EMS-Grivory Grilamid TR 90 NZ is an amorphous transparent polyamide classified under ISO 1874-1 as PA MACM12-I; the MACM monomer is bis(4-amino-3-methylcyclohexyl)methane and the 12 monomer is dodecanedioic acid. The material is supplied as a natural-color injection-molding grade for thin-wall optical components. Because the macromolecular backbone lacks sufficient chain regularity for spherulitic crystallization under normal cooling, the resin solidifies by vitrification at approximately 155 °C and retains optical clarity without nucleating agents or clarifiers. Density measured according to ISO 1183-1 is 1.00 g/cm³, which is lower than general-purpose polycarbonate and close to semicrystalline PA12.

Typical dry-molded properties from the manufacturer’s technical datasheet are summarized below. Values are for natural material and may shift with wall thickness, mold temperature, moisture conditioning, and pigment addition.

What Does the PAMACM12-I Designation Encode?

The PA prefix denotes a polyamide. The MACM12 segment specifies a repeat unit formed from bis(4-amino-3-methylcyclohexyl)methane and dodecanedioic acid. The cycloaliphatic diamine reduces chain regularity sufficiently to suppress crystallization during injection molding, so the material does not exhibit a melting endotherm in a standard differential scanning calorimetry scan at 20 K/min. The absence of crystallinity is responsible for both transparency and the near-isotropic mold shrinkage observed in practice. The -I suffix is part of the ISO 1874-1 designation block for an injection-molding formulation, but the complete designation includes viscosity and additive codes that are not reproduced in the abbreviated product name. The NZ suffix is an EMS-Grivory product suffix for a natural, clear formulation with mold-release and stabilizer components intended for subsequent masterbatch coloring or use as a clear natural resin.

The low density and amorphous morphology change processing behavior compared with semicrystalline PA6 or PA66. Mold shrinkage is nearly isotropic; the ISO 294-4 range of 0.7–0.9 % allows cavity dimensions to be cut closer to nominal than for many semicrystalline polyamides. Moisture conditioning at 23 °C and 50 % relative humidity reduces tensile modulus to approximately 1300 MPa and increases Charpy notched impact strength to about 12–15 kJ/m². This plasticizing effect must be incorporated into snap-fit recovery force calculations and into dimensional inspections that compare dry and conditioned parts.

Rheological data for PA MACM12-I show a pseudoplastic melt without a crystallization plateau. Gate freeze-off is governed by vitrification rather than latent heat release, so holding pressure must be maintained until thermal arrest closes the gate. On a 25 mm single-screw injection unit with an L/D ratio of 20, the barrel zones are typically set in a reverse profile: feed 230 °C, compression 250 °C, metering 260 °C, nozzle 265 °C. A melt temperature of 250–280 °C and mold temperature of 60–90 °C are recommended for a balance between optical clarity and cycle time. Screw back pressure is set at 3–8 bar and screw surface speed below 0.2 m/s to limit shear heating. Shot size should remain at 40–70 % of barrel capacity to control residence time.

Residence time is a critical processing boundary. Above 300 °C, melt degradation begins within minutes; production trials typically set static residence alarms at 5–10 min. In hot-runner systems, stagnation zones at the nozzle tip or manifold end can produce yellowed material and black specks. A low-compression screw with a compression ratio of 2.0–2.5 and a free-flow check ring is preferred over high-shear barrier screws, which can generate excessive viscous heating and reduce optical quality. When barrel temperature is reduced for tinted material, injection pressure rises because melt viscosity increases; the machine must therefore have sufficient clamp force capacity to prevent flash at the higher viscosity.

Drying-Dependent Optical Defects in Thin-Wall Components

External and internal moisture in PA MACM12-I produces splay, silver streaks, haze, and microvoids during molding. At 23 °C and 50 % relative humidity, pellets can accumulate enough surface moisture to exceed the recommended residual moisture for optical molding within a few hours of ambient exposure. The manufacturer recommends drying in a dehumidified air dryer at 80 °C for 4–8 h to a residual moisture content below 0.10 %. The dew point of the drying air should be below -30 °C. Drying below 60 °C does not achieve the required moisture level within a practical cycle, while drying above 100 °C can oxidize the stabilizer package and shift natural color toward yellow. Dried pellets should be conveyed with dry-air hopper loaders and should not remain in open hoppers at high ambient humidity.

Moisture-related defects are often concentrated at the flow front and around the gate. In multi-cavity tools, one cavity may exhibit splay while another remains visually acceptable because of differences in fill pressure and venting. This batch-to-batch and cavity-to-cavity variance is reduced by controlling hopper residence time after drying and by using closed-loop material handling from dryer to press. Optical inspection under polarized light should be performed on first-shot samples because splay in transparent polyamide can appear as a diffuse haze rather than as a distinct surface mark.

When Mold Temperature and Injection Velocity Approach the Birefringence Threshold

In transparent polyamides, flow-induced orientation freezes into the part as birefringence when the solidification rate is faster than chain relaxation. Mold temperature in the 60–90 °C range is not used to induce crystallinity but to slow vitrification and permit orientation relaxation. At mold temperatures below 50 °C, rapid skin solidification traps molecular orientation and produces higher optical path differences under polarized light. The flow front velocity should be profiled between 100 mm/s and 300 mm/s in walls below 2.0 mm; lower velocities may create hesitation marks at weld lines, while higher velocities can cause shear spikes at the gate and visible gate blush. Gate land length should be 0.8–1.0 mm for the first 0.5 mm of the land to reduce jetting. Hot-runner valve-gate timing below 0.5 s is often required for parts with wall thickness below 1.0 mm; published data for this specific configuration is limited, but mold trials show that delayed gate closure produces localized flow marks and anisotropic shrinkage around the gate.

Draft angles of 0.5–1.0° are generally sufficient because of low shrinkage, but textured surfaces require an additional 1° per 0.025 mm of texture depth. Venting channels of 0.01–0.02 mm depth along the parting line prevent burn marks and localized degradation. For large transparent lenses, vacuum venting may be required to eliminate trapped gas and maintain optical clarity.

Total luminous transmittance is evaluated according to ISO 13468, and haze is evaluated according to ISO 14782 or ASTM D1003. At 2 mm thickness, the natural grade typically exhibits transmission above 90 % and haze below 2 %; these values are influenced by mold polish, pigment dispersion, and moisture-induced microvoids. A polished mold surface corresponding to SPI A-1 or equivalent is necessary to maintain optical clarity. A rougher surface scatters light and raises measured haze independent of the polymer matrix.

Addition of masterbatch concentrates based on PA 12 or PA MACM12 is required to avoid phase separation and haze. Masterbatch let-down ratios above 4 % can increase melt viscosity and alter visual color; the effect should be characterized by capillary rheometry according to ISO 11443 before production. Incompatible carrier resins such as EVA or PE can create visible gel particles and should be avoided. Copper halide heat stabilizers designed for semicrystalline polyamides may generate haze and are not appropriate for optical grades.

The resin is selected for eyeglass frames, safety eyewear, and sports visors where repeated flexural loading is evaluated according to ISO 178. Low density, flexural fatigue resistance, and resistance to skin sebum and cosmetic solvents provide a lower-mass alternative to polycarbonate in rimless designs. However, the material is not equivalent to polycarbonate in heat resistance; components exposed above 90 °C under load should be redesigned with increased section thickness or metal inserts.

Environmental stress cracking under external load is evaluated according to ISO 22088. Molded-in stress increases susceptibility to crazing in contact with sunscreen esters, strong alcohols, and polar aprotic solvents. Stress-relief annealing at 80–100 °C for 2–4 h lowers internal stress but can produce dimensional change; annealing fixtures must therefore match the final part contour. Parts with thick-to-thin transitions should be designed with generous radii to reduce notch stresses at the transition boundary.

For medical diagnostic housings and fluid-contact components, the grade is evaluated for cytotoxicity and skin sensitization under ISO 10993-5 and ISO 10993-10, but grade-specific biocompatibility documentation must be confirmed with EMS-Grivory before qualification. The resin withstands short-term contact with many aliphatic hydrocarbons and cleaning agents but is not recommended for use with concentrated mineral acids, phenols, or strong polar aprotic solvents. Compatibility with specific disinfectants should be tested according to ISO 175 under the expected exposure temperature and load.

Comparative Position Against Semicrystalline PA12 and Polycarbonate

Compared with semicrystalline PA12, PA MACM12-I offers optical transparency and lower anisotropy because it does not form spherulites during cooling. Standard PA12 has a density of 1.01–1.02 g/cm³ and is translucent in natural thick moldings, with crystallinity and haze increasing with slow cooling. PA12 offers higher elongation at break and lower water absorption at saturation, but its heat deflection temperature is often below that of PAMACM12-I unless annealing is applied. Because PA12 develops crystallinity, its mold shrinkage and post-mold shrinkage are generally higher and more direction-dependent.

Compared with polycarbonate, PAMACM12-I has a lower density: 1.00 g/cm³ versus approximately 1.20 g/cm³ for general-purpose polycarbonate. It also exhibits better resistance to many cosmetic oils and aliphatic hydrocarbons in molded parts. Polycarbonate provides higher tensile modulus, with general-purpose grades near 2350 MPa, and higher heat resistance, with typical heat deflection temperatures above 125 °C at 1.8 MPa. Polycarbonate is normally dried at 120 °C and molded at 280–320 °C, whereas PAMACM12-I can be dried at 80 °C and molded at 250–280 °C. The lower melt temperature and lower density can reduce energy input per kilogram, but the final selection depends on part geometry, cycle time, and post-process requirements.

In applications requiring chemical resistance to hydrocarbons or cosmetic formulations, PAMACM12-I may avoid the surface cracking sometimes observed in polycarbonate; however, published comparative data under ISO 22088 for this specific configuration is limited. Polycarbonate remains preferable where high heat resistance or high notched impact at sub-zero temperatures is the dominant requirement. Neither polymer should be used without defined drying and moisture-control procedures in optically critical parts.

In automotive interior optical sensor brackets, the material is processed with a valve-gated hot runner and a mold temperature of 70 °C. The low density reduces component mass, but the upper continuous use temperature is limited by the glass transition; short-term exposure to 120 °C is possible only for unloaded or lightly loaded parts and must be validated by heat aging according to ISO 188. In injection-molded spectacle fronts with metal hinge inserts, insert preheating to 80 °C prevents local cold-wall shrinkage and reduces cracking around the hinge boss. The hinge boss thickness should be at least 1.5 mm to provide sufficient hoop stress capacity for hinge pin insertion, and insert tolerances should be verified under dry and conditioned states because the polyamide absorbs moisture during use.