CA1324711C

CA1324711C - High strength laminated film for chub packaging

Info

Publication number: CA1324711C
Application number: CA000608921A
Authority: CA
Inventors: Henry George Schirmer
Original assignee: WR Grace and Co Conn
Current assignee: Cryovac LLC
Priority date: 1988-09-26
Filing date: 1989-08-21
Publication date: 1993-11-30
Anticipated expiration: 2010-11-30
Also published as: JPH02134247A; JP2792685B2; AU3933189A; US5037683A; AU616037B2

Abstract

ABSTRACT OF THE DISCLOSURE

A multilayer laminated film useful in chub packaging comprises a core layer comprising a biaxially oriented film, and an outer hot blown film bonded to each of the opposing surfaces of the core layer, at least one of the core layer and outer hot blown films including a layer of an oxygen barrier polymeric material.

Description

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HIGH STRENGTH LAMINATED FI~I FOR CHUB PACKAGING

BACKGROUND OF THE' INVENTION

This in~erltion relates generally to a laminated film suitable for packaging, and more particularly to a laminated film suitable for use in chub packaging and having improved tensile streng,th and seal strength properties.
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Certain foods, and particularly meat products such as ground beef and other comminuted food substances, are commonly packaged in what are called chub packages. These packages are generally produced at central processing plants operated by supermarket chains or meat packing companies. These packages are generally produced using a vertical form fill seal (VFTS) process, in which a tube is formed from a flat sheet of roll stock film. The tube is formed vertically and longitudinally sealed with a vertical sealing bar. The bottom of the tube is then sealed with a clip applied to the bottom of the tube, the meat product such as ground beef is pumped into the open end of the tuhe, and the top is sealed ~ith a clip to produce the final chub packag In appearance, these chubs resemble semi-rigid tubes with the tubular film forming a skin tight layer around the food product.
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Package sizes may range from 1 to 20 poundsj depending on the intended mode of distribution. Pumping equipment typically used to stuff the food product into the tubular film can place great stress on the , : .
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64536-6~6 longitudinal eal of the tube. Thi3 longitudinal ~eal is usually a lap ~eal.
More recently, cru~t-froz~en items have become more popular, and the hardening of the outer surface of the food product in the tubular casing durlng the freezlng proce~s can produce further stre~s on the longltudlnal seal.
Successful film~ for use in such applications include the HS660 and HS2000 film~ produced commercially by the Cryovac Divi~ion of W. R. Grace & Co. The films are compo~ed of lay-flat tubular film. Prior to collap~e, the HS660 film includes an inner layer of ethylene vlnyl acetate copolymer (~VA) and an outer layer of polyethylene ~PE). The two core layers comprise nylon, ~ith an intermediate layer between each nylon layer and respective outer layer and inner layers comprising lonomer reslns. In ca~e of HS2000, an ethylene vlnyl alcohol copolymer replaces the nylon layer close~t to the inside of the structure.
Whlle such materlal~ have been very u~eful ln produclng chub packaging, it 1~ an ob~ect o$ the pre~ent lnvention to I further lmprove the performance of chub packaging materials, ,~ 20 especially under condltions whereln improved seal ~trength and `; lower transver~e elongatlon are deslrable.
SUMHARY OF THE INVENTION
In one aspect of the inventlon, a multilayer laminated fllm use~ul ln chub packaglng compri~es a core film comprislng a blaxially orlented fllm havlng a central layer of ethylene alpha-olefln copolymer selected from the group consisting of linear low density polyethylene and very low den~lty polyethylene and outer ~`: B ~

layers of ethylene vinyl acetate copolymer, and an outer film bonded to each of the opposing surfaces of the core fllm, and comprising a hot blown film, wherein at least one of the outer fiims includes a layer of an oxygen barrier polymeric material.
In a preferred embodiment the oxygen barrier polymeric material is selected from the group consisting of vinylidene chloride copolymer, ethylene vinyl alcohol copolymer, and polyamide.
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9 In a further preferred embodiment the biaxially orlented 3 10 fllm has a central and outer layers of ethylene vlnyl acetate copolymer, and, between said central layer and each of said outer layers, an intermediate layer of ethylene alpha-olefin copolymer.
Preferably the ethylene alpha-olefln copolymer is selected from the group consisting of linear low density polyethylene and very low density polyethylene.
In another embodiment the hot blown fllm has a central layer of ethylene vlnyl alcohol copolymer, an outer heat sealable layer, and an lnner bondlng layer of ethylene vinyl acetate copolymer. Preferably the hot blown film comprise~, a) a first layer of a heat sealable material b) a second layer of a linear low denslty polyethylene;
c) a third layer of a polymeric adhesive;
d) a fourth layer of an ethylene vinyl alcohol copolymer;
e) a fifth layer of a polymeric adhesive;
f) a sixth layer of a linear low density polyethylene; and g) a seventh layer of an ethylene vinyl acetate copolymer. ~ ~
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In another aspect of the present invention, a method of making a multilayer laminated film useful in chub packaging comprises melt extruding a first film having a layer of ethy-lene alpha-olefin copolymer and a layer of ethylene vinyl acetate copolymer; biaxially orienting said film; melt ex-truding two multilayer films by the hot blown method; and adhering each of the two hot blown films, at their bonding layers, to opposing surfaces of the first film; at least one of the first film and hot blown films including a layer of an oxygen barrier polymeric material.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be further understood by reference to the attached drawings wherein:
¦ FIGURE 1 is a schematic cross-sectional view of one I embodiment of the present invention; and i FIGURE 2 is a schematic diagram of a method of ¦ making the laminated film of Figure 1.
¦~ DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure 1, a multilayer laminated film ~ 20 10 includes a core layer or film comprising a biaxially ~;~
t~ oriented film 12.
In one embodiment, oriented layer 12 has a central , layer 18 made up of ethylene vinyl acetate copolymer, and outer layers 20a and 20b of linear low density polyethylene.

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In another embodimel~t, oriented layer 12 has a central layer 18 of ethylene vinyl acetate copolymer, twc, intermediate layers of linear low density polyethylene, and an additional layer of ethylene vinyl acetate copolymer on each surface to make up a five-layer film. This latter film is commercially available as SSD 310 film manufactured by W. R. Grace &
Co.-Conn. through its Cryovac Division.

An alternate material for layers bearing the linear low density polyethylene is very low or ultra low density polyethylene.

Film 12 is preferably cross-linked. This may be done by pre-blending prior to extrusion, a chemical cross-linking agent into one or more of the resins making up the oriented film.

Another, more preferred method is irradiation.

Irradiation may be accompli~hed by the use of high energy electrons, ultra violet radiation, X-rays, gamma rays, beta particles, etc. Preferably, electrons are employed up to about 20 megarads (MR) dosage level. The irradiation source can be any electron beam generator operating in a range of about 150 kilovolts to about 6 megavolts with a power output capable of supplying the desired dosage. The voltage can be adjusted to appropriate levels which may be for example 1,000,000 or 2,000,000 or 3,000,000 or 6,000,000 or higher or lower. Many apparatus for irradiating films are known to those of skill in the art. The irradiation is usually carried out at a dosage up to about 20 MR, typically between about 1 MR and about 20 MR, with a preferred dosage range of about 2 MR to about 12 MR. Irradiation can be carried out conveniently at room tempexature, although higher and lower temperatures, for example, 0C to 60C may be employed.

On each side or surface of the core layer, hot blown barrier films 14a and 14b- are respectively bonded. Film 14a has a central layer 22a of ethylene vinyl alcohol copolymer, an outer heat sealable layer 24a, and an inner bonding layer 26a of ethylene vinyl acetate copolymer.
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132~711 ~ 'ilm 14b, on the opposing surface of core layer 12, has a structure identical to film 14a. Thl~s, layer 22b will have the same composition as 22a, and layers 26b and 24b will have the same composition as layers 26a and 24a respectively.

In the most preferred embodiment, the outer heat sealable materials making up layers 24a and 24b are a blend of 90% linear low density polyethylene or ethylene vinyl acetate copolymer and about 10% of an antiblock material.

j Also in the preferred embodiment, a polymeric adhesive material, such as a graft copolymer or other modified copolymer of ethylene vinyl acetate copolymer is located on either surface of the ethylene vinyl alcohol copolymer. Although EVA-based polymeric adhesives with an anhydride functionality are preferred, other polyameric adhesives with various polyolefinic bases will also be ussful to som~ extent in providing interlaminar adhesion.

Finally, a l~yer of linear low denSity polyethylene is disposed J between the heat sealable outer layer and one of the polymeric adhesive ! layers, and between the inner bonding layer and the other of the polymeric i adhesive layers.
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Thus, in the most preferred el~odiment, hot blown film 14a and 14b is a seven layer structure in which the ethylene vinyl alcohol copolymer forms a central layer, and in which two discrete layers of linear low density polyethylene are present.
': ' It has been found that several advantages are obtained from the present invention.

The core layer of biaxially oriented, cross-linked film contributes to reduced elongation of the final laminate. This has an advantage in certain chub packaging applications where high elongation properties of the chub packaging material can detrimentally aEfect the dimensional stability of the filled package.

132~7~1 At the same tlme, it is believed that the blown films 14a and 14b provide the necessary oxygen barrier characteristics, and also resistance to shrink during sealing resulting in stronger longitudinal seals. Stronger seals are especially desirable to reduce the possi~ility of rupture of the filled package and loss of the package contents.

Where as in this case the elongation properties of the laminate are reduced, it is of greater importance to insure adequate seal strength.
This is because the stresses put on the package either externally or by reason of the contained food product cannot be as easily accommodated by elongation of the film.

In the preferred embodiment, the core layer of biaxially oriented film is irradiated to a dosage of about 9 MR. A preferable range of irradiation dosage is between about 4 MR and 12 MR.

Cross-linking may also be accomplished by the addition of chemical cross-linking agents to one or more of the components of the core film prior to extrusion.

Figures 2 and 5 show two alternate methods of making the multilayer laminated film of the present invention. Referring first to ~
Figure 2, a double wound half mil blown film is ply separated and one ~- -layer 14b is unwound 360 from roll 1 to place the inside of the previous double wound film on the outside. This is done so -that the inside bonding layer 26b can be blow dried prior to corona treatment. ~
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Figures 3 and 4 show in more schema-tic detail that hot blown film 14 is a douhl~ wound film collapsed along the interface between bonding layer 26a and 26b. This interface is indicated by a thicker line ---in Figure 3. ~
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Figure 4 shows that the double wound blown film of Figure 3 is ply separated. One ply is unwound 360 from roll 1. This exposes bonding layer 26b where it can be subsequently dried and then exposed to corona ..
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discharge trcatment at station 3. This station is indicated to the left of upper roll 1 in Figure 2.

~ he ply separated blown film is dried, and drawn over rollers past corona discharge stations 3.

At the s~ne time, a double wound .60 mil stretch/shrink film is ply separated at roller 2 and drawn past: other corona discharge stations 3 as depicted in the central portion of Figure 2. At pinch roll 6, the single wound corona treated blown films from rollers 1 sandwich the single wound stretch/shrink film from roller 2 to create the multilayer larninated film of the present invention. This film is taken up on finished rolls 7. It is clear from the schematic drawing of Figure 2 that this results in two simultaneous finished rolls 7 of film having the same construction.

Referring now to Figure 5, a double wound half mil blown film is ply separated and unwound 360 as in the case of the film of Figure 2 at rolls 1. In this case, however, the separated and unwound plies are rejoined to create a double wound film in which bonding layers 26a and 26b are now on the outside of the double wound film instead of on the inside as originally extruded. The blown film is treated on both its now external EVA surfaces at corona stations 3. For the sake of clarity, double wound blown film 14 is shown as a single line tracking through corona discharge stations 3.

At the same time, the double wound stretch/shrink film of roll 2 is treated on both its surfaces at other corona discharge stations 3 depicted in the central portion of the schematic drawing of Figure 3.

At rollers A and B depicted in the central part of Figure S, the double wound stretch/shrink film is ply separated, and the as yet untreated internal surfaces of each separated ply are treated to create a single wound stretch/shrink film corona treated on both external surfaces.

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64536-~86 At pinch rolls 4, the slngle wound stretch/shrink bi- -axlally orlented materlal, now corona treated on both lts external ;
surfaces, ls adhered to the hot blown fllm treated on lts bondlng EVA surfaces facing the blaxially orlented core film. The entlre assembly of fllms ls passed through plnch rollers 4 and onto seml-flnlshed rolls 5. Referrlng to Flgure 6, the nature of the laml-nated fllm as lt exlts pinch rolls 4 ls graphlcally deplcted. ~
Fllm C represents the two layers of fllm from roll 1 whlch have -been corona treated on the outer sur~aces, lndlcated by an X, but .
not on the lnner surfaces. Fllm D represents one of the layers of fllm from the double wound roll 2 which have been corona treated on both externaI sldes. The seml-finlshed roll 5, then ls trans-formed to flnlshed roll 5 by separatlng at the untreated inner surface of fllm 1 and unwlndlng 360.
The present inventlon may be further understood by ¦ reference to the followlng examples of lamlnated fllm construc-I tions made ln accordance wlth the present lnventlon.
I Exam~le 1 I A three layer thermoplastlc fllm was coextruded from a ¦ 20 flrst melt stream of llnear low denslty polyethylene (Dowlex ~ 2045) and a second spllt melt stream of ethylene vlnyl acetate : :,.-. ,. :.
I copolymer (PE 204 CS95 avallable from El Paso) havlng a vlnyl ~-~
I acetate content of about 3.6% by welght of the total resln. The coextrudate was lrradlated to a dosage of 9 megarads and blaxlally :
orlented by the blown bubble technlque.
The llnear low denslty polyethylene layers were extruded -from separate extruders.

Trade-mark 8 -. ' ' A second multllayer fllm was hot blown by standard co-extruslon technlques, and having the followlng composltlon:
EVA/LLDPE/Tle/EVOH/Tle/LLDPE~EVA where EVA = Exxon 32.89 (vlnyl acetate content of about 4.5%
by welght) LLDPE = Dowlex 2045 (0.920 gr~ms/cc denslty) Tle = Plexar 169 (EVA based polymerlc adheslve) EVOH = Soarnol DT
Ten percent of an antiblocklng agent was preblended wlth the EVA prlor to extruslon. Thls agent lncludes 90% low denslty polyethylene blended wlth 10% of a colloldal sillca master batch.
The hot blown fllm was unirradiated.
The biaxlally orlented flrst fllm had a flnal thickness of 60 gauge. The flnal thlcknes of the hot blown film was 50 I gauge.
¦ The surface of the hot blown fllm whlch had only EVA was I corona treated, as were both surfaces of the biaxially orlented j~ stretch/shrlnk fllm. A second hot blown film ldentical to the I flrst film wa~ corona treated at lts EVA surface and adhered to ¦~ 20 the opposlte surface of the stretch/shrink film to form a 3-fllm lamlnate.
Examle 2 A multllayer lamlnate llke that of Example 1 was pro-duced, wlth the dlfference that ln place of the outer layer havlng a blend of 90% EVA and 10~ antlblock, a blend of 90% LLDPE (Dowlex -2035) havlng a density of 0.920 grams/cc was blended wlth 10%
antlblock.

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' This laminated film had the same gauges as in Example 1, i.e.
two outer hot blown films having a thickness of 50 gauge each, and a central stretch/shrink film, biaxially or-ented, having a final thickness of 60 gauge.
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Exc~mple 3 A laminated film like that of Example 1 was produced, but with the outer hot blown films having a thickness of 75 gauge instead of 50 --~
gauge.

Gauge variation was obtained by decreasing the deflate speed of the hot blown tubular material.
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~ Example 4 ~, Y, A laminated film like that of Example 3 ws produced, with the exception that in place of the 60 gauqe stretch/shrink film for the core layer of the laminate, a 100 gauge biaxially oriented film having the composition LLDPE/EVA/LLDPE was utilizecl.

i The present laminated film is characterized by relatively low transverse elongation, (see Tables 1 & 2). This property ensures better dimensional stability of the filled tu~ular film during the filling step of a VFFS process. However, it also puts greater stress on the longitudinai seal of the packaging, since less of the force exerted on the - chub package during filling can be accommodated by transverse elongation j of the tubular package.
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important attribute of this film. In Tables 3 & 4, seal data is presented which demonstrates the improved seal strength of films of the present invention.
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_n Table 1 Examples 1 and ~ correspond to Examples 1 and 2 as described above. Comparative Example 1 refers to the HS660 film, and comparative Example 2 refers to the liS2()00 film.
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In Table 2, Examples 3 and 4 correspond to examples 3 and 4 as described a~ove. Comparative Example 1 refers to the HS660 film, and comparative Example 2 refers to the HS2000 film.

In Table 3, Examples 1 and 2 correspond to the same examples as described above. Comparative Example 2 refers to the HS2000 film.

In Table 4, Examples 3 and 4 correspond to the same examples as described above. Comparative Example 2 refers to the HS2000 film.

Seals were applied with a Sentinel Seal~ equipped with a 1/8 inch seal bar at 40 psi seal pressure. Seal temperatures of 250F and 275F were used. Seal strength was determined using a CRE1000 Scott Tester. The seals were pulled in the conventional manner (designated "peel strength" in Tables 3 and 4) and also sheared.

As Tables 3 and 4 indicate, peel and shear strength at both 250F and 275F were improved, in some cases greatly improved, for the four examples of the present invention in comparison with comparative Example 2, with the exception of a weaker peel strength at the lower temperature for Example 2.

~' Elonqationl(%) at 73F at Break I Comparative Comparative Example 1Example 2Example 1 ExamPle 2 Lon~itudinal185.7 211.8 521.6 337.8 (1.78)(1.71) ~2.08) (2.18) i Transverse 199.6 232.6 624.5 592.0 , (1.79)(1.78) (~.03) (2.10) , ,,, 11 -' .

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SEAL STRENGT~ DATA
Comparative Example 1 Example 2 ExamPle 2 Peel Strength 4.23 0.57 1.22 ' (at 250F) +0.61 +0.67 +0.16 Peel Strength 5.07 3.03 1.26 .
-(at 275F) +0.47 +0.59 +p.26 Shear Strength 10.98 9.42 6.37 (at 250F) +1.92 +1.15 -~0.21 Shear Strength 9.81 8.37 6.71 (at 275F) +1.14 +0.64 -~0.39 , ~
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Table 4 Seal Strenqth ~a~a (_o~np~rd tive Example 3Exam~le ~ Example 2 Peel Strength3.54 4.27 1.22 (at 250F) +0.93 +1.29 ~0.16 Peel Strength6.62 5.85 1.26 (at 275F) +0.90 +1.S2 +0.26 Shear Strength13.82 13.83 6.37 (at 250F) +1.67 +1.83 +0.21 Shear Strength11.43 17.73 6.71 (at 275F)+1.63 +2.65 . -~0 39 .. . .
:i F.x~mrJ~e 5 A five layer thermoplastic film is coextruded from a first and fourth melt stream of a blend of linear low density polyethylene, linear medium density polyethylene, and ethylene vinyI ace-tate copolymer. A
second melt stream of ethylene vinyl alcohol copolymer, and a split melt ~ stream of a polymeric adhesive are also coextruded with the blend, to 1 produce a five layer film having the construction:
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LLDPE+LMDPE+EVA/TIE/EVOFI/TIE/LLDPE+LMDPE+EV~ :
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surfaces to a hot blown film having the construction of the hot blown film - :
of any of the previous examples, but without the presence of EVOH.

he hot blo~n films are adhered to each of the major surfaces .
of the core layer of biaxially oriented film by means of corona bonding. ~:
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A laminated film like that oE Example 1 is produced, with the difference that in place of the EVOH, a vinylidene chloride copolymer having a methyl acrylate comonomer is used. This material is commonly known as Saran.

~xample 7 A laminated film like that of Example 5 is produced, but having ~
in the biaxially oriented film, in place of the EVOH, a vinylidene chlo- -ride copolymer with a methyl acrylate comonomer.

Example 8 A laminated film like that ol Example 6 is made, with the dif-ference that in place of the vinylidene chloride methyl acrylate copolymer, a vinylidene chloride vinyl chloride copolymer is used.

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A laminated film like that of Example 7 is made, with the dif- -ference that in place of the vinylidene chloride methyl acrylate copolymer, a vinylidene chloride vinyl chloride copolymer is used.

While the present invention has been described with respect to preferred embodiments and specific examples, it will be understood by those skilled in the art that modifications may be made after review of the description of the invention without departing from the spirit and scope of the claims that follow.
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Claims

1. A multilayer laminate useful in chub packaging comprising:
(a) a core film comprising a biaxially oriented film having (i) a central layer of ethylene alpha-olefin copolymer selected from the group consisting of linear low density polyethylene and very low density polyethylene; and (ii) outer layers of ethylene vinyl acetate copolymer;
and (b) an outer film bonded to each of the opposing surfaces of the core film, and comprising a hot blown film;
(c) wherein at least one of the outer films includes a layer of an oxygen barrier polymeric material.

2. The laminate according to claim 1 wherein the biaxially oriented film is cross-linked.

3. The laminate according to claim 2 wherein the biaxially oriented film is cross-linked by the use of a chemical cross-linking agent.

4. The laminate according to claim 2 wherein the biaxially oriented film is cross-linked by irradiation of the film.

5. The laminate according to claim 1 wherein the oxygen barrier polymeric material is selected from the group consisting of vinylidene chloride copolymer, ethylene vinyl alcohol copolymer, and polyamide.

6. A multilayer laminate according to claim 1 wherein the biaxially oriented film has a central and outer layers of ethylene vinyl acetate copolymer, and, between said central layer and each of said outer layers, an intermediate layer of ethylene alpha-olefin copolymer.

7. The laminate according to claim 6 wherein the ethylene alpha-olefin copolymer is selected from the group consisting of linear low density polyethylene and very low density polyethylene.

8. A multilayer laminate according to claim 1 wherein the hot blown film has a central layer of ethylene vinyl alcohol copolymer, an outer heat sealable layer, and an inner bonding layer of ethylene vinyl acetate copolymer.

9. A multilayer laminate according to claim 8 wherein the hot blown film comprises:
a) a first layer of a heat sealable material b) a second layer of a linear low density polyethylene;
c) a third layer of a polymeric adhesive;
d) a fourth layer of an ethylene vinyl alcohol copolymer;

e) a fifth layer of a polymeric adhesive;
f) a sixth layer of a linear low density polyethylene; and g) a seventh layer of an ethylene vinyl acetate copolymer.