How does a back-seal sachet work?
A back-seal sachet is formed from roll stock with a longitudinal seal running on the rear face and cross-seals closing the top and bottom. It is often a practical route where efficient film conversion and a compact flat pack are priorities. The rear seal still occupies space: artwork, code zones and the product bulge must be planned around its width and position.
The film web, forming set, pull system and longitudinal sealing arrangement are machine-specific. The approved drawing should state whether the rear seal is centred or offset and show the no-print and no-product zones around it.
What is a three-side-seal sachet?
A three-side-seal sachet has one folded edge and three sealed edges in the usual flat-pack description. That name is also used for premade pouches supplied open on one side, so the enquiry must say whether Lancing is evaluating roll-stock form-fill-seal machinery or a premade-pouch filling route. Those are materially different processes.
For roll-stock production, confirm how the web is folded or presented, which edge remains as the fold, where the dose enters and how the final closure is made. The fold, artwork and tear direction must all agree.
What is a four-side-seal sachet?
A four-side-seal sachet has heat-sealed margins around the full perimeter. This can provide a balanced flat presentation and clear separation between the product area and the outer edges, but it requires a machine and web path designed for that format. Do not assume that a standard back-seal machine can be converted by changing seal jaws alone.
Specify the two web faces or folded-web architecture, seal widths, product cavity, code area, tear feature and cut position. The trial must show that all four seals remain clean and continuous under the actual dose and film conditions.
Coordinate artwork, coding, tear features and the cutter
Place the print repeat, photocell mark, batch code, tear notch, perforation and cut line on one controlled drawing. A feature can be individually feasible yet conflict with another element when placed too close to a seal or registration mark. Multi-lane machines also need lane pitch and lane-specific positions.
- Keep variable coding inside a stable, readable zone.
- Keep opening features clear of critical seal corners unless the pack design is validated for that position.
- Define whether finished output is individual sachets, connected strips or another collation format.
- Include tolerances for registration, cut and feature position rather than approving only a nominal artwork view.
What should the seal-format trial prove?
The trial should use representative product and production-intent film. It should cover start-up, steady running, a planned stop, restart and any normal reel or recipe change. Sample packs should be checked for dose, seal continuity, contamination in the sealing area, code, registration, notch/perforation and cut position.
Agree the leak or seal-integrity method before testing. Record the run condition behind each result so a visually good hand sample is not mistaken for evidence of repeatable production.
Information needed before Lancing can confirm the format
| Finished pack | Dimensioned front and rear drawing, seal widths, cavity, headspace and allowable tolerances |
|---|---|
| Film | Structure, gauge, reel width, core, winding direction, print repeat, eye mark and sealing information |
| Product | Product type, dose range, temperature, viscosity or flow, particles, dust and seal-contamination risk |
| Features | Code, notch, perforation, individual cut or strip presentation and downstream requirement |
| Acceptance | Sampling plan, dose method, seal/leak method, visual criteria and accepted-output case |