U.S. patent application number 10/641656 was filed with the patent office on 2004-02-19 for heat-shrinkable, heat-sealable polyester film for packaging.
Invention is credited to Kendig, Terrance D..
Application Number | 20040033382 10/641656 |
Document ID | / |
Family ID | 23964135 |
Filed Date | 2004-02-19 |
United States Patent
Application |
20040033382 |
Kind Code |
A1 |
Kendig, Terrance D. |
February 19, 2004 |
Heat-shrinkable, heat-sealable polyester film for packaging
Abstract
The invention provides a packaging film comprising a
heat-shrinkable, heat-sealable polyester shrink film. The film
comprises a homopolymer or copolymer of polyethylene terephthalate,
preferably coated with a solvent-based, heat-seal coating, e.g., an
amorphous copolyester. The film may be metallized and/or laminated
to other films, e.g., ionomer films. The films and laminated are
useful in various packaging applications including cook-in or
non-cook bags for packaging meats, as well as lidding
applications
Inventors: |
Kendig, Terrance D.;
(Newark, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
23964135 |
Appl. No.: |
10/641656 |
Filed: |
August 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10641656 |
Aug 15, 2003 |
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09494354 |
Jan 31, 2000 |
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6623821 |
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09494354 |
Jan 31, 2000 |
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09105558 |
Jun 26, 1998 |
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09105558 |
Jun 26, 1998 |
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08854830 |
May 12, 1997 |
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5873218 |
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09105558 |
Jun 26, 1998 |
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08646195 |
May 7, 1996 |
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08646195 |
May 7, 1996 |
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08414568 |
Mar 31, 1995 |
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60049940 |
Jun 24, 1996 |
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Current U.S.
Class: |
428/518 ;
428/500; 53/442 |
Current CPC
Class: |
Y10T 428/31797 20150401;
C08J 7/043 20200101; B32B 2307/736 20130101; Y10T 428/1341
20150115; B32B 27/36 20130101; C08J 7/0427 20200101; C08J 2423/00
20130101; C08J 2467/00 20130101; C08J 7/052 20200101; Y10T 428/1338
20150115; Y10T 428/31692 20150401; C08J 2367/02 20130101; Y10T
428/31681 20150401; Y10T 428/31855 20150401; B32B 2439/70 20130101;
C08J 7/0423 20200101; C08J 7/048 20200101; B32B 2307/31 20130101;
B32B 27/08 20130101; B32B 38/0036 20130101; B65B 7/2885 20130101;
B32B 7/12 20130101; B32B 2307/518 20130101; Y10T 428/3192 20150401;
Y10T 428/1328 20150115; Y10T 428/31786 20150401 |
Class at
Publication: |
428/518 ; 53/442;
428/500 |
International
Class: |
B65B 053/02 |
Claims
What is claimed is:
1. A heat shrink film for packaging comprising: (a) a heat shrink
film comprising a polymer having at least 80% by weight
polyethylene terephthalate polymer, wherein said film is biaxially
oriented in the range of about 5% to about 55%, said film having an
outer surface and an inner surface; and (b) a solvent-based,
heat-seal coating on at least one of the outer surface and inner
surface.
2. The heat shrink film of claim 1 wherein the solvent-based,
heat-seal coating comprises an adhesive selected from the group
consisting of ethylene vinyl acetate copolymers, polyethylene
terephthalate copolymers, and combinations thereof.
3. The heat shrink film of claim 1 wherein the temperature at which
shrinkage of the film is initiated is about 80 degrees C. or
higher.
4. The heat shrink film of claim 1 wherein the heat shrink film
additionally comprises a metallized layer below the solvent-based,
heat-seal coating.
5. The heat shrink film of claim 1 wherein the film is laminated to
one or more additional layers to form a laminated film.
6. The heat shrink film of claim 4 wherein the one or more
additional layers are selected from the group consisting of: nylon,
polypropylene, polyethylene, ionomer, ACR, ethylene vinyl acetate,
polyethylene terephthalate, polystyrene, ethylene vinyl alcohol,
polyvinylidene chloride, and combinations thereof.
7. A bag formed from the heat shrink film of claim 1.
8. A package formed from the heat shrink film of claim 1.
9. The package of claim 8 wherein the heat shrink film additionally
comprises a metallized layer on the inner surface, and the
solvent-based, heat-seal coating resides on the metallized layer,
and wherein the package after shrinkage exhibits the property of
pearlessence while the functional barrier to oxygen and moisture is
retained.
10. A ovenable, cook-in package for packaging food formed from the
bag of claim 7.
11. A method to package an article, comprising the steps of: (a)
wrapping the article in a shrink film comprising a polymer having
at least 80% by weight polyethylene terephthalate polymer, wherein
said film is biaxially oriented in the range of about 5% to about
55%, said film having an outer surface and an inner surface, said
inner surface having coated thereon a solvent-based, heat-seal
coating; (b) heat-sealing the required sides to form a bag; (c)
sealing the bag with the article therein; and (d) shrinking the bag
by applying heat.
12. A tamper-resistant packaging container capable of venting vapor
comprising, in combination: a) an open rigid or semi-rigid
container having a floor portion and side walls upwardly extending
therefrom, said side walls having an outside surface; b) a
heat-shrink film having an inner surface and a solvent-based heat
seal coating applied on such inner surface, said inner surface of
said film in intimate sealing contact with at least a portion of
the outside surface of the side walls, and wherein the heat-shrink
film comprises: i) a polymer having at least 80% by weight
polyethylene terephthalate polymer; and ii) wherein said film is
biaxially oriented in the range of about 5% to about 30%.
13. The packaging container of claim 8, wherein the heat-shrink
film is biaxially oriented in the range of 10% to about 20% and
wherein the film has a thickness between 12 and 75 micrometers.
14. The packaging container of claim 8 wherein the heat-seal
coating comprises an adhesive selected from the group consisting of
ethylene vinyl acetate copolymers, polyethylene terephthalate
copolymers, and combinations thereof.
15. The packaging container of claim 8 wherein the inner surface of
the heat-shrink film additionally comprises a metallized layer
between the inner surface and solvent-based heat-seal coating.
16. A tamper-resistant heat-shrink lidding film, having an inner
surface, for covering a rigid or semi-rigid container having an
outside surface, said film comprising at least 80 percent by weight
of a polyethylene terephthalate homopolymer or copolymer, having a
plurality of sides and a thickness of 12-75 micrometers, and being
biaxially oriented in the range of about 5%-30% shrink factor; and
said inner surface comprising a solvent-based heat-seal coating
thereon, wherein: a) said film is intimate contact with at least a
portion of the outside surface of said container; b) when the sides
of said film are heated, said film remains in tamper resistant
engagement with said container, hermetically sealing said
container, yet allowing air and moisture to move in and out of said
lidding film upon heating.
17. The tamper-resistant lidding film of claim 12, wherein said
film is biaxially oriented in the range of about 7-20% shrink
factor, and said film has a thickness between 25 and 60
micrometers.
18. The tamper-resistant lidding film of claim 12 wherein said film
additionally has a metallized coating on the outside surface in
between such surface and the solvent-based, heat-seal coating.
19. The tamper-resistant lidding film of claim 12, wherein said
lidding film is torn or ruptured, indicating package removal or
tampering has occurred, when said container is no longer securely
sealed and said film is removed from the sealing position.
20. A heat-shrink film laminate for packaging comprising multiple
film layers wherein: (a) at least one film layer of the laminate
comprises a film of a polymer having at least 80% by weight
polyethylene terephthalate polymer, wherein said film is biaxially
oriented in the range of about 5% to about 55%; (b) a solvent-based
laminating adhesive between film layers of the laminate; and, (c) a
second or additional film layers of the laminate comprises a
polymer selected from the group consisting of: nylon,
polypropylene, polyethylene, ionomer, ACR, ethylene vinyl acetate,
polyethylene terephthalate, polystyrene, ethylene vinyl alcohol,
polyvinylidene chloride, and combinations thereof.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of pending prior
application Ser. No. 09/105,558, filed Jun. 26, 1998, which was a
division of patented prior application Ser. No. 08/854,830, filed
May 12, 1997, both entitled Packaging System Capable of Venting
Steam While Remaining Tamper Resistant and Methods Relating
Thereto, which was a continuation-in-part of pending prior
application Ser. No. 08/646,195, filed May 7, 1996, which was a
continuation-in-part of abandoned prior application Ser. No.
08/414,568, filed Mar. 31, 1995, and entitled Closed Container and
Packaging Process which was a continuation-in-part of pending
provisional application Serial No. 60/049,940, filed Jun. 24, 1996,
and entitled Packaging System Capable of Venting Steam While
Remaining Tamper Resistant and Methods Relating Thereto.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates broadly to a particular type
of polyester shrink film. More specifically, this invention relates
to a heat-shrinkable polyethylene terephthalate film coated with a
solvent-based heat-seal coating and/or laminated to other films,
useful in packaging, e.g., as bags or lidding stock.
[0004] 2. Discussion Of The Related Art
[0005] The use of heat-shrinkable thermoplastic films is well-known
to the packaging industry. For example, poultry products are
typically sealed within bags made from such films, and heated, thus
shrinking the bag until it fits tightly around the product. One
such bag is monolayer polyester film. These bags provide strength
and protection through tight adhesion to the product, though they
have the drawback that they must be sealed with an adhesive since
polyester is not heat-sealable except at exceptionally high
temperatures. Bags sealed with adhesive are generally not as strong
in the seal area as heat-sealed bags, and cannot be closed on the
open end by existing heat-seal equipment.
[0006] Coextruded films, such as polyolefins, are useful in
producing heat-shrinkable bags because they are heat-sealable and
therefore can be produced on existing heat-seal equipment
economically. They maintain good physical contact with a packaged
product after heat shrinking, and thereby retain juices within
packaged meats, but not as well as laminated shrink bags. However,
coextruded film have have less desirable mechanical properties,
such as tensile strength and modulus, and therefore bags from these
films are more apt to tear or otherwise become physically damaged
during handling. As well, they generally do not possess high
temperature heat resistance, which limits their application for
cook-in uses.
[0007] U.S. Pat. No. 4,971,845 discloses an oriented heat-sealable,
heat-shrinkable adhesive laminated film comprising, in one
instance, a polyester film layer and a polyolefin film layer,
wherein said film layers comprise similar shrink characteristics.
The one example discussed combines layers each having
"approximately the same shrinking characteristics", i.e., a
shrinkage of about 50%.
[0008] There exists a need for a thermoplastic film which has
high-strength, is heat-shrinkable and heat-sealable, as well as
high temperature heat resistant.
SUMMARY OF THE INVENTION
[0009] This invention provides a heat shrink film for packaging
comprising:
[0010] (a) a heat shrink film comprising a polymer having at least
80% by weight polyethylene terephthalate polymer, wherein said film
is biaxially oriented in the range of about 5% to about 55%, said
film having an outer surface and an inner surface; and
[0011] (b) a solvent-based, heat-seal coating on at least one of
the outer surface and inner surface.
[0012] This invention also provides a method to package an article,
comprising the steps of:
[0013] (a) wrapping the article in a shrink film comprising a
polymer having at least 80% by weight polyethylene terephthalate
polymer, wherein said film is biaxially oriented in the range of
about 5% to about 55%, said film having an outer surface and an
inner surface, said inner surface having coated thereon a
solvent-based, heat-seal coating;
[0014] (b) heat-sealing the required sides to form a bag;
[0015] (c) sealing the bag with the article therein; and
[0016] (c) shrinking the bag by applying heat.
[0017] This invention further provides a tamper-resistant packaging
container capable of venting vapor comprising, in combination:
[0018] a) an open rigid or semi-rigid container having a floor
portion and side walls upwardly extending therefrom, said side
walls having an outside surface;
[0019] b) a heat-shrink film having an inner surface and a
solvent-based heat seal coating applied on such inner surface, said
inner surface of said film in intimate sealing contact with at
least a portion of the outside surface of the side walls, and
wherein the heat-shrink film comprises:
[0020] i) a polymer having at least 80% by weight polyethylene
terephthalate polymer; and
[0021] ii) wherein said film is biaxially oriented in the range of
about 5% to about 30%.
[0022] This invention includes a tamper-resistant heat-shrink
lidding film, having an inner surface, for covering a rigid or
semi-rigid container having an outside surface, said film
comprising at least 80 percent by weight of a polyethylene
terephthalate homopolymer or copolymer, having a plurality of sides
and a thickness of 12-75 micrometers, and being biaxially oriented
in the range of about 5%-30% shrink factor; and said inner surface
comprising a solvent-based heat-seal coating thereon, wherein:
[0023] a) said film is intimate contact with at least a portion of
the outside surface of said container;
[0024] b) when the sides of said film are heated, said film remains
in tamper resistant engagement with said container, hermetically
sealing said container, yet allowing air and moisture to move in
and out of said lidding film upon heating.
[0025] This invention also provides an improved method for
laminating PET film to other films, comprising the steps of:
[0026] (a) coating a solvent-based laminating adhesive to the PET
film;
[0027] (b) heating to less than the shrink temperature to dry the
adhesive;
[0028] (c) laminating the film to other films without requiring
additional adhesive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a perspective view of a container prepared in
accordance with the present invention, prior to shrinking the sides
of the film cover.
[0030] FIG. 2 is a perspective view of a container prepared in
accordance with the present invention after shrinking the sides of
the film cover, and before shrinking the top of the cover.
[0031] FIG. 3 is a perspective view of a sealed container prepared
using the present invention.
[0032] FIGS. 4 and 5 are schematic cross-sectional views of an
apparatus in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0033] The present invention is directed to a particular type of
polyethylene terephthalate ("PET") shrink film, and methods related
thereto, that offers advantages in packaging for both non-cook and
cook-in applications. The invention is based on the platform of a
film of polyethylene terephthalate polymer, either homopolymer or
copolymer, that is both heat-shrinkable and heat-sealable,
typically thin-guage and having low shrinkage. The inventors have
found a way to pre-apply a solvent-based, heat-seal coating to the
film during manufacture of the film, thus avoiding the need for
post-applied adhesives, which has conventionally been required to
apply adhesive to low shrink temperature films.
[0034] This is a significant advance over the art, decreasing both
the time and cost of making the film, as well as providing for use
of the film in new applications. Conventional post-applied
adhesives must be registered in areas to be sealed, and cannot be
wound upon one another. They generally take 14 days to cure in air,
thus limiting their applications. Typically they have been limited
to making bagstock where film is sealed to itself. The invention
herein allows sealant application across the entire web, thereby
not limiting seal areas or configurations in which it can be
used.
[0035] In addition to the ability to apply a solvent-based
heat-seal coating to the base film, the invention herein also
provides for the application of a metallized coating to the base
film, and between the film and any solvent-based heat-seal coating,
as well as the application of antifog and other agents.
[0036] Furthermore, the base film, with or without a solvent-based
heat-seal coating, optionally metallized and/or coated with antifog
agents, can be laminated to other polymer films to provide unique
options and properties, of particular use in packaging
applications, e.g., one-bag systems for packaging meats to replace
the current two-bag packaging. Additional laminated layers could
provide increased strength, barrier properties, printing surfaces,
sealing characteristics, as well as decorative visual features when
metallization is used.
[0037] Heat-Shrinkable, Heat-Sealable Base Film
[0038] The heat-shrinkable, heat-sealable PET shrink film, i.e.
"base film" of the present invention comprises at least about 80 wt
% PET, more preferably at least about 90 wt % PET. The PET can be a
homopolymer or copolymer of PET. A PET homopolymer is intended to
mean a polymer substantially derived from the polymerization of
ethylene glycol with terephthalic acid, or alternatively, derived
from the ester forming equivalents thereof (e.g., any reactants
which can be polymerized to ultimately provide a polymer of
polyethylene terephthalate). A copolymer of PET is intended to mean
any polymer comprising (or derived from) at least about 50 mole
percent ethylene terephthalate, and the remainder of the polymer
being derived from monomers other than terephthalic acid and
ethylene glycol (or their ester forming equivalents).
[0039] The PET base films of the present invention are further
defined as:
[0040] 1. being biaxially oriented in the range of about 5%-55%
shrink factor, more preferably in the range of about 10-30% shrink
factor; and
[0041] 2. for lidding applications, having a thickness in the range
of 12-75 micrometers (more preferably 12-20 micrometers). Suitable
polyethylene terephthalate shrink films are available from E. I. du
Pont de Nemours and Company, Wilmington, Del. under the trademarks
Mylar.RTM. and Mellinex.RTM..
[0042] Relative to conventional shrink film, the shrink films of
the present invention are advantageous in packaging applications
for a number of reasons. The PET shrink film is tough relative to
many conventional shrink films, and the film's relatively small
amount of orientation ("low shrinkage") has been found to better
accommodate protrusions, by not shrinking to such an extent as to
risk puncturing the film or crushing protruding contents, and by
not shrinking to such an extent as to agglomerate an ugly mass of
shrunken film around the protrusion. As a lidding film, the thin
gauging of the shrink film (in combination with the low shrinkage),
causes the lidding film to tear when the package is opened, thereby
creating tamper evidence. Conventional shrink films will generally
shrink to a much greater film thickness, thereby providing a
lidding which can be pulled off without tearing, thus leaving no
tamper evidence.
[0043] When first shrunk to a package, the base film of the present
invention forms a tight hermetic seal due to the presence of the
adhesive coating. However, due to the thin gauging and low
shrinkage, the seal will still become self venting when heated in
an oven or the like. Conventional shrink films will either form a
tight conforming seal or be self venting, but generally cannot do
both. Per the invention herein, seals can be made to an outer wall,
outer lip edge, top of the lip and bridges separating compartments
to prevent spillage from one to the other. Another advantage is
this type of construction can be used in Modified Atmospheric
Packaging (MAP).
[0044] The relatively low shrink force films of the present
invention also provide excellent appearance and are generally more
economical to use than conventional (higher gauge, higher
shrinking) shrink films, especially for lidding applications,
because they minimize the amount of material needed for coverage of
the product and container being used.
[0045] The heat shrinkable PET base film has other additional
advantages. It can be surface printed or trap printed by itself or
when laminating. It can be laminated, carrying varying degrees of
shrink % 5-45, to materials used for cook in processes. Both
laminated and heat sealable versions can be used as heat shrinkable
lidstocks. Both versions can be used to package materials other
than foodstuffs
[0046] Application of Heat-Seal Coating
[0047] Applicants have identified a method to impart adhesive to
the base film that avoids time-consuming or difficult
post-processing. Surprisingly the applicants use a solvent-based
heat-seal coating which has typically been considered impossible
given the low shrink-initiation temperature of the base film,
typically about 80.degree. C. The heat-sealant material itself is
preferably a copolyester or ethylene vinyl acetate copolymer (EVA),
more preferably an amorphous copolyester. It is contemplated that
other sealants known to those of skill in the art could also be
used.
[0048] The more preferred copolyester heat-sealant is derived from
at least the following components: about 10 to about 60 mole %
terephthalic acid ("Monomer A"); about 10 to about 60 mole 5
ethylene glycol ("Monomer B"); and about 5 to about 60 mole 5 of a
third monomer being a secondary di-acid ("Monomer C") and/or a
secondary diol ("Monomer D").
[0049] Examples of Monomer C include: succinic acid, adipic acid,
azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, phthalic
acid, isophthalic acid, dodecanedioic acid, and the like. Examples
of Monomer D include: methoxypolyalkylene glycol, neopentyl glycol,
propylene glycol, 1,4-butane diol, trimethylene glycol,
hexamethylene glycol, tetramethylene glycol, diethylene glycol, and
the like. Preferred such comonomers include azelaic, sebacic,
and/or isophthalic acid.
[0050] The adhesive is applied as a solution. The key factors that
allow the solvent-based heat-seal coating of the heat shrinkable
PET base film are a) the proper choice of solvent(s) (e.g.,
preferably tetrahydrofuran) for the adhesive so that drying can be
achieved at temperatures less than 80 degrees C., and (2) the use
of lower than normal film winding tensions during processing.
[0051] The solvent-based, heat-seal coating can be applied to
one-side (or two-sides) of the heat shrinkable PET base sheet by
means of any of the many coating techniques known to those of skill
in the art. For example, the film may be coated by roller (e.g.
doctor roll) coating, spray coating, gravure coating, or slot
coating, preferably roller or gravure coating using a solution
coating process.
[0052] Specifically the conditions given below are critical due to
the fact the film is very unstable and will shrink prematurely when
exposed to elevated temperatures and will stretch when wound too
tightly.
[0053] Drying temperatures (degree C): approximately 70-75
[0054] Film Windup Tensions (pli): approx. -0.25-1.0
[0055] Coating/Windup Speed (ypm): approx. 100-500
[0056] Coating Weight (gms/m2): approx. 1.0-10
[0057] The resultant heat-sealable, heat shrinkable, PET film
exhibits heat seal strengths greater than 260 g/in, coating weights
of about 1 to about 10 g/m.sup.2, preferably about 1.5 to about 2.5
g/m.sup.2, and film shrinkage at 100 degrees C. of about 5% to
about 55%, preferably about 10% to about 30%.
[0058] Application of Metallized Layer and Other Additives
[0059] The solvent-based heat-seal coating described above provides
a heat-sealable surface to the heat shrinkable PET base film. An
additional metalllized layer can provide oxygen and moisture
barriers, as well as a decorative feature to the film.
[0060] The described heat-shrinkable PET base film, having an outer
surface and inner surface, may be coated on one or both surfaces
with a metal layer. The solvent-based, heat-seal coating may be
coated on top of the metal layer. The heat shrinkable PET base film
can be two-side heat-seal coated or two-side aluminum-metallized in
any combination.
[0061] The metal used can vary, though aluminum is preferred. The
metal layer may be applied to the heat shrinkable PET base film by
known methods, e.g., by the standard vacuum deposition
processes.
[0062] For the aluminized layer, the key conditions are
[0063] Optical Density (heavy metal deposition): approx. 0.75 to 4;
preferably 2.6-3.0
[0064] Optical Density (light metal deposition): approx.
0.25+/-10%
[0065] Optical density was measured using a digital-readout,
transmission densitometer, equipped with four selectable filters
for color and visual-density measurements within a range of 0 to
4.0. The measurements indicate American Standard (ANSI) opal-glass,
diffuse visual transmission density.
[0066] In addition to one or more metallized layers, other
components may be coated on the base film to impart other desired
properties. For example, an anti-fog agent or slip agent may be
incorporated into the solvent-based, heat-seal coating prior to
applying on the shrink film, to impart anti-fog or anti-slip
properties. Other additives typically used in the industry may be
incorporated in a similar fashion.
[0067] Laminating to Other Films
[0068] The heat-shrinkable PET base film can also be adhesive
laminated to other materials to enhance performance of the overall
structure, depending on the packaging need. The shrinkable base to
be used can be plain uncoated, solvent-based heat-seal coated,
and/or metallized. The other materials useful in the laminates will
vary greatly depending on the properties sought, but will include
nylon, polypropylene, polyethylene, ionomer, ACR, ethylene vinyl
acetate (EVA), polyethylene terephthalate (PET), polystyrene,
ethylene vinyl alcohol (EVOH), polyvinylidene chloride (PVDC), and
combinations thereof.
[0069] For example, uncoated base film can be laminated to an
ionomer film, as well as one-side metallized variety. Typically the
PET base films have an approximate shrinkage of 20% in both the
MD/TD directions. A two part polyester urethane adhesive can be
applied to the heat shrinkable PET via a gravure cylinder to serve
as the laminating adhesive. The laminating adhesive is applied
across the web, from solution.
[0070] The shrinkage of the PET base film and the additional films
to be laminated need not be similar; in fact shrinkage differences
of about 5% and much greater pose no problem. The amount of
shrinkage will be dictated by the heat-shrinkable PET base, but
just as important by the thickness and stiffness of the secondary
web. An example would be when adhesive laminating to a thicker or
stiffer substrate, in order to gain the shrinkage desired from the
laminate, a higher percentage of shrinkage may be required of the
PET base sheet. It is again very important to choose an
solvent-based laminating adhesive in which the dilutent solvent
used as well as the adhesive can be dried below 80C. This is due to
the heat sensitivity of the heat shrinkable PET for prevention of
premature shrinkage of the film before lamination to the secondary
web.
[0071] It is recommended to corona treat both web surfaces that
will be in contact with the applied adhesive. If no heat-sealant is
applied to the base film, then a secondary structure, such as an
ionomer film or a multilayer coextruded film, can serve as the
heat-seal layer for the resulting laminate, also providing added
puncture resistance and formability. Such a laminated film will
have unique applications in packaging, e.g., the ability to provide
a one-bag system for packaging meats where previously a two-bag
system has been used before. Such two-bag systems typically used an
olefin or nylon bag to package meat or poultry to hold the juices
close to the product, and then place the package in a second
non-shrink metallized bag for added barrier protection and
decoration.
[0072] The invention herein provides for a one-bag system which can
both retain juices and provide barrier and decorative
properties--and provide greater economic benefit due to reducing
the materials and labor of double-bagging. The metallized version
provides a high oxygen/moisture barrier plus a decorative feature
when fabricated into a bag or lidstock. The decorative feature is a
"pearl-essence", which occurs as the metal layer is deformed by the
shrinkage upon packaging, but still retains excellent barrier.
[0073] The laminating adhesive can be applied by any of the well
known coating techniques mentioned above, preferably roller or
gravure coating using a solution coating process. The types of
adhesive that are useful in making the laminates herein are those
typically used in the industry, though the right combination of
adhesive and solvent choice are critical due to the sensitivity of
the shrinkable base to heat.
[0074] Again, similar to the application of the solvent-based,
heat-seal adhesive coating, the significant operating conditions
for the coating process that allow the urethane adhesive coating of
the heat shrinkable base film are a) the proper choice of
solvent(s) (e.g. isopropanol or ethyl acetate) so that drying can
be achieved at less than 80 degrees C. and b) the use of a hot nip
roll to mate the heat shrinkable web and the secondary ionomer web
together activating the adhesive at below 80C without inducing
premature shrinkage of the heat shrinkable PET base. The same
requirements need to be followed when laminating the heat
shrinkable PET base to other substrates or films.
[0075] Approximate resultant properties of the laminate
structures
[0076] Adhesion strength between laminated film layers: >300
gms/in
[0077] Film shrinkage @ 100C (%): 5-45 with 10-30 preferred
[0078] Barrier before shrinkage OTR cc/100 in2/24 hr: 0.10/after
shrinkage 0.2-0.5
[0079] Barrier before shrinkage for the metallized version of the
laminate, WVTR gm/100 in2/24 hr: 0.05/after shrinkage 0.25-0.35
[0080] Note: Effect on barrier properties is dictated by how the
much the metal is deformed through the shrinkage stage. Even when
full 20% MD/TD shrinkage has taken place the barrier is still
functional and never went over 0.5 OTR/WVTR.
[0081] Use in Packaging Generally
[0082] In use, the film can be used in a myriad of application. For
lidding, the film is cut to size, and draped over a tray to be
lidded. The film is then held in place by a mechanical device,
vacuum or the like. Heat is then applied to the sides of the
package, thereby causing the film to shrink around the perimeter of
the package. Thereafter, the film can be shrunk along its center
portion to further tighten the film and eliminate wrinkles or the
like.
[0083] For other applications, the film may be presealed to form
open bags, which may then be filled with contents in an in-line
packaging machine. The bags are then sealed, and heated to shrink
the bag around the contents. Such bags are ovenable, and may become
self-venting once the internal temperature and pressure reach the
softening point of the sealant.
[0084] For lidding the films of the present invention are well
suited because the film, once shrunk, is substantially
non-elastomeric. Also, the film can be hermetically sealed to the
container. This is important for modified atmosphere packaging
(MAP) and applications requiring hermetic sealing to the tray and
between compartments. This prevents spillage during handling and
distribution. In addition, the package is designed to become
self-venting once the internal temperature and pressure reach the
softening point of the sealant. The sealant is purposely designed
to fail during those conditions. Even after sealant failure, the
package still remains tamper evident due to the construction of the
lidstock to the container.
[0085] The heat-shrinkable, heat-sealable base film is recommended
when lidding disposable containers, particularly trays made of
crystalline PET (CPET), amorphous PET (APET), paper, aluminum,
polypropylene (PP), polethylene (PE), polyvinyl chloride (PVC),
polvinylidene chloride (PVDC) or polystyrene (PS).
[0086] The films of the present invention also provide a relatively
small amount of shrinkage, relative to conventional shrink films,
while still providing the sealing advantages of a shrink film. This
makes the film simple and easy to use.
[0087] Use of Film in Lidding Applications
[0088] The present invention is also applicable to the
sealing/lidding of containers for foodstuffs, including rigid
(reusable) and semi-rigid (disposable) containers.
[0089] A preferred container construction comprises a wall which
extends away from the center of the tray. The wall design can vary
widely, but should be sufficient to retain the heat shrinkable film
on the sides of the container, when the film on top of the
container is being shrunk (first along the sides, then on top).
[0090] The shrink films of the present invention preferably have an
orientation in each direction in the range of about 5% to about
30%, more preferably from about 10-20%. Many commercially available
heat shrinkable polyethylene terephthalate films have an
orientation from about 40 to 50% or more, and such shrink films
would be unsuitable for use as lidding in the present invention.
Less shrinkage is preferred because higher shrinkage will deform
less rigid materials when applied to the tray, and also during the
reheat and/or cook cycles.
[0091] The thickness of the covering film is preferably in the
range of about 12-75 micrometers, more preferably about 12-20
micrometers. Suitable polyethylene terephthalate shrink films are
available from E. I. du Pont de Nemours and Company under the
trademark Mylar.RTM. LD for lidding applications.
[0092] In use, the heat-shrinkable film is placed over the top of
the container. Sufficient draping or overlap of the heat-shrinkable
film should be provided to anchor the film after shrinking below
the top surface of the container. The maximum overlap is not
critical, so long as the overlap does not substantially exceed the
depth of the sides of the container after shrinkage. The size of
the film before shrinkage can be adjusted, according to the known
shrink characteristics of the film. In general, a final overlap of
about from 1 to 7 centimeters is satisfactory.
[0093] Preferably, the film is then restrained on the container.
The film can be restrained on the top alone, as with a platen, or
on the sides, or both. The restraining mechanism can vary widely
and can include, for example, positive air pressure, vacuum,
mechanical fingers or gasketing. Rubber gasketing, particularly
silicone rubber, has been found to be particularly satisfactory for
restraining the sides. The gasketing can be fastened to the inside
of a frame or plate having an aperture formed therein which can
pass over the top surface of the container.
[0094] While the film is restrained on the container, the film is
heated to a temperature above the shrinkage/sealing temperature and
below the melting temperature of the heat shrinkable film. The
heating means can vary widely, and can include, for example, heated
fluid or radiant heat. The film is preferably heated by the use of
a heated fluid. This fluid can for example, be water or gas, air
being preferred for convenience and economy. In any case, the fluid
should be heated to above the shrinkage temperature of the
heat-shrinkable film.
[0095] Preferably, the film is heat shrunk along the sides of the
container, prior to heat shrinking/sealing the film along the top
of the container. In this way, the film along the sides will shrink
and form a hermetic seal around the edge of the container. Hot
fluid temperature needs to be above the shrinkage point of the film
as well as above the softening point of the sealant so as the film
shrinks the heat sealant is activated and is pulled and sealed
against an outer portion of the container forming a hermetic seal.
Any outer portion as well as the top can be hermetically sealed if
so desired.
[0096] The top portion of the film can then be heat shrunk, thereby
removing any wrinkles and providing a neat, taut lidding surface
along the top of the container. Such sequential shrinking of the
film can be accomplished by protecting the top surface of the
container with a platen, while the sides are exposed to either
heated fluid or a shrink tunnel; the platen can then be removed,
allowing the top portion of the film to then be heat shrunk.
[0097] The heated fluid can be generated in an number of
conventional or non conventional ways. For example, conventional
air heat guns can be used to heat the film, and the air temperature
can be controlled by resistance temperature detectors (RTDs)
incorporated into the heat gun. Circumferential or perimetric tubes
can be used to direct the heated air along the sides of the
container. The heated air flow can also be used to restrain the
film by impinging upon the film along the sides of the container.
In such an embodiment, perimetric tubing can be made to conform to
the shape of the container, and fitted to receive a heat gun.
[0098] The heating mechanism can vary widely, depending upon the
size of the container and the desired speed of operation. A 220
voltage, 2000 watt heat gun has been found to generate adequate
flow of heated fluid for average sized food containers to be
packaged in accordance with the present invention. The heat gun can
be controlled by a PID microprocessor temperature controller and an
RTD (resistance temperature detector) sensing device. The RTD
changes electrical resistance with changes in temperature and can
thereby signal the temperature controller to adjust the electrical
current, as needed for maintaining a constant temperature.
[0099] The precise nozzle location for the heated air can be
adjusted to the particular configuration of the container being
covered. For example, the hot air pipe can be above the top of the
container with the nozzles directed to a point below the top of the
container, thereby shrinking the draped and restrained film along
the sides of the container.
[0100] The temperature for heat shrinking the material across the
top can similarly vary widely, and (as with the shrinkage of the
film along the sides of the package) will be above the shrinking
temperature of the film, but below its melting temperature. Fluid
temperatures above the melting temperatures of the film and heat
seal coating can be used to shrink and seal the film to the
container provided appropriate adjustment to the exposure time is
made, so the film does not melt. Similarly, the shrinking of the
top of the film can be accomplished with a heated air gun, fitted
with a nozzle appropriate to the size and shape of the package
being treated.
[0101] The heat shrinkable film to be used is generally cut to a
size that will overlap or drape over the top of the container to be
lidded by at least about 1 centimeter on each side of the container
after shrinkage. Depending on the sequence of shrinkage, and the
particular apparatus used, the heat-shrinkable/heat-sealable film
can be cut to size before heat-shrinking/heat-sealing, simultaneous
with heat-shrinking/heat-sealin- g, or after
heat-shrinking/heat-sealing.
[0102] The present invention will be further understood by
reference to the drawings, in which FIG. 1 is a perspective view of
a container 1 having side walls 2. In the embodiment shown in the
Figures, side walls 2 are provided with outwardly turned flanges 3.
Although a flanged tray such as is shown is preferred, it is to be
understood that the invention is not limited to the use of such a
tray. The container is subdivided, for example, for various
portions of foods. A heat-shrinkable, heat-sealable film 4 is cut
to a size greater than the outer dimensions of the container top.
The film is retained below the top of the container along container
sides 5 by frame 6 having interior edge 7 to which gasket 8 is
attached. The inner edge of the gasket is somewhat smaller than the
outer perimeter of the container top, to permit the frame with the
gasket to be installed over the top of the container. Heated fluid,
such as air, can be directed to the film edge below the perimeter
of the container top, thus shrinking/sealing the film and anchoring
the film over the container.
[0103] FIG. 2 illustrates the container after heat shrinking the
sides of the film, in which the shrunk film is sealed to the side
walls 2 of the container. At this point, heated fluid can be
applied to the film on the top of the container, shrinking that
portion and resulting in a hermetically sealed package as shown in
FIG. 3. With sequential shrinking of the film, the restraining
means is typically removed prior to shrinking the film on the top
of the container.
[0104] While a sequential shrinking of the film around the package
is possible, as described above, the entire film can be shrunk
simultaneously with an appropriately sized platen for the heated
fluid.
[0105] FIGS. 4 and 5 are schematic illustrations of representative
apparatus that can be used in accordance with the present
invention.
[0106] In FIG. 4, trays 11, positioned on conveyor 12, are capped
with film 13 supplied by roll 14. The film is held in place on top
of each of the containers by platens 15 and the edges of the film
cut by die-cutters 16. The sides of the film are then shrunk using
hot air through heat guns 17. Hereafter, the trays are moved into a
shrink tunnel 18, in which the tops of the containers are
shrunk.
[0107] An alternative apparatus which can be used in accordance
with the present invention is shown in FIG. 5. There, trays 11, on
conveyor 12, are similarly capped with film 13 supplied from roll
14. However, the edges of the film are held in place around the
tops of the containers by tucking means 51, and die-cut by blades
52. With the sides thus restrained, the trays with the tucking or
restraining devices in place are moved to shrink tunnel 53, where
they are held in place by vacuum holding devices 54, applied to the
bottom of each container. In this apparatus the
heat-shrinkable/heat-sealable films on the side and the tops of the
containers are shrunk/sealed simultaneously in the shrink tunnel.
Waste heat-shrinkable, heat-sealable film is rewound on roll
55.
[0108] The heat-shrunk, heat-sealed polymeric film can be readily
removed from the sides and top of the container, by removing with
an exposed edge or tearing the top. An appropriate notch, tear tab
or peel tab can also be provided as desired.
[0109] While the cover hinders tampering of the food, being
hermetically sealed across and between top compartments, it also
prevents spillage from one compartment to the other during
transport or display of the product. Yet while cooking or reheating
the sealant is designed to fail and the package becomes
self-venting, otherwise prohibiting escape of expanding gases
within.
[0110] The present invention is further illustrated by the
following examples.
EXAMPLES 1-2
[0111] A rectilinear molded container for foodstuffs having
approximate dimensions of 61/4" by 81/2" by 2" (15.9 cm by 21.6 cm
by 5.1 cm) deep is lidded using heat-shrinkable, heat-sealable
polyethylene terephthalate films having a thickness of about 19
microns, and a shrinkage of 20% and 9%. Each film is cut to a size
relative to the shrink % in each dimension of the top surface on
each side of the container. The film is held in place below the
flange by a frame having a gasket on the inner surface of the
frame.
[0112] The trays contain a wooden block with two nails protruding
about 2.6 centimeters above the tray flange to simulate sharp-edged
package contents. The first tray is lidded with a shrink film
biaxially oriented about 20%, and the second tray is lidded with
film biaxially oriented about 9%. The film is first shrunk around
the sides by the application of air through a nozzle, is heated to
a temperature above the shrink temperature of the film and below
its melting temperature, after which the restraining gasket is
removed. Thereafter, the film on the top of the container is shrunk
with the same air source by consecutive passes of the nozzle over
the top of the film. After lidding film application and placement
in a 350.degree. F. (177.degree. C.) oven for about 20 minutes, no
film punctures would be expected, though the film remains
hermetically sealed around the entire tray flange.
EXAMPLES 3-5
Example 3
Cook-in Bags
[0113] The copolyester coated heat sealable/heat shrinkable base
can be formed into a bag stock for cooking or re-heating various
meats and or vegetables in a microwave or conventional oven. Both
the heat shrinkable PET base film and sealant are FDA approved for
temperatures up to 204 C. For example, a bag using the described
base film can be formed by known bag making techniques. By heat
sealing the copolyester sealant to itself or if desired to the
plain PET base.
[0114] In the test case heat seals were made sealant to sealant
using a one-inch heat seal bar to form a bag with three outer edge
seals leaving one end open. Two fully seasoned, whole six pound
chickens were then loaded into separate bags and heat sealed in the
same way as the other three seals closing the bags. The sealing
temperature was 150 C, 30 psi and 0.5 second dwell. The recommended
temperature window for sealing a copolyester sealant of this type
can be in the range of 93 C to 204 C dependent on the equipment
used or the sealing process. One of the sealed bags was placed in
an electric oven and the other in a gas oven. Both ovens were set
to a cooking temperature of 177 C.
[0115] No vent holes were placed in the bags as recommended with
other cook in bags. These type bags are generally made from
uncoated nylon or polyester and also require clips or ties for
closure. As the internal contents begin to reach elevated
temperatures the bag begins to balloon from the steam pressure
generated within the bag. When internal temperature reaches the
softening point of the sealant, which hold the heat-seals together,
the seal will fail at its weakest point and allow a self-venting
process. The benefits of self venting are 1) the allowance of an
oxygen exchange thus helping to promote a desired browning effect
on the contents 2) and also keeps moisture entrapped allowing the
foodstuff to cook in it's own juices keeping it moist and
flavorful.
[0116] After two hours both bags were removed. The result was the
chicken was very moist and flavorful with the meat falling from the
bone upon removal from the bag.
Example 4
Container/Lidding Application
[0117] The heat sealable/heat shrinkable PET film in the new
invention can be used in the same manner and provides all the
benefits as described in U.S. Pat. No. 5,873,218. The major
difference being that a hermetic heat seal can be made with the
copolyester sealant to the outer lip of the container in addition
to shrinking around and under the lip itself. An additional benefit
over the existing invention is containers which are separated by
bridges that form separate compartments can be sealed totally
across those bridge areas thus eliminating spillage not only around
the outer edge but from one compartment to another during
distribution.
[0118] For example, the film of the present invention was precut to
size, (draped over the opening and) draped over the outer wall(s)
of the container by a ratio relative to the shrinkage. The film is
then held in place as described in the referenced invention. Heat
is then applied to the container sides causing the film to shrink
around the tray perimeter. This securely anchors the film to the
container and also activates the heat seal layer forming a hermetic
seal to the outward lip. This method also applies to a container
having a sloped side wall(s) with no outer lip. By heating the film
above the sealant melt point but below the melt point of the film,
combined with the pressure generated by film shrinkage is enough to
bond the film to the container. The type of package construction
disclosed can be used for products which are cooked or re-heated
creating a tamper evident, dual ovenable self-venting package or
products requiring a tamper evident feature that are not meant for
exposure to elevated temperatures.
Example 5
Lamination
[0119] The laminated version of the heat shrinkable PET base film
in the invention herein, as described above, can also be formed
into a bag material. In cases where shrinkage, puncture, flex crack
resistance, metallization for barrier or decoration and heat
resistance may be desired. Any number of combinations can be
fabricated from the materials mentioned based on the application
need. For example, a bag was fabricated out of the following
laminate structure out to in: Heat shrinkable (0.5 mil)(20% MD/TD)
PET base/aluminum/adh/ionomer sealant layer (2 mil).
[0120] A bag was fabricated by taking a length of film and folding
the sealant layers on to one another and heat sealing them creating
two side seals and leaving the top open. Two cooked cuts of meat
were packaged in two separate bags. A turkey breast and a ham each
with a weight of approximately 4-6 pounds were used in the test.
The bag has to be made larger than the contents to compensate for
the shrinkage factor but not so much where the bag cannot be shrunk
tightly around the contents. Each package was individually placed
in a vacuum chamber to remove the oxygen and sealed. The packages
were then removed and exposed to hot air above the shrinkage
temperature but below the melting point of the film. The film
shrunk tightly, conforming around and picking up the texture of the
contents.
[0121] The advantages of this type of construction and process are
1) The metallization not only serves as a barrier adding shelf
life, but also provides the function of decoration 2) The shrinkage
factor eliminates the exposed edges by conforming to the package
and also brings out the surface texture of the product packaged.
Also by eliminating exposed edges the chance of puncture to other
packages is reduced. 3) The decorative function can be enhanced
through shrinkage. As the film structure shrinks, the metal deforms
and takes on a pearl essence effect. This effect can be controlled
by the amount shrinkage built into the structure.
Examples 6-13
Heat Seal Strengths
[0122] Heat-shrinkable copolyester film (50 guage Mylar.RTM. film,
available from DuPont, Wilmington Del.) was coated with
solvent-based amorphous copolyester adhesive. The coated film was
sealed to itself, as well as to semi-rigid substrates, i.e., trays,
made from PVC, amorphous PET and crystalline PET, at temperatures
of both 250.degree. F. and 300.degree. F. Heat seal strengths were
measured for each, as well as after aging 3 days at 32.degree. F.,
and after aging 3 days at 0.degree. F.
[0123] As well, the heat-shrinkable copolyester film was also first
metallized and then coated with the solvent-based amorphous
copolyester adhesive. Again the film was sealed to itself, as well
as to semi-rigid substrates, i.e., trays, made from PVC, amorphous
PET and crystalline PET PET, at temperatures of both 250.degree. F.
and 300.degree. F. Heat seal strengths were measured for each, as
well as after aging 3 days at 32.degree. F., and after aging 3 days
at 0.degree. F.
[0124] The heat seal strengths were measured on 1 inch wide samples
in triplicate. The seal strength is measured by peeling the seals
apart in the machine direction (MD) using the Instron. The heat
seal strength is the maximum force required to cause the seal to
fail to read from the appropriate scale of the tester, and is
measured in grams/inch width.
1TABLE 1 HEAT SEAL STRENGTHS Method & Conditions: CR-188 @ 12"
per min/0.50 sec dwell/20 psi 1" Strips Seals aged 24 hrs @ 72
F./50% R.H. Seals aged 3 days @ 32 F. Seals aged 3 days @ 0 F.
Amorphous Copolyester Coated Temperature 250 F. Failure 300 F.
Failure 250 F. Failure 300 F. Failure 250 F. Failure 300 F. Failure
Ex. 6 - Coated to 987 Peel 960 Peel 647 Peel/Tear 792 P/T 553 Break
676 P/T Coated Ex. 7 - Coated to PVC 616 Peel/Tear 671 Peel 817
Break 1237 Break 1115 Break 590 P/T Ex. 8 - Coated to APET 664 Peel
788 Peel 460 Peel/Tear 926 Break 540 Break 918 Break Ex. 9 - Coated
to CPET 477 Peel 668 Peel/Tear 569 Peel/Tear 605 P/T 374 Break 482
Break Amorphous Copolyester Coated Over Metal Temperature 250 F.
Failure 300 F. Failure 250 F. Failure 300 F. Failure 250 F. Failure
300 F. Failure Ex. 10 - Coated to 797 Peel/Tear 848 Peel/Tear 456
Break 906 P/T 416 Break 507 Break Coated Ex. 11 - Coated to PVC 446
Peel 510 Peel/Tear 702 Peel/Tear 862 P/T 411 Break 676 P/T Ex. 12 -
Coated to APET 565 Peel 844 Peel 685 Peel 980 P/T 465 Peel/Tear 683
P/T Ex. 13 - Coated to CPET 397 Peel 586 Peel 690 Peel 871 Peel 384
Break 485 Break Explanation of failure mode Peel - Film peels
cleanly away from substrate Peel/Tear (P/T) - Film peels some and
then tears Break - Seal strength is stronger than the film causing
a clean break at seal interface.
EXAMPLES 14-23
Properties of Laminated Heat-Shrinkable PET Base Film/Ionomer
Film
[0125] Heat-shrinkable, heat-sealable PET base film (Mylar.RTM.
film having approximately 20% shrinkage) was laminated to a 2 mil
ionomer film (Surlyn.RTM. 1601 ionomer film, available from DuPont,
Wilmington Del.) using a two-part polyester urethane adhesive. The
bond strength was measured using a method similar to the above for
heat-seal strength measurements. The conditions were 12 inches per
minute speed on the Instron, one week aging at 72.degree. F., 50%
relative humidity, and samples were one inch (2.54 cm) strips.
2TABLE 2 Laminated Bond Strength Specimen No. Grams per inch
Failure Plain Heat Shrinkable PET Base 14 458 Zipper Peel 15 470
Zipper Peel 16 448 Zipper Peel 17 450 Zipper Peel 18 449 Zipper
Peel Avg. 455 Metallized Heat shrinkable Base 19 174 Peel 20 210
Peel 21 158 Peel 22 221 Peel 23 37 Peel Avg. 160 Note: Failure is a
result of metal adhesion to the base sheet
Examples 24-31
Shrinkage Measurements for Films and Laminates
[0126] The shrinkage was measured for samples of various films and
laminates. The measurements were made in triplicate for each
specific sample. The test method generally involved placing a 5
inch by 5 inch samples in a heated bath of boiling water. The
samples were secured between clamped screens and placed in the bath
for 5 seconds. The length of the cooled sample was measured in both
the machine direction (MD) and transverse direction (TD) and the
shrinkage calculated as indicated.
[0127] The data clearly indicate that the heat-shrinkable polyester
film is controlling the amount of shrinkage for the laminates and
coated films.
3TABLE 3 Dimension Change: Shrinkage % Change 24) 0.5 mil Heat
Shrink PET (20% MD/TD)/Metal/adh/2 MD -21.5 mil lonomer 25) 0.5 mil
Heat Shrink PET (20% MD/TD)/Metal/adh/2 TD -17.5 mil lonomer 26)
0.65 mil Heat Shrink PET (45% MD/TD)/adh/2 mil MD -40.5 lonomer 27)
0.65 mil Heat Shrink PET (45% MD/TD)/adh/2 mil TD -38.5 lonomer 28)
0.50 mil Heat Shrink PET (20% MD/TD)/Copoly- MD -18.85 ester Coated
29) 0.50 mil Heat Shrink PET (20% MD/TD)/Copoly- TD -19 ester
Coated 30) 0.50 mil Heat Shrink PET (20% MD/TD)/Metal/ MD -18.2
Copolyester Coated 31) 0.50 mil Heat Shrink PET (20% MD/TD)/Metal/
TD -19.5 Copolyester Coated
Examples 32-33
Barrier Data
[0128] The barrier properties for heat-shrinkable, heat-sealable,
metallized film and the same laminated to ionomer film were tested
using the following test methods:
[0129] ASTM D3985 at 72.degree. F., oxygen test method; and
[0130] ASTM F1249 at 38.degree. C., 90% relative humidity for water
vapor test method.
4TABLE 4 Barrier Data cc/100in2/24 g/100in2/24 hrs hrs OTR H.sub.2O
32) Heat Shrinkable Metallized 20% MD/TD Before Shrinkage 0.0175
0.0777 After Shrinkage 0.11 0.315 33) Heat Shrinkable Metallized
Laminated 20% MD/TD Before Shrinkage 0.115 0.0777 After Shrinkage
0.434 0.296
* * * * *