Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-11-30
2003-09-23
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S425000, C524S437000, C524S444000, C524S449000, C524S495000, C524S847000, C152S209100, C152S209500
Reexamination Certificate
active
06624233
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tire for vehicles provided with a tread having a low rolling resistance.
The invention also relates to a premolded tread, in particular for covering worn tires, having a low rolling resistance, as well as to a method for reducing the rolling resistance of vehicle tires.
DESCRIPTION OF THE RELATED ART
As is known, in the field of vehicle tire manufacture, research is increasingly devoted to finding how to reduce as much as possible the rolling resistance of tires.
To this aim, it has been proposed in the art to use rubber compositions having a low content of carbon black in the manufacture of the tire tread.
In these rubber compositions, carbon black is partly or entirely replaced by the so-called “white” inorganic reinforcing fillers, such as gypsum, talc, kaolin, bentonite, titanium dioxide, various types of silicates, and in particular silica, as disclosed, for instance, in European Patent EP 0 501 227.
In particular, in order to reduce the rolling resistance of the tire without significantly affecting its wear resistance and wet skid resistance, the constant teaching of the prior art in this field is to use silica having a so-called high surface area, i.e. silica having a BET surface area generally greater than 130 m
2
/g.
According to the constant teaching of the prior art, in fact, the use of silicas having a high surface area allows to improve the mechanical properties of the tread, such as for instance tensile resistance, elongation, tear resistance, and in particular abrasion resistance.
Notwithstanding these advantageous effects, however, the use of silica-based reinforcing fillers involves several drawbacks substantially associated to the poor affinity of the same with the polymer base of the rubber compositions employed in the tire manufacture. Such poor affinity requires, in fact, the use of suitable coupling agents that are able to chemically bond silica to the polymer matrix.
However, the need of using such coupling agents poses a limit to the maximum temperature that may be attained during the steps of mixing and thermal-mechanical working of the rubber composition, on pain of an irreversible thermal degradation of the coupling agent.
But the respect of the aforementioned temperature constraint involves, in its turn, a marked reduction in the very mechanical mixing action that is of the essential—when using silica having a high surface area—for an optimum dispersion of the silica in the polymer matrix, as stressed by the aforementioned European Patent EP 0 501 227.
According to the teaching of this patent, in fact, it is possible to achieve a uniform dispersion in the polymer base of the silica having a high surface area only when the rubber composition is submitted to a thermal-mechanical working which is capable to reduce the projected area of silica aggregates from a starting value greater than 8500 nm
2
, shown by silica per se, to an end value comprised between 7000 and 8400 nm
2
, after a suitable thermal-mechanical working.
On the other hand, the insufficient dispersion of silica in the rubber composition which would ensue due to an insufficient thermal-mechanical working per se unable to comply with the aforementioned constraint of projected area of the silica aggregates, would cause, in its turn, the worsening of those very mechanical properties of the tread, and in the first place rolling resistance and abrasion resistance, that should be improved or maintained.
SUMMARY OF THE INVENTION
The technical problem underlying the present invention is that of providing a tire for vehicles provided with a tread including silica as reinforcing filler, which has a reduced rolling resistance, while keeping wear resistance and wet skid resistance substantially unaltered, and which allows at the same time to overcome the plant and process constraints associated to the need of reducing the projected area of the aggregates under 8400 nm
2
in order to achieve the desired homogeneous dispersion of silica, according to the teachings of the aforementioned prior art.
According to the invention, the Applicant has surprisingly found that it is possible to achieve the desired optimum compromise between rolling resistance, wear resistance and wet skid resistance even by using a silica-based reinforcing filler having a low surface area thanks to a particular combination of average projected area of the aggregates as measured before and after incorporation into the polymer base and dispersibility of the same in the polymer base of the tread.
More specifically, the Applicant has found that a silica-based reinforcing filler having a low surface area may be thoroughly dispersed in the vulcanized polymer base of the tread of a vehicle tire while still showing a projected area of the aggregates that exceeds 8500 nm
2
, i.e. greater—considering an average margin in the experimental measurement of the same of ±100 nm
2
—than the aforementioned maximum limit of 8400 nm
2
taught by the prior art.
Besides, the Applicant has surprisingly found that such silica-based reinforcing fillers having a low surface area may be homogeneously dispersed in the vulcanized polymer base of the tread, reaching the above value of the dispersion index also in the absence of an exceedingly high thermal-mechanical working of the rubber compositions.
According to a first aspect of the invention, the aforementioned technical problem is solved by a low rolling resistance tire for vehicles as defined in attached claim 1.
In the following description and in the appended claims, the term: “dispersion index”, is used to indicate the percentage of dispersed silica particles with respect to the total number of silica particles included in the polymer base of the tread. Conventionally, the silica is considered as dispersed when it is present in particle aggregates having a diameter smaller than 7 &mgr;m.
The Applicant has surprisingly found that by incorporating and homogeneously dispersing in the polymer base a silica having a particular combination of surface area, average projected area of the aggregates as measured before and after incorporation into the polymer base, it is possible on the one hand to further reduce the rolling resistance of the tire without adversely affecting wear resistance and wet skid resistance and, on the other hand, to reduce the thermal-mechanical working to be imparted to the rubber composition to obtain a good dispersion of said filler.
The Applicant has in fact found that in order to achieve the aforementioned advantageous effects it is not necessary to employ—as constantly suggested by the prior art—particles having a high surface area and characterized by a reduced particle size and, as such, difficult to be homogeneously dispersed in the polymer base of the tread, but it is possible to effectively use silicas having a low surface area, characterized by particles having a greater size compared to silicas having a high surface area, and requiring with respect to the latter a lower thermal-mechanical working to achieve a suitable dispersion level in the polymer base of the tread.
Additionally, since during the incorporation step of the silica having a low surface area in the polymer base a temperature increase occurs that is lower than that reached by the processes and apparatuses of the prior art, the risks of thermally degrading the coupling agent of the silica are advantageously reduced, while imparting a strong thermal-mechanical action in the step of silica incorporation in the polymer base.
Preferably, the silica-based reinforcing filler has the following properties:
an average projected area of the aggregates as measured before incorporation into the polymer base comprised between 9000 and 18000 nm
2
and, still more preferably, between 10000 and 15000 nm
2
;
a dispersion index not lower than 99% and, still more preferably, not lower than 99.5%;
an average projected area of the aggregates as measured after incorporation into the polymer base comprised between 9000 and 15000 nm
2
and, still more preferably,
Amaddeo Angela
Garro Luciano
Sala Fabrizia
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Pirelli Pneumatici S.p.A.
Yoon Tae H.
LandOfFree
Low rolling resistance tire for vehicles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low rolling resistance tire for vehicles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low rolling resistance tire for vehicles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3046720