Liquid silicone rubber for Screen Printing RH-G802

Designated as RH-G802, this two-part addition-cure liquid silicone rubber is compounded for screen-printing deposition rather than closed-mold injection or compression molding. The product class is used where thin, selective-area silicone films are required on textile, primed film, and polymer substrates without die-cutting, transfer tape, or molding tooling. Typical industrial applications include apparel grip patches, printed medical electrodes, wearable device membranes, and heat-transfer labels. Published data for this specific model remains limited; therefore, processing windows and cured-property values in this document are representative ranges for screen-printing addition-cure LSR systems and must be verified against the batch certificate of analysis before production release.

Which rheological variables distinguish screen-printable RH-G802 from injection molding LSR grades?

Low-shear viscosity measured by cone-plate rheometry in accordance with ASTM D4287 and ISO 3219 is generally maintained between 25,000 mPa·s and 80,000 mPa·s at 25 °C for screen-printable LSR; injection molding LSR grades often fall below 20,000 mPa·s because they rely on mold-filling pressure rather than aperture hold time. The screen-print grade also exhibits a thixotropic index of approximately 2.0–3.5 when apparent viscosity is compared at 1 s⁻¹ and 10 s⁻¹. This time-dependent structure retention allows the material to remain stationary after squeegee passage while still wetting the previous print layer. Yield stress in the uncured compound is commonly observed between 50 Pa and 250 Pa; too low a yield stress causes line growth and merging of adjacent print features, while too high a yield stress produces mesh clogging and uneven deposit thickness. Mixing ratio for RH-G802 is typically configured as 1:1 by volume or weight, but supplier documentation must confirm whether the system uses a direct addition cure or a solventless thixotropic grade. Pot life at 25 °C commonly ranges from 4 h to 24 h; shorter pot-life versions may be formulated for rapid thermal activation in high-cadence lines.

Mesh geometry, squeegee durometer, and off-contact distance define the practical operating envelope.

On flatbed and cylinder presses, screen-ready LSR is printed through monofilament polyester or stainless-steel mesh at counts from 43 threads/cm to 120 threads/cm (110–305 mesh). Mesh tension is held between 20 N/cm and 30 N/cm; low tension increases snap-off delay and causes edge-definition loss. Squeegee durometer of 60–75 Shore A is selected to shear the thixotropic compound without overdriving the material through coarse mesh. Off-contact distances of 1.5–3.0 mm and squeegee speeds of 100–300 mm/s are observed in production-scale garment printing; higher off-contact values raise required squeegee pressure and can crush the mesh or distort elastomeric squeegees. Emulsion thickness is controlled to 10–30 µm, but thicker stencils may be needed for high-opacity prints on dark textiles. Because the material is solvent-free and does not air-dry, viscosity remains stable across the press; however, in-press open time is governed by the mixed compound’s thermal inhibitor rather than evaporation rate. Production failure modes include streaking from bubble entrainment, image bridging when mesh openings are too small, and premature gelation when exposure to hot press pallets or metal squeegee hardware raises the ink temperature above the inhibitor threshold.

On untreated polyester and polyamide textiles, cured silicone prints require surface preparation because hydrosilylation-cure LSR does not generate amine-reactive or hydroxyl-reactive anchor groups at the substrate interface. Corona treatment at 2–4 kW/m²/min or air-plasma exposure increases surface energy, while a silane-based primer based on methacryloxy- or glycidoxy-functional trialkoxysilanes improves wet adhesion and wash durability. Adhesion is evaluated via crosshatch tape pull using ISO 2409, but wash-fastness testing under ISO 6330 with household detergent at 40 °C is required for apparel applications. In printed medical wearables, the film is deposited onto TPU or PET film; interfacial adhesion must be balanced against the requirement to avoid substrate swelling or plasticizer migration from PVC. Selective screen printing with RH-G802 is used to create isolated silicone pads on knit constructions, replacing die-cut silicone sheet that requires carrier film and pressure lamination. Penetration into fabric is controlled by mesh open area and squeegee pressure; excessive strike-through produces undesirable stiffness, while insufficient penetration yields weak mechanical anchoring.

Platinum-catalysed hydrosilylation, inhibitor packages, and contamination sensitivities

The curing reaction of RH-G802 follows platinum-catalysed hydrosilylation between vinyl-functional polydimethylsiloxane and hydride-functional crosslinker. Unlike condensation-cure RTV silicones, no methanol, oxime, or acetic acid byproduct is released; this allows closed-line processing near heat-sensitive substrates and reduces post-cure shrinkage. Thermal activation temperature is typically 120–180 °C for 30–300 s, with thicker prints requiring staged ramp profiles to prevent surface skinning before full cure. The addition-cure system is inhibited at room temperature by alkyne-type inhibitors; the inhibitor is consumed at elevated temperature, making the compound’s open time strongly dependent on mixed-component temperature. Uncured material exposed to 45 °C or higher may gel within minutes even before entering the oven. Contamination sensitivity is severe: amines, organotin compounds, sulfur-vulcanized rubber, certain latex gloves, and PVC stabilizer residues can poison the platinum catalyst and produce tacky or uncured surfaces. Mixing equipment must be solvent-free and dedicated; residual condensation-cure silicone or polyurethane systems should not share the same meter-mix dispenser without validated cleaning. Cured RH-G802 films may be post-cured at 200 °C for 2–4 h to reduce volatile siloxane content and stabilize durometer, as measured by ASTM D2240 or ISO 48-4.

Screen-printed medical electrode arrays and wearable biosensor housings use RH-G802 as a selective-area encapsulant where thin films must survive repeated autoclaving and skin-contact cleaning. Cured films are generally tested against ISO 10993-5 and ISO 10993-10 only after the complete device has been assembled; raw-material certification does not by itself establish biocompatibility. Steam sterilization cycles at 121 °C or 134 °C under ISO 17665-1 require the print to remain bonded to the substrate and free of blistering; therefore, the adhesive primer and substrate glass transition must be robust under saturated steam conditions. For apparel grip patches, the silicone print replaces PVC plastisol inks that can migrate plasticizer and stiffen at low temperatures. The addition-cure LSR remains elastomeric from approximately -50 °C to 200 °C depending on the cured formulation and filler package; published data for this specific configuration is limited, so application testing under ASTM D638 tensile conditions is necessary before design freeze.

When high-temperature performance and low extractables are required, addition-cure screen-printing LSR replaces plastisol and polyurethane inks.

Compared with plastisol screen-printing inks, RH-G802 contains no phthalate plasticizer and does not require high-molecular-weight PVC resin. This difference becomes measurable in accelerated aging at 70–100 °C, where plastisol films harden due to plasticizer loss and show surface crazing, while addition-cure LSR maintains elongation. Compared with solvent-based polyurethane inks, the silicone system emits no organic solvent during curing and can be used in low-VOC production environments where ventilation capacity is fixed; however, the screen must be cleaned with appropriate silicone-safe solvents because cured silicone cannot be removed by conventional solvent ink washup. Compared with condensation-cure RTV silicones, addition-cure RH-G802 is expected to offer faster thermal activation, reduced byproduct generation, and improved control of fine-line definition because the uncured compound does not rely on ambient moisture diffusion. The principal operational boundary is the narrow contamination tolerance described above: condensation RTV and polyurethane residues are less likely to catastrophically inhibit cure, while platinum-cured LSR requires dedicated squeegees, flood bars, and mixing vessels.

Across multi-station carousel presses, real-time monitoring of pallet temperature is required because residual heat from infrared flash units can prematurely advance cure. On a typical 8–12 station carousel with 600 mm × 800 mm pallets, mixed RH-G802 is loaded into squeegee reservoirs at 18–25 °C; pallet surface temperature must remain below 40 °C before print head contact. Meter-mix systems with static mixers of 24–40 elements deliver component ratio tolerance better than ±2%; off-ratio mixing produces either soft tacky surfaces from insufficient crosslinker or brittle films from overdosing hydride. Pressure-pot feeding with 0.2–0.4 MPa air pressure is used for high-viscosity formulations, but cavitation and air entrapment must be controlled through degassing at -0.09 MPa or higher vacuum for 5–10 min. In-line viscometry is rarely performed; instead, print thickness is monitored gravimetrically by coating weight per square meter, with typical wet-film weights between 80 g/m² and 300 g/m² depending on mesh and emulsion thickness. Published data for this specific configuration is limited, so process validation should include a design-of-experiments on squeegee angle, flood bar gap, and pallet temperature.

Batch-to-batch variance in screen-printing LSR is observed primarily in low-shear viscosity and thixotropic index rather than in ultimate cured hardness. A shift of ±10,000 mPa·s at 25 °C may be tolerable for coarse artwork but can alter fine-line width by more than 15% when printing through mesh counts above 90 threads/cm. Cured tensile strength is typically in the range 5–10 MPa, elongation at break 200–600%, tear strength 15–35 kN/m, and compression set below 25% after 22 h at 180 °C; these values are representative for addition-cure LSR, not batch-specific RH-G802 certificates. The formulation may contain fumed silica and precipitated silica rheology modifiers, which raise hardness and lower elongation relative to unfilled LSR; the screen-printing grade therefore represents a compromise between print holdout and cured elastomer toughness.

Storage stability before mixing is normally 6–12 months in sealed containers at 10–30 °C; Part A and Part B should be kept separate because accidental mixing initiates cure. Low-temperature storage below 5 °C may increase viscosity but does not normally damage the polymer; the material should be conditioned to 20–25 °C before pumping. Contact with uncured RTV silicones, epoxy amines, or sulfur-containing compounds must be avoided because these materials can either poison the platinum catalyst or destabilize the inhibitor package. At relative humidity above 60%, primed substrates should be pre-dried before printing to prevent discontinuous adhesion and microvoid formation under the cured film.