Self-sealing tyre for vehicle wheels

1. A self-sealing tyre for vehicle wheels obtained by vulcanizing a green self-sealing tyre comprising:

a carcass structure, a tread band applied in a radially external position to said carcass structure at least in a crown area of the tyre, a liner applied in a radially inner position to said carcass structure, and a layer of sealing material applied in a radially inner position to said carcass structure and which extends axially at least in all the crown area of the tyre, said layer of sealing material comprising at least a layer of sealing material comprising a sealing composition comprising:

(a) at least 20 phr of at least an unsaturated styrene thermoplastic elastomer;

(b) from 0 phr to 80 phr of at least a diene elastomer;

(c) from 4 phr to 6 phr of a crosslinking agent, the amount of the crosslinking agent in the sealing composition being such that:

V×S ′(10 Hz)= A

wherein:

V is an amount of the crosslinking agent expressed in meqv/100 g of composition;

S′ is a value of a moment of torsion strength in phase with deformation of the sealing material detected before crosslinking, expressed in dNm, measured with an oscillating rheometer at 50° C., at 25% of dynamic deformation and at 10 Hz; and

A is a parameter with value higher than 1.4; and

(d) from 100 to 200 phr of an extension oil.

2. The self-sealing tyre according to claim 1 , wherein the value of parameter A is lower than 10.

3. The self-sealing tyre according to claim 1 , wherein the value of parameter A is from 1.7 to 7.

4. The self-sealing tyre according to claim 1 , obtained by vulcanizing a green self-sealing tyre comprising at least a layer of sealing material comprising:

(a) at least 30 phr of at least one unsaturated styrene thermoplastic elastomer.

5. The self-sealing tyre according to claim 1 , wherein said sealing composition comprises:

(a) from 40 phr to 100 phr of at least one unsaturated styrene thermoplastic elastomer.

6. The self-sealing tyre according to claim 1 , wherein said sealing composition comprises:

(b) from 10 phr to 50 phr of at least one diene elastomer.

7. The self-sealing tyre according to claim 1 , wherein said sealing composition further comprises at least 20 phr of at least one adhesive resin.

8. The self-sealing tyre according to claim 7 , wherein the adhesive resin is selected from aliphatic resins, aromatic resins, natural resins and mixtures thereof.

9. The self-sealing tyre according to claim 1 , wherein said sealing composition further comprises from 30 phr to 200 phr of at least one adhesive resin.

10. The self-sealing tyre according to claim 1 , wherein the unsaturated styrene thermoplastic elastomer is a styrene polymer selected from block copolymers styrene/butadiene/styrene, styrene/isoprene/styrene, styrene/butadiene/isoprene/styrene, styrene-butadiene, styrene-isoprene, and mixtures thereof.

11. The self-sealing tyre according to claim 10 , wherein the unsaturated styrene thermoplastic elastomer is selected from styrene-butadiene and styrene-isoprene.

12. The self-sealing tyre according to claim 10 , wherein the unsaturated styrene thermoplastic elastomer is selected from the block copolymer styrene/isoprene/styrene or mixtures of one or more unsaturated styrene thermoplastic elastomers comprising at least 50% of block copolymer styrene/isoprene/styrene.

13. The self-sealing tyre according to claim 10 , wherein the block copolymer has a styrene content from 10% to 30%.

14. The self-sealing tyre according to claim 10 , wherein the block copolymer has a “di-block” percentage lower than 70%.

15. The self-sealing tyre according to claim 1 , wherein the crosslinking agent is selected from sulfur and molecules containing sulfur, and the sealing composition further comprises fatty acids or compounds containing zinc.

16. The self-sealing tyre according to claim 1 , wherein the crosslinking agent is a peroxide.

17. The self-sealing tyre according to claim 16 , wherein the crosslinking agent is selected from dicumyl peroxide, 2,5-dimethyl-2,5-di(t.butyl-peroxy)hexane, bis-(2,4-dichloro-benzoyl)peroxide and di-t.butyl-peroxide.

18. The self-sealing tyre according to claim 17 , wherein the peroxide is 2,5-dimethyl-2,5-di(t.butyl-peroxy)hexane.

19. The self-sealing tyre according to claim 1 , wherein said at least one diene elastomer is selected from elastomeric polymers and/or copolymers with at least an unsaturated chain having a glass transition temperature (Tg) lower than 20° C.

20. The self-sealing tyre according to claim 1 , wherein the extension oil is selected from polyolefin oils, paraffinic oils, naphthenic oils, aromatic oils, mineral oils and mixtures thereof.

21. The self-sealing tyre according to claim 1 , wherein said tyre comprises a carcass structure, a tread band applied in a radially external position to said carcass structure at least in a crown area, at least a liner applied in a radially inner position to said carcass structure, a sealing complex applied in a radially inner position to the liner and which axially extends at least in all the crown area of the tyre; said sealing complex comprising at least a self-supporting thermoplastic film and a layer of sealing material associated with and supported by said self-supporting thermoplastic film.

22. A process for the preparation of a self-sealing tyre for vehicle wheels comprising:

preparing a layer of sealing material; wherein the preparation of the layer of sealing material comprises:

feeding in a mixer comprising a housing, at least a screw revolving assembled in said housing comprising at least a feed opening and a discharge opening, said sealing composition comprising:

(a) at least 20 phr of at least an unsaturated styrene thermoplastic elastomer;

(b) from 0 phr to 80 phr of at least a diene elastomer;

(c) from 4 phr to 6 phr of a crosslinking agent,

wherein the amount of the crosslinking agent in the sealing composition is such that:

V×S ′(10 Hz)= A

wherein:

V is an amount of the crosslinking agent expressed in meqv/100 g of composition;

S′ is a value of a moment of torsion strength in phase with deformation of the sealing material detected before crosslinking, expressed in dNm, measured with an oscillating rheometer at 50° C., at 25% of dynamic deformation and at 10 Hz; and

A is a parameter with value higher than 1.4; and

(d) from 100 to 200 phr of an extension oil;

mixing said sealant composition; and

discharging said sealant composition from the mixer using the discharge opening;

forming a green tyre comprising a carcass structure, a tread band applied in a radially external position to said carcass structure at least in a crown area of the tyre, a liner applied in a radially inner position to said carcass structure, and said layer of sealing material applied in a radially inner position of said carcass structure and which extends axially at least in all the crown area of the tyre; and

conforming, molding and vulcanizing said green tyre.

23. The process for the preparation of a self-sealing tyre for vehicle wheels according to claim 22 , wherein the value of parameter A is lower than 10.

24. The process for the preparation of a self-sealing tyre for vehicle wheels according to claim 22 , wherein preparation of the layer of sealant material further comprises feeding of at least an adhesive resin to said mixer.

25. The process for the preparation of a self-sealing tyre for vehicle wheels according to claim 22 , wherein mixing said sealing composition is carried out at a temperature from 20° C. to 300° C.

26. The process for the preparation of a self-sealing tyre for vehicle wheels according to claim 22 , wherein said mixer is a sigma (Z-blades) mixer.

27. The process for the preparation of a self-sealing tyre for vehicle wheels according to claim 22 , wherein said mixer is a multi screw extruder.