# US 4,391,862 A · Pasteurizable thermoplastic film and receptacle therefrom

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- Number: US 4,391,862 A
- Document ID: US4391862A
- Status: Granted
- Kind: A
- Application number: 06/302,333
- Filed: 1981-09-15
- Granted: 1983-07-05
- Earliest claimed: 1981-07-02
- Assignees: W. R. Grace & Co., Cryovac Division
- Inventors: Norman D. Bornstein; Johnnie J. Walters
- Web page: https://patentgrep.com/patent/US4391862A

## CPC

- B32B 27/08: of synthetic resin
- B32B 27/16: specially treated, e.g. irradiated
- B32B 27/304: {comprising vinyl halide (co)polymers, e.g. PVC, PVDC, PVF, PVDF}
- B32B 27/306: {comprising vinyl acetate or vinyl alcohol (co)polymers}
- B32B 27/32: comprising polyolefins {(comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30)}
- B32B 38/0012: {Mechanical treatment, e.g. roughening, deforming, stretching}
- B32B 2307/31: Heat sealable
- B32B 2307/736: Shrinkable
- B32B 2323/10: Polypropylene
- B32B 2439/70: Food packaging
- Y10S 428/91: Product with molecular orientation
- Y10T 428/1324: Flexible food casing [e.g., sausage type, etc.]
- Y10T 428/1328: Shrinkable or shrunk [e.g., due to heat, solvent, volatile agent, restraint removal, etc.]
- Y10T 428/2826: Synthetic resin or polymer
- Y10T 428/31913: Monoolefin polymer
- Y10T 428/3192: Next to vinyl or vinylidene chloride polymer
- Y10T 428/31928: Ester, halide or nitrile of addition polymer
- Y10T 428/31935: Ester, halide or nitrile of addition polymer
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Disclosed is a multi-layer, heat shrinkable, thermoplastic packaging film which can be heat sealed to itself to provide strong seals at pasteurizing temperatures. The preferred film has four layers including, in order, a sealing surface layer comprising a blend of propylene-ethylene copolymer and (butene-1)-ethylene copolymer, a layer comprising ethylene-vinyl acetate copolymer which may be cross-linked to further increase high temperature strength of the film as desired; a relatively gas impermeable layer comprising a copolymer of vinylidene chloride; and, a surface layer of the same blend as the sealing layer. Receptacles such as end seal and side seal bags can be made from the film at a faster rate than with prior art films and these receptacles have the high temperature seal qualities of propylene polymers and the hot water shrink capabilities of ethylene polymers.

## Claims

### Claim 1

A multi-layer, heat shrinkable, thermoplastic packaging film which will produce heat selas having improved seal strength immediately after initially being heat sealed to itself comprising:
(a) a first or surface layer consisting essentially of a blend wherein one constituent of the blend is selected from the group consisting of propylene homopolymers and copolymers and the other constituent of the blend is selected from the group consisting of butene-1 homopolymers and copolymers;
(b) a second layer comprising a polymer selected from the group consisting of ethylene homoplymers and copolymers, said layer being heat shrinkable;
(c) a third or low gas transmission layer comprising a polymer selected from the group consisting of vinylidene chloride copolymers and hydrolyzed ethylene-vinyl acetate copolymers; and,
(d) a fourth or outer surface layer comprising a blend selected from the group of blends as specified for the first layer.

### Claim 2 (depends on 1)

The film of claim 1 wherein the blend for the first and fourth layers comprises a blend of 90% to 40% by weight or propylene-ethylene copolymer having 1.5% to 4.0% ethylene and 10% to 60% by weight of butene-1 homopolymer or (butene-1)-ethylene copolymer having up to 6.0% by weight of ethylene.

### Claim 3 (depends on 1)

The film of claim 1 wherein the second layer comprises an ethylene-vinyl acetate copolymer having 3% to 12% vinyl acetate content by weight.

### Claim 4 (depends on 1)

The film of claim 1 wherein the second layer comprises polyethylene.

### Claim 5 (depends on 3)

The film of claim 3 wherein the second layer comprises an ethylene-vinyl acetate copolymer and the first and second layers have been irradiated to a dosage level of at least 2 MR.

### Claim 6 (depends on 3)

The film of claim 3 wherein the ethylene-vinyl acetate copolymer comprises about 6% vinyl acetate by weight and the copolymer has been cross-linked to the equivalent of a dosage level in the range of 2 to 6 MR.

### Claim 7 (depends on 6)

The multi-layer film of claim 6 wherein said film has been stretch oriented and has a thickness in the range of 1.0 to 4.0 mils.

### Claim 8

A process for making a multi-layer, heat shrinkable, thermoplastic packaging film which will produce heat seals having improved seal strength immediately after being heat sealed to itself comprising the steps of:
(a) coextruding first and second polymeric layers, the first layer consisting essentially of a blend selected from the group consisting of (1) propylene homopolymers and copolymers and (2) butene-1 polymers and copolymers and the second layer comprising a polymer selected from the group consisting of ethylene polymers and copolymers;
(b) irradiating said coextruded layers to a dosage level of at least 2 MR; and,
(c) after the irradiation step has been completed, joining a third layer of polymeric material to the second layer and a fourth layer to the third layer.

### Claim 9 (depends on 8)

The process of claim 8 including the step of stretching the multi-layer film to orient same.

### Claim 10 (depends on 8)

The process of claim 8 wherein the first layer comprises a blend of 90% to 40% by weight propylene-ethylene copolymer with 10% to 60% by weight of (butene-1)-ethylene copolymer or butene-1 homopolymer and the second layer comprises an ethylene-vinyl acetate copolymer.

### Claim 11 (depends on 8)

The process of claim 8 including wherein the third layer is joined to the second by the step of extrusion coating a third layer onto the second, said third layer comprising a polymer selected from the group consisting of vinylidene chloride copolymers and hydrolyzed ethylene-vinyl acetate copolymers.

### Claim 12 (depends on 11)

The process of claim 11 wherein the fourth layer is joined to the second by the step of coating a fourth layer onto the third, said fourth layer comprising a blend selected from the group consisting of blends specified for the first layer.

### Claim 13 (depends on 1)

A receptacle formed by heat sealing together selected surface areas of the film of claim 1.

### Claim 14 (depends on 7)

A receptacle formed by heat sealing together selected surface areas of the film of claim 7.

### Claim 15 (depends on 7)

A casing formed from the film of claim 7 by heat sealing together two opposed edges of a sheet of said film to form a tube and thereafter gathering and closing one end of said tube.