2-Mercaptobenzothiazole Zinc Salt

What Maintains Whiteness in a 50‑Shore A EPDM Automotive Seal After 1 000 Hours of Xenon Aging?

EPDM sponge and dense profiles for automotive secondary sealing demand zero contact discolouration under heat and UV, eliminating options based on staining amine antidegradants. In continuous vulcanization tunnels — salt bath or hot air, line speed typically 12–22 m/min — the compound is loaded on a pin‑barrel extruder with a 90 mm screw, L/D 16:1, feeding a microwave‑hot air unit. Zinc 2‑mercaptobenzothiazole (ZMBT) is introduced at 1.0–1.8 phr into the second‑stage internal mixer pass alongside a low‑free‑amine sulfenamide primary accelerator and 0.3–0.5 phr of a thiuram monosulfide. The synergy allows a vulcanization plateau extending from 210 °C to 245 °C without reversion‑driven colour shift toward yellowing, a failure routinely detected by ΔE > 2.0 in CIELAB measurement per DIN EN ISO 105‑A02. Mixing history on a 1.5‑litre laboratory kneader replicating factory dispersion reflects a Mooney viscosity drop to ML(1+4)100 °C 52–58 (ASTM D1646); paired rollers downstream shape the profile to a tolerance of ±0.15 mm. Compliance with automotive OEM material specifications, notably VDA 675 101 and GMW 3221, requires fogging mass below 2 mg (DIN 75201) and formaldehyde emission under 10 µg/g (VDA 275). The zinc salt, because it contains no free 2‑mercaptobenzothiazole above 0.5 wt% residual, contributes negligible volatile condensate at 100 °C bead temperature, keeping the finished weatherstrip inside the specification envelope.

In latex compounding for medical examination gloves, the dispersion quality of ZMBT directly governs the coagulation‑rate homogeneity and the extractable nitrosamine profile of the finished film.

A ball‑milled aqueous dispersion of 50 wt% ZMBT, stabilized with 1.5 wt% sulfated fatty alcohol ethoxylate and ground to a Hegman gauge reading of ≤ 5 µm, is stirred into the prevulcanization kettle at a dosage corresponding to 0.8 phr of the dry rubber content, paired with zinc diethyldithiocarbamate (ZDEC) at 0.25 phr. Unlike MBT‑based formulations that release secondary amines capable of nitrosation, the mercaptobenzothiazole zinc salt lacks a hydrogen atom on the thiazole nitrogen, eliminating the precursor for N‑nitrosamine generation under the conditions of 90–95 °C hot‑air curing. Continuous‑chain dip lines operating at 3 200–4 500 gloves per hour demand a compound viscosity that holds steady between 18–25 mPa·s (Brookfield LV, spindle 2, 60 rpm) for at least 8 hours; the slight thixotropy imparted by finely divided ZMBT resists pigment and zinc oxide settling without jelling the bath. The cured glove film, measured at 0.08–0.12 mm palm thickness, reaches ≥ 24 MPa tensile strength and ≥ 750 % elongation before aging (ASTM D3578, ISO 11193‑1:2020). Extractable protein content stays below 50 µg/dm² under the modified Lowry assay (ASTM D5712), while simulated sweat nickel release — relevant for accelerator‑derived trace metal — is controlled below 0.5 µg/cm²/week (EN 1811:2011 + A1:2015). This combination enables CE marking under EU 2017/745 as a Class I medical device and compliance with the nitrosamine migration limit of 10 µg/kg in EN 12868:1999.

混炼胶停放期间的堆积粘度和门尼焦烧漂移

Truck tire inner liner compounds — typically 80 phr natural rubber blended with 20 phr bromobutyl — are mixed in a 270‑litre tangential internal mixer with a two‑stage upside‑down procedure, and the choice of secondary accelerator determines whether the batch survives a 24‑hour slab‑off rest before being fed to a calender. Substituting 0.5 phr MBT with an equimolar zinc‑thiolate activity from 0.6 phr ZMBT moves the Mooney scorch time t5 at 127 °C (ASTM D1646) from 18.2 min to 26.7 min without retarding the t90 cure time at 160 °C on a moving‑die rheometer (ASTM D5289) beyond 7.8 min. The thermal history gained during downstream extrusion into a 0.8 mm calender sheet on a φ 610 mm × 1 830 mm four‑roll Z‑calender, with bank temperature held at 95 ± 3 °C, fails to trigger scorch because the zinc‑chelate structure releases active MBT fragments only upon thermal dissociation around 135 °C. Stack‑up tack, measured by the rolling‑ball probe method (ISO 6133), remains stable between 0.6–0.9 N during an 8‑hour lay‑up under 30 °C and 55 % RH, preventing ply‑separation defects in the cured tire. Finished inner liner vulcanizates are tested for air permeability at 65 °C (ISO 2782‑1) and must maintain Q ≤ 2.1 × 10⁻¹⁷ m²/(Pa·s), a value that does not drift when ZMBT replaces amine‑generating thiazoles because no plasticizing amine by‑products accumulate at the interface.

Brass‑plated steel cord adhesion in radial‑ply tire belts inherits sensitivity to the thickness and copper‑sulfide stoichiometry of the interfacial reaction layer, which itself is modulated by the latency of the sulfur‑donor package. In a cobalt‑adhesion compound containing 1.2 phr cobalt naphthenate (Co 10.5 %) and 5.0 phr insoluble sulfur, replacing the MBT portion of the accelerator blend with 0.3–0.7 phr ZMBT delays the onset of vulcanization just long enough to permit proper wetting of the brass cord before CuₓS crystallites lock the interphase. Rubber‑to‑metal bond strength is assessed via ASTM D2229 with a 12.7 mm embedment length; pull‑out values at 100 °C typically exceed 420 N for 3 × 0.30 mm cord when cure is executed at 157 °C for 12 minutes. The post‑cure sulfidation index, tracked by time‑of‑flight secondary ion mass spectrometry on polished cross‑sections, shows a Cu/S atomic ratio of 1.92–1.98 — close to the chalcocite‑like stoichiometry desired for optimal adhesion retention after steam‑ageing at 95 °C for 48 hours (rubber coverage ≥ 85 %). Because ZMBT contributes no free amine, the moisture‑activated dezincification rate at the cord surface is slowed, maintaining adhesion degradation below 15 % relative to un‑aged controls, which qualifies the construction for ECE R 54 tyre endurance testing.

When a Direct Injection Molding Cycle Shrinks from 180 Seconds to 120 Seconds

Manufacture of industrial solid tyres and large grommets from natural‑rubber‑rich stocks on a 2 000‑tonne vertical injection molding machine with a 45 mm plasticizing screw, L/D 20:1, poses a classical trade‑off: fast cure temperatures above 170 °C risk scorch in the runner system, while slower cure rates bottleneck the press cycle. Introducing 0.8–1.2 phr ZMBT together with 1.5 phr N‑cyclohexyl‑2‑benzothiazyl sulfenamide (CBS) rewrites the scorch‑cure profile. The compound, pre‑heated to 85 °C in the barrel, exhibits a Mooney scorch t5 of 11.2 min at 135 °C, yet upon injection into a mold at 175 °C it reaches 90 % of the maximum torque in 2.8 min (MDR at ± 0.5° arc). The flash‑less positive mold, fitted with a cold‑runner block maintained at 92 °C, is clamped with 22 MPa cavity pressure; demolding occurs after a total cycle of 105 seconds. Physical property testing on ISO 37 type 2 dumbbells gives tensile strength 27.5 ± 1.2 MPa and elongation at break 520 ± 30 %. Compression set after 22 hours at 70 °C (ISO 815‑1) remains below 18 %, matching the requirements of EN 12508 for load‑bearing elastomeric components. The non‑staining nature of ZMBT permits mould release agents free of permanent discolouration; light‑coloured parts pass the RAL 7035 colour fidelity check after 100 hours QUV‑A exposure (ISO 4892‑3, cycle 1).

Values obtained on a Premier RPA2000 and Alpha MDR2000 under ASTM D1646 and ASTM D5289 respectively; cure rate index calculated as 100/(t90−t10). The extended scorch safety without proportional cure penalty is consistent with the thermally activated ligand dissociation unique to the zinc‑benzothiazole complex.

海绵胶的闭孔均匀性——一个被低估的变量

In EVA/NR microcellular sheets expanded to 0.35–0.45 g/cm³ apparent density, the temporal match between gas nucleation and crosslink development defines cell‑size distribution. A typical formulation mixing 60 phr EVA (VA 18 %), 40 phr SMR 20, azodicarbonamide at 4.5 phr (activation 205 °C by DSC exotherm peak), and zinc oxide 2.5 phr as kicker, requires a delayed‑action accelerator to prevent skin formation before internal gas pressure builds. The addition of 1.0 phr ZMBT, with its decomposition onset near 138 °C in the rubber matrix, ensures that the rubber phase develops a significant torque (≥ 4 dNm on MDR at 190 °C) within 45–55 seconds after the blowing agent decomposes. A pilot‑scale 1.6 m wide single‑pass belt press with three heated zones (185 °C, 200 °C, 195 °C) and dwell time of 6.5 minutes produces continuous rolls; cell uniformity, judged by image analysis of SEM cross‑sections, reaches 85 % of cells within ± 20 µm of the mean diameter. No amine blush develops on the surface, which is critical when the sheet is laminated with a textile print layer using a polyurethane adhesive cured at 120 °C.

Copper conductor insulation in medium‑voltage EPR cables requires long‑term thermal endurance and protection against metal‑catalysed oxidation in wet environments. When a peroxide‑cured ethylene‑propylene copolymer is applied over a tinned‑copper strand via a φ 90 mm, L/D 24:1 cold‑feed extruder, trace copper ions migrating into the dielectric can reduce the oxidation induction time measured at 200 °C (ASTM D3895) by more than 40 % after 21 days of immersion in 85 °C water (IEC 60502‑1 accelerated wet ageing). Incorporation of 0.25–0.45 phr ZMBT into the insulation compound, pre‑dispersed in a 70 °C kneader before being pelletized, functions as a metal deactivator: the thiolate ligand chelates mobile Cu⁺/Cu²⁺ at the boundary layer, forming a stable coordination complex that does not decompose hydroperoxides. Volume resistivity after 14 days in 90 °C water, measured at 500 V DC per IEC 62631‑3‑1, must remain above 1 × 10¹⁴ Ω·m. Long‑term thermal ageing at 135 °C for 42 days according to IEC 60216‑1 shows a retention of elongation at break above 65 %, enabling a temperature index classification of TI ≥ 100 °C. This application does not involve a traditional sulfur cure system; ZMBT acts here solely as a coordination‑type stabilizer, and its dosage must remain strictly below 0.5 phr to avoid dielectric loss tangent increase beyond 0.005 at 50 Hz.