Created on 01.19
PET/PP Film Printing: Tuning IR for Different Substrates
PET and PP films can look similar on a press, but they behave very differently under an IR dryer. When operators use one “universal recipe,” the results are predictable: film waviness, shrink, gloss inconsistency, and intermittent blocking.
This guide shows how to tune IR drying for PET (BOPET) and PP (BOPP) using production levers you can actually control: web temperature limits, staged heating, zoning, airflow, tension, and surface treatment.
The two differences that matter most: thermal behavior and surface energy
1) Thermal behavior: PET stays dimensionally stable longer; PP softens early
Typical thermal values for oriented packaging films illustrate the gap:
- BOPET: glass transition ~70°C, melting ~260°C
- BOPP: glass transition ~-20°C, melting ~166°C
Why it matters on press:
- PP’s low Tg means it enters a more compliant/rubbery state much earlier, so tension, hot spots, and uneven heating show up as waviness or distortion sooner.
- With oriented films, you also need to respect thermal shrink tendencies; references for BOPP commonly show measurable shrink levels at elevated temperatures.
2) Surface energy: PP is “low surface energy,” PET is naturally higher
- Polyolefins like PP are low surface energy and difficult to bond/print without treatment (corona/plasma/flame).
- Untreated PET is commonly cited around 42–46 dyne/cm, and treatment raises it further for better wetting/adhesion.
- Practical printing targets by chemistry (example tables used in web converting) often recommend higher dyne ranges for PET than PP, especially for water-based systems.
IR drying on films: control the profile, not just the power
IR is widely used in plastics processing because it can deliver high power without contact and respond quickly.
But polymer films differ in how they absorb, transmit, and reflect IR—and the absorption coefficient is an established subject in polymer/IR research.
Practical takeaway:
- Your goal is not “hotter.” Your goal is repeatable evaporation with minimal web temperature gradients (cross-web and through-thickness).
PET vs PP: the on-press tuning differences (table you can paste)
What you’re tuning | PET film (BOPET) | PP film (BOPP) | What to do on press |
Dimensional stability | Better at moderate web temps | More prone to distortion under uneven heating | PP needs tighter guardrails on peak temp and edge-center delta |
Shrink sensitivity | Lower at a given temp (typical) | Higher shrink risk at elevated temps in many references | For PP, avoid front-loaded energy; use staged ramp + support |
Surface energy / ink wetting | Naturally higher; still often treated | Low surface energy; treatment is usually critical | Verify dyne level at unwind; re-treat if needed |
Primary failure mode | Blocking from incomplete through-dry at high speed | Waviness/shrink from hotspots + tension + early heating | PET: add mid/late drying capacity; PP: reduce peaks, improve uniformity |
Best control strategy | Stage IR + balanced airflow | Conservative early IR + stronger uniform airflow, more zoning | PP benefits more from zoning and airflow uniformity |
A practical setup that works for both (then you fine-tune by film)
Step 1 — Set temperature guardrails (edge/center matters more than average)
For films, record:
- Web temperature after each zone (edge and center)
- Edge–center delta (hot edges are a common distortion trigger)
- Rewind behavior after dwell (blocking and “post-curl/post-warp” can show later)
Step 2 — Use staged heating (avoid front-loading energy)
A robust starting profile for both PET and PP:
- Zone 1 (stabilize): low IR + good vapor removal
- Zone 2 (drive-off): medium IR (main evaporation work)
- Zone 3 (finish): medium-to-low IR, tuned for rewind stability
Why: staged delivery reduces the risk of “dry on top, wet underneath” and reduces localized overheating—particularly important for PP.
Step 3 — Airflow is a process tool, not just cooling
Airflow removes solvent/water vapor boundary layers and helps stabilize the web. Overdoing it can create edge cooling asymmetry; underdoing it can cause vapor saturation and slow drying.
Quick-start tuning rules (PET vs PP)
PET (BOPET) rules
- If you see blocking/smearing at rewind: move capacity to Zone 2/3 (don’t spike Zone 1).
- If gloss is inconsistent: check cross-web uniformity and airflow stability first.
PP (BOPP) rules
- If you see waviness/oil-canning: reduce peak intensity and fix hot spots with zoning; verify web support/tension.
- Treat PP as “low surface energy”: confirm dyne/treatment and storage aging effects; re-treat when required.
Commissioning workflow (repeatable, not trial-and-error)
- Lock your baseline: speed, tension, airflow, zone setpoints
- Map cross-web temperature (edge/center) and correct hot spots
- Increase drying capacity downstream first (Zone 2/3)
- Only then increase Zone 1, and only as much as needed
- Validate on a full roll, then re-check after dwell
PET/PP film printing commissioning checklist (continuous numbering)
PRE-RUN (Before you start)
- Identify the substrate: PET (BOPET) or PP (BOPP), thickness, and film orientation grade.
- Confirm surface treatment status and target dyne level (verify at unwind when possible).
- Confirm ink system and acceptance criteria for “dry” (smear test, blocking at rewind, odor/residual solvent, adhesion).
- Verify web handling fundamentals: stable tension setpoints, edge guiding, adequate web support through the dryer, and rewind settings.
COMMISSIONING (During setup/optimization)
- Start with a staged IR profile: keep Zone 1 conservative; build capacity mainly in Zone 2/3.
- Measure web temperature after each zone at edge and center; define max web temperature and max edge–center delta.
- Correct hot spots and lane differences with zoning (edge/center and coverage lanes) before increasing overall power.
- Tune airflow for vapor removal without creating edge cooling asymmetry; confirm exhaust path is stable (no short-circuiting).
STABILITY (To keep it consistent)
- Save a recipe per SKU/film lot: substrate type, thickness, dyne/treatment level, speed, zone setpoints, airflow, tension, rewind settings.
- Re-validate after film lot changes or seasonal ambient shifts using quick audits: temperature map + rewind quality (blocking/smear/waviness) + adhesion check.
FAQ
What’s the fastest diagnostic to tell PET vs PP tuning is the root cause?
If you switch from PET to PP and see a sudden jump in waviness/shrink sensitivity at the same recipe, you are likely exceeding PP’s practical process window (hot spots + tension + early heating), not “lacking power.”
Do I need corona treatment on PET as well?
Often yes, depending on ink chemistry and adhesion requirements. PET tends to start higher than PP, but treatment is commonly used to raise wetting/adhesion margins.
Why does PP distort even when the average temperature looks acceptable?
Because local peaks and cross-web gradients matter more than average temperature—especially when the film becomes more compliant at low Tg and under tension.
How does IR wavelength choice factor in?
Polymers differ in IR absorption and transmission; absorption behavior is studied in polymer IR literature and can materially affect heating uniformity. In practice, validate via web temperature uniformity and defect rate, not heater nameplate.
Call to action
If you share your film type (PET/PP), thickness, ink system, web width, target speed, and available dryer length, YFR can propose a zoned IR + airflow tuning plan (and layout) that hits speed targets without distortion or blocking.
Data sources
- Comparative thermal values for BOPET vs BOPP (Tg and melting point).
- Low surface energy definition and PP as a low surface energy polyolefin (bonding/printing difficulty).
- Recommended dyne/treatment ranges for printing/coating on PP and PET (process targets).
- PET surface energy and treatment guidance (typical untreated PET dyne levels; impact of treatment).
- IR heating applicability to plastics processing; polymer IR absorption considerations (background).
Last modified: 2026-01-19
Home
Home
Copyright © 2025 Huai'an Infrared Heating Technology. All Rights Reserved.
Address: No 148, huaihai east road, huai'an city, jiangsu, china
Phone / WhatsApp: +86-13852327847
Contact : Ryan Chou
Email: info@yinfrared.com
Product List
Product List
Subscribe
Subscribe
For inquiries about our products or pricelist, please leave to us and we will be in touch within 24 hours.
Quick Links
Quick Links
medium wave ir lamp
medium wave ir lamp
short wave ir heater
short wave ir heater
power control
power control
carbon ir heater
carbon ir heater
uv lamps
uv lamps
replacement ir lamps
replacement ir lamps
About Us
About Us
Products
Products
News
News
Contact Us
Contact Us