Dry laminations are those in which the liquid adhesive is first dried before lamination. The adhesive can be either applied to one substrate and dried or it can be applied as a hot melt type or film. The solvent-based adhesive is then in the dry solid or slightly tacky stage when joined with the other substrate. The bonding is generally achieved during a high temperature, high pressure nip.
The temperature and pressure are sufficient to cause the adhesive to flow and create an instantaneous bond when it cools and gels. Dry lamination can be applied to a broader range of products such asfilm to film lamination and film to foil lamination.
The stress applied by the laminator is another parameter that is important. During the lamination process the substrate can experience unwinding, coating with adhesive, drying, lamination in a nip, and rewinding. It also will pass over many idler rolls and undergo the tension necessary to pull the films through the process. Certain films may be prone to web breaks or tearing.
Proper surface preparations and selection of the right adhesive will help ensure a long lasting bond & prevent delamination from occuring. In order for the adhesive to effectively wet and bond to the substrate, the adhesive should have a surface tension that is ideally lower than the critical surface tension of the substrate being coated. This may require the prebond surface preparation of certain low surface energy films such as polyethylene, polypropylene. Until recently such surface preparation of film was limited to corona treatment, which is aimed specifically at improving the efficiency of the lamination process.
