Process for the Manufacture of a Multi-Compound Tread for Pneumatic Tires for Road Vehicles

Abstract

A process for the manufacture of a tread band for pneumatic tyres, wherein the blocks thereof comprise different rubber portions characterized by a different hysteresis loss. The process comprises a shredding step, wherein from a first and from a second rubber tread compound a plurality of fragments is manufactured with dimensions of between 6 and 30 mesh; a mixing step, wherein the fragments from the first and second compound are mixed together in order to obtain a mixture wherein said fragments are distributed in a random manner and retain their chemical/physical individuality; and an extrusion step, wherein the mixture from the preceding step is extruded for the manufacture of the tread band. The first and second compounds have different dynamic properties in terms of: dynamic modulus at 30° C., tand at 0° C., tand at 30° C. and tand at 60° C. The fragments retain a chemical/physical individuality both within the mixture formed during the mixing step and within the tread band formed during the extrusion step.

Claims

1-9. (canceled)

10. A method for manufacturing a tread band for pneumatic tires wherein blocks thereof comprise portions with differing hysteresis losses, the method comprising: shredding a first rubber tread compound and a second rubber tread compound to produce a plurality of fragments with dimensions of between 6 and 30 mesh; mixing the plurality of fragments together to obtain a mixture wherein said fragments are distributed in a random manner and retain their chemical/physical individuality; and extruding the mixture from the mixing step to form the tread band wherein said fragments from, respectively, said first rubber tread and said second rubber tread compound are distributed randomly and retain their chemical/physical individuality; wherein said first rubber tread compound and said second rubber tread compound have different dynamic properties with respect to each of: dynamic modulus at 30° C.; tan δ at 0° C.; tan δ at 30° C.; and tan δ at 60° C.

11. The method of claim 10, wherein: said first rubber tread compound has a dynamic modulus at 30° C. of between 11.0 and 17.0 MPa, a tan δ at 0° C. of between 0.85 and 1.1, a tan δ at 30° C. of between 0.45 and 0.65 and a tan δ at 60° C. of between 0.19 and 0.30; said second rubber tread compound has a dynamic modulus at 30° C. of between 5.5 and 15 MPa and less than that of said first rubber tread compound by at least 2 MPa, a tan δ at 0° C. of between 0.70 and 0.99 and less than that of said first rubber tread compound by at least 0.02, a tan δ at 30° C. of between 0.21 and 0.63 and less than that of said first rubber tread compound by at least 0.02, a tan δ at 60° C. between 0.10 and 0.28 and less than that of said first rubber tread compound by at least 0.02.

12. The method of claim 10, wherein said shredding step comprises an extrusion operation for said first rubber tread compound and said second rubber tread compound, and a die-cutting operation for the extrusions of said first rubber tread compound and said second rubber tread compound.

13. The method of claim 12, wherein said mixing step and said extrusion step are actuated by a thrust deriving from the extrusion operation associated with the die-cutting operation.

14. A tread band for pneumatic tires wherein blocks thereof comprise portions with differing hysteresis losses, manufactured by: shredding a first rubber tread compound and a second rubber tread compound to produce a plurality of fragments with dimensions of between 6 and 30 mesh; mixing the plurality of fragments together to obtain a mixture wherein said fragments are distributed in a random manner and retain their chemical/physical individuality; and extruding the mixture from the mixing step to form the tread band wherein said fragments from, respectively, said first rubber tread and said second rubber tread compound are distributed randomly and retain their chemical/physical individuality; wherein said first rubber tread compound and said second rubber tread compound have different dynamic properties with respect to each of: dynamic modulus at 30° C.; tan δ at 0° C.; tan δ at 30° C.; and tan δ at 60° C.

15. The tread band of claim 14, wherein: said first rubber tread compound has a dynamic modulus at 30° C. of between 11.0 and 17.0 MPa, a tan δ at 0° C. of between 0.85 and 1.1, a tan δ at 30° C. of between 0.45 and 0.65 and a tan δ at 60° C. of between 0.19 and 0.30; and said second rubber tread compound has a dynamic modulus at 30° C. of between 5.5 and 15 MPa and less than that of said first rubber tread compound by at least 2 MPa, a tan δ at 0° C. of between 0.70 and 0.99 and less than that of said first rubber tread compound by at least 0.02, a tan δ at 30° C. of between 0.21 and 0.63 and less than that of said first rubber tread compound by at least 0.02, a tan δ at 60° C. between 0.10 and 0.28 and less than that of said first rubber tread compound by at least 0.02.

16. The tread band of claim 14, wherein the shredding step comprises an extrusion operation for said first rubber tread compound and said second rubber tread compound, and a die-cutting operation for the extrusions of said first rubber tread compound and said second rubber tread compound.

17. The tread band of claim 16, wherein said mixing step and said extrusion step are actuated by a thrust deriving from the extrusion operation associated with the die-cutting operation.

18. A plant for manufacture of a tread band for pneumatic tires, wherein blocks thereof comprise different rubber portions characterized by a different hysteresis loss, the plant comprising: a shredding station configured to produce a plurality of fragments from a first rubber tread compound and from a second rubber tread compound, each of the plurality of fragments having dimensions of between 6 and 30 mesh; a mixing station configured to mix the fragments from said first rubber tread compound and said second rubber tread compound together and form a mixture wherein said fragments are distributed in a random manner and retain their chemical/physical individuality; and an extrusion station configured to extrude the mixture from the mixing station to form said tread band, wherein said fragments from said first and said second compound are distributed randomly and retain their chemical/physical individuality.

19. The plant of claim 18, wherein the extrusion station is configured to extrude the mixture from the mixing station to a further manufacturing stage wherein at least the tread band is subjected to vulcanization.

20. The plant of claim 18, wherein: said shredding station comprises first and second extruders operating in parallel and wherein into each thereof a first rubber tread compound and a second rubber tread compound is respectively loaded; each of said first and second extruders respectively comprising a multiple extruder mouth made of a plurality of outflow tubes and a rotary die whereto respective free ends of the outflow tubes face and are configured to implement shredding for the production of said fragments.

21. The plant of claim 20, wherein said mixing station comprises a mixing chamber having an inlet opening connected to said rotary die and an outlet opening connected to said extrusion station.

22. The plant of claim 21, wherein said mixing chamber has a substantially truncated cone conformation, wherein upon a larger base thereof, said inlet opening is formed and upon a smaller base thereof, said outlet opening is formed.

Description

[0021] Below an exemplary, non-limiting embodiment of the present invention is given for illustrative purposes, with the aid of the accompanying figures, wherein:

[0022] FIG. 1 is a perspective view in exploded form of the plant according to the present invention; and

[0023] FIGS. 2 and 3 show, in exploded form, and from two different angles, an enlarged detail of the plant of FIG. 1.

[0024] In FIG. 1, the plant, the object of the present invention, is indicated in the entirety thereof with 1.

[0025] The plant 1 comprises a shredding station 2, a mixing station 3 and an extrusion station 4.

[0026] The shredding station 2 comprises two extruders 5a and 5b, which are loaded, through the hoppers thereof, respectively, with a first and a second tread compound. The two compounds have differing dynamic properties in terms of: dynamic modulus at 30° C., tand at 0° C., tand at 30° C. and tand at 60° C.

[0027] Table I gives the compositions of the first and second rubber compounds used.

TABLE-US-00001 TABLE I FIRST SECOND COMPOUND COMPOUND POLYMERIC S-SBR 100.0 80.0 BASE WITH E-SBR 0 20.0 OIL FILLER SILICA 70.0 80.0 CARBON BLACK 10.0 5.0 BINDER SILANE 7.0 7.0 AGENT MICROCRYS- 8.0 8.0 TALLINE WAX STEARIC ACID 1.0 1.0 AROMATIC OIL 4.0 4.0 Vulcanization ZINC OXIDE 2.0 2.0 agents SULFUR 1.0 1.5 MBTS 1.0 1.2 DPG 1.5 1.8 DRY POLYMERIC 100 100 BASE

[0028] E-SBR is a polymeric base obtained by means of an emulsion polymerization process with an average molecular weight of between 800-1500×10.sup.3 and 500-900×10.sup.3, respectively, with a styrene content of between 20 and 45% and used with an oil content of between 0 and 30%.

[0029] S-SBR is a polymeric base obtained by means of a solution polymerization process with an average molecular weight of between 800-1500×10.sup.3 and 500-900×10.sup.3, respectively, with a styrene content of between 20 and 45%.

[0030] The silica used is marketed under the name ULTRASIL VN3 by the DEGUSSA company.

[0031] The carbon black used is marketed under the name Vulcan 7H (N234) by the CABOT company.

[0032] The silane used is marketed under the name SI 69 by the DEGUSSA company.

[0033] MBTS is the abbreviation of the compound mercaptobenzothiazole disulfide which functions as a vulcanization accelerator; DPG is the acronym of the compound diphenylguanidine which functions as a vulcanization accelerator.

[0034] The first and the second compounds have a dynamic modulus at 30° C., respectively, of 14.4 and 9.4 MPa, a tand at 0° C., respectively, of 0.980 and 0.810, a tand at 30° C., respectively, of 0.532 and 0.238 and a tand at 60° C., respectively, of 0.220 and 0.124.

[0035] Both extruders 5a and 5b have a multiple extrusion mouth 6a and 6b comprising a plurality of tubes 7, wherein the free ends thereof are blocked within respective circular openings formed within a single support plate 8.

[0036] The shredding station 2 comprises a rotary die 9, wherein a plurality of openings is formed in order to allow for the die-cutting of the extruded compounds.

[0037] The extruded compounds, once they pass through the rotary die 9, are in fact cut by the action of the rotation of the rotary die 9 itself.

[0038] The extrusion speed of the extruders 5a and 5b and the speed of rotation of the rotary die 9 are set in order to obtain fragments with dimensions of between 6 and 30 mesh.

[0039] In FIGS. 2 and 3, the multiple extrusion mouths 6a and 6b are described in detail from two different angles together with the plurality of the tubes 7, the support plate 8 and the rotary die 9.

[0040] The mixing station 3 comprises a mixing chamber 10, of a substantially truncated cone shape, wherein the larger base thereof defines an inlet opening 11 connected to the rotary die 9, and wherein the smaller base thereof defines an outlet opening 12 connected to the extrusion station 4.

[0041] The fragments, once produced by the action of the rotary die 9, enter the mixing chamber 10 where, by virtue also of the shape of the mixing chamber 10 itself, they are mixed together thereby producing a new compound wherein, however, each fragment maintains its own chemical/physical individuality.

[0042] The fact that the different fragments retain their chemical/physical individuality is extremely important in ensuring the effectiveness of the invention.

[0043] In fact, only if the different fragments do not fuse together but retain their individuality is it possible to produce a tread band wherein the blocks thereof are composed of parts with differing hysteresis losses and with the advantages that this entails in terms of rolling resistance and wet grip.

[0044] Finally, the extrusion station 4 comprises an extrusion outlet 13 connected directly to the outlet opening 12 of the mixing chamber 10. The tread band emerges from the extrusion outlet 13 and is then combined with those other parts of the pneumatic tire that are then to be subjected to a vulcanization step.

[0045] From the description above it is apparent that the mixing within the mixing chamber 10 and the extrusion through the extrusion outlet 13 take place due to the thrust deriving from the action of the two extruders 5a and 5b.

[0046] As mentioned above, the method and plant of the present invention ensure the preparation of a tread band, wherein the blocks thereof are composed of the random combination of a plurality of portions with differing hysteresis losses.

[0047] In particular, it should be noted that the process and the plant of the present invention ensure the effective, high-throughput preparation of the aforementioned tread band.

[0048] In this way it will be possible to produce a tread band wherein the technical characteristics thereof are such as to ensure significant improvement effects in terms of wet grip performance, maintaining, at the same time, the advantages obtained in terms of rolling resistance.