CA2086493A1 - Multilayer shrinkable film with improved shrink, optics and sealability - Google Patents

Multilayer shrinkable film with improved shrink, optics and sealability

Info

Publication number
CA2086493A1
CA2086493A1 CA 2086493 CA2086493A CA2086493A1 CA 2086493 A1 CA2086493 A1 CA 2086493A1 CA 2086493 CA2086493 CA 2086493 CA 2086493 A CA2086493 A CA 2086493A CA 2086493 A1 CA2086493 A1 CA 2086493A1
Authority
CA
Canada
Prior art keywords
film
layer
vinyl acetate
copolymer
ethylene
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
CA 2086493
Other languages
French (fr)
Inventor
Robert Babrowicz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
WR Grace and Co Conn
Original Assignee
WR Grace and Co Conn
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by WR Grace and Co Conn filed Critical WR Grace and Co Conn
Publication of CA2086493A1 publication Critical patent/CA2086493A1/en
Abandoned legal-status Critical Current

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00Layered products comprising a layer of synthetic resin
    • B32B27/06Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00Stock material or miscellaneous articles
    • Y10S428/913Material designed to be responsive to temperature, light, moisture
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/13Hollow or container type article [e.g., tube, vase, etc.]
    • Y10T428/1328Shrinkable or shrunk [e.g., due to heat, solvent, volatile agent, restraint removal, etc.]
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/13Hollow or container type article [e.g., tube, vase, etc.]
    • Y10T428/1334Nonself-supporting tubular film or bag [e.g., pouch, envelope, packet, etc.]
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/13Hollow or container type article [e.g., tube, vase, etc.]
    • Y10T428/1334Nonself-supporting tubular film or bag [e.g., pouch, envelope, packet, etc.]
    • Y10T428/1345Single layer [continuous layer]
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/31504Composite [nonstructural laminate]
    • Y10T428/31855Of addition polymer from unsaturated monomers
    • Y10T428/31909Next to second addition polymer from unsaturated monomers
    • Y10T428/31913Monoolefin polymer
    • Y10T428/3192Next to vinyl or vinylidene chloride polymer
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/31504Composite [nonstructural laminate]
    • Y10T428/31855Of addition polymer from unsaturated monomers
    • Y10T428/31909Next to second addition polymer from unsaturated monomers
    • Y10T428/31928Ester, halide or nitrile of addition polymer

Abstract

ABSTRACT OF THE DISCLOSURE
A multilayer packaging film is provided comprising a first layer comprising a material selected from the group con-sisting of an acid copolymer, a very low density linear polyeth-ylene (VLDPE) and blends thereof; a second layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution, and a high degree of short chain branching; a third layer com-prising a barrier copolymer; a fourth layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branching; and a fifth layer compris-ing a very low density linear polyethylene (VLDPE).

3/920527.4/SPECFLDR

Description

~Y~ 3 ~LTILAYER SXRINKABLE FILM WITH IMPROVED S~RINg, ~PTICS AND SEAL~BILITY

B~CRGROUND OF THE IN~TION

This invention relates generally to thermoplastic, packaging films, and more particularly to a shrinkable ~ilm with improved heat-shrinkability properties, optics and strength. In certain multilayer embodLments, the films also have improved sealing characteristics, such as easier sealability and improved seal strength, particularly in the presence o~ grease.

Shrinka~le thermoplastic films have many useful appli-cations in the packaging industry ~or food and non-food prod-ucts. ~ heat shrinkable bag can be made from such ~ilms that has widespread use for meat and dairy products. Multilayer heat shrinkable films commonly contain ethylene-vinyl-acetate copolymers in one or more layers due to its toughness and low temperature shrinking characteristics.

A pac~a~ing film known by U.S. Patent No. 3,741~253 comprises a core layer of a vinylidene chloride copolymer ~com-monly known as saran, which has in the United States, lost its trademarX status and become generic) between a layer of ethylene-vinyl acetate copolymer and a layer of cross-linked ethylene-vinyl acetate copolymer. Vinylidene chloride copolymer is abbreviated as PVDC and ethylene vinyl acetate copolymer as E~A.
3/920527.4/SPECFLDR

.. . . .

, ~, . . . : . :
:. , ~ . . , . ~ .
.

. . . - . . :
. ~. .

~ ~ 3 ~ 3 A method for producing a film of E~A and P~DC is dis-close~ in u.s. ~atent No. 3,953,557 wherein the EVA has a narrow molecular weight distribution. rrhe saran composition is a blend of emulsion and suspension polymerized saran or is a saran compo-sition that includes emulsion polymerized vinylidene chloride of the type generally considered suitable for liquid coat~ng.

U.S. Patent No. 4,352,844 J commonly assigned herewith to W. R. Grace & Co.-Conn., discloses a multilayer, heat shrink-able, thermoplastic film which comprises at least two EVA lay-ers, the first EV~ layer being a surface layer and the second layer being adjacent thereto. The EVA copolymer of the first layer has a higher melting temperature than the E~ copolymer of the second layer. The EVA copolymers in both layers are cross-linked and each layer is stretch oriented. The first and second layers form the substrate to which other layers can be added.
In one embodiment, the film has third and fourth layers wherein the third layer is a barrier layer that comprises a thermoplastic material having low gas permeability such as vinylidene chloride copolymer or hydrolyzed ethylene-vinyl ace-tate copolymer (hereinafter abbreviated as EVOH, and also known as ethylene-vinyl alcohol copolymer) and the fourth layer com-prises an ethylene~vinyl acetate copolymer.
`:
U.S. Patent No. 4,640,856, which is commonly assigned herewith to W. R. Grace & Co.-Conn. and incorporated herein by reference, discloses multilayer films having a heat sealing VLDPE (very low density polyethylene~ layer, an oxygen barrier layer, and at least a further outer layer, preferably a VLDPE
layer. The patent discloses a multilayer thermoplastic barrier film having at least three layers comprising: (a) a layer con-sisting essentially of very low density polyethylene having a density of less than 0.910 gms/cc; Ib) a barrier layer compris-ing a material selected from the group consisting of: (1) copolymers of vinylidene chloride and (2) hydrolyzed ethylene-vi-nyl acetate copolymers; (c) a thermoplastic polymeric layer, said layer being on the side of the barrier layer opposite- to that of layer (a); and (d~ the shrinkage of layer (a) control-3/920527.4/SPECFLDR

.; .

3~3 ~ g the shrink~ge oE the entire multila~er barrier filrn, saidmultila~/er film having been oriented and rendered hea~ shrink-able at a temperature below 100C ~212F), said orientation tempera~ure being about ao~F or more below the melt temperature of the very low density polyethylene.

U.S. Patent No. 4,801,486 also to W. R. Grace &
Co.-Conn. discloses a ~hermoplastic multilayer packaging film comprising at least five layers in which one surface layer is a heat sealing layer and one of the internal layers is a barrier layer. The heat sealing surface layer comprises a copolymer of ethylene and an alpha-olefin having four to eight car~on atoms per molecule and the copolymer comprises ninety percent to seven-ty-five percent ethylene and ten percent to twenty-five percent alpha-~lefin having four to eight carbon molecules and a density of less than 915 kglmZ. This material is called very low density linear polyethylene (VLDPE). Additionally, the heat sealing layer may comprise a blend of the copolymer above with an ethylene~vinyl acetate copolymer or an ethylene/butyl-acrylate copolymer.

A packaging film suitable for making bags and pouches and commonly assigned to W. R. Grace & Co.-Conn. is disclosed in U.S. Patent 4,837,0a4, wherein a multilayer heat shrinkable film has at least one layer comprising a copolymer of ethylene and an alpha-olefin with six or more carbon atoms per molecule with the VLDPE copolymer havin~ a density of about 0.910 g~cc or less and a melt index of about 2 or less. The entire disclosure of U.S.
Patent No. 4,837,084 is incorporated herein by reference.

A variety of embodiments of heat-shrinkable films are disclosed in U.S. Patent No. 4,863,769 wherein in one em~odiment the film may be a biaxially oriented monolayer film of a very low density polyethylene copolymer (VLDPE~ with a density under O.910 g/cc. In another embodiment, the ~ilm may be a biaxially oriented multilayer film comprising a first outer layer of an ethylene-vinyl acetate copolymer, a core layer of a barrier material such as a polyvinylidene chloride copolymer or an 3/920527.4/SPECFLDR

'~

e~nylene-vinyl alcohol copol~er, and a second outer layer com-prising a blend of an ethylene-vinyl acetate copol~mer and a very low density polyethylene copolymer with a density under O.910 g/cc. The Eilms are made by the double bubble method of Pahlke, U.S. Patent No. 3,555,604.

U.S. Patent No~ 4,97~,898, which is a Divisional of U.S. Patent No. 4,863,769, discloses a method of manufacturing a heat shrinkable biaxially oriented 1:hermoplastic film by extrud-ing a primary tube, including very :Low density polyethylene with a density under 0.910 g/cc, heating the primary tube and biaxially stretching the heated primary tube using the dou~le bubble method of Pahlke, U.S. Patent 3,555,604, to form a tube which is heat-shrinkable.

Another multilayer film structure is disclosed in U.S.
Patent No. 5,041,316, assigned to W. R. Grace & Co~-Conn., where-in there is taught a multilayer thermoplastic shrinkable ilm with improved processing properties comprising at least a heat sealing VLDPE layer, a core oxygen barrier layer, an outer thermoplastic layer and also comprising a further intermediate VLDPE layer between the barrier and the outer thermoplastic layer.

~ biaxially oriented~ heat shrinkable fiLm is dis-closed by U.S. Patent No. 5,059,481, which is a Continuation of U.S. Paten~ No. 4,976,898, the film comprising VIDPE copolymex which comprises ethylene copolymerized with higher alpha olefin~
containing from four to eight carbon atoms such as butene, pentene, hexene, heptene and octene, and which has a density under 0.910 glcc.
":
European Patent Application 91104044.2, (Publication No. 0447988, pu~lished September 25, 1991), Forloni, Fornasiero, and Parnell, assignors to W.R. Grace & Co. - Conn., discloses a multilayer thermoplastic film from which containers may be made, sald film having ~ thermosealing layer, a gas barrier layer, and at least one additional polymeric layer characterized in that 3/920527.4/SPECFLDR

~T~ r~

t"~ thermos~aling 1CL~er can be sealed to itself to form a con-tainer ~ith an opening through which a product ma~ be loaded into the container and aEter the container has been loaded, the film c2n be sealed to itself through c~ntaminants left by the product to herm~tically C105e the container, said thermosealing layer comprising a copolymer selected from ethylene-methacrylic acid (~MAAI copolymers with methacrylic acid (MAA) content of about 4% to about 18 % by weight, ethylene acrylic acid (EAA) copolymers with an acrylic acid (AA) content of from about 4~ to about 22% by weight, and their blends.

Desirable properties in multilayer packaging films frequently include improved shrinkability, improved optics and improved seala~llity through contaminatio~. ~lthough multilayer packaging fi~ns in the prior art may satisfy some of the needs in the packaging art, room for improvement exists in pursuit of a packaging film with improved characteristics over materials used in the past.
:
03~ECTS AND Sl)M~RY OF TH~ I~VENlION

It is thus an object of the present invention to pro-vide a packaging film with improved heat shrinkability character-istics over prior packaging films.
:
It is still yet another o~ject of the present inven-tion to provide a packaging film having improved strength charac-teristics relative to other packagin~ film.

It is yet another object of the present invention to provide a packaging film having impro~ed optics relative to other packaging film~.

In certain multilayer embodiments, it is an object of the present invention to provide the above-mentioned characteris-tics of improved optics, improved heat shrinkability and im-proved strength characteristics, and also to provide some other objects as followsO
3/920527.4/SPECFLDR
`:
, .

Thus, it ls another object of the present invention to provide a multllayer heat shrinkable packaging fi~n having i.m-proved sealability characteristics over films used in the pas~.

It is another object of the present inven~ion to pro-vide a multilayer heat shrinkable packaging film with improved grease resistance over packaging films used in the past.

Finally, for the certain rnultilayer embodiments, i-t is an object of the present invention to provide a multilayer pack-aging film combining the above advantages, i.e. improved sealability thro~gh contamina-tion, improved grease resistance, improved optics, improved heat shrillkability characteristics and improved strength characteristics.

These and other objects are accomplished by a thermoplastic heat shrinkable film having i~proved shrink charac~
teristics comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecu-lar weight distribution and a high degree of short chain branch-ng .

. In certain multilayer embodiments these and other objects are accomplished by a thermoplastic heat shrin~ab~e film having improved shrink characteristics comprisin~ a first seal-ing layer comprising a material selected from the group consist-ing of an acid copolymer, a very low density linear polyethylene (VLDPE), and blends thereo~; and a second layer comprisi~g ethylene vinyl acetate copol~ner with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chai~ branching.

In a preferred embodiment, the present invention also provides a thermoplastic multilayer heat shrinkable film compris-ing a first layer comprising a material selected from the group consisting of an acid copolymer such as ethylene-methacrylic acid or ethylene-acrylic acid, a very low density linear polyeth-ylene (VLDPE), and blends. thereo; a second layer comprising 3/920527.4/SPECELDR
, ~ .

`

ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate with narrow molecular weight distribution and a high degree of short chain branching; a third layer com-prising a barrie~ copolymer; a fourth layer comprising ethylene vinyl acetate copolymer with nine to fi-~teen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branching; and a fifth layer compris-ing a very low density polyethylene (VLDPE).

There~ore, the present invention provides a thermoplastic heat shrinkable film having improved shrinX charac-teristics comprising ethylene vinyl acetate copolvmer with nine to fifteen percent by weight vinyl acetate, with narrow molecu-lar weight distribution and a high degree of short chain branch-ing.

The present invention also provides a bag formed from tubular film according to the above paragraph, where the bag is formed by a transverse seal across the flattened tube and the mouth is formed by severin~ the tube at a predetermined distance from said transverse seal.

.
- Also, in certain multilayer embodiments, the present invention provides a thermoplastic multilayer heat shrinkable film having improved shrinX, optics, toughness and sealability characteristics comprising a first sealing layer comprising a material selected from the group consisting of an acid copolymer, a very low density linear polyethylene (VLDPE), and blends thereof; and a second layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branching.
;
The present invention also provides a bag formed from -: tubular film according to the above paragraph, where the first layer is the face of the inner tuhe wall wherein the bottom of the bag is formed by a transverse seal across the flattened tube 3/920527.4~SPECFLDR
: 7 r ` ,'~i ~r ~ ~

and the mouth is formed by severing the tuhe at a predetermined distance from said transverse seal.

The present invention also provides a thermoplastic multilayer heat shrinkable film having improved shrink, optics, toughness and sealability characteristics co~prising ~ first sealing layer comprising a material selected from the group consisting of an acid copolymer, a very low density linear poly-ethylene (VLDPE), and blends thereof; a second layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branchi~g; a third layer com-prising a barrier copolymer; a fourth layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight di~tribution and a high degree of short chain branching; and a fifth layer compris-ing a very low density linear polyethylene ~VLDPE~.

The present invention also provides a bag formed from tubular film according to the above paragraph, where the first layer is the face of the inner tube wall wherein the bottom of the bag is formed by a transverse seal across the flattened tube .and the mouth is formed by severing the tu~e at a predeterm~ned distance from ~aid transverse seal.

~- DET~ILED DESCRIPTIO~

It has been found according to this invention that a novel shrinkable packa~ing film can be provided which has im-proved optics, improved heat shrinkability characteristics and improved stre~gth characteristics relative to prlor packagin~
films. The packaging ~ilm according to this invention has also demonstrated significant. improvemen~ in free shrink at varying shrink bath temperatures, and improved pre- and post-shrink op-tics have also been identified. Improving the toughness. or strength characteristics of the ilm by lowering the solid state deformation temperature has also been demonstrated. In certain multilayer embodiments, the film also has improved sealability 3/920527.4/SPECFLDR

,r ~ '1 q~
f; ~ ~ 9 ~ ~ ~ r ~ J 1~.
cnaracterlstics through contaminatio~, and improved yrease resis-tanc~, as well as improved optics, improved heat shrlnkability characteristics and lmproved s-treng-th cn~ acteristics relative to prior packaging films. It has also been found that the multilayer pac~aging film according to this invention demon-strates significant improvements in increased seal strength, instantaneous seal strength, sealability through contamination, and grease resistance.

Various other features and advantages will become apparent ~rom a reading of the ~ollowing description.

In a preferred embodiment:, the film according to the present invention comprises thermoplastic heat shrinkable film having improved shrink characteristics comprising ethylene vinyl acetate copolymer with nine to fi~teen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branching. This EVA copolymer provides considerably more heat shrinkability and at lower levels of vinyl acetate than prior art EVAs at such lower levels of vinyl acetate. Utilization of this EVA further provides improved optics and improved strength characteristics. Such EVAs are commercially available from Mitsui-duPont under the sales code V5714 or V5711.

In a preferred multilayer embo~iment, the seal layer comprises an ~cid copolymer such as ethylene-methacrylic acid or ethylene-acrylic acid, a very low density linear polyethylene having a density less than .915 g/cc, or blends thereof~ Utiliz-ing either of these as the seal layer provides improved sealability characteristics through contamination and improved grease resistance. EMAA is sold by duPont under the tradename Nucrel, EAA is sold by Dow under the tradename Primacor, and VLDPE is sold by Dow under the tradename Attane and by Union Carbide under the tradename Ucarflex.

In another pre~erred embodiment, the film according to the present invention comprises a five-ply structure including 3/920527 . 4/SPECFLDR

' ~ne following: a first la~er of an acid copolymer such as eth~lene-methacrylic acid (EMAA) or ethylene-acrylic acid (EAA), a very low density linear polyethylene (VLDPE) with a density less than .915 g/cc, or blends thereof; a second layer of ethylene vinyl acetate copolymer (EV~) with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribu.ion and a high degree of short chain bra~ching; a third layer o vinylidene chloride copol~ner (PVDC); a fourth layer of ethylene vinyl acetate copolymer (EVA~ with nine to fifteen percent by weight vinyl acetate, with narrow moleculax weight distribution, and a hi~h degree of short chain branching; and a fifth layer of a very low density polyethylene (VLDPE) (again o~
a density less than .915 g/cc). It is preferred that the film according to this invention, when it has a PVDC barrier layer, be made according to the extrusion coating process outlined and described in U.S. Patent No. 3,741,253 (Brax, et al.), which is incorporated herein by reference.

In preparation of the multilayer film according to the present invention, the extrusion coating method may be used.
Layers one and two are coextruded through a conventional tuhular extruder to form a tube. After leaving the die, the substrate is cooled and flattened. At this point, layers one and two are electron beam cross-linked at about 4.5 megara~ ~MR). Depend-ing on the characteristics desired, this dosage can vary from two to twenty MR. Layers three, four and five are then extrusion coated onto layers one and two, and the tape is then quenched and accumulated.

It is generally recogni~ed that irradiation with high energy electrons can be harmful to PVDC barrier layer composi-tions as such irradiation can degrade and discolor PVDC, making it turn brownish. The use of extrusion coating according to the present invention therefore allows for the irradiative treatment of layers one and two without subjecting the PVDC layer extrusion coated thereto to the harmful effects of the irradia-tion.

3/920527.4/SPECFLDR

''' '' " ~

3~

~ Et~r receiviny the final extrusLorl coating oE layers three, four and five, the se~mless tape is caoled, collapsed and rolled-up. The tape is subse~uently unrolled, ~ed through a bath o~ hot water held at 175F -to 210F, and as it leaves the hot water the tape is oriented by being in~lated and blown both in the machine direction and the transverse direction into thin tubing. This orientation is the well Xnown trapped bubble tech~
nique which imparts a heat shrinkable property to the ilm.

After being stretched, the film is quickly cooled while substantially retaining its stretched dimensions to cool the film rapidly and therefore set the oriented molecular config-uration. Once the orientation is set, the film is then rolled up for further processing. Control of the hot bath temperature determines the ultimate shrinkage, optics and toughness of the tu~ing.

A heat-shrinkable film will shrink when exposed to an appropriate temperature, typically 85 to 90C, at least 5% in at least one of the transverse or machine directions.

The film has a barrier layer according to a preferred embodlment of this invention. The barrier material may be made of any of the known barrier polymeric resins such as PVDC, EVOH, or nylon. Barrier means a good barrier to the trans~ission o~
gases such as oxygen. Preferably, the barrier material is a vinylide~e chloride copolymer. The term "saran~' or PVDC refers to a vinylidene chloride copolymer wherein a major amount of the copolymer comprises vinylidene chloride and a minor amount of the copolymer comprises one -or more unsaturated monomers copolymerizable therewith. When PVDC is not used as a barrier material (i.e. the barrier is a material such as EVO~ or nylon, or a barrier is not used at all), the ~ilm may be fully co-ex-truded and then, if desired, post electron-beam irradiated since polymers other than PVDC materials do not discolor from irradia-tion liXe PVDC does.
~ , 3/920527.4/SPECFLDR

~ 3 The second and fourth layers of a preferred embodiment of the film according to this invention comprise a unique ethylene vinyl acetate copolymer (EVA) which has narrow molecu-lar weight distribution and has a high degree of short chain branching. The EVA comprises nine to fif~een percent by weight vinyl acetate. This EVA provides considerably more heat shrinkability and at lower levels of vinyl acetate than prior art EVAs at such lower levels of vinyl acetate. Utilization of this EVA further provides improved optics and improved strength characteristics. Such EVAs are commercially available from Mitsui-duPont under the sales code V5714 or V5711.

Narrow molecular weight distribution is determined by the use of a gel permeation chromatograph on the EVA polymer resin to salculate the number average molecular weight. The number average molecular weight should be between about 15,000 and 30,000, more preferably between about 20,000 and about 25,000, with a standard deviation of about 1,000. The short chain branching of the EVA copolymer is determined by car~on 13 NMR (nuclear magnetic resonance) testing.

A further processing step can be taken to make end seal bags by transversely sealing and severing ~cross the seam-less tubular film as it is laid flat to make individua~ bags.
Side sealed bags may be made by slitting the seamless tubular film along one of its edges after which it is transversely sealed and severed into bags. The side seals are the sealing and severing seams and the bottom of the bag is the unslit edge of the film. Other bag and pouch making methods known in the art may be readily adapted to making receptacles from the multilayer film according to the present invention.

The film can be further utilized as are other materi-als of the heat-shrinkable (oriented) types. After a product, such as a food product, is wrapped with the film, the enclosed product can be subjected to elevated temperatures, for examp~e, by passing the enclosed product through a hot air tunnel or by placing the enclosed product in hot water. The enclosing heat 3/920527.4~SPECFLDR 12 ~r ~ 3t~

~llrinkaDle film is thereby caused to shrink around the product to produce a tight ~Jrapping that closely conforms to the contour of the product therein.

It ls thus seen that the presen-t invention provides a multilayer shrinkable packaging film which has improved sealability characteristics over materials used in the past. It is also seen that the present invention provides a multilayer packaging film with improved grease resistance over packaging films used in the past. It is fu:rther seen that a multilayer packaging film is provided which has improved optics and shrinkability characteristics over prior packaging films. It is further seen that the present invention provides a multilayér pacXaging film which has improved strength characteristics rela-tive to prior packaging film. Yet still further, it is seen that the present invention provides a multilayer packaging film which combines the above advantages, i.e. improved sealahility through contamination, improved grease resistance, improved optics, improved shrinkability characteristics and improved strength characteristics. Many variations are apparent to those of skill in the art, and such variations are embodied within the spirit and scope of the present invention as measured by the following appended claims.

3/920527.4/SPECFLDR

Claims (26)

1. A thermoplastic multilayer heat shrinkable film having improved shrink, optics, toughness and sealability charac-teristics comprising:
a first sealing layer comprising a material selected from the group consisting of an acid copolymer, a very low densi-ty linear polyethylene (VLDPE), and blends thereof; and a second layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branching.
2. The film of claim 1 wherein the first and second layers are cross-linked.
3. The film of claim 2 wherein the first and second layers are electron beam cross-linked.
4. The film of claim 1 wherein the first and second layers have been formed by coextrusion.
5. The film of claim 1 wherein the film is in the form of a seamless tube with the first layer being the face of the inner tube wall.
6. The film of claim 1 wherein the very low density linear polyethylene has a density of less than .915 g/cc.
7. The film of claim 1 wherein said acid copolymer of the first layer is ethylene-methacrylic acid, ethylene-acrylic acid, or a blend thereof.
8. A bag formed from tubular film according to claim 5 wherein the bottom of the bag is formed by a transverse seal across the flattened tube and the mouth is formed by severing the tube at a predetermined distance from said transverse seal.

3/920527.4/SPECFLDR 14
9. The bag of claim 8, heat-shrunk about a contained food product.
10. A thermoplastic multilayer heat shrinkable film having improved shrink, optics, toughness and sealability charac-teristics comprising:
a first sealing layer comprising a material selected from the group consisting of an acid copolymer, a very low densi-ty linear polyethylene (VLDPE), and blends thereof;
a second layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branching;
a third layer comprising a barrier copolymer;
a fourth layer comprising ethylene vinyl acetate copolymer with nine to fifteen percent vinyl acetate, with nar-row molecular weight distribution and a high degree of short chain branching; and a fifth layer comprising a very low density linear polyethylene (VLDPE).
11. The film of claim 10 wherein at least one layer is cross-linked.
12. The film of claim 11 wherein at least one layer is electron beam cross-linked.
13. The film of claim 10 wherein the third, fourth and fifth layers are extrusion coated onto a substrate tape, and the substrate includes the first and second layers.
14. The film of claim 10 wherein all the layers have been formed by coextrusion.
15. The film of claim 10 wherein the film is in the form of a seamless tube with the first layer being the face of the inner tube wall.

3/920527.4/SPECFLDR
16. The film of claim 10 wherein the very low density linear polyethylene has a density of less than .915 g/cc.
17. The film of claim 10 wherein said acid copolymer of the first layer is ethylene-methacrylic acid, ethylene-acryl-ic acid, or blends thereof.
18. A bag formed from tubular film according to claim 15 wherein the bottom of the bag is formed by a transverse seal across the flattened tube and the mouth is formed by severing the tube at a predetermined distance from said transverse seal.
19. The bag of claim 18, heat-shrunk about a con-tained food product.
20. A thermoplastic heat shrinkable film having im-proved shrink characteristics comprising ethylene vinyl acetate copolymer with nine to fifteen percent by weight vinyl acetate, with narrow molecular weight distribution and a high degree of short chain branching.
21. The film of claim 20 wherein the film is cross-linked.
22. The film of claim 21 wherein the film is electron beam cross-linked.
23. The film of claim 20 wherein the film has been formed by coextrusion.
24. The film of claim 20 wherein the film is in the form of a seamless tube.
25. A bag formed from tubular film according to claim 24 wherein the bottom of the bag is formed by a transverse seal across the flattened tube and the mouth is formed by severing the tube at a predetermined distance from said transverse seal.

3/920527.4/SPECFLDR
26. The bag of claim 25, heat-shrunk about a con-tained food product.

3/920527.4/SPECFLDR 17
CA 2086493 1992-07-02 1992-12-30 Multilayer shrinkable film with improved shrink, optics and sealability Abandoned CA2086493A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US90772592A 1992-07-02 1992-07-02
US907,725 1992-07-02

Publications (1)

Publication Number Publication Date
CA2086493A1 true CA2086493A1 (en) 1994-01-03

Family

ID=25424545

Family Applications (1)

Application Number Title Priority Date Filing Date
CA 2086493 Abandoned CA2086493A1 (en) 1992-07-02 1992-12-30 Multilayer shrinkable film with improved shrink, optics and sealability

Country Status (3)

Country Link
US (1) US6291038B1 (en)
CA (1) CA2086493A1 (en)
TW (1) TW267181B (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AUPP749398A0 (en) * 1998-12-03 1999-01-07 Sporos Sa Multilayer heat shrinkable film
US20030157354A1 (en) * 2002-02-15 2003-08-21 Van Veghel Michael W. Transparent, coated, shrinkable, oriented polypropylene film
JP2004088619A (en) * 2002-08-28 2004-03-18 Sony Corp Code string encryption method, apparatus and encryption release method, apparatus and recording medium
US7736726B2 (en) * 2002-12-17 2010-06-15 Cryovac, Inc. Polymeric film with low blocking and high slip properties
DE602004004222T2 (en) * 2003-08-11 2007-11-15 Exxonmobil Chemical Patents Inc., Baytown Polymers consisting of ethylene and optionally copolimerizable esters, films of these polymers and stretch film hood packaging process using these films
SG194484A1 (en) * 2011-04-14 2013-12-30 Mitsui Chemicals Tohcello Inc Resin sheet for sealing solar cell, solar cell module using same, and method for manufacturing solar cell module

Family Cites Families (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3555604A (en) * 1965-03-12 1971-01-19 Union Carbide Corp Biaxial orientation
US3953557A (en) * 1971-03-30 1976-04-27 W. R. Grace & Co. Polymer film with narrow molecular weight distribution and saran and laminates thereof
US3741253A (en) * 1971-03-30 1973-06-26 Grace W R & Co Laminates of ethylene vinyl acetate polymers and polymers of vinylidene chloride
DK152722C (en) * 1979-12-25 1988-09-26 Kureha Chemical Ind Co Ltd HEATING SHRINKABLE LAMINATED MOVIE AND PROCEDURE FOR ITS PREPARATION
US4352844A (en) * 1981-05-29 1982-10-05 W. R. Grace & Co. Thermoplastic film having improved handling and sealing characteristics and receptacle formed therefrom
FR2575483B1 (en) * 1984-12-28 1987-02-06 Bp Chimie Sa COMPOSITIONS BASED ON AN ETHYLENE POLYMER FOR THE MANUFACTURE OF SELF-ADHESIVE AND AMBIENT TEMPERATURE STRETCH FILM
US4640856A (en) * 1985-04-29 1987-02-03 W. R. Grace & Co., Cryovac Div. Multi-layer packaging film and receptacles made therefrom
US5059481A (en) * 1985-06-17 1991-10-22 Viskase Corporation Biaxially stretched, heat shrinkable VLDPE film
US4976898A (en) * 1985-06-17 1990-12-11 Viskase Corporation Process for making puncture resistant, heat-shrinkable films containing very low density polyethylene
CA1340037C (en) * 1985-06-17 1998-09-08 Stanley Lustig Puncture resistant, heat-shrinkable films containing very low density polyethylene copolymer
NZ217626A (en) * 1985-09-30 1989-11-28 W R Grace & Co Conn Formerly W Packaging film consisting of #a# olefin copolymers
JPH044149B2 (en) * 1986-06-19 1992-01-27
US4837084A (en) * 1987-07-02 1989-06-06 W. R. Grace & Co.-Conn. Thermoplastic multi-layer packaging film and bags made therefrom
GB2227448B (en) * 1988-11-18 1992-09-30 Grace W R & Co Multi-layer film structure for packaging and bags made therefrom
NZ237420A (en) * 1990-03-23 1993-11-25 Grace W R & Co Thermoplastic multilayer film having a thermosealing layer of ethylene-methacrylic (or acrylic) acid copolymer or a blend thereof

Also Published As

Publication number Publication date
US6291038B1 (en) 2001-09-18
TW267181B (en) 1996-01-01

Similar Documents

Publication Publication Date Title
US4178401A (en) Packaging film comprising a blended self-welding layer
CA2013587C (en) High shrink energy/high modulus thermoplastic multi-layer packaging film and bags made therefrom
CA1298681C (en) Thermoplastic packaging film of low
AU611166B2 (en) Thermoplastic multi-layer packaging film and bags made therefrom
CA1318582C (en) Stretch/shrink film with improved oxygen transmission
US4762748A (en) Multilayer film with better layer adhesion
US4734327A (en) Cook-in shrink film
US5298326A (en) Cook in film with improved seal strength and optics
CA1296854C (en) Eva based multi-layer, heat-shrinkable, packaging film and bags made therefrom
NZ200836A (en) Heat shrinkable multilayer packaging film and receptacles made therefrom
US4758463A (en) Cook-in shrink film
US5234731A (en) Thermoplastic multi-layer packaging film and bags made therefrom having two layers of very low density polyethylene
NZ280601A (en) Bag having a reinforcing patch, both the bag and the patch being of heat-shrinkable film, the patch film being ethylene-alpha-olefin copolymer
CA1181359A (en) Thermoplastic receptacle having improved high temperature seal
CA2099440C (en) Multilayer shrinkable film with improved shrink, optics and sealability
US4183882A (en) Self-welding packaging film
CA2086493A1 (en) Multilayer shrinkable film with improved shrink, optics and sealability
CA1300333C (en) Inter-ply adhesion between saran and linear ethylene copolymers by blending ethylene/butyl acrylate copolymer into the linear ethylene copolymers
CA2022846A1 (en) Cook-in film with very low density polyethylene
NZ243109A (en) Self-welding packaging film having layers of a self-welding ionomer, ethylene vinyl acetate copolymer, a copolymer of vinylidene chloride and vinyl chloride or methyl acrylate, and a blend of hdpe and ethylene vinyl acetate copolymer
GB2328674A (en) Patch bag comprising homogeneous ethylene/alpha-olefin copolymer
CA2335552C (en) Packaged food product including an added liquid and process for making same
Warren et al. Thermoplastic packaging film of low I 10/I 2

Legal Events

Date Code Title Description
FZDE Discontinued