Polycarbonate (PC): Exolon, Makrofol and the Other Polycarbonate Brands Met in a Specification

Polycarbonate based on bisphenol A is an amorphous engineering thermoplastic with a glass transition temperature of approximately 145 °C to 150 °C and a density of 1.20 g/cm³ when determined in accordance with ISO 1183-1. The polymer is produced by interfacial polymerization of bisphenol A with phosgene or by melt transesterification using diphenyl carbonate; the resulting bisphenol A carbonate backbone provides transparency, dimensional stability and creep resistance below the glass transition region. In specification practice, brand names such as Exolon, Makrofol, Makrolon, Lexan, Calibre, Panlite, Tarflon and Iupilon appear as grade or conversion constraints rather than generic material identifiers. Exolon is an extruded polycarbonate sheet brand; Makrofol is a polycarbonate film brand supplied by Covestro; Makrolon and Lexan are established pelletized resin designations for injection moulding and extrusion. The designation system for polycarbonate moulding and extrusion materials is covered by ISO 7391-1, which provides classification blocks for viscosity, impact and temperature resistance independently of trade names.

A specification requiring a clear polycarbonate film or sheet may call out Makrofol DE 1-1 or an Exolon sheet product because such designations impose defined optical, surface, thickness-tolerance and thermoforming requirements that are not assured by an unbranded polycarbonate resin description. When a brand is named in a specification, the verifier must identify the corresponding grade family and test data rather than assuming that all products under a broad brand are interchangeable. This distinction is particularly important in exterior glazing, medical device housings, electrical enclosures and printed film applications where performance boundaries are process-sensitive.

Which Test Methods Control Acceptance of Unfilled PC Sheet and Film?

Acceptance of unfilled polycarbonate sheet and film is normally anchored to mechanical, optical and thermal test methods. Test specimens are injection-moulded as multipurpose specimens according to ISO 294-1 for the ISO method set. Table 1 lists typical values for unfilled bisphenol A polycarbonate; a given branded grade may fall outside a listed range due to molecular weight, additive package or conversion process.

The notched impact values depend strongly on notch radius, molecular weight and moisture conditioning. A high-flow grade with a melt volume-flow rate of 20 cm³/10 min generally exhibits lower notched impact than an extrusion grade with a melt volume-flow rate below 6 cm³/10 min, because higher flow corresponds to shorter average chain length. This relationship explains why an Exolon sheet specification may require a melt volume-flow rate below 6 cm³/10 min to maintain thermoforming melt strength and extruded-sheet toughness.

Residual Moisture, Melt Temperature and Extrusion Geometry

Polycarbonate is susceptible to hydrolysis during melt processing. Residual moisture must be reduced to below 0.020 wt% before injection moulding or sheet extrusion. Predrying is typically performed at 120 °C for 4 h to 6 h in a desiccant dryer with an inlet dew point of -40 °C or lower. Moisture above this threshold produces splay, silver streaks and molecular weight reduction; the resulting loss of intrinsic viscosity is measurable through ISO 1628-4. Production-scale sheet extrusion of polycarbonate commonly uses a single-screw machine with an L/D ratio of 30:1 to 33:1, a barrier screw and vacuum venting. Melt temperature at the sheet die is generally held at 260 °C to 280 °C, while injection moulding operates at 280 °C to 320 °C.

The melt-processing window is narrow. Below 270 °C, melt viscosity is high and short shots or elevated injection pressure become more frequent; above 330 °C, thermal yellowing and carbonate-chain scission intensify. Processors therefore use melt volume-flow rate under ISO 1133-1:2022 as a grade-selection variable rather than as a universal quality limit. Injection grades frequently fall between 6 cm³/10 min and 20 cm³/10 min, while sheet and film extrusion grades are commonly specified at 3 cm³/10 min to 8 cm³/10 min to retain molecular weight and melt strength.

Flame-retardant polycarbonate compounds are produced on co-rotating twin-screw extruders with L/D ratios of 32:1 to 44:1. Phosphate-based or other flame-retardant additives are dispersed under controlled specific mechanical energy; poor dispersion can shift flammability performance even when total additive loading remains unchanged. Melt filtration and screen-changer designs are also critical for optical sheet and film grades because entrapped degraded gel or carbonized specks reduce transmission and haze.

In injection moulding of a flanged enclosure with a nominal wall thickness of 3.2 mm, mould temperature is commonly held at 80 °C to 120 °C and injection pressure is usually 80 MPa to 140 MPa. Mould temperatures below 70 °C are associated with elevated residual stress and reduced impact performance measured by ISO 179-1/1eA. The same component moulded at 70 °C and at 95 °C can differ significantly in notched impact energy even when tensile strength remains inside specification. The production conflict is with cycle time: higher mould temperature reduces orientation stress but lengthens cooling time, and wall sections above 4 mm extend the cooling cycle disproportionately.

When a Drawing Substitutes Makrofol for an Unbranded Polycarbonate Film

Makrofol grades are specified where the converter requires a defined film thickness, surface texture and thermoforming response over long production runs. Film thicknesses are commonly supplied from 125 µm to 1000 µm, depending on grade, and the material is converted by die cutting, bending, screen printing, lamination and thermoforming. A clear grade for a display lens or graphic overlay is normally checked for light transmission according to ISO 13468-2 and haze according to ASTM D1003; values of 89 % to 91 % transmission and <1.5 % haze are typical for uncoated clear film. Hard coats, anti-fog layers or UV-cured inks alter both optical and surface-energy conditions.

The substitution of an unbranded polycarbonate film by a Makrofol grade becomes significant where ink adhesion and dimensional stability are tested. Print adhesion may be assessed by cross-cut classification according to ISO 2409 after UV-cured ink on untreated or primed film. In-mould-decorating processes may require film shrinkage after 2 h at 80 °C to remain within a specified percentage. Published data for specific Makrofol configurations in deep three-dimensional forming is limited because draw ratio, corner geometry, pre-stretch speed and local sheet temperature dominate thickness distribution and surface-crack formation.

Exolon sheet stock is encountered in architectural glazing, machinery guarding, skylights and formed sign applications. The extrusion process for UV-protected polycarbonate sheet coextrudes a concentrated ultraviolet absorber layer on the exposed surface; the cap layer retards yellowing and impact-strength loss caused by weathering. Linear thermal expansion from 65 × 10⁻⁶ K⁻¹ to 70 × 10⁻⁶ K⁻¹ as measured by ISO 11359-2 requires an expansion allowance of approximately 0.65 mm/m for every 10 K temperature rise. Solid polycarbonate sheet specifications may additionally reference ISO 11963 for classification by thickness, light transmission, impact resistance and dimensional tolerance.

Installations with fixed bolted connections must avoid rigid clamping that constrains sheet movement. Field failures have been documented as stress cracks radiating from fastener holes after repeated thermal cycles when holes were undersized or when no expansion clearance was provided. Published data for specific Exolon sheet constructions under partial shading is limited because differential thermal expansion creates localized bending stresses that cannot be predicted from uniform-temperature laboratory tests alone.

Flame, Glow-Wire and Accelerated Weathering Data Across Commercial Grades

UL 94 classification for polycarbonate is grade-dependent and thickness-sensitive. Many unfilled transparent polycarbonate grades achieve V-2 at 1.5 mm; V-0 at 3.0 mm usually requires flame-retardant additives that can reduce clarity and alter melt rheology. The material must be assessed at the actual minimum part thickness because thickness reductions can alter the UL 94 class. For electrical and electronic parts, glow-wire flammability is assessed by IEC 60695-2-12 and glow-wire ignition temperature by IEC 60695-2-13. Material certification to these tests should be obtained for the specific grade and wall section rather than assumed from a general product brochure.

Accelerated weathering of UV-stabilized polycarbonate sheet is commonly performed by xenon-arc exposure according to ISO 4892-2 or ASTM G155. Yellowing index is measured by ASTM E313 or ISO 17223. Uncapped polycarbonate exposed to xenon light at 65 °C black-standard temperature and 65 % relative humidity shows appreciable yellowing within several hundred hours, while UV-capped sheet retains higher transmission. However, published data for specific Exolon sheet constructions across all real-world solar cut-off and moisture conditions is limited, and outdoor exposure at the intended orientation remains necessary for service-life validation.

Where aggressive cleaning agents or industrial fluids are present, polycarbonate must be evaluated for environmental stress cracking. Ketones, esters, aromatic hydrocarbons, chlorinated solvents, amines and strong alkaline solutions are documented stress-cracking agents for unfilled PC. Amine-based mold releases or amine-containing adhesives should not be specified unless compatibility has been verified by ISO 22088-2 or an equivalent constant-strain method. In medical equipment, disinfectants containing strong bases or aromatic hydrocarbons can cause crazing when moulded-in stress from low mould temperature is already present. The operational boundary is therefore not only chemical resistance but the combined effect of stress magnitude, chemical environment and exposure duration.