Heat resistant breathable films

#Lettuce is currently packaged in a non-stretchable heat resistant film. The film structure includes a layer of polyester bonded to a layer of polyethylene. This film offers low moisture permeability which is desirable in packaging lettuce and similar produce. However, it is also low in gas permeability, which reduces the shelf life of chopped lettuce when oriented heat set polyester is used.

#Other heat set films typically used in this application have oxygen transmission rates of less than 5000 cc/meter.sup.2 at 1 atmosphere 24 hours at 73.degree. F.

#With the packaging of lettuce and similar produce, it is desirable to provide a packaging material with a high gas permeability, preferably greater than 5000 cc per square meter, yet with low moisture transmission rates in order to resist loss of moisture from the food product.

#The invention can be further understood by reference to the drawing figures, wherein:

#FIG. 1 is a schematic cross sectional view of the multilayer laminate of the present invention;

#FIG. 2 is a schematic cross sectional view of an alternative embodiment of a multilayer laminate in accordance with the present invention;

#Referring to FIG. 1, the multilayer laminate 10 includes a perforated film 12 having perforations 14 therein. In the preferred embodiments, layer 12 comprises a propylene homopolymer (PP), although a propylene copolymer such as ethylene propylene copolymer (EPC) may be used. Various homopolymers and copolymers of polypropylene are commercially available and well known in the art. One film especially preferred for the present invention is a commercial oriented film designated PY supplied by the Cryovac Division of W. R. Grace & Co.-Conn.

#Alternative materials for perforated film 12 are oriented heat set polyester and oriented heat set polyamide (nylon).

#A coextruded film 16 is also depicted in FIG. 1. Film 16 includes a bonding layer 18, a core layer 19 of a heat resistant, breathable material, and an outer heat sealable layer 20.