U.S. patent application number 11/646034 was filed with the patent office on 2007-05-24 for heat sealable polyvinyl chloride films.
Invention is credited to Paul N. Georgelos, Thomas E. Hopton, Carl M. Sullivan.
Application Number | 20070117919 11/646034 |
Document ID | / |
Family ID | 37719625 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070117919 |
Kind Code |
A1 |
Hopton; Thomas E. ; et
al. |
May 24, 2007 |
Heat sealable polyvinyl chloride films
Abstract
A heat sealable film for use in food packaging comprises a resin
composition comprising vinyl chloride homopolymer, vinyl
chloride-vinyl acetate copolymer and plasticizer in an amount
greater than about 15% by weight of the resin composition. In one
embodiment, the film is adapted to provide a controlled oxygen
transmission of at least 500 cc/in.sup.2/24 hours. The embodiment
is also adapted to heat seal on conventional packaging
equipment.
Inventors: |
Hopton; Thomas E.; (Stow,
OH) ; Sullivan; Carl M.; (Copley, OH) ;
Georgelos; Paul N.; (Naperville, IL) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET
SUITE 3400
CHICAGO
IL
60661
US
|
Family ID: |
37719625 |
Appl. No.: |
11/646034 |
Filed: |
December 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10429054 |
May 2, 2003 |
7175903 |
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11646034 |
Dec 27, 2006 |
|
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09715874 |
Nov 17, 2000 |
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10429054 |
May 2, 2003 |
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Current U.S.
Class: |
524/563 ;
524/567 |
Current CPC
Class: |
C08J 2327/06 20130101;
Y10T 428/1334 20150115; Y10T 428/24942 20150115; B32B 27/08
20130101; C08J 5/18 20130101; Y10T 428/1379 20150115; Y10T 428/1352
20150115; Y10T 428/1393 20150115 |
Class at
Publication: |
524/563 ;
524/567 |
International
Class: |
C04B 24/26 20060101
C04B024/26 |
Claims
1. A heat sealable film for use in food packaging comprising: at
least one extruded film formed from a resin composition comprising
a blend of (a) polyvinyl chloride; (b) copolymer of vinyl chloride
and vinyl acetate; and (c) plasticizer, wherein the plasticizer is
present in an amount greater than about 15% by weight of the resin
composition; and wherein the extruded film is adapted to heat seal
to itself.
2. The heat sealable film of claim 1, wherein the plasticizer is
present in an amount greater than about 20% by weight of the resin
composition.
3. The heat sealable film of claim 1, wherein the plasticizer is
present in an amount ranging from about 15% to about 40% by weight
of the resin composition.
4. The heat sealable film of claim 1, wherein the plasticizer is
present in an amount ranging from about 15% to about 30% by weight
of the resin composition.
5. The heat sealable film of claim 1, wherein the film comprises
copolymer of vinyl chloride and vinyl acetate in an amount ranging
from about 1% to about 30% by weight of the resin composition.
6. The heat sealable film of claim 1, wherein the film comprises
copolymer of vinyl chloride and vinyl acetate in an amount ranging
from about 5% to about 20% by weight of the resin composition.
7. The heat sealable film of claim 1, wherein the film comprises
copolymer of vinyl chloride and vinyl acetate in an amount ranging
from about 10% to about 20% by weight of the resin composition.
8. The heat sealable film of claim 1, wherein the film comprises
copolymer of vinyl chloride and vinyl acetate in an amount ranging
from about 15% to about 20% by weight of the resin composition.
9. The heat sealable film of claim 1, wherein the film is oriented
biaxially in an amount ranging from about 50% to about 400% of its
original length in the machine direction and in the transverse
direction.
10. The heat sealable film of claim 1, wherein the film has a heat
sealing window of at least 20.degree. F.
11. The heat sealable film of claim 1, wherein the film has a heat
sealing window of at least 30.degree. F.
12. The heat sealable film of claim 1, wherein the film is an
irradiated film having crosslinked polymers.
13. The heat sealable film of claim 1, wherein the film has an
oxygen transmission rate of about 150 to about 1200 g/100
in.sup.2/24 hours.
14. The heat sealable film of claim 1, wherein the film comprises
slip in an amount ranging from about 0.05% to about 0.6% by weight
of the resin composition.
15. The heat sealable film of claim 1, wherein the film comprises
slip in an amount ranging from about 0.01% to about 0.6% by weight
of the resin composition.
16. A heat sealable film for use in food packaging comprising: at
least one extruded film formed from a resin composition comprising
a blend of: polyvinyl chloride; copolymer of vinyl chloride and
vinyl acetate in an amount ranging from about 1.5% to about 30% by
weight of the resin composition; and plasticizer in an amount
greater than about 15% by weight of the resin composition; and
wherein the extruded film is adapted to heat seal to itself.
17. The heat sealable film of claim 16, wherein the plasticizer is
present in an amount ranging from about 15% to about 40% by weight
of the resin composition.
18. The heat sealable film of claim 16, wherein the film has an
oxygen transmission rate of about 150 to about 1200 g/100 in
.sup.2/24 hours.
19. The heat sealable film of claim 16, wherein the film has a heat
sealing window of at least 20.degree. F.
20. A heat sealable film for use in food packaging comprising: at
least one extruded film formed from a resin composition comprising
a blend of (a) polyvinyl chloride; (b) copolymer of vinyl chloride
and vinyl acetate; and (c) plasticizer, wherein the plasticizer is
present in an amount greater than about 15% by weight of the resin
composition; wherein the extruded film has an oxygen transmission
rate of about 150 g/100 in.sup.2/24 hours to about 1200 g/100
in.sup.2/24 hours; and wherein the extruded film has a heat sealing
window of at least 20.degree. F.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/429,054, filed May 2, 2003, currently pending, which is a
continuation-in-part of U.S. application Ser. No. 09/715,874 titled
Polymer Composite Packaging Film for Fresh Meat and Vegetable
produce, currently pending. The disclosure of U.S. application Ser.
Nos. 09/715,874 and 10/429,054 is hereby incorporated by
reference.
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] [Not Applicable]
[MICROFICHE/COPYRIGHT REFERENCE]
[0003] [Not Applicable]
BACKGROUND OF THE INVENTION
[0004] This invention relates to packaging films for fresh meat and
vegetable produce and, in particular, a packaging film that is heat
sealable, heat shrinkable and has a controlled gas permeability
rate.
[0005] Optically transparent films useful for covering food product
containers and packaging food products are ideally formulated to
provide consumers with a clear view of the packaged food product
while maintaining its appearance and freshness. Films with oxygen
transmission rate (OTR) control properties extend the shelf life of
refrigerated freshly cut produce and fresh meat since the presence
of either too much or too little oxygen in the package lowers shelf
life. For example, in the packaging of lettuce, excessive oxygen in
the package results in enzymatic browning of cut surfaces of the
lettuce. On the other hand, insufficient oxygen in the package
results in lettuce spoilage caused by anaerobiosis. Similarly,
fresh meat packaging permits delivery of sufficient oxygen to the
myoglobin contained within the meat to maintain its natural red
color and thus achieve the fresh looking product preferred by
consumers.
[0006] Packaging films made from polyvinyl chloride (PVC) and
plasticizer have been used to wrap red meat and produce. PVC films
provide a sparkling clear view of the packaged product, and, when
formulated with plasticizers, exhibit cling and stretch properties.
However, it is often desirable to wrap the food product on a tray,
heat seal the film around the tray and heat shrink the film.
Conventional PVC packaging films have difficulty forming hermetic
seals because PVC has a narrow sealing range. The precision
required to seal conventional PVC films is too high for
manufacturing with conventional packaging equipment.
[0007] Packaging films made from olefinic materials can be
formulated to control OTR, to seal to themselves and to be heat
shrinkable at lower temperatures than conventional PVC films.
However, films of olefinic materials are susceptible to surface
moisture buildup in the form of small beads that obscure a
consumer's view of the product contained in the package. Reducing
fog (surface moisture buildup) in olefinic films by adding standard
anti-fog agents has been largely unsuccessful. Anti-fog agents are
difficult to contain on the film surface because they tend to wash
off. Anti-fog agents also interfere with other film surface
properties of the olefinic film making it difficult to print and
seal.
[0008] In other packaging technology areas, films for applications
such as contact packaging for bottles or base films for
pharmaceutical packaging have used blends of conventional PVC,
meaning non-crosslinked PVC resin, and conventional PVC/VA, meaning
non-crosslinked PVC/VA resin. For example, U.S. Pat. No. 6,265,041
discloses a film for use as a cover sheet in pharmaceutical
packaging. The disclosed film comprises between 1-80% by weight of
a PVC resin and 20-99% by weight of a PVC/VA resin. U.S. Pat. No.
4,264,010 discloses a shrink wrap film for contact packaging
products, such as a large bottle for carbonated beverages. The
disclosed film comprises PVC and 5 to 20 parts by weight
PVC/VA.
[0009] While the disclosed films comprise PVC/VA and PVC, these
films require no controlled OTR and contain only small amounts of
plasticizer. For example, in the film disclosed in U.S. Pat. No.
6,265,041, the amount of plasticizer is less than 2% by weight of
the resin portion of the film. U.S. Pat. No. 6,265,041 discloses
examples of film containing ESO, a plasticizer, in amounts ranging
from 1.5 parts by weight out of 114.5 parts of resin composition to
about 2.0 parts by weight out of 113 parts of resin composition.
Stated in percentages by weight, these amounts range from 1.3% by
weight of the resin composition to 1.8% by weight of the resin
composition.
[0010] For the examples of films with PVC and PVC/VA blends
disclosed in U.S. Pat. No. 4,264,010, the amount of plasticizer
ranges from 11 to 17 weight parts out of 119.7 parts to 141.7
parts. Stated in percentage by weight, the amount of plasticizer in
these examples ranges from about 9% to about 12% by weight of the
film.
[0011] While homogenous blends of conventional PVC and conventional
PVC/VA may have been achieved with these low levels of plasticizer,
it has generally been believed that blending highly plasticized PVC
with a copolymer such as PVC/VA was too difficult to manufacture
commercially. PVC resins are typically blended with a high speed
impeller, which creates heat by friction. PVC/VA fuses at a lower
temperature than PVC, so PVC/VA will tend to agglomerate and fuse
together at the temperatures required to blend PVC. If the PVC/VA
forms agglomerates, the PVC/VA agglomerate may discolor when
exposed to heat during processing, forming black impurities in any
film formed from the blend.
[0012] It would be desirable, therefore, to have available a film
that is optically transparent and has a controllable OTR. A film
that is heat shrinkable and that may be hermetically sealed to
itself by conventional packaging equipment is also needed.
BRIEF SUMMARY OF THE INVENTION
[0013] One embodiment of the film comprises a blend of vinyl
chloride homopolymer (hereinafter referred to as PVC) and copolymer
of vinyl chloride and vinyl acetate (hereinafter referred to as
PVC/VA). PVC/VA is sometimes referred to as poly(vinyl chloride-co
vinyl acetate). The embodiment comprises about 18% by weight
PVC/VA. The embodiment further comprises at least about 15% by
weight plasticizer. A homogenous blend of these components was
achieved by following the blending steps described in more detail
below.
[0014] Such a film has several properties beneficial for food
packaging film. The film has a broad heat sealing temperature range
that allows the film to be sealed on equipment capable of forming
hermetic seals. Depending on the particular composition, the film
can form a welded, hermetic seal at temperatures ranging from about
200.degree. F. sealing time typically ranges up to about 1000
milliseconds.
[0015] This embodiment is further capable of sealing over a heat
sealing window that is sufficiently broad so that the film may be
sealed on conventional packaging equipment. In addition, the film
has an OTR of about 500 cc/100 in.sup.2/24 hours or greater, which
is desirable for food packaging. During processing the film may be
either biaxially oriented or uniaxially oriented, depending on the
desired shrink properties. When exposed to temperatures ranging
from about 180.degree. F. to about 350.degree. F., the film will
heat shrink.
[0016] Additional aspects and advantages of this invention will be
apparent from the following detailed description of specific
embodiments, which proceeds with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0017] FIG. 1 is a graph of hot tack seal strength of sample film
of Example 1 and Comparative Example 1, measured 250 ms following
seal formation.
[0018] FIG. 2 is a graph of hot tack seal strength of sample films
of Example 1 and Comparative Example 1, measured 500 ms following
seal formation.
[0019] FIG. 3 is a graph of hot tack seal strength of sample films
of Example 2 and Comparative Example 1, measured 250 ms following
seal formation.
[0020] FIG. 4 is a graph of hot tack seal strength of sample films
of Example 2 and Comparative Example 1, measured 500 ms following
seal formation.
[0021] FIG. 5 is a graph of hot tack seal strength of sample films
of Example 2 and Example 3, measured 250 ms following seal
formation.
[0022] FIG. 6 is a graph of hot tack seal strength of sample films
of Example 2 and Example 3, measured 500 ms following seal
formation.
[0023] FIG. 7 is a graph of hot tack seal strength of sample of
Example 4 and Comparative Example 2, measured 250 ms following seal
formation.
[0024] FIG. 8 is a graph of hot tack seal strength of sample of
Example 4 and Comparative Example 2, measured 500 ms following seal
formation.
DETAILED DESCRIPTION OF THE INVENTION
[0025] In one embodiment, the film comprises a blend of two
polyvinyl chloride resins: vinyl chloride homopolymer and copolymer
of vinyl chloride and vinyl acetate. PVC/VA is sometimes referred
to as poly(vinyl chloride-co vinyl acetate). The embodiment
comprises about 18% by weight PVC/VA. The embodiment further
comprises at least about 15% by weight plasticizer. A homogenous
blend of these components was achieved by following the blending
steps described in more detail below.
[0026] Such a film has several properties beneficial for food
packaging film. The film has a broad heat sealing temperature range
that allows the film to be sealed on equipment capable of forming
hermetic seals, such as an OSSID 500E wrapping machine. Depending
on the particular composition, the film can form a hermetic seal at
temperatures ranging from about 200.degree. F. to about 400.degree.
F. on conventional packaging equipment. Sealing time typically
ranges from about 500 to about 1000 milliseconds.
[0027] In one embodiment, the film is capable of forming a welded
heat seal at temperatures ranging from about 320.degree. F. to
about 400.degree. F. A welded seal is a seal with strength greater
than the tear strength of the film, so that the film will tear
before the seal separates. In the embodiment discussed above,
comprising a homogenous blend of PVC, PVC/VA and at least 15% by
weight plasticizer, has a broad heat sealing window, as discussed
in greater detail below.
[0028] The film of this embodiment has an OTR of about 500 cc/100
in.sup.2/24 hours or greater, which is desirable for food
packaging. During processing the film may be either biaxially
oriented or uniaxially oriented, depending on the desired shrink
properties. When exposed to temperatures ranging from about
180.degree. F. to about 350.degree. F., the film will heat
shrink.
[0029] As mentioned above, PVC refers to vinyl chloride
homopolymer. As used herein, PVC refers to polymers formed by
conventional PVC-forming processes and does not include crosslinked
vinyl chloride polymers, such as those disclosed in U.S. Pat. No.
5,210,141. Suitable examples of PVC include those resins available
from Shintech under product numbers 1150 and 1300; those resins
available from Georgia Gulf under the tradename PVC 2095; those
resins available from OxyVinyls under the product numbers 240, 450,
and 455; and those resins available from ESSO under the product
numbers 369 and 469.
[0030] PVC/VA comprises PVC copolymerized with vinyl acetate and
has a melting temperature of less than about 200.degree. F. As used
herein, PVC/VA refers to polymers obtained by conventional
polymerization processes and does not include cross-linked
polymers. In one embodiment, the amount of vinyl acetate monomer
incorporated into the PVC/VA copolymer ranges between about 5% to
about 15%. In another embodiment, the amount of vinyl acetate
monomer incorporated into the PVC/VA copolymer ranges from about
10% to about 13%. Suitable examples of PVC/VA include the
following: those resins available from Occidental Chemical Cop.
under the tradename Oxychem Oxy 6338; those resins available from
Formosa Plastics Formolon under product numbers 171C, 168 and 113;
and those resins available from Vinnolit GmbH & Co. of Germany
under the tradename Vinnolit S, product numbers 3060/10 and
3157/11.
[0031] As discussed in more detail below, the amount of PVC/VA in
the film affects the sealing properties of the film. One embodiment
of the film comprises PVC/VA in an amount ranging between about 1%
to about 30% by weight of the film. Stated otherwise, the amount of
PVC/VA incorporated in the film is about 1 to about 30 weight
parts, based on 100 weight parts of resin composition.
[0032] Resin composition, as used herein, refers to the total PVC,
PVC/VA, plasticizer, and other film additives discussed below.
Percentage by weight is used below to describe the components of
the film, however, one skilled in the art would understand that
these percentages may also represent weight parts out of 100 weight
parts resin composition. The resin composition may be only a
portion of a film that contains additional components, such as
particulate fillers. Alternatively, a film may include only the
resin compositions disclosed. The amounts of each component
discussed above refer to its percentage by weight of the resin
composition (including resins, plasticizer and additives), whether
stated as a percentage by weight of a film or a percentage by
weight of a resin composition, and may not represent the percentage
by weight of the entire film, if other components, such as
particulate fillers, are added.
[0033] Referring to another embodiment, the film comprises PVC/VA
in an amount ranging from about 5% to about 20% by weight of the
resin composition or film. In yet another embodiment, the amount of
PVC/VA ranges from about 10% to about 20% by weight of the resin
composition. In still another embodiment, the amount of PVC/VA
ranges from about 17% to about 20% by weight of the resin
composition.
[0034] The PVC and PVC/VA resins are highly plasticized to provide
a film with flexibility and elasticity. In one embodiment, the film
comprises plasticizer in an amount greater than about 15% by weight
of the resin composition. In another embodiment, the film comprises
plasticizer in an amount ranging from about 15% to about 40% by
weight of the resin composition. In another embodiment, the film
comprises plasticizer in an amount ranging from about 15% to about
35% by resin composition weight. In yet another embodiment, the
film comprises plasticizer in an amount ranging from about 15% to
about 30% by weight of the resin composition. In one embodiment,
the film comprises a blend of plasticizers.
[0035] Suitable plasticizers for use in the film include
di(2ethylhexyl)adipate (DEHA) and epoxidized soybean oil (ESO). ESO
acts both as a plasticizer and a stabilizer. For example, the film
may comprise DEHA in an amount ranging from about 18% to about 25%
by weight of the resin composition and ESO in an amount ranging
from about 4% to about 10% by weight of the resin composition.
Examples of DEHA include the following: those available from Sunoco
under the product number PX-238; those available from Eastman under
the tradename Kodaflex DOA; and those available from Solutia under
the tradename DOA. Examples of ESO include the following: those
available from Acme-Hardesty under the tradename Jenkinol, product
number 680M; those available from Crompton Corporation under the
tradename Drapex, product number 6.8; those available from Ferro
Corporation under the tradename Plascheck, product number 775;
those available from Atofina under the tradename Vikoflex, product
number 7170; and those available from CP Hall under the tradename
Paraplex G-62.
[0036] The amount of plasticizer incorporated into the film and the
film's thickness control the OTR of the film. As the amount of
plasticizer increases and the gauge of the film decreases, the
breathability of the film increases. Therefore, if a higher OTR is
desired, the plasticizer may be increased. For example, in an
embodiment containing plasticizer in an amount of about 26% by
weight of the resin composition and a gauge of about 1 mil, the
film has an OTR of about 815 cc/100 in.sup.2/24 hours. OTR rates
for specific examples are discussed in the examples section below.
In another embodiment containing plasticizer in an amount of about
23% and a gauge of about 1 mil, the film has an OTR of about 792
cc/100 in.sup.2/24 hours. The thickness of the film may also be
adjusted to affect OTR. In one embodiment, comprising at least
about 15% plasticizer and a thickness of 1 mil, the film has an OTR
of at least about 500 cc/100 in.sup.2/24 hours. The OTR of this
film will increase by twice if the gauge of the film is reduced by
half and the OTR will decrease by half if the gauge of the film is
doubled. Thus an embodiment with an OTR of 500 cc/100 in.sup.2/24
hours at 1 mil would be expected to have an OTR of at least about
1000 cc/100 in.sup.2/24 hours at a thickness of 0.5 mil. Similarly,
an embodiment, that at 1.0 mil has an OTR of 500 cc/100 in.sup.2/24
hours, would be expected to have an OTR of at least about 250
cc/100 in.sup.2/24 hours at a thickness of 2 mils. A film of the
same composition would be expected to have an OTR of at least about
125 cc/100 in.sup.2/24 hours at a thickness of 3 mils.
[0037] The film may also comprise additives such as stabilizer,
antifog, lubricant, slip agent and antiblock. Suitable examples of
stabilizers include tris-nonylphenyl phosphite ("TNPP") , and a
blend of calcium and zinc fatty acid soaps ("Ca/Zn") . Examples of
TNPP include the following: those available from Witco under the
tradename Mark C; those available from Dover Chemical under the
tradename Doverphos; those available from Huntsman Chemical under
the tradename Weston TNPP; and those available from Uniroyal under
the tradenames Wytox 312 and Naugard P. Examples of CaZn include:
those available from Cognis under the tradename Stabiol VCZ-2200,
those available from Akzo Nobel under the tradename Interstab,
product numbers CZL-720 and CZ-11; those available from Ferro Corp
under the tradename Thermocheck, product numbers 760X and 760;
those available from Blatchford under the tradename Chemstab R6100;
and those available from Witco under the tradename Mark 152. In one
embodiment, the film comprises stabilizer in an amount up to about
2% by weight of the resin composition. In another embodiment, the
film comprises stabilizer in an amount ranging from about 0.4% to
about 2% by weight of the composition.
[0038] Suitable examples of antifog include: glycerol mono-oleate,
such as those available from American Ingredients under the
tradename Pationic, product numbers 1530 and 1087 and from Crompton
under the tradename Atmer 400; sorbitan mono-oleate, such as those
available from CIBA Specialty Chemical ("CIBA") under the tradename
Atmer 105; sorbitan mono-laurate such as those available from CIBA
Specialty Chemical ("CIBA") under the tradename Atmer 100; sorbitan
mono-stearate such as those available from CIBA under the tradename
Atmer 103; poly-oxy-ethylene (20) sorbitan mono-oleate such as
those available from CIBA Specialty Chemical ("CIBA") under the
tradename Atmer 116, from Witco under the tradenames Flo-Mo-SMO 20
and Witconol 2722, from Lonza under the tradename Glycosperse 0-20,
and from Specialty Ind. Chem. under the tradename Polysorbac 80;
and ethoxylated nonylphenol, such as those available from Huntsman
Chemical under the tradename Surfonic N-60. In one embodiment, the
film comprises antifog in an amount up to about 3% by weight of the
resin composition. In another embodiment, the film comprises
antifog in an amount ranging from about 0.8% to about 3.5% by
weight of the resin composition.
[0039] Suitable examples of lubricant include stearic acid, such as
stearic acid available from Crompton under the tradenames Hystrene
5016, Emersol 136 and Hystrene 5016 and from Acme Hardesty under
the tradename 6ORGSA; lauric acid; palmetic acid; and polyethylene
wax; such as the waxes available from Allied Signal under the
product numbers AC629A and AC316A and from Texas Eastman under the
tradename Epolene E-14P. In one embodiment, the film comprises
lubricant in an amount ranging from about 0.1% to about 0.6% by
weight of the resin composition.
[0040] Suitable examples of slip agent include ethylene
bis-oleamide and erucamide slip. Examples of ethylene bis-oleamide
include: those available from Crompton under the tradename Kemamide
W-20; those available from Croda under the tradename Crodaflex EBO;
those available from Morton International under the tradename
Advawax 240; and those available from Lonza under the tradename
Glycolub VL. Examples of erucamide slip include those available
from Crompton under the tradename Kemamide E. In one embodiment,
the film contains slip in an amount sufficient to enable the film
to shrink around a package without becoming caught on the edge of
the package when the film shrinks. In one embodiment, the film
comprises slip agent in an amount ranging from about 0.05% to about
0.6% by weight. In another embodiment, the film comprises slip
agent in an amount ranging from about 0.1% to about 0.5% by
weight.
[0041] Suitable examples of antiblock include: silica antiblock
such as those available from Crosfield under the tradename Gasil
144; silica aerogel, such as those available from Grace/Davison
under the tradename Syloid 74; and zeospheres, also known as clay
microbeads, such as those available from 3M under the product
number W210. In one embodiment, the antiblock is present in an
amount up to about 0.6% by weight of the resin composition.
[0042] The film may be a single layer film. Alternatively, one or
more layers of the resin compositions described herein may be
included in a film with layers of other compositions.
[0043] The embodiments of the film discussed above may be formed by
blending PVC homopolymer resin and all additive ingredients in a
high intensity mixer, such as a Henschel mixer. Other suitable
mixers include Papenmeier mixers and Welex mixers. The action of
the mixer drives the temperature of the PVC polymer resin particles
by shear and friction to a point at which the particles swell and
retain by adsorption the plasticizers, the other liquid additives,
solid additives with lower melt points coating the particles and
other solid additives dispersed among the PVC resin particles. The
PVC resin particles will form a granular free flowing powder called
a dry blend. PVC/VA resin is also added during this blending cycle,
in which it also adsorbs a share of plasticizers, stabilizers and
other additives, and all ingredients become evenly dispersed.
[0044] The blend is dropped into a holding and cooling blender at a
temperature which is high enough to permit even adsorption of
additives among the PVC resin particles and lower than the point at
which the resin particles begin to melt or agglomerate into clumps.
Suitable holding and cooling blenders include Ribbon Blenders and
High Intensity Henschel Cooler. The PVC/VA resin softens and begins
to melt at a much lower temperature than the PVC homopolymer resin.
As a result the maximum or drop temperature for blending highly
plasticized PVC and PVC/VA is lower than a blend PVC homopolymer
and plasticizer alone. A lower maximum temperature prevents the
PVC/VA resin particles from partially melting and agglomerating
into clumps, and allowing the plasticizers and other additives to
be uniformly adsorbed into the resin particles. PVC/VA resin, PVC
resin and plasticizer, in the amounts described above, can be
blended into a homogenous mixture at maximum temperatures less than
about 195.degree. F. In another embodiment, the resins and
plasticizer, in the amounts described above, can be blended into a
homogenous mixtures at maximum temperatures less than about
190.degree. F. In another embodiment, the resins and plasticizer,
in the amounts described above, can be blended into a homogenous
mixtures at maximum temperatures less than about 185.degree. F. In
another embodiment, the PVC, plasticizer, and PVC/VA are blended
into a homogeneous mixture at maximum temperatures ranging from
183.degree. F. to about 187.degree. F. As used herein, a homogenous
mixture of PVC/VA and PVC refers to a blend in which all materials
are evenly distributed, so that a film formed from the blend is
smooth and uniform, without gels or lumps.
[0045] The finished granular powder blend may be melted and
extruded directly into film using a single screw extruder.
Alternatively, the powder may be melted and extruded into pellets
with a suitable extruder. The pellets are melted and extruded into
film by blown or cast film extrusion method, using a single screw
extruder. The secondary step of making the powder blend into
pellets gives extra mixing to disperse the PVC/VA resin more
completely into the film structure. Following extrusion, the film
may be irradiated to crosslink polymers in the film.
[0046] Following formation of the film, the film is oriented. In
one embodiment, the film is oriented in the machine direction in an
amount ranging from about 50% to about 400% of its original length.
When exposed to temperatures ranging from about 180.degree. F. to
about 200.degree. F., the oriented film will shrink less than about
60% of its original length. In one embodiment, the film is
biaxially oriented, about 50% to about 400% of its original length
in both the machine direction and the transverse direction. When
exposed to temperatures ranging from about 180.degree. F. to about
200.degree. F., the film will heat shrink less than 80% in the
machine and transverse directions. In one embodiment, the biaxially
oriented film will heat shrink between about 30% to about 50% in
both the machine and transverse directions. The film may be
biaxially oriented with a double bubble method. Alternatively, the
film may be biaxially oriented using a tenter frame and a machine
direction orienter.
[0047] The embodiments discussed above provide good OTR, with an
OTR of at least 500 cc/100 inches/24 hours for a film with a
thickness of about 1 mil. Also, as discussed above, the OTR can be
controlled by varying the amount of plasticizer in the film. The
embodiments discussed above are also capable of forming a welded
heat seal on conventional packaging equipment, such as an OSSID
500E. Heat seals are permanent bonds between layers of film by the
application of pressure and heat over a specified period of time,
the dwell time. A heat seal is generally formed by causing the film
surfaces to melt and flow together. Unlike other polymer film
structures, plasticized PVC does not have a sharp or well defined
melt point, but goes through progressive softening levels. PVC is
an amorphous non-crystalline polymer, and with the addition of
relatively large amounts of plasticizer and other additives, forms
a rubbery state.
[0048] Additionally, the embodiments described above are capable of
forming welded seal at a wide temperature window. PVC films may
form three types of heat seals: cling seals, heat tack (or peel)
seals and welded seals, the first two of which are false seals. The
true heat seal is called a welded seal, and is defined by being as
strong or stronger than the surrounding film. When attempting to
separate the layers of a welded seal, the adjacent film tears
before the seal itself. Thus a welded seal has a strength
equivalent to or greater than the film's tear strength.
[0049] As mentioned above, in one embodiment the inventive film has
a broad heat sealing window over which the film can form a welded
seal. A broad heat sealing window permits manufacturing equipment
to overshoot the sealing temperature to provide a complete seal
without burning the films. The heat sealing window is the
difference between the temperature at which the film begins to form
a welded seal and the temperature at which the film begins to burn
through. Burn through means that the film separates and forms holes
or begins to disintegrate in response to heat. The heat sealing
window is determined by the amount of PVC/VA included in the film.
Additives can also affect the heat sealing window and the sealing
temperatures of the films. For example, in an embodiment of the
film comprising 61% PVC, 28% plasticizer and 12% PVC/VA, the film
begins to seal at 313.degree. F. and begins to burn through when
exposed to temperatures of about 398.degree. F. The difference
between the beginning sealing temperature, 313.degree. F., and the
bum through temperature, about 398.degree. F., is the heat sealing
range. For this embodiment, the heat sealing window is 85.degree.
F. More examples and their heat sealing ranges are discussed
below.
[0050] In one embodiment, the film is capable of forming a welded
heat seal above about 320.degree. F. and has a heat sealing window
greater than about 20.degree. F. In another embodiment the film has
a heat seal window greater than 30.degree. F. In yet another
embodiment, the heat sealing window is greater than 40.degree. F.
The heat sealing temperature range refers the range of temperatures
over which the film may form a welded heat seal. For example, for a
film with a heat sealing range of 40.degree. F., if the film begins
to seal at 300.degree. F., the film will be able to seal at
temperatures up to 340.degree. F.
[0051] Other, less desirable, seals may be formed at low
temperatures, such as delaminating seals and cling seals.
Delaminating seals appear to be welded, but can be worked loose or
can be separated by hand peeling at the interface between the
sealed layers. Cling seals are the result of a film's cling or
electrostatic attraction and also stress relaxation (dead fold)
properties as the surfaces wet together. Cling seals are more
easily loosened or separated than the delaminating seal during
package handling or transportation. Cling seals are also easily
separated by hand, and are affected by moisture. A cling seal may
occur at room temperature with sufficient pressure and time.
[0052] In addition to being capable of forming welded seals on
conventional equipment, the embodiments described above have good
hot tack seal strength. Hot tack refers to the strength of the seal
immediately following sealing and before the seal has fully cooled.
Typically, film used to wrap food products on a tray is oriented
and is heat shrinkable. When the film is heat sealed around a
product, the film will shrink somewhat in response to the heat used
to seal the film. If the film does not have sufficient hot tack
seal strength, the seal can come apart in response to shrinking
immediately upon heat sealing. In addition, in a manufacturing
plant, the wrapped product proceeds to a heat shrinking tunnel just
after the film is heat sealed. As a result, the seal may not have
cooled completely before the film heat shrinks around the product.
Good hot tack seal strength helps keep the seal intact when the
film heat shrinks following formation of the heat seal. In one
embodiment, the film forms a seal with a hot tack seal strength of
at least 60 grams/mil over a broad range of temperatures.
[0053] Seal strength is expressed in grams/mil (also referred to as
g/mil or grams force per mil of thickness) or grams/in (also
referred to as g/in or grams force per inch) in the description
above and in the examples below. Grams/mil may be converted into
N/mm (Newtons per millimeter of thickness) by the following
equation: g/mil x 0.386 =N/mm. Grams/in may be converted into N/m
(Newtons per meter) by the following equation: g/inch x 0.386
=N/m.
EXAMPLES
[0054] Specific embodiments of the film are described in detail
below, but the invention is not limited by these examples. In each
of the examples below, the PVC and PVC/VA, if included, were
blended in a high intensity blender with plasticizers and any other
additives. The resulting powder was extruded into pellets and the
pellets were extruded into film, forming film samples. Sealing
properties, tear strength and OTR were measured for Examples 1-3.
In addition, hot tack seal strength of the sample films were tested
by sealing at temperatures ranging from 220.degree. F. to
350.degree. F. The sample films were sealed in a fin seal with
sealing jaws at 60 psi of pressure with a dwell time of 1000
milliseconds or 500 milliseconds, as specified below. The hot tack
seal strengths for each sealing temperature were measured at 500
milliseconds or 250 milliseconds following seal formation. Note
that seal strengths of less than 20 g/in can be caused by cling
between the film and may not be the result of heat sealing.
Example 1
[0055] The sample films of Example 1 comprise: 54.84% by weight
PVC, 12.46% by weight PVC/VA, and 28.27% by weight plasticizer. The
films of Example 1 further comprise minor amounts of additives:
1.47% by weight stabilizer, 2.02% by weight antifog, 0.24% by
weight slip, 0.1% by weight lubricant, 0.17% by weight slip, and
0.44% by weight antiblock.
[0056] A film of Example 1 was formed with a gauge of 1 mil. The
film was tested for OTR and for heat sealing characteristics. The
film had an OTR of 1025.9 cc/100 in.sup.2/24 hours. The film formed
a welded seal, beginning at a temperature of 328.degree. F. and a
burn through temperature of 421.degree. F., providing a 93.degree.
F. heat sealing window.
Comparative Example 1
[0057] The sample films of Comparative Example 1 comprise: 68.51%
by weight PVC, 0% PVC/VA, and 28.09% by weight plasticizer. The
Comparative Example 1 film samples further comprise minor amounts
of additives: 2.06% by weight stabilizer, 1.16% by weight antifog,
0.18% by weight lubricant and 0.14% by weight slip.
[0058] Three sample films of Example 1 and Comparative Example 1
were extruded and tested by the methods discussed above. FIG. 1
shows the hot tack seal strength over seal temperature for samples
of Example 1 and Comparative Example 1, measured 250 milliseconds
following release of the sealing jaws. FIG. 2 shows seal strengths
over seal temperature, measured 500 millisecond following release
of the sealing jaws. For the data shown in both FIGS. 1 and 2, the
film was sealed with a dwell time of 500 milliseconds. The data
from this testing for Example 1 is shown in Table A, for 250
milliseconds following sealing, and in Table B, for 500
milliseconds following sealing. For Comparative Example 1, the
results of testing are shown in Table C, for 250 ms following
sealing, and in Table D, for 500 ms following sealing.
TABLE-US-00001 TABLE A (250 ms) Example 1 Seal Temperature
(.degree. F.) 220 230 240 250 260 270 280 290 300 310 320 330 340
350 Sample 1 0 0 27 39 48 48 57 64 92 115 97 64 58 53 Seal (g/in)
Sample 2 0 0 23 37 44 55 64 60 161 143 124 65 64 55 Seal (g/in)
Sample 3 0 0 25 37 46 62 62 69 150 147 81 67 60 55 Seal (g/in) Avg.
0 0 25 38 46 55 61 64 134 135 101 65 61 54 Seal (g/in)
[0059] TABLE-US-00002 TABLE B (500 ms) Example 1 Seal Temperature
(.degree. F.) 220 230 240 250 260 270 280 290 300 310 320 330 340
350 Sample 1 0 0 42 65 83 79 71 78 103 269 196 106 81 69 Seal
(g/in) Sample 2 0 0 39 67 72 81 88 73 76 267 124 117 103 65 Seal
(g/in) Sample 3 0 0 42 65 3 129 83 83 87 170 152 111 92 90 Seal
(g/in) Avg. 0 0 41 66 79 96 81 78 89 235 157 111 92 75 Seal
(g/in)
[0060] TABLE-US-00003 TABLE C (250 ms) Comparative Example 1 Seal
Temperature (.degree. F.) 220 230 240 250 260 270 280 290 300 310
320 330 340 350 Sample 1 25 28 18 23 37 62 48 35 35 19 44 80 74 49
Seal (g/in) Sample 2 21 18 30 35 57 51 32 39 32 41 37 90 55 53 Seal
(g/in) Sample 3 25 23 19 30 32 41 32 39 12 21 44 74 62 57 Seal
(g/in) Avg. 24 23 22 29 42 51 37 38 26 27 42 81 64 53 Seal
(g/in)
[0061] TABLE-US-00004 TABLE D (500 ms) Comparative Example 1 Seal
Temperature (.degree. F.) 220 230 240 250 260 270 280 290 300 310
320 330 340 350 Sample 1 42 71 41 39 60 83 57 44 35 19 44 65 129
134 Seal (g/in) Sample 2 30 37 51 48 64 53 30 39 48 35 34 62 197
148 Seal (g/in) Sample 3 39 41 39 44 41 55 44 46 11 18 35 106 201
205 Seal (g/in) Avg. 37 50 44 44 55 64 44 43 31 24 38 78 176 162
Seal (g/in)
[0062] As discussed above, films for packaging fresh produce should
be capable of sealing along a temperature range that is
sufficiently broad to allow conventional heat sealing equipment to
create a reliable seal that will remain intact when the film heat
shrinks as a result of heat sealing and proceeds into a heat
shrinking tunnel immediately following sealing. As shown by the
graphs in FIGS. 1 and 2 and the data from Tables A-D, the film of
Example 1 (a blend of plasticized PVC and PVC/VA copolymer)
achieves greater seal strength than the film of Comparative Example
1 (PVC without PVC/VA), over sealing temperatures ranging from
240.degree. F. to 320.degree. F. The film of Example 1 also
achieves hot tack seal strengths over 60 g/in at temperatures
ranging from 280.degree. F. to 320.degree. F.
Example 2
[0063] The sample films of Example 2 comprise: 54.92% by weight
PVC; 12.48% PVC/VA; and 28.31% by weight plasticizer. The sample
films further comprise minor amounts of additives: 1.47% by weight
of stabilizer; 2.02% by weight antifog; 0.33% by weight slip; 0.17%
by weight lubricant; and 0.30% by weight antiblock.
[0064] A film of Example 2 was formed with a gauge of I mil. The
film was tested for OTR and for heat sealing characteristics. The
film had an OTR of 904 cc/100 in.sup.2/24 hours. The film formed a
welded seal beginning at a temperature of 313.degree. F. and a burn
through temperature of 398.degree. F., providing an 85.degree. F.
heat sealing window.
[0065] Three samples of Example 2 were tested for hot tack seal
strength. The data from this testing is shown in Tables E-F.
[0066] FIG. 3 is a graph of the hot tack heat seal data 250 ms
following sealing as shown in Table E (Example 2) and Table C
(Comparative Example 1). FIG. 4 is a graph of hot tack heat seal
500 ms following sealing, as shown in Table F (Example 2) Table D
(Comparative Example 1). TABLE-US-00005 TABLE E (250 ms) Example 2
Seal Temperature (.degree. F.) 220 230 240 250 260 270 280 290 300
310 320 330 340 350 Sample 1 0 0 21 28 37 48 58 60 66 64 113 92 58
51 Seal (g/in) Sample 2 0 0 25 30 39 48 57 65 64 118 110 85 65 55
Seal (g/in) Sample 3 0 0 25 21 41 46 51 69 65 83 124 71 58 53 Seal
(g/in) Avg. 0 0 24 26 39 47 55 65 65 88 116 83 60 53 Seal
(g/in)
[0067] TABLE-US-00006 TABLE F (500 ms) Example 2 Seal Temperature
(.degree. F.) 220 230 240 250 260 270 280 290 300 310 320 330 340
350 Sample 1 0 0 41 42 71 76 96 80 71 44 111 170 95 76 Seal (g/in)
Sample 2 0 0 44 48 60 69 81 85 71 81 127 149 101 120 Seal (g/in)
Sample 3 0 0 30 42 87 64 76 76 78 32 163 147 87 78 Seal (g/in) Avg.
0 0 38 44 73 70 84 80 73 52 134 155 94 91 Seal (g/in)
[0068] As can be seen by the data in the above tables and by FIGS.
3 and 4, Example 2 provides higher tack seal strength than
Comparative Example 1 over a broad temperature range.
Examples 2-3
[0069] Sample films of Examples 2 and 3 were formed by the steps
described above. Example 2 sample films comprise the composition
disclosed above. Example 3 sample films comprise: 61.16% by weight
PVC, 6.24% PVC/VA, 28.31% by weight plasticizer. The films of
Example 3 further comprise minor amounts of additives: 1.48% by
weight stabilizer, 2.02% by weight stabilizer, 0.33% by weight
slip, 0.17% by weight lubricant, and 0.30% by weight antiblock.
[0070] A film of Example 3 was formed with a gauge of 1 mil. The
film was tested for OTR and for heat sealing characteristics. The
film had a OTR of 818.8 cc/100 in.sup.2/24 hours. The film formed a
welded seal, beginning at a temperature of 356.degree. and a burn
through temperature of 416.degree., providing a 60.degree. F. heat
sealing window.
[0071] Table E above and Table G below show hot tack heat seal
strengths for Examples 2 and 3 over different sealing temperatures,
measured 250 milliseconds following heat sealing. Table F above and
Table H below, show heat seal strengths for Examples 2 and 3 from
sealing at temperatures ranging from 220.degree. F. to 350.degree.
F. FIG. 5 is a graph of the data in Tables E and G and FIG. 6 is a
graph of the data in Tables F and H. TABLE-US-00007 TABLE G (250
ms) Example 3 Seal Temperature (.degree. F.) 220 230 240 250 260
270 280 290 300 310 320 330 340 350 Sample 1 0 0 23 35 34 39 49 57
55 81 97 69 64 44 Seal (g/in) Sample 2 0 0 21 19 41 37 46 46 73 127
64 83 58 53 Seal (g/in) Sample 3 0 0 21 18 27 42 49 44 69 50 99 94
62 57 Seal (g/in) Avg. 0 0 22 24 34 39 48 49 66 86 87 82 61 51 Seal
(g/in)
[0072] TABLE-US-00008 TABLE H (500 ms) Example 3 Seal Temperature
(.degree. F.) 220 230 240 250 260 270 280 290 300 310 320 330 340
350 Sample 1 0 0 34 55 49 60 81 74 60 53 106 170 106 80 Seal (g/in)
Sample 2 0 0 25 37 64 64 83 76 90 48 73 134 113 126 Seal (g/in)
Sample 3 0 0 34 28 46 62 74 81 90 34 131 166 140 103 Seal (g/in)
Avg. 0 0 31 40 53 62 79 77 80 45 103 157 120 103 Seal (g/in)
[0073] As discussed above, the films of Example 3 comprise 6.24% by
weight PVC/VA and the films of Example 2 comprise 12.48% by weight
PVC/VA. As shown in FIGS. 5 and 6, both Examples 2 and 3 provide
films with broad heat sealing temperature ranges and good hot tack
seal strength.
Example 4 and Comparative Example 2
[0074] The sample films of Example 4 comprise: 55.87% by weight
PVC, 10.00 PVC/VA, and 18.99% by weight plasticizer. The films of
Example 4 further comprise minor amounts of additives: 1.56% by
weight stabilizer; 0.96% antifog; 0.12% by weight slip, 0.23%
lubricant; and 2.27% by weight antiblock.
[0075] The sample films of Comparative Example 2 comprise: 68.06%
by weight of PVC; 0% by weight of PVC/VA; and 26.24% by weight of
plasticizer. The films of Example 5 further comprise additives:
1.48% by weight stabilizer; 1.23% by weight of antifog; 0.13% by
weight of slip; 0.24% by weight lubricant; and 2.46% by weight
antiblock.
[0076] Three sample films of Example 4 and for Comparative Example
2 were tested for hot tack seal strength. The data from this
testing is shown in Tables I-L. TABLE-US-00009 TABLE I (500 ms)
Example 4 Seal Temperature (.degree. F.) 220 230 240 250 260 270
280 290 300 310 320 330 340 350 Sample 1 14 18 27 30 37 69 53 64 53
65 64 80 113 67 Seal (g/in) Sample 2 23 18 37 32 57 37 57 41 60 65
60 110 88 83 Seal (g/in) Sample 3 25 21 27 41 42 50 48 67 51 51 103
94 80 80 Seal (g/in) Avg. 21 19 30 34 45 52 53 57 55 60 76 95 94 77
Seal (g/in)
[0077] TABLE-US-00010 TABLE J (500 ms) Example 4 Seal Temperature
(.degree. F.) 220 230 240 250 260 270 280 290 300 310 320 330 340
350 Sample 1 26 30 42 49 51 65 60 83 57 72 46 191 159 207 Seal
(g/in) Sample 2 28 37 55 51 57 48 57 42 80 44 53 191 173 203 Seal
(g/in) Sample 3 34 37 37 67 57 71 53 72 42 67 74 205 218 179 Seal
(g/in) Avg. 29 35 45 56 55 61 57 66 60 61 58 196 183 196 Seal
(g/in)
[0078] TABLE-US-00011 TABLE K (500 ms) Comparative Example 2 Seal
Temperature (.degree. F.) 220 230 240 250 260 270 280 290 300 310
320 330 340 350 Sample 1 4 5 12 16 21 28 35 44 71 34 51 42 83 80
Seal (g/in) Sample 2 9 11 9 14 28 25 30 55 48 46 51 53 49 74 Seal
(g/in) Sample 3 4 9 12 18 16 18 41 35 46 41 39 55 64 69 Seal (g/in)
Avg. 6 8 11 16 22 24 35 45 55 40 47 50 65 74 Seal (g/in)
[0079] TABLE-US-00012 TABLE L (500 ms) Comparative Example 2 Seal
Temperature (.degree. F.) 220 230 240 250 260 270 280 290 300 310
320 330 340 350 Sample 1 12 16 27 30 34 41 60 55 58 51 60 34 71 147
Seal (g/in) Sample 2 18 19 21 30 37 42 49 51 58 48 57 42 51 150
Seal (g/in) Sample 3 12 21 21 35 37 48 51 50 62 41 58 41 57 141
Seal (g/in) Avg. 14 19 23 32 36 44 53 52 59 50 58 39 60 146 Seal
(g/in)
[0080] Similar to the results seen in FIGS. 1-2 for Example 1 and
Comparative Example 1, Example 4 has a broader heat seal range than
Comparative Example 2. Example 4 also provides good hot tack seal
strengths over a wide range of sealing temperatures.
[0081] It will be obvious to those having skill in the art that
many changes may be made to the details of the above-described
embodiments without departing from the underlying principles of the
invention. The scope of the present invention should, therefore, be
determined only by the following claims.
* * * * *