The Effect of Retort Conditions on Clear High Barrier Laminated Structures

Transcription

1 The Effect of Retort Conditions on Clear High Barrier Laminated Structures Dante Ferrari Celplast Metallized Products Ltd. Presented at AIMCAL Fall Conference October, 2005 Introduction Retorting refers to the thermal sterilization of low-acid foods, to extend shelf life by killing bacteria and other microbial species in the food. It has traditionally been used to preserve foods packaged in metal cans or glass jars. Following WWII, flexible retort packaging was born, with the innovation of the meals-ready-to-eat (MRE) pouch for military rations. This replaced canned food, or C-rations, and today MRE pouches are still the packaging of choice for providing food to remote military personnel. They are made up of PET/nylon/foil/CPP or PET/foil/nylon/CPP 4-layer laminations. This is an extreme use requirement, as MRE s require a shelf life of up to three years at 80 F or six months at 100 F, translating to OTR < 0.06 cc/m 2 /day and WVTR < 0.01 g/m 2 /day 1. Retorted pouches can be either pillow or stand-up pouches, and are lighter in weight and easier to open than traditional cans or glass jars. In addition, retorted pouches offer improved food flavor over traditional rigid packaging. Since the pouch has more surface area and a thinner package than an equivalent volume jar or can, heat can be transferred through a retort pouch more quickly than a jar or can, allowing for quicker sterilization, which preserves the quality of the food 2. More recently, clear barrier films have gained acceptance in retort pouch applications. These are typically SiOx-coated or Al 2 O 3 -coated 48 gauge PET films, which replace the foil layer in a standard retort pouch structure. Advantages offered by these films over foil are their ability to be used in a microwave, they allow the use of metal detectors during pouch filling, the customer can view the product inside the package, and they meet metal-free recyclability requirements. The barrier properties of SiOx coatings on PET film have been the focus of some recent studies in unlaminated film structures 3,4, indicating factors that can be used to improve SiOx-coated PET barrier properties. In addition, improvements in flex crack resistance and reduced pinholing leading to better barrier properties in a lamination have been achieved with at least one high speed electron beam web coater 5. Experimental Two different clear barrier films were examined in this study, a SiOx-coated 48 g retortable PET film, and a SiOx-coated 60 g retortable grade nylon film. Laminations were prepared on pilot coating lines at Rohm & Haas s Technical Center in Ringwood, IL, and at Liofol s Technical Center in Cary, NC. Solvent-based adhesives were applied at 3 lbs/ream dry coating weight, whereas solventless adhesives were applied at 1.5 lbs/ream.

2 Rohm & Haas s technology uses an aliphatic isocyanate + hydroxyl-functional polyester chemistry to create a polyurethane adhesive between the innermost layers of the structure, closest to the sealant web, and an aromatic isocyanate hydroxyl-functional polyester chemistry was used for the polyurethane adhesive between the outermost layers. They incorporate both solvent-based and solventless adhesives in their structures. Rohm & Haas prepared samples based on both 3-ply and 4-ply structures. The 3-ply structures were 48 g PET/adhesive/SiOx coating/coated substrate(nylon or PET)/adhesive/3 mil CPP. The 4-ply structure was 48 g PET/adhesive/SiOx coating/coated PET/adhesive/nylon/adhesive/3 mil CPP. Liofol s technology uses two different solventless aliphatic polyurethane adhesives, for bonding the inner and outer plies of the laminations. For both studies, the solventless adhesives were allowed to cure for a minimum of 10 days before carrying out retort tests. All of their retort structures consisted of a 3-ply 48 g PET/adhesive/SiOx coating/coated substrate(nylon or PET)/adhesive/3 mil CPP. Retorting was carried out at 121 C for one hour. Retorting was carried out both in pouch and lamination form. Barrier Results Only a limited amount of data is available at this point, based on the Rohm & Haas study. Here, barrier properties of the clear retort laminations were examined before and after retorting. Retorting was carried out on both pouch and laminated strips, to determine if there was a difference between them. 0.3 Clear Barrier Oxygen Transmission Rate Results 0.25 OTR (cc/100 in2/day) Initial Post-Retort (strip) Post-Retort (pouch) PET/SiOx-PET/nylon/CPP PET/SiOx-PET/CPP PET/SiOx-nylon/CPP Lamination structure

3 Clear Barrier Water Vapor Transmission Rate Results WVTR (g/100 in2/day) Initial Post-Retort (strip) Post-Retort (pouch) PET/SiOx-PET/nylon/CPP PET/SiOx-PET/CPP PET/SiOx-nylon/CPP Lamination structure Conclusions The 3-ply lamination containing SiOx-coated PET performed as well as the 4-ply lamination, both before and after retorting. Therefore, the nylon layer is not required to withstand the retorting process, although further testing needs to be carried out comparing the 3-ply vs. 4-ply structures after flexing. The 3-ply lamination containing SiOx-coated nylon gave the best oxygen barrier performance before retorting, but was the worst after. In each case, the oxygen barrier was retained more effectively than the water vapor barrier during retorting. A full report, including the Liofol pre- and post-retort lamination data, will be included in the final presentation. Acknowledgments I would like to acknowledge Tom Mueller of Rohm & Haas and Grant Kenion of Liofol for assisting in preparing the adhesive laminations, carrying out retort testing, and providing barrier data. References 1. Froio, D., et al., Developments in High Barrier Non-foil Packaging Structures for Military Rations, Flexible Packaging Conference proceedings, 2005.

4 2. Whiteside, S.W., Introduction to Retort Pouch Technology, TAPPI PLACE Conference proceedings, Henry, B.M., et al., Permeation Studies of Transparent Barrier Coatings, 46 th Annual Technical Conference Proceedings, Society of Vacuum Coaters, A.P. Roberts, et al., Gas Permeation in Silicon-oxide/Polymer (SiOx/PET) Barrier Films : Role of the Oxide Lattice, Nano-defects and Macro-defects, J. Membrane Sci., 208, 75, Lohwasser, W., Development and Future of Clear Oxide Coatings, 3 rd Vacuum Web Coating Symposium, Applied Films, 2004.

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