Material identification for Mitsubishi FLEX 45 corresponds to a thermoplastic co-polyester elastomer (TPC) supplied as monofilament feedstock for fused filament fabrication. The product designation places the hardness at 45 Shore D when conditioned and tested according to ISO 868. The polymer is a segmented block copolymer in which aromatic polyester hard segments provide dimensional stability and aliphatic polyether soft segments provide low-temperature flexibility. Manufacturer technical documentation lists density in the range of 1.19–1.21 g/cm³ by ISO 1183-1 and a melt volume-flow rate of 12–18 cm³/10 min at 230 °C/2.16 kg by ISO 1133-1:2022. The grade is intended for fused filament fabrication equipment with closed-loop nozzle temperature control and hardened steel or coated brass nozzles. Filament is supplied in diameter classes of 1.75 ± 0.05 mm and 2.85 ± 0.05 mm, with ovality not exceeding 0.03 mm when measured by dual-axis laser gauging. The material is semi-crystalline, with melting onset near 170–185 °C and the main melting peak near 190–210 °C; differential scanning calorimetry traces are influenced by hard-segment crystalline order and the thermal history of the filament.

The segmented architecture influences printability. The aromatic polyester hard segment crystallizes into domains that act as physical crosslinks; the aliphatic polyether soft segment reduces the glass transition temperature and increases chain mobility. The resulting thermal profile typically shows a soft-phase glass transition near -40 to -20 °C and a broad hard-segment melting endotherm between 170 °C and 210 °C. The low soft-phase glass transition allows flexibility in cold environments, but it also reduces the heat deflection temperature. Difference from random copolyesters is observed in strain recovery after tensile loading; block copolymers exhibit a more defined elastic plateau in dynamic mechanical spectra. Processors using differential scanning calorimetry should note that annealing, filament cooling rate, and spool aging shift the enthalpy of fusion by 2–5 J/g; however, published reference values for this specific product lot are limited.

Tensile response under ISO 527-2/1A is characterized by a low secant modulus and high strain. Manufacturer-reported values place tensile modulus at 65–90 MPa, tensile stress at yield at 12–15 MPa, and nominal strain at break at 300–450 %. These values differentiate FLEX 45 from standard PETG, which exhibits tensile modulus above 1,900 MPa and nominal strain at break below 30 % when tested by the same method. Flexural modulus determined to ISO 178 is typically 60–80 MPa. The material retains ductile behavior at low strain rates, but published data for high-rate tensile behavior of this specific configuration is limited; creep, stress relaxation, and dynamic mechanical analysis should be performed for load-bearing parts.

Table 1 summarizes typical property ranges disclosed in manufacturer technical documentation. The values are not specification limits; certificate of analysis data for each production lot should be requested when parts require documented traceability under ISO 9001:2015 or IATF 16949:2016.

Thermal and Rheological Data Required for Stable Extrusion

Vicat softening temperature, measured under the A50 condition, falls between 95 °C and 110 °C. The melt is shear-thinning, and practical extrusion observations on direct-drive FFF workstations indicate that apparent melt viscosity at nozzle shear rates of 100–300 s⁻¹ is low enough for 0.4 mm nozzles at 230–250 °C. Published capillary rheometry data for this specific grade is limited; process validation should include pressure readings from the extruder motor current and consistent filament feed rate. Typical feed-rate settings for a 0.4 mm nozzle are 25–45 mm/s for outer walls and 50–80 mm/s for infill, with the speed lower for flexible TPC because of the need to avoid melt buckling in the hot end.

Moisture uptake is lower than aromatic polyamide filaments but not negligible. Manufacturer processing guidance recommends drying at 65 °C for 4 h in a forced-air or vacuum dryer to reach <0.02 % residual moisture by Karl Fischer titration. Undried filament may exhibit hydrolysis at the ester linkages, resulting in bubbles, die swell, and loss of interlayer fusion. On a filament extrusion line with single-screw L/D of 24:1 and melt pump, diameter is controlled to 2.85 ± 0.05 mm or 1.75 ± 0.05 mm using dual-axis laser gauging; spool winding tension is maintained below 2 N to prevent cold flow of the soft segment. For desiccant storage, the spool should be kept in a sealed polyethylene terephthalate bag with moisture-absorbent desiccant at <20 %RH after drying.

Layer height and extrusion width interact with the low modulus of the material. For a 0.4 mm nozzle, a layer height of 0.15–0.25 mm and extrusion width of 0.45–0.55 mm are typical; excessive extrusion multiplier above 1.02 can increase melt backpressure in the hot end and lead to filament grinding in gear-drive extruders. Direct-drive extruders with a soft-filament optimized hobbed gear and an adjustable idler pressure are preferred over long Bowden systems because the filament has lower column stiffness than PETG. During deposition, travel speed should not exceed 120 mm/s; rapid accelerations cause lag in the Bowden tube and produce under-extruded infill.

The low hardness creates specific constraints for support removal. Support interfaces should use a dedicated breakaway support material or increase the Z gap to 0.20–0.25 mm for dense support; tighter gaps create mechanical bonding that is difficult to separate without damaging low-modulus surfaces. Soluble support materials based on polyvinyl alcohol are not always compatible because the required processing temperatures are lower; the TPC nozzle temperature can exceed the thermal stability of some PVA grades. For parts with large overhangs, active part cooling fan operation between 40–60 % duty cycle is usually sufficient, but high fan speeds may reduce interlayer fusion by cooling the previous layer below the effective blocking temperature.

How Does FLEX 45 Differ from Shore A TPU and PETG Feedstock?

Comparison with Shore A TPU, PETG, and polyamide clarifies the selection boundary. TPU grades from 85A to 95A provide lower modulus and higher elastic recovery, but they typically have Vicat softening below 85 °C and require slower print speeds because of viscoelastic melt instability. FLEX 45 provides a Shore D hardness of 45, which is approximately equivalent to 90–95 Shore A on the durometer correlation, but retains a Vicat softening temperature of 95–110 °C. Against PETG, FLEX 45 reduces tensile modulus by roughly 95 % and increases nominal strain at break from 15–30 % to 300–450 %. Against polyamide 6, FLEX 45 exhibits lower moisture absorption and does not require the same drying severity, but it has lower tensile strength and lower upper service temperature.

The numerical values in Table 2 are typical published ranges and should be verified against certificate of analysis for the specific lot. For applications currently specified in PETG or ABS, FLEX 45 is selected when the design requires snap-fit insertion with multiple assembly cycles. ABS exhibits tensile modulus near 1,800–2,400 MPa and brittle failure at sharp corners; FLEX 45 eliminates the sharp yield transition but also reduces structural stiffness, so wall thickness must be increased or ribs added. For continuous service under load, the creep modulus of FLEX 45 at 23 °C is expected to be significantly below the short-term tensile modulus; creep data generated per ISO 899-2 should be used for design. At 60 °C, published creep data for this specific grade is limited, and a derating factor is advised.

Application contexts are concentrated in fused filament fabrication workstations with direct-drive extruders and 0.4 mm brass or hardened steel nozzles. Representative uses include living hinges, low-pressure cable shrouds, bellows, vibration isolation mounts, and reusable assembly jigs. In a living hinge evaluation, FLEX 45 samples of 1.5 mm thickness retained visual integrity after repeated manual flex cycles; however, published interlaboratory data for this specific configuration is limited, and qualification should be performed using ISO 13003 or ASTM D7774 cyclic fatigue methods. Sealing applications require consideration of compression set, which is higher than crosslinked elastomers; continuous service above 70 °C under constant compressive load is not recommended unless creep data are available. For air duct or enclosure use, flammability classification is not inherent to the material; the finished part must be tested to UL 94 or the relevant end-use standard.

When Preheat and Moisture Control Are Omitted from the Process Route

Process failures observed on production-scale FFF workstations fall into two categories. Moisture-induced hydrolysis occurs when spooled filament is exposed to ambient relative humidity above 60 %RH for more than 24 h without sealed storage. The ester linkages in the polyester hard segment undergo chain scission near the nozzle, producing a brittle weld line and a reduction in interlayer tensile strength of 20–40 % when tested by ISO 527-2/1A across printed Z-axis coupons. In extreme cases, steam bubbles produce surface delamination. The second failure mode is cold-bed shrinkage when the first layer is deposited on an unheated glass plate below 20 °C; the semicrystalline hard segments contract anisotropically, and corner lift-off exceeds 0.5 mm on parts longer than 100 mm. The corrective action is not to increase bed temperature above 60 °C, because softening above the Vicat onset causes loss of layer registration. Instead, an enclosed build volume and polyetherimide film with a setpoint of 35–50 °C provide adequate first-layer constraint. If stringing or oozing occurs during travel moves, retraction distance should be limited to 1–2 mm at 20–30 mm/s; longer retractions pull air into the melt pool and create surface pitting.

Thermal degradation occurs above 260 °C. The ester groups begin to decompose, producing acetaldehyde and carbon dioxide; the melt becomes discolored and brittle. Nozzle temperature should therefore not exceed 250 °C for continuous printing, and idle nozzle at 250 °C should be limited to 10 min to avoid degradation. Hot-end designs with poor thermal separation between the melt zone and filament feed path may soften the filament above 70 °C in the cold side, causing buckling and feed failure. A heat sink cooling fan is required if the ambient chamber temperature exceeds 40 °C.

Chemical resistance data for the TPC class indicate resistance to dilute aqueous acids, aliphatic hydrocarbons, and many automotive oils at ambient temperature; however, polar solvents such as ketones, esters, and chlorinated solvents can soften or dissolve the soft block. Continuous exposure to strong bases and amines is not recommended because ester groups are susceptible to saponification. For food-contact or medical use, compliance must be confirmed for the specific filament production lot under 21 CFR 177.2600, EU 10/2011, and applicable migration test method EN 1186; a generic material designation does not confer regulatory approval. Flame behavior is uncontrolled unless tested to UL 94 for a specific thickness; published data for this specific grade is limited.