The “lamination” actually means the films with different performance stick each other by some ways, and then protect the contents by sealing. The common lamination ways in packaging industry mainly include dry lamination, wet lamination, extrusion lamination, co-extrusion lamination.
Dry lamination
In the various processing technologies of laminated films, the dry lamination is the most traditional and widely used lamination technology in China, which is widely used for packaging in food, drugs, cosmetics, daily necessities, light industrial products, chemicals, electronic products, etc. The dry lamination mean the plastic film is coated with a layer of solvent-based adhesive in coating device (generally gravure mesh roller coating is used) , removed the solvent and dried by lamination device, then composited with other substrate materials in the hot press state, such as film, aluminum foil, etc. Because it is composited under “dry” adhesive state ( no solvent state) , so people called it dry lamination.
Dry lamination is suitable for a variety of substrates films & aluminum foil & paper. Because of the excellent resistance to chemical media erosion, such as alkali, acid, spicy, grease and other ingredients in food, water, flavor, emulsifier and other ingredients in cosmetics, solvents, pesticides and other ingredients in chemicals. So the dry laminated material is widely used in packaging with harsher conditions. Strong composited strength, good stability make it not only produce both high- and mid-grade composited film, but also produce composite film for frozen, fresh or high-temperature sterilization. Besides, flexible usage and simple laminated operation is suitable for the production with more varieties, less batch. However, dry lamination has some disadvantage with poor safety and health, environmental pollution, higher costs and others. While the development of alcohol-soluble, water-soluble adhesives slow down the pressure of solvent-based adhesives in these aspects. Dry composite in the composite processing method still takes up the high proportion and couldn’t be replaced by the extrusion composite, wet composite, solvent-free composite at the present.
Wet lamination
Wet lamination is coating the adhesive layer on the surface of the composite substrate material, like plastic film, aluminum foil, and then laminated with other materials like paper, cellophane by pressure rollers while the adhesive is not dry, and being the composite film after running through drying process. Its characteristic is simple operation, less adhesive, low cost and fast composite speed. The main adhesives include polyvinyl alcohol, sodium silicate, starch, polyvinyl acetate, ethylene – vinyl acetate copolymer, polyacrylate, natural resin, etc. Wet composite machine working principle is almost same as dry composite. The difference is as below: Dry lamination is the film with adhesive would be dried first, and after the organic solvents in the adhesive volatilize, laminated with other materials.
Wet lamination is the film with adhesive laminate with other materials first, and then dry by oven.
When the manufacturer use wet lamination, one of the two substrates material should be porous(e.g. paper or cardboard), so that the thinner in the adhesive is easy to evaporates when it dries. Therefore, the wet lamination is widely used for lamination of paper/fiber, paper/paper, paper/cardboard, paper/aluminum foil or others.
Extrusion Coating film
Extrusion coating means the thermoplastic plastics such as polyethylene is fused and flowed from a flat head, pressed against another substrate between two rollers in close contact, and be a laminated film after cooling. The substrate materials are usually printed PET, BOPP, paper, etc. The instant noodle bags is a typical example of extrusion coated product with the structure: BOPP printed film / LDPE (or PP).
Extrusion laminated film
Extrusion lamination is an extruded resin sandwiched between two substrates, which acts as an adhesive that binds the two substrates together, and is a composite layer at the same time. The first substrate is often PET, BOPP, PA, paper and other material. The second substrate is generally LDPE, CPP, aluminum foil, aluminized film and other materials. The extrusion resin is PE, PP, EVA, EAA and other resins. Generally, the laundry detergent packaging film can be laminated by this method, the structure is as follows: BOPP printing film / extrusion resin / PE film.
Solvent-free lamination
The adhesive used in solvent-free lamination is concerned due to no organic solvents. In Europe and the United States and other developed countries, the solvent-free lamination has become the main production method for flexible packaging composites. The solvent-free adhesive is coated on the substrate and directly laminated with other substrate. Although the adhesive is also used same as dry lamination, there is no organic solvents in adhesive, so the drying device isn’t required. Besides, this lamination way will be the development direction in the further, as its environment-friendly, and the product performance is as good as dry lamination.
Co-extrusion lamination
Co-extrusion lamination means two or more different kinds of plastics are melted and plasticized by two or more extruders, and then fed into a single die or fed into the die through a distributor that converges the plastics supplied by various extruders to prepare a composite film. The different plastics mentioned here could be different kinds of plastics, or the same kind but different grades plastics, or the same grade but different formulations of plastics. The cost of co-extrusion lamination is lower for 20%-30% than dry lamination. And no adhesive or anchor coating agent (AC agent) is used in the co-extrusion lamination process, so there is good hygiene and no environmental pollution problems. However, the materials are restricted obviously. The composite film for co-extrusion compounding process is limited to a variety of thermoplastics. The aluminum foil, paper and other composite materials can not be produced is co-extrusion compounding. In addition, the printing between composite films is not workable, and it only could be printed design, word on the surface of the composite film.
In summary, the lamination methods above have their own advantages and shortcomings. From the current stage of development, the dry lamination is the most extensive, accounting for the largest proportion. The extrusion lamination developed greatly, just next to the dry lamination in accounting for the proportion. The wet composite and co-extrusion composite process is restricted so obviously by the material that they can not to be the mainstream. The solvent-free composite technology has matured in developed countries, but still basically in start-up stage in developing countries. But many people believe it will be development direction in composite processing methods in the further.
