To provide superior impact resistance at a low temperature and prevent the fusion during the retorting and blocking of inner surfaces by forming an innermost layer in contact with the contents from a specific amount of a polypropylene resin and a specific amount of an ethylene-α olefin copolymer obtained through polymerization by a single-site catalyzer.
A retort packaging material basically comprises a base film, an intermediate layer and an inner layer resin when seen from the surface side. At least an innermost layer resin comprises 70 to 95wt.% of polypropylene and 5 to 30wt.% of an ethylene-α olefin copolymer obtained through polymerization by a single-site catalyzer. If the ethylene-α olefin copolymer is 5wt.% or less, the effectiveness on the impact resistance at low temperatures is small, while if it exceeds 30wt.%, the heat resistance becomes inferior. As a method for preparing these resins, for instance, a method is used that comprises the steps of formulating each composition, mixing them by a blender, a mixer or the like and fusion kneading by a biaxial kneading and extruding machine or a mixing roll, or a dry blend method is used in which pellets mix each other.
SEKINE NORIMASA
FURUSAWA NOBUO
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