Polyester Film Melting Temperature Technical Data
Conventional PET and BOPET films commonly show a polyester film melting temperature of about 245-260 C by DSC. The reported onset, peak, or endset varies with grade, orientation, thermal history, and scan conditions. Use it for base-film identification, not as a finished-film service limit. Confirm adhesive, coating, surface, dwell, and removal behavior under intended conditions.
The Number on a DSC Report Is Not a Use Temperature
This data applies to PET and BOPET base films, treated films, and PET-based adhesive protective-film constructions. It supports DSC reporting, grade comparison, and heat-exposure review. Projects requiring controlled shrinkage or modified thermal behavior should assess PET functional film grades separately.
A DSC peak is not a continuous operating temperature. PET may shrink before melting, while adhesive, primer, coating, ink, or liner may change earlier. Do not apply these values to PETG, PEN, PBT, or unidentified copolyesters.
Which Layer Is Actually Being Measured?
A protective film may include treatment or coating, PET/BOPET base film, primer, pressure-sensitive adhesive, and liner. DSC records all sampled layers, so bare-film and finished-construction results are not interchangeable.
Record film thickness and total thickness separately. Color, fillers, recycled content, and coating chemistry can alter heat flow or peak shape. Compare the substrate transition with thickness, clarity, haze, and mechanical data for transparent PET film. Where DSC is used to investigate unknown metallized production scrap, combine the thermal result with construction records and recycler requirements; see the metallized PET scrap identification and recycling guide for the full qualification workflow.
Thermal Reference Data and Reporting Status
Item | Typical Value / Reference Range | Test Method or Condition | Notes |
Material and construction | PET/BOPET; project-confirmed layers | Declaration and sample record | State bare film or finished construction. |
Typical melting region | Approx. 245-260 C reference | DSC with stated program | Not a batch or service guarantee. |
Onset / peak / endset | Report separately | ASTM D3418-21 or ISO 11357-3:2025 | Do not compare unlike points. |
First / second heating | Both when history matters | Controlled heating, cooling, reheating | Do not combine in one limit. |
Thermal shrinkage | Project-confirmed MD/TD value | Agreed temperature and dwell | May matter far below melting. |
Peel, mechanical, optical data | Tested grade or approved sample | Actual substrate and agreed methods | Depends on construction, surface, and storage. |
Reconstructing the DSC Test
Record specimen identity, mass, pan, atmosphere, temperature program, heating and cooling rates, and scan cycle. ASTM D3418-21 and ISO 11357-3:2025 cover polymer transitions and melting or crystallization enthalpy.
Test Item | What It Checks | Suggested Method or Reference | Why It Matters | When To Request It |
DSC analysis | Melting event and enthalpy | ASTM D3418-21 or ISO 11357-3:2025 | Defines the reported transition | For identification or grade comparison. |
First and second heating | As-received and reset thermal history | Record heating and cooling rates | Explains curve differences | When data sources disagree. |
Thickness and layers | Film, total thickness, and structure | Calibrated gauge; layer record | Prevents bare-film data misuse | For coated or adhesive film. |
Thermal shrinkage | MD/TD dimensional change | ASTM D2732 or agreed equivalent | Predicts pullback and wrinkles | When heating or drying occurs. |
Peel and dwell | Adhesion build-up and removal | Actual surface; agreed peel; 24 h, 72 h, 7 days | Connects data to use | Before sensitive or coated surfaces. |
Mechanical and optical retention | Tensile, elongation, haze, transmittance | ASTM D882, D1003, or equivalents | Detects tearing or clarity loss | When removal or appearance matters. |
Why the First Curve May Not Match the Second
First heating retains extrusion cooling, biaxial stretching, heat setting, annealing, coating cure, storage, and prior exposure. These factors affect cold crystallization, peak breadth, shoulders, and enthalpy; broad or double peaks may reflect different crystal populations or melting-recrystallization.
After complete melting and controlled cooling, second heating reflects an agreed reset history. Keep first- and second-heating values separate, and compare grade, rates, and reporting point before judging differences.
What Changes Before the PET Base Film Melts
Short heat exposure should be evaluated against polyester film heat resistance process limits, not inferred from the DSC peak. Thermal shrinkage, wrinkling, edge pullback, adhesive softening, discoloration, haze increase, or transmittance loss may occur earlier.
Thickness affects heating rate and handling. Tensile strength and elongation affect removal integrity. Low peel adhesion can permit lifting; excessive adhesion build-up can increase trace, marking, or tearing. Use values from the tested construction and surface.
Surface Checks That Cannot Be Replaced by DSC
Glass exposes bubbles, haze, or shadow, but cleaners and coatings alter adhesion. Bare metal transfers heat quickly. Painted or coated metal requires checking cure, hardness, gloss, and chemistry. PMMA, PC, PVC, ABS, and PETG differ in surface energy and heat sensitivity.
Rough and low-energy surfaces can show incomplete contact or edge lifting. Reproduce surface type, coating condition, temperature, humidity, sunlight, equipment setting, and operator method during surface protective film selection and validation.
A Three-Point Dwell Test
Use the actual surface and approved batch. Record surface identity, coating age, cleaning, application pressure, temperature, dwell, cooling, peel angle, speed, and removal temperature. Keep an unheated control.
Check at 24 h, 72 h, and 7 days when relevant. Record lifting, bubbles, adhesive trace, residue, shadow, gloss or haze change, coating disturbance, dimensional change, and tearing. Repeat after changes to equipment, operator, batch, or process time.
When a Valid Test Result Is Used Incorrectly
Data Point | If Too Low | If Too High | Risk in Application | Check Before Full Use |
Melting value | May be another resin or point | May be another grade or scan | False service-temperature assumption | Confirm grade, scan, rate, and reporting point. |
Thickness | Lower stiffness; faster heating | Lower conformability; slower heating | Uneven process or removal | Test intended gauge and full structure. |
Peel adhesion | Lifting, bubbles, movement | Trace, marking, tearing | Coverage loss or difficult removal | Use actual surface and staged dwell checks. |
Tensile / elongation | Splitting under strain | Excess stiffness or stretch | Incomplete removal | Compare before/after heat and peel. |
Thermal shrinkage | Usually favorable if verified | Pullback, wrinkles, exposed areas | Coverage loss during heat | Measure MD/TD at real temperature and dwell. |
Storage time / condition | Under-aged result may mislead | Build-up, deformation, contamination | Approved sample no longer representative | Record history and retest affected rolls. |
Keeping Stored Rolls Comparable to the Approved Sample
Keep rolls in original packaging within the confirmed temperature and humidity range, away from sunlight, UV, dust, and moisture. Stacking pressure, core or edge damage, telescoping, and broken packaging can affect unwind and application. Acclimatize rolls before testing.
Storage time can change adhesion without changing the PET melting transition. For transport protection, load weight, cargo shape, part geometry, transport distance, vibration, and temperature cycling can increase edge stress or effective dwell. Document any coating, slitting, or sample-preparation change and review film coating and converting capabilities. Retest rolls with a different storage or transport history.
FAQ
What is the typical polyester film melting temperature?
Conventional PET and BOPET commonly show a DSC melting region around 245-260 C. The value varies with grade, thermal history, heating rate, scan cycle, and reporting point. Treat it as a reference unless a tested grade and method are specified.
How should a PET film DSC curve be read?
Review Tg, cold crystallization, peak shape, onset, peak, endset, and enthalpy together. Confirm the rate and scan cycle: first heating retains processing history; second heating follows controlled cooling.
Is the PET melting point the finished-film service temperature?
No. Shrinkage, wrinkling, clarity loss, peel change, or adhesive and coating effects can occur far below melting. Set service limits from actual temperature, dwell, surface, load, and removal conditions.
Why is sample testing required before full use?
DSC cannot reproduce coating cure, humidity, sunlight, equipment, operator method, storage, transport, or surface chemistry. Test an approved sample at 24 h, 72 h, and 7 days when relevant, recording conditions and removal observations.
