At&t Technologies, Inc.

Western Electric Company, Inc.

Bell Telephone Laboratories

At&t Bell Laboratories

William M Kanotz

William C Vesperman

Max K Wilson

Jae H Choi

George F Piper

William Robert Lockhart

John J Mottine, Jr

Robert F Staats-Westover

A telephone cord employs as an insulator for the conductors therein an extrudable blend of a styrene-ethylenebutylene-styrene copolymer with polypropylene.

Extrudable blend

Insulating material for telephone cords and telephone cords

Insulating covering for strand material

A hybrid extruder provides plastic insulation which is as uniformly and tightly disposed about a substrate as that produced in a conventional pressure extruder and accommodates irregular substrates. The hybrid extruder includes a core tube which is positioned in a die cavity to form a flow passage which includes a restriction to the flow at the end of the core tube to maximize the pressure in the plastic material. The leading end of the core tube is spaced a distance from the land of a die which is substantially less than in conventional pressure extruders to form another portion of the flow passage having a predetermined configuration. After flowing through the restriction, the plastic material expands. This avoids any backflow of the plastic material into the core tube in the event the core tube is to allow the passage of oversized spliced portions of the substrate. Advantageously, this arrangement also prevents the occurrence of melt fracture when extruding relatively high molecular weight plastic materials which because of excellent mechanical and dielectric properties are desired for insulating particular substates.

Hybrid apparatus for insulating conductors

An extrusion system is provided for covering a conductor (14) with a crystalline thermoplastic elastomer insulating material. The plastic material is tubed onto the conductor by apparatus which includes a core tube (61) that is mounted in an extruder crosshead (41) such that its free end is positioned within the interior of a die (81, 101) and is spaced from an orifice of the die a predetermined percentage of the land length of the die. A flow passage between the core tube (61) and a wall which defines the die cavity is controlled in accordance with the relative value of the thermal energy which is released by the insulating material at the onset of crystallization. In one arrangement, which has been found to be suitable for a crystalline thermoplastic elastomer having a relatively high value of released thermal energy, the die cavity and the core tube are arranged to provide a gradually converging path toward the die opening. For an insulating material having a relatively low value of released thermal energy, the flow passage is modified to provide a diverging portion (105) and then a rapidly converging portion (110) which communicates with the land of the die.

Method for insulating conductors with a crystalline plastic material

A hybrid extruder provides plastic insulation which is as uniformly and tightly disposed about a substrate as that produced in a conventional pressure extruder and accommodates irregular substrates. The hybrid extruder includes a core tube which is positioned in a die cavity to form a flow passage which includes a restriction to the flow at the end of the core tube to maximize the pressure in the plastic material. The leading end of the core tube is spaced a distance from the land of a die which is substantially less than in conventional pressure extruders to form another portion of the flow passage having a predetermined configuration. After flowing through the restriction, the plastic material expands. This avoids any backflow of the plastic material into the core tube in the event the core tube is to allow the passage of oversized spliced portions of the substrate. Advantageously, this arrangement also prevents the occurrence of melt fracture when extruding relatively high molecular weight plastic materials which because of excellent mechanical and dielectric properties are desired for insulating particular substrates.

Hybrid extrusion methods

An extrusion system for covering a flexible conductor (14) with a crystalline thermoplastic elastomer insulating material by tubing the plastic onto the conductor includes a core tube (61) which is mounted in an extruder crosshead (41) such that its free end is positioned within the interior of the extruder die (59). The free end of the core tube is spaced from the die opening a predetermined percentage of the land length of the die. In this arrangement, which has been found to be suitable for a crystalline thermoplastic elastomer having a crystallization initiation temperature which is capable of being substantially near to its melting point temperature, the crosshead and the core tube are arranged to provide a streamlined flow path of the insulating material toward the die opening. Air at a higher pressure than has been used in the past is caused to flow through the core tube to cause the extrudate to balloon outwardly from the conductor for a length of travel to permit adequate crystallization of the extrudate so that when it engages the conductor, it will compress any upstanding metallic burrs. This arrangement substantially inhibits the adherence to and the accumulation of any plastic material on the outer surface of the core tube which would affect the concentric disposition of the insulation cover (18) about the conductor.

Apparatus for insulating relatively flexible conductors

An insulation comprising a polyether polyester thermoplastic copolymer obtained by reacting 1,4 butane diol terephthalate with terephthalate esters of polytetramethylene glycol is coated over an irregularly configured conductor, such as for example, a tinsel conductor, suitable for use in telecommunications cordage by moving the copolymer through an extruder and along a flow path formed between a core tube and wall of a die cavity. The die cavity adjacent to the throat of the die has a frustoconical portion formed with an approach angle of sufficient magnitude to minimize the pressure drop through the extruder to extrude the copolymer at a temperature slightly above the melting point of the copolymer. The copolymer is insulation tubed over the tinsel conductor with a gas at a controlled volume rate of flow being moved through the core tube along with the tinsel conductor to expand the copolymer extrudate as it flows out of the die opening to cool the extrudate and to facilitate advantageously oriented crystalline growth of the copolymer. Subsequently, the insulation is drawn down about the tinsel conductor with a slight spacing therefrom while treating the insulation with water at a predetermined temperature to anneal the insulation in a predetermined manner. A plurality of the insulated tinsel conductors are enclosed in a jacket which comprises a plasticized polyvinyl chloride composition.

Apparatus for insulating flexible conductors

An insulation comprising a polyether polyester thermoplastic copolymer obtained by reacting 1, 4 butane diol terephthalate with terepthalate esters of polytetramethylene glycol is coated over an irregularly configured conductor, such as for example, a tinsel conductor, suitable for use in telecommunications cordage by moving the copolymer through an extruder and along a flow path formed between a core tube and wall of a die cavity. The die cavity adjacent to the throat of the die has a frustoconical portion formed with an approach angle of sufficient magnitude to minimize the pressure drop through the extruder to extrude the copolymer at a temperature slightly above the melting point of the copolymer. The copolymer insulation is tubed over the tinsel conductor with a gas at a controlled volume rate of flow being moved through the core tube along with the tinsel conductor to expand the copolymer extrudate as it flows out of the die opening to cool the extrudate and to facilitate advantageously oriented crystalline growth of the copolymer. Subsequently, the insulation is drawn down about the tinsel conductor with a slight spacing therefrom while treating the insulation with water at a predetermined temperature to anneal the insulation in a predetermined manner. A plurality of the insulated tinsel conductors are enclosed in a jacket which comprises a plasticized polyvinyl chloride composition.

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Baldwin, MD, United States of America

William M Kanotz