Clear PET sheet for cups, lids, and trays fails more often from the wrong extruder than from the thermoformer. Moisture, IV drop, and bubbles show up as haze or brittle rims. This is the specification checklist we use on PET/PLA sheet lines before a quote goes out.
Do not start with screw count. Write width, thickness, kg/h, and whether the resin is virgin pellet, washed bottle flake, or PLA. Then match output to the downstream cup making machine so you do not starve cavities or warehouse unused rolls.
Specify the sheet before the screw
An 800 mm, 0.35–0.8 mm cup-grade web at 400 kg/h is a different line than 1000 mm stationery sheet. Typical cup sheet sits at 0.35–1.2 mm. Size the extruder 10–15% above the former’s net consumption (cups + skeleton).
| Sheet program | Typical width | Thickness | Order of magnitude |
|---|---|---|---|
| Drinking / yogurt cups | 700–850 mm | 0.35–0.80 mm | 350–700 kg/h |
| Lids and shallow trays | 750–950 mm | 0.25–0.50 mm | 300–600 kg/h |
| Deep bowls / food boxes | 800–1000 mm | 0.50–1.20 mm | 500–900 kg/h |
Twin-screw vs single-screw with numbers
Industry buying guides (Jwell and similar) put twin-screw specific energy around 0.18–0.28 kWh/kg and single-screw around 0.25–0.35 kWh/kg when a crystallizer/dryer is included. Twin-screw lines usually cost 30–50% more at purchase and skip or shrink the 4–6 hour predry step when vacuum vents are specified.
| Factor | Twin-screw (SI / XSI) | Single-screw + dry crystallizer (LSI) |
|---|---|---|
| Moisture control | In-barrel vacuum degassing | Predry to about 50 ppm before the die |
| Bottle flake / PCR | First choice; higher flake ratio | Only if flake is dry and IV is stable |
| Virgin PET / PLA | Works; overkill if you never touch flake | Lower capital, stricter dryer discipline |
| AMT models | SI-85-44-950, XSI-PET-PLA | LSI-PET-PLA |
Worked example — 24-cavity PP/PET cup former
Former takes ~420 kg/h of sheet (cups + 40% skeleton). Size the extruder at 420 × 1.12 ≈ 470 kg/h. Virgin pellet, no flake: LSI-PET-PLA plus a honest dryer is enough. RFQ says 50–70% washed flake: specify SI-85-44-950 or XSI-PET-PLA with vacuum, not a cheaper single-screw to “save budget.”
Drying targets you should put in the RFQ
PET sheet should enter the die below about 50 ppm moisture. PLA is looser at the resin-vendor level (often <250 ppm, prefer <100 ppm) but still fails if gaylords sit open. If you skip vacuum on flake to cut the quote, cloudy sheet is the usual result.
Send material (virgin / flake / PLA), width, thickness, kg/h, and the cup program. We reply with layout, dryer size, and roll-stack. Use Get a Quote or the turnkey sequence.
Fault map — what the line is telling you
| Symptom | Likely cause | First check |
|---|---|---|
| Cloudy or bubbly sheet in week one | Moisture at the die, or flake with no vacuum | Dew point, hopper lids, written 50 ppm / vacuum spec |
| Cups crack at the rim after a clear roll | IV drop from heat or wet flake | Target IV in the RFQ; flake photos; dryer hours |
| Thickness bands down the web | Roll stack fighting the extruder, or kg/h mismatch | Recalc cups + skeleton + 10–15%; roll temperatures |
| Yellow tint or gels after a PP run | Dirty screw / long residence | Purge plan; do not chase PET on a dirty PP screw |
| Former waits; warehouse fills with unused rolls | Extruder too small or too large vs the press | Balance kg/h to the cavity plan, not the catalogue peak |
RFQ checklist — send this in one email
Fill what you know; blank is better than a guess. Attach it on Get a Quote with photos of resin or flake.
- Sheet width, thickness range, and target kg/h
- Resin: virgin pellet / washed flake % / PLA — and an IV target if PET
- Downstream cup machine family or cavity × cpm plan
- Voltage / frequency (default 380 V / 50 Hz unless you say otherwise)
- Photos of flake or gaylords if PCR is in the recipe
- Hall sketch: dryer location away from the truck door
Frequently asked questions
Can one PET line feed two cup machines?
Yes if kg/h covers both formers plus skeleton, with a 10–15% margin. Otherwise the second press waits on rolls.
Is twin-screw always better for food-grade sheet?
No. Virgin pellet with a sized dryer on LSI-PET-PLA is cleaner and cheaper. Twin-screw wins when flake or mixed PCR is in the recipe.
What moisture number should I put in the contract?
About 50 ppm at the die for PET. Ask for a dryer or vacuum spec in writing, not “suitable drying.”
Do I need a new cup machine if I only change the extruder?
Not if forming area and sheet width already match. You may need a new dryer, roll temperatures, and mold cooling recipe.