Vinyl Terminated Silicone Oil RH-Vi320

Metered into closed-loop two-component LSR systems, RH-Vi320 serves as a vinyl-terminated polydimethylsiloxane with a nominal viscosity of 320 mm²/s at 25 °C in addition-cure liquid silicone rubber for medical fluid-transfer components. Both terminal vinyl moieties participate in hydrosilylation, which makes the polymer chain function as a reactive building block rather than a non-reactive diluent. The material is processed on closed-loop two-component metering systems with 12 to 24 static mixer elements at metering pressures between 20 bar and 80 bar. Cure is initiated with a Karstedt-type platinum catalyst at platinum concentrations of 5 ppm to 10 ppm, while the Si-H:Si-Vi ratio is maintained between 1.4:1 and 2.0:1 to prevent surface tack caused by under-cure or embrittlement caused by excess hydride. Fumed silica at 15 phr to 35 phr is dispersed under high shear before the addition of inhibitor, and the resulting compound typically cures at 120 °C to 170 °C in injection molding cycles of 30 s to 120 s depending on part cross-section. The processing window is narrow at the lower temperature limit; below 110 °C the hydrosilylation rate drops sharply and the inhibition system may not release within economically viable cycle times, while above 200 °C localized surface skinning occurs because the outer layer cures before entrapped air is vented from the cavity. Hardness is checked according to ASTM D2240, tensile strength according to ASTM D412, and tear strength according to ASTM D624; hardness shifts from approximately 20 Shore A to 70 Shore A by varying filler loading and crosslink density rather than by changing base polymer viscosity alone. Medical-grade lots are evaluated under ISO 10993-5 and ISO 10993-10, and extractables are controlled under FDA 21 CFR 177.2600 where repeated food-contact use is relevant. The operational boundary for platinum-catalyzed systems based on RH-Vi320 includes amine, organotin, sulfur, and phosphine exposure; even trace residues from latex handling or unsealed elastomer storage can slow cure at isolated points on the part surface. Incoming silica is pre-dried when ambient relative humidity exceeds 60% because adsorbed moisture competes with the Si-H group and can create microvoids in the post-cured part.

How Does Alumina Surface Moisture Destabilize the Si-H:Si-Vi Ratio in RH-Vi320 Gap Fillers?

In thermally conductive gap filler production, RH-Vi320 is combined with spherical alumina at filler loadings of 90 wt% to 95 wt% and a hydrogen-functional crosslinker at Si-H:Si-Vi ratios between 1.3:1 and 2.2:1. The low viscosity of the vinyl-terminated fluid permits wet-out of the alumina surface before the hydrosilylation cure, but the same silanol-rich surface can carry 0.5 wt% to 2.0 wt% physically adsorbed moisture when the filler has been stored below a dew point of 15 °C and then opened without conditioning. If not pre-dried, the adsorbed water hydrolyzes a portion of the hydride crosslinker during the first minutes of mixing, releasing hydrogen gas and shifting the effective Si-H:Si-Vi ratio downward; the resulting cured material exhibits higher compression set and lower thermal stability because unreacted vinyl groups remain as chain ends. Conditioning of the alumina in a vacuum oven at 120 °C for 4 h to 8 h under 5 mbar to 20 mbar is therefore standard before compounding, particularly in facilities with uncontrolled humidification. The mixed compound is degassed at 10 mbar to 30 mbar and then dispensed through a 0.5 mm to 2.0 mm static mixer onto a power module or heat sink. Cure is run at 100 °C to 150 °C for 10 min to 30 min, with the cure schedule selected to balance oxidation of the platinum catalyst at the upper end against incomplete Si-H consumption at the lower end. Thermal conductivity is heavily dependent on filler packing, surface treatment, and particle size distribution; published data for this specific RH-Vi320 configuration is limited, but industrial formulations in the same class commonly target 3.0 W/(m·K) to 5.0 W/(m·K) when measured by ASTM D5470. The role of RH-Vi320 is not to raise thermal conductivity directly but to allow higher filler loading while retaining dispense viscosity below 800 Pa·s at 1 s⁻¹, as measured by parallel-plate rheometry under ISO 3219. After cure, hardness is typically 30 Shore OO to 80 Shore OO according to ASTM D2240, with the Shore OO scale used because Shore A becomes insensitive for compressible gap filler materials. Volume resistivity is checked under ASTM D257, and dielectric strength is evaluated under ASTM D149. The main production failure mode observed in continuous meter-mix lines is a drift in mixing ratio caused by alumina agglomerates partially blocking the check valve of the hydride feed; this condition produces local uncured patches with residual tack that cannot be corrected by post-cure and requires inline differential pressure monitoring across the static mixer.

Solventless release coating with RH-Vi320 is deposited at silicone coat weights of 0.8 g/m² to 1.5 g/m² onto glassine, super-calendered kraft, or polypropylene film using five-roll offset gravure or multi-roll transfer coating heads. The low ambient viscosity of RH-Vi320 permits dilution and flow-out at coating speeds above 300 m/min, but the addition-cure reaction must be completed in the oven before the web reaches the rewind nip. A platinum catalyst at 50 ppm to 150 ppm platinum is used because the low total formulation mass per square meter leaves little room for catalyst dispersion error, and the Si-H:Si-Vi ratio is set at 1.5:1 to 2.5:1 to ensure rapid surface cure at 130 °C to 180 °C for 5 s to 15 s. Release force stability is measured by FINAT FTM 3 after lamination with a standard acrylic test tape and aging at 23 °C and 50% RH for 20 min and 24 h. The unwinding force is not a single material property of RH-Vi320 but is influenced by the hydride co-reactant structure, the substrate hold-out, and the migration of acrylic adhesive components into the silicone layer. If the paper contains residual amino-functional wet-strength agents or cationic starches, the platinum catalyst is partially inhibited and the release coating remains smeary and extractable, which is detected as an increase in silicone rub-off and a drop in subsequent release force after aging. The use of RH-Vi320 in food-contact release materials is bounded by EU 1935/2004 and, for paper and board, by FDA 21 CFR 176.170 when the substrate is intended for aqueous and fatty food contact. Terminal products include pressure-sensitive label release liners, single-side release film for diaper tapes, and dual-side differential release liners for medical electrode packaging.

When RH-Vi320 Replaces Higher-Viscosity Vinyl Gum in Solventless Silicone PSAs

When RH-Vi320 replaces a portion of higher-viscosity vinyl-terminated gum in solventless silicone pressure-sensitive adhesive formulations, the immediate processing consequence is a reduction in high-shear mixing torque and an increase in the wetting of MQ resin domains before cure. The adhesive compound is prepared with MQ silicate resin at resin-to-polymer ratios from 0.8:1 to 1.5:1, a hydrogen-functional crosslinker at Si-H:Si-Vi ratios of 1.0:1 to 1.8:1, and platinum catalyst at 10 ppm to 40 ppm. Mixing is performed in a planetary mixer under vacuum of 50 mbar to 100 mbar for 30 min to 60 min to remove entrapped air without removing low-molecular-weight cyclic siloxanes that are necessary for wetting. Coating is carried out on a slot-die coater or comma coater at 25 g/m² to 100 g/m² on primed PET or polyimide. The cure window of 100 °C to 150 °C for 3 min to 10 min is narrower than LSR because the adhesive cannot be post-cured after lamination without damaging the backing film. The cured adhesive is evaluated under ASTM D3330 for peel adhesion, ASTM D3654 for shear adhesion, and loop tack according to ASTM D6195 or an equivalent internal method. The formulation with RH-Vi320 tends to show lower zero-shear viscosity before cure, which allows lower coating temperatures but also increases the risk of ribbing and edge bead instability at line speeds above 50 m/min if the surface tension of the coating gap is not matched to the substrate. In production, the most frequent failure is residual methylhydrogen odor caused by incomplete Si-H consumption when the MQ resin contains acidic hydroxyl groups that bind platinum and slow cure; this is managed by neutralizing the resin or by adjusting the catalyst premix order to pre-reduce the catalyst with a small portion of the vinyl polymer.

Power Electronics Encapsulant Stress and UL 94 V-0 Classification Path

The power electronics encapsulant route using RH-Vi320 starts with a low-exotherm addition-cure potting composition that cures at 60 °C to 100 °C. The formulation includes a hydride crosslinker at 1.5:1 to 2.0:1, platinum catalyst at 5 ppm to 20 ppm, and a filler package consisting of aluminum trihydrate or magnesium hydroxide at 40 phr to 120 phr to achieve UL 94 V-0 classification at a thickness of 3.0 mm. Ignition behavior and afterflame times are determined under UL 94; thermal shock tolerance is screened by cycling from -40 °C to 125 °C according to IEC 60068-2-14. The low viscosity of RH-Vi320 permits degassing at 5 mbar to 15 mbar for 5 min to 15 min before pouring into modules with narrow gaps; bubbles that remain after degassing are a consistent production loss because they can reduce partial discharge inception voltage and create local hot spots under switching load. Cured hardness is typically adjusted to 20 Shore A to 40 Shore A to minimize stress on wire bonds, and elongation under ASTM D412 is used as an indirect indicator of thermal cycling tolerance. The material is tested under IPC-CC-830B for conformal coating and encapsulant qualification, including hydrolytic aging and thermal shock. Thermal conductivity is lower than gap filler, usually below 1.0 W/(m·K) when measured under ASTM D5470, unless a separate conductive filler is added. The main process boundary is shelf life: one-part premixed systems containing RH-Vi320, hydride crosslinker, and platinum catalyst must be stored at -40 °C or below to maintain pot life; two-part systems avoid frozen storage but require precise ratio control because the low viscosity leaves little resistance to segregation in static mixers.

High-voltage cable accessory compounds based on RH-Vi320 are processed as two-part addition-cure silicone rubber for field-installable terminations and joints. The base component is formulated with fumed silica, aluminum hydroxide, and vinyl-terminated PDMS and is degassed at 5 mbar to 20 mbar before the hydride and platinum components are combined. The compound is poured into porcelain or silicone rubber housings and cured at 80 °C to 120 °C for 30 min to 120 min, or cured at room temperature with a higher platinum loading and a longer open time. Tracking resistance is measured under IEC 60587 with the inclined-plane method, and erosion resistance is assessed after 6 h of test voltage. Volume resistivity is checked under ASTM D257, and tensile strength under ASTM D412. The low viscosity of RH-Vi320 permits complete filling of narrow stress cone geometries without trapping air at the semiconductor layer interface, which is a common source of partial discharge in high-voltage joints. However, the use of RH-Vi320 in outdoor-insulated cable accessories is bounded by contamination sensitivity; aromatic solvents and ionic residues on the prepared cable surface can inhibit the platinum cure or create conductive paths that reduce tracking performance. Terminal products include heat-shrinkable cable joints, indoor and outdoor terminations, and plug-in bushings.