CA1330696C - Monoaxially oriented shrink film - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A coextruded multiple layer film is oriented in primarily the longitudinal direction, and comprises a core layer comprising butadiene styrene copolymer or copolyester, outer layers comprising ethylene propylene copolymer, polypropylene, or blends thereof, and intermediate layers which bond the outer layers to the core layer and comprise an ethylene copolymer.

Description

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,sl !~ MONOAXIALLY ORIENTED SHRINK FILM
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BACKGROUND OF THE INVENTION
6~;~ The present application is a division of Canadian ~ Patent Application Serial No. 574,755 filed on ~ovember 13, 1987.

6`~ . The present invention relates generally to shrink films, and more particularly to monoaxially oriented shrink films.
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Various films and laminates have been proposed for use particularly as label material for the labels of beverage bottles and the like. These films or laminates are preferably monoaxially oriented in order to permit a tight label to be produced around the bottle or vessel, without the undesirable wrinkling and shrinking of the label which would occur with a biaxially oriented film. The films could also be used to produce band type seals for tamper evidence.

The label material idealiy possesses several properties making it p3rticularly useful for this end use.
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For example, the material should' have the re-quired stiffness (i.e. high modulus) to permit the use of the film in a rollstock form in conjunction with label manufactur-ing apparatus. Lower modulus material would not be useful in such apparatus.

Suitable material should also possess surface properties that allow printing of the label with information such as verbal and graphic trademarks, ingredients, and other 4/880621.8/SPECFLDR
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lnformation directed to the contents and capacity of the vessel.

It may additionally be desirable to have a film ¦ with good optical properties.
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Of interest is U. S. Patent No. 4,188,443 issued to Mueller et al wherein a five-layer film has two inner layers comprising ethylene vinyl acetate copolymer, and skin or outer layers comprising an ethylene propylene copolymer.

Of interest is U. S. Patent No. 4,355,076 issued to Gash wherein a monoaxially oriented polypropylene film may be laminated to a monoaxially oriented high density polyethyl-ene film, said films produced by e.g. tubular blowing.

It is therefore an object of the present inven-tion to provide a thermoplastic film useful in forming labels or tamper evidence bands for vessels such as bottles, cans, and the like.

It is also an object of the present invention to provide such a label which can be monoaxially oriented.

It is an additional object of the present inven-tion to provide such a film with relatively high modulus properties.

It is still another object of the present inven-tion to provide such a film with good printability.

It is also an object of the present invention to provide a film having excellent optical properties.

Polyvinyl chloride (PVC) materials are commonly used in many packaging applications. However, a monoaxially oriented shrink film is needed for labeling and tamper evi-dent banding of bottles and cans. The recycling of polyester 4/880621.8/SPECFLDR

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~ ::' 1 3306q6 bottles and cans requires a label material with a specific gravity less than 1Ø PVC has a specific gravity greater than 1.0, making ~his material undesirable in such applications.
It is therefore still another object of ~he present invention to provide a monoaxially oriented shrink film having a composite specific gravity of less than about 1Ø
SUMMARY OF THE INVENTION
In one aspect of the present invention, a multilayer film, oriented in primarily one direction, comprises a core layer comprising a butadiene styrene copolymer; two outer layers each comprising ethylene propylene copolymer, polypropylene, or blends thereof; and two intermediate layers each bonding the core layer to a respective outer layer, and comprising an ethylene copolymer.
In yet another aspect, a multilayer film, oriented in primarily one direction, comprises: (a) a cross-linked core layer comprising a butadiene styrene copolymer; (b) two cross-llnked outer layers each comprising ethylene propylene copolymer, polypropylene, or blends thereof; and (c) two cross-linked intermediate layers each bonding the core layer to a respective outer layer and comprising an ethylene copolymer.
In another aspect of the present invention, a method for making a multilayer film comprises simultaneously coextruding a first melt stream of the butadiene styrene copolymer from a first extruder, two split melt streams of an ethylene copolymer from a second extruder, a third melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a third extruder, and a fourth melt stream of ethylene propylene copolymer, . .~

~ 3306q6 polypropylene, or blends thereof from a fourth extruder; passing the coextruded melt streams through a coextrusion die to form a tubular film; rapidly cooling the tubular film; collapsing the cooled film; slitting the cooled film to form a sheet; heating the sheet to its orientation temperature; and drawing the sheet through rolls to stretch the film in the longitudinal direction.
In a further aspect, a method for making a multllayer film comprises~ (a) simultaneously coextruding a first melt stream of a butadiene styrene copolymer from a first extruder, two split melt streams of an ethylene copolymer from a second extruder, a third melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a third extruder, and a fourth melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a fourth extruder; (b) passing the coextruded melt streams through a coextrusion die to form a tubular film;(c) rapidly cooling the tubular film; (d) collapsing the cooled tubular film;
(e) heating the cooled tubular film to its orientation temperature; and (f) drawing the film through rolls to stretch the film in the longitudinal direction.

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1 3306~6 6~536-655 In stlll another aspect of the present lnventlon, a multllayer fllm, orlented ln prlmarlly one dlrectlon, comprlses a core layer comprlslng a copolyester~ two outer layers each comprlslng ethylene propylene copolymer, polypropylena, or ~lends thereof; and two lntermedlate layers each bondlng the core layer to a respectlve outer layer, and comprlslng an ethylene copolymer, and sald fllm havlng a shrlnk tension ln the range of between a~out 750 and 1200 p.s.l.
In another aspect, the present lnventlon provldes a multllayer fllm, orlented ln prlmarlly one dlrectlon, comprlslng:
a cross-llnked core layer comprlslng a copolyester~ two cross-llnked outer layers each comprlslng ethylene propylene copolymer, polypropylene, or blends thereoft and two cross-llnked lnter-¦ medlate layers each bondlng the core layer to a respectlve outer ¦ layer and comprlslng an ethylene copolymer; and sald fllm havlng a ¦ shrlnk tenslon ln the range of between about 750 and 1200 p.s.l.
¦ In yet another aspect of the present lnventlon, a method for maklng a multllayer fllm comprlses slmultaneously coextrudlng a flrst melt streem of a copolyester from a flrst extruder, two spllt melt streams of an ethylene copolymer from a second extruder, a thlrd melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a thlrd extruder, and a ~ fourth melt stream of ethylene propylene copolymer, polypropylene, '. ' or blends thereof from a fourth extruder~ passlng the coextruded I melt streams through a coextruslon dle to form a tubular fllm;
6 ' rapldly coollng the tubular fllm~ collapslng the cooled fllm;
~ sllttlng the cooled fllm to ~orm }heet~ heatlng the sheet to lts . ~
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1 3306q6 orientatlon temperature~ and drawlng the sheet through rolls to ~d stretch the fllm ln the longltudlnal dlrectlon.
~j~f In stlll another aspect, the present lnventlon provldes ¦ a method for maklng a multllayer fllm comprlslng: slmultaneously coextrudlng a flrst melt stream of a copolyester from a flrst extruder, two spllt melt streams of an ethylene copolymer from a second extruder, a thlrd melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a thlrd extruder, and a fourth melt stream of ethylene propylene copolymer, poly-propylene, or blends thereof from a fourth extruder~ passlng the coextruded melt streams through a coextruslon dle to form a tubular fllm such that the flrst melt stream forms a core layer, the two spllt melt streams form lntermedlate layers, and the thlrd and fourth melt streams form outer layers~ rapldly coollng the . tubular fllm; collapslng the cooled tubular fllm; heatlng the cooled tubular fllm to lts orlentatlon temperature; and drawlng tlle fllm through rolls to stretch the fllm ln the longltudlnal directlon.
DEFINITIONS
~-y 20 "Ethylene propylene copolymer" as used hereln refers to a copolymer of ethylene and propylene havlng between about 2% and 5% by welght of the ethylene comonomer.
~ "Ethylene copolymer" as used hereln refers to copolymers ,~ ' of ethylene and vlnyl acetate, alkyl acrylate and alphaolefln, and also refers to chemlcally modlfled derlvatlves of these materlals.
~f "Copolyester" as used hereln means a thermoplastlc, ~i,j fllm-formlng copolyester such as ethylene ~,:
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terephthalate-glycol, terephthallc/lsopthallc acld-cyclohexane dlmethanol, and butylene terephthalate-tetramethylene ether terephthalate. Polyester and copolyester reslns are avallable ¦ from suppllers such as Eastman Kodak Comp~ny.
BRIEF DESCRIPTION OF THE DRAWINGS
Further detall~ are glven below wlth reference to the sole drawlng whereln:
FIG. 1 ls a schematlc cross-sectlon of a preferred embodlment of a multllayer film of the lnventlon.

I Referrlng speclflcally to the drawlngs, ln FIG. 1 a ~chematlc cross-sectlon of a preferred embodlment of the multlply I fllm of the lnventlon ls shown.
¦ Thls fllm ls partlcularly useful ln formlng labels for vessels such as bottles and cans.
The fllm structure 18 a multllay~r composlte havlng a core layer 10 comprlslng a butadlene styrene copoiymer (B~S). A
preferred, commerclally avallable BDS 19 Phllllps KR-10 havlng a butadlene content of 25% by welght of the copolymer.
Outer layers 12 may be elther an ethylene propylene copolymer (EPC), a polypropylene (PP), or blends of these two materlals. In blends, lncreaslng the percentage of polypropylene lmparts added stlffness, l.e. a hlgher modulus to the multllayer fllm. In a preferred embodlment, outer layer 12 comprlses about 92% EPC and about 8~ 811p antlblock masterbatch ln a polypropylene base.

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` 1 3306q6 For a stlffer fllm, l.e. a fllm wlth hlgher modulus, a more preferred blend comprlses about 60% EPC and about 40~ PP.
For a more flexlble fllm, l.e. a fllm wlth lower modu-lus, a more preferred blend comprises about 92~ EPC and about 8~
PP. EPC contrlbutes to the shrlnk characterlstlcs of the fllm, so that the more flexlble fllm wlll also exhlblt better shrlnk char-acterlstlcs such as hlgher free shrlnk at a given temperature, e.g. 200F, than the stlffer fllm.
The outer layers 12 of the multllayer fllm each constl-tute preferably between about 20% and 30% of the total film thlck-ness and more preferably about 27% of the total fllm thlckness.
These layers are preferably thlcker when greater fllm buoyancy ls deslred.
A preferred EPC for outer layers 12 18 one avallable from Flna havlng a 4% ethylene content. A preferred PP for outer layer 12 1~ Hlmont X-7810-39 .
In the multllayer fllm, the outer layers are bonded to the core layer by lntermedlate layers 14 each comprlslng a copoly-mer of ethylene and preferably a vlnyl acetate comonomer (EVA), the copolymer havlng preferably between about 4% and 30~ vlnyl acetate by welght of the copolymer.
For stlffer fllms, the EVA preferably has about 12.5%
vlnyl acetate. A sultable resln ls Elvax 3508 ~du Pont~.
Other preferred materlals for layers 14 lnclude ethylene alkyl acrylate, especlally ethylene n-butyl acrylate copolymer;
very low denslty polyethylene; and chemlcal modl-Trade~mark 6 ' - 1 3306q6 L led polymeric adhesives having carboxylic acid or acid anhydride.

The intermediate layers 14 of the film each constitute preferably between about 5% and 15% of the total film thickness, and more preferably about 9% of the total film thic~ness.

The preferred butadiene styrene copolymer (BDS) of the core layer has a density of about 1.01 grams per cubic centimeter. The core layer preferably comprises between about 20~ and 30% of the total film thickness.

BDS resins having minor amounts of butadiene, ranging from about 1 to 50%, are most preferred in order to provide the optimum balance of stiffness and flexibility to the film.

As indicated earlier with respect tG the outer and intermediate layers, multilayer films having different modulus values can be produced by varying the composition or thickness of the core layer.

The film of the present invention is preferably made by coextrusion techniques in which melt streams of the various resins are extruded from respective extruders and passed through a die to form a tubular tape.

This tape has a thickness of preferably between about 4 and lO mils more preferably about 6.5 mils.

The relatively thick coextruded tape is ~uenched for example in water, and then optionally irradiated with between about 1 and 5 megarads, and more preferably about 3 megarads of irradiation.

The coextruded tape is then slit and opened out to form a sheet. The sheet is then heated to its orientation 4/880621.8/SPECFLDR

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1 3306q b temperature and then stretch oriented. The oriented sheet is then cooled. Preferable orientation ranges are 3:1 to 7:1, and more preferable is an orientation drawing ratio of about 5.0:1 in the longitudinal direction.

Any suitable longitudinal orientation equipment can be used for the stretching operation. A particularly useful apparatus is a unit available from Kampf. This unit includes heated rolls heated to preferably a temperature between about 180F and 280F. More preferably, the rolls are heated to a temperature between about 200F and 250F, and even more preferably to a temperature of about 230F.
The film is heated by passing in contact with the heated rollers. After the film has ~een heated, it is passed through a series of smaller rollers running at different rotational velocities to stretch the film longitudinally.

In another method of making the multilayer film, the cooled tubular film can be heated to its orientation temperature, and drawn through rollers of different speeds to stretch the film, without the need for slitting the cooled tube to form a sheet.
i Although the film is referred to as a monoaxially oriented film, and is oriented primarily in the longitudinal direction, some incidental orientation is some-times desirable in the transverse direction. This small degree of transverse direction orientation can help the film to grip a container or vessel after heat shrinking. The particular Kampf unit used in the examples does not afford significant incidental transverse orientation, ~ut those skilled in the art will understand that suitable apparatus are available to achieve a small amount of transverse orienta-tion if desired.

Typical film thicknesses may range from for example 0.5 to 4 mils. A preferred film thickness is about 2 mils. Increasing film thicknesses will provide more stiff-4/88062~.8/SPECFLDR

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ness to the film in cases where a higher modulus is desired because of limitations of label-making equipment.

The butadiene styrene copolymer core layer 10 provides the stiffness and rigidity needed to emulate PVC
films. The composite film has a specific gravity of about 0.934, thus providing a label material with a specific gravi-ty less than about 1Ø

The invention may be further understood by refer-ence to the following examples.
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, A core layer of butadiene styrene copolymer (Phillips KR-10) having a density of 1.01 grams per cubic centimeter was extruded from a first extruder in a coextrusion arrangement. Intermediate layers of a 12.5%
vinyl acetate EVA (DuPont Elvax 3508) were extruded as a split stream from a second extruder. Outer layers of a blend of 92% EPC (Fina 283~98) and 8% slip/antiblock masterbatch in a PP base-were extruded from third and fourth extruders re-spectively. The various melt streams were extruded as a tubular tape from a coextrusion die. The core layer com-prised about 27% of the total thickness of the tape and re-sulting film. The outer layers each comprised about 27% of total film thickness, and the intermediate layers each com-prised about 9% of total film thickness.

After rapid water quenching of the extruded tape, the tape was then slit and opened into a sheet, and passed through a Kampf*orienting unit with heated rolls until the sheet reached its orientation temperature.

The film was not irradiated.
*Trade-mark 4/880621.8/SPECFLDR
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~ - 1 3~06~6 The film was longitudinally drawn between a series of smaller rolls at an orientation ratio of 4.0:1Ø
Final film thickness was 1.5 mils. Modulus at 73F was 217,600 PSI (longitudinal direction) and 116,300 (transverse direction).

A film substan~ially similar in composition to that of EXAMPLE 1 has a draw ratio of 3.0:1Ø

Both examples produced films suitable for use in labeling equipment wherein the film, in rollstock form, is fed to a labeling unit. The labeling machine severs the film at a length corresponding to the final circumference of a label to be wrapped around a can, bottle, or similar vessel.
An adhesive may be applied to the interior side of the film, i-.e. that surface of the film which will contact the vessel, and/or the portion of the vessel itself which will bear the label.

Alternatively, labels can be precut from the film and prepared as sleeves, to be inserted over for example cans or bottles and slipped onto the portion of the vessel where the label is to be placed.

In either embodiment, the film can be preprinted to carry indicia such as trademark data, contents, weight, and like information.

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Suitable modifications may be made in the film, such as the introduction of desirable pigments to one or more of the resins used to prepared the multilayer film.

One particularly desirable feature of this film is its essentially monoaxial orientation. After the applica-4/880621.8tSPECFLDR
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tion of the label by either of the embodiments described above, the vessel bearing the label is passed through a hot air shrink tunnel or other shrinking means, to tighten the label around the vessel. Because of the essentially uniaxial orientation of the film, a tight fitting label is produced without significant shrinkage or warpage of the film in the transverse direction.

The film of Example 1 exhibited the following physical properties:

Tensile At Break1 Lonqitudinal Transverse Q 73F 17,600 3,170 (PSI) (2.09) (1.64) Elongation At Break2 37.9 2.5 ~ 73F (%) (2.09) (1.64) Modulus3 Q73F 217,100 116,300 (PSI) (2.18) (2.72) Free Shrink4 @200F 5 -1 (Elon-(%) gated) HazeS ~73F (2.96) ClaritY~ @73F 21.2 (%) (2.96) Gloss7 73F 76.
(45) (2.96) Shrink Tension8 I Q200F 302.23 56.64 ¦ (PSI) (1.92) (2.68) Q240F 527.17 35.67 ~ (1.85) (2.63) 1 Q280F 571.39 34.27 (2.20) (2.59) .
Ball Burst Impact9 Q73F 4.5 1 Inch Diameter (1.96) Sphere Head (CM-KG) 4/880621.8/SPECFLDR

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All val es are averages obtained from four (4) replicate measu ements.
ASTM D882-81 2 inches/minute draw rate; 4 in :h initial

2 ASTM D882-81 length

3 ASTM D882-81

4 ASTM D2732-70 (Reapproved 1976) . ~ ASTM D1003-61 (Reapproved 1977) ~/ ASTM D1746 71 ASTM D-2457-70 (Reapproved 1977) ~ ASTM D2838-81 Film gauges are indicated in parenthesis.

In an alternate embodiment, a film was coextruded with a core layer comprising a copolyester (Eas-tman PETG 6763).

The remainder of the film structure was substan-tially the same composition as in Example 1.

The film was produced substantially as described for Example 1, with an orientation ratio of 4.5:1.

The film of Example 3 had the following proper-ties:
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¦ Tensile At Break1 Longitudinal Transverse @ 73F 27,750 3,660 (PSI) ~1.62) (1.50) 12.9 388.7 Elonqation At BreakZ (1.62) (1.50) - ~-Modulus3 Q73F 440,400 151,500 (PSI) (1.61) (1.69 Free Shrink4 :::
~200F 9 -1 (Elon-(%) gated) 4/880621.8/SPECFLDR ::
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' '-- 1 3306q6 '--~aze5 @73F 4.0 (%) (1.70) Claritv~ @73F 18.0 (%) (1.70) Gloss7 73F 90.
j - (45) (1.70) Shrink Tension~
@200F 754.26 28.04 (PSI) (1.61) (1.97) @240F 1087.48 40.49 (1.58) (1.95) 280F 1194.65 69.18 (1.57) (1.92) Ball Burst Impact9 @73F 5.1 1 Inch Diameter ~1.64) Sphere Head (CM-KG) All valu~s are averages obtained from four (4) replicate me~surements.
ASTM D882-81 Longitudinal - 2 inches/min.
Draw rate; 4 inch initial length 2 ASTM D882-81 Transverse - 20 inches/min. Draw rate; 2 inch initial length 4 ASTM D2732-70 (Reapproved 1976) ASTM D1003-61 (Reapproved 19771 ~ ASTM D1746 7 ASTM D-2457-70 (Reapproved 1977) Film gauges are indicated in parenthesis.
Although the present invention has been de-scribed in connection with preferred embodiments, it should be understood that modifications may be made without depart-ing from the principles and scope of the invention, as those skilled in the art will readily understand. Accordingly, such modifications and variations may be practiced within the scope of the following claims.

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Claims (14)

-- THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS: --

1. A multilayer film, oriented in primarily one direction, comprising:

(a) a core layer comprising a butadiene styrene copolymer;

(b) two outer layers each comprising ethylene propylene copolymer, polypropylene, or blends thereof; and (c) two intermediate layers each bonding the core layer to a respective outer layer, and comprising an ethylene copolymer.

2. The film according to claim 1 wherein the outer layers each comprise a blend of about 92% ethylene propylene copolymer, and about 8% slip/antiblock masterbatch.

3. The film according to claim 1 wherein the intermediate layers each comprise an ethylene copolymer se-lected from the group consisting of ethylene vinyl acetate copolymer, ethylene alkyl acrylate copolymer, and very low density polyethylene and chemically modified polymeric adhe-sives.

4. A multilayer film, oriented in primarily one direction, comprising:

(a) a cross-linked core layer comprising a butadiene styrene copolymer;

(b) two cross-linked outer layers each comprising ethylene propylene copolymer, polypropylene, or blends thereof; and (c) two cross-linked intermediate layers each bonding the core layer to a respective outer layer and comprising an ethylene copolymer.

5. The film according to claim 4 wherein the cross-linked intermediate layers each comprise an ethylene copolymer selected from the group consisting of ethylene vinyl acetate copolymer, ethylene alkyl acrylate copolymer, and very low density polyethylene and chemically modified polymeric adhesives.

6. A method for making a multilayer film comprising:
(a) simultaneously coextruding a first melt stream of a butadiene styrene copolymer from a first extruder, two split melt streams of an ethylene copolymer from a second extruder, a third melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a third extruder, and a fourth melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a fourth extruder;
(b) passing the coextruded melt streams through a coextrusion die to form a tubular film;
(c) rapidly cooling the tubular film;
(d) collapsing the cooled film;
(e) slitting the cooled film to form a sheet;
(f) heating the sheet to its orientation temperature;
and (g) drawing the sheet through rolls to stretch the film in the longitudinal direction.

7. The method according to claim 6 wherein the sheet is drawn at a drawing ratio of between about 3.0:1 and 7:1 in the longitudinal direction.

8. The method according to claim 6 wherein the rolls are heated to between about 180°F and 280°F during the drawing operation.

9. The method according to claim 6 wherein the sheet is heated to its orientation temperature by passing the sheet through a series of heated rollers.

10. The method according to claim 6 further comprising cross-linking the cooled film prior to slitting.

11. The method according to claim 10 further comprising cross-linking the film by irradiating the cooled film, prior to slitting, with about between 1 and 5 megarads of irradiation.

12. A method for making a multilayer film comprising:
(a) simultaneously coextruding a first melt stream of a butadiene styrene copolymer from a first extruder, two split melt streams of an ethylene copolymer from a second extruder, a third melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a third extruder, and a fourth melt stream of ethylene propylene copolymer, polypropylene, or blends thereof from a fourth extruder;
(b) passing the coextruded melt streams through a coextrusion die to form a tubular film;
(c) rapidly cooling the tubular film;
(d) collapsing the cooled tubular film;
(e) heating the cooled tubular film to its orientation temperature; and (f) drawing the film through rolls to stretch the film in the longitudinal direction.

13. The method according to claim 12 wherein the sheet is drawn at a drawing ratio of between about 3.0:1 and 7:1 in the longitudinal direction.

14. The method according to claim 12 wherein the rolls are heated to between about 180°F and 280°F during the drawing operation.