Tyre tread formulations

Retrospective View of Vinyl-BR Properties In the 1950s, the Phillips Petroleum Company and the Firestone Tire and Rubber Company started commercial production of polybutadienes by organolithium polymerization for use in tyres. These solution BRs, having low vinyl contents (8-10%), were used in blends with emulsion SBR in tyre treads for balancing traction and wear performance properties. In the early 1970s when styrene monomer was in short supply, developments from Phillips Petroleum Company and EniChem (formerly the International Synthetic Rubber Company) showed that vinyl-BRs with 50-55% vinyl content behaved like emulsion polymerized SBR in tyre tread formulations and exhibited very similar tread wear and wet skid resistance. Tread compounds containing 45%-vinyl polybutadiene showed lower heat build-up and better blow-out resistance than E-SBR and blends of E-SBR with cw-BR. EniChem introduced trial quantities of a medium-vinyl butadiene rubber (MVBR) under the name Intolene 50 in 1973. 

Chandra and Pillai [28] used a low-molecular-weight recycled rubber as a processing aid in a number of tyre tread formulations and compared its performance with other commercial process aids. This process aid (Ecoreen T) is shown to function as well as or even better than depolymerised NR or similar process aids. The same workers also reported on the use of new products with low viscosity that are produced by blending low-molecular-weight virgin polymers with recycled butyl rubber [29]. When these products... 

Standardisation of EPDM characterisation tests (molecular composition, stabiliser and oil content) for QC and specification purposes was reported [64,65]. Infrared spectroscopy (rather than HPLC or photometry) is recommended for the determination of the stabiliser content (hindered phenol type) of EP(D)M [65]. Determination of the oil content of oil-extended EPDM is best carried out by Soxhlet extraction using MEK as a solvent [66], A round robin test was reported that evaluated the various techniques currently used in the investigation of unknown rubber compounds (passenger tyre tread stock formulations) [67]. 

The resins in the friction dust area tend to be rigid and the flexibility and plasticity associated with the long alkyl chain of phenolic lipids have been used in natural rubber vulcanisation by for example incorporating crosslinking with phosphorylated cardanol (ref. 252). Unpolymerised CNSL phenols have been used in natural or diene rubber compositions for tyre treads to give an improved dynamic elastic modulus but with the same hardness as formulations without the phenolic addition (ref. 253). 

As compared to natural rubber, epoxidized grades of natural rubber show improved reinforcement with silica without any coupling agent. Radial tyre tread prepared using formulations based on natural rubber with epoxide... 

Sandstrom and co-workers utilized the cyclized polyisoprene polymers incorporated into tyre tread compounds to improve traction, tread wear and tear resistance. Cyclized polyisoprene is further based upon the discovery that blends of cyclized polyisoprene polymers with halobutyl rubber and/or NR can be employed as tyre inner liner formulations. 

Tread. Tread is the wear resistance component of the tyre and is in direct contact with the road. It must provide traction, wet skid and good cornering characteristics with minimum noise generation and also low heat build-up. Tread components can consist of blends of NR, polybutadiene (BR) and SBR, compounded with carbon black, silica, oils and vulcanizing chemicals." Among recently reported formulations for tyre tread with economic and environmental merits is the work of Rattanasom, in which a blend of NR and tyre tread reclaimed rubber (RR) was prepared and mechanically characterized. Their results showed that the blends prepared with different curing systems, i.e. conventional vulcanization (CV) and efficient vulcanization (EV), exhibit an increase in their hardness and modulus with increasing RR content, while other mechanical properties were adversely affected. ... 

Although direct analysis of rubber compounds yields simultaneously information about polymer and additives, a quantitative determination of the additives is difficult. This requires separation of these components from the polymer and fillers by means of extraction. Following the standard procedure at Akron Rubber (cfr Chp. 2.2 of ref. [3a]), Coz et al. [25] have examined four unknown cured rubber compounds (radial passenger tyre tread, radiator hose, oil pan seal and engine gasket). Tables 6.7 and 6.8 compare the reconstructed formulations and actual recipes for the tyre and radiator hose. 

The Bayer Tear Analyser is described, and examples are presented of its use in predicting the cut growth performance of rubber compounds for high performance car tyre treads, car and truck tyre breakers, radial truck tyre treads and truck tyre inner liners. Good correlation between the test results and the service performance of various tyre components is demonstrated. The application of the machine in optimising tyre inner liner formulations based on bromobutyl robber and blends of bromobutyl and butyl rubber is also described. 6 refs. 

Since low c/5-polyisoprene is limited to approximately 20 % inclusion in natural rubber compounds due to the fall-off in physical properties, interest in this type of polymer has been specifically for processing reasons. Tyre performance has been shown to be unimpaired in tread formulations containing this level of both Cariflex IR 305 and IR 500 polymers. 

The use of high c/ -polyisoprene is not limited to tread formulations and it is used to significantly greater advantage in other tyre components. 

A typical formulation for a passenger tyre tread is shown in Table 37. To raise the curing temperature, the use of antireversion chemical, Perkalink 900 has been recommended (119). 

Aircraft tread requires a high modulus, better abrasion resistance and low heat generation. The above requirements could be satisfied by using a CV/SEV cure system with DCBS as accelerator and insoluble sulfur (IS) as crosslinker. For achieving high modulus, HMT and a resorcinol system is used. In order to reduce the heat generation, the use of Perkalink 900 has been suggested. A typical formulation for an aircraft tyre tread recipe is shown in Table 40. 

A typical formulation for a radial tyre tmck tread is shown in Table 35. For improving heat resistance, the use of Perkalink 900 is recommended (289). The recommended loading for this cure system is 0.5 phr. 

A typical formulation for a bias tyre truck tread is shown in Table 36. 

With the advent of Green tyres the use of silica has significantly increased. A typical Green tyre formulation for passenger tread is shown in Table 38. In order to achieve high temperature cure, the use of Perkalink 900 has been reported (26). 

Table 38 Green tyre formulation -passenger tread ...

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