Zinc2-Benzothiazolethiolate

In the compounding of passenger radial tire treads, zinc 2-benzothiazolethiolate is introduced as a secondary accelerator in sulfenamide-cured natural rubber/butadiene rubber (NR/BR) blends. The material’s characteristic delayed onset of crosslinking at processing temperatures between 110 °C and 130 °C provides a widened scorch safety margin in Banbury or Intermix internal mixers with tangential rotor geometries operating at fill factors of 0.70–0.80. In a typical silica-reinforced tread formulation containing solution-polymerized styrene-butadiene rubber (S-SBR) and high-cis BR, the addition level of zinc 2-benzothiazolethiolate ranges from 1.2 to 1.8 phr, partnered with 1.0–1.4 phr sulfur, 1.5–2.0 phr N-tert-butylbenzothiazole-2-sulfenamide (TBBS), and 0.3–0.5 phr diphenylguanidine (DPG) as a silica compatibilizer. The curative package is incorporated after the silanization stage on a two-roll mill set at a friction ratio of 1.0:1.15, with batch discharge temperatures deliberately kept below 95 °C to prevent premature scorch of the mixed compound. Industry compliance for tire applications draws on ISO 37:2017 for tensile stress-strain properties, ASTM D5289-19a for vulcanization kinetics by rotorless rheometry, and DIN 53529-1 for cure-reaction kinetics; European Union tire labeling regulations under EC 1222/2009 further mandate rolling resistance and wet grip indices, parameters indirectly influenced by the network architecture shaped by the chosen accelerator system. On the production floor, the mixed tread compound is extruded through a pin-barrel cold-feed extruder with an L/D ratio of 16, calendered onto a carcass assembly, and subsequently cured in a segmented press under saturated steam at 0.6–0.8 MPa for 12–18 min at 150–165 °C, depending on tread gauge. The use of zinc 2-benzothiazolethiolate in this context yields a plateau modulus that resists reversion during the late stages of vulcanization, reducing the drop in torque after t₉₀ to less than 2 dN·m on an RPA 2000 rheometer. The resulting tire treads—passenger, light truck, and high-performance summer categories—exhibit a fine-tuned balance between abrasion resistance and rolling loss, although published dynamic mechanical analysis data showing the precise shift in loss tangent at 60 °C for this specific accelerator ratio remain limited.

Prevulcanization of natural rubber latex with zinc 2-benzothiazolethiolate dispersions is employed in the continuous production of examination and surgical gloves via a coagulant dipping process. A water-based accelerator dispersion containing 0.5 to 1.0 phr zinc 2-benzothiazolethiolate, pre-milled in a bead mill to a particle fineness below 5 μm as verified by a Hegman gauge reading of 7, is added to a compounded latex blend alongside 0.3–0.5 phr zinc diethyldithiocarbamate (ZDEC) and 0.5–0.8 phr sulfur. The dipping bath is maintained at 25–30 °C with continuous low-shear agitation to prevent accelerator settling. Glove formers pre-heated to 55–65 °C pass sequentially through a coagulant tank containing calcium nitrate, a latex tank with a dwell time of 20–40 s, and a leaching stage that extracts residual water-soluble proteins and unreacted curatives. Vulcanization takes place in a hot-air tunnel with a temperature gradient from 90 °C at the entry to 130 °C at the core, with total residence time between 15 and 25 min adjusted to glove film thickness. The relatively low curing temperature and slow-accelerating behavior of zinc 2-benzothiazolethiolate contribute to a low concentration of extractable N-nitrosamines, a critical property for meeting the EN 455-3:2023 requirement for medical gloves and the ASTM D3578-19 specification for rubber examination gloves. After de-molding and a post-cure wash, the gloves are tested for tensile strength (≥ 21 MPa per ASTM D412) and ultimate elongation (≥ 700 %) to confirm the film has reached an adequate crosslink density. This dispersion-based route is particularly suited for powder-free chlorinated gloves, where residual accelerator fragments at the surface must be minimized to reduce the risk of type IV hypersensitivity reactions; zinc 2-benzothiazolethiolate’s low solubility in water and its gradual release of active sulfur atoms at the interface keep surface extractables within the 50 µg/dm² limit demanded by FDA 21 CFR 177.2600 for repeated-use rubber articles, though the exact leachate profile depends on the chlorine-neutralization step parameters.

What Adjusts Scorch Safety While Maintaining Plateau Modulus in Long-Run Conveyor Cover Mixes?

In SBR/natural rubber-based conveyor belt cover compounds processed on dedicated three-roll calender lines operating at linear speeds exceeding 30 m/min, zinc 2-benzothiazolethiolate at 0.8–1.2 phr serves as a cure modifier that retards the onset of crosslinking without sacrificing the final elastic modulus. The compound, containing 40–50 phr N330 carbon black and a sulfur loading of 1.5–2.0 phr, is mixed in an intermeshing twin-screw extruder with a temperature profile of 90/95/85 °C from feed throat to die, then calendered into 6–8 mm thick sheets that are vulcanized on a continuous Rotocure press with a steel band at 160 °C for 8–12 min. The compliance matrix includes ISO 15236-1:2017 for steel cord conveyor belts, DIN 22102-1 for fabric belts with general use, and MSHA IC-112/2 for underground mine flame resistance where applicable. Finished products range from abrasion-resistant surface covers for mining conveyors to oil-shield covers in grain handling terminals.

Compression Set Behaviour and Metal Adhesion in Static Gasket Compounds

When zinc 2-benzothiazolethiolate is formulated at 1.0–1.5 phr in an EPDM compound for static sealing applications, it influences the crosslink distribution sufficiently to reduce compression set measured after 22 h at 125 °C to values below 15 % as per ASTM D395-18 method B. The compound is prepared on a two-roll mill with a final cut-and-fold routine repeated 6 times to ensure accelerator dispersion, then sheeted to 2 mm and placed in a multi-cavity compression mold. Vulcanization occurs between 170 °C and 180 °C under a clamp force of 150 kN for 4–6 min. Because the gasket must often bond to a metal insert coated with a proprietary silane-based adhesive, the slower cure front generated by zinc 2-benzothiazolethiolate allows the adhesive film to wet the elastomer surface before the onset of gelation, yielding a 3 MPa peel strength minimum as tested by ISO 813:2019. Relevant standards governing food-contact gaskets include FDA 21 CFR 177.2600 and EU 1935/2004; for industrial flange gaskets, EN 682:2002 applies. The output covers hydraulic valve cover gaskets, pump housing seals, and flanged pipe joint rings operating in aqueous environments up to 100 °C.

When Ethylene-Vinyl Acetate Foam Requires a Delayed-Action Booster for Blowing Agent Decomposition

In the manufacture of closed-cell EVA foam for athletic footwear midsoles, zinc 2-benzothiazolethiolate is introduced not as a primary vulcanizing agent but as a kicker—a catalyst that modulates the decomposition temperature of azodicarbonamide blowing agents. A typical formulation includes 0.6–0.9 phr zinc 2-benzothiazolethiolate, 2.5–3.5 phr azodicarbonamide, 0.8–1.2 phr dicumyl peroxide, and 0.4 phr zinc oxide, all dispersed in EVA with 18–26 % vinyl acetate content via an intermeshing co-rotating twin-screw extruder with screw diameter 40 mm and an L/D ratio of 42. The presence of zinc 2-benzothiazolethiolate shifts the exothermic decomposition peak of the blowing agent from approximately 205 °C to 185 °C, bringing it closer to the peroxide crosslinking window and thereby producing a more uniform cell structure with cell size distribution standard deviation below 30 µm. The foam sheet, extruded through a flat die at 95 °C and subsequently expanded in a hot-air oven at 180 °C for 5–7 min, attains a density of 0.15–0.22 g/cm³ and an expansion ratio between 4.5 and 6.7. Testing follows ISO 1798:2008 for tensile properties of flexible cellular polymeric materials, ASTM D3574-17 for rebound resilience, and ISO 20871:2018 for shoe outsole abrasion. The end products—running shoe midsoles, comfort sandal footbeds, and orthotic inserts—must also satisfy the restricted substance requirements of REACH Annex XVII and the AFIRM RSL for benzothiazole residues, a constraint that necessitates a thorough aqueous washing step after foaming to keep surface extractables below 30 mg/kg. Published systematic investigations of the exact influence of zinc 2-benzothiazolethiolate particle size on foam cell nucleation are sparse, but plant-scale observations indicate that agglomerates larger than 10 µm cause localized hot spots visible as collapsed cells in micro-CT scans.

When compounding polychloroprene-based sheathing for subsea power cable jackets, zinc 2-benzothiazolethiolate is dosed at 0.5–0.7 phr alongside ethylene thiourea (0.8 phr) to achieve a moderately fast cure without compromising the dynamic flex resistance required for splashing-zone installations. The compound is extruded through a 90 mm three-zone single-screw extruder directly onto a copper conductor and subjected to continuous vulcanization in a pressurized liquid salt bath at 210 °C with a line speed of 15 m/min; the short residence time demands a precisely delayed scorch of at least 45 s at 121 °C as measured by ISO 289-1:2021. Compliance is anchored to IEC 60502-2:2014 for power cables with extruded insulation, NEK TS 606:2016 for submarine cable specifications, and IEEE 1580:2010 for fixed offshore installations; the jacket must also meet the oil resistance thresholds of IRM 903 per ISO 1817:2015. Finished cables range from medium-voltage (6/10 kV) power links to fiber-optic data cables with external protective sheaths, both deployed in marine renewable energy arrays.