Method of making a multilayer coextruded polyolefin stretch wrap film

• US 5,516,475 A
• Filed: 03/06/1995
• Issued: 05/14/1996
• Est. Priority Date: 12/18/1992
• Status: Expired due to Term

• Current Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Original Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Inventors: Wilson, Gregory M.
• Primary Examiner(s): THURLOW, JEFFERY
• Application Number:
  US08/398,937
• Time in Patent Office: 435 Days
• Field of Search: 264/171, 264/173, 264/514, 264/288.4, 264/171.28, 264/173.14, 264/173.15, 425/131.1
• US Class Current: 264/173.14
• CPC Class Codes: B32B 2323/046 LDPE, i.e. low density polyethylene
• CPC Class Codes: B32B 2323/10 Polypropylene
• CPC Class Codes: B32B 2553/00 Packaging equipment or accessories not otherwise provided for
• CPC Class Codes: B32B 27/08 of synthetic resin
• CPC Class Codes: B32B 27/32 comprising polyolefins comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30
• CPC Class Codes: Y10S 428/911 Penetration resistant layer
• CPC Class Codes: Y10T 428/1328 Shrinkable or shrunk [e.g., due to heat, solvent, volatile agent, restraint removal, etc.]
• CPC Class Codes: Y10T 428/1334 Nonself-supporting tubular film or bag [e.g., pouch, envelope, packet, etc.]
• CPC Class Codes: Y10T 428/1352 Polymer or resin containing [i.e., natural or synthetic]
• CPC Class Codes: Y10T 428/31913 Monoolefin polymer

Abstract

The present invention relates to a method for making a multilayer coextruded thermoplastic stretch wrap film useful for the packaging or pelletizing of goods. More particularly films made according to this invention include at least three layers: two outer layers and an intermediate layer positioned between the outer layers. The intermediate layer contains a mixture of a first linear low density polyethylene and a polyolefin selected for the group consisting of homopolymers of propylene, copolymers of propylene and ethylene and mixtures thereof. At least one of the two outer layers is a second polyethylene. The force required to stretch films made according to this method is controlled by varying the intermediate layer blend ratio between 85% polyethylene/15% propylene and 95% polyethylene/5% propylene.

Claims

1. A method for preparing a thermoplastic stretch wrap film capable of stretching upon exerting a force during application of the film to an article or group of articles to be wrapped comprising the step of:

coextruding a film having at least three layers, said three layers having two outer layers and an intermediate layer positioned between said outer layers,

said intermediate layer comprising a mixture of;

a) a first linear low density polyethylene and

b) a polyolefin selected from the group consisting of;

i) homopolymers of propylene,

ii) copolymers of propylene and ethylene and mixtures thereof,

wherein the amount of force required to stretch the stretch wrap film can be controlled by adjusting the blend ratio of said mixture from 95% propylene homopolymer/5% linear low density polyethylene to 85% propylene homopolymer/15% linear low density polyethylene, and at least one of said two outer layers comprising a second linear low density polyethylene,

said second linear low density polyethylene consisting essentially of ethylene copolymerized with at least one alpha olefin having from 4 to 10 carbon atoms and containing from 3.5 to 15 weight percent n-hexane extractibles,

said n-hexane extractibles being present in an amount sufficient to cause the stretch wrap film to exert a cling force of at least about 200 grams when in surface-to-surface contact with itself or another surface when used in the stretch overwrap packaging of articles.

2. The method of claim 1, wherein said coextruding step is a slot cast extruding step.

3. The method of claim 2, wherein each of said two outer layers comprises said second linear low density polyethylene.

4. The method of claim 1, wherein said first linear low density polyethylene and said second linear low density polyethylene are equivalent materials.

5. The method of claim 4, wherein said alpha olefin is present in said linear low density polyethylene in an amount of about 1 to 20 weight percent total and is a member selected from the group consisting of butene-1;

3-methyl-butene-1;

3-methyl-pentene-1;

4-methyl-pentene-1;

hexene-1;

3-methyl-hexene-1;

octene-1;

- decene-1 and mixtures thereof.

6. The method of claim 5, wherein said linear low density polyethylene has a density of about 0.905 to 0.940 grams/c.c. and a melt index of about 1.0 to 10.0.

7. The method of claim 6, wherein said high melt index linear low density polyethylene has a melt index from about 2.5 to 5.0 and a density from about 0.915 to 0.920 grams/c.c. and said alpha olefin is hexene-1.

8. A method for preparing a thermoplastic stretch wrap film capable of stretching upon exerting a force during application of the film to an article or group of articles to be wrapped comprising the step of:

coextruding a film having at least three layers, said three layers having two outer layers and an intermediate layer positioned between said outer layers,

said intermediate layer comprising a mixture of;

a) a first linear low density polyethylene and

b) a propylene homopolymer,

wherein the amount of force required to stretch the stretch wrap film can be controlled by adjusting the blend ratio of said mixture from 95% propylene homopolymer/5% linear low density polyethylene to 85% propylene homopolymer/15% linear low density polyethylene, and at least one of said two outer layers comprising a second linear low density polyethylene,

said second linear low density polyethylene consisting essentially of ethylene copolymerized with at least one alpha olefin having from 4 to 10 carbon atoms and containing from 3.5 to 15 weight percent n-hexane extractibles,

said n-hexane extractibles being present in an amount sufficient to cause the stretch wrap film to exert a cling force of at least about 200 grams when in surface-to-surface contact with itself or another surface when used in the stretch overwrap packaging of articles.