Scorch inhibitors

New efficient vulcanization systems have been introduced in the market based on quaternary ammonium salts initially developed in Italy (29—33) and later adopted in Japan (34) to vulcanize epoxy/carboxyl cure sites. They have been found effective in chlorine containing ACM dual cure site with carboxyl monomer (43). This accelerator system together with a retarder (or scorch inhibitor) based on stearic acid (43) and/or guanidine (29—33) can eliminate post-curing. More recently (47,48), in the United States a proprietary vulcanization package based on zinc diethyldithiocarbamate [14324-55-1]... 

Additives (antioxidants, antiozonants, softeners, tacfdfiers, peptisers, scorch inhibitors, colorants, flame retardants, blowing agents, process aids, etc.)... 

Brief information on the formation of anilino-derivatives from NaPsClg and HaNCeHjR-p (R=H, NO2, NH2, etc.) in pyridine solution, and on the preparation of structurally related compounds (84), which have applications as scorch inhibitors... 

Table 4 (16) makes a comparison of cure properties for the sulfenamides listed in Tables 1 and 2 relative to MBS. No exact replacements are available for MBS, MBSS, and DIBS, but DCBS can serve as an alternative for MBS and DIBS and CBS and TBBS can serve as alternatives for MBSS. Proper adjustments in sulfur and sulfenamide levels can provide similar cure performance. CBS and TBBS also satisfy the need in providing rapid curing kinetics where required. Additional scorch protection, if needed, can be obtained by application of the widely used scorch inhibitor A(-(cyclohexylthio)phthalimide (17). 

A variety of structurally dissimilar phenolic antioxidants were evaluated for performance as scorch inhibitors. The results of screening work are shown in Figure 4. In general, all of the antioxidants evaluated provided... 

A report is presented on the use of sulphylimines with various substituents as scorch inhibitors in sulphur and peroxide curing of natural rubber and EPDM. 8 refs. Articles from this j ournal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

Accelerated sulphur systems also require the use of an activator comprising a metal oxide, usually zinc oxide, and a fatty acid, commonly stearic acid. For some purposes, for example where a high degree of transparency is required, the activator may be a fatty acid salt such as zinc stearate. Thus a basic curing system has four components sulphur vulcanising agent, accelerator (sometimes combinations of accelerators), metal oxide and fatty acid. In addition, in order to improve the resistance to scorching, a prevulcanisation inhibitor such as A -cyclohexylthiophthalimide may be incorporated without adverse effects on either cure rate or physical properties. 

Premature cure at processing tenqperature ("scorch at 121 0 is conveniently delayed or prevented by snail amounts of various phenolic and amine free-radical inhibitors and antioxidants. When the inhibitor concentration is properly chosen, the retarding effect disappears on the curing temperature (177 0. 

This decay rate is nearly equivalent to that exhibited by one g of radium in equilibrium with its disintegration products. A miUicurie (mCi) is 0.001 curie, curie point See magnetized curie point, curing See autoclave nitrogen atmosphere cure extruder wire and cable process, dry cure inhibitor prepreg volatile content reinforced plastic resin transfer molding test, Barcol hardness test, scorch Mooney thermoset plastic vulcanization welding, induction. 

The effect of the addition of small concentrations of the premature vulcanization inhibitor (PVI), N-(cyclohexylthio)phthalimide, is also given by Figure 7.11. This retarder (Coran and Kerwood, 1970) is frequently used to independently control scorch resistance with little effect on the rate of crosslinking (Coran, 1978). Before the development of N-(cyclohexylthio)phthalimide as a PVI, acidic retarders like salicylic acid, acetylsaUcylic acid, phthaUc anhydride, and benzoic acid were used. These additives improved scorch resistance but also gave greatly reduced rates of crosslink formation after the delay. Another retarder of the past was N-nitrosodiphenylamine, which is less active and not now used because of toxicological concerns. 

Uses Antioxidant, antiozonant for rubbers, latex, crosslinked PE, lubricants stabilizer polymerization inhibitor staining antioxidant for stabilization of latex foams for carpet backcoating improves scorch resist. 

The Mooney scorch times of ENR mixes can be increased by the use of commercial prevulcanization inhibitors (PVI) once the base has been added. The response of these materials depends on the cure system employed and parallels that observed with NR and other unsaturated polymers. 

The addition of a base neutralizes the acids produced during ageing and substantially improves the ageing properties of ENR (Table 11). Sodium carbonate is the most effective base but significant amounts can result in scorch problems (Fig. 9). To control the scorch a prevulcanization inhibitor can be used in conjunction with sodium... 

The longer scorch safety of MBS compared to TBBS and CBS can be replicated somewhat by using vulcanization inhibitors. 

Inhibitors and retarders are sometimes used in the rubber curative package to extend scorch safety time for a rubber compound. 

---