Solventless lamination has advanced from a niche technology to the dominant process for flexible packaging in Europe, Japan, and increasingly in China. The driving forces are unmistakable: zero VOC emissions, no solvent recovery infrastructure, reduced energy consumption, higher line speeds, and improved food safety. Henkel’s Liofol laboratory — a dedicated solventless adhesive R&D center serving the global flexible packaging market — exemplifies the technology’s maturity. In Europe, solventless laminators account for 80–90% of new lamination equipment installations. In Japan, nearly 100 solventless laminators are in operation after two decades of adoption. Here is the technology’s current state and its development trajectory.
Advantages of Solventless Lamination
Solventless adhesives contain 100% solid content — no solvents, no water. The adhesive is applied at coating weights between 0.8 and 2.5 g/m² for most film-to-film laminations, and up to 4 g/m² for paper substrates. Solvent-borne adhesives typically require 2.0–4.5 g/m² dry coating weight, making solventless adhesives significantly more cost-effective on a per-square-meter basis.
The environmental and safety advantages are equally compelling. There are no volatile organic compound emissions, no explosion or fire risk, and no need for solvent storage and handling infrastructure. The adhesive is not classified as flammable, explosive, or corrosive — simplifying transportation, storage, and workplace safety compliance.
Because no drying tunnel is required, solventless laminators consume approximately 5% of the energy of a comparable solvent-borne laminator. A solvent-borne laminator’s drying section alone draws 150–250 kW. Average power consumption for a solventless machine is 50–70 kW — a fraction of the solvent-borne equivalent.
Line speeds are significantly higher. A typical solventless laminator runs at 250 m/min, with modern machines reaching 600 m/min — matching or exceeding the output of multiple solvent-borne lines. One solventless laminator can keep pace with three gravure printing presses.
Three Generations of Solventless PU Adhesives
First generation: Single-component moisture-curing adhesives based on polyether or polyester isocyanate-terminated prepolymers. These adhesives cured by reacting with atmospheric moisture, releasing CO₂ as a byproduct. The CO₂ caused bubble formation in the bond line — a persistent quality issue — and cure speed was slow, limiting production throughput.
Second generation: Two-component solventless adhesives introduced in the 1980s. Both components are reactive prepolymers — one with hydroxyl end groups, the other with isocyanate end groups. The two components are mixed immediately before application, and the chemical reaction begins at the mixer. The second generation improved cure speed and eliminated the CO₂ bubble problem but had two limitations: low initial tack (green strength), making the laminated rolls difficult to handle immediately after lamination, and poor adhesion to EVA sealants and aluminum foil.
Third generation: Improved two-component systems that resolve the second generation’s deficiencies. These adhesives offer high initial tack, low viscosity at application temperature, and excellent adhesion to EVA, nylon, and aluminum foil. Application temperature is lower than second-generation systems, reducing energy demand and thermal stress on heat-sensitive films. Bond strength after full cure matches or exceeds solvent-borne equivalents. Third-generation adhesives are now available with retort resistance for boil-in-bag and retort pouch applications.
Fast-Cure and UV-Cure Solventless Systems
Conventional two-component solventless adhesives require 24–72 hours at 40–50°C to reach full bond strength. For converters with tight order-to-delivery windows, this curing time is a bottleneck. Two accelerated approaches have been commercialized:
Fast-cure (high-reactivity) adhesives: Modified polyurethane formulations with optimized catalyst systems that achieve handling strength within 1–2 hours at elevated temperature. These systems require precise mix-ratio control and temperature management but enable same-day slitting and converting, dramatically reducing work-in-progress inventory.
UV-curable solventless adhesives: The newest approach. The adhesive is applied and immediately exposed to UV radiation, which triggers rapid crosslinking within seconds. UV-curable adhesives achieve handling strength within minutes — eliminating the curing oven entirely and enabling reel-to-reel lamination at maximum line speed. The technology is still limited by the need for UV transparency in at least one substrate film, which restricts its use to laminations where one layer is clear and UV-transmissive.
Equipment Differences
Solventless laminators differ from solvent-borne laminators in three critical aspects:
- No drying section. The machine is shorter, simpler, and consumes far less energy. A typical solventless laminator occupies 40% less floor space than a solvent-borne equivalent.
- Precision metering and mixing. Two-component adhesives require accurate ratio control (typically ±1% by weight) and homogeneous mixing. The metering and mixing head is the most critical component of the machine — its precision determines bond quality consistency.
- Heated application system. Most solventless adhesives are applied at 60–80°C. The adhesive supply lines, coating pan, and applicator roll are temperature-controlled to maintain viscosity within the optimal range.
Substrate Selection and Process Considerations
Solventless lamination is suitable for most common flexible packaging film combinations: BOPP, PET, OPA (nylon), VMCPP, VMPET, CPP, PE, and aluminum foil. Typically, the less extensible substrate (PET, BOPP, OPA, VMPET) is run on the primary unwind and coated with adhesive, while the more extensible substrate (PE, CPP, VMCPP) runs on the secondary unwind and is nipped to the coated web. This arrangement minimizes web handling issues with extensible films. The arrangement can be reversed depending on specific process requirements — for example, when laminating printed film to an inner sealant layer, the printed film may be placed on the secondary unwind to protect the print surface from roller contact.
Two specific contamination risks must be managed:
MDI migration: Monomeric MDI (methyl diphenyl diisocyanate) from the adhesive formulation can migrate through thin inner sealant layers and react with moisture on the package inner surface, forming crystalline polyurea deposits that appear as white spots or haze on the sealant layer. This is particularly problematic with thin PE sealant layers (below 40 μm). The solution is to use adhesives with low free-MDI content or to specify a thicker sealant layer.
Slip agent migration: PE and CPP films contain slip additives (erucamide, oleamide) that bloom to the film surface during storage. These additives can migrate into the adhesive layer after lamination, reducing bond strength and causing seal failure or coefficient of friction changes. When laminating high-slip films, the adhesive system must be selected for compatibility with the specific slip package, and the adhesive coating weight should be sufficient to provide a continuous bond line.
The selection of a solventless adhesive for a given application must consider the packaging contents (chemical resistance requirements), the film types and thicknesses, the ink system (compatibility between ink binders and the adhesive), the required bond strength (peel values and seal strength), and the converting conditions (line speed, curing temperature, slitting window). The continuous innovation in solventless adhesive chemistry — fast-cure, retort-resistant, low-MDI, high-initial-tick formulations — is steadily closing the performance gap with solvent-borne systems. In the prevailing carbon-reduction policy environment, the economic, safety, and environmental advantages of solventless lamination make it the default technology choice for new flexible packaging capacity worldwide.
References
- Wikipedia: Lamination: Overview of dry-bond, solventless, and extrusion lamination processes used in flexible packaging converting.
- Wikipedia: Polyurethane Adhesive: PU adhesive chemistry, two-component reaction mechanisms, and property tuning for flexible packaging applications.
- Wikipedia: MDI: Chemical properties, safety profile, and regulatory status of methyl diphenyl diisocyanate used in PU adhesive formulations.
- Wikipedia: Volatile Organic Compound: Environmental regulations driving the transition from solvent-borne to solventless technologies in packaging converting.
- Wikipedia: UV Curing: UV-curable adhesive technology for instant-cure solventless lamination — mechanism, equipment, and substrate limitations.