Polycarbonate (PC)

Definition

Polycarbonate (PC) is an amorphous, engineering thermoplastic made up of carbonate linkages (polyesters of carbonic acid), most commonly based on bisphenol A (BPA). It is known for an unusual combination of very high impact resistance, optical clarity, and heat resistance. PC typically has a high glass transition temperature (around 145–150 °C) and a relatively high heat deflection temperature for unfilled grades (about 120–140 °C). It is an excellent electrical insulator, inherently self-extinguishing (UL 94 V-2 without additives; V-0 achievable with flame-retardant formulations), and dimensionally stable. PC is hygroscopic and must be thoroughly dried before processing. It has only moderate scratch resistance and can be prone to environmental stress cracking when exposed to certain chemicals.

Key properties

  • Mechanical: Very high impact strength and toughness, good dimensional stability, low-to-moderate creep, good fatigue performance for clips and snap-fits.
  • Optical: High light transmission and clarity; optical grades can be molded to precise lens-quality surfaces.
  • Thermal: High Tg and good heat resistance; retains toughness over a wide temperature range.
  • Electrical: Good dielectric strength and insulation; FR grades can meet UL 94 V-0 and glow-wire/CTI requirements.
  • Weatherability: Baseline PC is UV-sensitive (yellowing and embrittlement over time); outdoor use typically requires UV stabilizers and/or hard coatings.
  • Chemical resistance: Generally good against dilute acids and alcohols; susceptible to attack or stress cracking from hydrocarbons, oils, esters, ketones, chlorinated solvents, and strong alkalis.
  • Surface: Moderate scratch/abrasion resistance; often improved with hard-coat or other surface treatments.
  • Processing considerations: Hygroscopic (must be dried), sensitive to molded-in stress (may benefit from careful mold temperature control and, for some applications, post-annealing).

Benefits and typical use cases

  • Benefits
    • Impact resistance and toughness: Provides shatter resistance superior to glass and many plastics.
    • Low weight with high strength-to-weight ratio: Enables lightweighting versus glass and metals.
    • Optical clarity and design freedom: Supports complex geometries, thin walls, and integrated features (e.g., clips, bosses, light guides).
    • Thermal/flame performance and electrical insulation: Suits many electrical and electronic components.
  • Representative applications
    • Automotive and mobility: Headlamp/taillamp lenses and bezels; LED/laser lighting optics; light guides; instrument cluster and display covers; sensor covers and radomes (RF-transparent); coated or laminated PC glazing for side windows, roofs, and sunroofs; interior trim; structural clips; battery module components such as cell spacers, covers, busbar and connector housings (with FR grades and blends).
    • Electrical/electronics: Housings and bezels, connectors, plugs and sockets, LED optics and light diffusers, chargers and power tool housings.
    • Building and safety: Extruded sheets and multiwall panels for glazing, skylights, machine guards, face shields, safety visors, riot shields.
    • Medical and consumer: Device housings, labware, durable consumer goods; historically optical discs and some refillable containers (subject to regulatory considerations for BPA).
    • Industrial: Transparent guards, manifolds, pneumatic components, jigs/fixtures requiring toughness and clarity.

Processing and finishing

  • Injection molding: Primary method for complex parts and optical components; requires thorough drying and controlled mold temperatures to minimize residual stress and ensure optical quality.
  • Extrusion: Sheets, films, and profiles; films can be used for film insert molding (FIM/IMD) and multilayer laminates.
  • Thermoforming: Forms large, complex 3D parts from extruded sheet (e.g., glazing, roof modules, machine guards).
  • Blow molding/injection blow molding: Used with select grades for hollow parts and ducts.
  • Overmolding and co-injection: Common for multi-material parts (e.g., PC/ABS housings), in-mold decoration, and functional integration.
  • Joining: Ultrasonic, vibration, hot-plate, and laser welding (with suitable absorbers); mechanical fastening; adhesive bonding and solvent welding are possible but require care to avoid stress cracking.
  • Surface treatments: Hard-coat, UV-resistant, abrasion-resistant, anti-fog, anti-glare coatings; painting and metallization are widely used for aesthetics and durability.
  • Additive manufacturing: High-temperature FDM/FFF PC filaments are used for functional prototypes and low-volume parts.

Grades, blends, and related terms

  • Common grades: Optical-grade PC, UV-stabilized PC, flame-retardant (FR) PC (including halogen-free), glass-fiber reinforced PC (GF-PC), impact-modified PC, antistatic/conductive PC, medical and food-contact grades, BPA-free and bio-based variants, and recycled-content grades.
  • Blends and laminates: PC/ABS (improved processability and low-temperature impact), PC/PBT or PC/PET (enhanced chemical resistance and dimensional stability), PC/ASA (weatherability), multilayer glazing laminates and coated stacks for exterior exposure.
  • Related materials: PMMA (better scratch resistance, lower impact), COP/COC (excellent optical purity, lower heat), PSU/PESU (higher heat, less optical clarity).
  • Trade names: Lexan (SABIC), Makrolon (Covestro), Panlite (Teijin), Trirex (Mitsubishi Engineering-Plastics).

Suitability for electric vehicle (EV) applications

  • Lightweighting and integration: Replaces glass and metal in lenses, glazing, and interior structures to reduce mass and enable large, integrated parts that improve assembly efficiency.
  • Electrical safety and enclosures: FR PC and PC-based blends are widely used for battery module components (e.g., spacers, covers), busbar and connector housings, and power electronics enclosures, meeting UL 94 V-0, CTI, and glow-wire requirements as specified.
  • Lighting, sensing, and HMI: Optical-grade PC supports advanced LED/laser lighting optics, radomes/camera covers, and large, curved display and touch interfaces that demand clarity and impact resistance.
  • Thermal considerations: While FR PC contributes to flame performance and electrical insulation, it is not a primary thermal barrier against battery thermal runaway; high-temperature or ceramic/mica-based materials are typically paired with PC where robust thermal shielding is required.
  • Sustainability: Availability of recycled and bio-based PC grades supports circularity; lightweight parts can contribute to improved vehicle energy efficiency.

Limitations and design considerations

  • Requires drying prior to processing; residual moisture causes splay and loss of properties.
  • Baseline PC is UV-sensitive and scratch-prone; exterior and glazing applications typically require hard-coat and UV stabilization.
  • Susceptible to stress cracking in the presence of certain solvents, fuels, oils, and strong alkalis; avoid incompatible chemistries and high residual stresses, and consider resistant grades or blends where needed.
  • Notch sensitivity and molded-in stress can reduce impact strength; use generous radii, avoid sharp corners, and manage gating and packing.
  • Regulatory: Many PC grades are BPA-based; selection for medical/food-contact applications must consider applicable regulations and approvals.

Synonyms and related terms

  • PC; FR-PC (flame-retardant PC); UV-stabilized PC; optical-grade PC; glass-filled PC; PC glazing; PC/ABS, PC/PBT, PC/PET, PC/ASA blends. Trade names include Lexan, Makrolon, Panlite, Trirex.

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