3D Systems Accura 25 Plastic for SLA Systems is a polypropylene-like liquid photopolymer resin formulated for stereolithography platforms operating with 355 nm solid-state lasers. The product carries the model designation Accura 25 and is supplied as an opaque white reactive photopolymer for vat polymerization systems. It is intended for functional prototypes, master patterns, and short-run indirect tooling where the flexural response and snap-fit behavior of molded polypropylene must be approximated without polypropylene injection tooling.

The cured material is not a thermoplastic polypropylene and does not share its melting, extrusion, or ultrasonic welding behavior. The resin is processed at 0.1 mm layer thickness and requires 355 nm UV laser exposure, recoating, support generation, solvent washing, and UV post-cure. The uncured resin has a nominal viscosity of approximately 250 cP at 30 °C, a value low enough for reliable blade recoating on SLA equipment but sensitive to temperature drift outside the 28 °C to 32 °C operating window.

What Distinguishes Accura 25 from Rigid SLA Photopolymers?

The principal difference is the cured-state flexural modulus and elongation. Accura 25 is specified at 1,380 MPa flexural modulus per ASTM D790-17 and 20% elongation at break per ASTM D638-14. By comparison, the polycarbonate-like resin Accura 60 is specified in the approximate range of 2,700 MPa to 3,000 MPa flexural modulus and 5% elongation at break under the same methods. This difference places Accura 25 below Accura 60 in static stiffness but above it in strain-to-failure, a trade-off that is relevant in thin-wall snap features, clips, and flexible conduit prototypes.

Accura 55, an ABS-like SLA photopolymer, provides higher rigidity than Accura 25 and lower elongation; published datasheet values generally report elongation at break below 10% and flexural modulus above 2,000 MPa. Accura 25 therefore should not be selected as a drop-in for ABS-like structural housings unless the lower stiffness is explicitly required. Accura 25 also differs optically: it is opaque white, whereas clear grades such as Accura ClearVue transmit visible light and are used for flow visualization and light-pipe prototypes.

The pigment and filler package in Accura 25 reduces the depth of cure sensitivity relative to clear unfilled resins, but it requires resin-specific laser working curves. A build prepared with Accura 25 parameters cannot be transferred directly to Accura 60 or Accura ClearVue without recalibration.

Mechanical Property Dataset and Testing Methodology

Published property sheets for Accura 25 report typical values from post-cured test specimens built in the XY orientation. Table 1 lists the commonly cited values and the associated test method designations. The data are not minimum specification limits; batch-to-batch variation, post-cure dose, and build orientation will shift the results.

The tensile modulus of 1,590 MPa and flexural modulus of 1,380 MPa illustrate that the material is not isotropic in every loading mode, even within a single test coupon. The difference is compounded by the layered build structure and residual stress from localized photopolymerization. Deflection predictions for living hinges should use the flexural modulus rather than the tensile modulus, and orientation-specific testing should be performed when the part is built with the hinge axis along the Z-axis.

The notched Izod impact of 29 J/m is lower than that of many injection-molded polypropylene impact copolymer grades, which can exceed 50 J/m to 100 J/m depending on filler content and temperature. Accura 25 is therefore more notch-sensitive than production polypropylene. Sharp internal corners and gate vestiges should be radiused before impact loading. Published fracture toughness data for Accura 25 is limited; high-strain energy release rate calculations should be supported by user-specific testing.

Creep behavior under constant load has not been standardized for Accura 25. The heat deflection temperature of 51 °C at 0.46 MPa indicates that clamped or gasket-loaded housings will relax more rapidly as temperature rises. Long-term creep compliance data generated under ASTM D2990-17 is not published; therefore, continuous clamp loads should be validated on prototype assemblies rather than inferred from short-term modulus values.

Moisture absorption data for Accura 25 is not consistently published under ASTM D570-98. The material is reported to exhibit lower equilibrium moisture uptake than nylon-like SLA grades, but users must not apply this trend to dimensional stability claims without measuring the specific batch. For outdoor prototypes, UV exposure yellows the solid and reduces surface hardness over time; a protective coating is required to maintain appearance.

Build chamber preparation for Accura 25 begins with resin bath temperature stabilization between 28 °C and 32 °C. At 30 °C, the liquid viscosity of approximately 250 cP allows reliable recoating at 0.1 mm layer thickness. If the bath drops below 28 °C, viscosity increase produces streaking, incomplete fill on large flat sections, and occasional recoater blade chatter on rigid blade systems. Above 32 °C, dark cure accelerates unwanted polymerization in unexposed areas and can close fine slots, drain holes, and thin-walled detail.

Laser exposure parameters are established through a working-curve calibration for each resin batch. Single-line test patches are built at varying laser dose to derive depth of penetration and critical exposure. A stored Accura 25 working curve should not be assumed valid after changing resin lots because pigment suspension and monomer lot aging shift the depth of cure. A calibration part with known spans, holes, and wall thicknesses is placed in the first build of each new batch to verify that cure depth has not moved outside the machine’s accepted dimensional band.

Support generation for Accura 25 typically uses larger contact points and reduced support spacing compared with rigid SLA resins because the green-state tear strength is lower. On 0.1 mm slice platforms, thin hinge and snap features can lift away from supports during peel, leaving partially detached layers or pinholes. Support touchpoint diameters are often increased by 15% to 20% relative to Accura 60 settings. Support removal is performed before post-cure, while the material is less brittle, to reduce surface fracturing and pull-out craters.

Washing and post-cure are critical to the final mechanical performance. Isopropyl alcohol or approved tripropylene glycol methyl ether solvents remove uncured residue, but immersion time is minimized because solvent uptake can swell thin walls. After forced-air drying, parts are rotated under 365 nm UV-A lamps for the post-cure cycle. Under-cure depresses HDT and tensile strength; over-cure reduces notched Izod impact and shifts the surface from white toward yellow. Large solid sections should be supported during post-cure so that local temperature does not exceed 51 °C, otherwise warpage is locked into the final part.

When Accura 25 Replaces Machined Polypropylene in Living Hinge Prototypes

When a design team substitutes Accura 25 for machined polypropylene in a living hinge, the hinge geometry must be modified to limit bending strain. Injection-molded polypropylene typically sustains yield elongation well above 100%, while Accura 25 has a published elongation at break of 20% per ASTM D638-14. A direct one-to-one substitution therefore reduces fatigue life and can crack during first assembly trials. The design adjustment usually involves a thinner hinge web and a larger radius, but the exact values depend on hinge length, opening angle, and cycle count.

Snap-fit features are more tolerant than living hinges because assembly strain is lower and load duration is shorter. The flexural modulus of 1,380 MPa per ASTM D790-17 supplies sufficient retention force for battery covers, access panels, and cable clips while avoiding the brittle fracture often observed in high-modulus rigid SLA resins. Repeated snap-fit cycling is not standardized for Accura 25, so performance should be benchmarked against molded polypropylene on the same fixture before release.

Ultrasonic welding is not a recommended joining method for Accura 25 because cured photopolymer does not melt and fuse like thermoplastic polypropylene. Adhesive bonding or mechanical fastening is used instead. Published ultrasonic welding data for Accura 25 is limited, and weld strength should not be assumed from polypropylene processing data.

In vacuum-casting master pattern workflows, Accura 25 is prepared by sealing the layered surface, wet-sanding, and priming before silicone tooling is poured. The low-modulus response lowers edge chipping during pattern demolding from RTV silicone, a failure mode seen with rigid SLA patterns extracted from undercut tooling. Uncured monomer residues can inhibit platinum-cure silicone systems, so the pattern must be fully post-cured and solvent-cleaned before tooling contact. Layer artifacts at 0.1 mm remain visible on shallow angles; the pattern is therefore sanded and sealed with a high-solids primer to fill the remaining striations. This step is part of the process window and cannot be omitted if the silicone cavity must reproduce a smooth surface.

Accura 25 is also used for low-volume vacuum-casting masters because the material can be bonded and polished with conventional prototype finishing operations. The thermal limit of 51 °C is not exceeded in room-temperature RTV curing, which is an advantage in this workflow. If the mold is cured at elevated temperatures, the pattern can distort and transfer dimensional error to cast parts; the oven cycle should remain below the heat deflection temperature.

Thermal Load Remains the Primary Constraint in Polypropylene-Like SLA Resins

Service temperature is the most restrictive variable. At 0.46 MPa flexural stress, Accura 25 deflects at 51 °C per ASTM D648-18. Under clamped assembly loads, the practical use temperature is below that value. Powder coating, steam sterilization, and under-hood validation cycles exceed the thermal ceiling and cause warpage, clamp relaxation, or stress cracking. Accura 25 should not be used in parts requiring continuous exposure above 50 °C, and this boundary must be applied before labeling, painting, or bonding choices are made.

Chemical resistance is limited and depends on contact time, stress state, and temperature. The cured network is attacked by strong acids, chlorinated solvents, and ketones. Low-molecular-weight fuel hydrocarbons produce swelling and can reduce tensile strength if the part is continuously wetted. The standard immersion method ASTM D543-20 should be used before the material is placed into fuel, oil, or cleaning-agent contact. Solvent contact in geometrically complex sections retains fluid at fillets and microcracks, so short wipe tests do not establish broad compatibility.

Liquid resin storage above 35 °C or under ambient UV exposure can form microgel particles in the vat. These particles create surface pimples and can adhere to recoater blades, producing line defects. Unused resin is filtered through a 100 µm filter before re-use, and open-vat time is minimized in high-humidity environments. If build environment relative humidity exceeds 60%, the resin container should be closed immediately after dispensing to limit moisture uptake and shifting of the working curve.