U.S. patent application number 10/991038 was filed with the patent office on 2006-05-18 for breathable packaging film having enhanced thermoformability.
Invention is credited to Andrew J. Lischefski, Kevin P. Nelson.
Application Number | 20060105166 10/991038 |
Document ID | / |
Family ID | 35781290 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060105166 |
Kind Code |
A1 |
Lischefski; Andrew J. ; et
al. |
May 18, 2006 |
Breathable packaging film having enhanced thermoformability
Abstract
The present invention describes thermoformable coextruded film
suitable for use in packaging applications having at least a first
polymeric layer serving as an outermost exterior-film layer and
comprising a cycloaliphatic polyester, an aromatic polyester or
blends thereof; a second polymeric layer serving as a
thermoforming-assist layer and comprising a polyolefin; and a third
polymeric layer serving as an innermost exterior-film layer and
comprising a heat-sealing polyolefinic material. The films of the
present invention are oxygen-permeable in that they exhibit an
oxygen transmission rate of between 2-1000 cm.sup.3/100 in.sup.2/24
h.atm.
Inventors: |
Lischefski; Andrew J.;
(Tampere, FI) ; Nelson; Kevin P.; (Appleton,
WI) |
Correspondence
Address: |
BEMIS COMPANY, INC.
2200 BADGER AVENUE
OSHKOSH
WI
54904
US
|
Family ID: |
35781290 |
Appl. No.: |
10/991038 |
Filed: |
November 17, 2004 |
Current U.S.
Class: |
428/349 ;
428/480; 428/483; 428/522; 428/523 |
Current CPC
Class: |
B32B 27/08 20130101;
B32B 2307/724 20130101; Y10T 428/27 20150115; Y10T 428/2817
20150115; B32B 27/308 20130101; Y10T 428/28 20150115; Y10T
428/31797 20150401; B32B 2250/24 20130101; Y10T 428/31938 20150401;
Y10T 428/31928 20150401; B32B 2439/70 20130101; B32B 27/36
20130101; Y10T 428/31786 20150401; Y10T 428/31855 20150401; Y10T
428/31935 20150401; B32B 27/32 20130101; Y10T 428/269 20150115;
B32B 2307/738 20130101; Y10T 428/26 20150115; Y10T 428/2826
20150115; Y10T 428/31913 20150401; Y10T 428/31909 20150401; B32B
2307/406 20130101; Y10T 428/2813 20150115; Y10T 428/2878
20150115 |
Class at
Publication: |
428/349 ;
428/480; 428/523; 428/483; 428/522 |
International
Class: |
B32B 27/08 20060101
B32B027/08; B32B 27/36 20060101 B32B027/36; B32B 27/30 20060101
B32B027/30; B32B 27/32 20060101 B32B027/32 |
Claims
1. A thermoformable coextruded packaging film comprising: (a) at
least a first polymeric layer, a second polymeric layer, and a
third polymeric layer; (b) wherein said first polymeric layer is an
outermost exterior-film layer and comprises a material selected
from the group consisting of cycloaliphatic polyesters,
polyethylene terephthalate (PET), polyethylene terephthalate glycol
(PETG), polypropylene terephthalate (PPT), polybutylene
terephthalate (PBT) and blends thereof.; (c) wherein said second
polymeric layer comprises polypropylene or cross-linked
polyethylene; (d) wherein said third polymeric layer is an
innermost exterior-film layer comprising a heat-sealable
polyolefin; (e) wherein said film has an oxygen transmission rate
at 73.degree. C. and 0% R.H. of between 2-1000 cm.sup.3/100
in.sup.2/24 h. (31-15,500 cm.sup.3/m.sup.2/24 h.) as measured in
accordance with ASTM D-3985-02 test method; and (f) wherein said
film comprises an unrestrained linear thermal shrinkage at
80.degree. C. of 0-20% in both the machine and transverse direction
as measured in accordance with ASTM D-2732-96 test method.
2. A thermoformable coextruded packaging film according to claim 1,
wherein said film is formed by blown film coextrusion.
3. A thermoformable coextruded packaging film according to claim 1,
wherein said first polymeric layer, said second polymeric layer,
and said third polymeric layer are free of polyamide.
4. A thermoformable coextruded packaging film according to claim 1,
wherein said film comprises an unrestrained linear thermal
shrinkage at 80.degree. C. of 0-10% in both the machine and
transverse direction as measured in accordance with ASTM D-2732-96
test method.
5. A thermoformable coextruded packaging film according to claim 4,
wherein said film comprises an unrestrained linear thermal
shrinkage at 80.degree. C. of 0-5% in both the machine and
transverse direction as measured in accordance with ASTM D-2732-96
test method.
6. A thermoformable coextruded packaging film according to claim 1,
wherein said film comprises a gloss value at 45.degree. of at least
60% as measured in accordance ASTM D-2457-03 test method.
7. A thermoformable coextruded packaging film according to claim 1,
wherein said film comprises a haze value of less than 20% as
measured in accordance with ASTM D-1003-00 test method.
8. A thermoformable coextruded packaging film according to claim 1,
wherein said film has an oxygen transmission rate at 73.degree. C.
and 0% R.H. of between 10-1000 cm.sup.3/100 in.sup.2/24 h.
(155-15,500 cm.sup.3/m.sup.2/24 h.) as measured in accordance with
ASTM D-3985-02 test method.
9. A thermoformable coextruded packaging film according to claim 1,
wherein said film has an oxygen transmission rate at 73.degree. C.
and 0% R.H. of between 20-1000 cm.sup.3/100 in.sup.2/24 h.
(310-15,500 cm.sup.3/m.sup.2/24 h.) as measured in accordance with
ASTM D-3985-02 test method.
10. A thermoformable coextruded packaging film according to claim
1, wherein said third polymeric layer comprises polyethylene.
11. A thermoformable multilayer packaging film according to claim
1, wherein said film further comprises a fourth polymeric layer
disposed between said first and second polymeric layers.
12. A thermoformable coextruded packaging film according to claim
11, wherein said film further comprises a fifth polymeric layer
disposed between said second and third polymeric layers.
13. A thermoformable coextruded packaging film according to claim
11, wherein said fourth polymeric layer comprises a polyalkyl
acrylate copolymer or blend thereof.
14. A thermoformable coextruded packaging film according to claim
13, wherein said polyalkyl acrylate copolymer comprises an
ethylene/alkyl acrylate copolymer or blends thereof.
15. A thermoformable coextruded packaging film according to claim
14, wherein said ethylene/alkyl acrylate copolymers comprise a
material selected from the group consisting of ethylene/methyl
acrylate copolymer (E/MA), ethylene/ethyl acrylate copolymer
(E/EA), ethylene/butyl acrylate copolymer (E/BA), and
ethylene/methyl methacrylate copolymer (E/MMA).
16. A thermoformable coextruded packaging film according to claim
12, wherein said fifth polymeric layer comprises a material
selected from the group consisting of polypropylene, polyethylene,
anhydride-modified polyolefin and blends thereof.
17. A thermoformable coextruded packaging film according to claim
12, wherein said film further comprises a sixth polymeric layer and
a seventh polymeric layer.
18. A thermoformable coextruded packaging film according to claim
17, wherein said sixth and seventh polymeric layers each comprises
a material selected from the group consisting of polyethylene,
polypropylene and blends thereof.
19. A thermoformable coextruded packaging film according to claim
1, wherein said film has a thickness range between 0.8-15 mils
(20.32-381 .mu.m).
20. A thermoformable coextruded packaging film according to claim
19, wherein said film has a thickness range between 0.8-10 mils
(20.32-254 .mu.m).
21. A thermoformable coextruded packaging film according to claim
20, wherein said film has a thickness range between 0.8-8.0 mil
(20.32-203.2 .mu.m).
22. A thermoformable coextruded packaging film according to claim
1, wherein said film forms a package or a portions thereof.
23. A thermoformable coextruded packaging film comprising: (a) at
least a first polymeric layer, a second polymeric layer, a third
polymeric layer, a fourth polymeric layer, and a fifth polymeric
layer; (b) wherein said first polymeric layer is an outermost
exterior-film layer and comprises a material selected from the
group consisting of cycloaliphatic polyesters, polyethylene
terephthalate (PET), polyethylene terephthalate glycol (PETG),
polypropylene terephthalate (PPT), polybutylene terephthalate (PBT)
and blends thereof.; (c) wherein said second polymeric layer is
directly contacting said first and third polymeric layers and
comprises an polyalkyl acrylate copolymer or blend thereof; (d)
wherein said third polymeric layer is directly contacting said
second and fourth polymeric layers and comprises either
polypropylene or cross-linked polyethylene; (e) wherein said fourth
polymeric layer is directly contacting said third and fifth
polymeric layers and comprises a material selected from the group
consisting of polyethylene, polypropylene, anhydride-modified
polyolefin and blends thereof; (f) wherein said fifth polymeric
layer is directly contacting said fourth and sixth polymeric layers
and comprises a heat-sealable polyolefin; (g) wherein said film has
an oxygen transmission rate at 73.degree. C. and 0% R.H. of between
2-1000 cm.sup.3/100 in.sup.2/24 h. (31-15,500 cm.sup.3/m.sup.2/24
h.) as measured in accordance with ASTM D-3985-02 test method; and
(h) wherein said film comprises an unrestrained linear thermal
shrinkage at 80.degree. C. of 0-5% in both the machine and
transverse direction as measured in accordance with ASTM D-2732-96
test method.
24. A thermoformable coextruded packaging film according to claim
23, wherein said film is formed by blown film coextrusion.
25. A thermoformable coextruded packaging film comprising: (a) at
least a first polymeric layer, a second polymeric layer, a third
polymeric layer, a fourth polymeric layer, a fifth polymeric layer,
a sixth polymeric layer, and a seventh polymeric layer; (b) wherein
said first polymeric layer is an outermost exterior-film layer and
comprises a material selected from the group consisting of
cycloaliphatic polyesters, polyethylene terephthalate (PET),
polyethylene terephthalate glycol (PETG), polypropylene
terephthalate (PPT), polybutylene terephthalate (PBT) and blends
thereof.; (c) wherein said second polymeric layer is directly
contacting said first and third polymeric layers and comprises an
polyalkyl acrylate copolymer of blend thereof; (d) wherein said
third polymeric layer is directly contacting said second and fourth
polymeric layers and comprises either polypropylene or cross-linked
polyethylene; (e) wherein said fourth polymeric layer is directly
contacting said third and fifth polymeric layers and comprises a
material selected from the group consisting of polyethylene,
polypropylene and blends thereof; (f) wherein said fifth polymeric
layer is directly contacting said fourth and sixth polymeric layers
and comprises a material selected from the group consisting of
polyethylene, polypropylene and blends thereof; (g) wherein said
sixth polymeric layer is directly contacting said fifth and seventh
polymeric layers and comprises a material selected from the group
consisting of polyethylene, polypropylene, anhydride-modified
polyolefin and blends thereof; (h) wherein said seventh polymeric
layer is an innermost exterior-film layer comprising a
heat-sealable polyolefin; (i) wherein said film has an oxygen
transmission rate at 73.degree. C. and 0% R.H. of between 2-1000
cm.sup.3/100 in.sup.2/24 h. (31-15,500 cm.sup.3/m.sup.2/24 h.) as
measured in with ASTM D-3985-02 test method; and (j) wherein said
film comprises an unrestrained linear thermal shrinkage at
80.degree. C. of 0-5% in both the machine and transverse direction
as measured in accordance with ASTM D-2732-96 test method.
26. A thermoformable coextruded packaging film according to claim
25, wherein said film is formed by blown film coextrusion.
27. A thermoformable coextruded packaging film according to claim
25, wherein said first polymeric layer, said second polymeric
layer, said third polymeric layer, said fourth polymeric layer,
said fifth polymeric layer, said sixth polymeric layer, and said
seventh polymeric layer are free of polyamide.
28. A thermoformable coextruded packaging film according to claim
25, wherein said film comprises a gloss value at 45.degree. of at
least 60% as measured in accordance ASTM D-2457 test method.
29. A thermoformable coextruded packaging film according to claim
25, wherein said film comprises a haze value of less than 20% as
measured in accordance with ASTM D-1003-00 test method.
30. A thermoformable coextruded packaging film according to claim
25, wherein said film has an oxygen transmission rate at 73.degree.
C. and 0% R.H. of between 10-1000 cm.sup.3/100 in.sup.2/24 h.
(155-15,500 cm.sup.3/m.sup.2/24 h.) as measured in accordance with
ASTM D-3985-02 test method.
31. A thermoformable coextruded packaging film according to claim
30, wherein said film has an oxygen transmission rate at 73.degree.
C. and 0% R.H. of between 20-1000 cm.sup.3/100 in.sup.2/24 h.
(310-15,500 cm.sup.3/m.sup.2/24 h.) as measured in accordance with
ASTM D-3985-02 test method.
32. A thermoformable coextruded packaging film according to claim
25, wherein said fourth polymeric layer comprises a polyalkyl
acrylate copolymer or blend thereof.
33. A thermoformable coextruded packaging film according to claim
32, wherein said polyalkyl acrylate copolymer comprises an
ethylene/alkyl acrylate copolymers or blends thereof.
34. A thermoformable coextruded packaging film according to claim
33, wherein said ethylene/alkyl acrylate copolymers comprise a
material selected from the group consisting of ethylene/methyl
acrylate copolymer (E/MA), ethylene/ethyl acrylate copolymer
(E/EA), ethylene/butyl acrylate copolymer (E/BA), and
ethylene/methyl methacrylate copolymer (E/MMA).
35. A thermoformable coextruded packaging film according to claim
25, wherein said anhydride-modified polyolefin comprise an
anhydride modified-polyethylene.
36. A thermoformable coextruded packaging film according to claim
25, wherein said heat-sealable polyolefin comprises
polyethylene.
37. A thermoformable coextruded packaging film according to claim
25, wherein said film has a thickness range between 0.8-15 mils
(20.32-381 .mu.m).
38. A thermoformable coextruded packaging film according to claim
37, wherein said film has a thickness range between 0.8-10 mils
(20.32-254 .mu.m).
39. A thermoformable coextruded packaging film according to claim
38, wherein said film has a thickness range between 0.8-8.0 mil
(20.32-203.2 .mu.m).
40. A thermoformable coextruded packaging film according to claim
25, wherein said film forms a package or a portion thereof.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to food packaging
films, and particularly, to thermoformable coextruded packaging
films having special utility in the packaging of fresh poultry,
meats, fruits and vegetables.
BACKGROUND OF THE INVENTION
[0002] Thermoforming and other similar techniques are well known in
the art for packaging products. Suitable thermoforming methods, for
example, include a vacuum forming or plug-assist vacuum forming
method. In the vacuum forming method, a first film is heated, for
example, by a contact heater and a vacuum is applied beneath the
film causing the web to be pushed by atmospheric pressure down into
a preformed mold. In a plug-assist vacuum forming method, after the
first or forming film has been heated and sealed across a mold
cavity, a plug shape similar to the mold shape impinges on the
forming film and, upon the application of vacuum, the forming film
transfers to the mold surface. After the forming film is in place,
a product is placed, such as by manual loading, on the forming film
and a second, substantially non-thermoforming film is disposed over
the product. At a sealing station, the packages are evacuated and
fusion sealed with a sealing device such as a heated jaw. The first
or thermoforming film encloses a substantial portion, generally
more than half, of the product to be packaged.
[0003] Thermoforming is a popular method of making packaging for
food products, particularly, fresh and frozen meats. In the
packaging of such products, it is desirable to allow oxygen to
permeate a film or package so as to contact the meat product
contained therein. For example, a package utilizing a permeable
film can permit oxygen to permeate to a fresh red meat in the
package, thereby allowing the meat product to oxygenate (often
referred to as blooming which causes the meat color to change from
purple to a consumer desirable red color). This can enhance
consumer appeal, and retail vendors of such meat products demand
this type of capability. Additionally, many types of produce
require the presence of oxygen to suppress anaerobic spoilage.
[0004] Also in packaging of such products, it is desirable to
provide a clear package to permit observation of the enclosed
product with the packaging having good optical properties such as
clarity and gloss in order to enhance package appearance for the
consumer.
[0005] Not withstanding the fairly high state of development in the
art, packaging manufacturers are continually striving to improve
the functionality of their packaging materials.
SUMMARY OF THE INVENTION
[0006] This present invention relates to thermoformable coextruded
packaging films which provide oxygen permeability, improved
thermoformability and good optical characteristics. It is a more
particular object of the present invention to provide a material
for packaging food products requiring oxygen permeability such as,
for example, fresh poultry, fresh and frozen red meat and fresh
produce. The present invention provides such films which have an
oxygen transmission rate at 73.degree. C. and 0% R.H. of between
2-1000 cm.sup.3/100 in.sup.2/24 h. (31-15,500 cm.sup.3/m.sup.2/24
h.) as measured in accordance with ASTM D-3985-02 test method.
[0007] It is another object of the present invention to provide a
coextruded packaging film having improved thermoformability. The
present invention provides such thermoformable multilayer films
which are particularly well suited for forming a package in which
the film is molded into a cavity in which a product may be placed.
Such multilayer films may be characterized as having a linear free
shrink at 80.degree. C. of 0-5% in both the machine and transverse
directions as measure in accordance with ASTM D-2732-96 test
method.
[0008] It is yet another object of the present invention to provide
a thermoformable coextruded packaging film which exhibits
exceptional optical properties. The present invention provides
multilayer films having a gloss value at 45.degree. of at least 60%
as measure in accordance with ASTM D-2457-03 test method and a haze
value of less than 20% as measured in accordance with ASTM
D-1003-00 test method.
[0009] Such objects generally are achieved by a thermoformable
coextruded packaging film having a multilayer film structure
comprising at least three polymeric layers which includes a first
polymeric layer as an outermost exterior-film layer comprising
homopolymers or copolymers of polypropylene an aromatic polyester,
a cycloaliphatic polyester or blends thereof, a second polymeric
layer as an interior-film, thermoforming-assist layer comprising
homopolymers or copolymers of polyolefin, preferably, polypropylene
or cross-linked polyethylene, and a third polymeric layer as an
innermost exterior-film layer comprising a heat-sealing
polyolefin.
[0010] Such objects more particularly may be achieved by
above-described film structures which include a first polymeric
layer comprising an aromatic ester derived from homopolymers and
copolymers of alkyl-aromatic esters, such as, for example,
polyethylene terephthalate ("PET"), amorphous polyethylene
terephthalate ("APET"), crystalline polyethylene terephthalate
("CPET"), glycol-modified polyethylene terephthalate ("PETG"), and
polybutylene terephthalate; copolymers of isophthalate, such as,
polyethylene terephthalate/isophthalate copolymer, or
cycloaliphatic esters, and blends of any of the aforementioned
materials. The films may include layers in addition to those
described above. For instance, the multilayer films of the present
invention may include a film structure comprising a fourth
polymeric layer such as a tie layer positioned between the first
polymeric layer and the second polymeric layer. Preferably, the
fourth layer includes a material derived from polyalkyl acrylate
copolymers, more preferably, ethylene/alkyl acrylate copolymers,
and most preferably, a material selected from the group consisting
of ethylene/methyl acrylate copolymer ("E/MA"), ethylene/ethyl
acrylate copolymer ("E/EA"), ethylene/butyl acrylate copolymer
("E/BA"), and ethylene/methyl methacrylate copolymer ("E/MMA").
[0011] These and other aspects, advantages, and features of the
invention will be more readily understood and appreciated by
reference to the detailed description of the invention and the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a partially schematic, cross-sectional view of one
embodiment of a multilayer packaging film according to the present
invention comprising four layers.
[0013] FIG. 2 is a partially schematic, cross-sectional view of
another embodiment of a multilayer film according to the present
invention comprising seven layers.
DETAILED DESCRIPTION OF THE INVENTION
[0014] As used herein, the term "film" is used in the generic to
include plastic web, regardless of whether it is a film or
sheet.
[0015] As used herein, the phrase "thermoplastic" refers to a
polymer or polymer mixture that softens when exposed to heat and
returns to its original condition when cooled to room temperature.
In general, thermoplastic materials include, but are not limited
too, synthetic polymers such as polyesters, polyolefins,
polyamides, polystyrenes, and the like. Thermoplastic materials may
also include synthetic polymers that are cross-linked by either
radiation or chemical reaction during a manufacturing or
post-manufacturing process operation.
[0016] As used herein, the term "polymeric" refers to a material
which is the product of a polymerization reaction of natural,
synthetic, or natural and synthetic ingredients, and is inclusive
of homopolymers, copolymers, terpolymers, etc. In general, the
layers of a film or substrate may comprise a single polymer, a
mixture of a single polymer and non-polymeric materials, a
combination of two or more polymeric materials blended together, or
a mixture of a blend of two or more polymeric materials and
non-polymeric materials.
[0017] As used herein, the term "copolymer" refers to polymers
formed by the polymerization reaction of at least two different
monomers. For example, the term "copolymer" includes the
co-polymerization reaction product of ethylene and an
.alpha.-olefin, such as 1-hexene. The term "copolymer" is also
inclusive of, for example, the co-polymerization of a mixture of
ethylene, propylene, 1-butene, 1-hexene, and 1-octene. As used
herein, a copolymer identified in terms of a plurality of monomers,
e.g., "propylene/ethylene copolymer", refers to a copolymer in
which either monomer may copolymerize in a higher weight or molar
percent than the other monomer or monomers. However, the term
"copolymer" as applied to film layers of the present invention
refers to the first listed monomer polymerized in a higher weight
percent than the second listed monomer.
[0018] As used herein, terminology employing a "/" with respect to
the chemical identity of a copolymer (e.g., polyvinylidene
chloride/methyl acrylate copolymer), identifies the comonomers
which are copolymerized to produce the copolymer.
[0019] As used herein, the phrase "oxygen transmission rate" also
known as "OTR" is measured according to ASTM D-3985-02 test method,
a test known to those skilled in the art. The oxygen transmission
rate refers to the quantity of oxygen gas passing through a unit
area of the parallel surfaces of a film per unit time under the
conditions of test, i.e., cm.sup.3/100 in..sup.2/24 h. or
cm.sup.3/m.sup.2/24 h. The OTR of a film is measured after the film
sample has equilibrated in a dry test environment and at standard
temperature and pressure conditions (STP) or at temperature and/or
pressure conditions as stated otherwise. Standard temperature and
pressure conditions for measuring oxygen transmission rate are
32.degree. F. (0.degree. C.) and 1 atmosphere of pressure (0.1013
MPa). The "dry" environment is considered to be one in which the
relative humidity is less than 1%.
[0020] As used herein, the term "thermoformable" as applied to the
present invention refers to films which are capable of being formed
into a desired shape upon the application of heat, and are
thermoformed about the product on a support member by means of heat
and differential pressure. In the thermoforming process, virtually
all of the air is evacuated from the interior of the package so
that the film conforms very closely to the contour of the packaged
product.
[0021] As used herein, the phrase "unrestrained linear thermal
shrinkage", also known as "linear free heat shrinkage", refers to
the irreversible and rapid reduction in linear dimension in a
specified direction occurring in film subjected to elevated
temperatures under conditions where nil or negligible restraint to
inhibit shrinkage is present. It is normally expressed as a
percentage of the original dimension. As a result of the
manufacturing process, internal stresses may be locked into the
film which can be released by heating. The temperature at which
shrinkage will occur is related to the processing techniques
employed to manufacture the film and may also be related to a phase
transition in the base resin. Thermoformable films according to the
present invention may be characterized as having a low unrestrained
linear thermal shrinkage, preferably, an unrestrained linear
thermal shrinkage at 80.degree. C. of less than 20%, more
preferably, less than 10%, and most preferably, between 0-5% in
both the machine and the transverse directions, as measured in
accordance with ASTM D-2732-96 test method.
[0022] As used herein, the term "coextrusion" refers to the process
of extruding two or more materials through a single die with two or
more orifices arranged so that the extrudates merge and weld
together into a laminar structure before chilling (chilling may
also be termed quenching). The thermoformable films of the present
invention may be formed using a coextrusion process, preferably,
blown film coextrusion, cast film coextrusion, or extrusion
coating, more preferably, blown film coextrusion, cast film
coextrusion, and most preferably, blown film coextrusion.
[0023] As used herein, the term "polyester" refers to homopolymers
or copolymers having an ester linkage between monomer units which
may be formed, for example, by condensation polymerization
reactions between a dicarboxylic acid and a glycol. The ester can
be represented by the general formula: [R--C(O)O--R'] where R and
R'=alkyl group. The dicarboxylic acid may be linear or aliphatic,
i.e., oxalic acid, malonic acid, succinic acid, glutaric acid,
adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic
acid, and the like; or may be aromatic or alkyl substituted
aromatic, i.e., various isomers of phthalic acid, such as
paraphthalic acid (or terephthalic acid), isophthalic acid and
naphthalic acid. Specific examples of alkyl substituted aromatic
acids include the various isomers of dimethylphthalic acid, such as
dimethylisophthalic acid, dimethylorthophthalic acid,
dimethylterephthalic acid, the various isomers of diethylphthalic
acid, such as diethylisophthalic acid, diethylorthophthalic acid,
the various isomers of dimethylnaphthalic acid, such as
2,6-dimethylnaphthalic acid and 2,5-dimethylnaphthalic acid, and
the various isomers of diethylnaphthalic acid. The glycols may be
straight-chained or branched. Specific examples include ethylene
glycol, propylene glycol, trimethylene glycol, 1,4-butane diol,
neopentyl glycol and the like. Suitable materials of aromatic
polyesters for use in the present invention include, but are not
limited to, polyethylene terephthalate (PET), amorphous
polyethylene terephthalate (APET), crystalline polyethylene
terephthalate (CPET), glycol-modified polyethylene terephthalate
(PETG), and polybutylene terephthalate; copolymers of isophthalate,
such as, polyethylene terephthalate/isophthalate copolymer; and the
like.
[0024] As used herein, the phrase "cycloaliphatic polyester" refers
to copolymers derived from a dicarboxylic acid component consisting
of 1,4-cyclohexanedicarboxylic, a diol component consists of
1,4-cyclohexanedimethanol and polytetramethyleneether glycol.
Cycloaliphatic polyesters are well known in the art and are
described, for example, in U.S. Pat. Nos. 3,023,192; 3,261,812;
3,651,014; 4,003,882; 4,221,703; and 4,349,469, all of which are
incorporated herein by reference.
[0025] As used herein, the phrase "polyolefin" refers to
homopolymers, copolymers, including e.g. bipolymers, terpolymers,
block copolymer, grafted copolymers, etc., having a methylene
linkage between monomer units which may be formed by any method
known to those skill in the art. Examples of polyolefins include
polyethylene ("PE") which include, but are not limited to,
low-density polyethylene "(LDPE"), linear low-density polyethylene
("LLDPE"), very low-density polyethylene ("VLDPE"), ultra
low-density polyethylene ("ULDPE"), medium-density polyethylene
("MDPE"), high-density polyethylene ("HDPE"), ultra high-density
polyethylene ("UHDPE"), and polyethylenes comprising
ethylene/.alpha.-olefin ("E/AO") which are copolymers of ethylene
with one or more .alpha.-olefins (alpha-olefins) such as butene-1,
hexene-1, octene-1, or the like as a comonomer, and the like.
[0026] As used herein, the phrase "ethylene/.alpha.-olefin", also
known as "EAO" refers to a modified or unmodified copolymer
produced by the co-polymerization of ethylene and any one or more
.alpha.-olefin. The .alpha.-olefin in the present invention has
between 3-20 pendant carbon atoms, preferably, 3-12 pendant carbon
atoms and more preferably, 3-6 pendant carbon atoms. The
co-polymerization of ethylene and an .alpha.-olefin may be produced
by heterogeneous catalysis, i.e., co-polymerization reactions with
Ziegler-Natta catalysis systems, for example, metal halides
activated by an organometallic catalyst, i.e., titanium chloride,
optionally containing magnesium chloride, complexed to trialkyl
aluminum and maybe found in patents such as U.S. Pat. No. 4,302,565
to Goeke, et al. and U.S. Pat. No. 4,302,566 to Karol, et al., both
of which are hereby incorporated, in their entireties, by reference
thereto. Heterogeneous catalyzed copolymers of ethylene and an
.alpha.-olefin may include linear low density polyethylene, very
low density polyethylene and ultra low density polyethylene. These
copolymers of this type are available from, for example, The Dow
Chemical Company, of Midland, Mich., U.S.A. and sold under the
trademark DOWLEX.TM. resins. Additionally, the co-polymerization of
ethylene and a .alpha.-olefin may also be produced by homogeneous
catalysis, for example, co-polymerization reactions with
metallocene catalysis systems which include constrained geometry
catalysts, i.e., monocyclopentadienyl transition-metal complexes
taught in U.S. Pat. No. 5,026,798, to Canich, the teachings of
which are incorporated herein by reference. Homogeneous catalyzed
ethylene/.alpha.-olefin copolymers may include
ethylene/.alpha.-olefin copolymers available from The Dow Chemical
Company, known as AFFINITY.TM. and ATTANE.TM. resins, TAFMER.TM.
linear copolymers obtainable from the Mitsui Petrochemical
Corporation of Tokyo, Japan and ethylene/.alpha.-olefin copolymers
known as EXACT.TM. resins obtainable from ExxonMobil Chemical
Company of Houston, Tex., U.S.A.
[0027] As used herein, the terms "heat-seal", "heat-sealing",
"heat-sealable", and the like refer to a first portion of a film
surface (i.e., formed from a single layer or multiple layers) which
is capable of forming a fusion bond to a second portion of a film
surface. A heat-seal layer is capable of fusion bonding by
conventional indirect heating means which generate sufficient heat
on at least one film contact surface for conduction to the
contiguous film contact surface and formation of a bond interface
therebetween without loss of the film integrity. It should be
recognized that heat sealing can be performed by any one or more of
a wide variety of manners, such as using a heat seal technique
(e.g., melt-bead sealing, thermal sealing, impulse sealing,
ultrasonic sealing, hot air, hot wire, infrared radiation, etc.)
and most often involves application of heat and pressure for a time
sufficient to create a seal upon cooling.
[0028] As used herein, the phrase "innermost exterior-film layer"
as applied to film layers of the present invention refers to the
exterior-film layer which is closest to the product relative to the
other layers of the multilayer film. The phrase "exterior-film
layer" as applied to film layers refers to any film layer having
less than two of its principal surfaces directly adhered to another
layer of the substrate or another substrate. In contrast, the
phrase "outermost exterior-film layer", as used herein refers to
the exterior-film layer which is furthest from the product relative
to the other layers of the multilayer film.
[0029] As used herein, the phrase "interior-film layer" as applied
to film layers refers to any film layers having both of its
principal surfaces directly adhered to another layer of the
film.
[0030] As used herein, the phrase "gloss" refers to the specular
gloss of the films of the present invention, which is a measure of
the relative luminous reflectance factor of a specimen in the
mirror direction. The relative luminous reflectance factor is the
amount of light reflected by the surface of the specimen in
reference to a standard and the angle of reflection (20.degree.,
45.degree., 60.degree. or 85.degree.). Gloss as it refers to the
present invention, means that property of a film measured according
to ASTM D-2457-03 test method. The specular gloss of the films of
the present invention are determined by using BYK Gardner micro TRI
Glossmeter.
[0031] As used herein, the phrase "haze" refers to that percentage
of transmitted light which in passing through the film specimen
deviates from the incident beam by forward scattering, and which is
measured in accordance with ASTM D-1003-00 test method, a test
known to those skilled in the art.
[0032] As used herein, the phrase "tie layer" refer to any film
layer which functions toadhere two layers to one another. The tie
layer may comprise any polymer, copolymer or blend of polymers
having a polar group thereon, or any other polymer, copolymer or
blend of polymers which provide sufficient interlayer adhesion to
adjacent layers comprising otherwise nonadhering polymers. Suitable
materials for use as tie layers in the present invention may
include, but are not limited to, ionomers, ethylene/vinyl acetate
copolymers (E/VA), anhydride-modified ethylene/vinyl acetate
copolymers ("m-E/VA"), ethylene/methacrylic acid copolymers
("E/MAA"), ethylene/methyl acrylate copolymers (E/MA),
ethylene/ethyl acrylate copolymers (E/EA), anhydride-modified
ethylene/.alpha.-olefin copolymers ("m-E/AO"), anhydride-modified
polyolefins, such as anhydride-modified polyethylene ("m-PE"), or a
blend thereof.
[0033] As used herein, the term "anhydride-modified" refers to any
form of anhydride functionality, such as the anhydride of maleic
acid, fumaric acid, etc., whether co-polymerized with an
anhydride-containing monomer with a second, different monomer,
grafted onto a polymer or copolymer, or blended with one or more
polymers, and is inclusive of derivatives of such functionalities,
such as acids, esters, and metal salts derived therefrom.
[0034] As used herein, the phrase "bulk layer" refers to any film
layer which serves to increase the abuse resistance, toughness, and
modulus of a multilayer film.
[0035] As used herein, the phrase "thermoforming-assist layer"
refers to any interior-film layer which functions to increase the
integrity of the multilayer film while the film is heated and drawn
into a cavity during the thermoforming process.
[0036] As used herein, the phrase "machine direction" refers to a
direction "along the length" of the film, i.e., in the elongate
direction of the film as the film is formed during extrusion,
lamination, and/or coating.
[0037] As used herein, the phrase "transverse direction" refers to
a direction across the film, perpendicular to the machine or
longitudinal direction.
[0038] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete and will fully convey the scope of the
invention to those skilled in the art.
[0039] Referring to FIG. 1, film 10 is a schematic, cross-sectional
view of one embodiment of a multilayered film according to the
present invention comprising a first polymeric layer 11, a second
polymeric layer 12, a third polymeric layer 13, and a fourth
polymeric layer 14. Film 10 has four layers: two exterior-film
layers (11, 14); and two interior-film layers (12, 13). As
depicted, polymeric first layer 11 is an innermost exterior-film
layer which may comprise either a cycloaliphatic polyester or an
aromatic polyester, such as, for example, polyethylene
terephthalate (PET). Layer 12 is an interior-film tie layer and may
comprise any adhesive material which serves to adhere layer 11 and
13 to itself. Preferably, layer 12 comprises an adhesive material
derived from copolymers of ethylene and an alkyl acrylate, i.e.,
for example, ethylene/methacrylate copolymers (E/MA). Layer 13
serves as a thermoforming-assist layer and may comprise any
polyolefin, preferably, either a homopolymer or copolymer of
polypropylene (PP) or a homopolymer or a copolymer of a
cross-linked polyethylene (PE). Layer 14 is an innermost
exterior-film layer which includes a heat-sealing material,
preferably, a heat-sealing polyolefin. Suitable heat-sealable
polyolefins for use in layer 14 may include, not are not limited
to, for example, polyethylene (PE), which includes ultra
low-density polyethylene (ULDPE), linear low-density polyethylene
(LLDPE), low-density polyethylene (LDPE), medium-density
polyethylene (MDPE), polypropylene (PP), ethylene/vinyl acetate
(E/VA), copolymers of ethylene or propylene with one or more
.alpha.-olefins, and ionomers. Other examples of suitable
heat-sealable polyolefins include cyclic olefin copolymers (COC),
ethylene/propylene copolymers (PE/P), polypropylene (PP),
propylene/ethylene copolymer (PP/E), polyisoprene, polybutylene
(PB), polybutene-1, poly-3-methylbutene-1, and copolymers of
ethylene and 4-methylpentene-1, and the like.
[0040] It will be appreciated that films according to the present
invention are not limited to the four-layered structure, i.e.,
layers 11, 12, 13, and 14, provided that layers 11 and 14 are
positioned as exterior-film layers and layer 13 is an interior-film
layer which functions as a thermoforming-assist layer. Layer 13 may
be placed in any position within the film structure and,
preferably, is in direct contact with layer 11, by either a fusion
bond to layer 11 or through contact with tie layer 12. It is within
the scope of the present invention that additional interior layers
may be included in the film structure provided that the oxygen
transmitability of the entire structure does not decrease below 2
cm.sup.3/100 in.sup.2/24 h. (31 cm.sup.3/m.sup.2/24 h.) as measured
in accordance with ASTM D-3985-02. Thus, the film of this invention
may include any number of additional layers in any position between
either outermost exterior-film layer 11 and innermost exterior-film
layer 14 or between interior-film layer 13 and innermost
exterior-film layer 14. It is contemplated that the films of the
present invention may comprise at least three layers, and may
include a total of four layers, five layers, seven layers, or any
number of layers so desired.
[0041] Turning now to FIG. 2, film 20 is schematic, cross-sectional
view of one embodiment of a multilayered film according to the
present invention comprising a seven-layer film structure. Film 20
includes a first polymeric layer 21, a second polymeric layer 22, a
third polymeric layer 23, a fourth polymeric layer 24, a fifth
polymeric layer 25, a sixth polymeric layer 26, and a seventh
polymeric layer 27, in which there exists two exterior-film layers
(21, 27), and five interior-film layers (22, 23, 24, 25, 26).
Layers 21, 22 and 23 may each have identical compositions and
sub-structure as described for layers 11, 12 and 13, respectively,
of film 10, as described hereinabove. As depicted, layer 21 is an
outermost exterior-film layer and layers 22 and 23 being both
interior-film layers which serve as a tie layer and
thermoforming-assist layer, respectively. Layers 24 and layer 25
function as bulk layers and may both be formed from the same
material or different materials. Preferably, layers 24 and 25
comprise any thermoplastic material, more preferably, any
polyolefin resin, and most preferably, homopolymers and copolymers
of polyethylene (PE), polypropylene (PP), polybutylene (PB) or
blends thereof. Layer 26 is an interior-film layer which may serve
as either a bulk layer or a tie layer. As a bulk layer, layer 26
preferably comprises any thermoplastic material, more preferably,
any polyolefin resin, and most preferably, homopolymers and
copolymers of polyethylene (PE), polypropylene (PP), polybutylene
(PB) or blends thereof. As a tie layer, layer 26 preferably
comprises any adhesive material which bonds layers 25 and 27 to
itself. Suitable polyolefins include, but are not limited to, for
example, homopolymers and copolymers of polyethylene (PE),
polypropylene (PP), polybutylene (PB) or blends thereof. It is
preferred that the modified polyolefin comprise anhydride-modified
polyolefin, which, but are not limited to, ionomers, ethylene/vinyl
acetate copolymers (E/VA), anhydride-modified ethylene/vinyl
acetate copolymers (m-E/VA), ethylene/methacrylic acid copolymers
(E/EAA), ethylene/methyl acrylate copolymers (E/MA), ethylene/ethyl
acrylate copolymers (E/EA), anhydride-modified
ethylene/.alpha.-olefin copolymers (m-E/AO), anhydride-modified
polyolefins, such as anhydride-modified polyethylene (m-PE), or a
blend thereof.
[0042] It will also be recognized by those skilled in the art that
films 10, 20 and any variations thereof may be used to form
flexible, semi-rigid and rigid containers, packages, pouches or any
portion thereof. In general the films and packages of the present
invention can be used in the packaging of any product, the films
and packages of the present invention are especially advantageous
for the packaging of food products, especially fresh meat products.
Among the fresh meat product which can be packaged in the films and
packages according to the present invention are poultry, pork,
beef, lamb, goat, horse, and fish.
[0043] It will be appreciated that the thicknesses of each of films
10, 20 and any variations thereof may vary and equal thicknesses in
the FIGS. 1 and 2 are presented only to facilitate
illustration.
[0044] It will also be appreciated that the films of the present
invention have an oxygen transmission rate at 73.degree. C. and 0%
R.H. of preferably between 2-1000 cm.sup.3/100 in.sup.2/24 h.
(31-15,500 cm.sup.3/m.sup.2/24 h.), more preferably, between
10-1000 cm.sup.3/100 in.sup.2/24 h. (155-15,500 cm.sup.3/m.sup.2/24
h.), and most preferably, between 20-1000 cm.sup.3/100 in.sup.2/24
h. (310-15,500 cm.sup.3/m.sup.2/24 h.) as measured in accordance
with ASTM D-3985-02 test method.
[0045] The films of the present invention may be formed by any
conventional technique for forming films, including extrusion
lamination, cast extrusion, extrusion coating, and coextrusion,
preferably, extrusion coating, cast coextrusion or blown film
coextrusion, and more preferably, cast coextrusion or blown film
coextrusion, most preferably, blown coextrusion. In blown
coextrusion, for example, the films of the present invention may be
produced by a single-bubble blown film process. In this process a
tubular film is produced using one or more extruders (the number of
extruders depends upon the number of layers in the film and each
layer composition). The polymer resins extruded by the extruders
are fed to a circular die head through which the film layers are
forced and formed into a cylindrical multilayer film bubble. The
bubble is extruded therefrom through an air ring and quenched e.g.,
via cooled water bath, solid surface and/or air, and then
ultimately collapsed and formed into a multilayer film.
[0046] In the practice of this invention, it may be desirable to
have one or more layers of the entire film cross-linked to improve
the thermoformability, abuse and/or puncture resistance and/or
other physical characteristics of the entire film. Crosslinking is
the predominant reaction which results in the formation of
carbon-carbon bonds between polymer chains. Crosslinking may be
accomplished, for example, by ionized radiation means such as high
energy electrons, gamma-rays, beta particles and the like, or
through chemical means by use of peroxides and the like. More
particularly, for crosslinking with ionizing radiation, the energy
source can be any electron beam generator operating in a range of
about 150 kilovolts to about 6 megavolts with a power output
capable of supplying the desired dosage. The voltage can be
adjusted to appropriate levels which may be for example 1 to 6
million volts or higher or lower. Many apparatus for irradiating
films are known to those skilled in the art. The films of the
present invention may be irradiated at a level of from 2-12 MRads,
more preferably 2-5 MRads. The most preferred amount of radiation
is dependent upon the film and its end use.
[0047] One method for determining the degree of "cross-linking" or
the amount of radiation absorbed by a material is to measure the
gel content in accordance with ASTM D-2765-01 which is hereby
incorporated, in its entirety, by reference. Gel content
corresponds to the relative extent of crosslinking within a
polymeric material having undergone irradiation.
[0048] Preferably, the coextruded multilayered packaging film of
the present invention can have any total film thickness desired,
preferably thicknesses may range between 0.8-15 mils (20.32-381
.mu.m), more preferably, between 0.8-10 mils (20.32-254 .mu.m), and
most preferably, between 0.8-8.0 mil (20.32-203.2 .mu.m).
EXAMPLES
[0049] The invention is illustrated by the following examples,
which are provided for the purpose of representation, and are not
to be construed as limiting the scope of the invention.
[0050] Unless otherwise noted, the thermoplastic resins utilized in
the present invention are generally commercially available in
pellet form and, as generally recognized in the art, may be melt
blended or mechanically mixed by well-known methods using
commercially available equipment including tumblers, mixers or
blenders. Also, if desired, well known additives such as processing
aids, slip agents, anti-blocking agents and pigments, and mixtures
thereof may be incorporated into the film, by blending prior to
extrusion. The resins and any additives are introduced to an
extruder where the resins are melt plastified by heating and then
transferred to an extrusion (or coextrusion) die for formation into
a tube. Extruder and die temperatures will generally depend upon
the particular resin or resin containing mixtures being processed
and suitable temperature ranges for commercially available resins
are generally known in the art, or are provided in technical
bulletins made available by resin manufacturers. Processing
temperatures may vary depending upon other processing parameters
chosen.
[0051] For the following examples, a single slash, "/", represents
the division between individual layers within a film structure.
Example 1
[0052] Example 1 is one embodiment of the present invention of a
film having seven layers (see film 20 in FIG. 2). The first
polymeric layer (21) comprised a mixture of polyester, anti-block
additive and slip additive. The polyester comprised polyethylene
terephthalate copolymer having a density of 1.4 g/cm.sup.3, a
melting point of 240.degree. C., a tensile strength at break
(machine direction/transverse direction) of 8.4/5.6 kpsi, and is
available under the trademark Voridian.TM. Polymer 9921 from
Eastman Chemical Company, Kingsport, Tenn., U.S.A. In Example 1,
the second layer (22) was a tie layer comprising ethylene/methyl
acrylate copolymer (E/MA) and modified linear low-density
polyethylene (m-LLDPE). The ethylene/methyl acrylate copolymer has
a density of 0.948 g/cm.sup.3, a melting point of 49.degree. C., a
melt index of 2.0 g/10 min., and is available from Eastman Chemical
Company, Kingsport, Tenn., U.S.A. The modified linear low-density
polyethylene was an anhydride linear low-density polyethylene
having a having a density of 0.92 g/cm.sup.3, a melting point of
125.degree. C., a melt index of 1.5 g/10 min., a Vicat softening
point of 102.degree. C., and is available under the trademark
Bynel.RTM. from E. I. du Pont de Nemours and Company, Wilmington,
Del., U.S.A. The third layer (23) and the sixth layer (26) each
comprised a polypropylene random copolymer (PP) having a melt index
of 2 g/10 min., a tensile strength at break of 4.5 kpsi, and is
sold as Grade 8244 from BP Amoco Polymers, Inc., Naperville, Ill.,
U.S.A. The fourth layer (24) and the fifth layer (25) each
comprised an ultra low-density polyethylene (ULDPE), particularly,
an ethylene/octene .alpha.-olefin copolymer (E/AO) having a density
of 0.912 g/cm.sup.3, a melting point of 123.degree. C., a melt
index of 1.0 g/10 min., a Vicat softening point of 93.degree. C., a
is available under the trademark Attane 4201G from The Dow Chemical
Company, Midland, Mich., U.S.A. The seventh layer (27) comprised
polyethylene (PE) and anti-block additive. The polyethylene was
identical to that used in the fourth and fifth layers of the film.
The Example 1 was produced having an overall film thickness of
about 5 mil and with the following structure and relative layer
thicknesses, beginning with the outermost exterior-film layer and
going to the innermost exterior-film layer (left to right):
[0053] 5% PET/15% E/MA/10% PP/12% PE/8% PE/27% PP/23% PE
Example 1 had an oxygen transmission rate at 73.degree. C. and 0%
R.H. of 40 cm.sup.3/100 in.sup.2/24 h. (620 cm.sup.3/m.sup.2/24 h.)
as measured in accordance with ASTM D-3985-02 test method.
Example 2
[0054] In Example 2, the film is another example of a seven-layer
embodiment of the present invention. All the film layers are
identical in structure and relative layer thickness as that used in
Example 1, except that the overall film thickness was about 8
mil.
[0055] Example 2 had an oxygen transmission rate at 73.degree. C.
and 0% R.H. of 20 cm.sup.3/100 in.sup.2/24 h. (310
cm.sup.3/m.sup.2/24 h.) as measured in accordance with ASTM
D-3985-02 test method.
[0056] Unless otherwise noted, the physical properties and
performance characteristics reported herein were measured by test
procedures similar to the following methods. The following ASTM
test procedures are each incorporated herein by reference in their
entireties. TABLE-US-00001 Density ASTM D-1505 Gel Content ASTM
D-2765-01 Gloss ASTM D-2457-03 Haze ASTM D-1003-00 Unrestrained
Linear Thermal Shrinkage ASTM D-2732-96 Melt Index ASTM D-1238
Melting Point ASTM D-3417 Oxygen Transmission Rate ASTM D-3985-02
Tensile Strength at Break ASTM D-882 Vicat Softening Temperature
ASTM D-1525
[0057] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *