Three machines buyers mean by "tablet sealing"
| Referent |
Seals |
Position in line |
Speed band |
Capex band |
| Bottle induction sealer |
Foil laminate to bottle mouth |
After capping |
40–200 bpm |
Low–mid |
| Blister lid-sealing station |
Lidstock to formed web |
In blister packer |
Tied to packer |
Part of packer |
| Strip-pack sealer |
Two film webs |
Standalone strip line |
30–120 cycles/min |
Mid |
Route A — Induction foil sealing for tablet bottles
How the seal is actually made
A cap lined with a pulp board / wax / aluminium / polymer laminate passes under an induction coil. The alternating field heats the aluminium, the wax melts and the polymer layer bonds to the bottle rim. The seal is made by heat flow through the rim, not by contact pressure — which is why rim geometry and cap application matter as much as the coil.
The four parameters that decide seal integrity
- Power setting: 1.5–4.0 kW depending on cap diameter and line speed; under-power leaves a partial bond.
- Line speed: faster lines need higher power or a longer coil; a 120 bpm line at 38 mm caps needs roughly double the dwell of a 60 bpm line.
- Coil-to-cap gap: 3–8 mm; a gap above 10 mm loses induction efficiency fast.
- Dwell under coil: set by speed and coil length; this is the variable most often ignored at commissioning.
Cap application torque interacts with all four. Under-torqued caps leave a gap the seal cannot bridge; over-torqued caps distort the rim and wrinkle the foil. For 28 / 33 / 38 mm closures we hold application torque at 8–12 / 12–16 / 14–20 N·cm and removal torque (the tamper-evidence proof) at 4–7 / 6–10 / 7–11 N·cm.
Failure modes and how to read them
| Symptom |
Probable cause |
Corrective action |
| No seal |
Under-power or wrong liner |
Raise power; verify liner grade |
| Weak / peelable edge |
Coil gap too large |
Lower gap to 3–6 mm |
| Burnt foil |
Over-power or stalled bottle |
Reduce power; check conveyor stop |
| Cap back-off |
Over-torque distortion |
Re-set capper torque band |
Route B — Sealing inside a tablet blister machine
This is the lidstock-to-web bond covered under the blister packer discipline: heat-seal lacquer, knurl pattern, temperature window. The one special case is cold-form ALU-ALU, which does not heat-seal at all — it is pressed and crimped, not melted. If your tablet needs a tropical barrier, confirm the packer uses a flat-plate crimp station rather than a lacquer-seal rotary head.
Verification and package integrity testing
- Torque test: removal torque within the band above, sampled per shift.
- Peel / bond strength: > 4 N/15 mm at the rim, measured after 24 h conditioning.
- Vacuum decay and dye ingress: deterministic leak check per USP <1207> for pharma; target < 5 × 10⁻³ mbar·L/s.
- Sampling plan: AQL 1.0 on a per-batch basis, with a documented quarantine path for rejects.
Anonymised case: Middle East tablet bottling, 45 °C ambient
A Gulf site reported 3.1 % foil-seal failures in distribution. Root cause was twofold: the capper torque band had drifted to 22–26 N·cm (over-spec), distorting 38 mm rims, and the coil gap had been opened to 12 mm to clear a new taller cap. Resetting torque to 14–20 N·cm, lowering the gap to 5 mm and re-tuning power dropped failures to 0.2 % over the next quarter. The sealer hardware was fine; the process around it was not.
Compliance
Induction sealing is a tamper-evidence step under GMP and 21 CFR 211; for sterile-adjacent products it sits inside EU GMP Annex 1 expectations. ISO 9001 covers the manufacturer, ISO 13485 applies where the sealed bottle is a medical device. Keep the liner material on the EU 10/2011 food-contact file if the tablet is an OTC product.
Procurement traps
- Buying a sealer without matching it to the cap and closure programme — the coil must fit your cap diameter and height.
- Specifying power but forgetting dwell and coil gap at your real line speed.
- Overlooking capper torque, which silently decides seal quality.
- No seal-strength or torque tester in the scope, so you cannot prove the seal at接收.
FAQ
Is an induction sealer the same as a blister sealer?
No. Induction seals a foil laminate to a bottle mouth after capping; blister sealing bonds lidstock to a formed web inside the packer. Different machines, different failure modes.
What torque should my capper hold?
For 28 / 33 / 38 mm closures, application 8–12 / 12–16 / 14–20 N·cm and removal 4–7 / 6–10 / 7–11 N·cm. Drift outside this is the usual cause of seal complaints.
Why are my foil seals burning?
Over-power or a bottle stalling under the coil. Lower the power setting and confirm the conveyor does not stop bottles mid-coil.
How do I prove the seal holds?
Torque test, peel strength above 4 N/15 mm, and vacuum-decay leak check per USP <1207>, sampled at AQL 1.0 per batch.
Does ALU-ALU need induction sealing?
No — it is crimp-pressed, not heat-sealed. Confirm the packer uses a flat-plate crimp station for cold-form webs.
Can one coil serve all my cap sizes?
Only within a narrow diameter range. Outside it, specify interchangeable coil beds or a programmable power profile per cap recipe.
What liner grade do I need?
Match the polymer layer to the bottle resin (PET, HDPE, PP) and keep it on the food-contact file for OTC products.
Is seal integrity a validated parameter?
For regulated products, yes — torque and seal verification belong in the OQ and are checked at接收 and periodically thereafter.
