Vinyl Terminated Silicone Oil RH-Vi305

In addition-cure liquid silicone rubber compounding, vinyl-terminated silicone oil RH-Vi305 is handled as a terminal reactive diluent rather than a non-reactive process aid. Meter-mixing systems deliver the two-part compound through a static mixer with 8 to 12 elements and then into a reciprocating screw injection unit with an L/D ratio of 12:1 to 14:1. The barrel is water-cooled to 20–25 °C to prevent premature hydrosilylation, while the mould is held at 140–180 °C depending on part wall thickness. Addition of 5–15 wt% RH-Vi305 to the A-side before static mixing reduces the crosslink density by introducing terminal vinyl chain extension, which lowers Shore A hardness without creating a migrating plasticiser fraction. Above 20 wt%, the effect reverses into a processing liability: compression set measured under ISO 815-1:2019 increases, flash tears during demoulding, and volatile oligomers accumulate on the cavity surface. The cured articles are often thin-walled seals, medical syringe stoppers, respiratory mask cushions, and engine-bay grommets. Qualification for medical components commonly requires ISO 10993-5 cytotoxicity data and USP Class VI biological reactivity testing, while automotive seal materials are evaluated by ASTM D2240-15e1 durometer and ASTM D624 tear resistance after long-term engine-temperature ageing. In production, clamp force is calculated from projected area at 0.5–1.0 t/cm², and holding pressure is maintained until gate freeze; for thin-walled seals at 180 °C, gate freeze may occur within 5–10 s. The result is a lower-hardness elastomer that retains the thermal stability and compression-set behaviour expected from a platinum-catalysed addition-cure system.

Solventless release coating compatibility and platinum-inhibition boundaries

Coat weight, catalyst inhibition, and web-speed-dependent cure are the dominant variables in solventless release liner production. Target coat weights on machine-glazed paper and biaxially oriented polypropylene are typically controlled between 0.8 g/m² and 1.6 g/m². Below 0.6 g/m², incomplete surface coverage produces zippy release; above 2.5 g/m², extractable silicone can contaminate the pressure-sensitive adhesive and shift its subsequent peel force. Five-roll and offset gravure coaters with water-cooled pan rolls maintain bath temperature at 20–25 °C. The terminal vinyl groups of RH-Vi305 participate in platinum-catalysed hydrosilylation with methylhydrogen polysiloxane crosslinker, and the SiH:SiVi ratio is formulated between 1.2:1 and 3.0:1. Ratios below this window produce incomplete cure and poor anchorage, while ratios above it increase extractable hydride and raise release force. Platinum is used at 5–30 ppm by mass of the coating formulation. Production interruptions are frequently caused by catalyst inhibition from sulfur-containing paper additives, amine-based slip agents, or tin-based heat stabilisers migrating from film substrates. In-line thermal curing is performed at 120–180 °C for 5–20 s, with cure verified by a migration-free smear test and by monitoring residual hydride through infrared spectroscopy. Release force is measured according to FINAT FTM 3; food-contact liners must comply with FDA 21 CFR 177.2600 and EU Regulation 1935/2004, with overall migration controlled under EU Regulation 10/2011/EU where national legislation requires direct-contact evaluation. End products include silicone release liners for pressure-sensitive label stock, medical patch liners, and single-sided tape carriers.

For electronic potting and encapsulation, RH-Vi305 is introduced as a reactive diluent to lower mixed viscosity before filler loading and vacuum degassing. Typical use levels fall between 5 phr and 20 phr; the exact window is determined by the base polymer molecular weight and the required penetration through gaps as narrow as 0.5 mm. The compound is vacuum degassed in a mixing vessel at −0.095 MPa for 5–10 min and then dispensed through a static mixing nozzle containing 12–24 elements. A common cure schedule for medium-volume electronic packages is 60 °C for 30 min followed by 100 °C for 60 min; larger thermal masses require staged heating to avoid exotherm-driven voiding. In filled formulations containing alumina or zinc oxide, the low surface tension of the silicone fluid improves particle wetting, but excess reactive diluent reduces flame retardancy and may prevent the cured compound from reaching UL 94 V-0 at 3.0 mm thickness. Volume resistivity is measured with ASTM D257, dielectric strength with ASTM D149, and outgassing with ASTM E595; space-grade devices typically require total mass loss below 1.0% and collected volatile condensable material below 0.1%. Because low-molecular-weight silicone fractions increase volatile condensables, the addition of RH-Vi305 must be experimentally calibrated against the outgassing budget. Published data for this specific configuration is limited because filler loading, inhibitor concentration, and cure schedule are formulation-specific. End products include battery management system modules, alternating-current charger potting, and sealed industrial power supplies that undergo thermal cycling from −40 °C to 125 °C and damp-heat exposure under IEC 60068-2-78.

When replacing non-reactive dimethyl silicone oil in heat-cured HCR compounding

When RH-Vi305 is added to a two-roll mill sheet, the stock becomes softer and exhibits lower nerve, with addition typically between 5 phr and 15 phr. The fluid should be added after precipitated or fumed silica has been dispersed and before peroxide catalyst addition; this prevents the vinyl groups from being consumed by adsorbed moisture or by surface silanol reactions earlier in the mixing cycle. In an internal mixer with ram pressure of 0.6 MPa, dump temperatures are maintained at 80–100 °C to avoid premature radical generation. A short screw extruder with an L/D ratio of 12:1 or 16:1 and screw speeds of 20–60 rpm is commonly used for profile and tubing extrusion. Above 15 phr, feed-throat slippage and low head pressure are observed, and the uncured sheet may stick to mill rolls because the terminal fluid reduces green strength. Vulcanization is monitored by moving-die rheometer under ASTM D5289 at 150 °C; the torques MH and ML both decline with increasing reactive diluent, while scorch time remains dependent on the peroxide half-life and on the vinyl concentration of the stock. Tensile strength is measured under ASTM D412, tear strength under ASTM D624, hardness under ASTM D2240-15e1, and low-temperature brittleness under ASTM D2137. Directionally, tensile strength and modulus decrease while elongation increases; published data for this specific configuration is limited, so exact values require formulation-specific testing. Post-curing at 200 °C for 4 h removes volatile oligomers and stabilizes the compression set. Final products include extruded silicone tubing, high-temperature wire jacketing, oven gaskets, and press-cured sheets.

Technical fabric coating compounds based on vinyl-terminated PDMS are processed by knife-over-roll coating without organic solvent. The knife gap is set at 0.1–0.3 mm above release-coated glass-fibre or polyester fabric; penetration is controlled by fabric tension and line speed of 5–20 m/min. A single-part formulation containing RH-Vi305 and methylhydrogen polysiloxane crosslinker is applied to glass cloth and cured in a hot-air oven at 150–180 °C for 2–5 min. The resulting coated fabric is used for expansion joints, welding blankets, and removable thermal insulation covers. Flammability is assessed with ISO 6940 and ISO 6941 for textile burning behaviour, and coated fabric mechanical properties are tested under ASTM D751. Heat ageing of coated fabrics is monitored under ISO 1419. Addition of RH-Vi305 lowers coating viscosity and enables single-pass coating, but it also reduces tear strength and can increase surface tack if the cure is incomplete. Production lines therefore control the SiH:SiVi ratio and platinum concentration by in-line viscosity checks before coating; the coated roll is checked for extractables and for bond strength before slitting. Because the process is solventless, oven ventilation can be reduced and explosion-proof construction is not the primary design constraint, but residual hydrogen evolution from the crosslinker must still be managed in enclosed drying tunnels.

Why does terminal vinyl content control tack and skin-removal force in silicone gel adhesives?

Terminal vinyl content sets the molecular weight between network junctions in two-part addition-cure silicone gels, which directly controls the softness and cohesive strength of the cured adhesive. In medical tape and wound contact layer production, RH-Vi305 is used at 5–30 phr to lower the mixed viscosity before coating onto polyurethane film at 50–150 g/m². Slot-die and knife-over-roll heads are used because the low coating weight requires uniform gap control; coating is followed immediately by thermal cure at 80–100 °C for 5–10 min to avoid damaging the thermoplastic polyurethane film. The adhesive is evaluated for peel adhesion to stainless steel under ASTM D3330 or FINAT FTM 1; skin-removal force and residue are tested on volunteer panels after the gel has been post-cured. A higher proportion of low-molecular-weight vinyl-terminated fluid increases the extractable fraction and can cause adhesive transfer to the skin; the formulation is therefore constrained by dynamic extraction limits and by the need to maintain cohesive failure over the full wear period. Medical-grade qualification requires ISO 10993-5 cytotoxicity testing, ISO 10993-10 sensitization testing, and ISO 10993-23 irritation testing. Extractables are characterized under ISO 10993-18. Condensation-cure tin systems are not suitable for this fluid because the terminal vinyl groups remain unreacted and the fluid remains extractable; only platinum-catalysed addition-cure formulations should be used. End products include silicone scar tapes, wearable sensor adhesive liners, and ostomy flange seals.