Dry lamination is the process of applying an adhesive onto a substrate, followed by drying and evaporating the solvent to increase the initial and bonding strength of the adhesive, and then laminating it onto another substrate. Wet composite, on the other hand, is the opposite, first applying adhesive and pressing the composite, and then heating, drying, and curing it. Obviously, wet lamination is not suitable for the lamination of plastic films. Because a large amount of adhesive solvent is pressed and laminated onto the composite film after adhesive bonding, the plastic film cannot evaporate these solvents during drying and curing, nor can they be absorbed by the plastic film. Therefore, wet lamination is not suitable for laminating between plastic films. Wet lamination is only suitable for the lamination of porous materials, such as paper, wood, plywood, etc. or porous foam plastics. Because these materials are loose and have a large number of pores, the solvents in the adhesive can be emitted or absorbed through the pores in these materials during the heating and curing process.
The adhesives used for wet composite are generally acrylic latex, EVA latex, phenolic resin adhesive, and other organic solvent adhesives. The substrate includes paper, fabric, non-woven fabric, glass paper, aluminum foil, etc. Wet composite adhesive can also use starch adhesive. The wet composite process of aluminum foil and paper is as follows: unwinding the aluminum foil → applying adhesive → pressing it onto the same paper → applying lubricant or gloss on the other surface of the aluminum foil → drying and curing in the drying oven → winding. This method of composite materials can be used for packaging cigarettes, chocolates, and other items, as well as for packaging candies, pharmaceuticals, and baked goods. However, the interlayer bonding strength has poor water resistance, heat resistance, and chemical resistance. Under high temperature and humidity conditions, these hydrophilic adhesives may experience delamination and corrosion of aluminum foil.
Compared with other composite processes, the dry composite method has the following advantages: (1) the available substrate surface is wide, which can be composite of plastic and plastic, plastic and paper, plastic and metal, fabric, non-woven fabric, etc., even without plastic, paper and metal can be composite; (2) The composite has high fastness, with interlayer peeling force of over 100025m wide, and can produce high-end packaging products such as high-temperature steaming bags; (3) The thickness of each layer can be freely selected and precisely controlled; (4) It can be printed on the surface or on the reverse side; (5) The production speed is fast, with a general operating speed of 150-180m/min and a maximum speed of over 200m/min. The disadvantage of dry composite is that: (1) the composite requires the use of adhesives, which poses a toxicity problem of residual solvents. Therefore, the packaging materials of dry composite, especially those cured with two-component polyurethane adhesive, cannot be used in the North American and European markets, but can only be sold in Southeast Asia, Africa and other places.
