Water-Based Heat-Seal Lacquers for Pan Masala and Mouth-Freshener Pouches

Executive summary

The single-serve pouch for pan masala, mouth fresheners and similar products is one of India’s highest-volume packaging formats: a paper / aluminium-foil or metallised laminate, gravure-printed, coated with a heat-seal lacquer (HSL) and formed, filled and sealed at high speed. The HSL has traditionally been a solvent-based vinyl or acrylic lacquer, applied at 4 – 8 g/m² and releasing several kilograms of solvent per thousand square metres. This paper sets out the performance an HSL must deliver, why converting it to water is technically demanding, and how Uniform Industries’ water-based HSL meets seal strength, blocking, aroma-barrier and hot-tack requirements without solvent.

1. What the lacquer has to do

A heat-seal lacquer is a thermoplastic coating that is solid and non-tacky at ambient temperature and flows to form a bond when pressed between heated jaws. On a pan masala pouch it must:

Seal to itself (fin seals) and to foil or paper (lap seals) at jaw temperatures of 120 – 180 °C and dwell times below 0.5 s, giving seal strengths of 300 – 600 g/15 mm or, for tamper evidence, a seal that tears the paper rather than peels.

Not block in the reel: coated web wound at 40 – 50 °C on a hot day must unwind cleanly after weeks in storage.

Provide aroma barrier: the product’s volatile flavours (menthol, cardamom, saffron essence) must stay in, and the lacquer must not itself impart odour or taste.

Resist the product: oils, essences and moisture in the contents must not soften or delaminate the seal.

Run on the packing machine: a hot-tack strong enough to hold the seal while the pouch is still warm, controlled slip for forming collars, and no build-up on sealing jaws.

2. Why water-based HSL is difficult

Solvent-based HSLs use vinyl-chloride/vinyl-acetate copolymers or acrylic resins dissolved in ketone/ester blends: the dry film is a single continuous polymer with a sharp softening point. A water-based HSL is an emulsion or dispersion — discrete polymer particles that must coalesce into a continuous film on drying and then behave like the solvent-cast film in the sealing jaw. Getting both properties from the same polymer is the core difficulty: a low glass-transition polymer coalesces and seals easily but blocks in the reel; a high-Tg polymer resists blocking but needs high jaw temperatures and fails hot-tack.

Figure 1 – Core-shell dispersion: tack-free shell in storage, flowing core in the sealing jaw (schematic).

3. The formulation approach

Uniform Industries’ water-based HSL uses a core-shell acrylic / EVA hybrid dispersion: a low-Tg, high-flow core that provides seal initiation and hot-tack, inside a higher-Tg shell that keeps the coated surface non-tacky at storage temperature. In the sealing jaw the shell softens, the cores flow together and a continuous seal layer forms in under half a second. Supporting components are:

a wax and slip package for blocking resistance and controlled coefficient of friction on the forming collar;

coalescent and film-forming aids chosen from the food-packaging-compatible list, so that film formation is complete at dryer temperatures of 80 – 100 °C;

a defoamer and wetting package for foil and metallised surfaces;

no plasticiser migrants and no odour-active raw materials, verified by sensory panel against the unlacquered laminate.

The lacquer is supplied at 40 – 45 % solids and applied by gravure at 3 – 5 g/m² dry — the same coat weight window as solvent HSL — with drying at 80 – 100 °C and the reel wound after a chill roll.

4. Performance data

Property

Water-based HSL

Test

Seal strength, lacquer to lacquer (fin)

≥ 400 g/15 mm; paper tear on paper laminate

150 °C, 0.5 s, 2 bar; ASTM F88

Seal strength, lacquer to foil (lap)

≥ 300 g/15 mm

as above

Sealing window

120 – 180 °C

jaw temperature sweep

Hot tack

≥ 150 g/15 mm at 150 °C, immediately after jaw opening

ASTM F1921

Blocking

No blocking

40 °C, 75 % RH, 1 kg/25 cm², 24 h, lacquer to print

Coefficient of friction

0.25 – 0.35

ISO 8295

Odour / taint

No difference from blank

sensory panel, 40 °C, 24 h

Retained solvent

Nil

GC headspace

Figures are laboratory typical values on 60 g/m² paper / 7 µm aluminium foil laminate; performance on metallised paper and PET laminates should be confirmed by trial.

Figure 2 – Sealing window: seal strength against jaw temperature, water-based versus solvent HSL (illustrative).

5. Converting the line

Dryer: water needs airflow; increase exhaust and impingement velocity before raising temperature, and fit a chill roll before rewind.

Cylinder: 60 – 80 lines/cm, cell volume for 3 – 5 g/m² dry at 40 – 45 % solids.

Press hygiene: stainless or lined ink pans and pumps; flush with water at shutdown; alkaline cleaner for dried lacquer.

Packing machine: most lines need no change; jaw temperature is set 10 – 20 °C below the solvent-HSL setting.

6. Why it matters

A pouch converter running 5000 m²/h of laminate at 6 g/m² wet solvent lacquer emits roughly 18 kg of solvent per hour; over a year that is more than 100 tonnes released or incinerated. Water-based HSL removes it, along with the fire risk of solvent storage, retained-solvent taint in a product eaten from the pouch, and the cost of solvent recovery — while keeping the same seal performance on the same laminate and machine.

Key takeaways

An HSL must seal fast, not block, keep aroma in and survive the product — a demanding property set.

Water-based HSL is a film-formation problem solved by core-shell polymer design.

Coat weight, sealing window and seal strength match solvent HSL; retained solvent is nil.

The dryer needs airflow and a chill roll; the packing machine usually needs nothing.

References: ASTM F88 (seal strength); ASTM F1921 (hot tack); ISO 8295 (COF); ASTM D1146 (blocking).