Retort packaging is a technique in which by subjecting a pharmaceutical product or foodstuff to high-temperature sterilization and then packaging, the package contents can be stored for long periods. Containers for retort packaging are prepared by forming a laminate (laminated film) of a plurality of laminated resin films into the shape of a bag.
The sealant layer which constitutes the surface that contacts the contents of the retort packaging container requires heat sealing properties and resistance to the high temperatures used during the retort process. In order to satisfy these performance requirements, the sealant layer of a retort packaging container generally employs a film that uses a polypropylene (PP)-based resin.
Polypropylene-based resin films typically contain an added antioxidant for the purpose of preventing thermal degradation caused by oxygen during heating and melting of the resin to produce a film. However, from the viewpoint of the hygiene of the package contents, it is preferable that the sealant layer contain as few additives as possible. Accordingly, the use of polyethylene (PE)-based resins, which require no additives during film production, for the sealant layer is currently being investigated (for example, Patent Literature (PTL) 1).
Further, the glass transition temperature of polypropylene is close to 0° C., meaning the polypropylene adopts a glass-like state and has poor impact resistance at low temperature. Packaging containers that use a polypropylene-based resin for the sealant layer exhibit poor bag drop strength at low temperature, and have tended to suffer from problems of rupture of the packaging container when dropped.
Among the laminates used in containers for packaging, laminates which contain a layer of a film having oxygen absorption properties (namely, an oxygen absorption layer) in order to prevent oxidation of the contents are already known. Specifically, oxygen-absorbing films include a resin having unsaturated bonds, but it is known that oxygen absorption is accompanied by the generation of unpleasant odors. PTL 2 discloses a packaging material which uses a laminate containing a deodorizing layer that captures odorous components emitted from the oxygen absorption layer.    {PTL 1} Japanese Unexamined Patent Application, Publication No. H08-142288    {PTL 2} Japanese Unexamined Patent Application, Publication No. 2011-152788