EMS-Grivory Grilamid TR 90 Dry is a transparent amorphous polyamide moulding compound based on PA 12 chemistry. The grade designation identifies a low-moisture supply form, not a different polymer backbone from standard PA 12. The dry nomenclature corresponds to sealed moisture-barrier packaging in which residual moisture is typically held at or below 0.10% by mass when measured by an evaporation method with Karl Fischer titration to ISO 15512; the batch certificate of analysis remains the controlling document for actual release values. Density determined on dry-as-moulded specimens to ISO 1183-1:2019 is 1.00 g/cm³, which is lower than polycarbonate and PMMA and close to semi-crystalline PA 12. The grade is used in ophthalmic frames, sports equipment, transparent housings, and medical device components where optical clarity, impact resistance, and stress-crack resistance to oils and cosmetic chemicals are design constraints. Differential scanning calorimetry to ISO 11357-2 shows a glass transition rather than a pronounced melting endotherm, confirming the amorphous morphology that gives isotropic shrinkage and low haze in polished mould surfaces.

What Distinguishes the Dry Grade from Standard PA 12 During Feeding and Plasticizing?

The dry designation alters start-up procedure and storage control even though the underlying repeat-unit chemistry is the same. Standard PA 12 is hygroscopic and equilibrates with atmospheric moisture; excess water during melt processing hydrolyses the polyamide, lowers molecular weight, and produces splay, silver streaks, or surface defects. Dry-grade material can be fed directly from an intact sealed package if it is consumed within a limited exposure window. If the resin is exposed to ambient air above 60% relative humidity or if hopper residence exceeds approximately 30 min, drying in a desiccant dryer at 80 °C for 4–6 h with a dew point of -30 °C or lower is recommended. The feed throat should be water-cooled to avoid pellet softening and bridging. On production-scale single-screw injection units, a general-purpose three-zone screw with an L/D ratio of 20:1 to 25:1 and a compression ratio of 2.0:1 to 2.5:1 is commonly used. Because the amorphous solidification route gives different pellet bulk density and feed behaviour from semi-crystalline PA 12, hopper level sensors and screw speed settings should be revalidated when switching materials. Hydrolysis risk increases sharply when melt moisture exceeds approximately 0.20%; therefore the dry grade is not a substitute for closed-loop drying when packaging has been damaged or stored in high-humidity conditions.

Representative values from the current material data sheet for dry-as-moulded specimens include a tensile modulus of elasticity of 1500 MPa by ISO 527-1:2019 and ISO 527-2:2012, a yield stress of 40 MPa, and nominal tensile strain at break greater than 50%. Charpy notched impact strength at 23 °C is approximately 15 kJ/m² when tested to ISO 179-1:2010 method 1eA; this value supports flexible thin-wall parts that can be deformed without brittle failure. Transmittance measured on a 2 mm plaque to ASTM D1003-21 exceeds 90%, with haze kept low when cavity surfaces are polished. The amorphous structure yields isotropic mould shrinkage commonly in the range of 0.6% to 0.8%, but the exact value depends on wall thickness, gate geometry, melt temperature, and holding pressure. The coefficient of linear thermal expansion is near 120 × 10⁻⁶ K⁻¹ by ISO 11359-1/-2, which is considerably higher than glass and metals used in insert moulding; multi-material designs must account for interfacial residual stress. Water uptake after 24 h at 23 °C is roughly 0.3% by ISO 62, with equilibrium uptake approaching 1.5% in saturated humid environments. Because absorbed water plasticises PA 12, design calculations for long-term service should use conditioned mechanical values rather than dry-as-moulded data.

Melt Rheology and Gate Freeze Time in Thin-Wall Ophthalmic Frames

For thin-wall transparent parts such as ophthalmic frames, the recommended melt temperature at the nozzle is 230 °C to 270 °C. Mould temperature is maintained between 40 °C and 80 °C; higher mould temperatures within this range improve micro-surface replication and reduce flow-induced birefringence but extend cycle time. Barrel profiles are set to ascend from the feed throat to the nozzle, with the nozzle kept near the middle of the melt range. Residence time at melt temperature should not exceed 5 min at the upper end because degradation above 280 °C produces measurable yellowing, molecular weight reduction, and gas bubbles in thick sections. Injection speed is medium to high; thin-wall frames often require fill times of 0.2–0.5 s to prevent premature freeze-off before cavity packing. Holding pressure is established from gate freeze time determined with cavity pressure sensors; published data for this specific configuration is limited because runner layout, gate dimensions, and hot-runner manifold balance vary by tool. Moulds are typically polished to a high-gloss surface finish of SPI A2 or better, and venting depths of 0.02–0.03 mm are used to evacuate air without creating flash. After ejection, parts may be stress-relieved at 60 °C to 70 °C for 1–2 h if drilling, lens insertion, or coating generates local residual stress. Flow-line visibility increases at low mould temperatures and low injection speeds; the defect is a frozen-layer skin phenomenon rather than a bulk crystallisation effect.

Chemical resistance in service is a differentiating property. Grilamid TR 90 Dry resists many oils, greases, dilute acids, aliphatic hydrocarbons, and non-polar solvents. Continuous exposure to strong acids, oxidising agents, hot polar solvents such as methanol or ketones, and hot chlorinated hydrocarbons is not recommended because swelling and stress cracking can occur. Environmental stress-cracking resistance against plasticizers, skin care products, and perspiration is higher than that of many amorphous transparent polymers, which has led to use in eyewear and personal equipment. In medical applications, the material may be considered for devices requiring biological evaluation under ISO 10993-1; cytotoxicity, sensitisation, irritation, and systemic toxicity remain the responsibility of the device manufacturer because additives and processing history affect the final formulation. Gamma irradiation above 50 kGy may yellow the polymer and reduce impact strength, so dose mapping and accelerated ageing should be part of validation. Ethylene oxide sterilisation at 55 °C is commonly used for polyamide devices, but residual gas limits under ISO 10993-7 must be validated. Steam autoclaving at 121 °C or 134 °C is not recommended for load-bearing parts because the heat deflection temperature under 1.8 MPa is approximately 70 °C. Dry-heat sterilisation above 80 °C is outside the continuous service window for unstabilised parts.

Regulatory compliance depends on the exact colour and additive package, not only on the base polymer. Suppliers can provide REACH and RoHS documentation through their compliance systems. Food-contact and drinking-water applications require the specific food-contact grade and may be evaluated under EU 10/2011 or relevant national standards; the base unfilled transparent grade should not be presumed compliant without explicit grade-specific documentation. The UL 94 flammability rating for unfilled thin sections is HB; transparent unfilled material is not UL 94 V-0, and thin-wall flame-retardant requirements must be addressed with a different formulation.

When Substituting Grilamid TR 90 for Polycarbonate or PMMA in Transparent Housings

Substitution decisions require simultaneous evaluation of density, stiffness, impact resistance, heat resistance, and chemical compatibility. The table below gives representative values from standardised tests for dry-as-moulded unfilled materials. It is a comparative overview, not a design specification; current material data sheets and application-specific testing must be used for qualification.

During moulding, the lower melt stiffness of Grilamid TR 90 compared with polycarbonate changes runner balance and gate sizing. Gates should be larger than those used for polycarbonate because the melt solidifies quickly in thin sections; direct edge gates or tab gates are preferred over pin gates for sections thicker than 1.5 mm. Drying is less critical than for polycarbonate if the sealed packaging is intact, but opened material must be protected from condensation. Nylon surface moisture at levels as low as 0.15% can generate splay. For painting or hard coating, the surface energy is different from PMMA; plasma or corona pretreatment may be required before UV-cured coating adhesion. Cross-cut adhesion may be tested to ISO 2409 and pull-off adhesion to ISO 16276, with target values dependent on the coating system. The substitution should also include a dimensional check because mould shrinkage and thermal expansion differ enough to alter snap-fit clearances, hinge gaps, and lens retention forces in assembled devices.