Adhesive Lamination
The process where a solution or emulsion of a low molecular weight polymer adhesive material is coated onto the surface of one web, before the joining of the second web, is typically called adhesive lamination. If the adhesive layer is dried before the joining of the second web, this is called dry lamination or dry bonding. lf the webs are joined while the adhesive is still wet, it is called wet lamination or wet bonding. For wet laminating, one of the webs must be porous to allow the evaporation of the water or solvent from the adhesive layer. A form of wet laminating can be done by using reactive adhesives which dry by cross-linking, and thus give off no volatiles, but this is usually called solventless adhesive lamination.
The process equipment for wet or dry laminating is rather similar. In both cases, the adhesive is applied by a roll applicator system. In dry laminating, the oven for drying comes in front of the nip for laminating, and in wet laminating it comes afterwards.
As mentioned above, the adhesive is applied to the web by a roll applicator system. These systems require some method of metering the amount of adhesive applied. This can be done by a blade on a gravure roll, a Mayer rod, or a doctor blade. The gravure roll is a metal roll covered with engraved cells. The coating is picked up from the coating pan; the excess is doctored from the roll by a metal blade running in contact with it. A Mayer rod is a stainless steel rod, wrapped with a wire that is rotated while in contact with the web after the adhesive has been applied. The excess adhesive is forced onto the rod, and flows back to the coating pan. A doctor blade is set at a certain distance from the web and removes any excess coating as the web runs by. The gravure roll applicator requires a low coating viscosity; the other systems are less viscosity sensitive.'
Adhesive lamination can also be done as a part of a printing press operation, if the press is properly equipped. This is the way many OPP/ink/adhesive/OPP/cold seal type structures are made. In this case the laminating station, with its secondary unwind and nip rolls, is inserted in line with the press, An additional printing station following the laminating section applies the cold seal adhesive.