Arkema Rilsan Fine Powders T SILVER 9108 is a polyamide 11 powder coating grade supplied as a silver-effect thermoplastic powder. The designation places it within the Rilsan Fine Powders range, in which the base polymer is a semicrystalline PA11 homopolymer synthesised from 11-aminoundecanoic acid. The silver code 9108 identifies a metallic pigment variant; the exact pigment composition, surface treatment, and bonding technology are proprietary. The material is intended for electrostatic spray or fluidized-bed application onto prepared metal substrates, followed by thermal fusion into a decorative and protective film without solvent. Product-specific datasheets are not fully reproduced in open literature, and the following discussion therefore draws on the documented behaviour of polyamide 11 base resin, standard coating practice, and the known boundary conditions for silver-pigmented thermoplastic powders. Arkema technical datasheets and safety data sheets remain the controlling documents for batch-specific values.

What Distinguishes PA11 from PA12 and PA6 in Corrosion-Resistant Coating Service?

Compared with PA12, PA11 has one fewer methylene unit between amide groups; compared with PA6, the amide concentration is substantially lower. The practical consequence is that saturated water absorption of PA11 is approximately 1.8–1.9% by mass under ISO 62, whereas PA6 typically absorbs 9.0–10.0% and PA12 approximately 1.5%. Dimensional change and plasticization caused by atmospheric humidity are therefore intermediate between PA12 and PA6, giving PA11 a balance of stiffness, chemical resistance, and dimensional stability. The melting peak of PA11 lies near 186–190 °C by differential scanning calorimetry under ISO 11357-3, which is higher than PA12 and lower than PA6. This thermal position allows PA11 coatings to withstand hot-oil, brake-fluid, and zinc-chloride salt exposure better than many lower-melting thermoplastics while still fusing at practical metal preheat temperatures.

Unlike thermoset epoxy or polyester powder coatings, Rilsan Fine Powders T SILVER 9108 does not form a film through curing or oxidative crosslinking. The fused layer is created by particle sintering and melt coalescence above the crystalline melt. The resulting film remains thermoplastic and can be remelted, which affects repair, recoating, and long-term service above the glass transition. This distinction is important when the coating is compared with crosslinked powders: thermosets may offer higher hardness at low film thickness, but PA11 delivers elongation, impact recovery, and abrasion resistance derived from its semicrystalline structure.

Silver-Pigment Dispersion and Electrostatic Transfer Boundaries

Metallic appearance in Rilsan Fine Powders T SILVER 9108 depends on flake orientation and the control of pigment segregation during transport and reclaim. In corona-charged electrostatic spray, the powder is charged by a high-voltage electrode and transported to a grounded part. Silver-effect pigments differ from natural or solid-colour polyamide powders in charge acceptance, shielding behaviour, and bulk resistivity. The measured transfer efficiency can shift when the ratio of reclaimed powder to virgin powder changes. Production lines using corona equipment typically observe that metallic flakes may concentrate in the recycle stream if the powder is not bonded or if the reclaim fraction exceeds the powder supplier’s specified limit. Excessive reclaim produces visible loss of metallic effect because flake content at the part surface no longer matches the formulated ratio.

Metal flake orientation is also sensitive to melt viscosity. Excessive oven temperature lowers melt viscosity and allows flake disorientation, producing cloudiness, mottling, or loss of brilliance. Insufficient temperature produces incomplete coalescence, visible orange peel, and low gloss. Industrial lines therefore control part surface temperature by pyrometer rather than relying solely on oven setpoint. The most common field defect in metallic electrostatic coating is edge-heavy film build, sometimes called picture framing. It is corrected by reducing gun current, increasing gun-to-part distance, or adjusting electrode air, not by adding more powder. Grounding resistance should be checked at the hook; values above 1 MΩ reduce the electrostatic field and lead to film thickness variation. Corona gun voltage in the range 80–100 kV is common for PA11 powder lines, but the exact setting must be mapped with charge-to-mass or transfer-efficiency tests for the silver-pigmented grade.

Incoming powder handling contributes strongly to batch-to-batch performance. PA11 powder is produced by cryogenic or low-temperature grinding, which generates irregular particles that fluidise well when the fines are controlled. Excessive fines below 10 µm reduce powder flow, increase dusting, and can clog electrostatic spray nozzles. Sieve residue and particle-size distribution should be verified per ISO 8130-2 or laser diffraction per ISO 13320. Published data for the silver-pigmented T SILVER 9108 configuration is limited, so incoming quality limits must be taken from the supplier-managed specification rather than from generic PA11 literature.

Adhesion testing of the fused film is normally performed after degreasing and abrasive blasting. On steel, a near-white blast profile with angular grit produces mechanical anchoring. A surface profile of 50–100 µm is common for heavy-duty PA11 coatings, but it must be matched to dry film thickness. If the substrate is not grit-blasted, PA11 can wet clean steel when the oxide layer is properly removed; however, neutral salt-spray resistance under ISO 9227 is strongly pretreatment-dependent. The film does not autonomously compensate for thin blast profiles, residual oils, or phosphate layers with low crystal density.

The silver-pigmented grade differs from natural Rilsan PA11 powders in that the visible metallic effect replaces translucency or solid hiding in non-metallic colours. In natural or partly pigmented grades, coating appearance can be thickness-dependent due to translucency. In T SILVER 9108, film thickness must be kept above the coverage threshold because silver flake orientation and hiding power are thickness-sensitive. Dry film thickness typically specified for PA11 electrostatic spray is 150–400 µm; for fluidized-bed immersion, 250–700 µm is common. Below the lower bound, the coating may expose substrate texture and lose corrosion resistance. Above the upper bound, the metallic flake can settle or disorder within the melt before solidification, producing a blotchy or grey surface. These limits are process-specific and must be adjusted with part geometry, oven recovery time, and desired salt-spray endurance.

When Fluidized-Bed Immersion Replaces Electrostatic Spray

Fluidized-bed dip coating of Rilsan Fine Powders T SILVER 9108 requires preheating the metal substrate above the PA11 melting point. The part is immersed in a fluidized powder bed, powder particles adhere by contact fusion, and the coated part is moved to a post-heat zone to complete coalescence. The fluidizing air must be dry and oil-free because moisture contamination creates surface craters and disrupts the film. Working lines typically set substrate preheat in the range 280–350 °C for steel sections; heavier sections require higher thermal mass or longer immersion than thin sheet. If the substrate preheat is too low, only a dusting of powder adheres and the film remains porous. If preheat is too high, the surface layer oxidises and the silver pigment dulls. The powder bed itself is normally maintained below the sintering point, often at 40–60 °C, to prevent clumping and to keep the bed homogeneous.

Immersion time is not a fixed value; it is derived from target thickness, part geometry, and substrate heat capacity. Production records for fluidized-bed PA11 show that an ambient temperature change of 10 °C is sufficient to shift the required preheat when the line lacks feed-forward pyrometer control. Operators must also monitor fluidization quality because channeling or slugging in the bed creates non-uniform thickness. The silver pigment may complicate fluidization compared with natural PA11 if the metallic flakes alter bulk density or powder cohesion, so the bed should be conditioned and the level verified before production runs.

Storage and Drying Requirements Are Not Ambient Defaults

Polyamide 11 powder absorbs atmospheric moisture. Bags should be resealed immediately after use and stored at 20–30 °C and 50% relative humidity or below. If the powder is exposed to ambient conditions above 60% relative humidity, it should be dried in a dehumidified hopper or oven before electrostatic spray. Moisture that reaches the melt stage flashes as steam and may cause microvoids, craters, or pinholes in the final film. Generic PA11 resin drying at 80 °C for 4–6 h is often cited for melt processing, but powder coatings have higher surface area and may require shorter times at lower temperature to avoid blocking. The powder should not be dried in a static oven bed thicker than 25–50 mm unless fluidised, because fusion can occur at particle contact points.

The material is not designed for direct application to untreated galvanised steel without zinc-phosphate or blasting. Adhesion to zinc surfaces is strong when the surface is prepared, but unetched zinc can act as a low-adhesion interface under wet conditions. The powder should not be blended with lower-melting thermoplastic powders that form an interlayer of reduced hardness or solvent resistance. Do not compound the powder with amine-based or strongly acidic additives unless formulated by the supplier because unexpected nucleating or degradation effects can shift crystallisation and film properties. Regulatory compliance for Rilsan Fine Powders T SILVER 9108 must be verified for the final article. The base PA11 homopolymer may be assessed under FDA 21 CFR 177.1500 for food-contact nylon resins; however, the silver pigment and additives are outside the scope of the base resin clearance. REACH and RoHS obligations depend on the downstream article and on the safety data sheet, not on the generic polymer type.

When coated parts are subjected to stone-chip impact, the test commonly specified is ISO 20567-1 or ASTM D2794 depending on the end-use specification. Abrasion resistance is assessed by Taber abraser per ASTM D4060; PA11 films at thicknesses above 250 µm generally show lower wear than thin thermoset powder films, but the silver pigment may influence the measured wear path and gloss retention. Gloss and metallic effect retention after accelerated weathering are evaluated by ISO 16474-2 or ASTM G154. Silver pigmented PA11 can darken if the outermost resin layer is removed by abrasion or if flake oxidation occurs during weathering. For exterior parts requiring long-term appearance retention, a clear polyamide or polyurethane topcoat is sometimes applied. Published data for T SILVER 9108 as a single-coat exterior metallic system is limited; performance claims must be subordinated to the Arkema technical datasheet and a statistically valid coated-panel programme.

In end-use replacement studies, Rilsan PA11 powder coatings are typically compared against PA12 powder, epoxy-polyester hybrids, and polyamide 11 liquid coatings. The fluidized-bed PA11 film provides higher abrasion resistance and stone-chip recovery than epoxy-polyester hybrids of equal dry film thickness, but it requires higher preheat and more aggressive substrate preparation. Against PA12, PA11 offers lower saturated water absorption and a higher melting point, but PA12 may show lower brittle-point sensitivity in extremely cold impact. Against liquid PA11 coatings, the powder process removes solvent incineration and permits thicker single-pass films. The selection of T SILVER 9108 specifically adds a decorative metallic surface to those service properties, with the operational burden of tighter reclaim control, pyrometer-based heat management, and batch-wise pigment dispersion verification.