The basic paperboard products are produced in a limited range of thicknesses because of the need for efficiency in paperboard manufacture. However, this thickness and stiffness range is extended considerably when two or more layers of paperboard are glue laminated together into equal-sided products with the same smooth and white printing surface on both sides. The many raw materials available provide numerous combinations so that many customer needs may be met.
Laminated paperboard offers good rigidity and smoothness which, when combined with excellent visual appeal, makes the package look more attractive to the consumer in the store.
Laminated paperboard is smooth and flat with good cohesion and adhesion. The combination of stiffness and converting possibilities makes it suitable for the packaging of expensive and luxury products.
Packaging that will come in direct contact with foodstuffs must be designed for each specific end use.
Evaluation of paperboard lamination
Most of the evaluation is done off-line. The aim is to determine and document that:
• the glue covers the whole web
• the glue keeps the webs together after drying
• the sheets are flat and free from twist
• the pallets are flat
• there is no damage (e.g. indentations) to the surfaces
• there is no visible dust or loose particles that can disturb the converting operation.
The glue lamination machine has four unwind stands.
IR (infra-red) driers are used to control the shape of the sheets.
Water-based adhesives are used to glue the board webs.
10. Press Nip
After gluing, the webs are pressed together.
11. Sheeting and Stacking
The glued board is sheeted and stacked on pallets in line.
Evaluation of extrusion coating and lamination
This process lends itself to control and continuous monitoring of the coat weight, coating profile, thickness and moisture profiles during production.
The following properties are measured off-line:
• surface smoothness (printing side, reverse side)
• surface tension (treated side)
• flatness of the sheet
• heat sealability (where applicable)
• odour and taint neutrality
• surface defects
• blistering (where applicable).
Conversion operations in practice
Slightly different settings and techniques are necessary with extrusion-coated and laminated products in printing, die-cutting, creasing, gluing, and sealing. They are well established and do not cause problems in practice.
Low odour printing inks and the programmed airing of pallets are important to prevent the absorption of taint into the plastic coating. Always use well-proven procedures as prescribed by the printing ink supplier.
Uniform coat weight is important for successful conversion.
When paperboard is glue laminated together to give a thicker and stiffer product, the following changes should be considered: