The present invention relates to a rubber composition with improved crack resistance and to a tyre comprising such a cured rubber composition.
The crack growth on a sidewall is a severe issue during tyre service life not only on Indian roads. This may be due to excessive flexing of sidewalls at low inflation pressure and/or damage caused by pot-holes and protrusions on the road and may lead to tyre bursts. This is particularly the case when driving on highways.
In certain markets, retreading is an important aspect of an off-the road (OTR) and Commercial Vehicle (CV) tyre's life span as a tyre casing can be retreaded at least 3-4 times. For example, the number of OTR tyres retreaded by some of the known retreaders in India in the last few years is three times the number of new OTR tyres purchased in India. The market for retreading is daily increasing with more people being aware of the concept and ready to take the Green path by using the same casing repeatedly also giving them additional cost benefit. However, cracks along the sidewall of tyres leads to poor casing value for retreading of CV and OTR tyres and sometimes tyre needs to be replaced.
US 5,386,860 discloses a cut resistant tyre, in particular a heavy duty pneumatic tyre comprising at least a pair of parallel annular beads, at least one carcass ply wrapped around said beads, reinforcement plies disposed radially over said at least one carcass ply in a crown area of the tyre, tread disposed radially over said reinforcement plies, and sidewalls disposed between said tread and said beads. Continuous monofilament wires having a diameter of 0.4 to 1.2 mm are disposed in parallel relation to one another in calendered rubber sheets and said calendered rubber sheets are included in or under said tread and sidewalls, and substantially cover said at least one carcass ply substantially from bead to bead while remaining radially above said beads.
WO 2010/051299 Al discloses a non-load bearing cut-resistant component for use in the sidewalls of a tyre. The component is made with yarns having staple fiber sheaths and cores of continuous inorganic filaments for improved cut resistance. Such a cut resistant tyre sidewall component comprises: a textile fabric, wherein a single layer of said fabric provides multi- directional cut . resistance in the plane of the fabric; the fabric further comprising at least one single yarn having a sheath/core construction, the sheath comprising cut-resistant polymeric staple fibers and the core comprising an inorganic fiber; and the fabric further having a coating for improved adhesion of the fabric to rubber such that the cut resistant tyre side-wall component has a free area of from 18 to 65 percent.
Sidewall compounds used in commercially available tyres mostly contain blends of natural rubber and synthetic rubbers. However, synthetic rubbers are known for their inferior crack-propagation resistance.

EP 2 157 127 Al provides a rubber composition for sidewalls containing 100 parts by mass of a rubber component consisting of at least a natural rubber or a modified natural rubber, 5 parts by mass or less of carbon black, 10 to 40 parts by mass of silica and 5 to 30 parts by mass of an inorganic filler component composed of one kind or two or more kinds of inorganic filler excluding carbon black and silica, and a pneumatic tire provided with a sidewall rubber prepared using the rubber composition. The used amounts of raw materials derived from petroleum resources have been reduced in this rubber composition. Moreover, the rubber composition exhibits low fuel consumption due to low rolling resistance and good flex crack growth resistance.
WO 2015/114653 A2 discloses a rubber blend composition, said composition comprising, based on parts per hundred of rubber (phr), 60 to 95 phr of a styrene-butadiene rubber (SBR), 4 to 24 phr of a polybutadiene rubber (BR) and 1 to 16 phr of a modified ethylene-alpha-olefm-diene rubber (modified EPDM); wherein said modified EPDM rubber is a graft copolymer comprising ethylene-alpha-olefm-diene rubber (EPDM) as a polymer backbone having grafted thereon a compound of the following formula:
wherein A is H, SCH3, OH, SH, COOCH3, and B is PI or CH3. This patent application states its objects, inter alia, as a) to provide a rubber blend composition with improved properties including, but not limiting to, high abrasion resistance, cut and chip resistance, low heat build-up, fatigue to failure properties, hardness and ageing as compared to the standard blend compositions available in the market and b) to provide a rubber blend composition with improved self- healing property, thereby repairing itself in the gum state under ambient conditions.
The present invention has the object of at least partially addressing at least one of the drawbacks in the prior art. hi particular, the present invention has the object of providing a rubber composition useful for the sidewall of a tyre with improved crack propagation resistance at a lower cost than the aminotriazole-based systems of WO 2015/114653 Al.
This object has been achieved by a cross-linkable rubber composition according to claim 1, a cross-linked rubber composition according to claim 10, a method of preparing a tyre according to claim 13 and a tyre comprising a cross-linked rubber composition according to claim 14. Advantageous embodiments are the subject of dependent claims. They can be combined freely unless the context clearly indicates otherwise.

Accordingly, the present invention is directed towards a cross-linkable rubber composition comprising a first diene-based elastomer, wherein the first diene-based elastomer further comprises structural units according to formula la) and/or 3b):
wherein POLY is a polymer chain of the diene-based elastomer and Z is a triazole residue according to one or more of formulas Ila) to lid):
with R and R independently of each other being H, SCH3, OH, SH, COOCH3 or CH3.
The first diene-based elastomer may be described as a maleic anhydride grafted polymer where the anhydride ring has been opened by reaction with the triazole nucleophile Z. In contrast to the aminotriazole bound via maleic acid grafts of WO 2015/114653 A2 the nitrogen atom of the heterocylic triazole to which a hydrogen atom is bound takes part in the ring-opening reaction of the anhydride. This allows for cheaper triazoles, especially the unsubstituted triazoles where R and R1 are both hydrogen, to be employed.
As expressed in formulas la) and lb), both possible outcomes of the ring-opening reaction of the anhydride are contemplated with respect to the location of the newly formed amide bond relative to the polymer chain. Also, as expressed in formulas Ila) to lid), all tautomers of all triazoles are contemplated: unsubstituted or substituted derivatives of 4/f-l,2,4-triazole, liT-1,2,4-triazole, 2H-1,2,3-triazole and 1/7-1,2,3-triazole.
The first diene-based elastomer may have a number average molecular weight Mn of, for example, > 100000 g/mol to < 5000000 g/mol. Li the practice of this invention, the first diene-based

elastomer may be of the type used in a tyre rubber composition. Thus, it is considered that the first diene-based elastomer may be a sulphur curable, vulcanisable elastomer.
In the preparation of the first diene-based elastomer, the triazole according to one of formulas (Ila) to (lid) (with a hydrogen atom bound to the divalent nitrogen atom depicted in these formulas) may be added to the diene-based elastomer in an amount of > 1 phr to < 20 phr, preferably > 2 phr to < lOphr. Furthermore, maleic anhydride may be added elastomer in an amount of > 1 phr to < 20 phr, preferably > 2 phr to < 15 phr.
In an embodiment of the composition according to the invention in formulas Ila) to lid) R and R' both are H. Hence the first diene-based elastomer may be described as a maleic anhydride grafted polymer where the anhydride ring has been opened by reaction with 477-1,2,4-triazole, 177-1,2,4-triazole, 2/7-1,2,3-triazole and/or l/M,2,3-triazole. These unsubstituted triazoles provide the greatest cost advantages.
In another embodiment of the composition according to the invention in formula la) and/or lb) POLY is a polymer chain of an ethylene/alpha-olefin/diene terpolymer. The diene may be a conjugated or a non-conjugated diene. Examples for suitable dienes are dicyclopentadiene, 1,4-hexadiene and ethylidene norbornene.
In another embodiment of the composition according to the invention the first diene-based elastomer comprises > 5 weight-% to < 10 weight-%, preferably > 6 weight-% to < 9 weight-% and more preferred > 7 weight-% to < 8 weight-% of units derived from the diene.
In another embodiment of the composition according to the invention the first diene-based elastomer has an ethylene content of > 50 weight-% to < 70 weight-%. Preferably the ethylene content is > 55 weight-% to < 65 weight-%, more preferred > 57 weight-% to < 62 weight-%.
In another embodiment of the composition according to the invention in formula la) and/or lb) POLY is a polymer chain of an ethylene/propylene/5-ethylidene-2-norbornene terpolymer. Then the first diene-based elastomer can be described as a maleic anhydride grafted EPDM rubber where the anhydride ring has been opened by reaction with the triazole nucleophile Z according to formulas Ila) to lid). It is preferred that the first diene-based elastomer is a maleic anhydride grafted EPDM rubber where the anhydride ring has been opened by reaction with 4/7-1,2,4-triazole, 177-1,2,4-triazole, 2.77-1,2,3-triazole and/or 177-1,2,3-triazole.
More preferred is the case that the first diene-based elastomer is a maleic anhydride grafted EPDM rubber where the anhydride ring has been opened by reaction with 477-1,2,4-triazole, 1/7-1,2,4-triazole, 277-1,2,3-triazole and/or 177-1,2,3-triazole and where the EPDM rubber comprises > 5

weight-% to < 10 weight-% (preferably > 6 weight-% to < 9 weight-% and more preferred > 7 weight-% to < 8 weight-%) of units derived from 5-ethylidene-2-norbornene.
Most preferred is the case that the first diene-based elastomer is a maleic anhydride grafted EPDM rubber where the anhydride ring has been opened by reaction with 4ff-l,2,4-triazole, 1/7-1,2,4-triazole, 2i£-l,2,3-triazole and/or lif-l,2,3-triazole, where the EPDM rubber comprises > 5 weight-% to < 10 weight-% (preferably > 6 weight-% to < 9 weight-% and more preferred > 7 weight-% to < 8 weight-%) of units derived from 5-ethylidene-2-norbornene and where the EPDM rubber comprises > 50 weight-% to < 70 weight-% (preferably > 55 weight-% to < 65 weight-%, more preferred > 57 weight-% to < 62 weight-%) of units derived from ethylene.
The following table lists possible weight ratios of EPDM, maleic anhydride and the triazole (4H-1,2,4-triazole, l#-l,2,4-triazole, 2#-l,2,3-triazole and/or 177-1,2,3-triazole).
In another embodiment of the composition according to the invention the first diene-based elastomer is present in the cross-linkable rubber composition in an amount of > 2.5 phrto <7.5 phr, preferably > 3 phr to < 7 phr and more preferred > 4 phr to < 6 phr.
. The cross-linkable rubber composition according to the invention may comprise further rubbers or elastomers. They are typically derived from the polymerisation of conjugated diene monomers which typically contain from 4 to 12 carbon atoms and preferably contain from 4 to about 8 carbon atoms. Representative examples of such conjugated diene monomers include, for example, 1,3-butadiene and isoprene. Such an elastomer can also contain units derived from the copolymerisation of various vinyl aromatic monomers with one or more of such conjugated dienes such as, for example, styrene and alpha-methylstyrene.
A non-exhaustive exemplary list of elastomers which can be prepared from these diene monomers and utilised in the cross-linkable rubber composition according to the invention include 1,4-polybutadiene (BR), styrene-butadiene rubber (SBR), synthetic c/5-l,4-polyisoprene, natural cis-1,4-polyisoprene (NR), isoprene/butadiene rubber, styrene/isoprene rubber, high vinyl polybutadiene rubber having a vinyl 1,2- content in a range of about 40 to about 95 percent, butadiene/acrylonitrile rubber, carboxylated butadiene/acrylonitrile rubber, and styrene/isoprene/ butadiene terpolymer rubbers. These elastomers may have an average molecular weight Mn in a

range of > 100000 to < 5000000 g/mol, which represent commonly used "solid" diene based elastomers.
In another embodiment of the composition according to the invention the composition further comprises as a second diene-based elastomer natural rubber (NR), as a third diene-based elastomer butadiene rubber (BR) and as a fourth diene-based elastomer styrene-butadiene rubber (SBR).
Preferably the first, second, third and fourth diene-based elastomer are present in the following amounts (it is understood that the phr amounts given add up to < 100 phr):
First diene-based elastomer: > 1 phr to < 10 phr, preferably > 2 phr to < 8 phr
Second diene-based elastomer: > 20 phr to < 80 phr, preferably > 30 phr to < 70 phr
Third diene-based elastomer: > 20 phr to < 80 phr, preferably > 30 phr to < 70 phr
Fourth diene-based elastomer: > 0 phr to < 30 phr, preferably > 0 phr to < 20 phr
In another embodiment of the composition according to the invention the composition comprises triazole residues Z according to one or more of formulas Ha) to lid) in an amount of > 0.04 weight-% to < 0.5 weight-%, based on the total weight of rubbers present in the composition. Preferably, this amount is from > 0.1 weight-% to < 0.47 weight-%, more preferred > 0.3 weight-% to < 0.41 weight-%.
Another aspect of the present invention is a cross-linked rubber composition obtained by cross-linking the cross-linkable rubber composition according to the invention.
In an embodiment the cross-linked rubber composition according to the invention has a De Mattia crack growth (ASTM D813) at 25000 cycles of < 15 mm, preferably < 10 mm.
In another embodiment the cross-linked rubber composition according to the invention has a Monsanto fatigue to failure life (JIS K 6301) of > 450 kilocycles, preferably > 470 kilocycles.
The invention also concerns a method of preparing a tyre, comprising the steps of:
providing a tyre assembly comprising a cross-linkable rubber composition according the invention;
cross-linking at least the cross-linkable rubber composition according to the invention in the tyre assembly.
The invention is also directed towards a tyre comprising a cross-linked rubber composition

according to the invention.
Preferably the sidewall of the tyre comprises a cross-linked rubber composition according to the invention.
The cross-linkable rubber composition according to the invention comprises cross-linkable groups > in the individual rubber components. They may be cross-linked (cured, vulcanised) by methods known to a skilled person in the rubber technology field.
The cross-linkable rubber compositions may be sulfur-vulcanisable and/or peroxide-vulcanisable. Other vulcanisation systems may also be used. The cross-linkable rubber composition is preferably cross-linked using a sulfur vulcanisation system, which is conducted in the presence of sulfur-) vulcanising agents. Examples of suitable sulfur-vulcanising agents include elemental sulfur (free sulfur) or sulfur donating vulcanising agents, for example, an amine disulphide, polymeric polysulfide or sulfur olefin adducts. Preferably, the sulfur vulcanising agent is elemental sulfur. As known to those skilled in the art, sulfur-vulcanising agents are used in an amount ranging from about 0.5 to about 4 phr, or even, in some circumstances, up to about 8 phr.
5 If desired accelerators can be added to the cross-linkable rubber composition to control the time and temperature required for vulcanisation. Examples of suitable types of accelerators are amines, disulphides, guanidines, thioureas, thiazoles, thiurams, sulfonamides, dithiocarbamates and xanthates. Vulcanisation retarders may also be used.
Zinc oxide can be added as activator, mostly in combination with fatty acids (for example, stearic ) acid).
As known to those skilled in the art, the cross -linkable rubber composition is normally vulcanised under elevated temperatures for a defined time. Typical temperatures for vulcanisation vary from 110 °C to 180 °C, whereas the typical time for vulcanization is normally between 5 minutes to 3 hours. These settings can be adjusted accordingly, for example to optimise the vulcanisation 5 conditions for the size of the tyre or for the cross-linkable rubber compositions in the tyre.
If desired, other additives can be added to the cross-linkable rubber composition. Examples of usual additives are stabilisers, antioxidants, lubricants, fillers, dyes, pigments, flame, retardants, conductive fibres and reinforcing fibres.
If desired, the cross-linkable rubber composition can also comprise a coupling agent. Suitable ) coupling agents comprise silane compounds. Particularly suitable silane compounds comprise di-and tetrasulphides. It is possible for the rubber composition to be provided with a conductive filler to make it at least partially conductive.

The cross-liiikable rubber composition according to the invention can also comprise from 0 to 60 phr, preferably from 0.1 to 50 phr, preferably from 0.1 to 40 phr, of at least one plasticiser. This plasticiser is one selected from the group consisting of mineral oils and/or synthetic plasticisers and/or fatty acids and/or fatty acid derivatives and/or resins and/or factices and/or glycerides and/or terpenes and/or biomass-to-liquid oils (BTL oils), particular preference being given here to mineral oils. If mineral oil is used, this is preferably one selected from the group consisting of DAE (Distillated Aromatic Extracts) and/or RAE (Residual Aromatic Extract) and/or TDAE (Treated Distillated Aromatic Extracts) and/or MES (Mild Extracted Solvents) and/or naphthenic oils.
It is also preferred that the cross-linkable rubber composition according to the invention comprises a filler component, examples of such a filler component are carbon black, silica or a combination of both. The total amount of filler in the rubber composition is preferably > 30 phr to < 180 phr, more preferably > 40 phr to < 150 phr, most preferably > 45 phr to < 130 phr.
The phr data (parts per hundred parts of rubber by weight) used in this specification are the conventional quantitative data used for mixture formulations in the rubber industry. The amount added in parts by weight of the individual substances in this specification is based on 100 parts by weight of the total mass of all of the high-molecular-weight, and therefore solid, rubbers present in the mixture.
The present invention will be further described with reference to the following figure and examples without wishing to be limited by them.
TMQ: 2,2,4-Trimcthyl-l,2-Dihydroquinolincpolymer
6-PPD: N-(l ,3-Dimethylbutyl)-N'-phenyl-l ,4-benzenediamine
EPDM: Ethylene-propylene-diene terpolymer
These elasotmers were prepared in a grafting reaction in melt-mixing method using free radical

mechanism. Amounts stated in the above table are in parts per hundred rubber by weight (phi). Mixing conditions: mixing temperature 100-120 °C; time: 5-10 min; RPM: 30-70, in an internal mixer comparable to a Banbury mixer.
FIG. 1 shows an ATR-FTIR spectrum of the modified EPDM rubber obtained from Ex-1. It is apparent that there is no anhydride peak of maleic anhydride (at 1864 and 1788 cm-1) present; the spectrum shows the presence of acid (1719 cm-1 ) and amide (1526 cm-1) peaks which can be generated by the ring opening of maleic anhydride groups by the triazole.

Strips of 50 mm width and 2 mm thickness of the cross-linkable rubber composition according to the invention and of the comparative composition were applied on either side of a green tyre (155/70 R 13 75 T Amazer 3G) and cured (steam curing; total curing time 9.5 min, internal steam pressure and temperature 16.8 kg/cm2 and 183 °C, respectively). The tyre was tested for crack growth monitoring by inducing 5 mm cracks in each quadrant on both the sides.

The cut growth was measured after 2 hours of a low inflation pressure test (test speed: 120 km/h, test temperature 38 °C, inflation pressure: 20.3 psi (i.e. 77% of rated inflation pressure), load applied: 100% of tyre's maximum load rating) on a road wheel. The results are given in the table below.
In conclusion, the cured composition according to the invention showed better cut-growth resistance without sacrificing other physical properties.

We claim:
1. A cross-linkable rubber composition comprising a first diene-based elastomer, characterised in that the first diene-based elastomer further comprises structural units according to formula la) and/or lb):
wherein POLY is a polymer chain of the diene-based elastomer and Z is a triazole residue according to one or more of formulas Ha) to lid):
with R and R1 independently of each other being H, SCH3, OH, SH, COOCH3 or CH3.
2. The composition according to claim 1, wherein in formulas Ha) to lid) R and R' both are H.
3. The composition according to claim 1 or 2, wherein in formula la) and/or lb) POLY is a polymer chain of an ethylene/alpha-olefm/diene terpolymer.
4. The composition according to one of claims 1 to 3, wherein the first diene-based elastomer comprises > 5 weight-% to < 10 weight-% of units derived from the diene.
5. The composition according to one of claims 1 to 4, wherein the first diene-based elastomer has an ethylene content of > 50 weight-% to < 70 weight-%.
6. The composition according to one of claims 1 to 5, wherein in formula la) and/or lb) POLY is a polymer chain of an ethylene/propylene/5-ethylidene-2-norbornene terpolymer.
7. The composition according to one of claims 1 to 5, wherein the first diene-based elastomer is

present in an amount of > 2.5 phr to < 7.5 phr.
8. The composition according to one of claims 1 to 7, further comprising as a second diene-based elastomer natural rubber (NR), as a. third diene-based elastomer butadiene rubber (BR) and as a fourth diene-based elastomer styrene-butadiene rubber (SBR).
9. The composition according to one of claims 1 to 8, comprising triazole residues Z according to one or more of formulas Ha) to lid) in an amount of > 0.04 weight-% to < 0.5 weight-%, based on the total weight of rubbers present in the composition.
10. A cross-linked rubber composition obtained by cross-linking the cross-linkable rubber
composition according to one of claims 1 to 9.
11. The cross-linked rubber composition according to claim 10, having a De Mattia crack growth (ASTM D813) at 25000 cycles of < 15 mm.
12. The cross-linked rubber composition according to claim 10 or 11, having a Monsanto fatigue to failure life (JIS K 6301) of > 450 kilocycles.
13. A method of preparing a tyre, comprising the steps of:
- - providing a tyre assembly comprising a cross-linkable rubber composition according to one of claims 1 to 9;
cross-linking at least the cross-linkable rubber composition according to one of claims 1 to 9 in the tyre assembly.
14. A tyre comprising a cross-linked rubber composition according to one of claims 10 to 12.
15. The tyre according to claim 14, wherein the sidewall of the tyre comprises a cross-linked rubber composition according to one of claims 10 to 12.