What causes hot melt to char or gel?
Char starts as gel: glue held hot too long, run hotter than it needs, exposed to air in a low or open tank, or contaminated with dust or another adhesive. The gel sticks to tank walls and hoses and turns black. Keep the tank covered and topped up, run the lowest temperature that does the job, use setback when idle, and do not mix incompatible hot melts.
Char costs you more than the glue. It plugs filters and nozzles, causes skips and stringing, and means downtime to clean. You can typically prevent most of it.
Hot melt and hot equipment can cause burns. Follow your equipment maker’s safety manual and lockout steps; qualified personnel only. Call us for data sheets
Causes and prevention
| Cause | What to do |
|---|---|
| Too hot | Run the lowest temperature that gives a good bond. Verify actual temperature, not just the setpoint. |
| Too long at heat | Use setback or turn the unit down when idle. Match tank size to usage so glue turns over. |
| Air (oxidation) | Keep the lid closed and the tank topped up. A low tank exposes more hot glue to air. |
| Dirt and paper dust | Keep the lid closed and the area clean. Use tank and inline filters and change them on schedule. |
| Mixing hot melts | Do not mix incompatible adhesives in one tank. Purge fully when you change grades. |
Already have char?
Purge and clean with the unit at operating temperature, change filters, and clean or replace nozzles. Follow your equipment maker’s procedure. See how to clean a hot melt system and the case sealer maintenance checklist. PUR is different: see how to purge PUR hot melt.
A grade that chars less
Cattie’s metallocene hot melts are built for pot-life stability and clear color. Metallocene hot melts typically resist char build-up, so nozzles typically clog less. Our low-temperature grades typically apply at about 250°F, not 350°F. A free line trial shows what changes on your line.
Request a sample Call 800-249-0337 Request a quote
Related
How to solve hot melt application problems · Hot melt application trouble-shooting tips · Hot melt system trouble-shooting tips · Hot melt adhesive · Stringing · Pop-opens · Low-temp vs standard
Hot melt char FAQ
What does char look like?
Black or brown specks in the bead, dark skins or crusts on tank walls, and gel that plugs filters, hoses and nozzles.
Does keeping the tank full help?
Yes. A low tank exposes more hot glue to air, which speeds oxidation and char. Keep it topped up and the lid closed.
Should I turn the melter off at night?
Use setback or turn it down when the line is idle for long periods, following your equipment maker’s guidance. Glue held at full temperature for hours with no flow is a common source of char.
Will metallocene hot melt stop char?
Metallocene hot melts are known for stable viscosity in the pot and resistance to char, which typically means fewer clogged nozzles and filters. Ask for a free line trial: 800-249-0337.
