Eliminating Wrinkles during Lamination

 

Creasing is when one of the substrates is separated or de-laminated from the other due to different extension properties in both films. This leads to the films extending at different rates when a tension is applied on them. This can be eliminated by the correct use of tensions applied, the proper evaporation provided by the ovens or by simply selecting the correct adhesive.

How creasing is caused

When considering the lamination of a printed PET (Polyethylene Terepthalate) film with an aluminium foil along with an PE (Polyethylene) layer on the other end, the product structure are shown below. In addition to that, for a product's web width of 42”, the suggested tensions could be obtained using the formula below.

Suggested Tension = Tension Level * Caliper * Web Width

The results obtained are as follows:

Material	Caliper (inch)	Thickness (%)	Tensile Modulus (psi)	Tension Levels (lbs/inch/mil)	Suggested Tension (#)
PET	0.00048	10.4	500000	0.5 – 1.5	10 to 30
Foil	0.00035	7.6	10000000	0.5 – 1.5	7 to 21
PE	0.00400	82	25000	0.25 – 0.3	40 to 48

For the lamination process to be completed effectively, the strain applied on each of the materials will have to be approximately equal before the lamination process takes place in order to prevent defects such as creasing.

Using the formula,

Stalin = Stress / Modulus of Elasticity = (Tension / Area) / Modulus of Elasticity = Tension / (Area * Modulus of Elasticity)

Since the Modulus of Elasticity for aluminium is about 20 times greater than that of PET, in order for both of them to undergo approximately equal strains, the aluminium will have to be pulled by its highest possible tension suggested and PET should be pulled by its lowest possible tension suggested.

However, another problem is prone to arise when the aluminium foil is pulled with high tension, which is the formation of diagonal wrinkles in the long web lead before it passes through the nip roller. These diagonal wrinkles are a product of cross machine difference in the web's thickness and could get a lot more noticeable with roller deflection or misalignment. The use of a Herringbone Spreader Roll will eliminate the wrinkles on the foil before being fed into the laminating nip roller. In addition to that, the spreader roll will also compensate for any deflections or misalignment that could cause any wrinkles to the foil.



A Herringbone Roller