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

Specify polycarbonate when a molded part must take impact, stay transparent, or survive temperatures that warp commodity plastics. It costs more than ABS and polyethylene, and it needs tighter process control from the molder. Place it in context with 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.

Bare polycarbonate has drawbacks in processing and surface hardness, so it is often blended. PC/ABS is an industry-standard alloy that lowers material cost and eases flow 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 need a secondary hard-coating operation, which adds 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 needs high melt temperatures. If a molder fails to dry it completely, polymer chains degrade in the barrel and mechanical properties suffer even when the part looks acceptable.

Common Applications

Polycarbonate is common where structural integrity and optical clarity both matter: 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 and breaks down the polymer. The part may show visual splay, but the more dangerous result is a large loss of impact strength. Ask your supplier how they verify moisture levels before molding PC.
• High processing temperatures. PC needs 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 needs diamond polishing (SPI A-1 or A-2). Gate locations and weld lines must be engineered to avoid visual defects.
• Design for flow. PC is highly viscous. Thin walls need adequate 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 much higher 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?

Use polycarbonate when impact or heat failure is unacceptable: safety glazing, automotive lenses, electrical housings (flame-retardant grades), medical equipment enclosures, and rugged devices. Choose it when ABS or PP cannot meet structural or thermal requirements.

What are the disadvantages of polycarbonate?

It scratches easily, so abrasive environments often need hard coats. Certain solvents and oils cause stress cracking. Sharp corners in CAD compromise toughness. It also needs strict drying before molding. Price those limits into the program before you award on toughness alone.

Why does polycarbonate need to be dried before molding?

PC is hygroscopic and absorbs moisture from ambient air. Moisture in the barrel triggers hydrolysis, which breaks polymer chains. Parts can look fine and still shatter under impact. Treat drying verification as a process control gate, not a preference.

What is PC/ABS and when is it used?

PC/ABS blends polycarbonate toughness and heat resistance with ABS cost and flow. It is a common default for consumer electronics, appliance housings, and automotive interior panels where pure PC is over-specified and pure ABS is insufficient. Prefer it when you need a middle path on cost and processability.

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.