Silicone Elastomers RH-SEB-6060

RH-SEB-6060 is a two-component, platinum-catalyzed, addition-cure high-consistency silicone elastomer supplied as a methyl-vinyl polysiloxane base and a platinum catalyst paste. The base and catalyst paste are mixed at a ratio of 1:1 by weight. The grade is designed for transfer molding, injection molding, and hot-air vulcanization extrusion of solid silicone components requiring a nominal post-cure hardness of 60 Shore A. Its manufacturer-declared specification envelope includes specific gravity between 1.12 and 1.18 per ISO 1183-1:2019, tensile strength not less than 8.0 MPa per ISO 37:2017, elongation at break not less than 450 %, and tear strength not less than 22 kN/m per ASTM D624-00(2020) Die B. The grade’s principal differentiation from general-purpose peroxide-cured high-consistency rubber is its lower post-cure volatile residue and improved compression set after prolonged hot-air aging. Published data for this specific product configuration are based on vendor technical bulletins and standard elastomer test programs; independent verification on final part geometries is required for each application.

Specification Envelope and Test Method Alignment

On a water-cooled two-roll mill with chromed rolls set to a nip gap of 2 mm to 3 mm, the base and catalyst paste are homogenized for 8 min to 12 min. Roll temperature should remain below 35 °C to preserve catalyst latency. Production-scale compounding records for addition-cure silicone elastomers indicate that batch-to-batch viscosity drift is reduced when the mixed stock is passed through a vacuum chamber at -0.08 MPa to -0.09 MPa for air removal before molding. If the mill sheet is not de-aired, entrapped air expands during cavity fill and produces surface porosity on the low-pressure side of the tool.

Multi-cavity cold-runner tools exhibit a critical processing boundary at the intersection of runner gelation and cavity under-cure. Mold temperature variation across cavities should be held within ±5 °C. At 170 °C, moving-die rheometer scorch time measured at 1 ° arc per ISO 6502-1:2018 typically falls between 60 s and 90 s, while core cure in a 3 mm section may require 180 s to 240 s. A cavity operating 5 °C hotter can reduce scorch time by approximately 30 %, causing premature gelation in the cold-runner block before complete cavity fill. A cavity operating 5 °C colder produces flash with lower tear strength and extends demolding time. The resulting process window is ±5 °C for wall sections above 3 mm.

For platinum-catalyzed addition cure, vulcanization kinetics are first-order with respect to vinyl concentration and platinum activity. The rate of cure approximately doubles for every 10 °C increase in mold temperature within the 150 °C to 200 °C range. This creates an inverse relationship between production cycle time and scorch margin: increasing mold temperature from 170 °C to 190 °C reduces press cure time by approximately 50 % but narrows the cold-runner thermal budget by the same factor. Tooling with poor thermal uniformity therefore operates at the lower end of the temperature range, sacrificing cycle speed to maintain runner stability.

How Does RH-SEB-6060 Differ from Peroxide-Cured Elastomers in Post-Cure Fouling?

Peroxide-cured high-consistency silicone releases acidic chlorinated residues when bis(2,4-dichlorobenzoyl) peroxide is used, leaving mold deposits and requiring post-cure to remove volatile byproducts. RH-SEB-6060 crosslinks through a platinum-catalyzed addition reaction that generates no stoichiometric volatile byproducts from the cure system. This difference reduces mold-fouling frequency in continuous production and permits lower post-cure weight loss. Its compression set after 22 h at 177 °C is specified at ≤15 %, whereas many 60 Shore A peroxide-cured grades are specified at ≤20 % under the same conditions. The trade-off is higher sensitivity to catalyst poisons: trace sulfur, amines, and tin-catalyzed silicone residues can inhibit cure and produce tacky surfaces.

For closed-loop injection molding, a screw L/D ratio of 12:1 to 18:1 and a compression ratio of 1.0:1 to 1.5:1 are recommended to limit shear heating. Barrel and screw temperatures are maintained between 25 °C and 35 °C, and the cold-runner manifold is held below 60 °C. Mold temperature is set between 170 °C and 200 °C depending on part mass and thickness. Demolding is performed when the core state of cure approaches 90 % of maximum torque; premature ejection creates interlayer delamination at knit lines. The compound is suitable for valve-gated cold-runner systems when the gate is thermally isolated to prevent premature freeze-off.

In food-and-beverage gasket production, RH-SEB-6060 is selected when low compression set and low extractable residue are required under repeated thermal cycling. Medical device seal molding uses the grade where post-cure cleanliness and dimensional stability after autoclave exposure are critical. Oven door profiles and wire jacketing exploit the compound’s hot-air cure and tear resistance. The user is advised to confirm final-article performance by extraction and mechanical testing, because insert materials, cure profile, and part geometry shift the as-molded property envelope from the manufacturer-declared values.

Tear Initiation Limits Are Controlled by Die B and Hot-Tear Behavior

Tear strength in RH-SEB-6060 is evaluated by ASTM D624-00(2020) Die B and is specified at ≥22 kN/m. In demolding, hot-tear resistance is the limiting property because addition-cure networks can exhibit lower green strength at high temperature than partially crosslinked peroxide systems. Undercut geometries should be designed with a minimum tool radius of 0.5 mm and a maximum demolding temperature of 100 °C to reduce tear initiation. Mold release should be limited to neutral, non-amine chemistries; amine-containing release agents lower the surface crosslink density and promote snag propagation at sharp corners.

In continuous hot-air vulcanization extrusion, RH-SEB-6060 is processed through a pin-tip crosshead or roller feed to minimize shear heating. Feed throat temperature is kept at 30 °C, head temperature at 40 °C to 50 °C, and curing-oven temperature between 250 °C and 350 °C. Atmospheric-pressure hot air supports continuous cure, but section thickness above 5 mm limits heat transfer and requires lower line speed to avoid a tacky core. An in-line spark test at 5 kV to 10 kV is used for jacketing profiles to detect voids and surface porosity, although spark-test results are not a substitute for mechanical tensile verification per ISO 37:2017.

Relative to liquid silicone rubber of similar hardness, RH-SEB-6060 has higher green strength in uncured sheet form, permitting calendering and profile extrusion that liquid silicone rubber cannot reliably sustain without pump and static mixer equipment. However, the high-consistency form demands two-roll mill or internal mixer compounding and cannot be processed in standard liquid silicone rubber metering systems. This distinction is significant when a converter is deciding between closed-loop injection units and continuous extrusion lines.

Measure Mixed-Compound Pot Life Before Running Multi-Shift Production

Mixed RH-SEB-6060 remains processable at 25 °C for approximately 48 h to 72 h. Pot life decreases to approximately 24 h at 30 °C and drops below 8 h at 50 °C. Airborne amines, sulfur-containing rubber dust, and tin-catalyzed silicone contamination shorten the working window and produce under-cured surfaces. Therefore, multi-shift molding cells should validate mixed-compound viscosity and moving-die rheometer scorch time before production startup. Published data for pot life under high-humidity conditions is limited; storage in sealed containers below 30 °C is mandatory.

Unopened containers are stable for 12 months from date of manufacture when stored below 30 °C. The catalyst component is sensitive to UV exposure and should be kept sealed. Once the base and catalyst are mixed, the compound is not recommended for frozen storage because ice crystal formation disrupts the filler network and produces hard agglomerates.

For food-contact articles, RH-SEB-6060 is certified under FDA 21 CFR 177.2600, EU 1935/2004, and BfR Recommendation XV when post-cured for 4 h at 200 °C. Final-article migration testing under EU 10/2011 remains the converter’s responsibility because surface-to-volume ratio and food simulant conditions alter extractive release. The grade is not recommended for continuous immersion in ketones, esters, aromatic hydrocarbons, or aqueous acids above 10 % concentration at temperatures above 50 °C. Avoid amine-based mold releases and sulfur-containing handling areas because catalyst poisoning yields incompletely crosslinked surfaces that fail extractive limits.

When RH-SEB-6060 Replaces General-Purpose HCR in Cold-Runner Tooling

Replacement of a general-purpose peroxide-cured compound with RH-SEB-6060 in an existing cold-runner mold requires verification of mold temperature balance, venting, and clamp force. Addition-cure shrinkage is lower than that of some peroxide-cured stocks; mold dimensions may require adjustment if the previous compound exhibited higher linear shrinkage. Cold-runner manifolds must be cleaned to remove sulfur residues and chloride deposits; otherwise localized inhibition produces soft spots at gate locations. The injection pressure generally remains within 20 MPa to 40 MPa for thin-wall parts, but gate freeze-off is faster when mold temperature exceeds 190 °C. The following table compares vendor-declared values for replacement decisions.

Under continuous dry-air service, the grade is generally validated up to 200 °C, with intermittent excursions to 250 °C only at low mechanical load. Continuous contact with superheated steam above 120 °C may hydrolyze the siloxane backbone and reduce tensile strength. Published data for this specific configuration in dynamic sealing applications is limited; a production trial in the final part geometry is required before commercial release.