Treadwear and Wet Grip Balance in High-Aromatic Oil-Extended SBR 1712 Compounds

In passenger car radial tread mixing, the oil-extended styrene-butadiene rubber SBR 1712 is handled as a 137.5 phr product weight per 100 phr rubber hydrocarbon because the bale contains 37.5 phr highly aromatic extender oil. A typical tread formulation on total polymer basis uses SBR 1712 at 70–90 phr rubber hydrocarbon and high-cis polybutadiene at 10–30 phr; carbon black N234 or N220 is charged at 65–85 phr, precipitated silica at 10–30 phr, and TESPT coupling agent at 6–8 wt% of silica. Additional petroleum oil is limited to 0–8 phr after accounting for the oil already present in SBR 1712. Zinc oxide is added at 2.5–3.5 phr, stearic acid at 1.5–2.0 phr, 6PPD at 1.5–2.0 phr, antiozonant wax at 0.8–1.2 phr, CBS at 1.2–1.6 phr, DPG at 0.3–0.6 phr when silica is present, and sulfur at 1.4–1.8 phr. The mixing sequence on a 270 L tangential Banbury with fill factor 0.72–0.76 and rotor speed 35–45 min⁻¹ starts with polymer and black, followed by silica and silane, with a ram pressure of 0.4–0.6 MPa and a first-pass dump temperature of 150–160°C to complete silanization without premature sulfur crosslinking. A second non-productive pass at 140–150°C further disperses silica and lowers Mooney viscosity, and the final curatives are added on an open mill at 45–55°C to prevent scorch. Incoming SBR 1712 should be verified for oil content by solvent extraction per ISO 1407:2011, because batch-to-batch variation of ±0.5 wt% in extender oil content can shift compound Mooney viscosity by several units and alter tread extrusion die swell. Extrusion of tread profiles through a pin-barrel extruder with L/D 16:1–20:1 uses barrel temperatures of 65–85°C and screw temperature of 70–90°C, while the tire cure proceeds at 160–170°C for 10–15 min depending tire size and press capacity. Terminal product types are passenger car radial tread strips and light truck tire treads. Compliance for the raw material and compound is anchored to ASTM D412-16 and ISO 37:2017 for tensile properties, ASTM D2240-15 for hardness, ISO 4649:2010 or DIN 53516 for relative abrasion loss, ISO 23529:2016 for specimen preparation, and ASTM D1646-19 for Mooney viscosity and scorch. Legal compliance for EU tire compounds is governed by REACH 1907/2006 Annex XVII Entry 50 paragraph 5, which limits benzo[a]pyrene to 1 mg/kg and the sum of eight listed PAHs to 10 mg/kg in extender oils used for tire production; the classical highly aromatic extender oil in SBR 1712 can exceed these limits, so specification for EU tire production should require a low-PAH DAE oil variant or replace the grade with a TDAE-extended SBR equivalent. The operational boundary for the compounded stock is a storage time of 24–48 h after final mixing at ambient temperatures exceeding 30°C, because the high oil content accelerates physical relaxation and reduces green tack in the building room.

What Limits Conveyor Belt Cover Compound Tear Strength after 40–80 phr SBR 1712 Addition?

Conveyor belt cover compounds for surface mining and quarry duty are formulated with SBR 1712 at 50–80 phr of total polymer and natural rubber at 20–50 phr, with total polymer normalized to 100 phr. Carbon black N220 or N330 is charged at 35–50 phr, precipitated silica at 0–15 phr when improved cutting resistance is specified, additional aromatic oil at 0–10 phr, zinc oxide at 3.0–5.0 phr, stearic acid at 1.5–2.0 phr, 6PPD at 1.0–1.5 phr, antiozonant wax at 0.5–1.0 phr, sulfur at 1.8–2.4 phr, CBS at 0.8–1.2 phr, and a secondary accelerator at 0.1–0.3 phr when required. Mixing in a 100–200 L Banbury at rotor speed 30–40 min⁻¹ uses a first-pass dump temperature of 130–150°C and a final mill temperature below 80°C; the mixed cover stock is then sheeted off a four-roll calender at 65–90°C and laminated directly onto EP fabric carcass plies. Continuous vulcanization in a Rotocure or steel band press is run at 150–170°C for 20–40 min depending cover thickness, with gauge control typically held at ±0.2 mm across a 1200–1600 mm wide line. The terminal product types are general-purpose abrasion-resistant conveyor belts with textile or steel cord carcasses. Compliance standards include ISO 14890:2013 for general-purpose textile-carcass belting, DIN 22102-3 for covers with grades such as DIN Y and DIN X, ISO 4649:2010 for relative volume loss, ISO 283:2015 for full-thickness tensile strength and elongation, and ISO 34-1:2015 for trouser and angle tear specimens. At SBR 1712 additions above 80 phr, tear strength becomes sensitive to carbon black morphology and crosslink density, and tear failure is observed at splice lines and cover lip edges when the compound is over-oiled and under-filled with reinforcing black. The operational boundary for SBR 1712 cover compounds is mineral oil exposure: the grade is not suited to oil-soaked service, and NBR or PVC/NBR covers are required for belt contact with petroleum-based oils. High aromatic oil can also exude to the cover surface if additional oil exceeds 10 phr and cure time is shortened below the recommended cycle.

In compression-molded soling sheet lines that target 75–85 Shore A finished hardness, SBR 1712 is weighed at 100 phr hydrocarbon and blended with precipitated silica at 35–45 phr, TESPT at 2.8–3.6 phr, N330 carbon black at 10–15 phr for color and conductivity, zinc oxide at 3.0 phr, stearic acid at 1.5 phr, sulfur at 1.8–2.2 phr, CBS at 1.0–1.3 phr, and DPG at 0.3–0.5 phr. Mixing is generally two-stage: the first pass in a kneader or Banbury is dumped at 140–150°C to disperse silica and complete silanization, and the second pass on an open mill introduces curatives at 70–80°C. For injection molding, the compound is fed through a reciprocating screw barrel at 65–80°C, and the mold is held at 155–170°C for 3–8 min depending sole thickness; compression molding of pre-cut blanks follows similar cure conditions but uses longer cycles up to 10–12 min for thick heel sections. Terminal products are work-boot soles, direct vulcanized canvas shoe bottoms, and slip-resistant soling sheets. Compliance and performance test methods include ISO 20871:2018 for abrasion resistance of outsoles, ISO 4649:2010 for material relative volume loss, EN ISO 20344:2011 for safety footwear mechanical tests, ASTM D412-16 for tensile properties, and ASTM D2240-15 for hardness. The aromatic extender oil in SBR 1712 can exude to the surface of light-colored soling and cause staining; formulations intended for pigmented translucent or light-tinted soles therefore either use non-staining paraffinic process oils, reduce SBR 1712 content, or apply a lacquered outer coating. The operational limit for direct molded canvas shoes is a compound scorch time sufficiently above the total residence time in the injection unit; at barrel temperatures above 80°C, scorch can occur during interrupted injection cycles.

When calendered SBR 1712 sheet is press-cured for moderate acid-resistant service

Industrial rubber sheeting for equipment pads and floor protection is produced from SBR 1712 at 100 phr hydrocarbon with N330 carbon black at 20–30 phr, N774 carbon black at 20–30 phr, kaolin clay at 40–60 phr, calcium carbonate at 20–40 phr, factice at 5–10 phr to reduce calendering shrinkage, zinc oxide at 5.0 phr, stearic acid at 1.5 phr, sulfur at 2.0–2.5 phr, MBTS at 1.0–1.5 phr, and TMTD at 0.2–0.3 phr. Mixing on an open two-roll mill is performed at 45–55°C with a friction ratio of 1:1.2, and the compound is calendered through a three-roll vertical calender at 70–90°C to produce sheet gauges from 2 mm to 10 mm. Curing is carried out in a multi-daylight hydraulic press at 140–150°C for 30–60 min, with the longer cycle required for 10 mm sections to avoid porosity at the center. Terminal products include acid-resistant floor mats, manway gaskets, equipment pads, and tank lining sheet. Compliance for sheet gaskets is anchored to ASTM D1330-04(2015), tensile and elongation to ASTM D412-16, and chemical contact behavior to ASTM D471-16a. The operational boundary for SBR 1712 sheeting is exposure to dilute inorganic acids at ambient temperature; concentrated oxidizing acids, ketones, and aromatic hydrocarbon service causes excessive swell and loss of tensile strength. Published data for specific acid concentration and temperature combinations in SBR 1712 sheeting is limited; each service condition therefore requires immersion testing per ASTM D471-16a before specifying replacement intervals.

In hot-cure retread shops where buffed truck tire casings are wrapped with extruded tread rubber, SBR 1712 is used at 60–80 phr of total polymer and blended with natural rubber at 20–40 phr, with total polymer normalized to 100 phr. The compound contains N220 carbon black at 50–60 phr, additional aromatic oil at 5–10 phr, alkylphenol tackifier resin at 3–5 phr, zinc oxide at 5.0 phr, stearic acid at 1.5–2.0 phr, sulfur at 2.0–2.5 phr, CBS at 0.8–1.2 phr, and DPG at 0.1–0.3 phr when silica is present. Banbury mixing is dumped at 130–150°C; the tread profile is then extruded through a cold-feed pin-barrel extruder at 70–85°C and cut to buffed casing dimensions. The cushion gum layer is calendered to 0.8–1.2 mm and must be used within 24–48 h after calendering because the aromatic oil in SBR 1712 migrates and reduces surface tack over time. Curing of hot-cure retreaded tires proceeds in an autoclave at 120–135°C for 2–4 h, depending tire bead diameter and section width. Terminal product types are retreaded bus and truck tires. Compliance is anchored to UN ECE R108 for retreaded pneumatic tires for motor vehicles and UN ECE R109 for retreaded pneumatic tires for commercial vehicles and trailers; physical property retention is screened using ASTM D412-16 and ASTM D2240-15. The process boundary is a minimum green tack: at relative humidity above 70% or shop temperature below 18°C, the calendered cushion gum must be warmed or treated with fresh tackifier because splice failure occurs during envelope inflation.

Compression-molded automotive trunk and floor mat lines compound SBR 1712 at 100 phr hydrocarbon with 80–100 phr reclaimed rubber, calcium carbonate at 80–120 phr, N550 carbon black at 30–60 phr, additional process oil at 20–30 phr, zinc oxide at 3.0 phr, stearic acid at 1.5 phr, sulfur at 1.5–2.0 phr, CBS at 1.0–1.2 phr, and antidegradant at 1.0–1.5 phr. Mixing is performed in a Banbury at 120–140°C, followed by sheeting on a two-roll mill at 50–70°C; the sheet is cut and compression molded at 150–160°C for 4–8 min. Terminal product types are automotive floor mats, trunk liners, and cab interior mats. Flammability compliance uses FMVSS 302 and ISO 3795:1989 horizontal burn rate, while emissions and odor behavior are screened by VDA 278:2011 for VOC and fog. The operational boundary for SBR 1712 in interior applications is the aromatic extender oil contribution to fogging; low-fogging specifications require replacement with a hydrogenated hydrocarbon oil or TDAE-type extended grade, and the compounder must verify VOC output by thermal desorption before vehicle program approval.