Vinyl Silicone Oil RH-Vi306

In addition-cure liquid silicone rubber (LSR) injection molding, RH-Vi306 is processed as the vinyl-functional dimethylpolysiloxane component in a two-part platinum-catalyzed hydrosilylation system. The exact terminal vinyl content and dynamic viscosity for RH-Vi306 must be taken from the supplier certificate of analysis, because grade nomenclature is not harmonized across manufacturers. Part A typically contains the vinyl polymer and a Karstedt-type platinum catalyst at 5–20 ppm of platinum metal relative to total formulation mass; Part B contains the same or a lower-viscosity vinyl polymer, a polymethylhydrogen siloxane crosslinker, and an inhibitor such as 1-ethynyl-1-cyclohexanol at 100–500 ppm to control room-temperature pot life. On a production-scale 120-ton injection molding machine with a 22 mm plastication screw having L/D 14 and compression ratio 1.1:1, the two components are fed at a 1:1 volumetric ratio through a static mixer with 12–20 helical elements before entering the cooled barrel at 18–28°C. The mixed compound is injected into a mold at 120–190°C; cycle times fall within 15–60 s for wall sections of 0.5–5.0 mm. The crosslinking chemistry requires a total Si-H to vinyl molar ratio between 1.2:1 and 1.8:1; lower values yield undercured surfaces with extractable siloxanes, while higher ratios can generate hydrogen evolution voids and a brittle network. Typical cured LSR values for tear resistance, tensile strength, elongation at break, and hardness are measured under ISO 37, ASTM D624, ISO 2781, and ASTM D2240; production compounds with a hardness of 20–70 Shore A usually exhibit tensile values of 6–10 MPa and tear values of 20–50 kN/m. Food-contact grades must satisfy FDA 21 CFR 177.2600 and EU 1935/2004 compliance when post-cured for 4 h at 200°C in a ventilated air oven; medical grades require ISO 10993-5 and ISO 10993-10 evaluation after extraction. The main production failure modes are platinum catalyst poisoning by amine-containing mold releases or sulfur residues in rubber molds, moisture uptake above 0.1% in fumed silica causing surface voids, and static mixer ratio drift due to feed pump cavitation; batch-to-batch viscosity variation of the vinyl oil should remain within ±10% of the nominal CoA value to maintain shot-to-shot consistency.

What Limits the Use of Vinyl Silicone Oil in High-Consistency Silicone Rubber Compounding?

High-consistency silicone rubber (HCR) compounding in peroxide systems makes use of RH-Vi306 as a reactive plasticizer added at 1.5–8.0 phr on a two-roll mill with roll speed ratio 1.2:1–1.4:1 and roll surface temperature 20–50°C, or in a 10–50 L internal mixer with ram pressure 0.4–0.6 MPa. The gum stock is a high molecular weight poly(dimethyl, methylvinyl)siloxane with vinyl groups distributed along the chain; the low-viscosity vinyl oil reduces compound Mooney viscosity and lowers durometer without introducing a non-reactive methyl silicone bleed. Published vulcanizate formulation studies indicate that addition of 5 phr of vinyl-functional oil can reduce Shore A hardness by 4–8 points and increase elongation at break by 50–150 percentage points, but batch-specific evaluation under ASTM D2240 and ISO 37 is necessary because filler surface treatment and silica hydroxyl content modify the response. The oil is added simultaneously with or after fumed silica dispersion to prevent silica agglomeration; typical fumed silica loading remains 20–40 phr with specific surface area 150–300 m²/g. In peroxide systems using 0.5–2.0 phr of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, excess vinyl oil above 10 phr can depress tear strength below 12 kN/m tested by ASTM D624, increase compression set above 25% after 22 h at 175°C under ASTM D395 Method B, and create surface tack after post-cure. In platinum-catalysed HCR, the vinyl oil competes with the gum vinyl groups for silicon hydride, so the Si-H to total vinyl molar ratio must be rebalanced to 1.1:1–1.5:1; oxygenated platinum inhibitors and sulfur-containing pigments must be excluded. The terminal products include extruded profiles, gaskets, seals, and calendered sheet where FDA 21 CFR 177.2600 or BfR Recommendation XV may be invoked if the product contacts food. On production scale, a common failure is batch-to-batch Mooney viscosity drift when the vinyl oil is added before filler wetting; the oil can lubricate the roll surfaces and extend mixing time until a breakdown phase of 3–6 min is completed.

Solventless platinum-catalysed release coatings on polyethylene terephthalate (PET) film, glassine, and PE-coated kraft use RH-Vi306 as the vinyl-functional base polymer or as a reactive diluent to adjust release force and coating viscosity. A typical formulation contains 100 parts of vinyl silicone oil, 2–6 parts of methyl hydrogen siloxane crosslinker, 50–150 ppm platinum metal as Karstedt catalyst, and 0.3–1.0 wt% of a volatile inhibitor such as ethynyl cyclohexanol to provide a bath life of 8–24 h at 25°C. The mixed bath is applied at 0.6–1.8 g/m² through a five-roll silicone coater or reverse gravure unit running at 150–400 m/min; the coated web passes through an air-flotation oven at 120–155°C with an oven residence time of 5–15 s. The Si-H to vinyl molar ratio in release coatings is generally maintained between 1.3:1 and 2.5:1; at the lower end, a softer, more elastic release surface gives peel values of 5–20 cN/25 mm, while at the higher end values may exceed 30 cN/25 mm when measured by FINAT FTM 3 at 180° peel and 300 mm/min. A production control failure occurs when dilution solvent or water contamination accelerates crosslinker hydrolysis; an increase in film surface tension above 30 mN/m as measured by ASTM D2578 is an early indication of bath degradation. Post-cure adhesion to the substrate is checked under ISO 2409 cross-cut, and flexibility after wrinkling under ISO 1519. For food-contact release liners, compliance is governed by FDA 21 CFR 175.300 and EU 1935/2004; migration testing under EN 1186 may be required. The terminal products are release liners for pressure-sensitive labels, transfer tapes, and medical adhesive dressings. The main batch-to-batch issue is the presence of low-molecular-weight cyclic siloxanes, which can vaporize in the oven and condense as oily mist on downstream rollers; suppliers generally report D4–D6 content on the CoA, and converters should verify that the total volatile content is below 1.0% before running high-speed lines.

When Vinyl Silicone Oil Is Used as Reactive Diluent in Silicone Gels for Electronics

In low-viscosity addition-cure silicone gels used for electronic potting, conformal coating, and thermal gap filler matrices, RH-Vi306 functions as a reactive diluent that reduces mixed viscosity before filler loading and contributes terminal vinyl groups for network formation. In one production-scale approach, Part A and Part B are blended at a 1:1 volumetric ratio in a planetary mixer at 500–1,500 rpm under vacuum of 1–5 mbar; after 5–10 min of degassing, the mixture is dispensed through a 30 cc Luer-lock syringe or an automated time-pressure dispenser at 2–5 bar. The pre-cure viscosity at 25°C measured with a Brookfield DV-II+ viscometer at 10 rpm using spindle 7 may range from 200 mPa·s to 2,000 mPa·s before thermal filler addition; after adding 60–90 wt% alumina or aluminium nitride with median particle size 2–40 µm, the thermal conductivity rises to 2–8 W/m·K, but the vinyl oil must wet the filler surface without generating free oil bleed. The crosslinking reaction proceeds at 80–120°C for 30–60 min, using 5–20 ppm platinum metal and an Si-H to vinyl molar ratio of 1.1:1–1.6:1. Hardness after cure is measured by cone penetration under ASTM D217 or ISO 2137; soft gels for stress-sensitive components typically show penetration values of 50–250 × 0.1 mm. The critical limitation of a low-viscosity vinyl silicone oil in this application is outgassing: if volatile siloxane content is above 0.5 wt%, ASTM E595 total mass loss can exceed 1.0% and collected volatile condensable material can exceed 0.1%, disqualifying the formulation for sealed optoelectronic or space-grade assemblies. Thermal cycling under IEC 60068-2-14 between −40°C and 125°C for 100–500 cycles reveals whether the low-viscosity vinyl component causes phase separation at the filler-matrix interface; increasing vinyl content without increasing Si-H crosslinker leaves unreacted vinyl groups and a tacky surface. The terminal products include silicone gap fillers, potted power modules, and encapsulation of MEMS sensors. REACH and RoHS 2011/65/EU compliance documentation must cover the platinum catalyst residues and cyclic siloxane impurities; users should avoid tin-containing solder flux residues because organotin compounds poison the platinum catalyst.

Addition-cure room-temperature vulcanizing (RTV-2) silicone for block molds and skin molds in polyurethane, epoxy, and gypsum casting receives RH-Vi306 at 10–30 wt% to reduce mixed viscosity and soften the cured mold. In a vacuum casting line, the base polymer, crosslinker, and vinyl oil are combined in a 20–50 L planetary mixer at 300–600 rpm, then degassed at 2–10 mbar until the bubbles collapse; the mixture is poured or brushed onto the pattern at 22–25°C. Pot life is adjusted to 30–120 min with 1-ethynyl-1-cyclohexanol at 0.05–0.3 wt%, and demold time is 4–12 h at 25°C or 0.5–2 h at 60–80°C. The Si-H to total vinyl molar ratio after dilution must be corrected to 1.2:1–1.8:1; if not corrected, the mold surface remains tacky and exudes uncured fluid, measured by solvent extraction or by a persistent fingerprint mark on the cavity surface. Typical diluted molds show Shore A hardness of 5–25, elongation at break above 500% under ISO 37, and linear shrinkage below 0.1% when measured by ASTM D6289. These molds are used for casting rigid polyurethane parts, epoxy resin decorative products, and plaster architectural elements. Production failures arise when the pattern is made of sulfur-cured rubber or contains tin-catalysed condensation silicone residues, because these contaminants poison the platinum catalyst and inhibit the surface cure. Humidity above 60% is not a primary cure inhibitor for addition-cure systems, but the fumed silica filler must be pre-dried at 120°C for 2–4 h to keep moisture below 0.1% and avoid bubble formation in thick sections. The main process advantage is a non-shrinking, non-reactive interior that does not deposit plasticizer onto polyurethane surfaces; this is verified by ISO 1519 flex testing after 25 cast cycles.

Vinyl-Modified Silicone Ink Chemistry for Textile Substrates

Textile screen printing and heat-transfer applications use RH-Vi306 in addition-cure silicone inks that combine a high-body vinyl polymer, fumed silica thixotrope, pigment dispersion, crosslinker, and platinum catalyst. A production screen-print paste may contain 40–60 wt% vinyl silicone oil, 5–15 wt% hydrophobic fumed silica with BET surface area 120–220 m²/g, 5–20 wt% organic or inorganic pigment, 5–12 wt% methyl hydrogen siloxane crosslinker, and 100–500 ppm platinum metal; the uncured paste viscosity at 25°C is 30,000–80,000 mPa·s when measured with a Brookfield viscometer using spindle 7 at 10 rpm. The paste is screen-printed through mesh counts from 32T to 90T onto cotton, polyester, or nylon fabrics, then cured in a tunnel oven at 130–160°C for 1–3 min. The Si-H to vinyl molar ratio is maintained between 1.2:1 and 2.0:1 to produce a flexible, abrasion-resistant film; excessive crosslinker yields a hard film that cracks under ISO 6330 washing, while insufficient crosslinker leaves an undercured surface with poor wash fastness under AATCC 135. Printed samples are tested for abrasion resistance under ASTM D4966 with 50,000 cycles as a common benchmark for industrial wash durability, and color fastness to perspiration under ISO 105-E04. The main production failure in textile silicone inks is the evaporation or decomposition of the platinum inhibitor at tunnel-oven entry zones; if the inhibitor concentration is set for a 25°C screen room but the paste is heated to 40°C during printing, the pot life can drop below 4 h, leading to partial gelation on the screen. Vinyl oil volatility is also controlled because cyclic siloxane volatiles condense on oven extraction ducts and can drip back onto the printed fabric. The terminal products include garment labels, non-slip sock soles, heat-transfer logos, and reflective safety prints. REACH and OEKO-TEX Standard 100 documentation is commonly required, and a supplier certificate of analysis should report D4–D6 cyclic siloxane content below 0.1 wt% when the printed textile is sold in the European Union.