A cohesive, also called cold seal, is designed to stick only to itself. You coat it on both faces and dry it. The bond forms when the two dry coats meet under pressure. No heat is needed.
Cohesive is a water-based latex. It is sensitive to drying, light, humidity and to the inks and overprint varnish (OPV) on the web. Many faults start on the press or in storage, not at the packaging machine.
For press set-up, see how to run cohesives on flexo and gravure presses. For handling and test schedules, see how to use cohesive.
What's in this guide
- Why won't my cold seal seal on the packaging machine?
- Why do my cold seals get weak after weeks in storage?
- Why are my cohesive rolls blocking?
- Why does my cohesive stick to the product or to fingers?
- Why does my cohesive foam in the pan?
- Why are there dry lumps or skins in my cohesive?
- Why does the coat pattern spread or build up on the plate edges?
- Why does seal strength vary across the web?
- Why did my cold seal fail after I changed ink, OPV, paper or film?
- Why does the coated web smell of ammonia or feel damp at rewind?
- Can I use your cohesive on food packaging?
Why won't my cold seal seal on the packaging machine?
Symptom: The seal is weak or opens by hand. Some packs do not seal at all.
Likely cause: The coat weight is too low, the two coat patterns do not line up, or crimp pressure is too low. An old web, a web left in light, or a web stored in very dry air also seals poorly.
Fix: Check the coat weight against the TDS. Check that the patterns are in register at the seal. Increase the crimp pressure in small steps. Use the oldest web first. Store finished rolls wrapped and out of light.
Why do my cold seals get weak after weeks in storage?
Symptom: Seals pass at the start. Seal strength drops after weeks or months.
Likely cause: Light and air oxidize the coat. Heat speeds this up. Ink, OPV or film additives can also move into the coat over time.
Fix: Wrap finished rolls and keep them out of light and heat. Run aged peel tests on a fixed schedule. Qualify each ink and OPV with the cohesive before production. Send aged failed packs to our lab.
Why are my cohesive rolls blocking?
Symptom: The coat sticks to the back of the next layer. The roll is noisy or hard to unwind, or the print picks off.
Likely cause: The release OPV on the reverse side is missing, too thin or not compatible. A web that is not fully dry, a warm web at rewind, high rewind tension or humid storage also cause blocking.
Fix: Confirm the release OPV on the reverse side with your ink supplier. Dry the coat fully. Cool the web before rewind. Lower the rewind tension. Store rolls in a controlled, not humid, area.
Why does my cohesive stick to the product or to fingers?
Symptom: The dry coat feels tacky. It sticks to the product, to fingers or to machine parts.
Likely cause: The coat is not fully dry, the coat weight is too high, or an ink or OPV softens the coat. The grade may not be right for the job.
Fix: Increase dryer air flow and check the coat is dry at rewind. Check the coat weight against the TDS. Test the coat over the actual ink and OPV. Ask our lab to check the grade.
Why does my cohesive foam in the pan?
Symptom: Foam builds in the pan or sump. The coat shows pinholes or bare spots.
Likely cause: High shear from pumps or mixing pulls air into the latex. The wrong defoamer also causes foam.
Fix: Use low-shear pumps or gravity feed. Use only the defoamer we specify, at the amount we specify. Never use a silicone defoamer in cohesive. Spray or atomize the defoamer at the pan.
Why are there dry lumps or skins in my cohesive?
Symptom: You see lumps, skins or flakes in the pan or on the coat.
Likely cause: Cohesive dried on a roll during an idle period. Dry cohesive does not mix back in. Frozen or old material can also form lumps.
Fix: Keep rolls turning when cohesive is in the pan. Drain used cohesive at shutdown and do not reuse it. Protect drums and totes from freezing. Rotate stock oldest first. Our guidance is to use cohesive within three months for best results; the TDS for your grade governs.
Why does the coat pattern spread or build up on the plate edges?
Symptom: The pattern edges get thick or ragged. The pattern grows during the run.
Likely cause: Cohesive builds up at the plate edges, mainly on central-impression presses. Loss of ammonia during long runs or idle time changes how it prints.
Fix: Coat the cohesive at the last station. Keep the pan covered. Check pH with a meter after idle time. Follow how to run cohesives on flexo and gravure presses.
Why does seal strength vary across the web?
Symptom: Some lanes seal well and others are weak.
Likely cause: The coat weight is not even. A worn or plugged anilox, an uneven nip or uneven drying causes it.
Fix: Measure the coat weight across the web. Clean the anilox and check it for wear. Check the nip and the dryer air across the web.
Why did my cold seal fail after I changed ink, OPV, paper or film?
Symptom: A job that ran well now fails after one material change.
Likely cause: The new material does not work with the cohesive. Inks, OPVs, slip additives and film treatment can all change the seal.
Fix: Qualify every new ink, OPV, paper or film before production. Run seal and aged peel tests on the new structure. Send the new materials to our lab.
Why does the coated web smell of ammonia or feel damp at rewind?
Symptom: The web smells of ammonia or feels cool and damp. Blocking or weak seals follow.
Likely cause: The coat is not fully dry. The dryer is too short, the air flow is too low, or the line is too fast.
Fix: Increase dryer air flow first. Slow the line if you must. Check the coat at rewind before you run full speed.
Can I use your cohesive on food packaging?
Symptom: You need a cold seal for a food wrap or candy wrapper.
Likely cause: Food packaging use depends on the grade, the structure and the conditions of use.
Fix: Some grades are formulated for food packaging. Confirm suitability for your structure with our lab before you specify a grade. Ask for the grade's regulatory statement in writing.
Stock grades
Stock cohesive grades from our cohesive adhesive page. Get the TDS for coat weight and viscosity.
| Product number | Use |
|---|---|
| 8209 | Candy bar wrappers. Fast initial tack. |
| 8217 | Cohesive wraps. Fast initial tack. Call to match your end use. |
| 8221 | Furniture wrap. Fast initial tack, strong final bonds. |
| 8222 | Bubble wrap. Fast initial tack, very strong final bonds. |
| 8223 | Furniture wrap. Fast initial tack, very strong final bonds. |
What to send before you call
Tell us the press type, the web, the ink and OPV, the dryer, and the packaging machine. Send coated web, a failed pack and the date the web was coated.
Related: cohesive adhesive, water-based adhesive, how to use cohesive, how to troubleshoot ink problems, how to recommend anilox roll and cell count.
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.