PUR hot melt bonds in two steps. First it sets as it cools. This gives green strength. Then it reacts with moisture and cures to a thermoset. After cure, it does not remelt.
Many PUR faults come from moisture in the wrong place. Too much moisture in the melt unit makes the adhesive skin, gel or clog. Too little moisture in the part or the plant air makes the cure slow.
This page is for PUR hot melt on edgebanders and profile wrapping lines. Liquid PUR (8730) is a different product. It is liquid at room temperature and does not use a melt unit. See liquid PUR.
What's in this guide
- Why is my PUR edgeband lifting at the corners or ends?
- Why does my PUR edge peel off clean with the glue left on the panel?
- Why does my PUR edge fail with the glue left on the edge, not the panel?
- Why is my PUR bond still weak the next day?
- Why is my PUR glue line foaming or full of bubbles?
- Why does PUR skin, thicken or gel in the melt unit?
- Why do my PUR nozzles or slot die keep clogging?
- When should I purge PUR from my melt unit, and with what?
- Why does my edge or wrap move before trimming?
- Why can I see a thick glue line or squeeze-out on my edges?
- Why is my vinyl or foil wrap lifting on the profile wrapping line?
- Why does PUR bleed through my paper or veneer wrap?
Why is my PUR edgeband lifting at the corners or ends?
Symptom: The edge lifts at the ends, at the corners or on tight radii. Often it lifts hours or a day after banding.
Likely cause: The edge pulls back before the bond has enough strength. Thick or stiff edges from the roll are under tension. Low press-roller pressure, a cold panel or a cold edge, and a starved glue line make it worse.
Fix: Increase press-roller pressure within the bander maker's range. Check the first roller at the point of contact. Let panels and edge rolls come to plant temperature before you band them. Increase coat weight in small steps within the TDS range. Shorten the time from glue application to the first press roller. For tight radii, ask our lab about a grade with more green strength.
Why does my PUR edge peel off clean with the glue left on the panel?
Symptom: The edge comes off with a clean or shiny back. The adhesive stays on the panel.
Likely cause: The adhesive did not wet or anchor to the back of the edge. The usual cause is a missing or wrong primer on the edge back. Release residue or a low surface energy plastic edge can also cause it.
Fix: Ask your edge supplier if the edge is primed for PUR. Make sure the primed side faces the adhesive. Check the edge back with dyne pens. Send our lab a short roll of the edge and a failed panel. See how to bond low surface energy substrates.
Why does my PUR edge fail with the glue left on the edge, not the panel?
Symptom: The adhesive stays on the edge. The panel edge shows little or no fiber on the glue line.
Likely cause: The adhesive did not wet the panel. A cold panel chills the glue before it wets. Dust, chips or a burnished panel edge from dull jointing cutters also block wetting.
Fix: Sharpen or replace the jointing cutters. Clean the panel edge with air or a brush before the glue unit. Warm cold panels to plant temperature. Check press-roller pressure. Do not raise the melt temperature above the TDS range to fix a cold panel.
Why is my PUR bond still weak the next day?
Symptom: Parts handle fine at the end of the line. Final bond strength is low after the time on the TDS.
Likely cause: The cure did not get enough moisture. Dry winter air, heated plants, metal and some plastics give little moisture. Cold storage slows the cure.
Fix: Measure the plant humidity, mainly in winter. Store bonded parts in a warm area that is not dry. Wait the full cure time on the TDS before you test final strength. Test green strength and final strength as two different checks. Ask our lab about the humidity range for your grade.
Why is my PUR glue line foaming or full of bubbles?
Symptom: You see bubbles or a foamed glue line. Sometimes blisters show up a day after banding or wrapping.
Likely cause: Moisture reacts with the PUR and makes carbon dioxide gas. Wet panels, wet edges or moisture in the melt unit cause it. Between two non-porous faces, the gas cannot escape.
Fix: Check the moisture of the panels and the edge material. Keep the melt unit closed and sealed. Check lid seals and any dry-gas blanket. Do not use an opened container that sat open. On two non-porous faces, ask our lab about coat weight and grade choice.
Why does PUR skin, thicken or gel in the melt unit?
Symptom: The melt gets thick, forms a skin, or has gel pieces. Flow drops during the shift.
Likely cause: Air moisture gets into the melt unit. Heat for too long also thickens PUR. Old material or a container left open makes it worse.
Fix: Keep the melt unit lid closed. Melt only the amount you will use in the time on the TDS. Lower the temperature during breaks as the TDS tells you. Do not run above the TDS range. Overheating raises isocyanate vapor in the work area, so follow the SDS for ventilation and personal protection. Do not top up with a partly used container that sat open. Use stock first in, first out. Purge on a schedule.
Why do my PUR nozzles or slot die keep clogging?
Symptom: The nozzle or slot die gives a broken bead or a streaked coat. Hard particles collect in filters.
Likely cause: Cured PUR particles break loose from the tank, hoses or filters. Moisture at the nozzle tip during idle time cures adhesive there. Overheating can also char the adhesive.
Fix: Close or protect the nozzle tip during short stops. Change filters on a schedule. Purge before long stops. Do not run above the TDS temperature. See how to apply, handle, clean up and store reactive hot melt adhesive.
When should I purge PUR from my melt unit, and with what?
Symptom: You plan a long shutdown, a grade change, or you see cured particles in the hose.
Likely cause: Cured PUR does not remelt. You must remove it before it cures in the system. After cure, you can only remove it mechanically.
Fix: Purge before long shutdowns, before a grade change, and when particles show up. PUR-Purge-1000 is our stock PUR purge compound. Follow your melt unit maker's procedure and the purge TDS. Run until the stream is clean. Ask us which purge fits your melt unit and your stop time.
Why does my edge or wrap move before trimming?
Symptom: The edge slips or the wrap shifts at the end trim, the flush trim or the scraper.
Likely cause: The glue line is still too soft at the trim station. The line is too fast for the grade, the glue line is too thick, or the glue is too hot.
Fix: Give the glue line more cooling time before the trim station. Lower the coat weight in small steps. Lower the temperature in small steps within the TDS range. Ask our lab about a faster-set or higher green-strength grade for your line; 8600 is our stock edgebanding PUR.
Why can I see a thick glue line or squeeze-out on my edges?
Symptom: A visible line shows between the edge and the panel. Glue squeezes out on the face or the back.
Likely cause: The coat weight is too high, the panel edge is not square, or roller pressure is not even.
Fix: Lower the coat weight in small steps. Check the jointing cutters for a square, clean cut. Set the press rollers for even pressure. Remove squeeze-out before it cures. After cure, you can only remove it mechanically.
Why is my vinyl or foil wrap lifting on the profile wrapping line?
Symptom: The wrap lifts on radii, edges or grooves. Blisters show up after the line.
Likely cause: Release residue on the profile, an unprimed foil back, a cold profile or high wrap tension. Pressure rollers that miss part of the shape also cause it. On non-porous profiles, trapped gas can blister the wrap.
Fix: Clean the profile before the glue unit. Confirm the foil back is primed for PUR. Let profiles reach plant temperature. Set each pressure roller to the shape. Lower the wrap tension. For uPVC profiles, see how to use PUR hot melt for vinyl-wrapped uPVC glazing beads.
Why does PUR bleed through my paper or veneer wrap?
Symptom: Glue spots or a dark shadow show through thin paper or veneer.
Likely cause: The coat weight is too high for the wrap, or the glue is too hot and too thin. Porous wraps take up more adhesive.
Fix: Lower the coat weight in small steps. Lower the temperature in small steps within the TDS range. Ask our lab about a grade with a higher viscosity. Test each new wrap before a production run.
Stock grades
PUR hot melt and purge grades from our stock PUR table. Get the TDS for temperatures, open time and cure time.
| Product number | Use |
|---|---|
| 8600 | PUR hot melt for edgebanding. Fast tack. Also listed for cabinets, steel, woods and EPS. See edgebanding. |
| 8463 | PUR hot melt. High green strength. Listed for RV panels. |
| 8493 | PUR hot melt. Long open time. Listed for EPS foam and flexible bonds. |
| PUR-Purge-1000 | Purge compound for PUR melt systems. |
| 8730 | Liquid PUR, not a hot melt. Room temperature, clamp during first cure. Not for vinyl (PVC), PP, PE or other polyolefins. See liquid PUR. |
What to send before you call
Tell us the edge or wrap material, the panel or profile, the bander or wrapper, its melt unit, and the plant humidity. Send a failed part and a short length of the edge or foil.
Related: PUR hot melt, edgebanding, profile wrapping, how to solve hot melt application problems, how to solve common edge gluing and laminating problems with wood glues.
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.