Arkema Rilsan Fine Powders T ALU 9115 SA is a polyamide 11 (PA11) fine powder formulated with an aluminum pigment package. The product belongs to the Rilsan Fine Powders T series, in which 9115 identifies the base PA11 grade and the ALU suffix denotes aluminum-pigmented construction. Published technical data for the aluminum-containing variant are less comprehensive than for the unfilled T 9115 SA base; where specific values are unavailable, reference should be made to the lot certificate or to Arkema technical service. The PA11 matrix is produced from 11-aminoundecanoic acid, a castor-oil-derived monomer, and is characterized by a density near 1.04 g/cm³ (ISO 1183-1:2019), a melting onset in the range 183°C to 188°C (ISO 11357-3:2018), and equilibrium water absorption of approximately 1.9% by mass at 23°C in water (ISO 62:2008). The fine powder form is intended for electrostatic spray and fluidized-bed deposition on metallic substrates, where the PA11 matrix provides resistance to abrasion, impact, and salt-spray exposure after fusion. The grade is not a structural molding compound; it is designed for coating thicknesses typically from 150 µm to 400 µm after cure.

What separates the aluminum-pigmented 9115 SA from the unpigmented T 9115 SA during corona charging?

In electrostatic spray application, the aluminum flake contained in T ALU 9115 SA modifies the charge acceptance and dissipation behaviour of the powder cloud. Powder particles acquire a negative charge from corona electrodes operated at 30 kV to 90 kV; metal flake increases the electrical conductivity of individual particles, which can depress the charge-to-mass ratio and increase the proportion of free ions reaching the grounded substrate. This effect requires adjustment of gun voltage or current limiting to prevent back-ionization and surface defects in thick films. Aluminum flake also increases the density and opacity of the deposited film; a single pass may produce a hiding dry film thickness of 80 µm to 120 µm, whereas the unpigmented T 9115 SA typically requires a heavier film for equivalent visual opacity. Because the flake can orient in the electrostatic field, film appearance and edge coverage are sensitive to electrode distance, transport air pressure, and substrate grounding. Published data for this specific configuration are limited; standard practice on production lines is to map deposition efficiency using powder resistivity measurements and to check film continuity on recessed areas according to ASTM D5162-15 or ISO 2178:2016.

Fluidized-bed immersion coating with T ALU 9115 SA is performed on metal parts preheated to 220°C to 260°C, depending on mass and heat capacity. The powder bed is fluidized with dry, oil-free air regulated to 0.3 bar to 0.7 bar through a porous plate; the bed density is maintained between 0.4 g/cm³ and 0.8 g/cm³ according to ISO 8130-9:1992. Substrates are first cleaned to Sa 2.5 (ISO 8501-1:2007) and, for severe corrosion service, treated with a zinc phosphate conversion layer or a suitable primer. After powder deposition, the coating is cured in a convection oven at 200°C to 230°C for 5 min to 10 min, with part metal temperature recorded by contact thermocouple. Pre-drying of the powder is required when storage relative humidity exceeds RH 60%; absorbed moisture reduces fluidization quality and can create pinholes or foam during fusion. Drying at 60°C to 80°C for 2 h to 4 h in a desiccant-air system restores flowability. Cross-contamination with epoxy or polyester powder must be avoided because the cure windows and air cleanliness requirements differ significantly, and mixed powders can generate intercoat adhesion failure.

Powder particle size distribution, bulk density, and deposition efficiency under corona charging

Laser diffraction data for T-series PA11 fine powders according to ISO 13320-1:2020 typically place the D50 between 35 µm and 45 µm; the D90 is commonly below 80 µm to allow smooth films at dry thicknesses down to 150 µm. The aluminum-pigmented grade may exhibit a slightly coarser tail because of flake-shaped pigment, so sieving through 125 µm mesh before charging is recommended on high-recovery cyclone systems. Table 1 compares the unfilled T 9115 SA base with the ALU-containing grade using typical values; these are not lot-certified data and must be confirmed against the certificate of analysis.

Deposition efficiency is not governed solely by particle size. Charge-to-mass ratio, powder resistivity, and carrier-air velocity determine whether the ALU flake accumulates evenly on edges and inside cavities. Production lines using corona guns with current limiting below 20 µA and substrate grounding resistance below 1 MΩ generally achieve more reproducible films; however, published data for this specific ALU configuration is limited, and first-article trials are required to set gun parameters.

When aluminum flake alignment changes moisture permeation and salt-spray resistance

After fusion, the aluminum flakes in T ALU 9115 SA orient predominantly parallel to the substrate surface when applied by electrostatic spray or fluidized bed. This lamellar arrangement increases the tortuosity for oxygen and water transport through the polyamide matrix; comparative permeation data for the unfilled base versus the ALU variant are not widely published, but industrial practice indicates that the metallic pigment reduces moisture vapour transmission and improves the resistance to blistering under immersion. On steel substrates, the same flake can alter local galvanic current paths if the film is cut back to bare metal in the presence of chloride solution. Salt-spray testing according to ISO 9227:2022 or ASTM B117-19 therefore requires scribe creep assessment according to ISO 4628-8:2012. The aluminum-pigmented grade is not a substitute for adequate pretreatment; zinc phosphate substrates tested with 240 h to 1000 h continuous salt spray show less scribe creep than the unpigmented PA11 only when the coating remains intact. Under cathodic disbondment conditions (ISO 21809-3 or ASTM G8-19), the presence of metallic pigment can alter the current paths and must be evaluated per specification.

Compared with PA12 fine powders, the PA11 matrix of T ALU 9115 SA has a higher melting point and a narrower preheat tolerance; PA12 powders typically require lower peak metal temperature because of the lower melting range near 176°C to 180°C. PA11 offers lower equilibrium water absorption than PA6 and PA66, which reduces dimensional change in humid service. Compared with an unfilled Rilsan Fine Powders T 9115 SA, the ALU variant provides a metallic visual finish and different barrier behaviour; however, gloss retention and colour stability are influenced by flake orientation. Unlike filled epoxy or polyester powders, PA11-based T ALU 9115 SA retains impact flexibility at low temperature, a property valued in coated automotive fluid-handling components and industrial equipment. The grade differs from coarse Rilsan PA11 powders intended for rotomolding or extrusion; the fine particle size distribution of the T series is optimized for thin-film electrostatic spray and fluidized-bed coating, not for thick-wall melt processing. If a high-build structural coating is required, a coarser PA11 powder or a PA11 granulate should be specified instead.

Thermal and rheological boundaries during coalescence

The PA11 base of T ALU 9115 SA begins to soften near 183°C and reaches full coalescence only when the metal surface remains above 210°C for a sufficient residence time. If the peak metal temperature exceeds 260°C, oxidative yellowing and chain scission can occur; if the temperature falls below 210°C, the powder particles retain their granular boundaries and the film develops pinholes. The practical processing window is therefore approximately ±5°C around the target part temperature for a given line speed. Infrared ovens and convection ovens used for this product must be mapped with thermocouples at the thickest and thinnest sections to ensure uniform heating. Melt flow index of the unfilled PA11 base at 235°C and 2.16 kg is commonly reported in the range 20 g/10 min to 40 g/10 min (ISO 1133-1:2022); the aluminum flake suppresses apparent flow and can require higher oven residence or slightly higher peak metal temperature. Post-fusion cooling should be controlled because rapid quenching creates fine spherulites and higher crystallinity but can increase internal stress; forced-air cooling at 5°C/min to 15°C/min is typical for flat parts, while thick substrates may be allowed to cool more slowly to reduce delamination at edges.

Compliance documentation for T ALU 9115 SA must be checked against the specific lot certificate because the presence of aluminum flake affects heavy metal reporting under RoHS Directive 2011/65/EU Annex II and may require EU REACH registration confirmation for coated articles. For potable water service, the coated component must be tested to NSF/ANSI 61 or AS/NZS 4020; the metallic pigment may not be accepted in all formulations. For food-contact applications, the PA11 base may be evaluated under FDA 21 CFR 175.300 and EU Regulation 10/2011, but the aluminum pigment and any processing aids require separate migration assessment. Table 2 lists the test standards most frequently cited for qualification of PA11-coated metal parts.

Storage of the powder should be in sealed moisture-resistant containers at 5°C to 30°C; opened material should be consumed within 6 months or re-dried before use. The ALU grade should not be processed in the same fluidized bed as iron-free or zinc-rich powders without complete cleaning because metallic pigment carryover can alter coating colour and electrochemical behaviour.