Arkema Rilsan BES BLACK PR PA11 is a black-pigmented polyamide 11 powder supplied for electrostatic spray, fluidized-bed immersion, and rotational lining of metal components. The base polymer is synthesized from 11-aminoundecanoic acid, which is obtained from castor oil; the carbon-black pigmentation and melt-flow additive package distinguish this grade from unfilled natural PA11 powders. Typical unfilled PA11 base-resin data include density of 1.04 g/cm³ when tested to ISO 1183-1, a peak melting temperature of 186 °C by differential scanning calorimetry under ISO 11357-3, and equilibrium water absorption at 23 °C of 1.8 % according to ISO 62. The exact apparent powder density, particle size distribution, and melt viscosity of the BES BLACK PR compound must be taken from the supplier batch certificate; published data for this specific compounded powder configuration are limited. The product is used where a black, chemically resistant PA11 film is required on metal substrates, particularly in automotive fluid fittings, pipe manifolds, outdoor furniture brackets, and hydraulic system components.

Material selection for corrosion-prone steel and aluminum parts frequently moves from PA12-coated or PA6-coated systems to PA11 because PA11 exhibits lower saturated water absorption than PA6 and a higher melting point than PA12. The BES BLACK PR grade adds carbon black, which increases opacity and ultraviolet absorption while reducing visible gloss. This is relevant for outdoor applications where color retention and resistance to chalking are evaluated by ISO 4892-2 and ISO 2810.

What Distinguishes Rilsan BES BLACK PR PA11 from Other Polyamide 11 Grades?

The base PA11 chemistry is common to several Arkema coating and molding grades, but BES BLACK PR is not a melt-processable pellet. Unlike Rilsan BESNO, which is supplied as pellets for extrusion and injection molding, BES BLACK PR is supplied as a dry powder with a fixed black pigmentation package. Direct melt feeding of the powder into single-screw extruders without densification is not recommended because the low bulk density, typically 0.40–0.50 g/cm³, produces entrapped air and unstable gravimetric feeding. The black pigmentation also reduces surface resistivity compared with natural PA11 powder. In electrostatic spray application, powder resistivity above 10¹¹ Ω·m is generally required for corona-charged guns; if carbon black content lowers resistivity below this threshold, transfer efficiency may decline and gun spitting can occur.

These comparative values are typical for unfilled base polymers and provide a relative ranking rather than a specification for the black powder compound. The carbon black and flow additives in Rilsan BES BLACK PR PA11 may slightly increase stiffness and reduce impact values compared with natural PA11. The supplier batch certificate remains the controlling document for the exact delivered compound.

On production-scale coating lines, the powder is applied to metal surfaces that have been degreased and grit-blasted to Sa 2.5 per ISO 8501-1. The cleaned substrate is heated in a convection oven to 250–300 °C; after removal, the part is either immersed in a fluidized bed or passed through an electrostatic spray booth with charging voltages of 60–80 kV. Film thickness is typically 150–300 µm, although thicker deposits are used for abrasion zones. The thermal energy stored in the substrate fuses the powder into a continuous film. In fluidized-bed lines, hopper air pressure and porous-plate pressure drop are adjusted until the powder bed expands to 2–4 times its settled height; the exact setting is grade-specific and must be established from the supplier particle size distribution. Moisture control is critical because PA11 powder stored above 60 % RH absorbs surface moisture that produces steam pinholes, foam cells, and intercoat delamination. Drying at 80 °C for 4 h in a desiccant dryer, or until the moisture content is below 0.15 %, is recommended before use. Published run-to-run variation on commercial fluidized-bed lines is most often driven by substrate temperature drop during transfer from preheat oven to coating station; maintaining transfer time below 10 s prevents crystallization-induced shrinkage differences.

When Outdoor UV Exposure and Salt Spray Resistance Determine Coating Selection

For exterior metal parts, the black pigmentation in Rilsan BES BLACK PR PA11 influences service life by absorbing UV radiation and by reducing photochemical chain scission at the coating surface. The relevant accelerated weathering condition is defined by ISO 4892-2 with xenon-arc light, 0.35 W/m² irradiance at 340 nm, and black-standard temperature of 65 °C. Published data for this exact grade are limited, but PA11 coating systems generally retain tensile elongation after 1000 h of exposure when the coating thickness remains above 150 µm. Salt spray exposure is conducted under ISO 9227 neutral salt spray; performance depends on film thickness, absence of pinholes, and adhesion. Adhesion is commonly evaluated by pull-off testing under ISO 4624, with production control values typically above 12 MPa on blasted steel. The black grade should not be selected when high gloss is required, because carbon black reduces specular reflectance; gloss measured at 60° under ISO 2813 is ordinarily below 30 GU. Solvent resistance is assessed by immersion in toluene or xylene at 23 °C for 24 h; PA11 coatings show mass increase below 1 %, while continuous exposure to concentrated formic acid or hot acetic acid above 60 °C causes surface attack and should be excluded.

Rheological and thermal parameters govern the processing window for BES BLACK PR PA11. Differential scanning calorimetry of PA11 shows a sharp melt endotherm at 186 °C and crystallization exotherm onset near 158 °C; the crystallization half-time at 180 °C is less than 1 min, meaning that substrate temperature must remain above the melt point until film coalescence is complete. In a parallel-plate rheometer at 230 °C and 1 rad/s, unfilled PA11 typically exhibits complex viscosity near 300 Pa·s; the carbon black and additive package in BES BLACK PR can raise this by 10–20 % depending on pigment dispersion. Shear thinning is pronounced, and the power-law index at 100 s⁻¹ is commonly between 0.6 and 0.8. The upper processing temperature is limited by oxidative degradation; residence time above 260 °C should be kept below 5 min to avoid yellowing and a drop in elongation at break. The lower limit for film formation is approximately 220 °C at the substrate surface; below this temperature, interparticle coalescence is incomplete and pinhole density increases. The temperature window is therefore narrow, and rework of partially fused films is not possible because reprocessing the powder after it has exceeded the melt point causes uncontrolled crystallization and particle agglomeration.

Rotational lining and electrostatic coating operations differ in their particle size demands. Fluidized-bed grades require a broad particle size distribution with fine particles to improve bed expansion; electrostatic spray grades require narrower distribution and controlled resistivity. BES BLACK PR is supplied as a black powder whose triboelectric and volume resistivity must be confirmed before electrostatic application because carbon black lowers surface resistivity. If powder resistivity falls below 10¹¹ Ω·m, transfer efficiency in corona-charged spray guns may decline; no single value applies to all humidity conditions. The supplier certificate should state the percentage retained on a 125 µm sieve and the fraction below 45 µm, because fines control edge coverage and film smoothness. On production lines, excessive fines can cause dust formation and gun spitting; coarse fraction above 250 µm can create melt-induced orange peel. These effects are batch-dependent and are best controlled by sieve analysis under ISO 2591-1 before charging the hopper.

Chemical Resistance, Impact Performance, and Regulatory Conformance

The PA11 backbone in Rilsan BES BLACK PR PA11 provides resistance to aliphatic hydrocarbons, diesel fuel, hydraulic oils, and zinc chloride salt solutions. Tensile property retention after immersion in ASTM D471 Reference Fuel C at 40 °C for 500 h is typically above 85 % for unfilled PA11. Low-temperature impact resistance of PA11 coatings remains measurable down to -40 °C, where notched Izod impact per ISO 180/A on the base polymer is approximately 6 kJ/m². The black compound, however, shows slight stiffness increase due to carbon black, and the exact value must be verified on the final coating. Compliance is not automatic and must be confirmed with the supplier for the specific pigment package; the matrix below lists the relevant regulatory texts and the conditions under which the product may be evaluated.