Silicone Elastomers RH-SEB-9060

Coolant Seal Retention in Turbocharged Gasoline Engine Cooling Circuits

Compression-set failure in silicone coolant seals typically initiates at the inner wall where glycol-water coolant at 120–130°C and 1.4–1.8 bar system pressure creates a sustained oxidative environment. In turbocharged gasoline engine cooling circuits, RH-SEB-9060 is specified as a replacement for EPDM where dry-heat aging above 150°C causes EPDM seal softening and extrusion into the flange gap. Candidate compounds conform to ASTM D2000 M4GE 510 B36, with heat aging evaluated under ASTM D573-04 for 70 h at 175°C and compression set tested under ASTM D395-18 Method B for 22 h at 150°C. Coolant immersion is assessed according to ASTM D471-16a using 50/50 vol% ethylene glycol-water at 125°C for 168 h, with volume swell controlled below 5% to prevent flange compression loss. Low-temperature retraction is measured under ASTM D1329-16 with a TR10 value required below -40°C for cold-climate thermostat housing applications.

Formulation addition levels for coolant-circuit sealing with RH-SEB-9060 are bounded by scorch resistance and low compression set. Typical addition ratios are 0.8–1.2 phr dicumyl peroxide, 25–35 phr fumed silica masterbatch, and 1.0–3.0 phr iron oxide heat stabilizer. Increasing peroxide above 1.2 phr lowers compression set but reduces hot-tear strength below acceptable demoulding limits for parts with internal undercuts. The iron oxide addition above 3.0 phr provides no measurable heat-aging advantage and raises Shore A hardness by 3–5 points, which increases insertion force in radiator end-tank O-ring seats. Addition of plasticizing silicone oil above 5 wt% is not recommended because hydrocarbon-coolant absorption increases and the seal can lose dimensional stability during thermal cycling.

Downstream processing is carried out on a two-roll mill with a friction ratio of 1.15:1–1.25:1 and roll temperature maintained at 30–40°C to avoid premature dicumyl peroxide decomposition. Preforms are sheeted at 6–8 mm and injection molded at 170–190°C with a screw L/D of 12:1–14:1 and clamp force sized according to projected mold area. Production-scale failure data indicate that moisture absorption in preforms stored above 60% RH creates porosity in sections thicker than 8 mm; pre-drying at 80°C for 2 h is required under such ambient conditions. Demoulding of complex seal geometries is performed at 60–80°C mold temperature to avoid back-rinding at sharp flange transitions. Post-cure is performed at 200°C for 4 h to remove acidic peroxide decomposition residues and stabilize compression set. Terminal product types include coolant pump seals, thermostat housing gaskets, radiator end-tank O-ring seats, and charge-air cooler end gaskets.

Why Does Post-Cure Heating Alter Extractable Profiles in Silicone Medical Components?

Extractable mass in platinum-cured silicone elastomer is not a fixed material property but a function of cure state, inhibitor depletion, and residual oligomer content. For RH-SEB-9060 in medical fluid-contact components, the post-cure holding time at 200°C is a critical control parameter because cyclic siloxanes and residual methylhydrogen crosslinker fragments remain detectable by headspace GC-MS after short demoulding cycles. Biocompatibility is evaluated under ISO 10993-1:2018 with a test selection matrix for surface-contacting, limited-duration devices. The relevant endpoints include ISO 10993-5:2009 cytotoxicity using L929 mouse fibroblasts, ISO 10993-10:2010 skin sensitization and intracutaneous irritation, and USP <88> Class VI systemic toxicity after saline and cottonseed-oil extraction. Chemical characterization is performed according to ISO 10993-18:2020, with identification of volatile and semi-volatile extractables; published data for this specific grade are limited to batch-specific certificates from registered compounders.

For addition-cure processing, RH-SEB-9060 is mixed in a two-part system with Part A containing platinum complex catalyst at 0.5–1.2 ppm of total compound and Part B containing methylhydrogen siloxane crosslinker at 0.8–1.6 phr. The inhibitor 1-ethynyl-1-cyclohexanol is added at 0.04–0.12 phr to achieve a pot life of 72 h at 23°C. Inhibitor concentration below 0.04 phr causes premature gelation in the static mixer of the injection machine; concentration above 0.12 phr changes vulcanization kinetics and can leave residual alkyne peaks in the extractable profile if the post-cure is truncated. Amine-containing additives, sulfur-accelerated compounds, and latex-contaminated tooling must be excluded from the manufacturing cell because they poison the platinum catalyst and shift cure time by 30–60 s at 175°C.

Downstream manufacturing is carried out in ISO Class 8 or better cleanrooms using transfer molding or liquid injection molding at 165–185°C. For 2 mm sections, demoulding occurs after 2–3 min, but post-cure in forced-air ovens at 200°C for 4 h is mandatory to reduce extractable siloxane content and stabilize durometer. Batch-to-batch variance is observed when the same mixing head is alternated between peroxide- and platinum-catalyzed compounds; dedicated static mixers and feed lines are required to avoid catalyst poisoning and inconsistent cure kinetics. Terminal product types include ventilator mask cushions, enteral feeding connectors, surgical wound drainage stoppers, and microfluidic medical check valves.

Release consistency in reusable silicone bakeware is determined by crosslink-density gradients at the tool-surface interface rather than by external release agents. When RH-SEB-9060 is formulated for food-contact moulds, the addition of 0.6–1.2 phr bis(2,4-dichlorobenzoyl) peroxide and 2–5 wt% polydimethylsiloxane process oil yields a Shore A 45–55 elastomer with sufficient hot-tear strength for repeated mechanical demoulding at bake temperatures up to 230°C. Pigment masterbatch at 1.0–3.0 wt% must be food-grade and pre-dispersed to avoid surface speck formation and inconsistent release. Compliance for this application requires extraction testing under FDA 21 CFR 177.2600 paragraphs (d) and (e), BfR Recommendation XV, and Regulation (EC) No 1935/2004. In European food-contact practice, post-cured and washed parts are assessed for overall migration in olive oil at 175°C for 2 h; published acceptance limits vary by member state and article thickness.

Compression molding for bakeware uses vacuum chamber cycles that vent below 30 mbar for 45–60 s before final pressure application; insufficient vacuum at this stage traps air in muffin mould ribs and causes visible surface blisters after the first bake cycle. Moulding temperatures are held at 160–180°C for 8–12 min depending on wall thickness. Post-curing at 200°C for 4 h is followed by hot-water washing at 80°C for 1 h to remove residual peroxide decomposition products and low-molecular-weight siloxanes. Terminal product types include reusable baking mats, collapsible food storage containers, muffin moulds, and lid sealing rings.

Where Partial Discharge Thresholds Depend on Inorganic Filler Packing Efficiency

In medium-voltage separable connectors, partial discharge inception in silicone insulation is dominated by the packing density and surface chemistry of alumina trihydrate filler, not by base polymer molecular weight alone. RH-SEB-9060 loaded with 60–120 phr of silane-treated alumina trihydrate serves as stress control insulation where high tracking resistance and low dielectric loss are required. Compliance is anchored to IEC 60502-4:2010 for cable accessories, HD 629.1 S2 for test requirements, ASTM D150-18 for permittivity and dissipation factor, and IEC 60243-1:2013 for dielectric strength. Partial discharge acceptance testing is performed under IEC 60502-4 at 1.73 U0 for 30 min; in production, ultrasonic and high-frequency current pulse detection are used on cured insulation sleeves. Published data for RH-SEB-9060 above 120 phr alumina trihydrate is limited, and process validation beyond this filler level requires custom compounding trials.

Practical addition ratios for cable accessory compounds are 60–120 phr alumina trihydrate, 20–30 phr fumed silica masterbatch, 0.8–1.5 phr 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 0.3–1.0 phr vinyl tris(2-methoxyethoxy)silane as filler coupling agent. At ATH loading beyond 120 phr, tensile strength falls below 5 MPa and the extruder screen pack filtration pressure increases rapidly due to filler agglomeration. The silane coupling package below 0.3 phr produces interfacial tracking after accelerated water immersion per IEC 60502-4, while additions above 1.0 phr release methanol during compounding and require additional ventilation controls.

Extrusion is carried out on a continuous hot-air vulcanization line with a 20:1–24:1 L/D cold-feed extruder and barrel zones from 120°C to 220°C. A crosshead die profiles the elastomer onto prepared cable joints; production-scale bottlenecks include filter pressure rise caused by ATH moisture absorption above 0.5 wt% and porosity in thick sections when the hot-air oven line speed exceeds 3 m/min. Cure is completed by post-curing at 200°C for 4 h, which also reduces residual peroxide byproducts that can contribute to dielectric loss after heat cycling. Terminal product types include medium-voltage separable connector housings, stress relief cones, cable joint insulation sleeves, and busbar boot insulation.

What Limits Siloxane Volatile Condensation in Gold-Nickel Contact Systems?

Low-molecular-weight cyclic siloxanes escaping from cured silicone keypads condense on gold-nickel contacts and form insulating silicon dioxide films under dry-circuit switching. RH-SEB-9060 used in electrical switch membranes and enclosure seals therefore requires a volatile-containment and post-cure protocol intended to reduce residual octamethylcyclotetrasiloxane below 0.1 wt% as measured by headspace GC-MS after 200°C for 4 h. Compliance for outgassing is anchored to ASTM E595-15 with total mass loss target ≤ 0.50% and collected volatile condensable material ≤ 0.10%; electrical contact contamination is evaluated under IEC 60068-2-17:1994 and dry-circuit contact resistance drift testing based on IEC 60512-2-1. Halogenated flame retardants are excluded because their decomposition products can react with siloxane volatiles and accelerate contact film growth.

Formulation addition levels for low-outgassing electronic seals are 0.8–1.0 phr 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 3–5 wt% boron nitride for thermal conductivity without surface tack, and 0.5–1.0 phr conductive carbon black masterbatch for static dissipation. Conductive carbon black addition above 1.0 phr reduces volume resistivity below 10^6 Ω·cm but increases outgassing surface area and is generally avoided in keypad contact webs. Release-surface properties are adjusted with 0.5–1.5 wt% vinyl-terminated silicone oil rather than fatty acid mould release, which can contaminate gold contacts and increase contact resistance variability after 10,000 dry-circuit cycles.

Downstream processing uses compression molding with vacuum de-aeration at 150–180°C; moulding without vacuum can entrain air at the base of keypad webs and create corona discharge sites in high-voltage test circuits. Production lines for keypads running above 60% RH show variable cure time because absorbed moisture consumes peroxide decomposition radicals; conditioned preforms at 30% RH for 24 h reduce this variance. Post-cure is conducted in forced-air ovens at 200°C for 4 h and parts are sealed in polyethylene packaging within 72 h to prevent re-adsorption of siloxane volatiles from ambient air. Terminal product types include mobile phone keypads, outdoor enclosure compression gaskets, remote-control membrane switch webs, and industrial keyboard contact membranes.

During high-tack adhesive film casting onto silicone release belts, release force consistency across the belt width is governed by the uniformity of siloxane chain mobility at the cured surface, not by average coating thickness alone. RH-SEB-9060 is formulated for industrial release and lamination applications with 0.7–1.2 phr of dialkyl peroxide, 1–3 wt% phenyl silicone oil to reduce surface free energy, and 18–25 phr fumed silica to maintain tear resistance at thin coating edges. Compliance under REACH Regulation (EC) No 1907/2006 and RoHS Directive 2011/65/EU is required for industrial belt production; when belts contact food products, FDA 21 CFR 177.2600 or BfR Recommendation XV is applied after post-cure and washing. Release force is measured under FINAT FTM 3 or equivalent peel adhesion procedures with transfer adhesives, and lot-to-lot release variation below 15% is typical for qualified production lines.

Knife-over-roll coating onto aramid-reinforced fabric uses multiple passes of 150–300 µm wet thickness, with forced-air tunnel cure at 180–210°C for 10–20 min per pass. Coating heads with knife gap below 0.2 mm generate edge tearing in aramid reinforcement when filler agglomerates exceed 30 µm; screen filtration through 200 mesh is therefore required before coating. Post-cure at 200°C for 4 h is followed by a wash cycle at 80°C for 1 h to reduce residual peroxide byproducts and cyclic siloxanes, which otherwise transfer to adhesive films and alter peel force. Terminal product types include adhesive film casting belts, non-stick industrial conveyor belts, and bakery tunnel liners.