Polycarbonate (PC): Policarbonato, Polycarbonate, and Lexan—The Spanish and Portuguese Buying Terms

Polycarbonate (PC), CAS 25037-45-0, is an amorphous thermoplastic produced by interfacial phosgenation of bisphenol A or by melt transesterification using diphenyl carbonate. Unfilled polycarbonate records a density of 1.20 g/cm³ under ISO 1183-1:2019, a refractive index of 1.586 under ISO 489:2022, and total luminous transmittance of 88–91% through a 3.0 mm plaque under ASTM D1003. General-purpose injection grades exhibit tensile yield stress of 60–70 MPa per ISO 527-1:2019, flexural modulus of 2350–2450 MPa per ISO 178:2019, and notched Izod impact of 650–850 J/m at 3.18 mm thickness per ASTM D256. Heat deflection temperature under 1.82 MPa is 124–132 °C per ISO 75-2:2013. In Spanish- and Portuguese-language purchasing channels, the polymer is identified as policarbonato, while the trademark Lexan is routinely inserted as a generic descriptor for clear sheet, rod, and engineering resin. Because Lexan denotes a specific SABIC product line, procurement documents should state “policarbonato/polycarbonate” as the polymer name and reserve Lexan only for qualified grade substitutions.

Melt flow rate reflects weight-average molecular weight in inverse relation. Extrusion blow-moulding grades are commonly supplied at 3–8 g/10 min, general-purpose injection moulding grades at 10–25 g/10 min, and thin-wall electrical grades at 30–60 g/10 min. The selected value modifies tensile elongation, notched Izod impact, and environmental stress-cracking resistance, with higher MFR lowering long-term ductility under constant strain.

What Limits Melt Processing Stability in High-Temperature PC Grades?

The apparent viscosity of unfilled PC at 300 °C and 100 s⁻¹ typically falls between 200 Pa·s and 400 Pa·s for a 10 g/10 min melt-flow grade; at 1000 s⁻¹ the value declines to less than 150 Pa·s. The shear-thinning profile is moderate compared with polyolefins, but high zero-shear viscosity generates significant frozen-in orientation when rapid cooling occurs. Thermal stability becomes the limiting parameter above 320 °C. Barrel residence time should not exceed 8–10 min at 300 °C; above 360 °C chain scission releases carbon dioxide and produces yellowing. On all-electric injection presses with 25–40 mm screw diameters, a shot size below 30% of maximum capacity can increase residence time to the point where MFR drifts upward by 2–3 g/10 min after 3 cycles. Branched grades used for sheet extrusion and blow moulding show stronger shear thinning and are less prone to draw-down sag but require higher melt temperature at 280–300 °C to fill complex profiles.

Hot-runner manifold temperature should be held at 290–310 °C. For optical parts, mould surface temperature uniformity should be maintained within ±5 °C across the cavity; a cavity surface of 90–110 °C reduces visible flow lines and delamination risk in clear lenses. Gate geometry is critical because polycarbonate freezes rapidly. Restricted gate diameters below 1.0 mm can create jetting and reduce weld-line strength by 20–30% relative to the nominal tensile value. Sequential valve-gate control is used on multi-cavity automotive lighting tools to manage flow-front meeting lines and prevent gas entrapment at high injection speeds.

Pre-drying becomes mandatory when storage relative humidity exceeds 60%. Unprotected PC reaches equilibrium moisture of 0.15–0.20%, while stable melt processing requires moisture below 0.02%. Desiccant dryers with dew-point delivery of −40 °C to −50 °C and inlet air temperature of 120 °C for 4–6 h are the standard configuration. In twin-screw sheet lines running at 500–800 kg/h, central drying systems from Motan, Conair, or Koch are set to deliver polymer at 100–110 °C directly to the feed throat. Moisture levels above 0.03% at 300 °C nucleate splay on the melt surface, reduce notched Izod impact, and produce an upward MFR shift that is measurable within 30 min of hopper residence after dryer breakthrough. In high-humidity subtropical plants, regrind above 40% should not be introduced without a real-time dew-point alarm and closed-loop hopper heater control. Failure modes observed on production lines include random hazing in transparent lenses, vent flow, and intermittent black specks when desiccant beds are not cycled at the press-side loader interval.

When Solvent Exposure Turns Residual Moulded-In Stress into Cracking

Polycarbonate resists dilute acids, aliphatic hydrocarbons, and water, but contact with ketones, aromatic solvents, chlorinated hydrocarbons, esters, and strong alkaline detergents initiates environmental stress cracking when the part carries residual moulded-in strain above 0.5–1.0%. The failure sequence is characterized under ISO 22088-2:2006 with constant-strain bending jigs and under ASTM D543 for chemical immersion. Medical device and automotive lamp suppliers report that cleaning with 70% isopropyl alcohol can trigger microcrazing on connector snaps if injection-moulded stress is not annealed. Continuous exposure to sodium hydroxide solution at pH >10 and 60 °C produces surface haze, reduction in transmission below 80%, and eventual embrittlement. Annealing at 120 °C for 2–4 h lowers frozen-in stress to below 5 MPa as measured by photoelastic fringe order and solvent immersion. Qualification of greases, adhesives, and disinfectants must be performed on the finished geometry rather than on unstressed plaques because stress concentration at gates and weld lines increases local strain by a factor of 2–3.

Injection moulding of unfilled PC operates with melt temperature 280–320 °C, mould temperature 80–120 °C, injection pressure 80–140 MPa, and hold pressure 60–80% of peak injection pressure. Clamp force calculations use 3–5 kN/cm² of projected area for parts with wall thickness between 2.0 mm and 4.0 mm. Reciprocating screws should have L/D ratios of 18:1–22:1, compression ratios of 2.0:1–2.5:1, and a low-shear general-purpose profile; high-compression or high-shear mixing elements increase frictional heat and create yellowing risk. Sheet extrusion uses single-screw extruders with 30:1–36:1 L/D, barrier screws, and polished three-roll stacks maintained at 120–150 °C for optical-grade film and sheet. Twin-wall or cellular sheet thermoforming is conducted at 180–210 °C, whereas solid sheet forms at 160–190 °C. Lexan-branded sheet is frequently specified in architectural glazing with thickness tolerances of ±5% and roll-stack gap control of ±0.05 mm. For glass-reinforced PC, cylinder temperatures are raised by 10–20 °C to reduce glass-fiber attrition, and mould steel must be hardened because 30% glass-filled grades generate abrasive wear on uncoated cores.

Mould shrinkage for unfilled PC is 0.005–0.007 mm/mm; glass-filled grades reduce shrinkage anisotropy to 0.001–0.003 mm/mm depending on fiber orientation. Venting depths below 0.02 mm are required to prevent gas burns at flow-front convergence. Warpage in large flat parts is managed by differential cooling rather than by increasing packing pressure alone, because overpacking raises residual stress and reduces environmental stress-crack resistance.

Policarbonato and Lexan Procurement Terms in Spanish and Portuguese Channels

In Spanish-language trade documentation, polycarbonate sheet appears as lámina de policarbonato, lámina compacta de policarbonato, placa de policarbonato, and plancha de policarbonato. Twin-wall glazing is listed as lámina alveolar de policarbonato, lámina celular de policarbonato, or policarbonato multicapa. Machinable stock is requested as barra maciza de policarbonato, tubo de policarbonato, and placa de policarbonato para mecanizado. Portuguese-language catalogs in Brazil and Portugal use chapa de policarbonato, chapa alveolar de policarbonato, chapa compacta de policarbonato, placa de policarbonato, barra de policarbonato, and tubo de policarbonato. The trademark Lexan appears in requests such as Lexan transparente, placa Lexan, and chapa Lexan, often without a manufacturer prefix. Buyers and suppliers in both linguistic zones should distinguish acrylic from polycarbonate by polymer name: Spanish acrílico and Portuguese acrílico refer to PMMA, not PC. Technical datasheets should carry the polymer descriptor PC or policarbonato, the melt flow rate under ISO 1133-1:2022, the UV stabilization package, and the relevant food-contact or flammability certification; reliance on the Lexan trade name alone is not an adequate procurement specification.

Food-contact polycarbonate is covered by FDA 21 CFR 177.1580 for resins and finished articles intended for repeated use, subject to end-testing for migration. European food-contact compliance requires conformity with Regulation (EU) No 10/2011 and its amendments; the specific migration limit for bisphenol A is 0.05 mg/kg under Commission Regulation (EU) 2018/213. The use of polycarbonate in infant feeding bottles is restricted in the European Union, and this restriction is reflected in procurement specifications for childcare articles. Medical applications reference USP 661.1 for plastic packaging systems and ISO 10993-5 for cytotoxicity. Flame-retardant grades are classified under UL 94; a V-0 rating at 3.0 mm or 1.5 mm is grade-dependent, and glow-wire ignition requirements are tested under IEC 60695-2-11. Compliance matrices for export typically include RoHS Directive 2011/65/EU and REACH SVHC disclosure. Table 2 summarizes the recurring certificates requested from material suppliers.

Transparent polycarbonate replaced glass in automotive headlamp lenses, lighting diffusers, electrical meter windows, and medical connectors because of high impact resistance and the ability to be injection moulded to optical surface tolerances. Hard-coated lenses are tested for abrasion under ASTM D1044 using CS-10F wheels for 100 cycles; acceptable coated parts show delta haze below 10%. Outdoor glazing requires UV-stabilized resin or a co-extruded cap layer; accelerated weathering under ISO 4892-2:2013 for 2000 h xenon-arc exposure typically allows colour deviation ΔE 3–5 and transmission loss below 5% for protected sheet. Electrical enclosure applications exploit the UL 94 rating and comparative tracking index above 250 V per IEC 60112. The operational boundary for unfilled PC under continuous mechanical load is 100–120 °C; above 135 °C creep modulus decreases sharply. Contacts with polyvinyl chloride plasticizers, aromatic solvents, and amine-cured adhesives should be excluded. Published data for certain highly specific configurations—such as long-term dry-arc tracking in polluted coastal atmospheres or sustained exposure to hydrogen peroxide plasma sterilization—is limited and must be generated by end-use qualification.