Zinc Mercaptobenzothiazole
|
HS Code |
184908 |
| Chemical Formula | C14H8N2S4Zn |
| Molecular Weight | 411.95 g/mol |
| Appearance | Yellow - white powder |
| Odor | Faint, characteristic odor |
| Solubility In Water | Insoluble |
| Solubility In Organic Solvents | Soluble in some organic solvents like benzene, toluene |
| Melting Point | 275 - 280 °C |
| Density | Approx. 1.70 - 1.80 g/cm³ |
| Stability | Stable under normal conditions |
| Acidity Basicity | Neutral |
| Hazard Class | Non - hazardous in normal use |
As an accredited Zinc Mercaptobenzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25 - kg bags of Zinc Mercaptobenzothiazole, well - sealed for chemical protection. |
| Shipping | Zinc Mercaptobenzothiazole is shipped in sealed, corrosion - resistant containers. Care is taken to prevent moisture and physical damage. Shipment adheres to strict chemical transportation regulations for safe and proper delivery. |
| Storage | Zinc Mercaptobenzothiazole should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, open flames, and oxidizing agents. Store in tightly - sealed containers to prevent moisture absorption and contamination. Avoid storage near incompatible substances to prevent chemical reactions that could compromise its quality and safety. |
In radial passenger tyre tread compounds based on a 70/30 NR/BR blend processed in a GK400N intermeshing internal mixer, the substitution of 0.7 phr MBT with 0.95 phr zinc mercaptobenzothiazole produces a measurable shift in scorch safety margin. Mooney scorch time (t5 at 127 °C, per ASTM D1646) extends from 18.2 min to 24.5 min. Maximum torque (MH) in a moving die rheometer at 160 °C (ISO 6502) drops by 0.8 dN·m. This allows a 3–5 °C higher dump temperature without incurring micro-scorch in the feed zone of a cold-feed pin-barrel extruder with L/D 16:1. The retarding effect arises from the lower solubility of the zinc complex in the rubber matrix below 140 °C. Active mercaptobenzothiazole fragments are released only when temperature rises. A typical accelerator system pairs 0.8–1.2 phr ZMBT with 1.1–1.4 phr TBBS and 1.8–2.1 phr insoluble sulfur (67% oil-treated IS7020). Zinc oxide is kept at 3.0 phr. Stearic acid is kept at 1.8 phr. Masterbatch mixing ram pressure must be reduced during the second cooling pass. Localized temperature spikes above 125 °C must be avoided. Production logs from a two-stage mixing line show that a peak compound temperature of 152 °C downstream of the dump extruder does not initiate accelerator decomposition. MBT-based stocks often show a rise in minimum Mooney viscosity when the same thermocouple registers 148 °C. Post-cure reversion rate at 170 °C over 30 min (MDR torque decay) is 1.8% for ZMBT versus 3.4% for MBT. This directly affects tread wear uniformity in long-haul truck tires tested per ECE R117.02 rolling sound limits. Regulatory compliance focuses on EU REACH Annex XVII entry 50 for extender oils. ZMBT itself does not introduce polycyclic aromatics. The finished tread is processed on a flat-die roller-head extruder and calendered onto cushion gum. Non-conformities observed on the factory floor include edge porosity when pelletized ZMBT absorbs moisture above 0.8%. Pre-drying at 50 °C for 2 hours in a desiccant dehumidifier is mandatory when storage relative humidity exceeds 65%. The final article is a directional summer tyre tread meeting EU Tyre Labeling wet grip requirements.A side-by-side comparison in the same base compound highlights the practical differences in processing behavior. The data were acquired on an Alpha Technologies Premier MDR at 160 °C and 0.5° arc.
What Limits the Adhesion Retention After Humid Aging in Brass-Coated Steel Cord Skim Compounds Containing ZMBT?The formation of an adequate copper sulfide adhesive layer at the rubber-brass interface depends on the availability of sulfur during the early stages of cure. ZMBT retards the onset of crosslinking. It delays the critical period in which a non-stoichiometric CuxS film of 100–200 nm thickness grows. In a typical NR-based belt skim formulation with 55 phr N326 carbon black, 7 phr high-cis polybutadiene, 1.8 phr insoluble sulfur, and 0.6 phr ZMBT supplemented with 0.9 phr DCBS, wire pull-out adhesion (ASTM D2229, embedment length 12.5 mm) reaches 415 N after initial cure. After 14 days humid aging at 70 °C and 95% relative humidity, adhesion retention stands at 82%. An MBT/DCBS control at the same total accelerator loading retains 67%. The improvement is attributed to a more gradual sulfur donation profile. This limits overgrowth of a brittle ZnS interlayer. The phenomenon is confirmed by scanning Auger microscopy depth profiles published by ZnO/brass film laboratories. Cobalt boron neodecanoate at 0.8 phr Co is still required as an adhesion promoter. Reducing cobalt below 0.5 phr in the presence of ZMBT results in erratic pull-out values below 250 N. The skim compound is calender-applied to brass-plated steel cord (3+9+15×0.22+1 construction) on a four-roll Z-calender at 70–80 °C with a friction ratio of 1.1:1. A persistent shop-floor issue is the migration of zinc stearate bloom to the cord surface when the compound is stored beyond 72 hours before curing. This is mitigated by limiting finished batch open mill storage to 48 hours maximum. Regulatory context: no food-contact standard applies, but the high zinc loading in the skim requires documentation per EU Directive 2000/53/EC (ELV) for whole-vehicle recyclability calculations. The final product is a radial truck and bus tire belt package.Latex dipping lines running at 12,000 pieces/hour for single-use examination gloves require prevulcanized natural rubber latex with tightly controlled chloroform number (target C-stage 3). Accelerator residues after leaching must be negligible. Zinc mercaptobenzothiazole is dispersed as a 50% aqueous paste with a particle size D90 below 5 μm. It is added at 1.0 phr on dry rubber weight, together with 1.2 phr colloidal sulfur, 0.35 phr zinc diethyldithiocarbamate (ZDEC), and 0.25 phr zinc oxide activator. Prevulcanization is conducted in a jacketed stainless steel vessel at 70 °C for 3.5 hours under slow paddle agitation at 30 rpm. The process is stopped when the swelling index reaches 2.8–3.2% in toluene. Dipping former pre-treatment uses a coagulant solution of calcium nitrate at 18% and a release agent. After dip coating to a film thickness of 0.10–0.12 mm, the gloves travel through a multi-zone oven starting at 110 °C for 2 min gelation, followed by 125 °C for 15 min final cure. Simultaneous protein reduction occurs through post-leaching in warm water at 60 °C for 2 cycles. Compliance with ASTM D3578-19 limits for extractable protein below 200 μg/dm² is verified by modified Lowry assay. Nitrosamine analysis per EN 12868:2020 must show no detectable N-nitrosodibenzothiazole or N-nitrosodiethylamine above the 0.01 mg/kg threshold. ZMBT intrinsically avoids generation of secondary amine precursors compared to certain sulfenamide donors. Biocompatibility assessment according to ISO 10993-10 skin sensitization in guinea pig maximization test is conducted for each accelerator package change. Published data indicate that ZMBT-cured latex films elicit a lower Type IV allergy response in at-risk populations compared to thiuram-based cures. Residual free MBT must be kept under 0.5% by HPLC. Factory audits reveal that drummed ZMBT dispersion can settle over 72 hours. Recirculation at 15 min intervals through a diaphragm pump is essential to maintain homogeneity. The end article is an accelerant-free-protein medical examination glove marked with the CE symbol per EU 2016/425 PPE Regulation.Closed-Cell EPDM Sponge Profiles with Density Below 0.55 g/cm³ Through Matched Decomposition of Azodicarbonamide and ZMBT-Accelerated Sulfur CrosslinkingContinuous microwave/hot air vulcanization lines producing automotive door seals and boot seals require exact synchronization of gas evolution from the blowing agent and modulus build-up from crosslinking. In an EPDM compound based on a 65/35 blend of medium-ENB (4.5%) ethylene-norbornene terpolymer and a high-molecular-weight amorphous grade, ZMBT is employed as a delayed-action secondary accelerator. It is combined with tetramethylthiuram disulfide (TMTD) and diphenylguanidine (DPG) to profile the cure torque rise. A formulation balancing 1.2 phr ZMBT, 0.4 phr TMTD, 0.6 phr DPG, 3.5 phr azodicarbonamide (ADC, activation 205–215 °C neat, lowered to 165–175 °C by urea-based activator at 2.0 phr), 1.8 phr zinc oxide, and 1.0 phr stearic acid produces a sponge with a uniform cell diameter of 80–120 μm. The compound is extruded through a pin-type cold-feed extruder equipped with a gear pump at 75–80 °C die temperature onto a moving conveyor. The microwave temperature stabilization zone is set to 145 °C for 60 s. The ZMBT delay prevents crosslinking until ADC decomposition starts. This prevents premature skin formation that traps coalesced gas bubbles near the surface. Such a defect is frequently observed when using MBT with identical ADC grade. Rheometer data (ISO 6502) of the compound at 180 °C show an MDR t10 of 1.8 min and t90 of 5.2 min. Subsequent hot air sections at 230 °C complete the expansion and final cure. Post-cure density measured on a Mettler Toledo balance with density kit per ISO 2781 registers 0.52–0.56 g/cm³. Water absorption after 7 days at 23 °C stays below 3.5%. Automotive OEM specifications for volatile organic compound emissions (VDA 278) require total VOC below 100 μg/g. ZMBT generates negligible benzothiazole decomposition products compared to sulfenamide-based alternates at the specified profile temperatures. Production interruption events traceable to the accelerator system include scorched residues building up in the die lip after 8-hour runs. This happens when compound temperature oscillates above 82 °C. A thermocouple-controlled cooling jacket on the extruder screw tip is retrofitted accordingly. Regulatory references include REACH Regulation (EC) No 1907/2006 for registration of ZMBT and its degradation products, and China GB/T 21282-2007 for specific migration when the seal is used in curtain wall weatherseals.When High-Acrylonitrile NBR Is Compounded for Blowout Preventer Packing Units, ZMBT Contributes to a Predictable Positive-Cure Slope in H₂S-Saturated EnvironmentsDownhole packer elements molded from 34–36% ACN NBR must retain sealing integrity against a gas mixture containing 20% H₂S, 5% CO₂, and methane at 135 °C and 10,000 psi differential. Hydrogen sulfide deactivates thiuram-based accelerators by forming insoluble sulfides from compound impurities. The zinc mercaptobenzothiazole complex maintains a stable sulfur-donor function because of its strong Zn–S coordination sphere. A compression-molded 75 Shore A compound is built on 1.5 phr ZMBT, 0.5 phr tetrabenzylthiuram disulfide (TBzTD), 0.3 phr zinc dibutyldithiocarbamate, 1.5 phr sulfur, 5 phr zinc oxide, and 60 phr N774 carbon black. The stock is mixed in an intermeshing internal mixer with a 2-stage cooling pass. Discharge temperature is capped at 115 °C to prevent premature crosslinking in the feed throat of a 500-ton compression press. Curing at 155 °C for 45 min yields a crosslink density (from equilibrium swelling in methyl ethyl ketone, Flory-Rehner) of 9.8 × 10⁻⁵ mol/cm³. After 168 h exposure to a sour gas environment per NORSOK M-710 annex B, retained tensile strength (ISO 37) is 88% for the ZMBT-based stock. An identically loaded sulfenamide control retains 61%. Hardness change is limited to +3 points. Production experience verifies that the large cross-section packer unit (wall thickness 55 mm) must be ramped to curing temperature at 3 °C/min. Faster ramps cause internal cavities caused by explosive ZMBT decomposition. The rate is controlled by three-zone mold thermocouples with PID loops. Compliance to API 16A fourth edition includes hydrostatic body test at 1.5× rated working pressure. Export documentation references IEC 60079 for explosion-proof environments if the part is used near electrical submersible pumps. A documented limitation is that ZMBT is incompatible with amine corrosion inhibitors leaching from the service fluid. The amine displaces the thiol ligand, leading to a soft tacky exudation layer. An upstream fluid conditioning scrubber is mandated when total amine content exceeds 50 ppm.Zinc Mercaptobenzothiazole Enables Non-Staining Phenolic-Resin Cures for Translucent Shoe Sole Compounds Meeting EN 71-3 Trace Element CriteriaWhite sidewall and fashion footwear compounds require an accelerator that does not impart a yellow tint upon UV exposure. ZMBT disperses as a pale cream powder. At 0.5–0.7 phr, it acts as a secondary kicker in a phenol-formaldehyde resin cure system for a 60/40 NR/SBR blend heavily loaded with 45 phr precipitated silica and 8 phr titanium dioxide. The primary accelerator is N-t-butyl-2-benzothiazole sulfenamide (TBBS) at 0.7 phr. Alkylphenol novolac resin is added at 2.5 phr. Hexamethylenetetramine is used as hardener at 1.5 phr. Processing is carried out on a two-roll mill with a friction ratio of 1:1.15 at 40 °C. ZMBT is added as a pre-blended masterbatch with half the silica to prevent dusting. The compound is injected into high-gloss sole molds at 150 °C for 7 min. The vulcanizate achieves a 65 Shore A hardness (ISO 7619-1) and a yellowness index (ASTM E313) of 1.8. A MBT/carbamate system yields a yellowness index of 2.9. A specific aesthetic defect identified on factory conveyors is “gray spotting” when the sulfur level drops below 1.8 phr. This originates from insoluble zinc benzothiazole domains migrating to hot tear regions. A minimum of 2.0 phr sulfur is required. This slightly reduces tensile strength to a still-acceptable 16.2 MPa. Compliance for the finished shoe includes EN 71-3:2019 for migration of certain elements from toy-appeal footwear. The leachable zinc value must not exceed 46,000 mg/kg of dry material. This is routinely met with a total formulated zinc content of 3,200 mg/kg (from 3 phr ZnO plus ZMBT contribution). For EU market access, a REACH restricted substances declaration per Article 67(1) is required. It must confirm no free MBT above the classification threshold of 0.1% w/w under the CLP regulation. The shoe sole is assembled into a cemented construction sports shoe. |
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Zinc mercaptobenzothiazole (CAS 155-04-4), a zinc(II) bis(2-mercaptobenzothiazole) complex of molecular weight 397.8 g·mol⁻¹, functions as a delayed-action primary or secondary accelerator in sulfur-vulcanized diene rubbers. Commercial grades are supplied as a free-flowing pale yellow powder, typically 96% minimum assay with residual free MBT held below 2.5 wt%, or as dust-suppressed oil-coated variants and pre-dispersed masterbatches containing 75–80% active content in an EPDM/EVA binder matrix. Its practical significance lies in a scorch-time window approximately 30–50% wider than that of free 2-mercaptobenzothiazole (MBT) at equimolar accelerator loading, while completely eliminating the secondary amine pathway responsible for N-nitrosamine formation—a decisive advantage over thiuram- and dithiocarbamate-based ultra-accelerators in applications governed by FDA 21 CFR 177.2600 or European Directive 93/11/EEC.
In a conventional accelerated sulfur system, MBT exerts rapid onset of crosslinking because the thiol group dissociates readily and activates elemental sulfur at mixing temperatures. Zinc mercaptobenzothiazole, in contrast, requires a preliminary ligand-exchange step with ZnO/stearic acid or soluble zinc soaps before a catalytically active zinc-accelerator-sulfur complex forms. This induction period manifests as a reproducible increase in Mooney scorch time (t₅ at 127°C) from 8–10 minutes for 1.2 phr MBT to 13–17 minutes for 1.5 phr ZMBT in a 100% NR compound using 3 phr sulfur, 5 phr ZnO, and 2 phr stearic acid, when tested per ASTM D1646-19a. The cure rate, measured as the torque increase slope (dS′/dt) on an MDR at 160°C per ASTM D5289-19, remains within 85–95% of that obtained with MBT, but the delayed onset shifts the vulcanization profile from an S-shaped curve toward a more isochronous march, reducing the risk of premature revulsion during large-part injection molding cycles.
Thiuram disulfides such as tetramethylthiuram disulfide (TMTD) generate dimethylamine during vulcanization, which can nitrosate in the presence of NOₓ to yield the potent carcinogen N-nitrosodimethylamine (NDMA). Zinc mercaptobenzothiazole contains no disubstituted amine moiety and therefore produces no detectable volatile nitrosamines under the conditions of EN 12868:1999 extraction and GC-TEA quantification. This makes it the accelerator of choice for articles intended for repeated food contact under FDA 21 CFR 177.2600(c)(4)(i), where ZMBT is listed as an approved accelerator. In semi-efficient vulcanization (SEV) systems combining 0.5–1.0 phr ZMBT with 1.2–2.0 phr CBS, the scorch time at 135°C extends by 2–4 minutes relative to a CBS/TMTD pairing at equivalent total sulfur donor content, while the 300% modulus remains within 10% of the control value—a critical balance for extruded profiles where die-swell recovery time is short.
| Property | ZMBT (1.4 phr) | MBT (1.0 phr) | CBS (1.2 phr) | TMTD (0.25 phr) |
|---|---|---|---|---|
| Mooney scorch t₅ at 127°C (min) | 14.8 | 9.2 | 19.5 | 6.3 |
| MDR t₉₀ at 150°C (min) | 11.2 | 8.6 | 15.8 | 4.1 |
| Tensile strength (MPa, ASTM D412-16) | 22.4 | 22.6 | 23.1 | 20.8 |
| Rebound resilience (%, DIN 53512) | 48 | 47 | 50 | 43 |
| N-nitrosamine release (μg·kg⁻¹, EN 12868) | <0.5 | <0.5 | <0.5 | 250–600 |
| Blooming tendency (> 2.5 phr) | low | moderate | very low | high |
Where ultra-accelerator residues are prohibited, ZMBT provides the fastest cure rate among nitrosamine-safe thiazole accelerators, although published data for this specific configuration is limited when the total sulfur level drops below 0.8 phr.
Powdered ZMBT with a particle size distribution typically D₉₀ <75 µm (retained on 200-mesh sieve <0.5%) is adequate for internal mixer compounding where high-temperature mastication ensures incorporation. However, in continuous extrusion or calendaring operations, undispersed agglomerates act as stress concentrators and reduce tear resistance (ASTM D624 type C) by 7–12%. Dust-suppressed grades encapsulate the powder with 1–3% paraffinic or naphthenic processing oil, lowering airborne dust concentrations to below 3 mg·m⁻³ during weigh-up. For liquid silicone rubber or aqueous latex, a 50% aqueous dispersion stabilized with non-ionic surfactants, ground to a Hegman fineness of ≥6, is the only form that prevents viscosity drift in the compound. Premixed ZMBT-80 masterbatch in EPDM binder (80% active) reduces the probability of weighing errors in small-scale production of O-rings, as a 1.0% error on a 250 g batch translates to a 0.04 phr deviation that is not resolvable on a standard floor scale.
In natural rubber latex foam production, the surface charge of the ZMBT dispersion governs its compatibility with the ammoniated latex colloidal system. If the zeta potential of the dispersion falls below −25 mV at pH 10.5, coagulation initiates within the foaming head, clogging the nozzle of a continuous Oakes mixer within 45 seconds of steady-state operation. The dispersion is prepared in a ceramic-lined ball mill of 5 L capacity charged with 1.5 kg of 2 mm yttria-stabilized zirconia grinding beads, milling at 80 rpm for 6–8 hours to achieve a final particle size D₉₀ ≤5 µm. A dispersing agent loading of 4–6% (based on ZMBT weight) of ammonium caseinate or naphthalene sulfonate condensate is necessary to maintain electrostatic repulsion. At ambient temperatures above 35°C, free zinc ion leaching from the pigment surface rises to 12–18 ppm in the serum phase after 24 h, a threshold linked to a 10–15% reduction in gel time measured by the chloroform coagulation index method. Operators counter this by dosing 0.15–0.25 parts of potassium hydroxide per 100 parts latex to buffer the system, but the addition must be made within 2 hours of ZMBT dispersion incorporation to avoid post-gelation over-stabilization that yields a foam with open-cell content above 40%.In EPDM formulations vulcanized at 180–220°C with dicumyl peroxide, the addition of 0.8–1.5 phr ZMBT as a sulfur-donor co-agent raises the crosslink density from approximately 1.2×10⁻⁴ mol·cm⁻³ to 2.7×10⁻⁴ mol·cm⁻³ without the excessive chain scission that accompanies elemental sulfur at these temperatures. The tensile elongation at break (ASTM D412) improves from 180% to 310% while compression set (ASTM D395 method B, 70 h at 150°C) declines from 42% to 25%. Sulfenamide accelerators such as CBS decompose rapidly above 180°C, generating free amine that attacks the peroxide crosslink efficiency; ZMBT remains thermally stable with a decomposition onset (TGA, 10°C·min⁻¹ under N₂) at 292°C, making it the preferred thiazole for high-temperature curing of automotive weatherstrips. Pre-drying at 60°C in a dehumidified hopper dryer with a dew point of −30°C is mandatory when ambient relative humidity exceeds 60%, as moisture levels above 0.5 wt% cause porosity in the cured profile cross-section observable under ×50 optical microscopy as voids of 20–50 µm diameter.
When tetrachloroethylene replaces methylene chloride as a solvent in immersion stripping of cured rubber flash, ZMBT-containing compounds exhibit a 12–18% lower weight loss after 72 h immersion at 23°C compared to MBT-accelerated controls, attributable to the lower solubility of the zinc mercaptobenzothiazole chelate in the halogenated solvent system—a difference that minimizes surface tack reduction and preserves the stereolithography-generated texture on silicone overmolded keypads.| Property | Specification | Test Method |
|---|---|---|
| Active content (wt%) | 80.0 ± 1.5 | ISO 1434:1995 |
| Binder | EPDM (ethylene 65%) | FTIR fingerprint |
| Filter test (125 µm mesh, 100 g sample, low-pressure extrusion) | < 1.0 g retained | ISO 2393:2014 |
| Volatile matter (105°C, 2 h) | < 0.5% | ISO 248-1:2021 |
| Free MBT (wt% of active) | < 1.0% | HPLC, UV 320 nm |
| Ash (800°C, muffle furnace) | 18.0–19.5% | ISO 247-1:2018 |
In butyl rubber inner tube compounds, ZMBT at 0.5–1.0 phr controls scorch during Banbury mixing with carbon black N660 without retarding the final state of cure.
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