Dow EVOLV3D™ LC 3335 LSR Liquid Silicone Rubber for 3D Printing is a two-component, platinum-catalysed addition-cure liquid silicone rubber. The A and B components are formulated for metered mixing at a 1:1 volumetric ratio and subsequent deposition through a disposable static mixer at ambient factory temperatures. The cured material is a silicone elastomer in the nominal 35 Shore A durometer class, though the exact printed value is determined by toolpath direction and post-cure schedule. The grade is not a condensation-cure room-temperature vulcanising compound and does not rely on atmospheric moisture, tin catalysts, or UV exposure. The material is intended for extrusion-based liquid deposition printing systems that can handle two-component mixing at room temperature. Users should not assume equivalence to injection-moulded sheets; printed specimens must be cut from plaques or buttons produced with the intended nozzle diameter, layer height, and curing oven profile.

In comparison with fused filament fabrication of thermoplastic elastomers, LC 3335 can be deposited through a fine nozzle without melt torque because the uncured material is a pumpable fluid containing yield-stress modifiers that hold the bead after exit. Unlike UV-curable elastomers, the hydrosilylation cure can proceed in shadowed cavities and does not require layer-by-layer UV exposure; however, full mechanical properties develop only after oven exposure. Compared with high-consistency silicone rubber, LC 3335 is supplied as a liquid and does not require high-shear kneading or compression moulding. These differences make it a candidate for short-run seals, damping pads, wearable bands, and prototype components requiring a 30–40 Shore A elastomer with thermal stability. The base resin alone does not confer food-contact or medical regulatory approval.

When LC 3335 Is Dispensed Through a Static Mixer Under Lean Flow Conditions

Deposition of LC 3335 is best performed with positive-displacement metering rather than pressure-only reservoir feed. Progressive-cavity pumps or rotary-displacement pumps with ceramic or hardened stainless rotors are used to deliver the A and B components to a static mixer. The mixer is usually a disposable plastic element unit of 24 to 32 elements, selected to match the mixed viscosity and target output. A gravimetric or volumetric calibration should demonstrate A/B ratio within ±1 % by weight; larger deviations shift stoichiometry and can produce a permanently tacky bead or low elongation. The wetted path from pump outlet to nozzle tip is considered a consumable because mixed material gradually advances in viscosity and can adhere to metal.

Nozzle diameter is chosen against the intended layer width. Orifices from 0.4 mm to 1.2 mm are common; a 0.6 mm orifice at a printed layer height of 0.3 mm yields a relaxed bead wider than the orifice after deposition. If the nozzle is too small for the required build rate, shear rate in the opening rises and the pressure requirement at the pump head increases. At shear rates above 10 s⁻¹, the material shear-thins, but the pressure drop through a 0.25 mm nozzle can still become limiting. Conversely, a nozzle above 1.5 mm produces heavy beads that may slump before cure if the yield stress is exceeded. Print speed is matched to volumetric output; movement rates from 10 mm/s to 40 mm/s are typically used, but the allowable range depends on nozzle diameter, layer height, and the green-strength requirement of the unsupported wall.

Mixed material temperature is maintained between 18 °C and 30 °C. At temperatures below 15 °C, viscosity increases and metering repeatability can degrade. Above 35 °C, the working life of the mixed A/B decreases rapidly. Pot-life measurements should be made by oscillatory rheometry at the print-head temperature; time to a defined multiple of the initial complex viscosity is a more useful limit than visual gel time. A mixed batch at 25 °C commonly remains printable for several hours for this addition-cure class, but heated production lines may reduce this to under 20 min. Mixed material should not be recirculated or returned to component pails.

Green strength of the deposited bead is the key differentiator from standard injection-moulding LSR. The formulated yield stress prevents slumping of a vertical bead, but it does not permit unlimited bridging. Unsupported spans beyond approximately 5 mm can sag before cure; short overhangs and steep sidewalls may require a support strategy. The support material, if used, must be compatible with platinum-catalysed hydrosilylation. Catalytic poisons in support residue are a known source of tacky surfaces. Where published data is limited, the user should print a stepwise bridging test at the intended layer time to define the maximum span for each nozzle geometry.

What post-cure thermal histories bring compression set below 20 % after 22 h at 175 °C?

Thermal cure proceeds by platinum-catalysed hydrosilylation, and the rate is strongly temperature-dependent. A printed part that is tack-free after 10 min at 100 °C may not be fully vulcanised; residual Si-H and vinyl groups can continue to react during storage and alter hardness, elongation, and compression set. Compression-set testing is therefore used as a process-check for cure completeness. The usual target is a compression set below 20 % after 22 h at 175 °C when tested according to ASTM D395-18 Method B. If the value is higher, the cure cycle is modified rather than the base resin.

A forced-air convection oven with an air-change rate of 5 to 10 air changes per hour is recommended. Dwell time is set by part mass, wall thickness, and whether the part is cured on a metal plate. Thin printed pads of 2 mm to 3 mm can reach practical cure in 20 min to 30 min at 120 °C; thick blocks can require 60 min or more. Oven set points below 100 °C slow vulcanisation and can leave an under-cured core. Very high temperature cycles, such as 4 h at 200 °C, are usually reserved for volatile removal and food-contact post-cure rather than routine property development. Such cycles can embrittle very thin sections if the oven atmosphere is not controlled.

Mechanical qualification of printed LC 3335 must account for anisotropic deposition. Tensile specimens cut parallel to the toolpath often show higher elongation at break than specimens cut perpendicular to the layer stack. A flat plaque printed with 100 % raster infill and post-cured before cutting is the standard starting point. Hardness is measured on a stacked section of at least 6 mm thickness; values in the 30–40 Shore A range are typical for this material class. Tensile strength of an adequately cured part is generally found between 6 MPa and 9 MPa; elongation at break is often in the 300 % to 600 % range. These are class-level ranges for a 35 Shore A addition-cure LSR and must not be treated as a product guarantee without datasheet verification.

Tear strength per ASTM D624-00(2020) Die B for this durometer class usually falls between 20 kN/m and 30 kN/m. Lower tear values in printed parts can indicate poor interlayer adhesion; a useful diagnostic is to examine the fracture surface for bead boundaries. Density is measured by ASTM D792-20. A well-fused printed silicone part should be close to a moulded LSR density of approximately 1.10 g/cm³. A measured density below 1.05 g/cm³ suggests porosity, and associated tensile and tear values will be unreliable.

Rheological, Mechanical, and Comparative Boundaries in Printed LC 3335 Versus Moulded LSR

Relative to injection-moulding LSR, uncured LC 3335 has a different rheological signature. Standard moulding grades are designed to fill thin cavities under high pressure; they often show a mixed viscosity below 100 Pa·s at 25 °C and low yield stress. The printable grade is stiffer at rest to retain bead shape, but it still shear-thins in the nozzle. A valid comparison therefore requires viscosity curves over shear rates from 0.1 s⁻¹ to 100 s⁻¹, using ISO 3219 or ASTM D4287. The printable material usually has a higher complex viscosity at low frequency and a more pronounced reduction at high shear.

Moulded LSR parts are typically isotropic, while printed LC 3335 parts have a layered structure. Planar tensile strength of a printed part may be 5 % to 20 % lower than a fully moulded slab of the same hardness, depending on layer fusion and toolpath pattern. This reduction is not unique to LC 3335; it is a consequence of liquid-deposition additive manufacturing. The user can partially mitigate the loss by shortening the interval between adjacent beads and by post-curing at a temperature sufficient to permit interlayer network formation. In sealing applications, layer lines can also create a leak path; compression set, surface geometry, and contact pressure must be verified with the actual printed gasket.

Compared with flexible FDM thermoplastics, cured LC 3335 tolerates repeated exposure to higher operating temperatures. Addition-cure silicone retains elastomeric behaviour below -50 °C and above 180 °C for short excursions, but thermal ageing must be verified according to ISO 188 or ASTM D573. Flexible TPU, by contrast, commonly has a softening range below 100 °C and is difficult to print in soft, low-durometer grades. Chemically, cured silicone is resistant to many polar solvents and to oxidation, but it swells in nonpolar hydrocarbons; resistance to a specific fluid must be tested by immersion per ASTM D471, not inferred from polymer class alone.

Uncured LC 3335 is subject to platinum-catalyst inhibition. Sulfur-containing gloves, tin-catalysed room-temperature silicones, amine-cured epoxies, nitrile rubber, and vapours from certain adhesives can create a tacky, under-cured interface. Dedicated polypropylene or stainless-steel wetted parts are used; brass and tin-containing bronzes are avoided. Components should be stored in closed containers at 5 °C to 30 °C, and mixed material should not be returned to A or B containers. Cured LC 3335 is not automatically compliant with food-contact or medical standards; end-use regulation is a separate validation. Testing under the intended migration or leachables protocol, such as FDA 21 CFR 177.2600 or USP Class VI, is required before a commercial claim is made. Published data for the printed configuration remains limited, so qualification protocols must include printed plaques, not compression-moulded or cast sheets.