The Key Control Points in the Solventless Lamination Process

The use of solventless lamination is gaining increasing popularity, and how to effectively employ this process is a topic of great concern. To make the most of solventless lamination, it is strongly recommended that companies with the capability invest in multiple solventless machines or dual adhesive mixer, using two mixers: one for a universal adhesive covering the majority of product structures, and another to supplement with a functional adhesive suitable for surface or inner layers, tailored to your customer's product structure.

The advantages of dual adhesive mixers are clear: they extend the range of applications for solventless lamination, reduce emissions, lower costs, and improve efficiency. Moreover, it eliminates the need for frequent cylinder cleaning and adhesive switching, reducing waste. This approach allows you to select adhesives based on specific product and customer requirements, ensuring product quality.

In my extensive experience serving customers, I have also identified several critical process control points that must be carefully managed to excel in solventless lamination.

1. Cleanliness - To excel in solventless lamination, cleanliness is of utmost importance and often overlooked by many companies. Rollers, metering rollers, coating rollers, coating pressure rollers, composite steel rollers, composite pressure rollers, adhesive mixing ducts, adhesive buckets, and all guiding rollers must be free of foreign particles. Even the smallest foreign particle in these areas can result in bubbles and white spots on the laminated film.
2. Temperature Control - Solventless adhesives consist of NCO (usually called the NCO component) and OH (usually called the OH component) components. The density, viscosity, performance of the main adhesive and curing agent, adhesive usage life, operating temperature, curing temperature, and time, among other factors, affect lamination quality. It is crucial to control the coating temperature, as too high a temperature can lead to gelation and the formation of high molecular weight resins, making coating difficult or uneven. Most adhesive suppliers provide reference parameters, including a temperature range, for customers. The higher the temperature before mixing, the lower the viscosity, while a higher temperature after mixing results in higher viscosity. Typically, the coating roller temperature should be maintained at around 50±5°C.
3. Coating Amount Control - Different coating amounts may be used depending on the substrate. The control of coating amounts is primarily determined by the gap and speed ratio between the metering roller and the fixed rollerTransparent lamination film 0.8~1.2 gsmPrinted lamination film 1.2~1.5 gsmMeltalised lamination film 1.5~1.8 gsmBoiled lamination film 1.5~1.8 gsmRetort lamination film 1.8~2.2 gsm
4. Tension Control - Tension control is crucial in solventless lamination. Due to the low initial tack of solventless adhesives, a mismatch in tension between the front and back films can result in the appearance of air bubbles and tunnels during curing.
5. Pressure Control - Pressure control is also vital since the coating pressure directly affects the coating amount. For adhesives with good leveling properties, higher pressure leads to a lower coating amount.
6. Ink and Adhesive Compatibility - While the compatibility between solventless adhesives and inks is generally good, compatibility testing should be performed when changing ink suppliers or adhesive systems.
7. Humidity and Environmental Control - Regularly monitor humidity levels and adjust the NCO and OH component ratios accordingly. High humidity can affect adhesive transfer. Solventless lamination is a high-speed process, and as a result, the substrates generate static electricity. This can lead to the adhesion of dust and impurities, affecting product appearance. It is essential to maintain a relatively enclosed production environment to meet temperature and humidity requirements.
8. Preheating Adhesive - Adhesive should be preheated before entering the cylinder. Mixing adhesive should occur after reaching a certain temperature to ensure proper adhesive transfer.

In conclusion, in the current landscape where solventless and dry lamination coexist, companies should maximize equipment utilization and profits by innovating processes and developing unique products. Anything others can do, we can do, and what we can do, others cannot. By adopting proper and effective production scheduling, fully utilizing existing equipment, and striving for maximum production capacity, production losses can be minimized through precise work instructions.