The effect of bond strength of flexible laminates on puncture resistance.

摘要

This work was aimed at understanding whether the bond strength of laminates will affect the puncture resistance of the laminate. Even though a strongly bonded adhesive layer in between two webs will considerably improve the mechanical properties of the laminate compared to that of the individual materials, there is a general belief in the packaging industry that having a lower bond strength helps to improve the bending or, in other words, the flexibility of the laminate thereby increases the tear and puncture resistance.;Laminations of aluminum foil and polyethylene terephthalate (PET) were used as a model system to determine the validity of this industry paradigm. The variables used in this study were adhesive coating weight, adhesive system and additives used to control bond strength. The weight of coating was controlled to around 1.5 pounds per ream using different Meyer rods. Two popular polyurethane based adhesive systems, Tycel from LiofolRTM and Adcote RTM from Rohm and Haas were used with talc and microcrystalline polypropylene wax as additives. The additive loading was adjusted at 5%, 10%, 15% and 20% with respect to the total percent solids in the pure adhesive mixture. The cured, off-machine and time based values for adhesive bond strength and puncture resistance were measured. Two probes, ASTM probe and a hemispherical probe were used to measure the puncture resistance of the laminates from both PET and Foil sides. The off-machine bond strength for both the adhesive systems using talc and PP wax shows a gradual decrease in values. The cured laminates underwent material failure at low percentage loading of the additive up to 10 % as the cured bond strength values were higher than the strength of PET film. Above 10% additive loading, the bond strength values showed a quadratic decrease similar to off-machine bond strength values. However, the puncture strength of cured laminates did not show any corresponding change for different percent loading of additives. The ASTM probe gave higher puncture values than the hemispherical probe. The puncture strength showed a gradual increase over a time period of 4 to 4.5 hours. The trend is initially linear changing to a quadratic mode at longer time periods. It was also noted that the mode of puncture changed from multiple substrate failure with delamination to a single substrate failure with no appreciable delamination as curing time approached 4.5 hours showing that most of the curing process takes place in the initial 4 hours after lamination.