EMS-Grivory Grilamid® L 20 EC PA12-CD25 is an electrically conductive carbon black-modified polyamide 12 compound supplied in pellet form. The product identifier combines the PA12 base polymer “L 20” with the electrically conductive “EC” product class and the carbon black modifier “CD25.” The compound is used in injection-molded components for electrostatic dissipation and controlled grounding: fuel-system clips, sensor retainers, conveyor rollers, and enclosures for electronic manufacturing equipment. In dry-as-molded condition, the material exhibits volume resistivity in the range of 1 × 10¹ Ω·cm to 1 × 10³ Ω·cm and surface resistivity in the range of 1 × 10² Ω to 1 × 10⁵ Ω when evaluated with IEC 62631-3-1 and IEC 62631-3-2. The surface resistance is therefore below the 1 × 10⁶ Ω upper limit commonly applied to conductive materials for ESD control under IEC 61340-5-1, but final assembly performance depends on geometry, contact pressure, and environmental history.

The dry-as-molded mechanical profile is different from unfilled PA12 because the carbon black network raises modulus and reduces ductility. Supplier technical literature for this formulation class reports density of 1.10 g/cm³ to 1.25 g/cm³ per ISO 1183-1, tensile modulus of 1,500 MPa to 2,500 MPa per ISO 527-1/2, and Charpy notched impact strength of 3 kJ/m² to 8 kJ/m² per ISO 179-1/1eA. Elongation at break is typically between 3 % and 20 %. The melting peak of the PA12 matrix is 175 °C to 180 °C per ISO 11357-3, and the dry glass transition temperature is approximately 45 °C. After conditioning at 23 °C and 50 % RH, absorbed moisture plasticizes the amorphous phase and shifts the glass transition below 10 °C, lowering modulus and increasing impact toughness.

The conductive carbon black network requires a minimum part wall thickness to avoid through-plane resistivity gradients. In sections thinner than 0.8 mm, the probability of a continuous conductive path decreases and surface resistivity may rise by several decades. The supplier’s application guidelines recommend maintaining wall thickness above 1.0 mm for parts requiring uniform conductivity; thinner sections should be evaluated with a guarded electrode test under IEC 62631-3-2.

Before melt processing, the pellets require desiccant drying. A dry-air dryer with a dew point of −40 °C or lower and a bed temperature of 80 °C is used for 4 h to 8 h. Residual moisture should remain below 0.10 %; moisture levels above 0.15 % promote hydrolytic degradation during melting, which can reduce molecular weight, produce silver streaking, and disrupt the conductive network. Residual moisture should be verified by Karl Fischer titration according to ISO 15512. Dried pellets should not remain in an open hopper for more than 1 h unless the hopper is blanketed with dry air.

What Limits Melt Residence Time in Carbon Black–Modified PA12?

Injection molding is performed with cylinder temperatures from 220 °C to 260 °C and mold temperatures from 60 °C to 90 °C. The lower boundary is set by melt viscosity and carbon black dispersion; the upper boundary is set by thermo-oxidative chain scission and surface degradation. Cumulative melt residence time should not exceed 10 min at 240 °C or 5 min at 260 °C. A reverse barrel temperature profile is preferred to avoid excessive shear heating in the compression zone.

Because carbon black raises melt viscosity, the plasticating unit requires a longer screw recovery time than unfilled PA12. Back pressure of 0.5 MPa to 1.5 MPa improves homogenization; pressures above 2.0 MPa can cause local overheating and degrade the carbon black network. Injection speeds should be moderate to high to prevent gate freeze-off, but linear velocities above 200 mm/s may produce jetting and surface defects. Tooling should use edge gates of 1.0 mm to 1.5 mm for wall sections of 2 mm to 3 mm, and direct gates should maintain a diameter of at least 50 % of nominal wall thickness.

Molding shrinkage is anisotropic because carbon black particles orient during flow. Longitudinal shrinkage is commonly 0.4 % to 0.8 % and transverse shrinkage is 0.6 % to 1.2 % per ISO 294-4. Weld lines are electrically weak points: surface resistivity across a weld line can be 1 to 3 decades higher than the bulk value. Gate locations should therefore avoid placing weld lines in grounding paths or across conductive contact surfaces. Carbon black-filled polyamide is also abrasive to tooling steel; nitrided or hardened inserts are recommended for high-volume production.

Humid Ageing and Surface Resistivity Recovery

Moisture uptake in PA12-CD25 is lower than in PA6 but remains a design variable. At 23 °C and 50 % RH, equilibrium moisture content is approximately 0.5 % to 0.8 % by mass per ISO 62. The absorbed water plasticizes the polyamide matrix, reducing tensile modulus by 10 % to 20 % and increasing Charpy impact relative to dry-as-molded values. Dimensional growth after conditioning is typically 0.1 % to 0.3 % and must be included in press-fit and bearing clearance calculations.

Electrical resistivity is more sensitive to moisture than mechanical properties. Water-induced swelling separates carbon black aggregates and increases surface resistivity by 1 to 3 decades in severe humid environments. Re-drying at 80 °C for 4 h can partially restore conductivity, but repeated moisture cycling or hydrolytic matrix damage can create permanent network disruptions. Parts intended for condensing environments should be electrically qualified after damp-heat ageing at 85 °C and 85 % RH per IEC 60068-2-78, not only in dry-as-molded condition.

The following indicative property ranges apply to injection-molded test specimens conditioned at 23 °C and 50 % RH unless otherwise noted. They are compiled from supplier technical literature and are not design allowables.

All electrical values are measured after conditioning per ISO 291 at 23 °C and 50 % RH for 48 h. The electrification time is 60 s and the applied voltage is 100 V DC for resistivity testing. Lower voltages may produce unstable readings on conductive compounds because contact resistance dominates.

The principal difference between Grilamid L 20 EC PA12-CD25 and unfilled Grilamid L 20 is the percolating carbon black network. Unfilled PA12 has a surface resistivity above 1 × 10¹³ Ω, while the conductive grade operates in the 1 × 10² Ω to 1 × 10⁵ Ω range. The network raises tensile modulus and melt viscosity, reduces elongation at break, and imparts isotropic conductivity in molded parts. Carbon fiber–filled PA12 can provide lower surface resistivity and much higher modulus, but its conductivity is flow-direction-dependent and drops significantly across weld lines; carbon black-filled PA12 retains more uniform conductivity in all directions and offers better surface finish for sliding contact parts.

Replacing a machined metal housing with conductive PA12 reduces mass by approximately 80 % to 85 % compared with steel of density 7.85 g/cm³. The polymer is not a structural earthing conductor and cannot carry fault current; it is limited to static dissipation and low-energy discharge paths. Grounding contact geometry must be sized to maintain the required surface resistance of the assembled part, and metal inserts may be required at connection points. Compared with PA6 conductive grades, the PA12 backbone reduces equilibrium moisture absorption and improves dimensional stability in humid environments but provides a lower deflection temperature under load. The HDT at 1.8 MPa is typically 50 °C to 60 °C per ISO 75-1/2, so load-bearing parts at elevated temperature require design verification.

The comparative matrix below is intended for preliminary material selection and assumes dry-as-molded test specimens.

The PA12 matrix provides resistance to aliphatic hydrocarbons, automotive fuels, oils, and glycol-based coolants, but strong mineral acids and polar solvents can swell or degrade the surface. The carbon black filler may increase solvent uptake at the surface and create conductive paths that are affected by fuel soak. Components in continuous fuel contact should be tested for extraction and electrical stability according to the relevant automotive specification, such as ISO 16750-5 for chemical loading.

Regulatory status should be confirmed from the supplier’s product data sheet. Conductive PA12 compounds based on carbon black are generally outside food-contact approval when loaded with conductive carbon black; if food contact is required, a specific food-compliant grade should be selected. For components used in potentially explosive atmospheres, equipment-level certification requires surface resistance testing on finished components according to EN IEC 60079-0. The material should be evaluated for creep, chemical resistance, and electrical performance after exposure to all service fluids and cleaning agents. Recycled material can be added at levels up to 20 % by mass without eliminating the conductive network, but higher regrind fractions may increase surface resistivity variability and should be qualified by production-scale trials.