Method of manufacturing a two-layer metal cord rubberized in situ using an unsaturated thermoplastic elastomer
A method of manufacturing a metal cord with two concentric layers of wires is provided. The cord includes an internal layer of M wires, M having a value from 1 to 4, and an external layer of N wires. The cord is rubberized from within in situ. That is, during manufacture of the cord, the cord is rubberized from inside. According to the method, the internal layer is sheathed with rubber or a rubber compound by passing the internal layer through an extrusion head, and the N wires of the external layer are assembled around the sheathed internal layer to form a two-layer cord rubberized from the inside. The rubber is an unsaturated thermoplastic elastomer that is extruded in a molten state, and preferably is a thermoplastic styrene (TPS) type of thermoplastic elastomer, such as an SBS or an SIS block copolymer, for example.
1. A method of manufacturing a metal cord that includes two concentric layers of wires having an M+N construction, the cord being rubberized in situ from within or inside during manufacture of the cord, the method comprising steps of:
sheathing an internal layer with rubber or a rubber compound by passing the internal layer through an extrusion head, the internal layer including M wires, with M having a value in a range from 1 to 4; and
assembling an external layer of N wires around the internal layer to form a two-layer cord that is rubberized from within or inside,
wherein the rubber or the rubber compound includes an unsaturated thermoplastic elastomer and is extruded in a molten state.
2. The method according to claim 1 , wherein the unsaturated thermoplastic elastomer is an unsaturated styrene thermoplastic elastomer.
3. The method according to claim 2 , wherein the unsaturated styrene thermoplastic elastomer includes polystyrene blocks and polydiene blocks.
4. The method according to claim 3 , wherein the polydiene blocks are selected from a group of blocks consisting of polyisoprene blocks, polybutadiene blocks, and mixtures thereof.
5. The method according to claim 4 , wherein the unsaturated styrene thermoplastic elastomer is a copolymer selected from a group of copolymers consisting of styrene/butadiene/styrene copolymers, styrene/butadiene/butylene/styrene copolymers, styrene/isoprene/styrene copolymers, styrene/butadiene/isoprene/styrene block copolymers, and mixtures thereof.
6. The method according to claim 1 , wherein a temperature at which the thermoplastic elastomer is extruded is between 100° C. and 250° C.
7. The method according to claim 1 ,
wherein the internal layer includes more than one wire (M>1), and
wherein the N wires of the external layer are wound in a helix at a same pitch and in a same direction of twisting as the M wires of the internal layer, such that the layers of the cord are manufactured to be compact layers.
8. The method according to claim 1 ,
wherein the internal layer includes more than one wire (M>1),
wherein the M wires of the internal layer and the N wires of the external layer are wound in helixes at different pitches, or in opposite directions of twisting, or both, and
wherein the layers of the cord are cylindrical layers.
9. The method according to claim 1 ,
wherein the step of assembling includes twisting the N wires of the external layer, and
wherein, if M is greater than 1, the step of assembling includes twisting the M wires of the internal layer.
10. The method according to claim 9 , further comprising a step of, after the step of assembling, twist balancing by passing the cord through a twist balancer.