Multi-Web Inline Lamination: Simultaneous Coating and Bonding for Complex Composites
Complex composite products such as medical dressings, high-barrier packaging films, and multi-layer labels often require laminating three or more webs in a single pass. Multi-web inline lamination with hot melt coating enables this by adding multiple coating stations and laminating nips in sequence. A typical three-layer construction might be: release liner / PSA / face stock / adhesive / top film. The process flow begins with the primary substrate (release liner) being coated with hot melt PSA using a slot die. A secondary substrate (face stock) is laminated immediately after the die. The resulting two-layer laminate then passes to a second coating station where a different adhesive (e.g., a lower-tack PSA) is applied to the exposed side of the face stock. A third web (top film) is laminated in a second nip. The composite then proceeds through cooling and winding. Each coating station must have independent temperature, pump speed, and tension control to accommodate different adhesives and substrates. The configurable Nordson melt and metering units allow various types of hot melt adhesives, sealants, lotions, surfactants, and other materials to be processed, with melt rates from 1 to 1000 kg/hr and up to eight separately-controlled metering pumps per unit.
Register control becomes critical when coating or laminating onto printed webs. A registration sensor (optical or ultrasonic) detects a printed mark on the web. The PLC compares the actual position to the target position and adjusts the speed of the coating station or laminating nip slightly to align the adhesive pattern with the printed graphics. For pattern coating on labels, the slot die’s shim may produce adhesive stripes that must exactly match the label repeat length. Registration accuracy of ±0.5mm is typically required; for high-end medical or security products, ±0.1mm may be needed. The HM-Flex line from Elite Cameron, with Schneider PLC and servo drives, achieves perfect registration and tension control throughout. The in-line lamination unit re-laminates a variety of materials in one pass, dramatically reducing machine non-operational phases, waste of printed material or adhesive, and energy consumption. The in-line combination of flexo and rotogravure printing with hot melt lamination allows executing multiple packaging processes in one single passage. The hot melt coating unit, using a roto cylinder, applies layers or spots of hot glue on the back of printed substrates in one pass, saving money, waste, and human resources.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Handling stretch-sensitive substrates in multi-web lamination requires careful tension management. If a stretchy substrate (e.g., elastane nonwoven) is laminated to a non-stretch substrate (e.g., PET film), the composite may pucker if tensions are mismatched. The solution is to use an “unwind with dancer” that maintains very low tension (0.5-2 N/cm) on the stretchy web, and to set the laminating nip pressure just high enough to bond but not so high as to compress the fabric. For multi-layer labels with a foam core, the foam may compress under high nip pressure, causing label thickness variation; use a soft rubber nip roll (Shore A 30-40) and lower pressure (2-4 N/mm). Nordson coaters and coating stands are available for applications requiring a coating width up to 350 mm (CT 4400 series) with a cantilevered design making it an economical “one-man machine,” and for widths up to 800 mm (CT 5500 series) with a dual-frame roll mounting and distinct, functional design, making it one of the most flexible units of its kind.
Multi-web lamination for flexible packaging often includes inline printing, coating, and laminating. The process flow may be: unwind PET film, print graphics (flexo station), apply corona treatment to increase surface energy, apply hot melt adhesive via slot die (full width), laminate to a second substrate (aluminum foil or PE film), cool, and rewind. All stations are synchronized by a master line shaft or electronic gearing. The NDC measurement system continuously monitors and displays coat weight. The totally integrated solution is controlled using a Schneider PLC, with servo drives for perfect registration and tension control throughout. For packaging applications requiring a barrier, the adhesive must be applied at a consistent weight (e.g., 5-10 gsm) to avoid pinholes that would compromise the barrier. Online pinhole detection using a high-voltage spark tester can be integrated after the laminating nip. The Rhino GEW UV system with chill rolls, double-sided Vetaphone corona treater, and Proact web cleaner are often incorporated to prepare the substrate surface and cure any UV-releasable coatings.
Process startup for multi-web lamination requires careful threading. The primary substrate is threaded first, then each subsequent web is added after its respective laminating nip. Many lines have “thread-up” modes that run at low speed (5-10 m/min) until all webs are aligned. Operators should verify that all splices are properly made and that the adhesive patterns are registered. Once the line is at speed, the closed-loop coat weight control and tension control take over. For products with high quality requirements (e.g., medical composites), the first 50-100 meters of each roll are considered “transition” and may be discarded. Data logging records all parameters for traceability. The remote diagnostic system using an internet-based connection allows the manufacturer to troubleshoot issues from off-site, reducing downtime. The latest machines incorporate closed-loop unwind tension control, edge guiding for the two unwinds and the rewind, closed-loop rewind tension control, gap winding capability, extensive recipe and diagnostic systems, and a remote diagnostic system using an internet-based connection.
Defect analysis in multi-web lamination is more complex than single-web coating because defects can originate in any layer. A delamination between layers 2 and 3 may be due to low bond strength of adhesive #2, or contamination on the surface of substrate #2. A systematic approach: take samples and peel each interface separately. Measure coat weight of each adhesive layer by dissolving or peeling the layers. Inspect each substrate for surface energy (dyne pens). Check tension logs for the period when the defect occurred; a tension spike may have caused stretching, leading to misalignment. Many modern lines have a defect mapping system that records the position of defects detected by vision cameras; a downstream rewinder can automatically cut out defective sections. By mastering the complexities of multi-web inline lamination, manufacturers produce sophisticated composite products that meet the demanding requirements of medical, packaging, and industrial markets with high efficiency and quality.
