Lexan Suffixes Explained: R, RU and A on a Polycarbonate Grade Code

Alphanumeric suffixes in polycarbonate grade codes are operational controls rather than arbitrary identifiers. Lexan™ PC grades derived from bisphenol A and carbonyl chloride or diphenyl carbonate exhibit a glass-transition temperature of 147°C, density of 1.20 g/cm³, and amorphous transparency. Typical unfilled PC properties include tensile yield of 60–65 MPa per ISO 527-2, notched Izod impact of 10–12 kJ/m² per ISO 180/1A, luminous transmittance of 88–91% per ASTM D1003 at 3.2 mm, and mold shrinkage of 0.5–0.7% per ASTM D955. The suffixes R, RU, and A encode the presence of release, UV stabilization, or application-specific stabilizer packages in the SABIC Lexan system.

Misreading an R-suffix resin as an A-suffix resin places an unstabilized or release-only formulation into exterior clear glazing. The failure is not immediate; it appears as accelerated yellowing, microcracking, and Izod impact loss after ultraviolet exposure. Conversely, specifying an A-suffix automotive lens grade for an indoor mechanical housing may add cost and introduce food-contact or optical qualification constraints that the component does not require.

On a 40:1 L/D twin-screw compounding line, the R suffix denotes an internal mold release package. The release agent lowers ejection force and reduces dependence on external mold release spray, but it also migrates to the part surface over time. That surface layer is a processing advantage and a bonding disadvantage. Flame treatment, corona discharge, or plasma cleaning is frequently required before silicone hardcoat, adhesive bonding, or metallization. The effect on cycle time is mold-geometry dependent; published data for this specific configuration is limited. Molding equipment parameters remain comparable across unfilled R, RU, and A grades: mold temperature 80–100°C, injection pressure 70–140 MPa, and clamp force of 5–8 kN per cm² projected area.

Does the R Suffix Change Drying and Melt-Flow Behavior Before Molding?

R-suffix PC is not exempt from the drying rules applied to unmodified polycarbonate. Desiccant drying at 120°C for 3–4 h to a maximum residual moisture of 0.02% is mandatory. A desiccant-wheel dryer with return-air dew point below -40°C can reach equilibrium moisture below 0.01% in 4 h. Water absorption at saturation can reach 0.35% per ISO 62, which is one reason pre-drying is non-negotiable. Residual moisture above 0.02% hydrolyzes the carbonate linkage in the melt, producing surface splay, molecular-weight loss, and notched Izod impact reductions measured by ASTM D256. Melt volume-flow rate remains the grade fingerprint; a medium-viscosity R-suffix resin typically exhibits 8–12 cm³/10 min at 300°C/1.2 kg when tested per ISO 1133-1:2022. The release package does not materially alter this rheology specification relative to an otherwise equivalent unreleased grade, but blending, compounding, and regrind use must be controlled because release agent concentration reaches the surface at low addition levels.

Reading the Two-Letter RU Designation in Clear Exterior Applications

RU-suffix grades combine the internal release function of R with a UV-stabilizer package. The UV-stabilizer function is not a pigment or light-diffusion additive; it absorbs or quenches ultraviolet energy in the 290–380 nm region that would otherwise initiate photo-oxidation at the polymer surface. Accelerated weathering evaluations are conducted under ISO 4892-2 or ASTM G155, with optical retention measured by ASTM D1003 luminous transmittance and ASTM E313 yellowing index. Acceptance limits are application-specific; published data for the exact threshold of every RU grade is limited. In clear multiwall sheet profile extrusion running a RU-suffix grade at melt temperatures of 260–290°C, the stabilizer package must survive short residence-time excursions and still provide outdoor weathering performance. Processors therefore avoid overheating hot spots, dead spots, and screw speeds that generate excessive shear heating. For unfilled PC, tensile yield remains in the 60–65 MPa range per ISO 527-2, but weathering retention rather than initial tensile strength is the critical specification for this suffix.

Thermal Residence and Molecular-Weight Drift in PC Molding

Injection molding of polycarbonate imposes a thermal residence limit. At a melt temperature of 310°C, residence beyond 6 min can shift molecular weight distribution enough to increase melt volume-flow rate and reduce impact strength. Barrel profiles are typically zoned from 280°C in the rear to 310°C at the nozzle for unfilled medium-viscosity grades. Mold temperatures below 80°C can increase frozen-in stress and reduce optical isotropy; mold temperatures above 100°C extend cycle time and can promote release-agent vaporization. Production equipment generally uses reciprocating screws with 20:1–25:1 L/D and 2.5:1 compression ratio. For a 25 mm screw, recovery speeds of 50–120 rpm are typical, but the specific speed must be adjusted to avoid excessive shear heating. Residence-time excursions are more severe in hot-runner systems with manifold temperatures above 300°C; these zones should be purged or shut down during line stoppages exceeding 5 min. Drying and thermal residence are deeper process conflicts than suffix variability: a well-stabilized A or RU grade will still yellow and embrittle if the moisture specification or residence limit is violated.

Solid sheet and multiwall sheet extrusion converts R, RU, and A suffix resins through a different thermal profile. Melt temperatures in the 260–290°C range reduce thermal degradation relative to injection molding, while die temperatures are maintained at 250–270°C. Roll-stack temperatures for sheet finishing are typically 110–130°C, and sheet thicknesses from 0.2 mm to 6 mm are produced. In sheet applications, the selection of a weatherable grade is driven by exposure classification: indoor glazing may accept an R-suffix PC, while exterior clear or translucent panels require a UV-stabilized suffix. Extrusion throughput and melt pressure stability depend on gear-pump control, screw cooling, and screen-pack selection; the additive package in release-modified and UV-stabilized grades can alter melt viscosity slightly, but the major process variables are temperature, screw speed, and regrind fraction.

When an A-Suffix Grade Is Specified for Automotive Exterior Lenses

In the Lexan 900 series, the A suffix appears on grades such as 943A and 945A. These are UV-stabilized, medium-viscosity polycarbonate formulations intended for injection-molded automotive exterior lighting. The A suffix in this series should not be treated as a generic abbreviation for UV stabilizer outside the automotive lighting datasheets. Mold temperatures for clear lens molding are maintained at 90–100°C, and filling speeds are set high to reduce weld-line visibility and gas traps. Projected area clamp force requirements remain 5–8 kN per cm². After molding, the release component can leave a surface layer that reduces adhesion of silicone hardcoats. Plasma or flame treatment is therefore used to restore surface energy before coating; surface-energy verification per ASTM D2578 is common. The A-suffix resin’s weatherability is assessed by accelerated weathering under ISO 4892-2 or ASTM G155, and optical clarity is measured by ASTM D1003. A downgrade to an R-suffix general-purpose PC without full requalification introduces a weathering failure risk in exterior lens applications.

Surface chemistry differences between an R-suffix release-modified grade and a weatherable A-suffix grade are measurable in the first 72 h after molding. Internal release agents migrate to the part surface as a function of time, temperature, and part thickness. A silicone hardcoat applied without surface activation can show adhesion failure at the PC-hardcoat interface. Surface energy testing per ASTM D2578 on an activated surface typically moves from below 34 mN/m to above 50 mN/m after plasma or flame treatment. In production, treatment is validated by peel adhesion after thermal aging per ASTM D3359 or a cross-cut tape pull. This is not a suffix-level problem alone; it is intensified by high mold temperatures, high release-agent loading, and long cooling cycles. Published data for specific release-agent migration coefficients in Lexan R and A grades is limited.

Because suffix semantics are contextual, suppliers’ datasheets and regulatory documents are the only valid source for a given base grade. R, RU, and A codes are not globally harmonized across all Lexan families, older GE Plastics legacy grades, or other polycarbonate suppliers. The matrix below lists minimum test and compliance standards used in suffix-selected PC applications.