Shrink Sleeve Seaming — Solvent Selection, Defect Diagnosis & Film Guides

Shrink sleeve seaming is the process of solvent-welding the overlapping edges of a flat-printed shrink film into a continuous tube. A thin layer of solvent dissolves a few microns of polymer on both mating faces; the chains interdiffuse and re-entangle as the solvent evaporates, producing a joint with no adhesive or third material.

The solvent depends on the film substrate. Solvents are grouped into five classes based on solvency strength and evaporation rate. Classes 1–3 cover PVC and PETG, Class 4 is dedicated to PET and rPET, and Class 5 covers polyolefin sleeves which require a fundamentally different bond mechanism.

Seam splitting is almost always a dosing or drying-speed issue, not a solvent-selection issue. The diagnostic sequence is: verify the substrate, check the flow rate, confirm drying speed is matched to line speed, and only then consider changing solvency class.

Conventional solvent welding does not work on polyolefin (PP, PE). These polymers are non-polar and semicrystalline — practical solvents cannot penetrate the ordered domains at room temperature. Polyolefin sleeves require purpose-formulated products, UV-cured adhesive, or thermal/laser sealing.

PETG is a copolyester where a comonomer (typically CHDM) disrupts chain regularity and suppresses crystallisation, leaving an amorphous polymer that solvent can penetrate. Standard PET retains its ability to crystallise, and crystalline domains resist solvent. A solvent that seams PETG reliably may not weld PET at all.

A common starting point is 1.5 mL/min per 100 m/min of line speed. At 200 m/min over a 3 mm overlap, that lays down a liquid film roughly 5 microns thick — about a tenth of the sleeve film’s own thickness. Most seam defects are dosing defects.

Blocking — where wound layers stick together on the reel — is caused by residual solvent that has not fully evaporated before winding. The fix is matching drying time to line speed, either by increasing the web path between nip and winder, reducing solvent flow, or moving to a faster-evaporating class.

Stretch film is wound under tension around a load and clings mechanically — it is not heated. Shrink wrap is a loose sleeve or sheet that contracts tightly when heat is applied. They serve different purposes: stretch film for pallet wrapping and transit stability, shrink wrap for product-conforming packaging and tamper evidence.