Rubber mix to produce tyres

Abstract

A rubber mix for tires including at least one cross-linkable polymer base, a reinforcing filler, a vulcanization system, a reinforcing resin and a dithiol chemical according to the formula SHRSH, wherein, in the formula, R is an aliphatic or aromatic group composed of 3 to 12 atoms.

Claims

1. A rubber mix comprising at least one cross-linkable polymer base, a reinforcing filler, a vulcanization system, a reinforcing resin, and a dithiol chemical represented by formula (I):
SH(CH.sub.2).sub.nSH(I), wherein, in formula (I), n is an integer ranging from 3 to 12; said dithiol chemical is present in the mix in a quantity ranging from 5 to 20 phr; said reinforcing filler is present in the mix in a quantity ranging from 5 to 30 phr; said reinforcing resin is present in the mix in a quantity ranging from 1 to 50 phr; said reinforcing resin is a two-component resin; and a methyl acceptor chemical of said two-component resin is added to the mix in preparation in a masterbatch mixing step and a methylene donor chemical is added to the mix in preparation together with said vulcanization system.

2. The rubber mix according to claim 1, characterised in that the dithiol chemical is SH(CH.sub.2).sub.6SH.

3. The rubber mix according to claim 1, wherein said reinforcing filler is a carbon black.

4. The rubber mix according to claim 1, wherein said vulcanization system comprises sulphur and a vulcanization accelerator.

5. The rubber mix according to claim 1, wherein said reinforcing filler is present in the mix in the quantity ranging from 5 to 20 phr.

6. The rubber mix according to claim 1, wherein said reinforcing resin is present in the mix in the quantity ranging from 20 to 50 phr.

7. A tyre portion produced with a mix according to claim 1.

8. A tyre comprising the portion according to claim 7.

9. A tyre tread produced with a mix according to claim 1.

Description

BEST MODE FOR CARRYING OUT THE INVENTION

(1) For a better understanding of the invention, embodiment examples are given below purely for illustrative non-limiting purposes.

Examples

(2) Four comparison mixes were produced (Mixes A-D) and a mix according to the present invention (Mix E).

(3) The comparison mixes can be described as follows: Mix A is a standard compound without the dithiol chemical and without the reinforcing resin; Mix B differs from Mix A due to the fact that it has half the quantity of carbon black; Mix C has the same quantity of carbon black as Mix B and comprises the dithiol chemical but not the reinforcing resin; Mix D also has the same quantity of carbon black as Mix B and comprises the reinforcing resin but not the dithiol chemical.

(4) The mix produced according to the principles of the present invention (Mix E) differs from the comparison mixes due to the fact that it has half the quantity of carbon black, and comprises both the reinforcing resin and the dithiol chemical.

(5) The Mixes A-E were prepared according to the procedure described below.

(6) Preparation of the Mixes

(7) (1st Mixing StepMasterbatch)

(8) Prior to the beginning of the mixing, the polymer base, the carbon black and the methylene acceptor chemical of the reinforcing resin were loaded in a mixer with tangential rotors and internal volume ranging from 230 to 270 liters, reaching a filling factor ranging from 66 to 72%.

(9) The mixer was operated at a speed ranging from 40 to 60 r.p.m., and the mixture formed was discharged once a temperature ranging from 140 to 160 C. had been reached.

(10) (2nd Mixing Step)

(11) The mixture obtained from the preceding step was mixed again in the mixer operated at a speed ranging from 40 to 60 r.p.m. and, subsequently, discharged once a temperature ranging from 130 to 150 C. had been reached.

(12) (3rd Mixing Step)

(13) The vulcanization system consisting of sulphur and accelerators, the dithiol chemical and the methylene donor chemical of the reinforcing resin was added to the mixture obtained from the preceding step, reaching a filling factor ranging from 63 to 67%.

(14) The mixer was operated at a speed ranging from 20 to 40 r.p.m. and the mixture formed was discharged once a temperature ranging from 90 to 110 C. had been reached.

(15) Differently from the procedure described above, the dithiol chemical and the reinforcing resin, regardless of whether it is single-component or two-component, can be added to the mix in the masterbatch mixing step, taking certain precautions to avoid the cross-linking reaction.

(16) Table I shows in phr the compositions of the mixes.

(17) TABLE-US-00001 TABLE I Compound A B C D E Natural rubber 70.0 70.0 70.0 70.0 70.0 Butyl rubber 30.0 30.0 30.0 30.0 30.0 Carbon black 40.0 20.0 20.0 20.0 20.0 Dithiol chemical 5.0 5.0 Phenol formaldehyde 15.0 15.0 HMMM 5.0 5.0 Sulphur 2.5 2.5 2.5 2.5 2.5 Accelerator 0.6 0.6 0.6 0.6 0.6

(18) The carbon black used is N234.

(19) The Phenol Formaldehyde and HMMM (hexamethoxymethylamine) are respectively the methylene acceptor chemical and the methlyene donor chemical of the two-component reinforcing resin.

(20) The dithiol chemical used is SH(CH.sub.2).sub.6SH.

(21) The accelerator used is N-tert-butyl-2-benzothiazylsulfenamide (TBBS).

(22) Experimental Tests

(23) The mixes, once vulcanized, underwent experimental tests to ascertain the advantages of the mix according to the present invention with respect to the comparison mixes.

(24) In particular, the mixes underwent tests relative to the mechanical and dynamic properties. The mechanical properties were measured according to the ASTM D412C standard, while the dynamic properties were measured according to the ISO 4664 standard.

(25) As is known to a person skilled in the art, the rolling resistance parameter is strictly correlated with the hysteresis values: the lower the hysteresis value, the better the rolling resistance.

(26) For an evaluation of the stability of the mixes, they underwent an ageing procedure during which the mixes were kept at a temperature of 100 C. for six days in compliance with the ISO 188 standard.

(27) Table II shows the values of the experimental tests carried out. The hysteresis and toughness values were indexed to the values of the comparison mix A, while the long-term stability values are expressed in percentage terms with respect to the datum recorded on said mix in the absence of ageing (the higher the index, the better the property).

(28) TABLE-US-00002 TABLE II Compound A B C D E Hysteresis 100 130 120 120 130 Toughness 100 65 100 100 110 Toughness after 40 55 55 60 90 6 days of ageing

(29) As can be seen from the data given in Table II, the synergic effect due to the combination of a reinforcing resin and a dithiol chemical guarantees both an improvement in terms of rolling resistance, without compromising the mechanical tensile properties, and, above all, an even more surprising improvement in terms of long-term stability.

(30) The comparison Mixes C and D confirm that an only partial condition of the above-mentioned combination is not able to guarantee the advantages described above.

(31) In particular, the effect of the above-mentioned synergy in the stability of the mixes is extremely surprising. In fact, the comparison mixes show that the sole presence of the reinforcing resin (Mix C) or the sole presence of the dithiol chemical (Mix D) result in a much lower stability of the respective mixes than what is obtained with the combined presence of a reinforcing resin and the dithiol chemical.

(32) To conclude, the combined presence of a reinforcing resin and a dithiol chemical allows the quantity of reinforcing filler to be reduced without compromising the mechanical characteristics and, surprisingly, guarantees high values in terms of long-term stability of the mix.