How to solve heat seal coating and lidding problems

A heat seal coating goes on the lid stock and dries tack-free. The bond forms later, when heat and pressure activate the coating against the cup or tray. The coating, whether water-based, solvent-based or hot melt, is applied and set first; the sealer reactivates it with heat and pressure.

Seal quality depends on three settings at the seal: temperature, pressure and dwell time. The platen temperature is not the temperature at the seal interface. Map your seal window on your own lid and cup before you change grades.

For coating choice, see how to select heat seal coatings for lidding applications. For induction cap liners, see how to solve common problems with induction seal cap liners.

Why won't my lid seal to the cup or tray?

Symptom: The lid lifts off with no effort. The seal shows no transfer or only a partial ring.

Likely cause: The seal interface does not get hot enough, the dwell is too short, or the pressure is too low. The coat weight may be low. The coating may not match the cup or tray material.

Fix: Raise the seal temperature in small steps within the TDS activation range. Add dwell or pressure one setting at a time. Check the coat weight against the TDS. Confirm the coating is made for your cup or tray material.

Why does my lid tear instead of peeling clean?

Symptom: The lid tears, delaminates or leaves lid material on the cup.

Likely cause: The seal is stronger than the lid. Too much heat, dwell or pressure causes this. The coating may be a weld-type seal, not a peel seal.

Fix: Lower the seal temperature in small steps. Shorten the dwell. Map the seal window and run in the middle of it. Ask our lab for a grade designed for a peel seal on your structure.

Why do my lids leak after hot fill?

Symptom: Lids pass when cold but leak or lift after a hot fill.

Likely cause: The seal opens while it is still hot. Product in the seal area also blocks the seal.

Fix: Keep the seal area clean and dry at filling. Let the seal cool under pressure if your sealer allows. Tell our lab the fill temperature and the product. Ask for a grade with hot tack for that condition.

Why are my heat seal coated rolls blocking?

Symptom: Layers stick together on the roll. The coating picks off or the print lifts.

Likely cause: The coating is not fully dry, or the web is warm at rewind. High rewind tension or humid storage adds to it.

Fix: Dry the coat fully. Cool the web before rewind. Lower the rewind tension. Store rolls cool and dry. Stock grade 8240 is listed as non-blocking.

Why does the lid stick to the seal head?

Symptom: The lid pulls off with the seal head. Coating or ink builds up on the head.

Likely cause: The outside of the lid does not release from a hot seal head. The head may be too hot or dirty.

Fix: Clean the seal head. Lower the head temperature in small steps. Use a heat-resistant overprint on the outside face. Stock grade #8605 is a matte overprint listed for hot release. Stock grade #8610 is listed as super high heat; glossy 2-part overprint. Ask which suits your lid.

Why does the heat seal coating come off the lid film or foil?

Symptom: On opening, the coating stays on the cup and the lid is bare.

Likely cause: The coating did not anchor to the lid stock. Untreated film, slip additives or a release surface cause this. A missing primer is also a common cause.

Fix: Check the film surface with dyne pens. Ask your film supplier about treat level and slip. Use a primer under the heat seal coat. Stock grade #8611 is a primer for release, slip and untreated films, paper and primed aluminum foil. See how to choose the best treatment method for adhesion to film.

Why is seal strength uneven around the lid?

Symptom: One side of the lid seals well and the other side is weak.

Likely cause: The platen is not flat or not level, the pressure is not even, or the coat weight is not even.

Fix: Check the platen contact with pressure-sensitive paper. Replace worn sealing rubber. Measure the coat weight across the web and along it.

Why are my seals weak after cold storage?

Symptom: Seals pass at packing but fail in the cooler or the freezer.

Likely cause: The coating gets stiff at low temperature. Product chemistry such as oil or acid can also attack the seal.

Fix: Test seals after storage at your real cold temperature. Test with the real product in the pack. Ask our lab for a grade for cold service and your product.

Why won't my reseal lid stick again after opening?

Symptom: The lid opens fine but will not reseal.

Likely cause: Too much seal heat can make a reseal coating bond like a permanent seal. Stay in the TDS activation range. The grade may also be a permanent seal. Product on the seal area also stops reseal.

Fix: Lower the seal temperature in small steps. Confirm the grade is a reseal grade. Stock grade 8215 is listed for low-heat reseal on PET and foils. See peel and reseal lidding.

Why does my heat seal coat show streaks, pinholes or uneven gloss?

Symptom: The dry coat has streaks, pinholes, craters or gloss changes.

Likely cause: The viscosity drifted, the doctor blade is worn or dirty, the coating has foam, or the coating does not wet the web.

Fix: Measure viscosity on a schedule and correct to the TDS. Change or clean the doctor blade. Filter the coating. Check the web surface with dyne pens. See how to fix rod coating defects and how to solve common coating flaws in reverse roll coating.

Which FDA regulation applies to my lidding coating?

Symptom: A customer asks for an FDA statement for your lid.

Likely cause: The answer depends on the grade, the lid structure, the food and the conditions of use. One statement does not cover every food and every use.

Fix: Tell our lab the lid structure, the food and the fill and storage conditions. Ask for the grade's regulatory statement in writing before you quote it to a customer.

Stock grades

Stock heat seal grades from our heat seal adhesive page. Get the TDS for activation temperature and coat weight.

What to send before you call

Tell us the lid stock, the cup or tray material, the product, the fill temperature, and the sealer settings. Send coated lid stock, cups and failed packs.

Related: heat seal adhesive, heat seal for labels and lidding, heat seal for blister packs, heat seals: qualifying questions you must consider, how to fix common defects in laminated film structures.

Still stuck on the line?

Call 800-249-0337 or contact us. Ask for a sample, an SDS, or a TDS. Our lab can test your substrate and your failed parts.

Call 800-249-0337 Request a sample Request an SDS

General plant guidance only — not a substitute for your process, SDS/TDS, or line trials. Call 800-249-0337 to match a grade.