Polymer-Modified Bitumen for Dense-Graded Asphalt Wearing Courses

Kumho Petrochemical KTR® SBS 602 is introduced into penetration-grade road bitumen at 3.0–4.5 wt% by binder mass for dense-graded wearing-course polymer-modified bitumen, a range bounded at the lower limit by the threshold for continuous polymer network formation and at the upper limit by the viscosity rise that pushes hot-storage temperatures beyond 180 °C unless a compatibilising oil is included. The production process uses a rotor-stator high-shear mill at 170–190 °C for 2–4 h, with the polymer dispersion state checked by fluorescence microscopy per EN 13632; the SBS-rich phase must transition from discrete swollen particles to an interlocking continuous network before the batch is transferred to storage. Under EN 14023:2010 and AASHTO M 320, the modified binder is qualified against softening point by ASTM D36 or EN 1427, elastic recovery at 25 °C by ASTM D6084-21 or EN 13398, storage stability by EN 13399, and low-temperature rheological performance through the bending beam rheometer within the performance-graded specification. Production-scale tanks exhibit two recurrent bottlenecks: phase inversion in low-asphaltene bitumen streams when SBS 602 addition exceeds 4.5 wt% without sufficient aromatic oil, and oxidative gel skin formation on tank walls during storage above 170 °C; both are controlled through nitrogen blanketing and restricted residence time in the high-shear zone. The finished PMB is transferred to asphalt plants at 160–175 °C for production of stone mastic asphalt, polymer-modified dense-graded wearing course, and high-modulus asphalt concrete; terminal products include highway surface courses, bridge deck pavements, and airport taxiway overlays.

In SBS-modified bituminous torch-applied membrane manufacture, KTR SBS 602 is dosed at 8–12 wt% of the bitumen-filler masterbatch because the roofing membrane must retain dimensional stability under torch heating while developing sufficient elastomeric recovery for crack bridging at negative temperatures. The manufacturing line uses a vertical anchor agitator or planetary mixer at 180–200 °C to disperse the polymer into oxidised bitumen before the addition of 20–30 wt% micronized limestone filler; the filled compound is then conveyed through a calender or continuous impregnation unit where a spunbond polyester or glass-fibre carrier web is saturated and surface-finished with sand or slate granules. Compliance is verified under EN 13707:2017 for flexible roof waterproofing sheets and ASTM D6164/D6164M for SBS-modified bituminous sheet materials, with cold-flex performance tested per EN 1109, tensile properties per EN 12311-1, and thickness per EN 1849-1. The main process constraint is the balance between compound viscosity required for full carrier saturation and the heat history that can degrade the butadiene mid-block; published data for this specific grade in oxidised-bitumen systems is limited, but plant records show that filler moisture above 0.2 % generates foam in the mix vessel and pinholes in the finished sheet. Terminal products include torch-applied roofing membranes, self-adhesive underlayments for standing-seam metal roofs, bridge-deck waterproofing sheets, and below-grade foundation tanking membranes.

Why Does SBS 602 Require a Narrow Injection Temperature Window in Unit Sole Moulding?

Soling compounds based on KTR SBS 602 are compounded at 25–40 phr polymer, with 10–25 phr paraffinic or naphthenic process oil, 10–20 phr general-purpose polystyrene, and 5–15 phr mineral filler, then pelletised for reciprocating-screw injection moulding of unit soles; the formulation ratio is set by the target Shore hardness range of 55–75 A and by the need to avoid phase separation at the screw tip. The downstream production sequence employs an internal mixer or co-rotating twin-screw compounding line at 150–180 °C, followed by injection moulding at barrel temperatures of 160–190 °C and mould temperatures of 25–45 °C; on 250–350 t clamp machines, lot-to-lot variation in melt flow of more than 0.5 g/10 min can produce jetting and visible weld lines on high-relief outsoles. Mechanical verification follows ISO 868 for Shore A hardness, ISO 37 for tensile strength and elongation, ISO 815-1 for compression set, and ISO 4649 for abrasion loss; finished footwear entering EU markets is additionally assessed under REACH EC 1907/2006 Annex XVII restrictions, particularly for phthalate migration in children's soling. The terminal outputs are injection-moulded unit soles, direct-injected casual shoe soles, safety footwear midsole/outsole co-mouldings, and chemically foamed cellular soling produced by injection moulding with blowing-agent masterbatch.

In hot-melt pressure-sensitive adhesive mixing cells, KTR SBS 602 is dosed at 25–35 wt% of the adhesive solids, with the balance split between C5/C9 aliphatic-aromatic tackifier resins at 40–55 wt% and white mineral oil at 10–20 wt%; this window keeps storage modulus low enough for room-temperature tack while preventing cohesive failure at shear temperatures above 70 °C. The production line begins with a jacketed anchor mixer or continuous hot-melt extruder operating at 150–170 °C, transfers the melt through heated gear pumps and slot-die coaters onto release liner at line speeds of 50–200 m/min, and cools the laminate on a chilled drum before slitting. Adhesive performance is tested by ASTM D3236 for viscosity at 177 °C, ASTM D3330 for 180° peel adhesion, ASTM D3654 for loop tack, and ASTM D4498 for elevated-temperature shear failure temperature; food-contact label and tape uses require the formulated adhesive to meet the extractive framework of FDA 21 CFR 175.105. Processing failure modes observed on continuous coaters include oxidative gel specks at the die lip when pot temperature exceeds 170 °C without nitrogen blanketing, and phase separation between SBS 602 and high-ester rosin esters that causes transfer tack loss on recycled board stock. The terminal product types are multilayer labelstocks, carton sealing tapes, hygiene elastic attachment adhesives, and specialty graphic film mounting adhesives.

Twin-Screw Compounding Lines Operate Within a Defined Thermal Envelope for SBS 602/PP Blends

Impact modification of polypropylene with KTR SBS 602 uses 10–25 wt% SBS in a co-rotating twin-screw extruder with L/D 40:1 and zone temperatures held between 170 °C and 210 °C, with notched Izod impact resistance verified per ISO 180 or ASTM D256, tensile and flexural properties per ISO 527-2 and ISO 178, and melt flow stability per ISO 1133-1, for terminal products such as automotive interior trim, appliance housings, luggage shells, and toys.

When Solvent Retention Limits SBS 602 in Contact Adhesives

Solvent-borne contact adhesives formulated with KTR SBS 602 at 12–18 wt% in a ketone-toluene blend require post-lamination open-time control because the styrenic end-block network retards solvent egress from the bond line; the mixing sequence uses a high-speed dissolver at 15–20 m/s tip speed, followed by sealed drum storage and forced-air drying at 55–65 °C before lamination under nip-roller pressure. Bond performance is evaluated by ASTM D903 for peel strength and ISO 4587 for lap shear, while volatile organic content is determined by ASTM D2369 or EPA Method 24. The process constraint is most severe on dense substrates: retained solvent above 2 % by mass in a closed-cell foam assembly generates bubble defects and delayed bond-line softening; production records from continuous laminating lines show that forced-air dew point above 10 °C and open time beyond 20 min correlate with peel-strength variance exceeding 15 % across the coil width. Terminal applications include flexible PVC edgebanding, automotive headliner lamination, furniture panel contact bonding, and shoe upper-to-sole pre-treatment adhesives.