LAMINATION
What is lamination?
Film and multilayer laminates, also known as complex film, include those flexible materials obtained by combining two or more films made up of single materials.
Why are films laminated?
Obtaining multilayer structures has enabled us to increase the applications of plastic materials for food packaging. Sometimes there is no single material that meets all the requirements needed to preserve the product. The combination of various materials with different properties and functions therefore makes it possible to offer an optimum structure for packaging.
What properties should packaging materials have?
Generally, the critical properties required by the plastic materials used for food packaging should include the following: The capacity to provide a barrier to preserve the nutritional and organoleptic qualities of the product. This means preventing gasses from entering(oxygen and water vapour), and also from leaking (aromas, loss of CO2 in carbonated beverages, modified atmospheric loss). Tear and puncture resistance of the material plus sealing capacity to guarantee the watertightness of the packaged product. All application in which the container needs to be subjected to sterilisation processes or microwave heating should have good heat resistance. The material should have a visual appearance that can attract the consumer’s attention, and provide the ideal support for transmitting the brand’s image, plus information on the characteristics of the packaged product.
Laminating processThe main support reel is given a continuous coating of adhesive solution, and without coming into contact with the rollers or the other support unit, it then passes through a drying tunnel, where a forced stream of warm air and a powerful extraction process eliminate the solvent included in the coating.The only thing remaining on the support unit of the adhesive resin mixture is the solid part, which now has initial tack properties enabling it to be pressed against the other support element once it comes out of the tunnel. This initial tack prevents the joined supports from slipping and sliding. The assembly of both these supports is wound on to the reel, maintaining a certain amount of pressure between turns to ensure good contact and a strong final bond between the two. The crosslinking reaction of the adhesive progresses over time and the strength of the bond increases, with at least 24 hours being required before a satisfactory bond is achieved, which enables the manufacturing process to continue (rewinding and cutting).
Why is solventless lamination used?
The solventless system is the system that is most commonly used. We use high-performance solvent-free adhesives, which are guaranteed to work in most applications. This means costs are optimised and there is less impact on the environment.
Solventless adhesives were developed as an industrial response aimed at:
Reducing the environmental impact caused by the evaporation of the solvents (there is some very strict legislation limiting the emission of volatile organic compounds (VOCs). Improving the energy performance of water-based adhesives, requiring higher drying temperatures in the kilns, and making it impossible to offer faster speeds of production. Due to the high viscosity of this type of adhesive, it needs to be applied at 70-100°C for easy machinability. Furthermore, the adhesive open time is very short – about 15 minutes.
Why is solvent-based lamination used?Normally a solvent-based adhesive is used in extreme lamination cases for post-packaging applications, due to the type of treatment the product to be packaged will undergo, such as pasteurisation for example. The solvent evaporates when it passes through the drying tunnel.The resins forming the adhesive are dissolved in organic solvents that might be one or more of the following: ethyl acetate, ethanol, isopropanol, methyl ethyl ketone (2-butanone). When they are to be used in the laminating machine, regardless of the solvent used in the formulation, a greater quantity needs to be added to obtain the right viscosity for the application in question.
