PILCURE CBS

Normal dosages of Zinc oxide and Stearic acid are necessary for all sulfenamide accelerators. However, excess dosage of Stearic acid does not offer additional advantage as in case of thiazoles. The normal dosage of Pilcure CBS is in the range of 0.5-1.0 phr for conventional cure systems, 1.5-2.0 phr for Semi-EV cures and 3.0-5.0 phr for low sulphur EV cures. Pilcure CBS is used at 1.0 phr dosage as an effective retarder for sulphur-less cures based on thiuram accelerators.

Pilcure CBS is very active above curing temperature of approx. 140°C and hence offers very good scorch safety during rubber compound processing operations (e.g. extrusion, calendaring, etc.) and improves the storage life of processed rubber stocks as compared to thiazole accelerators. Pilcure CBS/other sulphenamides are preferred when higher loadings of tread grade furnace blacks, (which are basic in nature and generate substantial heat during processing of NR/BR/SBR based stocks) are used. However; prolonged / repeated rub-ber stock processing above 120°C should be avoided, particularly in the absence of appropriate dosage of Pilgard PVI), to minimize the risk of ‘scorch’.

Pilcure CBS / other sulphenamide accelerators are usually incorporated in the rubber compound at the end of mixing cycle when the temperature is above the melting point of the accelerator to ensure proper dispersion. However; generation of excessive heat is avoided to prevent decomposition of sulphenamide accelerators. In case, the sulphenamide accelerators are to be added at a later stage; addition in the form of sulphenamide-rubber master batch (prepared above the melting point of sulphenamide accelerator) is recommended.

When used alone; Pilcure CBS exhibits faster cure rate (above 140°C), higher state of cure and moderate plateau effect as compared to thiazole accelerators. Vulcanizates based on Pilcure CBS / other sulphenamide accelerators have a typical ‘amine’ odor and exhibit higher stress-strain properties along with better resilience and Flex-Fatigue resistance as compared to thiazoles.

Pilcure CBS / other sulphenamide accelerators can be further activated by using small proportions of thiurams or dithiocarbamate accelerators with a compromise on processing safety, reversion resistance and ageing resistance. Use of DPG / DOTG is generally avoided as booster accelerators due to their tendency of imparting higher heat build-up properties to the rubber vulcanizates as compared to thiuram boosted cure systems.

Pilgard PVI is a very effective pre vulcanization (scorch) inhibitor for sulphenamide and activated sulphenamide cure systems without any compromise on the rate of cure. The improvement in scorch safety is directly proportional to the dosage of Pilgard PVI and hence the minimum dosage required for obtaining desired scorch safety can easily be determined. Use of excess dosage of Pilgard PVI is avoided as the same may cause undesired delay for the on-set of cure besides affecting the state of cure to some extent.

Pilcure CBS / other sulphenamide accelerators decompose rapidly in the presence of hot steam and hence preferred for the manufacture of open steam cured rubber products requiring faster on-set of cure for better shape retention. However; due to delayed on-set of cure in the absence of moisture, sulphenamide accelerators are not preferred for hot air cured products.

Pilcure CBS itself is non-staining. However, when higher dosages are used, slight yellowing effect may be observed on white / light colored rubber products on exposure to sunlight.