U.S. patent application number 13/822886 was filed with the patent office on 2013-09-12 for thermoformable copolyester laminate.
This patent application is currently assigned to DuPont Teijin Films U.S. Limited Partnership. The applicant listed for this patent is Fenghua Deng, Stephen K. Franzyshen, Reps M. Haskins, Peter N. Nugara. Invention is credited to Fenghua Deng, Stephen K. Franzyshen, Reps M. Haskins, Peter N. Nugara.
Application Number | 20130236612 13/822886 |
Document ID | / |
Family ID | 44674910 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130236612 |
Kind Code |
A1 |
Deng; Fenghua ; et
al. |
September 12, 2013 |
Thermoformable Copolyester Laminate
Abstract
A laminate includes the following substantially coextensive
layers in the following order: (a) a non-sealable, self-supporting,
thermoformable copolyester film layer having a first surface and a
second surface, the second surface constituting an outermost,
exposed surface of the laminate; (b) a laminating adhesive layer on
the first surface of the thermoformable copolyester film layer; and
(c) a self-supporting, thermoformable structural film layer having
a first surface and a second surface, the first surface contacting
the laminating adhesive layer. Polyethylene terephthalate
constitutes at least 80% by weight of the self-supporting
thermoformable copolyester film layer; the thermoformable
structural film layer includes a polymer selected from the group
consisting of polyamides, polypropylene, polyethylene, polyethylene
terephthalate, ionomers, ethylene acrylic acid copolymers, ethylene
vinyl acetate copolymers, polystyrene, ethylene vinyl alcohol
copolymers and polyvinylidene chloride; the thermoformable
copolyester film layer, the structural film layer and the laminate
each shrink less than 5% in length and width upon exposure to
boiling water for five seconds; and the laminate is thermoformable
and its chloroform-soluble extractives meet the requirements of
paragraph h(1) of 21 CFR .sctn.177.1630 as defined herein.
Inventors: |
Deng; Fenghua; (Richmond,
VA) ; Nugara; Peter N.; (Richmond, VA) ;
Franzyshen; Stephen K.; (Richmond, VA) ; Haskins;
Reps M.; (Midlothian, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Deng; Fenghua
Nugara; Peter N.
Franzyshen; Stephen K.
Haskins; Reps M. |
Richmond
Richmond
Richmond
Midlothian |
VA
VA
VA
VA |
US
US
US
US |
|
|
Assignee: |
DuPont Teijin Films U.S. Limited
Partnership
Chester
VA
|
Family ID: |
44674910 |
Appl. No.: |
13/822886 |
Filed: |
September 13, 2011 |
PCT Filed: |
September 13, 2011 |
PCT NO: |
PCT/US11/51346 |
371 Date: |
May 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61382658 |
Sep 14, 2010 |
|
|
|
Current U.S.
Class: |
426/129 ;
426/106; 428/35.2; 428/475.2; 428/475.5; 428/480; 428/483;
53/467 |
Current CPC
Class: |
B32B 2307/306 20130101;
B65B 1/02 20130101; B32B 27/34 20130101; Y10T 428/31739 20150401;
B32B 27/36 20130101; B65D 81/34 20130101; B32B 27/08 20130101; B32B
2307/31 20130101; B32B 27/304 20130101; Y10T 428/1334 20150115;
Y10T 428/31786 20150401; Y10T 428/31736 20150401; B32B 2439/70
20130101; B32B 2307/738 20130101; Y10T 428/31797 20150401; B32B
1/02 20130101 |
Class at
Publication: |
426/129 ;
428/480; 428/475.5; 428/483; 428/475.2; 428/35.2; 426/106;
53/467 |
International
Class: |
B65D 81/34 20060101
B65D081/34; B32B 1/02 20060101 B32B001/02; B65B 1/02 20060101
B65B001/02; B32B 27/08 20060101 B32B027/08 |
Claims
1. A laminate comprising the following substantially coextensive
layers in the following order (a) a non-sealable, self-supporting,
thermoformable copolyester film layer having a first surface and a
second surface, said second surface constituting an outermost,
exposed surface of the laminate, wherein the copolyester in the
thermoformable copolyester film layer comprises from 90 mol % to 97
mol % of at least one aromatic dicarboxylic acid and
correspondingly from 10 mol % to 3 mol % of at least one aliphatic
dicarboxylic acid; (b) a laminating adhesive layer on the first
surface of the thermoformable copolyester film layer; and (c) a
self-supporting, thermoformable structural film layer having a
first surface and a second surface, said first surface contacting
the laminating adhesive layer; wherein polyethylene terephthalate
constitutes at least 80% by weight of the self-supporting
thermoformable copolyester film layer; the thermoformabie
structural film layer comprises a polymer selected from the group
consisting of polyamides, polypropylene, polyethylene, polyethylene
terephthalate, ionomers, ethylene acrylic acid copolymers, ethylene
vinyl acetate copolymers, polystyrene, ethylene vinyl alcohol
copolymers and polyvinylidene chloride; the thermoformabie
copolyester film layer, the structural film layer and the laminate
each shrink less than 5% in length and width upon exposure to
bulling water for five seconds; and the laminate is thermoformable
and its chloroform-soluble extractives meet the requirements of
paragraph h(1) of 21 CFR .sctn.177.1630 as defined herein,
2. The laminate of claim 1, wherein the structural film layer
comprises a polyamide.
3. The laminate of claim 1, wherein the structural film layer
comprises nylon 6,6.
4. The laminate of claim 1, further comprising a barrier layer
substantially coextensive with the copolyester film layer and the
structural film layer, on a side of the structural film layer
opposite the copolyester film layer, wherein the barrier layer
comprises a polymer selected from the group consisting of oriented
polyethylene terephthalate, polyvinylidene chloride, ethylene vinyl
alcohol copolymers and polyamides.
5. The laminate of claim 4, consisting of the copolyester film
layer, the laminating adhesive layer, the structural film layer,
and the barrier layer.
6. The laminate of claim 4, wherein the barrier layer comprises
polyvinylidene chloride.
7. The laminate of claim 4, wherein the barrier layer is on the
second surface of the structural film layer.
8. The laminate of claim 1, consisting of the copolyester film
layer, the laminating adhesive layer and the structural film
layer.
9. The laminate of claim 1, wherein the laminate is in the shape of
a thermoformed receptacle haying a pocket with a flange and an
opening, the second surface of the copolyester film layer forming
an inner surface of the pocket and a mating surface of the
flange.
10. A package comprising the laminate of claim 9 and a
heat-sealable film, wherein the opening of the receptacle is closed
by the heat-sealable film, said heat-sealable film comprising a
self-supporting polymeric film having on a surface thereof a
substantially coextensive heat-seal layer; wherein the heat-seal
layer of the heat-sealable film is in contact with and bonded to
the mating surface of the flange of the thermoformed receptacle;
and wherein chloroform-soluble extractives of the heat-sealable
film meet the requirements of paragraph h(1) of 21 CFR
.sctn.177.1630 as defined herein.
11. The package of claim 10, wherein the heat-seal layer comprises
an amorphous copolyester.
12. The package of claim 10, wherein the laminate is capable of
forming a heat-seal bond to the capping web with a bond strength of
at least 250 g/25 mm and at most 2500 g/25 mm.
13. The package of claim 10, further comprising a contained
foodstuff.
14. The package of claim 10, wherein the heat-seal layer ruptures
and vents the package at a temperature in a range from 150.degree.
F. (65.6.degree. C.) to 450.degree. F. (232.2.degree. C.).
15. The package of claim 14, wherein the heat-seal layer ruptures
and the package vents only at a temperature above 210.degree. F.
(98.9.degree. C.).
16. The package of claim 14, wherein the heat-seal layer ruptures
and the package vents only at a temperature above 250.degree. F.
(121.1.degree. C.).
17. The package of claim 13, wherein the foodstuff is meat,
poultry, or seafood.
18. A method of packaging a foodstuff, comprising placing the
foodstuff in the pocket of the laminate of claim 9 and subsequently
sealing the opening by heat-sealing a film to the flange.
19. The package of claim 14, wherein the foodstuff is meat,
poultry, or seafood.
Description
BACKGROUND OF THE INVENTION
[0001] Articles such as food items and more specifically meat,
poultry and seafood products are often packaged in thermoplastic
films or laminates to protect the product from exterior abuse and
environmental contamination, and to provide a convenient and
durable package for distribution of the product and display in a
display case or other point of sale. Packages made from films that
are formed, filled with product and sealed exist in many shapes and
forms for many applications, and are commonly used for such
packaging. When dealing with meat products in particular, it is
usually desirable to provide a film having good oxygen barrier
characteristics, in order to reduce the passage of oxygen through
the film so that detrimental effects on freshness, color, and other
properties of the meat product are minimized.
[0002] In many cases it is desirable to provide a package that can
be used to cook the contained foodstuff without removing the
packaging material (a "cook-in" package). It is also desirable that
such packages be suitable for heating or cooking in conventional,
convection or microwave ovens ("dual-ovenable") or for heating in
boiling water. It is particularly convenient to be able to purchase
a fresh, partially, or fully cooked or value-added foodstuff in a
package at the retail level and merely insert the package directly
into a conventional or microwave oven and cook and reheat the
foodstuff.
[0003] Thermoforming methods such as vacuum forming or plug-assist
vacuum forming are often used to produce suitable packages. In
general terms, thermoforming involves heating a thermoplastic film
or laminate and forming it into a shape suitable for containing the
product, which is subsequently inserted. The film or laminate is
sometimes referred to as a "forming web", and the package is closed
with a "capping web" film that is adhered to the thermoformed
package.
[0004] Coextruded films comprising polyolefins such as polyethylene
are sometimes useful in producing thermoformed packages. Laminate
films have also been employed. For example, U.S. Pat. No. 4,940,634
discloses biaxially oriented thermoplastic composite films
comprising polyolefins, suitable for use as forming webs in
thermoforming operations. It is common practice to join the capping
web to the thermoformed package by heat-sealing the two together.
Each films accordingly has a heat-sealable layer on its surface, or
consists entirely of a heat-sealable polymer. The two films are
pressed together with heating to effect the bond.
[0005] However, films comprising polyolefins generally do not
possess high temperature heat resistance, which limits their
application to microwave cooking or reheating. On the other hand,
polyethylene terephthalate (PET) films have high heat resistance,
making them suitable for cook-in uses, but PET itself is not
heat-sealable except at exceptionally high temperatures. If a
heat-seal layer is provided on both PET surfaces, an acceptable
seal can be obtained, but this adds time and expense to the film
manufacturing process. However, if ones attempts to heat-seal a PET
film having a heat-seal adhesive layer to a typical polyester film
having no heat-seal adhesive layer, the bond strength is
unacceptably weak for most applications. The need to provide a
heat-seal layer on both film surfaces adds time and expense to the
film manufacturing process. Thus, it would be advantageous to
provide a thermoformable polyester film that does not bear a
separate heat-seal layer, but that is nonetheless capable of being
effectively heat-sealed to a polyester capping web that does.
SUMMARY OF THE INVENTION
[0006] In one aspect, the invention provides a laminate including
the following substantially coextensive layers in the following
order:
[0007] (a) a non-sealable , self-supporting, thermoformable
copolyester film layer having a first surface and a second surface,
the second surface constituting an outermost, exposed surface of
the laminate;
[0008] (b) a laminating adhesive layer on the first surface of the
thermoformable copolyester film layer; and
[0009] (c) a self-supporting, thermoformable structural film layer
having a first surface and a second surface, the first surface
contacting the laminating adhesive layer.
[0010] Polyethylene terephthalate constitutes at least 80% by
weight of the self-supporting thermoformable copolyester film
layer;
[0011] the thermoformable structural film layer includes a polymer
selected from the group consisting of polyamides, polypropylene,
polyethylene, polyethylene terephthalate, ionomers, ethylene
acrylic acid copolymers, ethylene vinyl acetate copolymers,
polystyrene, ethylene vinyl alcohol copolymers and polyvinylidene
chloride;
[0012] the thermoformable copolyester film layer, the structural
film layer and the laminate each shrink less than 5% in length and
width upon exposure to boiling water for five seconds; and
[0013] the laminate is thermoformable and its chloroform-soluble
extractives meet the requirements of paragraph h(1) of 21 CFR
.sctn.177.1630 as defined herein.
[0014] In another aspect, the invention provides a package
including a laminate as described above, wherein the laminate is in
the shape of a thermoformed receptacle having a pocket with a
flange and an opening, the second surface of the copolyester film
layer forming an inner surface of the pocket and a mating surface
of the flange, and a heat-sealable film. The opening of the
receptacle is closed by the heat-sealable film, which includes a
self-supporting polymeric film having on a surface thereof a
substantially coextensive heat-seal layer. The heat-seal layer of
the heat-sealable film is in contact with and bonded to the mating
surface of the flange of the thermoformed receptacle, and
chloroform-soluble extractives of the heat-sealable film meet the
requirements of paragraph h(1) of 21 CFR .sctn.177.1630 as defined
herein.
[0015] In yet another aspect, the invention provides a method of
packaging a foodstuff, including placing the foodstuff in the
pocket of the laminate as described above and subsequently sealing
the opening by heat-sealing a film to the flange.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Laminates according to the invention include a non-sealable
thermoformable copolyester film layer on a surface of the laminate,
bonded by a laminating adhesive to a thermoformable structural film
layer. As used herein, the term "non-sealable" means that attempts
to bond two like pieces of the material together by heat-sealing
using the test method specified in the Examples fail to produce a
bond strength of at least 200 g/25 mm. While the copolyester face
of such a laminate is not itself heat-sealable, it is receptive to
heat-sealing, meaning that another film having a heat-sealable
surface layer can form a strong bond to the copolyester face of the
inventive film under heat-sealing conditions.
[0017] Laminates according to the invention meet the requirements
of paragraph h(1) of 21 CFR .sctn.177.1630 dated Apr. 1, 2003,
incorporated herein as Appendix A, and are dual-ovenable. Laminates
and multilayer films described herein will be understood to have
all of the layers mutually coextensive, unless the context makes it
clear otherwise. Each of the layers of the laminate will now be
described in detail, followed by a description of the structure and
use of suitable capping webs that may be used to seal thermoformed
packages made from the laminates.
Thermoformable Copolyester Film Layer
[0018] Thermoforming comprises heating a film to a temperature
(T.sub.1) above the glass transition temperature (T.sub.g) of the
material but below the crystalline melting temperature (T.sub.m) of
the material (if it has a crystalline component), and then applying
a deforming force to the material while it is in its softened,
rubbery, solid state. The film is then cooled to a temperature
below its glass transition temperature, and it must retain the
deformation that was introduced while it was in the softened
rubbery state.
[0019] In addition, the elongation (strain) at break (ETB) should
be greater than the strains experienced during the thermoforming
operation, and the tensile strength at maximum elongation (UTS)
should be greater than the yield stress.
[0020] Thermoformability requires that the deformed film retains
the deformed shape, once cooled. Accordingly, an important
characteristic of a thermoformable film is relaxation of induced
stress at the processing temperature after stretching the film to
the desired strain. This characteristic is usually expressed as a
percentage of stress retained after a defined time period (in
seconds), or as the time required to relax stress by a defined
percentage, and in a thermoformable film the values of these
parameters should be as low as possible, as is well known in the
art (see for instance "Viscoelastic Properties of Polymers"; John
D. Ferry, page 8 et seq., 3rd Ed, Wiley, NY; ISBN 0-471-04894-1;
and "Mechanical Properties of Solid Polymers", I. M. Ward, 2.sup.nd
Ed., John Wiley)).
[0021] For purposes of this invention, a film or laminate will be
considered thermoformable if the elongation (strain) at break when
measured at 130.degree. C. is greater than 220% in both machine
(MD) and transverse (TD) directions.
[0022] The thermoformable copolyester film layer is partially
amorphous, with the result that shrinkage of the layer (prior to
any thermoforming) is typically very low upon heating. Typically
the shrinkage is less than 5%, more typically less than 3%, in both
the machine (MD) and transverse (TD) directions (i.e., in both
length and width). The ability of the layer to be thermoformed
without substantial shrinkage is important, because excessive
shrinkage may lead to forming difficulties such as loss of ability
to maintain grip on the film during the forming step.
[0023] The crystallinity percentage indirectly gives a measure of
the amorphous content of the polymer, with lower crystallinity
meaning higher amorphous content, which in turn may give an
indication of the ability of a film to thermoform. In some
embodiments, the thermoformable copolyester has a crystallinity
percentage below about 50%, more preferably below about 45%, more
preferably in the range from 5 to about 42%, more preferably in the
range from 3 to about 40%.
[0024] The thermoformable copolyester film layer is a
self-supporting film or sheet, by which is meant a film or sheet
capable of independent existence in the absence of a supporting
base. A film-forming thermoplastic copolyester resin constitutes
the major component of the thermoformable copolyester film layer,
and makes up at least 50%, preferably at least 65%, preferably at
least 80%, preferably at least 90%, and preferably at least 95% by
weight of the total weight of the layer. Typically, one or more
fillers may make up the balance of the layer. In some cases, the
layer consists of the film-forming thermoplastic copolyester
resin.
[0025] The synthetic linear copolyesters useful for the
thermoformable copolyester film layer may be obtained by condensing
the dicarboxylic acids or their lower alkyl diesters, e.g.
terephthalic acid (TA), isophthalic acid, phthalic acid, 2,5-, 2,6-
or 2,7-naphthalenedicarboxylic acid, succinic acid, sebacic acid,
adipic acid, azelaic acid, 4,4'-diphenyldicarboxylic acid,
hexahydro-terephthalic acid or 1,2-bis-p-carboxyphenoxyethane
(optionally with a monocarboxylic acid, such as pivalic acid) with
one or more glycols, particularly an aliphatic or cycloaliphatic
glycol, e.g. ethylene glycol, 1,3-propanediol, 1,4-butanediol,
neopentyl glycol, 1,4-cyclohexanedimethanol and diethylene glycol.
In general, suitable glycols are of low molecular weight (i.e.
below about 250), and in some embodiments it is desirable to avoid
the use of glycols having an average molecular weight of over 250,
such as poly(alkylene oxide) glycols. Aliphatic glycols are
preferred, particularly ethylene glycol. In some embodiments,
diethylene glycol constitutes at least 1.5 mol % of the total diol,
or at least 2 mol %, with the balance being ethylene glycol. In
some embodiments, at most 5 mol % is diethylene glycol, or at most
3.5%.
[0026] The copolyester contains at least one aromatic dicarboxylic
acid, preferably selected from the aromatic dicarboxylic acids
noted above, and preferably said at least one aromatic dicarboxylic
acid is TA. In one embodiment, the copolyester contains only one
aromatic dicarboxylic acid, which is preferably TA. In some
embodiments, it is desirable to avoid the use of dicarboxylic acid
monomers that are sulphonated, i.e. dicarboxylic acids containing a
sulphonic acid group or salt thereof (i.e. dicarboxylic acids which
contain an --SO.sub.3X moiety where X is H or an alkali metal, such
as sodium sulfo-isophthalate).
[0027] The copolyester further contains at least one (typically
only one) saturated aliphatic dicarboxylic acid of the general
formula C.sub.nH.sub.2n(COOH).sub.2 wherein n is 2 to 8, such as
azelaic acid. In one embodiment, the dicarboxylic acid fraction of
the copolyester of the thermoformable copolyester film layer
consists of at least one (and preferably only one) aromatic
dicarboxylic acid, as defined above, and at least one (and
preferably only one) aliphatic dicarboxylic acid, as defined
above.
[0028] Preferably, the copolyester comprises at least 90 mol %
relative to the total diacid fraction of the copolyester of an
aromatic dicarboxylic acid, with the remainder being an aliphatic
dicarboxylic acid. More typically, the amount is at least 92 mol %.
Typically, at most 97 mol % of the total diacid is aromatic, more
typically at most 95 mol %.
[0029] The thermoformable copolyester film layer may contain
recycle material up to a level of 50% by weight of the layer, and
preferably at least 10%, preferably at least 25%, and more
preferably at least 40% by weight of the layer. By "recycle
material", we mean waste material consisting of the composite film
of the present invention, and such waste material may be derived
from edge-trimming (typically the edge portions of the film which
are held by the stenter clips during film manufacture), from excess
film left over after the film has been slit along its longitudinal
dimension, from start-up film (i.e. the film produced at the start
of a manufacturing run), or from film that has been failed for
other reasons, as is well-known in the art. It is surprising that
recycle material may be used in the thermoformable copolyester film
layer in such high proportions given that it contains the wax from
the heat-sealable layer without causing problems in the film making
process.
[0030] The thermoformable copolyester film layer may comprise one
or more discrete coextruded sublayers of the above film-forming
materials. The polymeric materials of the respective sublayers may
be the same or different. For instance, the thermoformable
copolyester film layer may comprise one, two, three, four or five
or more sublayers, and typical multi-layer structures may be of the
AB, ABA, ABC, ABAB, ABABA or ABCBA type. Preferably, the
thermoformable copolyester film layer is monolithic and comprises
only one layer, i.e., multiple coextruded copolyester layers are
not present. The thermoformable copolyester layer typically has a
thickness in a range from 0.5 mil to 4 mil, depending on the
desired end structure. It can be unoriented, but typically it is
biaxially oriented.
[0031] Laminates according to the invention are capable of forming
a heat-seal bond (on the thermoformable copolyester side) to a
capping web with a bond strength typically of at least 250 g/25 mm,
and more typically at least 400 g/25 mm, when measured as described
in the Examples, using MYLAR.RTM. OL13 film (DuPont Teijin Films,
Richmond, Va.) as the capping web. The heat-seal bond strength will
typically be at most 2500 g/25 mm, and more typically at most 1000
g/25 mm. Packages according to the invention may use capping webs
other than MYLAR.RTM. OL13 film, but the ranges of heat-seal bond
strengths between the laminate and the capping web will still fall
within the ranges described above. As noted earlier, the
thermoformable copolyester film layer of laminates according to the
invention is itself non-sealable, meaning that when bonded to
itself the heat-seal strength is less than 200 g/25 mm when
measured as described in the Examples.
Laminating Adhesive Layer
[0032] The thermoformable copolyester layer is laminated to the
structural film layer by use of a laminating adhesive, which may
for example be a polyester urethane. The adhesive may typically be
applied as a solution.
[0033] Solvent-based adhesives can be applied to one side (or two
sides) of the base sheet by any means 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.
[0034] For example, a two-part polyester urethane adhesive can be
applied to the thermoformable PET via a gravure cylinder to serve
as the laminating adhesive. The laminating adhesive is applied
across the web from solution. Removal of any solvent may require
the application of heat. The two film layers are then laminated
using standard laminating conditions.
[0035] The laminating adhesive may also be "solventless."
Solventless laminating adhesives are well known in the art and
illustratively include waterborne acrylic emulsions, polyurethane
dispersions and one and two part polyurethane systems with 100%
solids. Waterborne systems require dryers after adhesive
application at elevated temperatures to eliminate the water before
combining with another substrate. On the other hand, polyurethane
systems with 100% solids rely on a chemical reaction for curing and
little or no heat is required. In some applications it is preferred
that the laminating adhesive be elastomeric, with exemplary
embodiments being polyurethanes.
[0036] The laminating adhesive can be applied either to the
thermoformable copolyester film layer or the structural film layer,
or both. One or both of these films may also be surface treated,
such as by corona. In some cases both surfaces may be corona
treated prior to application of an adhesive in order to promote
better bonding between the film surfaces in contact with the
applied adhesive. The laminating adhesive can be applied by well
known coating techniques such as metering a low viscosity adhesive
onto a multiple application roll system configuration that applies
the adhesive to a first web or substrate. The first web is then
mated to a second web or substrate by use of a heated nip roll.
[0037] Thermosetting compositions may also be used for the
laminating adhesive. One such adhesive consists of equal parts by
volume of MOR-FREE.TM. 225 polyester polyol and MOR-FREE.TM. C-33
isocyanate, both available from Rohm and Haas of Spring House, Pa.
Other examples include solvent adhesives such as ADCOTE.TM. 812 and
ADCOTE.TM. 811B or a mixture of ADCOTE.TM. 250HV and Coreactant 86,
all available from Rohm and Haas of Spring House, Pa. The
laminating layer typically has a thickness in a range from 0.5 mil
to 10 mil including the thickness of the adhesive layer.
Thermoformable Structural Film Layer
[0038] The thermoformable copolyester film layer is adhesively
laminated to a thermoformable structural film layer to enhance
performance of the overall structure, depending on the packaging
need and intended condition of use. Examples of polymeric films
useful for the structural film layer are polyamide (for example,
nylon), polypropylene, polyethylene, ionomer, ethylene acrylic acid
copolymer, ethylene vinyl acetate copolymer, polyethylene
terephthalate, polystyrene, ethylene vinyl alcohol and
polyvinylidene chloride. One exemplary ionomer is sold by E.I. du
Pont de Nemours and Company, Wilmington, Del. (DuPont) under the
trade name SURLYN.RTM..
[0039] In some embodiments, the layer may be an abuse layer
comprising oriented polyamide (nylon). This layer is preferably
unaffected by the sealing temperatures used to make the package.
The thickness of this layer can control the stiffness of the
package, and may be in a range from about 10 to about 250 .mu.m
(0.4 to 10 mils), typically in a range from 50 to 200 .mu.m (2 to 8
mils). This layer may be provided with graphic elements such as
printing and embossing to provide information for the consumer
and/or a pleasing appearance to the package. Preferably this layer
is reverse printable. The particular film used will in part depend
upon the end use of the package. For example, packages containing
bones or other hard projections will require thicker film laminate
structures. The thickness of the laminate structure will also
depend on the depth of the draw desired during thermoforming. A
preferred material for the strength layers is a polyamide such as
biaxially oriented nylon from about 0.5 mil to about 5 mils in
thickness. Nylon used as an outer layer can be from about 1 to 5
mils thick. Nylon used as an inner layer in combination with
another layer can be from about 0.5 to 10 mils thick.
[0040] Polyamides suitable for use in making the structural film
layer include aliphatic polyamides, amorphous polyamides, or a
mixture thereof. "Aliphatic polyamides" as the term is used herein
can refer to aliphatic polyamides, aliphatic copolyamides, and
blends or mixtures of these. Preferred aliphatic polyamides for use
in the invention are nylon 6,6; nylon 6; nylon 6.66; nylon 6,10;
and blends and mixtures thereof. Nylon 6,6 is commercially
available, for example, under the trade name DARTEK.RTM. from
Exopack Performance Films Inc., Whitby, Canada. Nylon 6 is
commercially available, for example, under the trade name Nylon
4.12 from DuPont. Nylon 6.66 is commercially available under the
trade names "ULTRAMID.RTM. C4" and "ULTRAMID.RTM. C35" from BASF,
or under the trade name "UBE 5033FXD27" from Ube Industries Ltd.
Heat stabilizer-modified version of the above nylons, and blends
and mixtures of the nylons, may also be used.
[0041] The laminates of this invention comply with the requirements
of paragraph h(1) of 21 CFR .sctn.177.1630 dated Apr. 1, 2003. This
paragraph requires that the food contact surface, when exposed to
distilled water at 250.degree. F. (121.degree. C.) for 2 hours,
yields chloroform-soluble extractives not to exceed 0.02
mg/in.sup.2 (0.0031 mg/cm.sup.2) of food contact surface exposed to
the solvent; and that the food contact surface, when exposed to
n-heptane at 150.degree. F. (66.degree. C.) for 2 hours, yields
chloroform-soluble extractives not to exceed 0.02 mg/in.sup.2
(0.0031 mg/cm.sup.2) of food contact surface exposed to the
solvent.
Capping Web
[0042] Suitable capping webs comprise a heat-sealable polymer
layer, either alone or on the surface of a substrate layer, and in
use the heat-sealable layer is eventually heat-sealed to the
laminate on its thermoformable copolyester surface. The substrate
layer of the capping web (if present) is typically polymeric and
may be monolithic, although other layers may be added on the side
of the substrate layer opposite the heat-sealable polymer layer. A
polymeric material is the major component of the heat-sealable
layer, constituting at least 50%, preferably at least 65%,
preferably at least 80%, preferably at least 90%, and preferably at
least 95% by weight of the total weight of the heat-sealable layer.
Typically, one or more tackifiers, antifog agents, etc. may make up
the balance of the layer. In some cases, the heat-sealable layer
consists of the polymeric material.
[0043] During heat-sealing, the polymeric material of the
heat-sealable layer softens to a sufficient extent that its
viscosity becomes low enough to allow adequate wetting for it to
adhere to the surface to which it is being bonded. The heat-seal
bond is effected by heating to soften the polymeric material of the
heat-sealable layer without melting any of the other layers in
either film, and applying pressure. Thus, the polymeric material of
the heat-sealable layer should begin to soften at a temperature
such that the heat-seal bond can be formed at a temperature which
is less than the melting temperature of the polymeric material of
the substrate. In one embodiment, the polymeric material of the
heat-sealable layer should begin to soften at a temperature such
that the heat-seal bond can be formed at a temperature which is
between about 5 and 50.degree. C. below, preferably between about 5
and 30.degree. C. below, and preferably at least about 10.degree.
C. below the melting temperature of the polymer material of the
substrate.
[0044] In a preferred embodiment, the heat-sealable layer
comprises, and typically consists essentially of, a copolyester
resin derived from at least one (and preferably only one) aromatic
dicarboxylic acid and at least one (and preferably only one)
aliphatic dicarboxylic acid (or their lower alkyl (i.e. up to 14
carbon atoms) diesters) with one or more glycol(s). Formation of
the copolyester is conveniently effected in known manner by
condensation, or ester-interchange, at temperatures generally up to
275.degree. C.
[0045] Preferred aromatic dicarboxylic acids include terephthalic
acid, isophthalic acid, phthalic acid, and 2,5-, 2,6- or
2,7-naphthalenedicarboxylic acid, and preferably the aromatic
dicarboxylic acid is terephthalic acid. Preferred aliphatic
dicarboxylic acids are saturated aliphatic dicarboxylic acids of
the general formula C.sub.nH.sub.2n (COOH).sub.2 wherein n is 2 to
8, such as succinic acid, sebacic acid, adipic acid, azelaic acid,
suberic acid or pimelic acid, preferably sebacic acid, adipic acid
and azelaic acid, and more preferably azelaic acid. In one
embodiment, the polyester contains no more than 90% of aromatic
dicarboxylic acid (preferably TA) and at least 10% of aliphatic
dicarboxylic acid, the percentages being the mole percentage of the
total diacid content of the polyester, provided that the
copolyester of the heat-sealable layer is of different composition
than the substrate layer, as discussed hereinabove with regard to
relative softening temperatures. Preferably, the concentration of
the aromatic dicarboxylic acid present in the heat-sealable
copolyester is no more than about 80 mole %, and preferably in the
range from 45 to 80 mole %, more preferably 50 to 70 mole %, and
particularly 55 to 65 mole % based on the dicarboxylic acid
components of the copolyester. The concentration of the aliphatic
dicarboxylic acid present in the heat-sealable copolyester is at
least about 20 mole %, and preferably in the range from 20 to 55,
more preferably 30 to 50, and particularly 35 to 45 mole % based on
the dicarboxylic acid components of the copolyester. In some
embodiments, it is desirable to avoid the use of dicarboxylic acid
monomers that are sulphonated, i.e. dicarboxylic acids containing a
sulphonic acid group or salt thereof (i.e. dicarboxylic acids which
contain an --SO.sub.3X moiety where X is H or an alkali metal, such
as sodium sulfo-isophthalate).
[0046] Preferred glycols are aliphatic glycols, and more preferably
alkylene glycols. Thus, suitable glycol(s) include aliphatic diols
such as ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol,
2,2-dimethyl-1,3-propanediol, neopentyl glycol and 1,6-hexanediol.
Ethylene glycol or 1,4-butanediol is preferred. Thus, the glycols
are suitably low molecular weight diols (i.e. having a molecular
weight below about 250). In some embodiments, it is desirable to
avoid the use of glycols having an average molecular weight of over
250, such as poly(alkylene oxide) glycols. The copolyester of the
heat-sealable layer is thus suitably a linear copolyester. The
heat-sealable layer typically uses but a single polyester species,
rather than a blend of different polyesters.
[0047] Preferably, the T.sub.g of the copolyester is no more than
about 20.degree. C., preferably no more than about 10.degree. C.,
preferably no more than about 0.degree. C., and preferably no more
than about -20.degree. C. In one embodiment, the melting point
T.sub.m of the copolyester is preferably no more than about
160.degree. C., preferably no more than about 150.degree. C., more
preferably no more than about 140.degree. C., and preferably no
more than about 130.degree. C.
[0048] Particularly preferred examples of such copolyesters are (i)
copolyesters of azelaic acid and terephthalic acid with an
aliphatic glycol, preferably ethylene glycol; (ii) copolyesters of
adipic acid and terephthalic acid with an aliphatic glycol,
preferably ethylene glycol; and (iii) copolyesters of sebacic acid
and terephthalic acid with an aliphatic glycol, preferably butylene
glycol. Preferred polymers include a copolyester of sebacic
acid/terephthalic acid/butylene glycol (preferably having the
components in the relative molar ratios of 45-55/55-45/100, more
preferably 50/50/100) having a glass transition point (T.sub.g) of
-40.degree. C. and a melting point (T.sub.m) of 117.degree. C.),
and a copolyester of azelaic acid/terephthalic acid/ethylene glycol
(preferably having the components in the relative molar ratios of
40-50/60-50/100, more preferably 45/55/100) having a T.sub.g of
-15.degree. C. and a T.sub.m of 150.degree. C. The heat-sealable
layer typically has a thickness in a range from 0.5 mil to 2.0 mil
(13 to 51 .mu.m), depending on the desired end structure.
[0049] The substrate layer may consist of any of a wide variety of
materials, including but not limited to biaxially oriented
polyethylene terephthalate films, PET scrim, and Nylon films. One
exemplary coextruded film suitable for use as a capping web
comprises a clear, crystalline PET layer and an amorphous
copolyester heat seal layer. A film of this type is available from
DuPont Teijin Films under the trade name MYLAR.RTM. 851. The
substrate layer typically has a thickness in a range from 0.5 mil
to 2.0 mil (13 to 51 .mu.m). The substrate layer may be unoriented,
but preferably it is biaxially oriented.
[0050] Optionally, the capping web is surface printed or reverse
printed (i.e. printed on a face that will be internal in the final
film) to provide graphics, product information and the like.
Printing is advantageously applied to the capping web, which is not
subjected to thermoforming, so that the graphics are not distorted.
Specific examples of capping webs including printed features
include, from outermost layer to innermost layer: PVDC
Coating/nylon/ink/adhesive/PET/heat-seal layer; Nylon/PVDC
Coating/ink/adhesive/PET/heat-seal layer; or
Nylon/ink/adhesive/PVDC Coating/PET/heat-seal layer. In these
examples, the ink layer represents printed graphics that are
applied to the second film prior to adhesive lamination, which may
be effected with any of the laminating adhesives described earlier
herein. For example, base films comprising oriented PET with an
amorphous copolyester heat-seal layer can be adhesively laminated
to a second film comprising a nylon layer and a PVDC barrier
coating. The PVDC coating may also face the PET film.
Film Formation Processes
[0051] Films useful preparing the laminates or the capping webs may
be made by virtually any method of film forming known to those
skilled in this art. They may for example be cast, extruded,
co-extruded, laminated and the like, including orientation (either
uniaxially or biaxially) by various methodologies (e.g., blown
film, mechanical stretching or the like). Various additives known
to one skilled in the art can be present in the respective film
layers including the presence of tie layers and the like. Additives
include antioxidants and thermal stabilizers, ultraviolet (UV)
light stabilizers, pigments and dyes, fillers, delustrants,
anti-slip agents, plasticizers, anti-block agents, other processing
aids, and the like.
[0052] Film manufacture can be carried out according to any known
methods. It is possible, for example, to manufacture a primary film
by extruding the compositions using so-called "blown film" or "flat
die" methods. A blown film is made by extruding a polymeric
composition through an annular die and expanding the resulting
tubular film with an air current to provide a blown film. Cast flat
films are made by extruding a composition through a flat die. The
film leaving the die can be cooled by at least one roll containing
internally circulating fluid (a chill roll) or by a water bath to
provide a cast film.
[0053] A monolayer or multilayer film may be hot-blown from an
extrusion die at a relatively high blow-up ratio. Suitable
thermoplastic polyesters are preferably crystalline and of
relatively high molecular weight to maintain film integrity during
the blow-up procedure. The polyester can be stretched sufficiently
during the hot blowing process to provide balanced orientation in
both the longitudinal (machine) and transverse directions.
[0054] Alternatively, thermoplastic crystalline materials may be
stretch oriented to obtain a biaxially oriented film. For example,
a tubing is extruded and then cooled and reheated, and then
stretched by, for example, a blown bubble process. This process is
well known in the art. In the case of stretch-oriented materials,
the tubing is being stretched and oriented at a relatively low
temperature in comparison with the hot blown process disclosed
above.
Thermoformed Laminate Package Sealed with Capping Web
[0055] The film laminate can be used in a myriad of applications
such as to form packages using existing form, fill and seal (FFS)
machines available from a number of manufacturers (e.g., Repak,
Tiromat ULMA, and Multi-Vac). In a typical process, the laminate is
thermoformed into the shape of a receptacle having a pocket with a
flange and an opening, with the copolyester film layer forming an
inner surface of the pocket and a mating surface of the flange. The
heat-sealable layer of the capping web is sealed under vacuum to
the flange to hermetically seal the package.
[0056] The packages may typically contain foodstuffs such as meat,
poultry, seafood, non-meat products. Examples of foodstuffs that
may be packaged in packages of this invention include processed
meats such as sausages, hot dogs and the like. The foodstuffs also
include value-added, seasoned, marinated and/or precooked meat
products or prepared meals. The foodstuffs may also be whole-muscle
and/or bone-in meat and poultry portions such as, for example but
not limitation, pork loin, turkey or chicken breasts and the like.
Poultry also includes ready-to-cook whole birds. Packages may also
be used to enclose fresh meat, poultry and seafood in modified
atmospheric packaging applications or vacuum packaging
applications. The packages are dual-ovenable, and can be designed
to self-vent during cooking as the heat-seal layer softens.
[0057] A preferred package of this invention consists essentially
of (a) a thermoformable laminate disclosed herein and (b) a capping
web, in which the capping web is heat sealed to the laminate after
it has been thermoformed. Typically, the thermoformable laminate
can be used to form pockets and then the pockets are filled with
contents (for example, poultry) in an in-line packaging machine.
The pockets can then be closed by heat sealing the margins of the
laminate to a capping web in horizontal form, fill and seal
applications such that the laminate and the capping web are
hermetically sealed to each other.
[0058] Vent areas can be made anywhere on the package simply by
providing a slit in the package face at the time of heating.
[0059] Packages made as described above are dual-ovenable, and may
also be self-venting at typical cooking temperatures, depending on
the choice of laminate and capping web. Self venting is a desirable
safety feature to minimize the occurrence of steam blast on opening
the package. In a conventional oven, once the sealant reaches its
softening point and enough pressure is generated internally, the
seal will rupture and vent the package. This venting also promotes
air exchange for browning the meat if so desired. In another
example, the sealant thickness and seal temperature can be designed
to provide a vent (via rupture) once the foodstuff reaches
170.degree. F. (76.7.degree. C.). This may be useful when heating a
foodstuff in a microwave, where the self-venting feature serves as
a temperature indicator to show that the food is heated to the
proper temperature and is ready for consumption.
[0060] One exemplary heat-seal polymer suitable for making seals
that vent on heating is an amorphous copolyester. A coextruded film
suitable for preparation of forming webs or capping webs that can
be used in self-venting packages comprises a clear PET layer and an
amorphous heat seal layer. Films of this type (having various
thicknesses of clear PET and heat seal layer) are available from
DuPont Teijin Films under the trade name MYLAR.RTM. OL.
[0061] In some embodiments, the package may vent when the
temperature of the package reaches 150.RTM. F. (65.6.RTM. C.) to
450.RTM. F. (232.2.RTM. C.). In some embodiments, the package vents
only at a temperature above 210.RTM. F. (98.9.RTM. C.), or only at
a temperature above 250.RTM. F. (121.1.RTM. C.).
[0062] Packages according to the invention may incorporate other
features such as perforations, tear zones and the like that
facilitate opening the package. Polyamide and PET (heat sealable)
combinations provide excellent directional tear properties in that
a pre-notched package can be torn open in a straight line in either
the machine direction or transverse direction. These tear
properties provide greater flexibility in package configuration and
design. Thus, the opening area to access the foodstuff after
heating is not limited to a particular part (e.g. the top) of the
package. This can allow for locating a notch at the side of the
package in the desired area for opening.
EXAMPLES
[0063] The following test methods may be used to determine certain
properties of the laminates of this invention, and packages made
from them.
[0064] Heat-seal strength of the composite film to the capping web
is measured as follows. The capping web is sealed to the surface of
the thermoformable copolyester layer of the thermoformable laminate
using a Sentinel sealer at a temperature of 160.degree. C. for 1.0
second under a pressure of 80 psi (0.55 N/mm.sup.2). Strips (25 mm
wide) of the sealed capping web and thermoformable laminate are cut
out at 90.degree. to the seal, and the load required to pull the
seal apart measured using an Instron operating at a crosshead speed
of 0.25 m/minute. The procedure is generally repeated 5 times, and
a mean value of 5 results calculated.
[0065] Heat-seal strength of the composite film to itself to itself
is measured by positioning together and heating the heat-sealable
layers of two samples of the film at 160.degree. C. for 0.5 second
under a pressure of 80 psi (0.55 N/mm.sup.2). The sealed film is
cooled to room temperature, and the sealed composite cut into 25 mm
wide strips. The heat-seal strength is determined by measuring the
force required under linear tension per unit width of seal to peel
the layers of the film apart at a constant speed of 0.25
m/minute.
[0066] Shrinkage is measured by placing the sample in an oven at a
temperature of 190.degree. C. for 5 minutes and determining the
average % shrinkage in both the machine and transverse directions,
based on five film samples.
[0067] Glass transition temperature is measured by Differential
Scanning Calorimetry (DSC). A 10 mg polymer specimen taken from the
film is dried for 12 hours under vacuum at 80.degree. C. The dried
specimen is heated at 290.degree. C. for 2 minutes and then
quenched onto a cold block. The quenched specimen is heated from
0.degree. C. to 290.degree. C. at a rate of 20.degree. C./minute
using a Perkin-Elmer DSC7B Differential Scanning Calorimeter. The
calorimeter is calibrated at a heating rate of 20.degree.
C./minute, so cooling temperatures are corrected by adding
3.9.degree. C. to the computer-generated results.
[0068] The crystallinity percentage is measured using a Perkin
Elmer DSC7B Differential Scanning Calorimeter. A 5 mg sample taken
from the film is heated from 0 to 300.degree. C. at 80.degree.
C./minute, and the percent crystallinity is calculated by methods
well known in the art.
Laminate Preparation and Thermoforming
[0069] A typical process for forming a laminate according to the
invention is as follows. The thermoformable copolyester film and
the structural film are corona-treated on the surfaces to be
joined. A 1:1 mixture by volume of MOR-FREE.TM. 225
(polyester)/MOR-FREE.TM. C-33 (isocyanate) is applied by a gravure
roll at room temperature at a rate of 2.0-2.5g/m.sup.2. The
laminated film goes through a heated nip roll at 52-56.degree. C.
at a speed of about 500 ft/min, and the film is then rolled up and
stands at room temperature for 48 h for the initial curing to take
place. The film rolls are then transferred to heated room which is
at 40-45.degree. C. and kept for 5 days at which time the curing is
complete. At this time the lamination bond strengths typically
range from 1000 g/25 mm to destructive. Examples 1-4 describe
exemplary laminates according to the invention.
[0070] A typical process of thermoforming the laminate according to
the invention is as follows. The thermoformable laminate is heated
and formed using a Multivac packaging machine such as a Multivac
530 which is equipped with a pear-shaped mold where the deepest
point is about 4 inches. The forming temperature is set in a range
from 130.degree. C. to 215.degree. C., and the forming time and
vacuum are typically set at 2.0 seconds and 10 mbar,
respectively.
EXAMPLE 1
[0071] A 2-mil biaxially oriented polyester film was laminated with
4-mil DARTEK.RTM. H917 heat-stabilized nylon 6,6 film (Exopack
Performance Films Inc., Whitby, Canada) using a solventless
adhesive consisting of MOR-FREE.TM. 225 and MOR-FREE.TM. C-33 mixed
at a 1:1 ratio at room temperature. Both films were corona treated
prior to lamination. The diacid content of the polyester was 93/7
wt/wt terephthalic acid/azelaic acid, and the diol content was
95.7/4.3 wt/wt ethylene glycol/diethylene glycol. The amount of
adhesive applied was 2.5 g/m.sup.2. The adhesive was applied to the
corona treated H917 surface and the films were laminated together
at 500 ft/minute. The temperature of the nip roll was 54.degree. C.
The composite film was kept at ambient temperature for 2 days and
then moved to the heated room which was at 43.degree. C. for 5 days
to complete the curing process.
EXAMPLE 2
[0072] A corona-treated 2-mil polyester film having the same
polyester composition as in Example 1 but with a 1.5 .mu.m PVdC
coating on the side opposite the corona treatment is laminated to a
corona-treated 4-mil DARTEK.RTM. H917 heat-stabilized nylon 6,6
film. The laminating adhesive is a solventless adhesive consisting
of MOR-FREE.TM. 225 and MOR-FREE.TM. C33 mixed at a 1:1 ratio at
room temperature. The adhesive loading is 2.5 g/m.sup.2. The
adhesive is applied to the corona treated H917 surface and the PET
film surface. The temperature of the nip roll is 54.degree. C. The
composite laminate is kept at ambient temperature for 2 days and
then placed in a heated room at 43.degree. C. for 5 days to
complete the curing process.
EXAMPLE 3
[0073] A 2-mil polyester film having the same composition as the
polyester in Example 1 was laminated to 2-mil DARTEK.RTM. H917
heat-stabilized nylon 6,6 film. A process similar to that of
Example 1 was followed.
EXAMPLE 4
[0074] A corona-treated 2-mil PVdC coated polyester film as
described in Example 2 is laminated to 2-mil DARTEK.RTM. H917
heat-stabilized nylon 6,6 film, using a process similar to that of
Example 2.
Capping Webs
[0075] Examples 5-7 describe exemplary capping webs suitable for
use with the thermoformable copolyester laminates of this
invention.
EXAMPLE 5
[0076] A 1-mil biaxially oriented PET film with an amorphous
copolyester sealant layer (MYLAR.RTM. OL13, DuPont Teijin Films,
Richmond, Va.) was laminated to 1-mil DARTEK.RTM. H917
heat-stabilized nylon 6,6 film. A similar process to Example 1 was
followed. The non sealant side of the polyester film was corona
treated and in contact with the adhesive when the laminate was
formed.
EXAMPLE 6
[0077] A 1-mil polyester film with an amorphous copolyester sealant
layer on one side and a PVdC barrier layer on the other (Mylar.RTM.
OB13, DuPont Teijin Films, Richmond, Va.) was laminated to 1-mil
DARTEK.RTM. H917 heat-stabilized nylon 6,6 film, with the barrier
layer adhered to the nylon. A process similar to that of Example 2
was followed.
EXAMPLE 7
[0078] A 1.2-mil polyester film having an amorphous copolyester
heat-seal layer on one side (MYLAR.RTM. OL22, DuPont Teijin Films,
Richmond, Va.) was laminated to 1-mil DARTEK.RTM. H917
heat-stabilized nylon 6,6 film. A process similar to that of
Example 1 was followed. The non sealant side of the MYLAR.RTM. OL22
was corona treated and in contact with the adhesive when the
laminate was formed.
EXAMPLE 8
[0079] A thermoformable copolyester laminate made as in Example 1
was used as a formable web, and a laminate made as in Example 5 was
used as the capping web, as follows. A Multivac R530 packaging
machine was equipped with a pear-shaped mold where the deepest
point was about 4 inches, and the form temperature was set to
160.degree. C. The thermoformable laminate was heated and formed at
the same location, using a forming time of about 2.0 seconds and a
vacuum of about 10 mbar.
[0080] The cavity was then filled with product, a marinated sirloin
roast having a weight of about 1 lb 12 oz, leaving about 1/2-1 inch
head space, and the package was sealed with the capping web at
180.degree. C. with a dwell or sealing time of about 1.0 second. A
total heating seal plate was used, but in typical practice a
perimeter sealing plate may be used.
[0081] Two sirloin roasts each having a weight of about 1 lb 12 oz
were marinated with seasonings and vacuum packaged as described
above. The meats were frozen solid, and one was removed from its
package just prior to cooking. The packaged and unpackaged roasts
were cooked side-by-side without thawing in a conventional oven set
to 350.degree. F. After 25 minutes in the oven, the package
spontaneously opened by venting through a tiny vent and continued
to cook under partial steam in a bubble with a raised top web.
Elapsed times to reach 160.degree. F. internal meat temperature
were 75 and 83 minutes for the packaged and unpackaged roasts,
respectively. The roast that had been cooked in the package was
distinctly more juicy and moist than the unpackaged roast.
EXAMPLE 9
[0082] A turkey roast having a weight of about 9 lbs was marinated
with seasonings and vacuum packaged as follows. A Multivac R530
packaging machine was equipped with a pear shaped mold where the
deepest point was about 4 inches, and the form temperature was set
to 160.degree. C. The laminate film of Example 1 was heated and
formed at the same location, using a forming time of about 2.0
seconds and a vacuum of about 10 mbar.
[0083] The cavity was then filled with product, leaving about 1/2-1
inch head space, and the package was sealed with the capping web
made in Example 7 at 180.degree. C. with a dwell or sealing time of
about 2.0 second. A total heating seal plate was used, but in
typical practice a perimeter sealing plate may be used.
[0084] The packaged meat was placed in an Alkar.TM. oven set to
190.degree. F. for six hours. The package was removed and frozen in
a freezer. No venting or rupture of the seal occurred. The package
was taken from the freezer and placed in a conventional oven set to
250.degree. F. for reheat. After 30 minutes in the oven, the
package spontaneously opened by venting through a tiny vent and
continued to be heated under partial steam in a bubble with a
raised top web for a total of 90 minutes reheat time.
[0085] Although the invention is illustrated and described herein
with reference to specific embodiments, the invention is not
intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims without departing from the
invention.
* * * * *