Non-oil-extended SBR (Dry SBR)

When Does Dry SBR Replace Oil-Extended Grades in PCR Tread and Retread Compounds?

Dry SBR 1502 with a bound styrene content of 22.5–24.5% and Mooney viscosity ML(1+4) 100 °C in the range 46–54 is specified for passenger car radial tread compounds when the extender oil present in oil-extended grades would lower wet grip or when the downstream extrusion operation requires a narrower viscosity band for profile dimensional control. The material is not a universal tyre solution: truck and bus radial treads more commonly select oil-extended SBR 1712, NR, or high-cis BR blends to reduce heat build-up at high load. For EU market access, passenger car tyre treads are type-approved under ECE R117.02, with rolling resistance measured per ISO 28580:2018 and wet grip index determined per ISO 23671:2015; the test limits vary by tyre category, load index, and speed symbol. REACH Annex XVII Entry 50 applies to PAH-bearing extender oils and rubber/plastic articles supplied to the general public, and tyre-grade carbon black is screened using IP 346 DMSO extractables under supplier specification to restrict benzo[a]pyrene and the listed PAH profile. A production tread formulation uses dry SBR 1502 at 65–80 phr, BR 9000 at 20–35 phr, N234 carbon black at 70–85 phr, treated distillate aromatic extract at 5–15 phr, zinc oxide at 2.5–3.5 phr, stearic acid at 1.5–2.0 phr, 6PPD antiozonant at 2.0–3.0 phr, TMQ at 1.0–1.5 phr, sulphur at 1.5–2.0 phr, and CBS accelerator at 1.2–1.8 phr. Mixing is performed in a Banbury-type internal mixer with a 160 L chamber, two-wing rotor at 50 rpm, fill factor 0.75, and ram pressure 0.4–0.6 MPa; the first non-productive pass drops at 145–160 °C, and after batch cooling on an open mill to 45–55 °C, the productive pass adds sulphur and accelerator and drops below 105 °C to limit scorch. The compound is then fed through a 120 mm pin-barrel cold-feed extruder with die temperature 90–105 °C, calendered into tread profile at 1.8–2.4 mm skim gauge, and cut into ply-assembled green tyres. Curing takes place at 150–170 °C for 12–15 min under bladder pressure 1.6–2.1 MPa, depending on tyre section width and aspect ratio. Terminal finished product types include summer and performance passenger radial treads in sizes 205/55R16 through 225/45R17, precured retread strips for regional and urban bus service, and sidewall veneer compounds where black surface integrity and low tack are process advantages.

In textile-reinforced conveyor belt cover compounds, non-oil-extended SBR 1502 is selected when the belt must resist abrasive mineral service without the surface bloom and dimensional drift associated with oil-extended grades. The compound is blended as dry SBR 1502 at 50–70 phr, SMR 20 natural rubber at 20–30 phr, and BR 9000 at 10–20 phr to balance cut resistance, tear propagation, and tensile fatigue under pulley flexing. The cover compound is classified under ISO 14890:2013 for textile-reinforced conveyor belts; abrasion loss is measured per ISO 4649:2010 Method A with cover-class limits typically in the range 100–150 mm³ for abrasion-resistant stock. Tensile properties are tested per ISO 37:2017, ozone resistance per ISO 1431-1:2022 at 50 pphm, 40 °C, 20% strain for 96 h, and tear strength per ISO 34-1:2015. In underground mining service, flame-resistant conveyor belts are governed by MSHA 30 CFR Part 18 in the United States, while EU applications must satisfy REACH Annex XVII restrictions on PAH-containing extender oils and short-chain chlorinated paraffins if present. The formulation addition ratio uses SBR at 50–70 phr, N220 or N330 carbon black at 35–55 phr, naphthenic oil at 5–10 phr, zinc oxide at 3–5 phr, stearic acid at 1–2 phr, TMQ at 1–2 phr, 6PPD at 1.5–2.5 phr, sulphur at 1.5–2.5 phr, and TBBS at 0.8–1.4 phr. Mixing is carried out in a 270 L intermeshing internal mixer at a fill factor of 0.68; the masterbatch drop temperature is 155–165 °C and the finalisation pass drops at 95–105 °C. Cover sheets are produced on a four-roll Z-type calender with roll face temperatures 60–80 °C, giving cover gauges from 3 mm to 10 mm. Belt assembly uses a double-deck hydraulic press with platen length up to 12 m, curing at 150 °C and 1.2–1.6 MPa for 20–35 min depending on cover thickness; continuous Rotocure lines are used for long-run export belts. Terminal finished products are abrasion-resistant conveyor belt covers for iron ore, crushed granite, cement clinker, potash, and grain handling, including single-ply and multi-ply textile belts. Field failure records from production-scale installations identify edge tearing from mis-tracking and splice fatigue in belts shorter than 50 m as the principal returns, which supports the use of dry SBR over oil-extended grades to reduce surface oil migration and splice adhesion loss.

Footwear Outsole Vulcanization and Slip-Resistance Certification Interfaces

Safety and work footwear outsoles based on dry SBR 1502 are formulated to meet ISO 20345:2021 basic requirements, abrasion resistance under ISO 20871:2018, and slip resistance under ISO 13287:2019 on ceramic tile with NaLS solution and glycerol as test lubricants. REACH Annex XVII Entry 52 restricts DEHP, DBP, BBP, and DIBP in footwear components supplied to the general public to 0.1% by mass per plasticised material, which excludes many ortho-phthalate ester plasticisers from the formulation. The addition ratio in a moulded outsole stock is dry SBR 1502 at 70–100 phr, high-styrene resin with a softening point of 85–95 °C at 20–40 phr, precipitated silica at 10–20 phr, calcium carbonate at 20–30 phr, naphthenic oil at 5–10 phr, zinc oxide at 3–5 phr, stearic acid at 1–2 phr, sulphur at 1.8–2.2 phr, and a thiazole/thiuram accelerator system with DPG at 0.3–0.8 phr. Mixing is performed in a 75 L kneader at 40 rpm with a masterbatch drop temperature of 130–145 °C; curatives are added on a two-roll mill at 45–55 °C with a nip gap of 4–6 mm. Outsole blanks are compression moulded in multi-cavity hydraulic presses at 160 ± 3 °C for 5–8 min at 15–20 MPa for 6 mm sheet, or injection moulded as unit soles on a reciprocating screw machine with barrel temperature 70–90 °C and mould temperature 165–180 °C. The terminal finished product types include safety boot outsoles, work shoe outsoles, and vulcanised rubber sole sheets for casual footwear, with Shore A hardness 68–78 and density 1.15–1.25 g/cm³. Production lines record outsole weight variation of ±3% when calender thickness tolerance exceeds ±0.15 mm; in-house thickness control is therefore set to ±0.1 mm to stabilise mould filling and final sole mass.

Compression-moulded automotive floor mats, pedal pads, and firewall grommets frequently specify dry SBR 1502 where the finished part must satisfy an ASTM D2000 M2AA708 line call-out with A14 heat resistance and B13 compression set limits. Tensile strength and elongation are tested per ASTM D412, hardness per ASTM D2240, hot air ageing per ASTM D573 at 70 °C for 70 h, and compression set per ASTM D395 Method B at 70 °C for 22 h. Automotive rubber parts shipped to EU vehicle manufacturers must also comply with REACH Annex XVII and the RoHS 2011/65/EU recast, with lead ≤1000 ppm, cadmium ≤100 ppm, and hexavalent chromium ≤1000 ppm by homogeneous material. The compound uses dry SBR 1502 at 80–100 phr, N550 carbon black at 40–70 phr, calcium carbonate at 30–60 phr, paraffinic oil at 5–15 phr, zinc oxide at 3–5 phr, stearic acid at 1–2 phr, sulphur at 1.5–2.2 phr, and a thiuram/thiazole accelerator package. Injection moulding is run on a 200–350 ton clamp-force machine with cold runner tooling, barrel temperature profile 70–90 °C, mould temperature 160–180 °C, injection pressure 80–120 MPa, and cure time 3–6 min for wall thickness up to 5 mm. Compression moulding of floor mats uses a 500 ton platen press at 155–165 °C for 8–12 min. Terminal finished product types are pedal pads, brake and clutch pedal covers, firewall grommets, battery mat liners, and interior floor mats for commercial vehicles. A known production issue on multi-cavity injection tools is flow-line cracking in grommets when melt temperature falls below 70 °C; the corrective action is to raise nozzle temperature to 85 °C and limit mould release agent concentration to ≤0.5% by weight of the compound.

Where Solventborne SBR Adhesives Must Satisfy FDA 21 CFR 175.105 and REACH Restrictions

Solventborne adhesive and carpet-backing compounds use non-oil-extended SBR 1502 as the primary elastomer when the adhesive is intended for indirect food-packaging contact under FDA 21 CFR 175.105 or for resilient flooring installation where SBR latex grades are more common but dry SBR is selected for higher tack retention. The dry SBR content in the final adhesive mass is 25–40 wt%; a typical compounding formula includes SBR 1502 at 100 phr, rosin ester tackifier at 10–20 phr, hindered phenol antioxidant at 0.5–1.5 phr, and a solvent blend of toluene, methyl ethyl ketone, and hexane in a 3:2:5 ratio to a solids content of 18–25%. Brookfield viscosity at 25 °C is controlled to 2000–4000 mPa·s for knife coating or roller application. Production is performed in an explosion-proof sigma-blade mixer of 500 L working volume under nitrogen blanketing, with dissolution at 45–55 °C for 6–8 h; the adhesive is discharged through a 150 µm filter and drummed. For carpet secondary backing, the adhesive is applied by knife-over-roll coating at 30–50 g/m² dry weight and dried in a forced-air oven at 80–100 °C. Terminal finished products are solventborne contact adhesives for rubber tile and sheet flooring, carpet secondary-backing laminates, and paper-to-film packaging adhesives. The process boundary at relative humidity above 60% requires nitrogen purging and moisture-monitored solvent stock to prevent phase inversion and gel formation. Published data for this specific dry SBR configuration under ISO 13007-2:2014 is limited because that standard is normally validated for cementitious or dispersion adhesives; application-specific bond strength and indirect food-contact documentation therefore remain the primary compliance basis.

Calendered SBR sheet for waterproofing membranes and pond liners is produced from dry SBR 1502 because oil migration in oil-extended grades reduces heat-welding seam strength and accelerates outdoor embrittlement after repeated thermal cycling. The sheet is specified under EN 13956:2013 for flexible sheets for roof waterproofing, with tensile strength and elongation after artificial ageing tested per ISO 37:2017, tear strength per ISO 34-1:2015, and hardness per ISO 868:2003. Seam shear resistance for factory seams is evaluated by the tensile shear method referenced in EN 13956 on a 50 mm wide joint. The formulation is dry SBR 1502 at 100 phr, N550 carbon black at 40–60 phr, calcium carbonate at 40–80 phr, chlorinated paraffin at 10–20 phr, paraffinic oil at 5–10 phr, zinc oxide at 4–5 phr, stearic acid at 1–2 phr, sulphur at 1.5–2.5 phr, and CBS at 0.8–1.5 phr. Flame-retardant grades add antimony trioxide at 8–12 phr and aluminium hydroxide at 20–40 phr for roof fire classification testing. Mixing is performed in a 160 L internal mixer with a drop temperature of 145–155 °C; the sheet is calendered on a four-roll inclined-Z calender to 1.0–1.5 mm gauge and laminated to polyester scrim of 110–130 g/m². Vulcanization is carried out in an autoclave at 140–150 °C for 4–6 h under steam pressure 0.35–0.50 MPa, or by continuous drum vulcanization at 160 °C for 15–25 min. Terminal finished product types are loose-laid and mechanically fastened roofing membranes, pond liners, tank liners, and concrete joint seals. Membrane line records show seam failures when calender gauge variation exceeds ±0.1 mm, with joints failing below 50 N/50 mm; laser thickness scanning is therefore set to reject sheet outside ±0.08 mm before lamination.

Industrial Roller Cover Compounds with Dry SBR: Hardness, Hysteresis, and Workpiece Marking Limits

Rubber-covered rollers used in printing, paper, textile, and steel processing specify dry SBR 1502 when the cover must combine controlled hardness with low extractable oil content to prevent workpiece marking. Roller cover requirements and tolerances are specified under ISO 6123-1:2015; surface hardness is tested per ISO 48-4:2018, abrasion resistance per ISO 4649:2010 Method A, and chemical resistance screening per ISO 1817:2015. The formulation addition ratio uses dry SBR 1502 at 80–100 phr, N770 carbon black at 40–70 phr, precipitated silica at 10–20 phr, paraffinic oil at 5–10 phr, zinc oxide at 3–5 phr, stearic acid at 1–2 phr, sulphur at 1.5–2.0 phr, and a sulfenamide accelerator at 0.8–1.4 phr. Mixing is carried out in a 110 L internal mixer with a masterbatch drop at 145–155 °C and finalisation below 100 °C. Roller building is performed by extruding the compound onto a degreased steel core, followed by spiral wrapping with nylon film under tension to consolidate the cover before autoclave cure at 140–150 °C for 3–5 h. The cured roll is ground to a total indicated run-out of ≤0.02 mm using a cylindrical grinder with water-cooled silicon carbide wheel. Terminal finished product types include printing press ink duct rollers, paper mill guide and press rollers, textile drafting rollers, and steel coil feeder rolls. Operating limits apply: continuous service above 80 °C can degrade the SBR cover by thermo-oxidative chain scission, and exposure to aromatic hydrocarbon solvents above 5% by volume in wash-up solutions can cause swelling beyond the ISO 1817 tolerance band.