Introduction
Flexible packaging materials offer new and exciting opportunities for food and packaging industries. However, before applying these materials, it is important to understand the barrier properties to their function. This paper provides a basic overview of the structure of flexible packaging materials and the associated permeability and mechanical properties that are of interest to food packaging scientists and engineers. The structure of polymers, as discussed is an important determinant of the potential end use applications for the material. The mechanical properties of the materials, which relate to both the materials performance on high speed packaging lines and the protection of the food product, will also be covered. Material in this essay has been drawn from many sources in the food packaging literature and references to specific works have been provided where appropriate.
Properties of Flexible Packaging Materials
Ash test: A method to determine the filler content of a material (calcium carbonate, titanium dioxide, and others) by burning a known weight of material and measuring weight of residue.
Aluminum foil: A thin gauge (.285-3.5 mils) of aluminum metal. The foil is produced by rolling aluminum slabs cast from molten aluminum, then re-rolling on sheet and foil rolling mills to the desired thickness, or by continuously casting and cold rolling.
Adhesion: The molecular force holding two surfaces of material in contact. Internal bond strength.
Abrasion resistance: The ability of a flexible packaging material to withstand scuffing and wearing, also the ability to resist a dragging force.
Glossary: The following list of terms and their definitions is a special feature of this publication to assist educational and scientific research of flexible packaging materials.
Manufacturing Process of Flexible Packaging Materials
Coating or laminating secondary layer(s)
If the substrate is to have a coating applied to it, the material is run through a heated metal block between two rolls which melts the resin. This is then transferred onto the substrate via a nip roll section to produce a coated substrate. The coated or uncoated substrate is then wound up and stored for future laminating or use as the final product. A coater will also be used to coat the various resins made in the first step directly onto the substrate. This would involve various changes of die and/or roll to coat each different resin and will be done once for each layer of a multilayer material. A laminator involves a similar process in that it will laminate a roll of the formulated resin onto the substrate and will also be done once for each layer of a multilayer material.
Producing the substrate
The substrate is the base material that is to be coated or laminated. The actual process to perform this will depend on the machinery offered. If the substrate is too a resin to be extruded, it would involve loading the hopper with the formulated resin and extruding the sheet at the proper thickness onto a set of cooling rolls. A 3-layer material would involve this step being conducted 3 times, once for each different layer. If the substrate is a material such as biaxially oriented polypropylene, the company may have a line of this and choose to run this through the coater/laminator as is. Earlier, I mentioned it is expected the reader has an understanding in extrusion and thus I will not cover it here.
Resin selection
This first step in the manufacturing process involves the compounding of various raw materials to create the right base resin with specific properties for each layer to be extruded. For example, nylon is an excellent moisture barrier and would be used in a food packaging application to preserve freshness. The first step entails compounding nylon and various additional polymers and additives into the desired moisture barrier resin. This would be done for each layer of the multilayer material.
The production of flexible packaging material can involve many different aspects and potentially vary from formulation to formulation. What follows is a typical step-by-step process of a common multilayer flexible packaging material. This type of material would consist of 3, 5, 7, 9, or 11-layer coextruded film with each layer having a specific function. This style of material would be produced by a company who has large-scale extrusion equipment and thus it is expected that the reader has some background knowledge in extrusion, polymer chemistry, and coating/laminating.
The manufacturing process of the flexible packaging material
Applications of Flexible Packaging Materials
Stand-Up Pouches: The adoption of stand-up pouches as a replacement for bags or trays has seen dramatic growth in the past two decades, particularly in food product applications. Stand-up pouches offer strong retail shelf presence with billboard graphics and a large surface area for information, and they are viewed as a modern package with an image of convenience. This is another example of a new package concept which has been enabled by the development of custom materials and new processing technologies.
Replacement of rigid packages: Flexible packaging materials can be custom engineered to match the performance characteristics of a traditional rigid package at a lower cost and with added convenience. The development of new easy open/reclose features has made this possible in a wider range of product applications, such as the replacement of cans or trays with pouches. A similar example is the replacement of plastic pails with a high-performance flexible bag.
Any modern manufacturing enterprise would be able to develop a variety of applications for flexible packaging materials. However, due to the unique versatility of flexible materials, the tendency should be to forget the existing package and rethink the system to make the best use of these materials. Flexible packaging materials are recommended for the following new and existing applications:
Future Trends in Flexible Packaging Materials
Packaging manufacturers are developing more sustainable packaging materials in response to retailer and consumer demand. These materials must effectively protect the product but have less impact on the environment. The FPA summarily looked into trends in materials, design and processes in the bioplastics area and also the potential ramifications to the flexible packaging industry. Active and intelligent packaging development and use is another area of increased focus for the packaging industry. This area of packaging has the ability to improve safety and quality of food, and provide consumers with more information about the products they are consuming. The active and intelligent packaging market is expected to see significant growth due to consumer demand as well as an aging population wanting better access to healthcare. Flexible packaging is expected to benefit from these new technologies due to its ability to form and fill a wide variety of formats.
Environmental issues are a major concern worldwide, and the flexible packaging industry is no exception. The Flexible Packaging Association has designed to increase adaptation of flexible packaging to further minimize the environmental impact and energy in comparison to other packaging formats. This is being accomplished by implementing the use of lifecycle and economic assessments to understand tradeoffs and inform design decisions. These assessments seek to optimize material use, downgauging, and material substitution while assuring that functional requirements are met. The FPA is striving to become a more sustainable organization and to encourage sustainability throughout the entire flexible packaging supply chain.
