Rubber compound for portions of pneumatic tyres

Abstract

A rubber compound for the preparation of portions of pneumatic tyres comprising a cross-linking unsaturated chain polymer base, a filler system and a vulcanization system. The filler system comprises (a) a first carbon black having a surface area less than or equal to 170 m.sup.2/gr in a quantity greater than or equal to 25 phr; (b) a second carbon black having a surface area greater than or equal to 250 m.sup.2/gr in a quantity such that the ratio between the quantity of the first carbon black and the quantity of the second carbon black is greater than or equal to 3 and less than or equal to 10; (c) a carbon black dispersing agent in a quantity of less than or equal to 1 phr.

Claims

1. A tire tread comprising a rubber compound comprising a cross-linking unsaturated chain polymer base, a filler system and a vulcanizing system; said compound being characterized in that said filler system comprises (a) a first carbon black having a surface area measured according to a nitrogen adsorption test of less than or equal to 170 m.sup.2/gr in a quantity greater than or equal to 25 phr; (b) a second carbon black having a surface area measured according to a nitrogen adsorption test of greater than or equal to 250 m.sup.2/gr in a quantity such that the ratio between the quantity of said first carbon black and the quantity of said second carbon black is greater than or equal to 3 and less than or equal to 10; (c) a carbon black dispersing agent consisting of N′-(1,3-dimethylbutylidene)-3-hydroxy-2-naphthohydrazide is present in a quantity of more than zero and less than or equal to 1 phr.

2. The tire tread according to claim 1, wherein the rubber compound is characterized in that said second carbon black has a surface area measured according to a nitrogen adsorption test of greater than or equal to 800 m.sup.2/gr.

3. The tire tread according to claim 1, wherein the rubber compound is characterized in that said first carbon black has a surface area measured according to a nitrogen adsorption test of greater than or equal to 100 m.sup.2/gr.

4. The tire tread according to claim 1, wherein the rubber compound characterized in that the ratio between the quantity of said first carbon black and the quantity of said second carbon black is greater than or equal to 5 and less than or equal to 8.

5. The tire tread according to claim 1 wherein the first carbon black is N550 grade.

6. The tire tread of claim 1, wherein the second carbon black has a surface area measured according to a nitrogen adsorption test of 800 to 1000 m.sup.2/gr.

7. The tire tread of claim 1, wherein the second carbon black has a surface area measured according to a nitrogen adsorption test of 300 to 1000 m.sup.2/gr.

8. The tire tread of claim 1, wherein the first carbon black is present in an amount of about 35 phr.

9. The tire tread of claim 1, wherein the second carbon black is present in an amount of about 5 to about 10 phr.

10. The tire tread of claim 8, wherein the second carbon black is present in an amount of about 5 to about 10 phr.

11. Pneumatic tire comprising a tire tread according to claim 1.

12. A tire tread comprising a rubber compound comprising a cross-linking unsaturated chain polymer base, a filler system and a vulcanizing system; said compound being characterized in that said filler system comprises (a) a first carbon black having a surface area measured according to a nitrogen adsorption test of less than or equal to 170 m.sup.2/gr in a quantity greater than or equal to 25 phr; (b) a second carbon black having a surface area measured according to a nitrogen adsorption test of greater than or equal to 250 m.sup.2/gr in a quantity such that the ratio between the quantity of said first carbon black and the quantity of said second carbon black is greater than or equal to 3 and less than or equal to 10; (c) a carbon black dispersing agent consisting of N′-(1,3-dimethylbutylidene)-3-hydroxy-2-naphthohydrazide in a quantity of about 0.6 phr to 1 phr.

13. The tire tread according to claim 12, wherein the rubber compound according to claim 1 is characterized in that said second carbon black has a surface area measured according to a nitrogen adsorption test of greater than or equal to 800 m.sup.2/gr.

14. The tire tread according to claim 12, wherein the rubber compound according to claim 1 is characterized in that said first carbon black has a surface area measured according to a nitrogen adsorption test of greater than or equal to 100 m.sup.2/gr.

15. The tire tread according to claim 12, wherein the rubber compound according to claim 1 characterized in that the ratio between the quantity of said first carbon black and the quantity of said second carbon black is greater than or equal to 5 and less than or equal to 8.

16. The tire tread of claim 12, wherein the second carbon black has a surface area measured according to a nitrogen adsorption test of 800 to 1000 m.sup.2/gr.

17. The tire tread of claim 12, wherein the second carbon black has a surface area measured according to a nitrogen adsorption test of 300 to 1000 m.sup.2/gr.

18. The tire tread of claim 12, wherein the first carbon black is present in an amount of about 35 phr.

19. The tire tread of claim 12, wherein the second carbon black is present in an amount of about 5 to about 10 phr.

20. Pneumatic tire comprising a tire tread according to claim 12.

Description

EXAMPLES

(1) Nine compounds were prepared seven of which are comparison compounds and two of which are compounds of the invention.

(2) In particular, the first compound (Compound A) constitutes a first comparison example and represents a standard compound used for manufacturing a portion of a casing. The Compound A comprises as a filler a carbon black with a surface area of 50 m.sup.2/gr (falling within the definition of “first carbon black” according to the wording of the annexed claims) whilst not comprising any type of dispersing agent. The second compound (Compound B) constitutes another comparison example and differs from Compound A insofar as it provides for the addition of a further carbon black with a surface area of 150 m.sup.2/gr (falling within the definition of “first carbon black” according to the wording of the annexed claims). The third compound (Compound C) constitutes a further comparison compound and differs from Compound B insofar as it provides for the addition of a dispersing agent. The fourth compound (Compound D) constitutes a further comparison compound and differs from Compound A insofar as it provides for the addition of a further carbon black with a surface area of 300 m.sup.2/gr (falling within the definition of “first carbon black” according to the wording of the annexed claims). The fifth compound (Compound E) constitutes a compound according to the invention and differs from Compound D insofar as it provides for the addition of a dispersing agent. The sixth compound (Compound F) constitutes another comparison compound and differs from Compound A insofar as it provides for the addition of a further carbon black with a surface area of 1000 m.sup.2/gr (falling within the definition of “first carbon black” according to the wording of the annexed claims). The seventh compound (Compound G) constitutes a compound according to the invention and differs from Compound F insofar as it provides for the addition of a dispersing agent. The eighth and ninth compounds differ respectively from Compound E and Compound G insofar as they have a different ratio between the quantity of low surface area carbon black and the quantity of high surface area carbon black.

(3) The compounds of the examples were prepared according to a standard procedure, which is not relevant to the purposes of the present invention.

(4) —Preparation of the Compounds—

(5) (1.sup.st Mixing Step)

(6) Before the start of the mixing, a mixer with tangential rotors and an internal volume of between 230 and 270 liters was loaded with the cross-linkable polymer base and the carbon black and, when provided for, the dispersing agent, thus reaching a filling factor of 66-72%.

(7) The mixer was operated at a speed of 40-60 revolutions/minute, and the mixture thus formed was discharged once a temperature of 140-160° C. had been reached.

(8) (2.sup.nd Mixing Step)

(9) The mixture obtained from the previous step was reworked in a mixer that was operated at a speed of 40-60 revolutions/minute and, thereafter, discharged once a temperature of 130-150° C. had been reached.

(10) (Final Mixing Step)

(11) The vulcanization system was added to the mixture obtained from the previous step, reaching a filling factor of 63-67%.

(12) The mixer was operated at a speed of 20-40 revolutions/minute, and the mixture thus formed was discharged once a temperature of 100-110° C. had been reached.

(13) Table I lists the compositions in phr of the nine compounds described above.

(14) TABLE-US-00001 TABLE I A B C D E F G H I NR 40 BR 60 CB N550 35 CB N134 — 20 20 — — — — — — CB* — — — 10 10 — — 15 — CB** — — — — — 5 5 — 3 Dispersing — — 0.6 — 0.6 — 0.6 0.6 0.6 agent CB 3.5 3.5 7 7 2 12 N550/CB* or CB N550/CB** Sulfur 2.0 Accelerants 2.5 Antioxidants 4.5 ZnO 3.0 Stearic acid 2.0

(15) NR is a 1,4-cis-polyisoprene rubber of natural origin.

(16) BR is a butadiene rubber with a 1,4-cis content of at least 40%.

(17) The acronym N550 denotes a carbon black surface area of 50 m.sup.2/gr.

(18) The acronym N134 denotes a carbon black surface area of 150 m.sup.2/gr.

(19) CB* denotes a carbon black with a surface area equal to 300 m.sup.2/gr.

(20) CB** denotes a carbon black with a surface area equal to 1000 m.sup.2/gr.

(21) The dispersing agent used is N′-(1,3-dimethylbutylidene)-3-hydroxy-2-naphthohydrazide (BMH).

(22) The compounds listed in Table I were subjected to a viscosity measurement and, once vulcanized, to a measurement of the electrical resistance, rolling resistance and mechanical properties.

(23) The viscosity values were obtained according to the ASTM 1646 standard.

(24) The rolling resistance values are strictly correlated to the tan δ values measured at 60° C. (the lower the tan δ value at 60° C., the better the resulting rolling resistance), as dynamic mechanical properties according to the ISO 4664 standard.

(25) The mechanical properties were measured in accordance with the ISO 37 standard.

(26) Table II lists the results obtained from the tests described above.

(27) In order to more immediately highlight those advantages deriving from the present invention, the values of Table II are indexed to the comparison compound values (Compound A).

(28) TABLE-US-00002 TABLE II A B C D E F G H I Rolling 100 90 95 95 100 95 100 95 105 resistance Electrical 10.sup.10 10.sup.6 10.sup.7 10.sup.6 10.sup.6 10.sup.5 10.sup.5 10.sup.6 10.sup.8 resistance Viscosity 100 130 120 130 120 120 110 130 105 TB 100 110 108 110 108 105 103 110 102 EB 100 100 100 100 100 100 100 100 100 M300 100 110 108 110 105 105 103 110 100 E′ (1%) 100 110 106 110 105 110 105 110 105

(29) From the values listed in Table II, it is clear that only Compounds E and G, which meet the claimed technical characteristics, are able to ensure the sought after low levels of electrical resistance whilst, contemporaneously, maintaining high levels of rolling resistance.

(30) In particular, it is worth noting that: although Compound C comprises the dispersing agent and a mixture of two carbon blacks with differing surface areas, it is nonetheless unable to prevent a deterioration in the value of rolling resistance insofar as the added carbon black does not meet the claimed conditions; even though Compounds D and F comprise a mixture of carbon black that satisfies the claimed characteristics, they are nonetheless unable to prevent a deterioration in the value of rolling resistance due to the absence of the dispersing agent.

(31) Finally, Compounds H and I demonstrate that if the ratio between the respective quantities of the two carbon blacks is not as per that claimed, the advantages sought in terms of rolling resistance or electrical resistance cannot be obtained.