By incorporating a laminator into any production environment, the possibilities for product diversity and penetration into new markets can be greatly increased. Beyond the commercial benefits of adhesive laminating, however, press operators also need to know about the operational elements and parameters of the laminating process that need to be considered--and adhered to--for optimal performance and high-quality results. This article will address those elements.

The Materials
Substrates. The end product is only as good as the substrates and adhesives that are put into it. Films that are of good quality, properly wound, with uniform thickness and gauge control are essential to producing an acceptable laminated structure. Extensible substrates that exhibit curl, wrinkles and other anomalies going into the process will exhibit--or even accentuate--these same characteristics in the finished product.

Inks. Keep in mind that it is typical for one of the laminated substrates to be printed. This means that the ink being applied must be suitable for laminating. Complete drying of the ink is extremely important, as any residual water or solvent will adversely affect adhesion and appearance. To ensure that ink is adequately dried, an analysis for retained solvents is normally performed, particularly for applications involving food packaging, where odor and product safety concerns are paramount.

Adhesives. Proper storage and handling of adhesives is important. It is always recommended to keep them in a clean, dry environment, without exposure to extreme temperatures. With many adhesives--especially solventless--meter / mix / dispense (MMD) equipment is required to dispense several components (e.g., adhesive and co-reactant) at a predetermined mix ratio (as specified by the adhesive supplier) to the laminator.

Because the mix ratios vary, it is critical for an MMD unit to have the capability to maintain the correct ratio and monitor this ratio on a regular basis. An improper mix ratio will prevent the adhesive from curing properly, resulting in marginal or defective product.

The Laminating Process
Certain guidelines and principles for operation of the laminator govern the necessary control over this process. They are listed below.

Accurate and reliable web tension control. It is of critical importance that the machine is designed to precisely regulate the tension of the substrates--from the unwinds to the rewind--to avoid formation of creases, wrinkles, curl, etc. and obtain a good finished roll of laminated material. This is especially true when using solventless (100-percent solid) adhesives, due to their low initial green tack and the corresponding effect this has on controlling substrate tension before and after lamination.

Regular and uniform adhesive application. In the dry-bond laminating process, the volume of the engraved gravure cylinder will determine the amount of adhesive applied to the web. In the solventless process, however, adhesive quantity is determined by the speed differential, temperature and gap between coating rolls.

The ability to control and monitor these variables in an accurate and reliable manner will not only influence the overall properties of the final laminated structure, but also affect the economics of the process; i.e., the lower the prescribed coating weight possible for any given application, the lower the applied cost. For this reason, coating weight should be checked regularly, using material run at the process line speed.

Nip pressure and temperature control. In order to ensure intimate contact when the two webs are combined, nip pressure should be adjustable on both sides. Nip temperature affects the appearance and tension of the laminated structure and should be controlled through a separate heat-control unit.

Corona treatment. While some films may be treated to the proper level, other films will need additional treatment on the laminator to promote adhesion. The rubric "pay me now or pay me later" may apply to one's decision to use (or not use) a corona treater. The capital investment for a treater can easily be offset by a roll of laminated material rendered defective by inadequate surface treatment.

Roll storage. Finished rolls of laminated stock should be stored in an environment that is not too cold (to retard curing). Depending on the adhesive and application, they are also sometimes put into "hot rooms" to accelerate curing. To avoid rolls taking a "set" during the curing process, they should be suspended and stored in a rack.