Flexible packaging and lamination

In short

Flexible packaging is any package whose wall is a thin, bendable web — film, foil, paper or a laminate of these — formed into pouches, sachets, wrappers, bags or tubes, usually on form-fill-seal machines. Lamination is the process of bonding two or more such webs into one composite so that each layer contributes what the others cannot: print carrier, barrier, strength, sealability. It matters because no single polymer gives printability, oxygen and moisture barrier, puncture strength and a reliable seal at once, and because flexible packs use far less material per unit product than rigid ones. The topic is examined in printing/packaging technology papers (post-press and converting units), and it is the core technical round at Indian converters and brand owners — Uflex, Huhtamaki India, Cosmo Films, Jindal Poly Films, Polyplex, SB Packagings, Paharpur 3P, Parakh/Positive Packaging, Essel Propack (EPL), Amcor Flexibles India, Constantia, and the packaging development teams of HUL, Nestlé India, ITC, Britannia, Dabur, Marico and Amul.

Explained

What flexible packaging is, and the structure grammar

• Definition: a package with a wall thickness typically below 250 µm that takes the shape of its contents and whose empty weight is a small fraction of the filled weight.
• Monoweb vs laminate: a monoweb (single film, e.g. 40 µm LDPE bread bag) is cheap but limited; a laminate combines webs. A laminate is written outside-in with layer thicknesses/grammages, e.g. 12 µm BOPET / 9 µm Al foil / 40 µm LDPE or 20 µm BOPP (reverse printed) / 20 µm metallised BOPP.
• Functional roles in a structure:
  • Outer/print layer — stiffness, gloss, printability, heat resistance under the sealing jaws: BOPET, BOPP, paper.
  • Barrier layer (middle) — aluminium foil, metallised film, EVOH, coated films (AlOx, SiOx), PVDC coating.
  • Sealant/product-contact layer (inner) — LDPE, LLDPE, mLLDPE, EVA, ionomer, CPP (plain or retort-grade), peelable sealants.
• Nomenclature: films are specified in microns or in gauge (1 gauge = 0.254 µm; 100 gauge = 25.4 µm ≈ 1 mil) and sometimes in grammage (gsm); foil and paper are normally gsm, polymer films in µm.
• Why layers at all: barrier, strength and sealability are mutually exclusive in one resin; also, the print must be protected — hence reverse printing on the inside of the outer web, with the ink buried in the bond.

Raw materials: films, foil, paper and their properties

• BOPET (polyester, 12–23 µm): high tensile strength and stiffness, excellent heat resistance (good for lid films and retort), moderate barrier, prints beautifully. Not heat-sealable to itself unless coated.
• BOPP (15–40 µm): best moisture barrier of the common films, low cost, good clarity; poorer oxygen barrier; metallised BOPP lifts both barriers sharply. Available as plain, heat-sealable (coex), matte, pearlised (cavitated, for wrappers and labels).
• BOPA/nylon (15–25 µm): outstanding puncture and flex-crack resistance, good oxygen barrier but hygroscopic (barrier falls with humidity) — used for cheese, meat and bone-in products.
• Aluminium foil (6.3–12 µm; 9 µm typical): the only near-absolute barrier to light, gases and moisture at ≥ 9 µm; dead-fold; but pinholes and flex cracking make it fragile — always laminated both sides.
• Metallised film: 200–400 Å of vacuum-deposited aluminium; barrier improvement of 10–100× over the base film at a fraction of foil's cost, but not absolute and the metal layer can crack or transfer.
• Sealants: LDPE (seals ~110–120 °C), LLDPE/mLLDPE (tougher, hot-tack, good through contamination), EVA (low seal initiation), CPP (higher temperature, oil resistance, retort), ionomer (Surlyn-type, seals through powder/fat).
• Paper: gives stiffness, matte look and dead-fold but no barrier; used in sachet and sugar-stick laminates (paper/PE, paper/foil/PE).
• Barrier coatings: PVDC, EVOH (co-extruded, sandwiched because it is moisture-sensitive), transparent AlOx/SiOx for microwaveable and metal-detectable packs.

Lamination processes — step by step

1. Adhesive (dry/wet) lamination

• Steps: unwind web 1 → corona/flame treatment check → adhesive application (gravure cylinder or smooth roll with a metering/reverse roll) → drying tunnel (solvent-based only; hot air at 50–90 °C in zones) → nip between a rubber pressure roll and a heated steel roll → lamination with web 2 → chill/rewind → curing in a hot room (40–50 °C) for 24–72 h for polyurethane adhesives.
• Dry lamination: adhesive dried before the nip — standard for film/film and film/foil.
• Wet lamination: adhesive still wet at the nip; needs one porous web (paper), water-based adhesive, dried after nipping.
• Coating weight (GSM of dry adhesive) typically 1.5–2.5 gsm for film/film, 3–5 gsm for foil and retort structures.

2. Solventless (solvent-free) lamination

• Two-component polyurethane at 100% solids, metered through a 4–5 roll heated coating head at 35–45 °C, applied at 0.8–1.8 gsm, laminated immediately; no drying oven, no solvent recovery.
• Runs fast (300–500 m/min), uses far less energy and emits no VOC; but green bond strength is low — the laminate must cure 24–48 h before slitting and is unsuitable for some aggressive-fill and high-coat-weight applications unless a high-performance grade is used.

3. Extrusion lamination and extrusion coating

• Molten LDPE at 290–320 °C is extruded as a curtain from a T-die into the nip between the chill roll and the pressure roll, bonding two webs (extrusion lamination) or coating one web (extrusion coating).
• The melt's oxidised surface creates the bond; ozone treatment of the melt curtain and primer (AP/organic titanate or PEI) on the substrate raise adhesion, especially to foil.
• Tie layer thickness 10–25 µm; also serves as a functional layer. Economical for long runs; thickness adds weight.

4. Thermal/heat lamination and co-extrusion

• Thermal lamination: a pre-coated adhesive film is bonded by heat and nip pressure only — mostly for print finishing of cartons and covers rather than high-barrier flexibles.
• Co-extrusion: 3, 5, 7 or 9 layers formed in one die with tie layers (maleic-anhydride grafted PE) — produces barrier structures (PE/tie/EVOH/tie/PE) with no adhesive at all; dominant in blown-film barrier bags.

Surface treatment, adhesion and quality control

• Why treatment: polyolefins and BOPP are non-polar, surface energy ~29–31 mN/m; ink and adhesive need ~38–42 mN/m. Corona discharge oxidises the surface and raises the dyne level; it decays with time and temperature, so films are re-treated in line ("bump treatment").
• Dyne level test: calibrated test inks/pens — the highest ink that wets without beading within 2 s is the surface energy. Target ≥ 38 dyne/cm for lamination, 40–44 for metallising.
• Bond strength (peel/ply adhesion): 15 mm strip, T-peel or 180° peel at 100–300 mm/min on a tensile tester; reported in g/15 mm or N/15 mm. Typical acceptance: film/film 150–400 g/15 mm; foil structures 300–600 g/15 mm; retort > 600 g/15 mm, and after retort the bond must not fall below spec.
• Seal tests: heat seal strength (same tensile test on a sealed strip), hot tack (strength while still hot), seal integrity by dye penetration (methylene blue/toluidine) or vacuum/bubble (burst) test.
• Barrier tests: WVTR in g/m²/day at 38 °C, 90% RH (gravimetric cup or Permatran/Lyssy instruments); OTR in cc/m²/day·atm at 23 °C, 0% or 50% RH (coulometric, Mocon-type).
• Other QC: COF (static/kinetic, for machine runnability), GSM/thickness, tensile and elongation, pinhole and flex (Gelbo) test, solvent retention by gas chromatography, curl, blocking, and residual solvent limits — the industry works to ≤ 5 mg/m² total (and much lower for specific solvents) for food packs; confirm the customer's and the current regulatory specification, as limits differ by buyer and market.
• Odour/sensory and migration (overall and specific) tests for food contact.

Converting, pouch styles and machinery

• Slitting and rewinding: laminate is slit after curing; defects counted as tunnelling, curl, telescoping, bagginess, blocking.
• Pouch types: three-side-seal (pillow and flat pouch), centre-seal/fin-seal pillow pack (chips, biscuits), gusseted, standup pouch (SUP/doypack) with a K-seal or round bottom, spouted pouch, retort pouch (foil-based, 121 °C/30 min or 135 °C), shaped/laser-contour pouch, stick pack, easy-open laser-scored and peelable packs, zipper reclose.
• Filling systems: VFFS (vertical form-fill-seal, for granules, powders, liquids), HFFS (horizontal, for pre-made pouches and flow wrap), pre-made pouch filling, sachet and stick-pack machines, aseptic and MAP lines.
• Seal types: fin seal (sealant to sealant), lap seal (sealant to outer — needs an outer that seals), impulse, band and ultrasonic sealing.
• Faults and causes: tunnelling (tension/modulus mismatch between webs), delamination (low dyne, low coat weight, under-cure, aggressive product), leakers (contamination in the seal, wrong jaw temperature/dwell/pressure), pinholes (foil flexing, abrasive product), curl (unbalanced structure or moisture pick-up), hazing in solventless (moisture reacting with isocyanate), ink set-off and blocking, and aromatic amine formation from unreacted aromatic isocyanate — a food-safety issue, which is why curing and PAA testing matter.

Standards, Indian regulation and sustainability

• FSSAI (Packaging) Regulations, 2018 govern food-contact packaging in India: they mandate food-grade materials, prohibit recycled plastic in direct food contact (with narrow permitted exceptions such as certain PET applications under specified conditions), bar printing inks from the food-contact surface, and list the Indian Standards each material must meet with overall and specific migration limits. Check the current amended text, since the schedules are amended periodically.
• Indian Standards commonly called up: IS 9845 (determination of overall migration of constituents of plastics materials in contact with foodstuffs), IS 10146 (polyethylene for its safe use in contact with foodstuffs), and the corresponding safe-use standards for polypropylene, PET and multilayer films; IS 9396 series covers paper and board cups/containers. Quote the clause from the current edition; several older film-specification IS numbers have been revised or withdrawn.
• Legal Metrology (Packaged Commodities) Rules, 2011 require the declarations on the pack: name and address of the manufacturer/packer/importer, common name of the commodity, net quantity, month and year of manufacture, retail sale price (MRP inclusive of all taxes), consumer-care details and the unit sale price. Artwork and plate-making must carry these.
• Food Safety and Standards (Labelling and Display) Regulations, 2020 add the veg/non-veg mark, FSSAI logo and licence number, ingredient list, nutrition panel, allergen and date markings.
• Plastic Waste Management Rules, 2016 as amended (EPR Guidelines, 2022 onwards): brand owners, producers and importers must register on the CPCB EPR portal and meet recycling and recycled-content targets by plastic category — rigid plastic packaging is Category I, flexible plastic packaging (single-layer or multilayer made only of plastics) is Category II, and Category III is multilayered plastic packaging with at least one layer of plastic and at least one layer of a material other than plastic (foil- or paper-based MLP), with compostable plastic sheet/carry bags as Category IV. "Non-recyclable, non-energy-recoverable, no alternate use" MLP was targeted for phase-out; the operative dates and recycled-content percentages have been amended more than once, so verify the current notified schedule.
• Solid Waste Management Rules, 2026 (in force from 1 April 2026, replacing the 2016 Rules) govern municipal handling of the discarded packaging.
• Mono-material design is the industry's answer: all-PE (MDO-PE/PE, with EVOH or coated barrier) and all-PP (BOPP/CPP) laminates that are mechanically recyclable, plus paper-based structures with barrier coatings, and "wash-off" or solvent-free adhesives; recyclability claims are assessed against design-for-recycling guidelines (CPCB/industry and global protocols).
• Factory safety and environment: solvent-based lamination and gravure printing lines are flammable-solvent operations — area classification, flameproof fittings, LEL monitoring, solvent recovery or thermal/catalytic oxidisers, and consent to operate under the Air and Water Acts; occupational safety now sits under the OSH&WC Code, 2020 and the other Labour Codes, in force from 21 November 2025, which replaced the Factories Act.
• GST on packaging films and laminates falls in the 18% slab under the 5/18/40% structure effective 22 September 2025; confirm the HSN-wise rate before quoting a price.

Key points

• Flexible packaging — thin, bendable package wall (film/foil/paper), formed on FFS machines, very low pack-to-product weight.
• Lamination — bonding two or more webs so each contributes print, barrier, strength or sealability.
• Structure notation — written outside-in with thickness/grammage; outer = print, middle = barrier, inner = sealant.
• Reverse printing — printing on the inner face of the outer web so the ink is protected inside the laminate.
• Dry (adhesive) lamination — solvent-based adhesive, dried, nipped, then cured 24–72 h at 40–50 °C.
• Solventless lamination — 100% solids 2K PU at 0.8–1.8 gsm, no oven, no VOC, fastest and cheapest, needs cure before slitting.
• Extrusion lamination — molten LDPE curtain (290–320 °C) bonds the webs; ozone and primer raise adhesion, especially to foil.
• Co-extrusion — barrier built inside the film with tie layers; no adhesive, lower cost per layer.
• Corona treatment — raises surface energy of non-polar films from ~30 to ≥ 38 dyne/cm; decays over time.
• Dyne level — surface energy measured with test inks; the gate for printing, coating, lamination and metallising.
• Bond strength — T-peel on a 15 mm strip, in g/15 mm; retort structures need the highest and must hold after processing.
• WVTR and OTR — moisture (g/m²/day, 38 °C/90% RH) and oxygen (cc/m²/day·atm, 23 °C) transmission; the two barrier numbers.
• Aluminium foil ≥ 9 µm — practically absolute barrier; metallised film is cheaper but not absolute.
• Tunnelling — bubbles/ridges from tension or modulus mismatch between webs; a tension-control fault, not an adhesive fault.
• Residual solvent and primary aromatic amines — the two food-safety outputs of solvent lamination; controlled by drying and full curing.
• Retort pouch — PET/foil/CPP, survives 121 °C steam sterilisation; CPP (not LDPE) is the sealant.
• COF — coefficient of friction; too high jams the FFS machine, too low makes the stack slip.
• EPR — MLP is Category III plastic packaging on the CPCB portal; mono-material all-PE or all-PP designs are the recyclable replacement.

Formulas and examples

Example 1 — GSM, yield and cost of a laminate Structure: 12 µm BOPET (density 1.40) / adhesive 2.0 gsm / 9 µm Al foil (2.70) / adhesive 3.0 gsm / 40 µm LDPE (0.92).

• BOPET = 12 × 1.40 = 16.8 gsm; foil = 9 × 2.70 = 24.3 gsm; LDPE = 40 × 0.92 = 36.8 gsm.
• Total = 16.8 + 2.0 + 24.3 + 3.0 + 36.8 = 82.9 gsm.
• Yield = 1000/82.9 = 12.06 m²/kg.
• If the blended material cost is ₹240/kg, cost per m² = 240/12.06 = ₹19.90/m².
• A 150 mm × 220 mm three-side-seal pouch (seal allowance 8 mm): area = 2 × (150 + 16) × (220 + 8) = 2 × 166 × 228 = 75,696 mm² = 0.0757 m² → material cost ≈ 0.0757 × 19.90 = ₹1.51 per pouch.

Example 2 — Adhesive consumption, solvent-based vs solventless Order: 50,000 m² of laminate.

• Solvent-based at 2.2 gsm dry, adhesive supplied at 30% solids: dry = 2.2 × 50,000/1000 = 110 kg dry; wet mix = 110/0.30 = 366.7 kg of 30% solution, i.e. 110 kg solids + 256.7 kg solvent evaporated and to be recovered or oxidised.
• Solventless at 1.4 gsm: 1.4 × 50,000/1000 = 70 kg, zero solvent.
• Saving = 40 kg of adhesive solids; at ₹320/kg (solids basis) that is ₹12,800, plus the entire solvent cost and the drying energy.

Example 3 — Laminate WVTR by series resistance Two layers measured alone at their use thickness: BOPP(20 µm) WVTR = 5.0 g/m²/day; LDPE(40 µm) WVTR = 9.0 g/m²/day (38 °C/90% RH).

• 1/WVTR_total = 1/5.0 + 1/9.0 = 0.2000 + 0.1111 = 0.3111 → WVTR_total = 3.21 g/m²/day.
• Replace the plain BOPP with metallised BOPP at 0.30 g/m²/day: 1/WVTR = 1/0.30 + 1/9.0 = 3.3333 + 0.1111 = 3.4444 → 0.29 g/m²/day — an 11-fold improvement, and the barrier is now set almost entirely by the metallised layer (the usual outcome: the best layer dominates in series).

Example 4 — Moisture-limited shelf life of a biscuit pack Pack: 100 g biscuits, initial moisture 2.0%, spoils at 5.0% (dry-basis change treated on product mass for a quick estimate). Pack area 0.050 m², laminate WVTR 0.29 g/m²/day at 38 °C/90% RH, storage assumed at the test condition.

• Permissible gain W = 100 × (5.0 − 2.0)/100 = 3.0 g.
• Ingress per day = 0.29 × 0.050 = 0.0145 g/day.
• Shelf life = 3.0/0.0145 = 207 days ≈ 7 months.
• With the plain-BOPP laminate (3.21 g/m²/day): 3.21 × 0.050 = 0.1605 g/day → 3.0/0.1605 = 18.7 days — the whole commercial case for metallising in one calculation. (Real shelf life is shorter: Indian ambient is not a constant 38/90, the pack has seals and creases, and the critical moisture is product-specific.)

Example 5 — Reel length and bond strength conversion

• A 1,020 mm wide reel of the Example 1 laminate (82.9 gsm) weighs 420 kg net. L = 1000 × 420/(82.9 × 1.020) = 420,000/84.56 = 4,967 m.
• A peel test gives 4.5 N on a 15 mm strip → 4.5 × 102 = 459 g/15 mm — acceptable for a foil retort-grade structure's pre-retort specification, and it must be re-tested after retorting.

Where it is used

• Food and snacks: metallised BOPP wrappers for chips and namkeen, BOPET/met-BOPET for biscuits and confectionery, PET/foil/CPP retort pouches for ready-to-eat curries (ITC, MTR, Haldiram's) — roles: converting/process engineer, QA, packaging development.
• Dairy and beverages: 3-layer co-extruded PE pouches for milk (Amul, Mother Dairy, Nandini) run on form-fill-seal at the dairy; PE/EVOH for curd and paneer; spouted pouches for juices.
• Pharmaceuticals and personal care: foil-based strip packs and sachets, laminated tubes (EPL/Essel Propack — the laminated collapsible tube for toothpaste is an Indian export success), PET/met/PE for shampoo sachets at ₹1–2 price points.
• Agro, pesticides and industrial: barrier laminates with chemical-resistant sealants, FIBC liners, fertiliser and cement BOPP woven-laminated bags.
• Printing and converting plants: rotogravure and CI flexo printing followed by lamination, curing, slitting and pouching — the hiring base at Uflex, Huhtamaki, Paharpur 3P, SB Packagings, Parksons and hundreds of SMEs in Noida, Daman, Vapi, Hyderabad and Chennai.
• Compliance and sustainability roles: EPR registration and reporting on the CPCB portal, design-for-recycling projects converting MLP structures to mono-PE or mono-PP for brand owners.

Interview questions

• Q: Why laminate at all instead of using a thicker single film? A: No single resin gives printability, barrier, strength and a good seal together; layering lets each material do one job, usually at lower total weight and cost.
• Q: What is reverse printing and why is it used in flexibles? A: Printing in mirror image on the inner surface of the outer web so that after lamination the ink lies inside the structure — protected from abrasion and away from food contact, and viewed through a glossy film.
• Q: Difference between extrusion lamination and extrusion coating? A: Lamination bonds two webs with the molten polymer curtain between them; coating applies the molten polymer to one web as a functional surface layer.
• Q: Why does a laminate need curing, and what happens if you slit too early? A: Two-component polyurethane adhesive needs 24–72 h for the isocyanate to react fully; early slitting gives low bond strength, delamination, tunnelling and leftover primary aromatic amines that can migrate into food.
• Q: Film shows 30 dyne/cm. Will it laminate? A: No — aim for ≥ 38 dyne/cm; the surface must be corona-treated (or re-treated in line, since treatment decays) or the adhesive will not wet and the bond will fail.
• Q: What causes tunnelling in a laminate? A: Mismatched web tensions or moduli at the nip and during rewind — one layer relaxes more than the other, forming ridges or bubbles; it is a tension/curing problem, not usually an adhesive-chemistry problem.
• Q: Why is CPP, not LDPE, the sealant in a retort pouch? A: The pouch is sterilised at about 121 °C; LDPE softens and loses seal strength at that temperature, while retort-grade CPP holds its seal and bond.
• Q: How do you decide between 9 µm foil and metallised film? A: Foil when near-absolute barrier, light-blocking and long shelf life are needed (retort, pharma, infant food); metallised film when the barrier required is moderate, cost matters and flex cracking or pinholing is a risk.
• Q: How does the barrier of layers in series combine? A: Resistances add: 1/P_total = Σ 1/P_i, so the best barrier layer dominates and adding a poor layer barely helps.
• Q: What does residual solvent testing measure and why does it matter? A: Solvent trapped in the laminate after drying, measured by gas chromatography of the headspace; it causes odour/taint and is a food-safety and compliance issue, so it is kept to a few mg/m² against the customer and regulatory limit.
• Q: What are the key Indian regulations for a food flexible pack? A: The FSSAI (Packaging) Regulations, 2018 (food-grade material, migration limits, no ink on the food-contact surface, restriction on recycled plastic in direct contact), the FSS Labelling and Display Regulations, 2020, the Legal Metrology (Packaged Commodities) Rules, 2011 for declarations, and the Plastic Waste Management Rules with EPR obligations on the CPCB portal.
• Q: Your SUP leaks at the bottom gusset after filling. How do you investigate? A: Check seal integrity by dye penetration to locate it, then review jaw temperature/pressure/dwell and cooling, product contamination in the seal area, sealant grade and thickness at the four-layer corner, and whether the laminate was fully cured.
• Q: What is COF and why does the FFS machine care? A: Coefficient of friction of the outer and sealant surfaces; too high and the web will not slip through the forming collar, too low and pouches slide or the reel telescopes — it is specified as static and kinetic values.

Common mistakes

• Writing a structure without the layer orientation — putting the printed or barrier layer in contact with the product, or using an unsealable film as the inner layer.
• Adding WVTR or OTR values of the layers instead of combining them as resistances in series (1/P_total = Σ 1/P_i).
• Confusing thickness with grammage: forgetting to multiply µm by density, so a 9 µm foil (24.3 gsm) is treated as lighter than a 40 µm LDPE (36.8 gsm) by thickness alone.
• Quoting dry adhesive coat weight as wet consumption — for a 30% solids adhesive the wet quantity is more than three times the dry.
• Treating corona treatment as permanent; dyne level decays with storage time and temperature and must be checked before coating.
• Blaming the adhesive for tunnelling, curl or delamination that is actually a web-tension, cure-time or surface-energy problem.
• Using LDPE as a sealant for retort or hot-fill, or ignoring that BOPA's oxygen barrier falls as it absorbs moisture.
• Quoting withdrawn or superseded standards and the repealed Factories Act — safety at a lamination plant now falls under the OSH&WC Code, 2020 and the other Labour Codes in force since 21 November 2025, and the Solid Waste Management Rules, 2026 replaced the 2016 Rules from 1 April 2026.

Related topics

Packaging materials: paper, plastics, glass and metal · Food packaging · Packaging design and testing · Extrusion and blow moulding · Print finishing and binding · Rotogravure and flexographic printing