Cyclohexylthiophthalimide CTP

CTP is an inhibitor commercialized by Monsanto in the 1970s. Monsanto was the sole producer of CTP under their trade name of Santogard PVI (prevulcanization inhibitor). However, with the expiration of their patent, there are several manufacturers of CTP in the world today. 

United Rubber Chemical Corp. (Beijing, China) 

CTP is used as a rubber compound additive to extend scorch safety time so that the rubber compound can be processed further in the factory without generating scrap. Also, CTP does not reduce the cured hardness or slow the cure rate as a conventional retarder would. The addition of CTP generates little or no change in the properties and performance of the cured compounded rubber. 

CTP as an inhibitor is rather unique. Conventional retarders will extend scorch safety time but also hurt the state of cure and the cure rate of the rubber compound. If rubber is processed at lower temperatures or subject to less heat history, it is possible to avoid scorch-related problems. However, this is not always feasible. Sometimes adjustments in the cure package, such as changes in the ratio of secondary to primary accelerator, can also lengthen the scorch safety time but possibly hurt cure rate. 

Tight Supply Situations in the Past and Future Supply Outlook 

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The induction time or scorch resistance of a compound can be improved by addition of a retarder. A-Cyclohexylthiophthalimide (CTP) is by far the largest-tonnage retarder used in the rubber industry. See the review by Morita for... 

The first delayed action accelerators were introduced in 1925 with the development of 2-mercaptobenzothiazole (MET) and 2-mercaptobenzothiazole disulfide (or 2,2"-dithiobisbenzothiazole) (MBTS) (a.5-a.7). Even more delayed action and yet faster-curing vulcanisation became possible in 1937 with the introduction of the first commercial benzothiazolesulfenamide accelerator (a.8, a.9). Further progress was made in 1968 with the introduction (a. 10) of pre-vulcanisation inhibitor (PVI), A-cyclohexylthiophthalimide (CTP), which can be used in small concentrations together with benzothiazole sulfenamide accelerators. The history of the progress toward faster vulcanisation with better control of premature vulcanisation or scorch is illustrated by Figure 2. 

Retarders. The purpose of vulcanization retarders is to delay the initial onset of cure in order to guarantee sufficient time to process the unvulcanized mbber. Three main classes of materials are used commercially, including organic acids and anhydrides, cyclohexylthiophthalimide (Santogard PVI or CTP), and a sulfenamide material (Vulkalent E). 

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