Key Takeaways
- Blends behave as neither parent polymer — the ratio changes marking behaviour materially.
- Both mark readily without an additive, because both are aromatic and char well.
- ASA replaces the butadiene phase with a weather-resistant acrylate rubber, which changes thermal response.
- Over-marking is the usual error, not under-marking.
Very little automotive interior or appliance plastic is a single polymer.
Polycarbonate–ABS
blends dominate instrument panels, pillar trim, housings and consoles because they combine
polycarbonate’s toughness and heat resistance with ABS’s processability and lower cost. ASA
appears wherever the same aesthetic is needed outdoors. Both mark well, and both are
routinely qualified as though they were their parent resins, which is where problems
start.
What the Blend Ratio Changes
PC-ABS is supplied across a wide range of ratios, commonly from around 50:50 to 70:30 in
favour of polycarbonate, and the ratio is frequently not stated on a drawing. It should be,
because it moves the marking result:
| Property | Higher PC content | Higher ABS content |
|---|---|---|
| Char yield and mark darkness | Higher — polycarbonate chars strongly | Good, but the butadiene phase degrades before the styrene does |
| Heat resistance during marking | Better — wider process window | Narrower; surface distortion at lower energy |
| Tendency to yellow around the mark | Moderate | Higher, from butadiene degradation |
| Stress crazing risk | Higher — polycarbonate is susceptible | Also present; ABS crazes with solvents |
| Typical use | Structural, higher-temperature parts | Cosmetic, lower-cost trim |
Two grades of “PC-ABS” from different suppliers can therefore need noticeably different
recipes. Treat the specific grade as the material, not the blend family.
ASA and Why It Is Specified
ASA is structurally ABS with the butadiene rubber phase replaced by an acrylate rubber. That
single substitution removes the weakness that limits ABS outdoors: butadiene is vulnerable to
ultraviolet attack, causing yellowing, chalking and embrittlement. ASA holds colour and impact
strength through weathering, which is why it appears on exterior mirror housings, grilles,
garden equipment and satellite dishes.
For marking, the practical differences are modest but real:
- Similar contrast behaviour to ABS, since the aromatic styrene and
acrylonitrile content is unchanged. - Slightly better thermal stability at the mark edge, because the acrylate
rubber degrades less readily than butadiene. - Weathering of the mark matters more, because ASA parts are specified for
outdoor service. A mark that is legible at assembly should be qualified after ultraviolet
exposure, not assumed permanent.
Marking Guidance
- Start low. Both blends char readily, so the risk is over-marking —
a brown halo, surface distortion or a degraded rubber phase around the feature. Begin below
the expected setting and work up. - Raise speed rather than cutting power when the mark is too aggressive,
which preserves definition while reducing energy. - Keep marks away from gates and weld lines. The polycarbonate content
brings stress
crazing risk, and crazing may appear hours or days after marking rather than at the
machine. - Qualify per colour. These blends are used in a wide colour range, and the
pigment package moves the result as much as the blend ratio does. - Check the flame-retardant variant separately. FR grades of PC-ABS are
common in appliances and electronics, and the FR package changes both absorption and char
behaviour. - Re-inspect after 24 hours during qualification, so delayed crazing is
caught before release rather than in the field.
Common Problems
| Symptom | Likely cause | Correction |
|---|---|---|
| Brown or yellow halo around the mark | Rubber phase degrading beyond the intended feature | Reduce energy and shorten pulse width to tighten the heat-affected zone. |
| Fine cracks appearing a day later | Stress crazing from the polycarbonate content | Relocate away from stress concentrations; consider annealing; reduce energy per pass. |
| Contrast differs between two “PC-ABS” grades | Different blend ratio or supplier | Expected. Qualify per grade rather than per blend family. |
| Surface gloss disturbed around the mark | Local softening — the ABS phase has a low softening point | Raise speed. On cosmetic surfaces qualify appearance as well as contrast. |
| Mark fades on an outdoor ASA part | Weathering of the marked region | Qualify after ultraviolet exposure rather than at assembly only. |
| FR grade marks differently from the standard one | Flame-retardant package altering absorption and char | Separate qualification; never infer from the non-FR grade. |
Decorating and Bonding These Blends
Marking is rarely the only downstream operation on an automotive or appliance part, and the
blends behave differently from their parents here too:
- Surface energy is moderate rather than low, so pretreatment is usually
about cleaning and consistency rather than raising energy from nothing as it is on
polypropylene. Verify with a
contact angle or dyne check rather
than assuming. - Solvent sensitivity is inherited from both parents. Cleaning agents and
adhesion promoters should be qualified against stressed samples, since both polycarbonate and
ABS craze under solvent contact when stressed. - Painting is common and generally successful, which is why these blends
dominate painted interior trim — but adhesion promoters are frequently still specified on
higher-ABS grades. - Plating is possible on higher-ABS grades, because the butadiene phase can
be etched for mechanical keying. Higher polycarbonate content reduces that capability.
Related Reading
- Acrylonitrile Butadiene Styrene (ABS)
- Laser Marking ABS Plastics
- Laser Marking Polycarbonate
- Laser Marking in Automotive
- Carbonization
Need help with this?
The Sabreen Group provides independent engineering support for marking qualification on engineering blends for automotive and appliance components. Our engineering services team works with manufacturers on process development, material qualification and production troubleshooting. Contact us to discuss your application.
Frequently Asked Questions
Does PC-ABS need a laser additive?
Normally not. Both parent polymers are aromatic and char readily, so PC-ABS gives good dark contrast under a fiber laser unaided. The engineering problem is restraint rather than absorption — over-marking produces a brown halo and disturbs surface gloss, so the recipe is usually developed downward from an over-aggressive starting point rather than upward from nothing.
Why do two PC-ABS grades mark differently?
Blend ratio, which is commonly not stated on a drawing. Grades range from roughly 50:50 to 70:30 in favour of polycarbonate, and higher polycarbonate content gives a higher char yield and a wider thermal process window while higher ABS content narrows it and increases yellowing around the mark. Qualify the specific grade rather than the blend family.
What is the difference between ABS and ASA for marking?
ASA replaces the butadiene rubber phase with an acrylate rubber, which is markedly more weather resistant. Marking contrast is similar because the aromatic content is unchanged, and edge quality is slightly better because acrylate rubber degrades less readily than butadiene. The important difference is downstream: ASA parts are used outdoors, so the mark should be qualified after ultraviolet exposure.
Why do cracks appear around marks a day after processing?
Stress crazing from the polycarbonate content, where thermal input from marking adds to residual moulding stress. It develops over time rather than appearing immediately, so a part can pass inspection at the machine and fail the next shift. Keep marks away from gates and weld lines, reduce energy per pass, and build a 24-hour re-inspection into the qualification.
Do flame-retardant PC-ABS grades mark the same way?
No. FR packages are common in appliance and electronics applications and they change both absorption and char behaviour, sometimes substantially. A recipe developed on standard PC-ABS can give quite different contrast on the FR version of the same grade, so qualify it separately and treat an FR package change as requiring requalification.
