TBR PNEUMATIC TIRE

Abstract

A TBR pneumatic tyre comprising a carcass, a tread and at least one high elongation belt formed from a single cord with a laying angle of between 0.03 and 0.1 and comprising an axial extension CW wherein the ratio thereof to the axial extension of said tread (TW/CW) is between 1.1 and 1.4. The tread is made of a rubber compound comprising a cross-linkable unsaturated chain polymeric base comprising at least 50% by weight of natural rubber (NR), a mixture of fillers comprising (a) a carbon black having a surface area of between 99 and 170 m2/g and with a structure of greater than 120 cc/100 g, (b) a first silica having a surface area of less than 100 m2/g, and (c) a second silica having a surface area of more than 190 m2/g.

Claims

1-9. (canceled)

10. A truck and bus radial (TBR) pneumatic tire comprising: a carcass; a tread; and at least one high elongation belt formed from a single cord with a laying angle of between 0.03 and 0.1 and comprising an axial extension, wherein a ratio of the axial extension thereof to the axial extension of the tread is between 1.1 and 1.4; wherein the tread is manufactured from a rubber compound comprising a cross-linkable unsaturated chain polymeric base comprising at least 50% by weight of natural rubber, a mixture of fillers comprising silica and carbon black and a vulcanization system; and wherein the mixture of fillers comprises: a carbon black having a surface area of between 99 and 170 m.sup.2/g and with a structure of greater than 120 cc/100 g; a first silica having a surface area of less than 100 m.sup.2/g; and a second silica having a surface area of more than 190 m.sup.2/g.

11. The pneumatic tire of claim 10, wherein the mixture of fillers comprises: 15-40% by weight of the carbon black; 10-35% by weight of the first silica; and 40-80% by weight of the second silica.

12. The pneumatic tire of claim 10, wherein the mixture of fillers comprises: 25-35% by weight of the carbon black; 15-25% by weight of the first silica; and 50-60% by weight of the second silica.

13. The pneumatic tire of claim 10, wherein the carbon black has a surface area of between 120 and 150 m.sup.2/g and with a structure of between 120 and 170 cc/100 g.

14. The pneumatic tire of claim 10, wherein the first silica has a surface area of between 70 and 100 m.sup.2/g.

15. The pneumatic tire of claim 10, wherein the second silica has a surface area of between 190 and 250 m.sup.2/g.

16. The pneumatic tire of claim 10, comprising four belts of which a second belt starting from the carcass is a first high elongation belt of the at least one high elongation belt.

17. The pneumatic tire of claim 16, wherein the first high elongation belt has a laying angle of 0.042 and an axial extension wherein a ratio thereof to the axial extension of the tread is 1.25.

18. The pneumatic tire of claim 10, wherein the at least one high elongation belt has a laying angle of 0.042 and an axial extension wherein a ratio thereof to the axial extension of the tread is 1.25.

19. The pneumatic tire of claim 10, wherein the high elongation belt is manufactured from RT (Regular Tensile) steel.

20. The pneumatic tire of claim 10, wherein the high elongation belt is manufactured from HT (High Tensile) steel.

21. The pneumatic tire of claim 10, wherein the high elongation belt is manufactured from SHT (Super High Tensile) steel.

22. The pneumatic tire of claim 10, wherein the high elongation belt is manufactured from UHT (Ultra High Tensile) steel.

Description

EXAMPLES

[0031] A pneumatic tire according to the present invention is indicated in the entirety thereof with 1 in the FIGURE. The pneumatic tire 1 comprises a carcass 2, a tread 3 and a plurality of belts 4.

[0032] The tread comprises a central portion 3a and a pair of shoulders 3b.

[0033] The belts 4 comprise at least one belt 5 of the high elongation belt type as defined above. As illustrated in the FIGURE, the belt 5 has an axial extension that meets the requirements defined in the claims.

[0034] In particular, the pneumatic tire 1 comprises four belts of which the second, starting from the carcass 2, is a high elongation belt 5.

[0035] Three tread compounds (A-C) were made to be used for the manufacture of test pneumatic tires wherein properties will be studied in relation to rolling resistance, wear resistance and uneven wear.

[0036] The compound A comprises a mixture of fillers which does not satisfy the composition of the present invention, while the B and C compounds comprise a mixture of fillers that does satisfy the composition of the present invention.

[0037] Herebelow, the procedure is given for the preparation of the compounds described in the examples. This procedure does not represent a limitation for the present invention.

[0038] The term Intermesh Mixer refers to a machine for mixing rubber as described and claimed in U.S. Pat. No. 5,368,383.

[0039] The term non-productive mixing step refers to a mixing step during which the ingredients of the compound, excluding the vulcanization system, are added and mixed with the cross-linkable unsaturated chain polymeric base; while the term productive mixing step refers to a mixing step during which the vulcanization system is added and mixed with the mixture under preparation.

[0040] Preparation of the Compounds

(First Non-Productive Mixing Step)

[0041] Before mixing, a first mixing chamber of a 5 liter Intermesh Mixer was loaded with the ingredients listed in Tables I and II with the exception of the sulfur, stearic acid and the accelerant, with a fill factor of 60-70%.

[0042] This first mixing step was performed while maintaining a temperature of 140 C. for 60 seconds.

(Second Non-Productive Mixing Step)

[0043] The mixture of the first step was discharged into a second 5 liter chamber of the Intermesh mixer reaching a fill factor of 35-41%.

[0044] This second mixing step was performed while maintaining a temperature of 155 C. for 210 seconds.

(Productive Mixing Step)

[0045] The mixture obtained from the second non-productive mixing step was discharged into a 2 liter tangential rotor mixer and to it were added sulfur, stearic acid and an accelerant reaching a fill factor equal to 70%.

[0046] The mixer was operated at a speed of 20-40 rpm, and the resulting mixture was unloaded upon reaching a temperature of 100-110 C.

[0047] Table I shows the compositions in phr of the compounds of the examples.

TABLE-US-00001 TABLE I A B C NR 70 70 70 SBR 30 30 30 Carbon black 37 15 18 First silica (VLSA) 20 10 Second silica (HSA) 10 23 30 Sulfur 1.2 1.2 1.2 Stearic acid 3.5 3.5 3.5 Accelerant 2.15 2.15 2.15 NR is a 1,4-cis-polyisoprene rubber of natural origin. S-SBR is a polymeric base obtained by means of a solution polymerization process with an average molecular weight ranging, respectively, between 800-1500 10.sup.3 and between 500-900 10.sup.3, with a stirene content ranging between 10 and 45% and a vinyl content ranging between 20 and 70%. The carbon black has a surface area of 138 m.sup.2/g. The first silica (VLSA) has a surface area of 80 m.sup.2/g. The second silica (HSA) has a surface area of 200 m.sup.2/g. The vulcanization accelerant utilized is N-tert-butyl-2-benzothiazyl-sulfenamide (TBBS).

[0048] The compounds reported in Table I were used for the construction of five pneumatic tires (I-V). In particular, the pneumatic tires I-IV are comparative examples, while the pneumatic tire V represents a pneumatic tire according to the invention.

[0049] In particular, the pneumatic tire I does not comprise a high elongation belt and comprises a tread made using a compound wherein the mixture of fillers thereof comprises carbon black and only the silica with the high surface area (compound A); the pneumatic tire II does not comprise a high elongation belt and comprises a tread made using a compound wherein the mixture of fillers thereof comprises carbon black, the high surface area silica and the low surface area silica according to the invention, in a ratio different than that according to the invention (compound B); the pneumatic tire III does not comprise a high elongation belt and comprises a tread made using a compound wherein the mixture of fillers thereof comprises carbon black, the high surface area silica and the low surface area silica in the ratio according to the invention (compound C); the pneumatic tire IV comprises a high elongation belt according to the characteristics of the invention and comprises a tread made using a compound wherein the mixture of fillers thereof comprises carbon black and only the high surface area silica (compound A); the pneumatic tire V comprises a high elongation belt according to the characteristics of the invention and comprises a tread made using a compound wherein the mixture of fillers thereof comprises carbon black, the high surface area silica and the low surface area silica in the ratio according to the invention (compound C).

[0050] For the pneumatic tires IV and V, the high elongation belt was made in applying the cord at a laying angle of 0.042.

[0051] For the pneumatic tires IV and V, the TW/CW ratio is 1.25.

[0052] For the pneumatic tires I-III, the TW/CW ratio (CW in these cases is the extension of the widest belt) is 1.5.

[0053] The pneumatic tires I-V were subjected to a series of tests in order to evaluate those properties in relation to rolling resistance, wear resistance and uneven wear.

[0054] The rolling resistance was measured according to the R117 standard.

[0055] The wear resistance was evaluated using the procedure described below: [0056] The pneumatic tires were mounted on comparable tractors and trailers and subjected to the same operating conditions (for example, the type of road traveled, the number of kilometers traveled and the load).

[0057] During the procedure, the depth was recorded of the main grooves of the tread of the pneumatic tire and whether the tread was developing signs of uneven wear such as cupping, depression of the ribs, alternating wear of the wings or wearing of the shoulders.

[0058] The data recorded for the wear resistance are the following:

WTD=OTDRTD

KPM=(KM covered)/WTD [0059] OTD=Original Tread Depth [0060] RTD=Remaining Tread Depth

[0061] KPM is the parameter for classifying the wear amongst the specifications.

[0062] In Table II the results relating to the rolling resistance and the wear resistance are expressed in indexed form on the basis of the results obtained in relation to the pneumatic tire I. The greater the reported values, the better the rolling resistance and wear resistance.

[0063] The uneven wear was evaluated using a rigid profile shaped according to the shape of the new tread. After using the pneumatic tire, the rigid profile is rested against the tread, and whether or not the tread is still adhering to the rigid profile is evaluated. If, after using the pneumatic tire, the tread is uniformly worn, then the portion in relation to the shoulders of the tread will still adhere to the rigid profile. Conversely, if the tread is worn in an irregular manner, then those portions in relation to the tread shoulders will no longer adhere to the rigid profile.

[0064] In Table II the irregular wear values are given in % of missing volume of rubber adhering to the rigid profile in relation to the missing volume of rubber adhering to the rigid profile in the pneumatic tire I used as a reference.

TABLE-US-00002 TABLE II I II III IV V Rolling resistance 100 105 107 101 110 Wear resistance 100 60 80 145 145 Uneven wear 100 60 70 50 50

[0065] As appears evident from the data reported in Table II, the pneumatic tire obtained according to the invention ensures, by means of the combined use of the particular mixture of fillers and of the high elongation belt, a significant improvement in terms of rolling resistance, wear resistance and uneven wear.

[0066] In this respect, it should be noted that there is an unexpected synergistic effect in terms of rolling resistance. In fact, the pneumatic tire of the invention (pneumatic tire V) gives a rolling resistance result that is better than that of the pneumatic tire III despite both using the same compound (Compound C).

[0067] In other words, the use of a high elongation belt ensures an improvement in terms of wear resistance and in terms of uneven wear and, surprisingly, produces a synergistic effect, with a particular combination of tread compound fillers, in terms of rolling resistance.

[0068] In this way it will be possible to manufacture a pneumatic tire with improved rolling resistance without, for this reason, resulting in any worsening of the wear resistance.