Multilayer, heat-shrinkable film comprising a plurality of microlayers
View Patent ↗A multilayer, heat-shrinkable film generally includes at least one bulk layer and a microlayer section comprising a plurality of microlayers. The ratio of the thickness of any of the microlayers to the thickness of the bulk layer ranges from about 1:2 to about 1:40.
1. A method of making a multilayer, heat-shrinkable film, comprising:
a. extruding a bulk layer;
b. coextruding a plurality of microlayers to form a microlayer section;
c. merging said bulk layer and said microlayer section to form a multilayer film; and
d. stretch-orienting said multilayer film under conditions that impart heat-shrinkability to said film;
wherein, each of said microlayers and said bulk layer have a thickness, the ratio of the thickness of any of said microlayers to the thickness of said bulk layer ranging from about 1:2 to about 1:40; and
wherein, said film has a total free shrink (ASTM D2732-03) of at least about 10% at 200° F., and an Elmendorf Tear value (ASTM D1922-06a) of at least 10 grams, as measured in at least one direction along a length or width dimension of said film.
2. The method of claim 1 , wherein, said film has a thickness of less than about 0.7 mil.
3. The method of claim 1 , wherein said film is stretch-oriented at a ratio of at least 3 in at least one direction along a length or width dimension of said film.
4. The method of claim 3 , wherein said film is stretch-oriented at a ratio of at least 4 in at least one direction along a length or width dimension of said film.
5. The method of claim 1 , wherein said film is stretch-oriented at a ratio of at least 5 in at least one direction along a length or width dimension of said film.
6. The method of claim 1 , wherein
said microlayers each have a thickness ranging from about 0.001 to 0.015 mil; and
said bulk layer has a thickness ranging from about 0.03 to 0.5 mil.
7. The method of claim 1 , wherein said heat-shrinkable film has an Elmendorf Tear value (ASTM D1922-06a) of at least about 30 grams/mil, as measured in at least one direction along a length or width dimension of said film.
8. The method of claim 1 , wherein said microlayer section comprises a repeating sequence of layers represented by the structure:
A/B,
wherein,
A represents a microlayer comprising one or more polymers,
B represents a microlayer comprising a blend of two or more polymers, and
A has a composition that is different from that of B.
9. The method of claim 8 , wherein A and B comprise one or more of ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, polypropylene homopolymer or copolymer, ethylene/methacrylic acid copolymer, maleic-anhydride-grafted polyethylene, polyamide, or low density polyethylene.