Tyre for vehicle wheels
The present invention relates to a tyre ( 100 ) comprising a particular elastomeric compound in the underlayer ( 111 ), i.e. in the layer arranged between the tread band ( 109 ) and the belt structure ( 106 ) of the tyre. According to the invention, the tyre has a considerably reduced rolling resistance compared to known tyres, and at the same time, good road grip, excellent maneuverability and comfort.
1 . A tyre for vehicle wheels comprising:
a carcass structure having opposing side edges associated with respective annular anchoring structures;
a belt structure located in a position radially external to the carcass structure;
a tread band located in a position radially external to the belt structure;
a pair of sidewall structures, wherein each sidewall structure comprises a sidewall extended in a position axially external to the carcass structure and extended radially between one of the annular anchoring structures and an axially external portion of the tread band; and
at least one underlayer, wherein the underlayer is in a radially internal position with respect to the tread band and radially external with respect to the belt structure, and wherein the at least one underlayer is positioned in contact with the tread band along its entire axial length,
wherein the at least one underlayer comprises a vulcanised elastomeric compound having a shear modulus value G′, measured with a Rubber Process Analyzer (RPA) at 70° C., 10 Hz, 9% strain, of less than 0.90 MPa, a dynamic elastic compression modulus value E′ ranging from 3.00 MPa to 8.00 MPa, and a dynamic viscous compression modulus value E″ of less than 0.24 MPa,
wherein the moduli E′ and E″ are measured at 23° C. with an Instron model 1341 dynamic device in a tension-compression mode on cylindrical samples of 25 mm in length and 14 mm in diameter, cross-linked at 170° C. for 10 minutes, longitudinally pre-compressed by 25% and subjected to a dynamic sinusoidal stress of ±3.5% of amplitude and 10 Hz of frequency.
2 . The tyre according to claim 1 , wherein the vulcanised elastomeric compound has a shear modulus value G′ of less than 0.87 MPa, a dynamic elastic compression modulus value E′ ranging from 3.50 MPa to 7.50 MPa, and a dynamic viscous compression modulus value E″ of less than 0.23 MPa.
3 . The tyre according to claim 1 , wherein the tyre has one underlayer.
4 . The tyre according to claim 1 , wherein the at least one underlayer comprises at least 50%, 60%, 70%, or 80%, by weight of the vulcanised elastomeric compound.
5 . The tyre according to claim 4 , wherein the at least one underlayer comprises at least 90%, by weight of the vulcanised elastomeric compound.
6 . The tyre according to claim 1 , wherein the vulcanised elastomeric compound of the at least one underlayer comprises, before vulcanisation, an elastomeric composition comprising:
−100 phr of at least one diene elastomeric polymer,
one or more reinforcing fillers in a total amount of not more than 25 phr, wherein the one or more fillers comprise at least 5 phr of optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions, and
at least 0.1 phr of at least one vulcanisation agent.
7 . The tyre according to claim 6 , wherein the 100 phr of at least one diene elastomeric polymer of the composition comprises:
from 70 phr to 100 phr of a synthetic or a natural polyisoprene, or mixtures thereof, and
from 0 phr to 30 phr of a polybutadiene.
8 . The tyre according to claim 6 , wherein the composition comprises one or more reinforcing fillers in a total amount of less than 20%, 18%, or 16%, by weight with respect to the total weight of the composition.
9 . The tyre according to claim 6 , wherein the composition comprises one or more reinforcing fillers in a total amount of not more than 25 phr and not less than 10 phr, and wherein the fillers comprise at least 6 phr of optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions.
10 . The tyre according to claim 6 , wherein the one or more reinforcing filler comprises a mixture of silica and optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions.
11 . The tyre according to claim 10 , wherein the silica and the optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions are present in a weight ratio of between 0.5:1 and 5:1.
12 . The tyre according to claim 11 , wherein the silica and the optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions are present in a weight ratio between 0.7:1 and 5:1.
13 . The tyre according to claim 12 , wherein the silica and the optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions are present in a weight ratio between 0.8:1 and 3:1.
14 . The tyre according to claim 13 , wherein the silica and the optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions are present in a weight ratio between 0.9:1 and 1.1:1.
15 . The tyre according to claim 6 , wherein the one or more reinforcing fillers comprises carbon black.
16 . The tyre according to claim 6 , wherein the one or more reinforcing filler comprises from 0 phr to 15 phr of carbon black, from 5 to 20 phr of silica, and from 5 phr to 20 phr of optionally modified silicate fibres with needle-shaped morphology of nanometric dimensions.
17 . The tyre according to claim 6 , wherein the silicate fibres with needle-shaped morphology of nanometric dimensions are optionally modified sepiolite fibres.
18 . The tyre according to claim 1 , wherein the vulcanised elastomeric compound of the underlayer has a Tan Delta value lower than 0.065, measured with the RPA at 70° C., 10 Hz, 9% strain.
19 . The tyre according to claim 18 , wherein the vulcanised elastomeric compound of the underlayer has a Tan Delta value lower than 0.060.
20 . The tyre according to claim 19 , wherein the vulcanised elastomeric compound of the underlayer has a Tan Delta value lower than 0.055.