Extrusion laminated film has superior performance than the adhesive method in terms of scratch damage, according to a study.
Extrusion laminated film showed superior mechanical integrity between the metalized polyethylene terephthalate (PET) and sealant layers.
There is also a need to develop a laboratory test method that is more aligned with real world performance, said the researchers.
Scratch-induced puncture damages on adhesive and extrusion laminated multilayer food packaging films were investigated.
Two model films were used, an extrusion laminated (EL) and an adhesive laminated (AL) film.
Processing method difference
Both films use the same sealant layers, the difference being the processing method in which they are adhered to the metalized PET layer.
During multilayer film production, lamination is used to adhere the multiple film webs together.
A major concern is film puncture failure that causes a loss of barrier properties, package integrity, and/or pressure change.
The scratch test method (ASTM D7027-05/ISO 19252:2008) was used to evaluate the packaging films using identical PE based sealant layers laminated to metalized PET through different lamination methods.
Test results from the scratch were combined with cross-sectional imaging of the scratch-damaged films. The stronger layer integrity from extrusion lamination converting method provided superior stress redistribution and subsequently superior scratch performance.
Films were tested using a modified standardized linearly increasing load scratch test method, which has demonstrated an ability to correlate damages in use of packaging films to laboratory findings.
Modified scratch test
Hare et al. modified and verified the applicability of the standardized ASTM/ISO scratch test methodology to provide results that correlated to field performance data.
Samples were cross-sectioned to view the damage in a layer-by-layer fashion to determine any potential weak-link in the laminate.
The extrusion laminated film showed superior scratch performance and layer adhesion with increasing scratch load, particularly upon severe film deformation.
The extrusion lamination process may be used to produce strong, scratch-resistant packaging films without additional adhesive layers and associated health and environmental concerns.
“The extrusion laminated film displays the highest loads required to generate puncture of the two systems," said the researchers.
“This is indicative that the EL film exhibits superior mechanical integrity between the metalized PET and sealant layers, and is therefore able to better distribute the scratch-induced stresses through its structure.”
Because of limitations of most laboratory test methodologies for packaging films and lack of direct correlation from results to field performance, accurate puncture resistance is traditionally tested on a production line in a plant or pilot plant environment.
This is time-consuming and creates product waste so a laboratory method is needed to offer better correlation with real world performance.
Tests such as tensile, slow puncture, Elmendorf tear, and Gelboflex show a lack of applicability to reflect real world packaging performance.
Evaluating films of different lamination methods layer-by-layer after undergoing damage will be very helpful, said the researchers.
A clearer understanding of how each layer of a film contributes to its damage resistance can help in laminated film design and optimization to develop better puncture resistant films.
Source: Polymer Engineering and Science 2014
Authors: Brian A. Hare. Hung-Jue Sue, Lora Ying Liang, Panos Kinigakis