increase, the melt drop temperature of the filler material.
• the melting point of the petroleum wax is greater than 90°C.
• a suitable petroleum wax is a polyethylene wax having a melting point greater than 90°C.
• Suitable, commercially available petroleum wax that can be used in the present invention include PARAFLiNT ® C105 Paraffin Wax, which is reported to have a melting point of 97.8°C, and PARAFLINT ® HI Paraffin Wax, which is reported to have a melting point of 107.8°C. Both PARAFLINT ® Paraffin Waxes listed above are considered to be synthetic wax made by the Fischer-Tropsch process and are available from Moore & Munger, Inc., Shelton, Connecticut.
• the filler material contains hollow glass microspheres present at maximum of 20% by weight.
• Useful hollow glass microspheres have a particle size (by volume and at effective top size (95%)) of 10 to 140 micrometers and a true density of 0.1 g/cm 3 to 0.4 g/cm 3 .
• Suitable, commercially available hollow glass microspheres that can be used in the present invention include the S Series, K Series, and A Series of 3M TM SCOTCHLITE TM Glass Bubbles from 3M Company, St. Paul, Minnesota.
• the S22, Kl, K15, K20 and A16 type hollow glass microspheres can be used and Table 1 below lists their true density and particle size.
• the term "true density” is a concentration of matter, as measured by mass (weight) per unit volume. It is within the scope of the present invention to use functionalized hollow glass microspheres.
• the hollow glass microspheres used in the present invention contain a large volume fraction of air (e.g., on the order of 90% to 95% air) having a dielectric constant of 1.0, they function to reduce the overall dielectric constant of the filler material. Because the hollow glass microspheres have a low density, as compared to the rest of the filler material constituents, the microspheres tend to phase separate when the filler material is melted at processing temperatures. As one skilled in the art will readily recognize, phase separation of the hollow glass microspheres from the filler material when it is in a molten state presents processing challenges and will result in a non-uniform performing filler material. It has been learned that the use of a thixotropic agent can help to minimize if not eliminate the problem of phase separation of the hollow glass microspheres.
• air e.g., on the order of 90% to 95% air
• Sedimentation or flotation of particles i.e., phase separation
• particles i.e., phase separation
• No is the terminal float velocity of a single hollow sphere with diameter "d” and density “p t ,” in a gravitational field, g, through a fluid medium of viscosity " ⁇ m " and density "p m ".
• Stokes' Law is used to predict stability against sedimentation or flotation of hollow spheres in dilute dispersions, the concept can be extended to the filler material of the present invention.
• the minimum fluid viscosity needed to keep the hollow sphere from phase separating can be estimated for a given hollow sphere diameter and density.
• the fluid viscosity of the filler material can be controlled through the use of thixotropic agent.
• the filler contains thixotropoic agent present at a maximum of 10% by weight.
• Thixotropic agents that are useful in the present invention can be selected from the group consisting of clay, colloidal metal oxide, fumed metal oxide, and combinations thereof.
• Useful metal oxides, whether colloidal or fumed include, but are not limited to silica, alumina, zirconia, and titania.
• a suitable thixotropic agent should produce a filler material having a shear viscosity vs. shear rate response similar to that shown in Figure 2. That is, for a given temperature, the viscosity of the filler material at low shear rate is higher than the viscosity at a high shear rate.
• the viscosity should be sufficiently high to entrap the hollow glass microspheres in solution so that they will not phase separate and at high shear rate, the viscosity is sufficiently low so that the filler material solution can flow for processing purposes, e.g., the filler material can be pumped.
• a constant stress rheometer such as the Advanced Rheometer 2000 from TA Instruments, New Castle, Delaware
• the "k" value of the filler material increases and the "n” value decreases.
• the minimum viscosity of the inventive filler material occurs at an "n” value of 0.8 and a "k” value of 0.25 Pa-s.
• the maximum viscosity of the inventive filler material occurs at an "n” value of 0.2 and a "k” value of 7.0 Pa-s.
• the thixotropic agent is a fumed metal oxide, such as fumed silica.
• Suitable, commercially available surface treated fumed silica that can be used in the present invention include CAB-O-SIL ® TS-530 Treated Fumed Silica (a hexamethyldisilazane treated hydrophobic fumed silica), CAB-O- SIL ® TS-610 Treated Fumed Silica (a dimethyldichlorosilane treated hydrophobic fumed silica), and CAB-O-SIL ® TS-720 Treated Fumed Silica (a dimethyl silicone fluid treated hydrophobic fumed silica), from Cabot Corporation of Tuscola, Illinois.
• Suitable, commercially available surface treated fumed silica include AEROSIL ® R-104 and R-106 Fumed Silica (octamethylcylotetrasiloxane treated hydrophobic fumed silica), and AEROSIL ® R-972 and R-974 Fumed Silica (dimethyldichlorosilane a treated hydrophobic fumed silica) from Degussa Corporation of Allendale, New Jersey.
• the fumed silicas listed above are substantially hydrophobic after surface treatment.
• the filler material can optionally contain antioxidants or stabilizers at less than 1% by weight to improve processing or to protect against environmental aging caused by heat.
• Suitable antioxidants or stabilizers include phenols, phosphites, phosphorites, thiosynergists, amines, benzoates, and combinations thereof.
• Useful, commercially available phenolic-based antioxidants include IRGANOX ® 1035, IRGANOX ® 1010, 1RGANOX ® 1076 Antioxidant and Heat Stabilizer for wire and cable applications, from Ciba Specialty Chemicals Corp., Tarrytown, New York.
• the filler material exhibits the following functional properties. At 1 megahertz, it has a dielectric constant of less than 2.0 and a dissipation factor of less than 0.001, both as measures according to ASTM D-150. h another embodiment, the filler material has a dielectric constant of less than 1.85 at 1 megahertz. In yet another embodiment, the filler material has a dielectric constant of less than 1.65 at 1 "
• the filler material has a maximum solution viscosity of 200 cP (0.2 Pa-s) at 110°C and a shear rate of 40 sec "1 . In another embodiment, the filler has a solution viscosity of 75 cP (0.075 Pa-s) at 110°C and a shear rate of 40 sec "1 .
• the solution viscosity can be measured according to ASTM D-3236 using a Brookfield RNT Thermocel viscometer with a SC 4-27 spindle and a rotational speed of 100 rpm.
• the filler material can be made using the following exemplary process.
• the mineral oil, block copolymer, and petroleum wax are mixed in a vessel heated to at least
• the thixotropic agent is added and homogenized until it is substantially dispersed in the solution.
• the solution is placed in a vacuum oven heated to between 110° to 120°C. A vacuum of 30 inches Hg (102 kPa) is used. Thereafter, hollow glass microspheres are added to the solution while its temperature is maintained at 110°C.
• the inventive filler material can be maintained in solution form at a temperature of at least 110°C, for at least 1 hour without phase separation of the hollow glass microspheres.
• the filler material can be maintained in solution at a temperature of at least 110°C for 24 hours without phase separation.
• Phase separation of the hollow glass microspheres can be determined using various methods.
• One exemplary method involves collecting the filler material in solution form and storing it in a container, such as a vial, at 110°C. After a specific amount of time, e.g., after 1 hour, 4 hours, 8 hours, 12 hours, etc., the vial is removed from the oven and the contents cooled at room temperature. The solidified filler material is then cut in half and the density of the top half is compared with the density of the bottom half. A difference in density of less than 0.01 density units between the top half and bottom half indicates no separation.
• the inventive filler material is used in an electrical cable.
• An exemplary electrical cable contains 25 pairs of twisted metal (such as copper) wires.
• the individual pairs of twisted wires are fed into a hopper containing the inventive filler material.
• the filler material fills the interstitial space between the wires.
• the pairs of twisted wires are disposed closely to one another and a polymeric sheath is used to bundle the pairs of twisted wires together.
• the filler material not only occupies the interstitial space between the wires but also the interstitial space between the pairs of wires.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Insulated Conductors (AREA)
• Sealing Material Composition (AREA)

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Cited By (6)

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Citations (4)

• 2005
  • 2005-01-04 KR KR1020067015189A patent/KR20060129327A/ko not_active Application Discontinuation
  • 2005-01-04 WO PCT/US2005/000105 patent/WO2005073983A1/en not_active Application Discontinuation
  • 2005-01-04 JP JP2006551102A patent/JP2007522282A/ja not_active Withdrawn
  • 2005-01-04 EP EP05704939A patent/EP1709647A1/en not_active Withdrawn
  • 2005-01-04 CN CNA2005800061409A patent/CN1926642A/zh active Pending
  • 2005-01-17 TW TW094101333A patent/TW200604267A/zh unknown

Patent Citations (4)

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