Method for manufacturing a coaxial cable with a strippable center conductor precoat
View Patent ↗A coaxial cable is provided with a specially prepared precoat layer that facilitates removal of the precoat layer when the end of the cable is cored in preparation for receiving a connector. The cable includes an inner conductor; a foam polyolefin dielectric layer surrounding the inner conductor; an outer conductor surrounding said dielectric layer; and a precoat layer disposed between the inner conductor and the dielectric layer. The precoat layer forms a first bond interface with the inner conductor and a second bond interface with the dielectric layer, wherein the ratio of the axial shear adhesion force of the first (“A”) bond to the axial shear adhesive force of the second (“B”) bond is less than 1, and wherein the ratio of the axial shear adhesion force of the “A” bond formed by the precoat layer between the inner conductor to the dielectric layer to the rotational shear adhesion force of the bond is 5 or greater.
1. A method of manufacturing a coaxial cable comprising:
directing a conductor along a predetermined path of travel into and through a preheater and preheating the conductor;
melting in a first extruder a thermoplastic polymer precoat composition;
directing the preheated conductor into and through the first extruder and extruding onto the surface of the center conductor a continuous thin coating layer of the molten precoat composition;
allowing the layer of precoat composition to cool and solidify forming a first bond interface (“A” bond) with the inner conductor;
maintaining the temperature of the conductor and layer of precoat composition no more than 200° F.;
directing the conductor and layer of precoat composition into and through a second extruder and extruding onto the coated conductor a foamable polymer composition,
allowing the foamable polymer composition to expand, cool and solidify to form a foam dielectric surrounding the conductor with a second bond interface (“B” bond) between the layer of precoat composition and the dielectric;
surrounding the foam dielectric with a continuous metallic sheath forming the outer conductor of the coaxial cable; and
controlling the bond adhesion forces at the first and second bond interfaces so that the ratio of the axial shear strength of the first (“A”) bond to the axial shear strength of the second (“B”) bond is less than 1.
2. The method of claim 1 , wherein the polymer precoat composition comprises a homopolymer or copolymer composition selected from the group consisting of polyethylene homopolymer, amorphous and atactic polypropylene homopolymer, polyolefin copolymer, styrene copolymer, polyvinyl acetate, polyvinyl alcohol, paraffin waxes, and blends of two or more of the foregoing, and wherein the preheating step heats the conductor to a surface temperature of 100° F. to 300° F.
3. The method of claim 1 , wherein the first extruder forms a precoat layer with a thickness of from 0.0001 to 0.020 inch.
4. A method of manufacturing a coaxial cable comprising:
directing a conductor along a predetermined path of travel into and through a preheater and preheating the conductor to a surface temperature of 75 ° F. to 300° F.;
melting in a first extruder a thermoplastic polymer precoat composition comprising a blend of low density polyethylene having a melt index of at least 50 g/10 min and ethylene acrylic acid copolymer;
directing the preheated conductor into and through the first extruder and extruding onto the surface of the center conductor a continuous coating layer of the molten precoat composition with a thickness of from 0.0001 to 0.020 inch;
allowing the layer of precoat composition to cool and solidify forming a first bond interface (“A” bond) with the inner conductor;
directing the conductor and layer of precoat composition into and through a second extruder and extruding onto the coated conductor a foamable polyolefin polymer composition;
allowing the foamable polymer composition to expand, cool and solidify to form a closed cell polyolefin foam dielectric surrounding the conductor with a second bond interface (“B” bond) between the layer of precoat composition and the dielectric;
surrounding the foam dielectric with a continuous metallic sheath forming the outer conductor of the coaxial cable; and
controlling the bond adhesion forces at the first and second bond interfaces so that the ratio of the axial shear strength of the first (“A”) bond to the axial shear strength of the second (“B”) bond is less than 1.
5. The method of claim 4 , including also controlling the bond adhesion forces so that the ratio of the rotational shear strength of the first (“A”) bond to the rotational shear strength of the second (“B”) bond is less than 1.
6. The method cable of claim 4 , including also controlling the bond adhesion forces so that the ratio of the axial shear adhesion force of the “A” bond to the rotational shear adhesion force of the “A” bond is 5 or greater.