What different types of lamination or coating for flexible packaging materials?
Flexible packaging materials are used in an increasing way globally, as they fulfil the need for reduced packaging volume and weight, and simplicity.
In many cases, the material is laminated, to combine the properties of two different materials, or coated, to protect the printed layer and add barrier properties.
There are several common methods:
Adhesive (Wet) Lamination
In this method, a material is coated with a thin layer of adhesive, usually in a liquid form. Then this is fed through rollers to press it against another material, and the two bond together. The adhesive gradually dries, with a combination of heat and time, leaving a finished bonded material. Some adhesives contain solvents that evaporate off in the drying process, others are solvent-free. This method is common and relatively cheap, but requires considerable set up and clean-down time, and a cure time before the next process, maybe several days. Also most digitally printed materials will need the addition of a primer before lamination, which adds another process and cost.
This process involves extruding a molten plastic resin through a very small slot onto another material. The two materials bond together and are passed between large rollers, and form a single laminated material. This is a cost-effective method for very high volumes, but is generally purpose built for a particular product, and requires considerable space and long-term investment.
Pressure Sensitive Lamination
Here we have one material that has already been coated with an adhesive by a third party. Like a giant roll of sticky tape, the material is pressed against another material, and the two squeezed together between rollers – no heat involved. The finished material is bonded together by the layer of adhesive between them. This method is ideal for heat-sensitive materials, or low volumes, but tends to be more hazy than other lamination methods, and lower bond strengths.
Water based or UV-cured Varnish
These varnishes are applied in a thin layer to the material, and provide a clear protective layer. The varnish is dried by heat or UV light. The finished result is thinner than lamination, but less durable, and may scratch. Also there is a risk of contamination of the packaged product if the material is not fully UV-cured.
This is another method of curing a liquid coating or varnish. There are many benefits, including reliable instant curing and lower ink/varnish costs. However, the process equipment is much more expensive and relatively complex.
In this method one layer of material is pre-coated with a clear resin. This material is heated in the laminator to soften the resin, and pressed against the other material between large rollers. The resulting bond is very strong, and fully cured as the material comes off the laminator. The printing inks are trapped between the two layers giving a very robust and safe finished product, and a material that combines the barrier properties of both materials. This method is also very simple, quick and easy to set up and clean down, and the resin-coated films are widely available. Also, most digitally printed materials can be laminated without the need adding a primer. As with all laminating, one disadvantage has been the recyclability of two different products bonded together, but many people are working on this, and solutions are now available.