Packaging Adhesives Chemicals

Solventborne PU laminating adhesives (20–50% solids in ethyl acetate) allow excellent wetting and film formation at low coat weights but require solvent recovery systems. Solventless PU adhesives (100% active, no solvent) are applied at elevated temperature — they eliminate solvent costs, are preferred for new lines, and reduce VOC. They require precise metering and higher processing discipline.

Food packaging laminating adhesives must meet migration requirements of FDA 21 CFR (USA), EU Regulation 10/2011 (EU), and GB standards (China). The finished laminate must be tested for overall and specific migration. Primary aromatic amine (PAA) migration testing is critical for PU adhesives — result must be < 10 ppb total PAA.

Corrugated board uses starch-based adhesive (converted starch or dextrin with borax as carrier) — the standard for single-face and double-face combining. PVA (polyvinyl acetate) adhesive is used for specialty corrugated where faster cure or higher bond strength is needed. Hot-melt EVA is used at corrugator edges and for high-speed case-erecting.

Retort packaging is sterilized at 121–135°C in pressurized steam for up to 60 min — laminate must survive without delamination or flavor change. Two-component PU lamination adhesives based on aromatic isocyanate (MDI) with high crosslink density are used. Coat weight is increased to 3.5–5 g/m². Migration testing under retort conditions (and primary aromatic amine analysis) is mandatory before commercial release.

Multi-layer flexible packaging laminates use different adhesives for different bonds: solventless PU for film-to-film, solventborne PU for film-to-foil, and hot-melt PE for film-to-paper. The adhesive must wet both substrates, have appropriate viscosity for the application equipment, and meet food-contact regulations. Bond strength is verified by T-peel testing on the cured laminate.

Solventless PU laminating adhesives form structural bonds in flexible packaging laminates — used between print and barrier layers (film/foil/film constructions). Acrylic emulsion PSAs are used for self-adhesive labels and tapes that need pressure-activated bonding. The two are not interchangeable: PU forms permanent crosslinked bonds for retort and aggressive content, while PSAs allow removability and repositioning.