Polycarbonate (PC) Injection Molding: A Buyer's Guide

Polycarbonate is specified when an injection-molded part must withstand impact, maintain transparency, or survive operating temperatures that deform commodity plastics. As an engineering resin, it commands a price premium over ABS and polyethylene, and it requires tighter process controls from the molder.

This guide outlines polycarbonate’s capabilities and constraints for buyers, placing it within the broader context of the material selection guide.

What Polycarbonate Is

Polycarbonate (PC) is an amorphous engineering thermoplastic. It is widely recognized under trade names like Lexan and Makrolon. Its defining trait is high impact strength combined with optical clarity and dimensional stability under heat.

Because bare polycarbonate has drawbacks in processing and surface hardness, it is frequently blended. PC/ABS is an industry-standard alloy that reduces material cost and eases flow into the mold while retaining much of PC’s impact resistance.

Why Buyers Choose PC

Characteristic	Engineering and Commercial Value
Very high impact strength	Yields rather than shattering under severe impact; excellent for housings and guards.
Optical clarity	Achieves high light transmission, allowing for transparent windows and lenses.
Heat resistance	Withstands continuous exposure to temperatures that warp ABS or PP.
Dimensional stability	Maintains tight tolerances under mechanical load and thermal cycling.
Flame retardancy	Readily available in V-0 rated grades for electrical compliance.

Where PC Falls Short

• Surface hardness. Bare PC scratches easily. Transparent parts subjected to wiping or abrasion usually require a secondary hard-coating operation, adding cost.
• Chemical sensitivity. PC degrades and stress-cracks when exposed to certain solvents, fuels, industrial cleaners, and adhesives.
• Notch sensitivity. Despite high overall toughness, sharp internal corners create stress concentrators that severely reduce impact resistance.
• Processing demands. PC is highly hygroscopic and requires high melt temperatures. If a molder fails to dry it completely, the polymer chains degrade in the barrel, ruining mechanical properties even if the part looks acceptable.

Common Applications

Polycarbonate is dominant in applications requiring structural integrity and optical clarity: safety shields, automotive headlamp lenses, ruggedized electronic housings, medical device enclosures, and power tool housings. Flame-retardant (FR) grades are standard for electrical components and battery enclosures.

What Buyers Should Know About Molding PC

• Drying discipline is mandatory. Water in the resin barrel causes hydrolysis, breaking down the polymer. The part may show visual splay, but the more dangerous result is a massive loss of impact strength. Ask your supplier how they verify moisture levels before molding PC.
• High processing temperatures. PC requires hot molds (often 80–110 °C) to minimize molded-in stress and fill thin sections.
• Tooling for clarity. If the part is transparent, the cavity requires diamond polishing (SPI A-1 or A-2). Gate locations and weld lines must be carefully engineered to avoid visual defects.
• Design for flow. PC is highly viscous. Thin walls require robust gating and high injection pressures.

Typical Processing Window

The processing window for polycarbonate reflects its engineering nature: high temperatures and strict moisture control.

Parameter	Typical range (unfilled PC)
Drying	~110–120 °C for 2–4 h (Critical; failure causes hydrolysis)
Melt temperature	~280–320 °C
Mold temperature	~80–110 °C
Mold shrinkage	~0.5–0.7%

These ranges represent unfilled, general-purpose grades. Glass-filled PC grades exhibit significantly lower, direction-dependent shrinkage. Confirm all parameters against the manufacturer’s datasheet.

How PC Compares

Compared to ABS, PC provides vastly superior impact strength, optical clarity, and thermal stability, but costs more and is harder to mold. PC/ABS blends offer a deliberate compromise between the two.

Compared to PMMA (acrylic), PC is much tougher and handles higher heat, but PMMA is clearer, harder to scratch, and naturally UV-stable. If a lens must survive a rock strike, use PC. If a lens must survive ten years of sunlight without yellowing, use PMMA.

Buyer FAQs

What is polycarbonate used for in injection molding?

Polycarbonate is specified for parts where failure is unacceptable under impact or heat. Common uses include safety glazing, automotive lenses, electrical housings (using flame-retardant grades), medical equipment enclosures, and rugged devices. It is chosen when commodity plastics like ABS or PP cannot meet structural or thermal requirements.

What are the disadvantages of polycarbonate?

Polycarbonate scratches easily, requiring expensive hard coats for abrasive environments. It is susceptible to chemical attack from certain solvents and oils, which causes stress cracking. It is also notch-sensitive, meaning poor CAD design (sharp corners) compromises its toughness. Finally, it requires stringent drying protocols prior to molding.

Why does polycarbonate need to be dried before molding?

PC is hygroscopic, absorbing moisture from ambient air. If moisture is present when the resin is heated in the injection barrel, a chemical reaction called hydrolysis occurs. This breaks the polymer chains, resulting in parts that look fine but shatter under impact. Proper drying is a non-negotiable process control.

What is PC/ABS and when is it used?

PC/ABS is a polymer blend that balances the extreme toughness and heat resistance of polycarbonate with the lower cost and easier processing of ABS. It is the default material for many consumer electronics, appliance housings, and automotive interior panels where pure PC is over-engineered and pure ABS is insufficient.

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts, sell materials, or certify suppliers. Material behavior is grade-specific; confirm properties and suitability against the manufacturer’s datasheet and your supplier’s engineering review.