Patent Application
20120296008
The present invention relates to a tread mix.
As is known, part of the research carried out in the tyre industry is aimed at achieving treads with improved wet-pavement road-holding, rolling resistance, and wear resistance performance.
While all three of the above characteristics can be improved independently, it is more difficult to improve them simultaneously, without improvement to one impairing one or both of the others.
In this connection, silica has long been used, as a partial or total substitute for carbon black, as a tread mix reinforcing filler, because of its advantages in terms of rolling resistance and wet-pavement road-holding performance.
Silica is used in combination with silane bonding agents, which bond with silanol groups to prevent the formation of hydrogen bonds between silica particles, while at the same time attaching silica chemically to the polymer base.
Trialkoxymercaptoalkyl-silanes are a particularly interesting class of silane bonding agents, mainly because of the advantages they afford in terms of reducing rolling resistance and volatile substance emission.
The best advantages are obtained from the compound of formula I.
SH (CH2)3SiR1R22 (I)
where:
R2 is —OCH2CH3 and
R2 is —O(CH2CH2O)5(CH2)12CH3
A need is felt for a mix capable of producing a tread which, with respect to the known art, presents a simultaneous improvement in wet-pavement road-holding, rolling resistance, and wear resistance performance.
The Applicant has surprisingly devised a tread mix capable of achieving this goal.
According to the present invention, there is provided a tread mix comprising a cross-linkable unsaturated-chain polymer base; curing agents; silica; and a silane bonding agent; said mix being characterized in that said polymer base comprises a first SBR rubber comprising 20-40% of a first fraction with a mean molecular weight of 50-100×103 and a molecular weight distribution of <1.5, and 80-60% of a second fraction with a mean molecular weight of 800-1500×103 and a mean molecular weight distribution of <3.0; and in that said silane bonding agent is a mercaptosilane of formula I:
SH(CH2)1SiR1R22 (I)
where:
1 is an integer of 1 to 6,
R1 is —O(CH2)gCH3,
R2 is —O(CH2CH2O)m(CH2)nCH3,
g is an integer of 0 to 5,
m is an integer of 2 to 8, and
n is an integer of 3 to 20.
The silica preferably has a surface area of 170 to 230 m2/g.
1 is preferably 3.
Preferably, g is 1, m is 5, and n is 12. The tread mix preferably comprises 40-130 phr of said silica, and 4-18 phr of said silane bonding agent.
The first SBR rubber preferably has a 25-45% styrene content, and a 20-70% vinyl content.
The tread mix preferably comprises 20-60 phr of said first SBR rubber.
The tread mix preferably comprises 20-80 phr of a second SBR rubber. Even more preferably, the second SBR rubber comprises 20-60 phr of S-SBR with a mean molecular weight of 800-1500×103; and 20-60 phr of E-SBR with a mean molecular weight of 500-900×103.
The following are non-limiting examples, for a clearer understanding of the present invention.
S-SBR indicates a styrene-butadiene rubber obtained from a solution; and E-SBR a styrene-butadiene rubber obtained from emulsion.
Two control mixes (A, B) and three mixes in accordance with the teachings of the present invention (C, D, E) were produced, and each was tested to determine its characteristics in terms of wet-pavement road-holding, rolling resistance, and wear resistance.
The mixes described in the examples were produced as follows:
—Mix Preparation—
(First Mixing Stage)
A stationary 230-270-litre tangential-rotor mixer was first loaded with the cross-linkable polymer base, silica, silane bonding agent, and oil, to a fill factor of 66-72%.
The mixer was operated at a speed of 40-60 rpm, and the resulting mix unloaded on reaching a temperature of 140-160° C.
(Second Mixing Stage)
The mix from the preceding stage was mixed again in a mixer operated at a speed of 40-60 rpm, and unloaded on reaching a temperature of 130-150° C.
(Third Mixing Stage)
The curing system was added to the mix from the preceding stage, to a fill factor of 63-67%.
The mixer was operated at a speed of 20-40 rpm, and the resulting mix unloaded on reaching a temperature of 100-110° C.
Table I shows the compositions of the five mixes in phr.
As stated, mixes A-E were tested to determine wet-pavement road-holding, rolling resistance, and wear resistance performance.
More specifically, E′ values were measured at 30° C. and TanD values at different temperatures as per ASTM Standard D5992, and wear resistance was measured as per DIN Standard 53 516.
As anyone skilled in the art knows, the TanD values indicate wet-pavement road-holding and rolling resistance.
To show more clearly the advantages of the mixes according to the present invention, the wet-pavement road-holding, rolling resistance, and wear resistance values were indexed on the basis of the mix A results.
Table II shows the test results.
As shown in Table II, the mixes according to the present invention ensure a greater overall improvement in all three characteristics as compared with control mixes A and B, which lack high-surface-area silica combined with mercaptosilane of formula I.
Mixes D and E represent a preferred embodiment of the present invention, in which, together with high-surface-area silica combined with mercaptosilane of formula I, a particular S-SBR rubber is used containing a low-molecular-weight fraction and a high-molecular-weight fraction, so that mixes D and E provide for an even greater simultaneous improvement in all three characteristics.
| Number | Date | Country | Kind |
|---|---|---|---|
| TO2009A000859 | Nov 2009 | IT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB10/03082 | 11/10/2010 | WO | 00 | 7/26/2012 |
