The product designated 3D Systems Figure 4™ FLEX-BLK 10 Plastic is a black, non-filled, single-component photopolymer formulated for vat photopolymerization on the Figure 4 platform. It is classified as a flexible elastomeric material, supplied as a low-viscosity liquid that is imaged with a 405 nm light engine and subsequently post-cured to develop final mechanical response. The material is specified for parts requiring low tensile modulus, high elongation, and Shore A hardness. Representative applications include gaskets, seals, bellows, grippers, protective covers, and low-load living hinges. Unlike rigid structural resins in the Figure 4 family, FLEX-BLK 10 is not intended to replace glass- or mineral-filled polymers in load-bearing, high-stiffness environments. Its datasheet defines mechanical properties according to ASTM D638, ASTM D2240, and ASTM D624, with property values obtained from post-cured specimens conditioned at standard laboratory temperature and humidity. Users should treat supplier datasheet values as representative, not as certified design allowables, because photocured networks are sensitive to build orientation, post-cure dose, cleaning residue, and section thickness.

Before printing, the liquid material is brought to 20–30°C and agitated to redisperse pigment and any settled oligomeric components. The resin is processed in the Figure 4 build chamber without a heated resin tank. The 405 nm digital light projection step initiates radical polymerization in the exposed layers. The material profile controls layer thickness, exposure time, and base adhesion. Common elastomer builds use 30 µm or 50 µm layer thicknesses. Thinner layers reduce stair-step artifacts on curved seal surfaces but increase build time. Thicker layers improve throughput but may increase anisotropy in tensile elongation because the photopolymerization conversion gradient through the layer thickness is not uniform. The black pigmentation reduces light penetration depth compared with transparent or amber Figure 4 resins. This behavior requires careful management of cure depth in narrow cavities, blind holes, and undercut regions. If exposure is insufficient in a closed feature, uncured material can remain trapped after part extraction and later exude or soften after post-cure.

What Distinguishes FLEX-BLK 10 from Rigid Figure 4 Resins and Cast Elastomers?

FLEX-BLK 10 occupies a low-modulus elastomer position within the Figure 4 resin portfolio. In comparison, Figure 4 TOUGH-BLK 20 is specified with high tensile modulus and Shore D hardness for rigid housings, clips, and structural prototypes. TOUGH-BLK 20 resists deflection and is evaluated under ASTM D638 and ASTM D256, whereas FLEX-BLK 10 is evaluated for conformability, tear resistance, and compression set under ASTM D638, ASTM D624, and ASTM D395. The difference is not primarily color or build speed; it is the post-cured network architecture. FLEX-BLK 10 is formulated with a lower crosslink density and a lower glass transition temperature than the rigid Figure 4 materials. This yields rubber-like recovery after low-strain deformation but also lower resistance to creep under continuous load.

Compared with cast polyurethane elastomers, FLEX-BLK 10 is not limited by pot life or mixing ratio drift, but it does exhibit the layer-wise cure transformation typical of vat photopolymerization. The mechanical response is not identical to a thermally cured polyurethane because the photopolymer network contains different backbone chemistry and residual unreacted species after post-cure. Processors replacing a Shore A 60–70 cast urethane should verify that the FLEX-BLK 10 part meets the same ASTM D395 compression set and ASTM D624 tear requirements in the actual service environment. Published data for this specific configuration is limited; direct substitution without application testing is not recommended.

Mechanical Property Reporting Under ASTM D638, ASTM D2240, and ASTM D624

The table below summarizes representative property classes for post-cured FLEX-BLK 10 using the manufacturer’s published test methods. Values are considered indicative of the material class rather than certified design allowables. The current supplier datasheet remains the controlling document for lot-specific values. Build orientation, post-cure unit type, solvent exposure, and dwell time before testing all influence the measured result.

The low tensile modulus of FLEX-BLK 10 permits conformability to irregular mating surfaces. However, the same low modulus reduces extrusion resistance in pressure-loaded seals. Gland design must limit unsupported clearance when the fluid pressure exceeds the material’s stiffness-dependent sealing capability. Hardness alone is not a substitute for compression set data. ASTM D395 Method B compression set testing after 22 h at the intended service temperature is the appropriate screening method for seal applications. The datasheet may not include compression set for every possible post-cure condition; therefore, an application-specific test coupon is required.

When Cleaning Solvent Is Retained in Closed-Cell Elastomer Sections

After printing, parts are removed from the build platform and support material is separated before post-curing. Cleaning is performed in a Figure 4 wash unit or an equivalent solvent-based system. The preferred solvents are those approved by 3D Systems for elastomer materials. Residual solvent left in the part before post-cure can plasticize the polymer network and lower hardness, or it can produce surface tack and dimensional change after thermal exposure. Closed-cell structures and blind holes without drain features are especially susceptible. Production lines using automated support removal have reported trapped solvent in cavities with openings smaller than approximately 1.5 mm. A post-wash drying step, followed by mass measurement before UV post-cure, is recommended for parts thicker than 8 mm or parts with sealed internal channels. The drying time is not universal because it depends on part geometry, solvent type, and wash temperature.

Post-curing is required to complete conversion. The manufacturer provides material-specific post-cure settings for the Figure 4 UV cure unit. Insufficient post-cure leaves unreacted species that can migrate to the surface, reduce tensile strength, and increase creep. Excessive post-cure can produce surface oxidation, color shift, and a harder surface layer that does not match the bulk material. Users who substitute a non-approved UV chamber must map irradiance, wavelength band, and dose to the supplier protocol. Without this mapping, batch-to-batch property variation can appear even when the printer parameters are unchanged.

Shore A Hardness and Compression Set Validation for Seal Applications

Shore A durometer testing under ASTM D2240 provides a rapid incoming or post-cure check, but it is a surface measurement with a finite indenter depth. For a heterogeneous surface skin developed during post-cure, the Shore A reading can be biased by the outer layer and may not reflect the bulk network. Tensile specimens under ASTM D638 and tear specimens under ASTM D624 provide more complete bulk mechanical data. Compression set under ASTM D395 is more relevant for seals because it measures whether the part retains a desired thickness after prolonged compressive strain. In applications with cyclic temperature exposure, compression set should be measured at both the maximum and minimum service temperatures. The ratio of tear strength to tensile modulus also informs design against cut growth. A low-modulus material with acceptable elongation may still fail in tear-critical designs if sharp mating features or dynamic flexure are present.

The comparative position of FLEX-BLK 10 is important when selecting a resin for a part that must survive snap-fit assembly or repeated flexure. A rigid resin such as TOUGH-BLK 20 maintains its geometry under load but may crack or stress-whiten if the design exceeds its elongation. FLEX-BLK 10 accommodates higher strain but may not provide the same dimensional stability under load. If the part requires Shore A 65 rubber-like performance, Figure 4 RUBBER-65A BLK may be evaluated alongside FLEX-BLK 10. The choice should be made from the full set of post-cured properties rather than from durometer alone. Tear resistance, compression set, and solvent resistance often distinguish otherwise similar elastomer formulations.

In fluid-contact applications, cured parts should be immersed in the intended service fluid according to ASTM D543 and then retested for mass, hardness, and tensile properties. Flexible photopolymers are susceptible to swelling in ketones, esters, and aromatic hydrocarbons. Swelling can appear as an increase in mass and a decrease in Shore A hardness. The part may return to its original dimensions only after the solvent evaporates, but mechanical properties may be permanently altered if the solvent extracted low-molecular-weight species or caused microcracking. Strong oxidizing acids and high-pH cleaning agents are not recommended without validation. Published data for this specific configuration is limited in public literature; chemical compatibility must be confirmed under the exact concentration, temperature, and exposure duration expected in service.

The liquid resin should be stored away from 405 nm light and heat to avoid premature polymerization. Metallic contamination can initiate polymerization or destabilize the photoinitiator package. Material from different lots should not be mixed without following the manufacturer’s guidance. Incoming material should be logged and qualified by printing a fixed control specimen and measuring Shore A hardness per ASTM D2240 and tensile elongation per ASTM D638 after post-cure. Control limits for production should be derived from capability studies on the specific machine array, post-cure unit, and solvent handling procedure used on site. Lot-specific variation is a known process variable in vat photopolymerization and must be separated from printer or post-cure drift.