Vinyl Terminated Silicone Oil RH-Vi311

When a 1:1 Addition-Cure LSR System Carries 0.10 wt% Ethynyl Cyclohexanol Through a Static Mixer

Liquid silicone rubber compounds formulated with RH-Vi311 are compounded as two matched 1:1 feed streams. Part A contains the vinyl-dimethylsiloxy terminated poly(dimethylsiloxane), a Karstedt platinum catalyst at 5–20 ppm Pt based on total compound mass, and ethynyl cyclohexanol as cure inhibitor; Part B contains the same vinyl polymer and a methylhydrogen polysiloxane crosslinker. Metering is completed by a 30 mm L/D 12-element static mixer feeding an injection molding unit with barrel temperatures held at 20–25 °C, injection pressure 80–300 bar, and mold temperatures of 120–180 °C. The molar ratio SiH:SiVi is maintained within 1.2–1.8 to balance tear strength and surface cure. Below 1.1, the cured article shows persistent surface tack and toluene-extractable polymer above 5 wt% when tested by ASTM D7210; above 2.0, residual hydride groups oxidize slowly, shifting Shore A hardness after 7 days at 200 °C and reducing elongation. Mechanical tensile properties measured on 2 mm slabs per ISO 37 typically fall at 7–11 MPa tensile strength, 400–700% elongation at break, and 30–70 Shore A hardness per ISO 868. The process window for barrel idle time is severe: at 25 °C, a compound containing 0.05 wt% ethynyl cyclohexanol may scorch after 6–10 h in the mixing block, whereas 0.15 wt% inhibitor delays cure at 150 °C beyond 2.5 min and prolongs cycle time. Field experience on 40–200 t clamp force LSR injection machines shows that water-cooled static mixers and minimized shutdown intervals suppress gate blush and flow-line defects. O-rings, connector seals, infant bottle nipple adaptors, and automotive MEMS gaskets are typical end products; all require post-cure at 150–180 °C for 1–2 h to volatilize residual low-molecular-weight siloxanes and stabilize compression set.

High-voltage power module encapsulation is specified at a cone penetration of 45–65 (0.1 mm) per ASTM D1403 to avoid piezoelectric stress on aluminum bond wires while preserving enough network integrity to prevent gel fracture under thermal cycling from −40 °C to 125 °C. RH-Vi311 is used as the base structure for a gel network with a hydride crosslinker at an SiH:SiVi ratio of 0.6–1.0 and Pt catalyst loading at 2–5 ppm, producing a low-modulus material without fumed silica reinforcement. The compounded liquid is vacuum degassed to less than 5 hPa absolute pressure before dispensing into IGBT housings to clear interstitial regions under wire-bond loops with gap dimensions as low as 150 µm. Cure schedules vary from 100 °C for 60 min to 150 °C for 15 min; the faster schedule is used in placement lines with in-line IR ovens. Unfilled gel thermal conductivity remains 0.15–0.20 W·m⁻¹·K⁻¹, which is accepted for planar modules but insufficient for high-power-dissipation dies requiring alumina or boron nitride fillers. Electrical performance measured on cast 2 mm specimens per IEC 60243-1 gives dielectric strength of 18–22 kV·mm⁻¹, while AC tracking resistance per IEC 60112 is commonly reported to exceed 600 V CTI for unfilled addition-cure gels. The critical operational boundary is moisture ingress from uncured epoxy or solder flux residues; water levels above 500 ppm in the reactive mass can inhibit hydrosilylation, leaving a tacky uncured meniscus at the silicone-substrate interface. End products include IGBT modules for traction inverters, photovoltaic string inverters, and industrial motor drives, where the gel functions as corona suppression and vibration damping layer.

What Limits Coating Bath Pot Life in Solventless Silicone Release Systems?

In solventless silicone release coating lines, the critical operational variable is the room-temperature bath residence time because RH-Vi311, methylhydrogen polysiloxane, platinum catalyst, and ethynyl cyclohexanol begin hydrosilylation slowly even at 25 °C. A five-roll offset gravure coater with differential speed control applies the inhibited liquid at coating weights of 0.8–1.4 g·m⁻² onto glassine, clay-coated kraft, or polyolefin-coated paper; the bath is held at 20–25 °C and the line speed is set for oven dwell of 4–12 s at 150–180 °C. Platinum concentration for release applications is higher than for molded rubber, typically 50–150 ppm based on total solids, because the very thin film exposes a large surface area to airborne poisons and the crosslinker must be consumed before the web reaches the rewind station. SiH:SiVi molar ratio is set from 1.4–2.0 to generate a dense, migration-resistant film; the release ratio is then adjusted with release-control resin additions rather than by starving crosslinking. Peeling force measured at 300 mm·min⁻¹ per FINAT FTM 3 ranges from 5 cN·25 mm⁻¹ for easy-release liners to 150 cN·25 mm⁻¹ for tight-release applications, and subsequent adhesive tack retention per FINAT FTM 11 should exceed 80% of the initial value. The main failure mode on production coaters is catalyst poisons released by amine-containing paper coatings, recycled fiber streams, or phenolic antioxidants in film substrates; these poisons appear as pale amber reels and edge-tack defects that are confirmed by offline cure trials on the contaminated substrate. Molecular oxygen is not the dominant inhibitor for platinum addition cure, but high air entrainment in grooved-roll puddles can cause microvoids that reduce film coverage. End products are release liners for pressure-sensitive labels, diaper tape, medical dressing adhesives, and high-temperature masking constructions.

Prior to transfer coating, silicone pressure-sensitive adhesive formulations containing MQ silicate resin and RH-Vi311 are prepared by condensation polymerization at 140–160 °C under ammonia catalysis and stripped to a high-solids paste. The vinyl-terminal group on the polysiloxane allows post-compounding addition cure with methylhydrogen polysiloxane at an SiH:SiVi ratio of 0.8–1.2 and Pt loading of 10–30 ppm, so the adhesive film builds shear-holding capability without the acidic residues associated with peroxide-cured silicone PSAs. The compounded mass is diluted with a volatile silicone solvent to coating viscosity and direct-coated or transfer-coated onto polyimide film, fluoropolymer-treated glass fabric, or polyester film at dry coat weights from 25–50 g·m⁻². After solvent flash-off, cure at 150–170 °C for 2–5 min produces a continuous adhesive layer with 180° peel values of 0.8–8.0 N·25 mm⁻¹ per ASTM D3330/D3330M and static shear hold times exceeding 24 h at 70 °C per ASTM D3654/D3654M. Formulations with low crosslink density are selected for clean-removal masking tapes used in powder coating lines where bake cycles reach 200–230 °C; high crosslink density grades are used for plasma spray masking and silicone splicing tapes that must resist solvent attack. The operational boundary is the condensation-stripping step: residual ammonia above 20 ppm in the compounded gum reacts with platinum and suppresses addition cure, leading to patchy anchorage on the fluoropolymer-treated liner. End products include high-temperature masking tapes for aerospace and automotive coating, plasma spray protection, and single-sided silicone pressure-sensitive tapes for coil insulation.

Peroxide-Cured Extruded Silicone Profiles with 3–8 phr Vinyl-Terminated Diluent

Addition of 3–8 phr RH-Vi311 to peroxide-cured high-consistency silicone rubber is performed on a two-roll mill at 40–60 °C before the peroxide paste is introduced. The low-viscosity vinyl fluid modifies the steady-shear rheology of the gum compound; on a 16:1 L/D cold-feed extruder with barrel temperatures of 50–60 °C, die head temperature of 80 °C, and screw speeds of 10–40 rpm, a 3 phr addition can reduce head pressure by 10–20% compared with unmodified base stock, allowing higher line speed for the same die pressure. The vinyl-terminated species participates in the peroxide cure by consuming alkoxy radicals, so the cure package must be rebalanced; a typical formulation includes 0.8–1.5 phr bis(2,4-dichlorobenzoyl) peroxide for low-odor profiles or 0.5–1.0 phr 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane for hot-air vulcanization. Continuous hot-air tunnels operate at 250–400 °C with the first zone set to the highest air temperature to remove surface volatiles and prevent blistering. Cured articles exhibit Shore A hardness of 40–75 per ISO 868, tensile strength of 6–10 MPa per ISO 37, and compression set after 22 h at 175 °C of 25–35% per ISO 815-1:2019. Above 8 phr, the fluid compromises green strength and can exude to the profile surface after oven cure, causing block adhesion on coiled extrusions and reduced ink adhesion in downstream printing. The main industrial use is in continuous vulcanization lines for oven door gaskets, automotive turbocharger air ducts, wire and cable sheathing, and food-contact profiles, where the low-molecular-weight vinyl fluid must be removed by post-cure at 200 °C for 2 h to reduce food-contact extractables.

Dental vinyl polysiloxane impression materials are dispensed and mixed through an automix cartridge with a 10:1 static mixing tip. The base paste contains RH-Vi311, surface-treated fumed silica, quartz filler, MQ resin, and a platinum-divinyltetramethyldisiloxane complex; the catalyst paste contains the same vinyl polymer, methylhydrogen-polysiloxane crosslinker, and inorganic thickener. Weight ratio of base to catalyst is 1:1 for standard trays and 10:1 for heavy-body/tray systems; working time at 35 °C is 30–90 s and intra-oral setting time is 2.5–4 min per ISO 4823:2021. The cured material reaches Shore A hardness of 40–70, elastic recovery above 96.5%, and tear strength of 2.0–4.5 N·mm⁻¹ per ISO 34-1, which permits removal from subgingival margins without tearing. The addition-cure vinyl polysiloxane system is dimensionally stable because the hydrosilylation reaction does not release volatile byproducts; die-stone casts can be poured up to 14 days after impression taking if the impression is stored dry. The principal handling restriction is platinum catalyst poisoning by sulfur compounds from natural rubber latex gloves, hemostatic agents, ferric sulfate, and some retraction cords; therefore procedure gloves must be nitrile or vinyl, and the prepared tooth should be rinsed aggressively before seating the impression tray. End products are crown and bridge impressions, inlay/onlay trays, bite registration cartridges, and implant transfer index materials.

Post-Cure Volatile Siloxane Depletion in Long-Term Implant Elastomers

Long-term implantable silicone elastomers processed from addition-cure systems retain low-molecular-weight cyclic siloxanes and platinum residues after the initial cure, so a forced-air post-cure at 200 °C for 4 h is required to bring hexane extractables below 0.5 wt% when measured by reflux extraction. RH-Vi311 is compounded with a low-volatile SiH crosslinker at an SiH:SiVi ratio of 0.9–1.3 and platinum catalyst at 2–8 ppm; the addition-cure route is selected over peroxide vulcanization to avoid acidic decomposition byproducts that may affect tissue response. Molding is completed in sealed tools with vacuum degassing at 20–50 hPa, followed by demolding and post-cure in a positive-air-flow oven; the post-cure also reduces platinum-containing silicone odour and stabilizes compression set. Mechanical properties after post-cure, on 2 mm slabs per ISO 37, are 7–10 MPa tensile strength, 500–800% elongation, and 30–60 Shore A hardness per ISO 868. The limiting condition for medical-grade conversion is the cleanroom environment: traces of amine-containing disinfectants, uncured epoxy, or autoclave seal residues inhibit hydrosilylation at the part surface and produce tack-free failure. Process monitoring should include a moving-die rheometer T90 check on each batch before release to reduce batch-to-batch variation in load-bearing implant components. End products include pacemaker lead strain relief components, neurostimulator encapsulation seals, insulin pump gaskets, and long-term implantable drug delivery reservoir seals.

Textile silicone ink systems formulated with RH-Vi311 at 60–80 wt% of the liquid addition-cure binder are printed through mesh sizes of 60–120 threads·cm⁻¹ onto cotton, polyester, polyamide, and blended fabrics. The crosslinker is added at 2–5 wt% with Pt catalyst at 5–10 ppm; fumed silica matting and bodying agents are incorporated at 3–6 wt% to prevent capillary strike-through after screen printing. Print thickness before cure is 0.2–0.6 mm, and conveyorized hot-air ovens cure the deposit at 150–170 °C for 60–120 s; tack-free open time after gelation is typically less than 15 s at the higher end of the cure range. Cured prints display Shore A hardness of 25–40, elongation of 400–800%, and dry/wet crock fastness of grade 4 or higher per ISO 105-X12, depending on pigment loading and fabric pretreatment. The main production constraint is exposure to sulfurised fabric dyes, chlorine residues from bleach, and amine-based softeners; these species adsorb onto the Pt complex and slow cure, leaving a tacky underlayer that fails wash-fastness testing. End products are non-slip grip patches, sock treads, athletic garment logos, automotive airbag seam reinforcement, and abrasion-resistant silicone prints on industrial safety textiles.