Paper Cup Defects FAQ

Why do paper cups leak at the bottom seal?

Bottom-seal leaks come from three places: sealing temperature off the coating's spec, dwell time too short for a full bond, or inconsistent bottom paper. The fix sequence is to check temperature against the stock's coating spec, confirm dwell and pressure, then verify the bottom blank's dimensions and coating weight.

What causes wrinkles on the cup side wall?

Side-wall wrinkles trace mainly to the stock: moisture content too high or low, stiffness direction mismatched to forming, or inconsistent coating. Machine-side causes include feed timing and curl control. Correct stock conditioning first, then check the forming station's timing and pressure.

How do you reduce paper cup rejects?

Reject reduction is a data discipline: log every defect by type and station, chart the dominant category, fix that root cause, and verify the change. Most cup plants find 80% of rejects come from a few recurring causes that a structured log exposes quickly.

Why do cups come out of round or hard to stack?

Out-of-round and stacking problems usually trace to taper or tolerance drift in the forming tooling, cooling too fast after forming, or stock conditioning changes. Check the tooling dimensions against spec, confirm the cooling path, and audit the stock's moisture consistency.

How often should a cup line be checked for defect causes?

Run a structured defect log continuously and review the chart daily; audit tooling, temperatures, and stock conditioning on a fixed schedule — typically shift-level checks and weekly deep reviews. Control charts on key quality measures catch drift before rejects climb.

What is the first step when rejects suddenly spike?

Do not adjust blindly. Check what changed: new stock reel, recent tooling change, temperature or humidity shift, or a different operator shift. The cause is almost always in the last change — find it, fix it, and log the pattern so the spike does not recur.