Process for manufacturing a tyre and tyre bead structure

Abstract

Process for manufacturing a tyre, includes the following steps: (a) winding at least one metal wire so as to form a plurality of coils, the coils being radially superimposed and axially arranged side-by-side with respect to one another, so as to obtain a bead core; (b) applying at least one layer of a crosslinkable elastomeric material to the bead core obtained in step (a), so as to obtain a coated bead core; (c) partially crosslinking the at least one layer of crosslinkable elastomeric material, so as to obtain an amount of free sulfur of 30% by weight to 70% by weight, preferably of 40% by weight to 65% by weight, more preferably of 50% by weight to 60% by weight, with respect to the total weight of the sulfur present in the crosslinkable elastomeric material; and (d) applying a bead filler to the radial outer surface of the bead core obtained in step (c), so as to obtain a bead structure for a green tyre.

1 - 36 . (canceled) 
     
     
         37 . A process for manufacturing a tyre comprising:
 a carcass structure of a substantially toroidal shape, having opposite lateral edges associated with respective right-hand and left-hand bead structures, each bead structure comprising at least one bead core and at least one bead filler;   a belt structure applied in a radially external position with respect to said carcass structure;   a tread band radially superimposed on said belt structure; and   a pair of sidewalls applied laterally on opposite sides with respect to said carcass structure,   
       wherein said bead structure is manufactured by a process comprising the following steps:
 (a) winding at least one metal wire so as to form a plurality of coils, said coils being radially superimposed and axially arranged side-by-side with respect to one another, so as to obtain a bead core; 
 (b) applying at least one layer of a crosslinkable elastomeric material to the bead core obtained in step (a), so as to obtain a coated bead core; 
 (c) partially crosslinking said at least one layer of crosslinkable elastomeric material, so as to obtain 30% by weight to 70% by weight free sulfur with respect to the total weight of the sulfur present in said crosslinkable elastomeric material; 
 (d) applying a bead filler to the radial outer surface of the bead core obtained in step (c), so as to obtain a bead structure; 
 (e) applying the bead structure obtained in step (d) to a green carcass structure; 
 (f) completing the green carcass structure to obtain a green tyre structure; and 
 (g) moulding and vulcanizing the green tyre structure obtained in step (f) so as to obtain a finished tyre. 
 
     
     
         38 . The process for manufacturing a tyre according to  claim 37 , wherein said free sulfur is 40% by weight to 65% by weight with respect to the total weight of the sulfur present in said crosslinkable elastomeric material. 
     
     
         39 . The process for manufacturing a tyre according to  claim 38 , wherein said free sulfur is 50% by weight to 60% by weight with respect to the total weight of the sulfur present in said crosslinkable elastomeric material. 
     
     
         40 . The process for manufacturing a tyre according to  claim 37 , wherein said metal wire is a bare metal wire. 
     
     
         41 . The process for manufacturing a tyre according to  claim 37 , wherein after said partially crosslinking step (c) is carried out, said at least one layer of elastomeric material has a dynamic elastic modulus, measured at 100° C., lower than or equal to 28 MPa. 
     
     
         42 . The process for manufacturing a tyre according to  claim 41 , wherein after said partially crosslinking step (c) is carried out, said at least one layer of elastomeric material has a dynamic elastic modulus, measured at 100° C., of 18 MPa to 25 MPa. 
     
     
         43 . The process for manufacturing a tyre according to  claim 37 , wherein after said partially crosslinking step (c) is carried out, said at least one layer of elastomeric material has a dynamic elastic modulus, measured at 70° C., at a frequency of 10 Hz, with a deformation of 9%, lower than or equal to 15 MPa. 
     
     
         44 . The process for manufacturing a tyre according to  claim 43 , wherein after said partially crosslinking step (c) is carried out, said at least one layer of elastomeric material has a dynamic elastic modulus, measured at 70° C., at a frequency of 10 Hz, with a deformation of 9%, of 7 MPa to 12 MPa. 
     
     
         45 . The process for manufacturing a tyre according to  claim 37 , wherein step (a) is carried out by winding a plurality of metal wires or cords, each individual metal wire or cord being radially coiled onto itself so as to form a stack of radially superimposed wound coils. 
     
     
         46 . The process for manufacturing a tyre according to  claim 37 , wherein said metal wire or cord is made of steel. 
     
     
         47 . The process for manufacturing a tyre according to  claim 37 , wherein step (b) of applying at least one layer of a crosslinkable elastomeric material to the bead core obtained in step (a), is carried out by loop-wise wrapping around the bead core said at least one layer of crosslinkable elastomeric material. 
     
     
         48 . The process for manufacturing a tyre according to  claim 37 , wherein step (b) of applying said at least one layer of a crosslinkable elastomeric material to the bead core obtained in step (a), is carried out by helically winding said at least one layer of crosslinkable elastomeric material around the bead core. 
     
     
         49 . The process for manufacturing a tyre according to  claim 37 , wherein said at least one layer of crosslinkable elastomeric material has a thickness of 0.2 mm to 2 mm. 
     
     
         50 . The process for manufacturing a tyre according to  claim 49 , wherein said at least one layer of crosslinkable elastomeric material has a thickness of 0.5 mm to 1.5 mm. 
     
     
         51 . The process for manufacturing a tyre according to  claim 37 , wherein said partially crosslinking step (c) is carried out at a temperature of 110° C. to 160° C. 
     
     
         52 . The process for manufacturing a tyre according to  claim 51 , wherein said partially crosslinking step (c) is carried out at a temperature of 125° C. to 150° C. 
     
     
         53 . The process for manufacturing a tyre according to  claim 37 , wherein said partially crosslinking step (c) is carried out for 10 min to 40 min. 
     
     
         54 . The process for manufacturing a tyre according to  claim 53 , wherein said partially crosslinking step (c) is carried out for 15 min to 25 min. 
     
     
         55 . The process for manufacturing a tyre according to  claim 37 , wherein said process further comprises step (b 1 ) of applying at least one layer of crosslinkable elastomeric material into which reinforcing cords of heat-shrinkable material are embedded, around the coated bead core obtained in step (b). 
     
     
         56 . The process for manufacturing a tyre according to  claim 37 , wherein said process further comprises step (c 1 ) of applying at least one layer of crosslinkable elastomeric material around a coated bead core obtained in step (c). 
     
     
         57 . The process for manufacturing a tyre bead structure according to  claim 56 , wherein reinforcing cords of heat-shrinkable material are embedded into said at least one layer of crosslinkable elastomeric material. 
     
     
         58 . The process for manufacturing a tyre according to  claim 55 , wherein said reinforcing cords of heat-shrinkable material are made of thermoplastic polymers, nylon, polyethyleneterephthalate, or polyethylene-naphthalate. 
     
     
         59 . The process for manufacturing a tyre according to  claim 37 , wherein said process further comprises step (c 2 ) of surface-treating a coated bead core obtained in step (c). 
     
     
         60 . The process for manufacturing a tyre according to  claim 59 , wherein step (c 2 ) is carried out by dipping the coated bead core obtained in step (c) into an elastomeric solution. 
     
     
         61 . The process for manufacturing a tyre according to  claim 37 , wherein said at least one layer of crosslinkable elastomeric material used in step (b), comprises a crosslinkable elastomeric composition comprising:
 at least one elastomeric polymer;   at least one adhesion promoting additive; and   sulfur or derivatives thereof in an amount higher than or equal to 6 phr.   
     
     
         62 . The process for manufacturing a tyre bead structure according to  claim 61 , wherein said sulfur or derivatives thereof are present in an amount of 8 phr to 12 phr. 
     
     
         63 . A tyre bead structure comprising:
 at least one bead core comprising a plurality of coils of at least one metal wire, said coils being radially superimposed and axially arranged side-by-side with respect to one another; and   at least one bead filler,   wherein said bead core is coated with at least one partially crosslinked layer of a crosslinkable elastomeric material, said partially crosslinked layer comprising 30% by weight to 70% by weight free sulfur with respect to the total weight of the sulfur present in said crosslinkable elastomeric material.   
     
     
         64 . The tyre bead structure according to  claim 63 , wherein said partially crosslinked layer comprises 40% by weight to 65% by weight free sulfur with respect to the total weight of the sulfur present in said crosslinkable elastomeric material. 
     
     
         65 . The tyre bead structure according to  claim 64 , wherein said partially crosslinked layer comprises 50% by weight to 60% by weight free sulfur with respect to the total weight of the sulfur present in said crosslinkable elastomeric material. 
     
     
         66 . The tyre bead structure according to  claim 63 , wherein said metal wire is a bare metal wire. 
     
     
         67 . The tyre bead structure according to  claim 63 , wherein said partially crosslinked layer has a dynamic elastic modulus, measured at 100° C., lower than or equal to 28 MPa. 
     
     
         68 . The tyre bead structure according to  claim 67 , wherein said partially crosslinked layer has a dynamic elastic modulus, measured at 100° C., of 18 MPa to 25 MPa. 
     
     
         69 . The tyre bead structure according to  claim 63 , wherein said partially crosslinked layer has a dynamic elastic modulus measured at 70° C., at a frequency of 10 Hz, with a deformation of 9%, lower than or equal to 15 MPa. 
     
     
         70 . The tyre bead structure according to  claim 69 , wherein said partially crosslinked layer has a dynamic elastic modulus, measured at 70° C., at a frequency of 10 Hz, with a deformation of 9%, of 7 MPa to 12 MPa. 
     
     
         71 . The tyre bead structure according to  claim 63 , wherein said crosslinkable elastomeric material comprises a crosslinkable elastomeric composition comprising:
 at least one elastomeric polymer;   at least one adhesion promoting additive; and   sulfur or derivatives thereof in an amount higher than or equal to 6 phr.   
     
     
         72 . The tyre bead structure according to  claim 71 , wherein said crosslinkable elastomeric composition comprises 8 phr to 12 phr sulfur or derivatives thereof.