Vinyl Terminated Silicone Oil RH-Vi322

When Vinyl Stoichiometry Controls Tear Strength in Injection-Molded LSR

Because tear resistance in injection-molded liquid silicone rubber is governed by crosslinker stoichiometry and the effective vinyl molar concentration rather than by base polymer viscosity alone, RH-Vi322 is handled as a linear vinyl-terminated polydimethylsiloxane whose lot-specific certificate of analysis is used to calculate the silicon hydride-to-vinyl ratio before compounding. The A-component is compounded with RH-Vi322 at 55–72 wt%, fumed silica at 18–28 wt%, and vinyl MQ resin at 5–15 wt%, while the B-component carries methylhydrogen polysiloxane at a SiH/SiVi molar ratio of 1.4–1.8:1, 1-ethynyl-1-cyclohexanol inhibitor at 0.03–0.08 wt%, and a platinum(0)-divinyltetramethyldisiloxane complex supplying 5–12 ppm platinum. Cured tensile data are qualified under ISO 37:2017 and ASTM D412-16, tear propagation under ISO 34-1:2015 and ASTM D624-00(2020) Die B, compression set under ISO 815-1:2014 and ASTM D395-16 Method B, and hardness under ISO 48-4:2018 or ASTM D2240-15.

Processing is conducted on a 1:1 LSR injection machine in which the two components are transferred by pneumatic pumps into an 8–12 element static mixer, then through a temperature-controlled runner held at 15–30 °C to avoid pre-gel. Mold temperatures are maintained within 120–180 °C, injection pressure is set between 5–20 MPa, clamp force is held at 0.5–1.2 tonnes per square inch of projected part area, and cure dwell is 30–180 s for wall thicknesses up to 10 mm. On the shop floor, the dominant processing fault occurs when the inhibitor level drifts below 0.02 wt%; the mixed compound then gels in the static mixer during brief line stops, requiring a new mixer cartridge and depressurization of the feed lines. A second recurrent failure appears as high compression set after molding when atmospheric moisture above 60% relative humidity has been taken up by fumed silica; silica pre-drying at 120–150 °C for 4 h is therefore enforced before pigment and polymer letdown. Compounds containing RH-Vi322 must not be blended on lines previously used for sulfur-cured organic rubber or on equipment contaminated with amine-based mold release, because sulfur, amines, and tin carboxylates poison the platinum catalyst and produce tacky interfacial cure. Terminal parts produced in this processing window include high-voltage connector seals with Shore A hardness of 30–60, battery module vent membranes, coolant-circuit gaskets, sensor grommets, and overmolded connectors for engine-control modules. The limiting design variable is not tensile strength alone but tear path resistance after thermal aging; a part with a sharp internal radius and a wall thickness below 1.5 mm will exhibit lower tear strength because the silica network cannot be fully dispersed under the same shear history.

For power module encapsulation lines in which insulated-gate bipolar transistor stacks are potted with a low-modulus addition-cure gel, RH-Vi322 is blended with MQ resin at 20–40 phr to provide stress-relief without cracking wire bonds. The gel formulation places RH-Vi322 at 45–70 wt% of the siloxane phase, the methylhydrogen crosslinker at a SiH/SiVi ratio of 0.8–1.2:1, platinum catalyst at 3–8 ppm, and 1-ethynyl-1-cyclohexanol at 0.005–0.02 wt% so that mixed pot life at 25 °C exceeds 24 h. Cured specimens are qualified under ASTM E595-15 for outgassing, with total mass loss below 1.00% and collected volatile condensable material below 0.10%; electrical insulation is measured by ASTM D149-20 dielectric breakdown and ASTM D257-14 volume resistivity. Thermal cycling is performed according to IEC 60068-2-14:2009 from -40 °C to 125 °C, and the cured compound is exposed to housing-level flame testing under UL 94 because the gel itself is not a standalone flame barrier.

The dispensing process uses a two-part meter-mix unit with vacuum degassing at 1–5 kPa for 2–5 min to remove air entrapped during MQ resin addition. The gel is dispensed into a preheated module housing at 25–40 °C and cured at 80–120 °C for 30–60 min; thicker modules are ramped no faster than 2 °C/min between 40 °C and 90 °C to avoid viscosity inversion before gel point. The defining analytical issue is not the initial gel hardness but the development of interfacial delamination after repeated thermal cycles. Batched materials with MQ resin hydroxyl content above 0.5 wt% will react with platinum at 80 °C and suppress the hydrosilylation front; therefore the MQ resin is pre-dried under vacuum at 100–120 °C for 2 h and tested for silanol content by Fourier-transform infrared spectroscopy before RH-Vi322 is introduced. Failure modes observed in production include voiding at the underside of aluminum nitride substrates when degas pressure is not held below 5 kPa, and a tan-colored residue on the gel surface when the oven atmosphere contains nitrile gasket decomposition products. These observations are not usually detected by a twenty-four-hour dielectric test alone; they require thermal cycling with simultaneous partial discharge measurement according to IEC 60270:2000. Operational boundaries are explicit: substrates with soldering flux residues, phosphine stabilizers, or sulfur-containing seals must be cleaned before dispensing because these species bind the platinum and prevent interfacial cure; moisture condensation on the substrate above 60% relative humidity can generate voids at the ceramic-copper interface. Terminal products include IGBT power module encapsulants, SiC MOSFET baseplate stress relief, automotive DC-DC converter potting, and transformer bushing fillers.

What Limits Line Speed in Solventless Release Coating of Silicone Liners?

Coating of silicone release liners on 50 µm polyester film uses RH-Vi322 as a high-viscosity vinyl-functional co-reactant within a solventless thermal-cure bath; line speed is not limited by the base polymer alone but by platinum availability and crosslinker volatility at the top oven zone. RH-Vi322 is incorporated at 20–40 phr based on low-viscosity vinyl-functional polysiloxane, with methylhydrogen dimethylsiloxane at 10–20 phr and a SiH/SiVi ratio of 1.5–2.5:1; platinum catalyst is dosed at 80–150 ppm, and 1-ethynyl-1-cyclohexanol at 0.02–0.10 wt% to delay bath gelation. Finished release force is measured per FINAT FTM 10 against TESA 7475 tape, with typical targets falling below 50 cN/50 mm after 24 h aging at 50 °C; residual adhesion is checked per ASTM D3330/D3330M to ensure adhesive performance remains above 85% of the non-released control.

A five-roll solventless coating head applies the mixture at 0.8–1.5 g/m² on polyester or glassine; oven temperature is held at 150–200 °C with dwell time of 3–6 s, permitting line speeds of 300–600 m/min on modern tandem coating lines. At coat weight below 0.8 g/m², release consistency falls outside the test window because uncoated fibrils allow the pressure-sensitive adhesive to contact the substrate; at coat weight above 1.5 g/m², oven drag-out of low-molecular-weight siloxanes increases and residual adhesion drops. The coater is therefore fitted with a beta-gauge scanning system that rejects web tracks outside the ±0.10 g/m² window. On corona-treated polyester film, silicone wet-out is not inferred from dyne pens alone; a water contact-angle measurement below 65° is used to gate incoming film. The most common failure is carry-over of vinyl-bath gel particles that form when the platinum inhibitor is insufficient for a horizontal bath temperature above 35 °C; addition of the RH-Vi322 lot at viscosity above 20,000 mPa·s without pre-warming to 30–40 °C produces metering-roll starve and transverse coat-weight variation. Splices with amine-containing slip agents are prohibited because the catalyst poison migrates into the coating bath and reduces cure at random intervals. Terminal products include PET release liners for double-sided pressure-sensitive adhesive tapes, glassine liners for hygienic labelstock, and industrial tape release facings.

Medical-Grade LSR Molding Windows for Wearable Skin-Contact Devices

Medical-grade silicone elastomers for skin-contact devices require RH-Vi322 to be formulated into a two-part addition-cure LSR whose production cell is segregated from industrial silicones because peroxide-cured or tin-cured materials cannot meet cytotoxicity and skin sensitization requirements. The A-component contains RH-Vi322 at 55–70 wt% with treated fumed silica at 15–25 wt% and vinyl MQ resin at 3–8 wt%; the B-component is dosed to a SiH/SiVi ratio of 1.5–2.0:1 with platinum at 5–12 ppm and an inhibitor at 0.02–0.05 wt%. Final parts are post-cured at 200 °C for 4 h in a forced-air oven to reduce total siloxane volatiles below 0.5 wt%; the molded article is tested to ISO 10993-5:2009 for cytotoxicity, ISO 10993-10:2010 for skin sensitization, USP <87> and USP <88> Class VI for biological reactivity, and ISO 10993-12:2021 for extractables sample preparation. Manufacturing is controlled under ISO 13485:2016 and the device documentation is structured for EU MDR 2017/745; food-contact grades may also reference FDA 21 CFR 177.2600.

Molding is performed in an ISO Class 7 cleanroom on a dedicated LSR injection machine with 1:1 static mixing and a cold-runner system held at 15–25 °C; mold temperature is 120–160 °C and cure time is 60–180 s. Post-cure verification uses a forced-air oven chart recorder to prove that the center of stacked parts remains at 200 °C for at least 4 h; a center-stack probe reading below 200 °C triggers an alarm and rework. Extractables are then assessed by headspace gas chromatography with flame ionization detection for total siloxane volatiles below 0.5 wt%. The critical boundary is not solely the molding cycle but the post-cure oven loading: stacking parts above 50 mm bed depth prevents adequate hot-air sweep and leaves surface-resident volatile species that fail the cytotoxicity assay. Terminal products include wearable continuous glucose monitor seals, respiratory mask cushions, hearing aid strain reliefs, and electrocardiogram patch elastomers. This is not an implant-grade process unless an implant-specific master file and long-term animal studies under ISO 10993-6 are completed.

Compounding of addition-cure high-consistency rubber on a two-roll mill with a friction ratio of 1.2:1 uses RH-Vi322 as a reactive plasticizer at 5–20 wt% of the total compound to reduce Shore A hardness without increasing acetone-extractable content. The base vinyl-terminated gum is present at 60–80 wt%, fumed silica at 20–40 wt% with silane surface treatment, vinyl MQ resin at 2–8 wt%, and crosslinker to a SiH/SiVi ratio of 1.2–1.6:1; platinum is dosed at 5–15 ppm and 1-ethynyl-1-cyclohexanol at 0.02–0.05 wt%. Food-contact extrusion compounds are qualified under FDA 21 CFR 177.2600 and Commission Regulation (EU) No 10/2011 migration limits; mechanical properties are tested by ISO 37:2017 tensile elongation and ISO 34-1:2015 tear.

Mixing on an open two-roll mill is followed by straining through a 60–120 mesh screen in a cooled screw extruder with L/D typically 8:1–12:1 to remove unmixed silica agglomerates. For higher-output compounding, a co-rotating twin-screw extruder with L/D 40:1 and barrel temperature 40–80 °C is used to disperse silica into the gum before RH-Vi322 is injected downstream; this prevents shear heating above 80 °C, at which inhibitor loss triggers pre-crosslinking in the barrel. The compound is then extruded into profiles or jacketed tubing and vulcanized in a hot-air tunnel at 200–400 °C with line speed set by wall thickness, typically 10–30 m/min for thin-wall tubing. The main production constraint is silica wetting: RH-Vi322 added too late in the mix procedure leads to silica structuring and a viscosity spike that stops the mill motor; pre-wetting silica with a silane treatment before adding RH-Vi322 avoids the failure. Terminal products include platinum-cured dairy transfer tubing, peristaltic pump tubing, food-contact gaskets, and extruded profiles for cleanroom equipment.

To Prevent Cell-to-Pack Transfer Path Delamination, EV Gap Filler Foam Demands Low SiH/SiVi Ratios

Because cell-to-pack gap-filling foams must remain removable yet capable of absorbing vibration stress across tens of thousands of module charge-discharge cycles, RH-Vi322 is formulated into an addition-cure silicone foam with a deliberately low SiH/SiVi ratio to retain limited interfacial wetting and avoid early skin-over delamination. The formulation contains RH-Vi322 at 50–70 wt%, MQ resin at 10–30 wt%, fumed silica at 2–8 wt%, and water or a short-chain alcohol as blowing agent at 0.5–3.0 wt%; the crosslinker is added to a SiH/SiVi ratio of 0.6–1.0:1, and platinum catalyst is dosed at 5–15 ppm. Cured foam density is checked under ISO 845 with a target working range of 0.3–0.8 g/cm³, compression set is measured under ISO 1856:2018, and flame class is qualified to UL 94 V-0 at the foam thickness used in the module. Published data for this specific RH-Vi322 foam configuration are limited; batch-level density and compression set must be generated against the module geometry.

Production uses a planetary vacuum mixer that degasses the A-component at 2–5 kPa before adding the B-component and blowing agent; the mixture is dispensed through a disposable static-mixer nozzle onto the module surface and cured at 60–100 °C for 20–40 min. Delamination occurs when the foam skin forms before the wet compound has wetted the aluminum or polycarbonate module wall; this is constrained by holding the SiH/SiVi ratio below 1.0:1 and by preheating the substrate to 40–60 °C. Because the foam is cured in a closed module with limited venting, entrapped hydrogen generated from water blowing can lead to pinholes if the crosslinker ratio exceeds 1.2:1 for high-vinyl RH-Vi322 lots; the crosslinker is therefore not formulated to full stoichiometric excess. The system is incompatible with ambient gases carrying sulfur dioxide, hydrogen sulfide, or phosphine because these species stop platinum catalytic activity at the foam-substrate interface. Terminal products include EV battery module gap fillers, cell-to-pack vibration pads, crushable corner protectors, and removable thermal insulation mat facings.