Arkema Rilsan Fine Powders T GREY 7452 PA11 is a polyamide 11 thermoplastic coating powder in the Rilsan Fine Powders series. The designation T GREY 7452 identifies a fine powder cut with a grey pigment package; the T cut is intended for thin-film electrostatic spray and fluidised-bed dip deposition where a controlled maximum particle size is required to obtain continuous films at dry film thicknesses below 150 µm. The base polymer, polyamide 11, is produced from 11-aminoundecanoic acid derived from castor oil. In unfilled form, Rilsan PA11 coating powders are characterised by a melting point of 186–190 °C measured by ISO 11357-3, a density of 1.04–1.06 g/cm³ measured by ISO 1183-1, and a water absorption at saturation of approximately 1.8–1.9 % under ISO 62. Published data for the exact pigmented T GREY 7452 grade are limited; batch certificates should be consulted for particle-size distribution, bulk density, pigment content, and rheological characteristics. The product is used in corrosion protection of carbon steel components such as dishwasher baskets, automotive brake tubing, outdoor furniture, electrical distribution hardware, and marine fittings. The final film thickness is normally verified by ISO 2178 on ferrous substrates and by ISO 2360 on non-ferrous substrates after cooling.

Because PA11 is thermoplastic, the coated film can be remelted and locally repaired. The grey 7452 colour package is intended for exterior exposure; colour retention is assessed by ISO 4892-2 or ASTM G154 depending on the specification. The powder is compounded in a co-rotating twin-screw extruder, then ground under cryogenic conditions and sieved. The resulting particle-size distribution is commonly measured by ISO 13320 on a laser diffraction analyser; fine powder cuts typically exhibit a d50 between 20 µm and 40 µm and a top cut below 100 µm, but the actual distribution for T GREY 7452 is batch-specific.

What distinguishes Rilsan PA11 from other thermoplastic powder coating media?

Comparative data for coating-grade PA11 and PA12 show that PA11 offers a higher melting point and a harder surface while retaining similar elongation. These differences affect process setup and service limits. Table 1 lists typical published ranges for Rilsan PA11 fine powder and a coating-grade PA12 reference; the PA12 column is not specific to any single Arkema grade and is included only for differentiation. Rilsan PA11 can also be distinguished from PA12 by monomer source: PA11 is obtained from castor oil-derived 11-aminoundecanoic acid, and renewable carbon content can be quantified by ASTM D6866 on the batch certificate; PA12 remains largely petrochemical.

Fluidised-bed deposition of the grey 7452 powder is conducted by preheating a steel or aluminium part to a metal surface temperature of 300–400 °C before immersion in a fluidised bed. The immersion time is normally 3–10 s; thicker deposits up to 500 µm are obtained on large thermal masses, while thin films of 80–150 µm are produced by electrostatic spray onto a part preheated to 200–260 °C. Post-fusion is completed at 190–230 °C until the coating develops a continuous film. Thickness is controlled by gravimetric deposition during dipping and is confirmed after cooling by ISO 2178 or ISO 2360. Adhesion on blast-cleaned steel prepared to Sa 2½ according to ISO 8501-1 is typically above 10 MPa in pull-off testing under ISO 4624 when a compatible primer is used; published data for the pigmented T GREY 7452 configuration is limited and should be verified on production parts.

Electrostatic spray application of T GREY 7452 is performed with corona charging guns operating at 60–100 kV; the powder is conveyed from a fluidised hopper to the gun with dried air at 0.5–3.0 bar and injected through flat-spray nozzles. The part is earthed through the conveyor; transfer efficiency is influenced by powder resistivity, which is measured by ASTM D257, and by the relative humidity of the booth. A low-resistivity powder that charges and releases too quickly can produce back-ionisation and orange-peel defects; a high-resistivity powder can build up excessive charge and produce uneven film build at recessed areas. Booth exhaust air is filtered and recirculated to maintain humidity below 50 %. Film thickness before fusion is measured gravimetrically; after fusion and cooling, final thickness is measured by ISO 2178 on a calibrated magnetic induction gauge.

Rheological and Thermomechanical Boundaries for Fluidised-Bed Deposition

The melting point of PA11 establishes the lower thermal limit for fusion. Below 186 °C, incomplete particle coalescence leaves voids and reduces adhesion; above 230 °C, oxidative yellowing and chain scission can occur in air. In a continuous fluidised-bed line, the furnace set point is therefore maintained within ±5 °C of the selected post-heat temperature to limit colour shift. For grey 7452, colour drift is monitored by CIELAB ΔE according to ISO 11664-4; a drift above ΔE 1.0 triggers recalibration of the heating zone. The powder does not crosslink because PA11 is thermoplastic; remelting above the melting point allows rework of deposited films, but repeated thermal cycles above 230 °C accelerate degradation. Twin-screw compounding of the pigment into the PA11 base resin is performed in a co-rotating extruder with a length-to-diameter ratio of at least 40:1 to disperse carbon black and inorganic pigments without excessive shear heating. After compounding, cryogenic grinding is used to obtain the fine powder cut; grinding chamber temperature is held below the glass transition region of PA11 to avoid particle deformation.

During post-fusion, the deposited layer undergoes a viscosity minimum that controls levelling. If the furnace temperature is too low, the surface remains undulating with a roughness exceeding 10 µm Rz as measured by ISO 4287. If the furnace temperature is too high, oxidation at the air-film interface raises the carbonyl index and shifts the grey colour toward yellow. For batch ovens, the load is arranged to avoid shielding the part and to restore the set-point within ±5 °C after door opening. Continuous ovens used for PA11 powder coating commonly have zoned infrared or convection modules; infrared modules are paired with convection to prevent overheating of thin edges. The exact dwell time is a function of metal thickness and film mass, not only oven temperature.

Moisture control is a critical boundary. At ambient relative humidity above 60 %, the powder should be dried to a residual moisture below 0.2 % by ISO 15512 before electrostatic spray or fluidised-bed loading. Undried powder at high humidity can form agglomerates, bridge in hoppers, or produce bubble defects in the fused film. The fluidised bed itself uses a porous membrane diffuser and dried compressed air; a bed height selected from vessel volume and part envelope is maintained with an air velocity sufficient for dense-phase expansion without slugging. The exact air velocity is determined by the fine-particle fraction; published data for T GREY 7452 is limited, so inline laser diffraction or sieve analysis at batch receipt is used to adjust the bed.

When T GREY 7452 Replaces a Solvent-Borne Anti-Corrosion Primer on Grit-Blasted Steel

On a production-scale line replacing a solvent-borne anti-corrosion primer, the carbon steel surface is first degreased, then blast-cleaned to Sa 2½ with an angular profile of 75–100 µm according to ISO 8501-1 and ISO 8503-2. A zinc-rich or adhesion-promoting primer may be applied and cured before PA11 deposition. The PA11 coating is then applied by fluidised bed or electrostatic spray and post-heated. The completed system is tested for thickness by ISO 2178, cross-hatch adhesion by ASTM D3359, direct impact by ASTM D2794, cupping flexibility by ISO 1520, and salt spray resistance by ASTM B117. Table 2 gives commonly specified acceptance criteria for Rilsan PA11 anti-corrosion coatings; the limits should be adjusted to the grey 7452 end-use specification.

In comparison to natural Rilsan Fine Powders PA11, the grey 7452 pigmented grade is formulated for exterior colour stability and opacity. It differs from thermoset epoxy and polyester powders because it remains thermoplastic, permitting local heat repair and rework, but the service temperature is limited to below the melting point. Continuous exposure above 100 °C in air can lead to progressive oxidative embrittlement; continuous contact with strong mineral acids, high concentrations of polar organic solvents above 50 °C, or oxidising agents is not recommended. The powder is supplied in batch-certified containers; storage temperature, moisture limits, and shelf life are stated on the certificate of analysis. For food-contact or potable water use, compliance with FDA 21 CFR 177.1500, EC 10/2011, or local positive lists must be confirmed for the exact grey 7452 formulation, because pigment additives may change the final compliance status. Product-specific particle-size, melt viscosity, and colour data for T GREY 7452 are limited in public documents, so qualification testing on the intended production line is required before use.