U.S. patent application number 12/272469 was filed with the patent office on 2009-08-20 for polyester film having latent shrink properties and process for producing same.
This patent application is currently assigned to Mitsubishi Polyester Film, Inc.. Invention is credited to Jose Alfaro, Robert W. Finke, Ghulam Mustafa A. Sange.
Application Number | 20090208682 12/272469 |
Document ID | / |
Family ID | 40340556 |
Filed Date | 2009-08-20 |
United States Patent
Application |
20090208682 |
Kind Code |
A1 |
Alfaro; Jose ; et
al. |
August 20, 2009 |
Polyester Film Having Latent Shrink Properties and Process for
Producing Same
Abstract
A film layer is disclosed that is capable of shrinking when
subjected to energy, such as heat. The film layer, for instance,
can be formed and then stretched in one or two directions at a
relatively low temperature. In particular, the film is stretched
while the film layer is at a temperature near the glass transition
temperature of the polymer used to form the film. Drawing the film
at a relatively low temperature has been found to improve the
shrink properties of the film. In one embodiment, the film layer is
comprised of a non-modified polyester, such as polyethylene
terephthalate. For example, the polyethylene terephthalate can be
made by reacting terephthalic acid with ethylene glycol or
polyethylene glycol.
Inventors: |
Alfaro; Jose; (Greenville,
SC) ; Finke; Robert W.; (Greer, SC) ; Sange;
Ghulam Mustafa A.; (Greer, SC) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Assignee: |
Mitsubishi Polyester Film,
Inc.
Greer
SC
|
Family ID: |
40340556 |
Appl. No.: |
12/272469 |
Filed: |
November 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61036746 |
Mar 14, 2008 |
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61035159 |
Mar 10, 2008 |
|
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60989644 |
Nov 21, 2007 |
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Current U.S.
Class: |
428/34.9 ;
264/173.16; 264/210.1; 264/291; 428/195.1; 428/203; 428/343;
428/480; 524/425; 524/599; 528/271; 528/272 |
Current CPC
Class: |
B32B 2264/104 20130101;
C08J 5/18 20130101; Y10T 428/1328 20150115; B32B 2307/412 20130101;
B32B 2250/244 20130101; B32B 2307/414 20130101; B32B 2264/102
20130101; C08J 2367/00 20130101; B32B 27/42 20130101; B32B 27/08
20130101; B32B 2250/03 20130101; B32B 2307/704 20130101; C09J 7/29
20180101; B32B 2519/00 20130101; Y10T 428/28 20150115; Y10T
428/31786 20150401; B32B 1/08 20130101; B32B 27/20 20130101; B32B
2255/10 20130101; B32B 2307/518 20130101; C09J 5/06 20130101; Y10T
428/24802 20150115; C08J 2367/02 20130101; Y10T 428/24868 20150115;
C09J 2203/334 20130101; B32B 27/32 20130101; B32B 2307/736
20130101; B32B 2264/108 20130101; B32B 7/02 20130101; C09J 2301/502
20200801; B32B 27/36 20130101; B32B 2307/4026 20130101; C09J
2467/006 20130101; B29C 55/005 20130101; B32B 2405/00 20130101 |
Class at
Publication: |
428/34.9 ;
428/480; 428/343; 428/195.1; 428/203; 264/291; 264/210.1;
264/173.16; 528/271; 528/272; 524/599; 524/425 |
International
Class: |
B65B 53/02 20060101
B65B053/02; B32B 27/36 20060101 B32B027/36; B32B 7/12 20060101
B32B007/12; B32B 3/10 20060101 B32B003/10; B29C 55/16 20060101
B29C055/16; B29C 55/04 20060101 B29C055/04; B29C 47/06 20060101
B29C047/06; C08G 63/00 20060101 C08G063/00; C08G 63/02 20060101
C08G063/02; C08L 67/00 20060101 C08L067/00; C08K 3/26 20060101
C08K003/26 |
Claims
1. A film product comprising: a film layer comprising a polyester
polymer, the film layer having been stretched in at least one
direction, the polyester polymer being at least partially in
crystalline form, and wherein the film layer shrinks at least 10%
in the one direction when subjected to a temperature of 80.degree.
C. for three minutes.
2. A film product as defined in claim 1, wherein the film layer
comprises a mono layer of the polyester polymer.
3. A film product as defined in claim 1, wherein the film product
comprises a plurality of coextruded film layers.
4. A film product as defined in claim 1, wherein the polyester
polymer comprises polyethylene terephthalate.
5. A film product as defined in claim 1, wherein the film layer has
been biaxially stretched in both a longitudinal direction and in a
lateral direction, and wherein the film layer shrinks at least 10%
in both the lateral direction and the longitudinal direction when
subjected to a temperature of 80.degree. C. for three minutes.
6. A film product as defined in claim 1, wherein the film layer has
been biaxially stretched in both a longitudinal direction and in a
lateral direction, and wherein the film layer shrinks at least 20%
in both the lateral direction and the longitudinal direction when
subjected to a temperature of 80.degree. C. for three minutes.
7. A film product as defined in claim 1, wherein the film layer
contains a filler.
8. A film product as defined in claim 7, wherein the filler
comprises calcium carbonate particles.
9. A film product as defined in claim 1, wherein the polyester
polymer comprises a non-modified polyester polymer.
10. A film product as defined in claim 9, wherein the polyester
polymer comprises the polycondensation reaction product of ethylene
glycol and terephthalic acid.
11. A label incorporating the film product defined in claim 1.
12. A label as defined in claim 11, further comprising an adhesive
layer disposed on an exterior surface of the film product for
adhering the label to adjacent objects.
13. A label as defined in claim 12, further comprising a print
layer containing printed matter, the print layer being visible from
an exterior surface of the label opposite where the adhesive layer
is disposed.
14. A label as defined in claim 13, wherein the print layer is
positioned in between the adhesive layer and the film layer.
15. A label as defined in claim 13, wherein the film layer is
positioned in between the adhesive layer and the print layer.
16. A film product as defined in claim 1, wherein the product is in
the shape of a continuous tube that is configured to be shrink
wrapped over a container.
17. A process for producing a shrinkable film comprising: forming a
film layer, the film layer comprising a polyester polymer; cooling
the film layer to a temperature that is within about 30% of the
glass transition temperature of the polyester polymer; and
thereafter stretching the film layer in at least one direction.
18. A process as defined in claim 17, wherein the film layer is
stretched both in a longitudinal direction and in a lateral
direction.
19. A process as defined in claim 18, wherein the film layer has an
original length in the longitudinal direction and an original
length in the lateral direction and wherein the film is stretched
from about 1 to about 4 times its original length in both
directions.
20. A process as defined in claim 17, wherein the polyester polymer
comprises a non-modified polyethylene terephthalate.
21. A process as defined in claim 17, wherein the film layer is
formed by heating the polyester polymer into a molten state and
then extruding the molten polymer through an extruder.
22. A process as defined in claim 21, wherein the film layer is
extruded with at least one other film layer.
23. A process as defined in claim 17, wherein the film layer is
cooled by passing the film layer over a surface of a chilled
roller, the surface of the chilled roller being at a temperature of
less than about 30.degree. C.
24. A process as defined in claim 17, wherein the film layer is
stretched while the film layer is at a temperature of less than
about 120.degree. C.
25. A process as defined in claim 17, wherein the film layer is
stretched while the film layer is at a temperature of less than
about 90.degree. C.
26. A process as defined in claim 17, wherein the film layer is not
heat treated after being stretched.
Description
RELATED APPLICATIONS
[0001] The present application is based upon and claims priority to
U.S. Provisional Patent Application Ser. No. 61/036,746, filed on
Mar. 14, 2008, U.S. Provisional Patent Application Ser. No.
61/035,159, filed on Mar. 10, 2008, and U.S. Provisional Patent
Application Ser. No. 60/989,644, filed on Nov. 21, 2007.
BACKGROUND
[0002] Polymer films that are designed to shrink when exposed to
heat are useful for many diverse and different applications. Such
films, for instance, can be used as packaging materials, binding
materials, covering materials, sealing materials, or labeling
materials.
[0003] When used as a label, for instance, the film may be formed
into a tube and then placed around a container. Once placed around
the container, the film may be exposed to heat causing the tube to
shrink and tightly fit around the container.
[0004] In an alternative embodiment, the shrinkable film can be
coated with an adhesive and applied to a container. After the
container has been used, the container is subjected to heat causing
the film to shrink and detach from the container. Once detached,
the container can then be cleaned, refilled and reused as
desired.
[0005] In the past, various different types of films have been
proposed for shrink applications. Polyester-based shrink films are
particularly advantageous for use on polyester containers, as they
facilitate the recycling process by allowing the polyester
containers to be reclaimed along with their polyester labels
without introducing incompatible resins into the recycling stream.
Thus, in the past, polyester polymers have been modified in order
to increase their shrink properties. Such polyester films, for
instance, are disclosed in U.S. Pat. No. 5,407,752, U.S. Pat. No.
6,630,230, U.S. Pat. No. 6,765,070, U.S. Pat. No. 7,008,698, and
U.S. Pat. No. 7,195,822, which are all incorporated herein by
reference.
[0006] Although the above patents have made great advances in the
art, as described above, the polyester polymers were chemically
modified or copolymerized with other materials in order to obtain
the desired shrink properties.
[0007] Various other polymers have also been proposed for use in
producing shrinkable films. For instance, in U.S. Pat. No.
6,680,097, which is also incorporated herein by reference,
self-adhesive film labels are disclosed containing a stretched film
layer, which shrinks when subjected to elevated temperatures. In
the '097 patent, polyvinyl chloride is taught as the preferred
material used to form the shrinkable film. The '097 patent also
discusses using shrinkable polyester films. The polyester films,
however, are shown to have less than 10% shrinkage when subjected
to a temperature of 80.degree. C. and generally showed a
significantly more weakly pronounced longitudinal shrinkage when
compared to PVC films.
[0008] Various disadvantages, however, may be experienced when
attempting to use polyvinyl chloride as a shrinkable film.
Polyvinyl chloride resins, for instance, have had problems with
heat resistance, weather resistance, chemical resistance, and the
like. Polyvinyl chloride films, for instance, are liable to
experience the frequent occurrence of fish eye when the film is
subjected to printing. Further, problems have also been experienced
in properly disposing polyvinyl chloride films, especially when
trying to incinerate the films.
[0009] In view of the above, a need currently exists for an
improved shrinkable film. In particular, a need currently exists
for a shrinkable film made from a polyester polymer that does not
necessarily have to be modified or combined with other polymers in
order to impart desirable shrink properties.
SUMMARY
[0010] In general, the present disclosure is directed to a
shrinkable film product. The film product, for instance, includes
at least one film layer that shrinks when exposed to sufficient
amounts of a suitable energy, such as heat. Of particular
advantage, in one embodiment, the shrinkable film layer can be
formed primarily from a non-modified polyester polymer. As used
herein, an "non-modified" polyester polymer refers to a polyester
polymer in which one of the monomers to form the polymer has not
been at least partially replaced with an additional monomer and/or
does not include polyester polymers that have been copolymerized
with other polymers. For example, in one embodiment, the polyester
polymer can be formed through a polycondensation reaction
essentially from a glycol with a dicarboxylic acid. For example, in
one particular embodiment, the polyester polymer comprises
polyethylene terephthalate formed essentially from polyethylene
glycol and terephthalic acid.
[0011] It should be understood, however, that in other embodiments
a modified polyester may be used.
[0012] Shrinkable films are made according to the present
disclosure by stretching or drawing the films while at a relatively
low temperature, such as near the glass transition temperature of
the polymer. As used herein, the glass transition temperature is
determined using differential scanning calorimetery (DSC). The
present inventors have discovered that cold drawing the film can
significantly enhance the shrink properties of the polymer.
[0013] In one embodiment, for instance, the present disclosure is
directed to a process for producing a shrinkable film. The process
includes the steps of first forming a film layer that comprises a
polyester polymer. The polyester polymer may comprise, for
instance, polyethylene terephthalate. In one embodiment, the
polyester polymer is non-modified. For instance, the polyester
polymer can comprise the polycondensation reaction product of
primarily a single diol, such as polyethylene glycol, and
terephthalic acid.
[0014] The film layer can be initially formed by heating the
polyester polymer to form a molten polymer and then extruding the
molten polymer through an extruder to form the film.
[0015] After the film layer is formed, the film layer is cooled to
a temperature near the glass transition temperature of the
polyester polymer. In accordance with the present disclosure, the
film layer is then thereafter stretched in at least one direction.
For instance, in one embodiment, the film layer can be uniaxially
stretched. Alternatively, the film layer may be biaxially stretched
such as in both the longitudinal direction and the lateral
direction. The film layer can be stretched, for instance, from
about 1 to about 5 times its original length, such as from about 3
times to about 4 times its original length in one or both
directions.
[0016] In order to cool the film layer after being formed, in one
embodiment, the film layer can be conveyed over the surface of a
chilled roller. The surface of the chilled roller can be at a
temperature, for instance, of less than about 30.degree. C., such
as less than about 25.degree. C. Once cooled, the film layer can be
stretched. For example, in one embodiment, the film layer can be
cooled to a temperature of less than about 120.degree. C., such as
less than about 100.degree. C., such as less than about 90.degree.
C., such as from about 60.degree. C. to about 120.degree. C. In one
embodiment, after being stretched, the film layer is not subjected
to any heat treatment or annealing.
[0017] Films made in accordance with the present disclosure can be
used in numerous products and have various benefits and advantages.
Film layers made according to the present disclosure, for instance,
can be at least partially crystalline after being stretched and can
be configured to shrink at least 10% in at least one direction when
subjected to a temperature of 80.degree. C. for three minutes. For
instance, in one embodiment, film layers can be produced from a
polyester polymer that can shrink from about 10% to about 40%, such
as from about 20% to about 40% when subjected to a temperature of
80.degree. C. for three minutes. As described above, shrinkage can
occur in only one direction or, alternatively, shrinkage can occur
in both the longitudinal direction and the lateral direction.
[0018] Film products made according to the present disclosure can
comprise a monolayer product containing the polyester polymer or
can comprise a coextruded product having a plurality of layers.
When containing a plurality of layers, each layer can be made from
the same polymer or from a different polymer.
[0019] In one embodiment, the film product can be incorporated into
a label. In one particular application, for instance, the label may
include an adhesive layer positioned on an exterior surface. The
adhesive layer may be for adhering the label to a container or
other object. After the container or other object has been used,
the label can then be washed off by subjecting the label to water
at an elevated temperature.
[0020] In an alternative embodiment, the film product of the
present disclosure can be formed into a tube and then placed around
a container. In this embodiment, the tube can be subjected to heat
or another energy source that causes the tube to shrink and tightly
fit around the container.
[0021] When the film product is incorporated into a label, in one
embodiment, the label may include a print layer. For instance, in
one embodiment, the print layer can be positioned in between an
adhesive layer and the film layer containing the polyester polymer.
In an alternative embodiment, the film layer containing the
polyester polymer may be positioned in between the adhesive layer
and the print layer.
[0022] Other features and aspects of the present disclosure are
discussed in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] A full and enabling disclosure of the present invention,
including the best mode thereof to one skilled in the art, is set
forth more particularly in the remainder of the specification,
including reference to the accompanying figures, in which:
[0024] FIG. 1 is a cross sectional view of one embodiment of a film
product made in accordance with the present disclosure;
[0025] FIG. 2 is a cross sectional view of another embodiment of a
film product made in accordance with the present disclosure;
[0026] FIG. 3 is a cross sectional view of still another embodiment
of a film product made in accordance with the present disclosure
that has been formed into a tube; and
[0027] FIGS. 4 through 6 are graphical representations of the
results obtained in the Examples below.
[0028] Repeat use of reference characters in the present
specification and drawings is intended to represent the same or
analogous features or elements of the present invention.
DETAILED DESCRIPTION
[0029] It is to be understood by one of ordinary skill in the art
that the present discussion is a description of exemplary
embodiments only, and is not intended as limiting the broader
aspects of the present invention.
[0030] In general, the present disclosure is directed to a
shrinkable film made from a polyester polymer. The film can be used
in numerous products and applications. For instance, films made
according to the present disclosure may be used as a packaging
material in order to shrink wrap perishable and non-perishable
goods. The film can also be incorporated into binding materials,
covering materials, and sealing materials. In yet another
embodiment, the film can be incorporated into a label that is
applied to a container. The latent shrink properties of the film
can be used to either adhere the label to a container in a shrink
wrap process or to remove the label from the container once the
container has been emptied or otherwise used.
[0031] The shrinkable film layer of the present disclosure is
generally made from a polyester polymer. In order to enhance the
shrink properties of the film, the film is uniaxially or biaxially
stretched while the film is at a relatively low temperature. For
instance, in accordance with the present disclosure, the film is
subjected to a "cold draw" process by which the film is drawn in
one direction or in two directions while at a temperature of less
than about 120.degree. C. such as near the glass transition
temperature of the polyester polymer. For instance, each time the
film is stretched, the film can be at a temperature that is within
about 30%, such as within about 25%, such as within about 20%, such
as within about 15% of the glass transition temperature of the
polymer (above or below). After the film is stretched, the film is
generally not subjected to any heat treatment or annealing
process.
[0032] The present inventors have discovered that by drawing the
film at relatively low temperatures, the shrink properties of the
film are greatly enhanced when the film is later subjected to
energy, such as heat. Although unknown, it is believed that by
drawing the film at a relatively low temperature, the film assumes
a crystalline structure that, when later heated, causes the film to
retract and shrink a great deal more than if the film were
stretched at a higher temperature.
[0033] Films made according to the present disclosure, for example,
shrink at least 10% of their length in at least one direction when
subjected to a temperature of 80.degree. C. for three minutes. The
films can be subjected to the above temperature by, for instance,
submerging the film into a water bath, contacting the film with a
heated gas, such as air, contacting the film with radiation such as
infrared radiation, or by otherwise heating the film. Films made
according to the present disclosure typically shrink in each
direction that the film has been stretched. Thus, if the film has
been biaxially stretched at a relatively low temperature, then the
film will shrink in both the longitudinal direction and the lateral
direction when subjected to energy in a sufficient amount.
[0034] The amount of shrinkage incorporated into the film can vary
depending upon different factors. For instance, in certain
embodiments, the film may shrink at least 20%, such as at least
30%, such as at least 40%, such as at least 50%, such as even
greater than about 60% in at least one direction when subjected to
a temperature of 80.degree. C. for three minutes. In addition, the
film can be constructed so as to have dual shrink properties
meaning that the film can stretch not only in the longitudinal
direction, but also in the lateral direction. In fact, films can be
constructed so that they will shrink in both the longitudinal
direction and in the lateral direction in the amounts described
above.
[0035] In one particular embodiment, for instance, a polyester film
can be constructed according to the present disclosure that begins
to shrink at temperatures less than 70.degree. C., such at
temperatures of less than 65.degree. C. when, for instance,
submerged in a water bath. For example, polyester films made
according to the present disclosure can shrink from about 2% to
about 5% in both the longitudinal direction and the lateral
direction when submerged in a water bath at a temperature of
60.degree. C. At 70.degree. C., the films can shrink at least 10%
in both the longitudinal direction and the lateral direction, such
as in an amount from about 10% to about 25%. At 80.degree. C., the
films can shrink at least about 15% in both directions, such as
from about 15% to about 30%. At 90.degree. C., the films can shrink
at least about 20% in both directions, such as from about 20% to
about 35%. At 100.degree. C., the films can shrink in both
directions in an amount of greater than about 25%, such as from
about 25% to about 40% or greater.
[0036] During shrinking, the films display a force in the direction
of contraction known as the shrink force. Films made according to
the present disclosure, for instance, can display a maximum shrink
force of greater than about 5 N/15 mm, such as greater than about 8
N/15 mm, such as greater than about 10 N/15 mm, such as greater
than about 12 N/15 mm, such as even greater than about 15 N/15 mm.
For instance, the films can display a shrink force in the
longitudinal direction or machine direction in an amount from about
5 N/15 mm to about 10 N/15 mm. In the transverse direction, on the
other hand, the films can display a shrink force of from about 8
N/15 mm to about 15 N/15 mm. The maximum shrink force can occur at
a temperature of from about 65.degree. C. to about 85.degree.
C.
[0037] Films made according to the present disclosure can also be
relatively stiff in comparison to other polyester films at the same
thickness. Increased stiffness can provide various advantages. For
instance, the relatively stiff film may be easier to handle when
applied or removed from an adjacent object.
[0038] Of particular advantage, in one embodiment, the polyester
polymer used to form the film can be non-modified. In the past, for
instance, non-modified polyester polymers were generally considered
not to have sufficient shrinkage properties for incorporation into
many shrink applications. Thus, in order to increase the shrinkage
properties of the polymer, the polyester polymers were typically
chemically modified or copolymerized. In accordance with the
present disclosure, however, a film made primarily from an
non-modified polyester polymer can be constructed so as to shrink
from about 10% to about 40% or even greater in at least one
direction when subjected to a temperature of 80.degree. C. for
three minutes.
[0039] The shrinkable film layer, for instance, can contain the
non-modified polyester polymer in an amount greater than 60% by
weight, such as greater than 70% by weight, such as greater than
80% by weight, such as greater than 90% by weight, such as even
greater than about 95% by weight.
[0040] The polyester polymer used to form the film layer in
accordance with the present disclosure may comprise the
polycondensation reaction product of a glycol or diol with a
dicarboxylic acid or its ester equivalent. Dicarboxylic acids that
may be used include terephthalic acid, isophthalic acid, sebacic
acid, malonic acid, adipic acid, azelaic acid, glutaric acid,
suberic acid, succinic acid, and the like, or mixtures of two or
more of the following may be used. Suitable glycols include
ethylene glycol, diethylene glycol, polyethylene glycol and polyols
such as butane diol and the like. The polyester may comprise, for
instance, polyethylene terephthalate, polyethylene naphthalate or
polybutylene terephthalate.
[0041] When using a non-modified polyester to produce the film
layer, for instance, the polyester may comprise essentially the
reaction product of the dicarboxylic acid with a glycol or diol.
For instance, in one particular embodiment, the polyester polymer
comprises a non-modified polymer consisting essentially of the
polycondensation reaction product of ethylene glycol, diethylene
glycol, or polyethylene glycol and terephthalic acid to produce
polyethylene terephthalate.
[0042] It should be understood, however, that modified polyesters
may also be used in the process. In particular, the cold drawing
process of the present disclosure may also increase the shrinkage
properties of chemically modified polymers, which includes
copolymers. For instance, in one embodiment, the polyester polymer
may comprise a copolyester polymer such as polyethylene
terephthalate isophthalate.
[0043] Modified polyesters that may be used in the present
disclosure include, for instance, polymers that are formed from
modified acids and/or modified glycols. In one embodiment, for
instance, the polyester polymer might be only slightly modified.
For instance, less than 10 mole percent, such as less than about 5
mole percent of the acid component and/or the glycol component can
be modified.
[0044] In another embodiment, a modified polymer may be used that
comprises a blend of polyester polymers. For instance, a film can
be produced from a polyester polymer blended with a copolyester.
Such polyester blends are disclosed, for instance, in U.S. Pat. No.
6,599,994, which is incorporated herein by reference.
[0045] In producing the shrinkable film layer, the polyester
polymer may be combined with various additives as may be desired.
Such additives can include, for instance, fillers that may impart
slip, opacity or color, lubricants, antioxidants, and the like.
Fillers that may impart a slipping property into the film layer,
for example, may include inorganic particles such as microparticles
of silca, talc, kaolin, and calcium carbonate, organic polymer
microparticles such as those of poly(meta)acrylic resin,
polystyrene resin, and polytetrafluoroethylene resin, cross-linked
microparticles of these organic polymers and the like. These
particles can have a mean particle diameter, for instance, of from
about 0.1 to about 10 microns.
[0046] Fillers can also be added to the film layer in order to
provide color. In this embodiment, for instance, the filler or
pigment may comprise, for instance, titanium dioxide particles,
metal oxide particles, carbon particles, and the like. In general,
any suitable pigment particle may be incorporated into the film in
order to provide the film layer with the proper color and/or
opacity.
[0047] Other additives that may be incorporated into the film layer
may include, for instance, lubricants, such as calcium stearate,
sodium stearate, magnesium stearate, and the like, antioxidants,
delusterants, and/or antistatic agents.
[0048] In order to form the film layer, in one embodiment, the film
layer can be produced through an extrusion process. For example,
the polyester polymer and any additives used to form the film layer
can be melted and then extruded into a sheet onto a polished
revolving casting drum to form a cast film. The film can then be
quickly cooled and then stretch oriented in one or more directions.
In accordance with the present disclosure, as described above, the
film is cooled to a temperature near the glass transition
temperature of the polyester polymer prior to stretching.
[0049] The formed film can be cooled using any suitable method or
technique. In one embodiment, for instance, the film may be
contacted with a rotating chilled roller. The chilled roller, for
instance, may include an outside surface that is brought into
contact with the film. The roller may be cooled using any suitable
technique, such as by circulating cold water through the roller.
For example, in one embodiment, the surface temperature of the
roller may be less than about 40.degree. C., such as less than
about 30.degree. C., such as from about 15.degree. C. to about
25.degree. C.
[0050] The film layer is contacted with the surface of the roller
an amount of time sufficient to lower the temperature of the film
layer to near or below the glass transition temperature of the
polyester polymer. The glass transition temperature of the polymer
may depend, for instance, on the crystallinity of the polymer. The
more crystalline the polymer is, for instance, the higher the glass
transition temperature.
[0051] When the formed film is cooled as described above and
effectively quenched, the film, in one embodiment, can be primarily
amorphous. When processing polyethylene terephthlate, for example,
the glass transition temperature of the amorphous film can be
approximately 67.degree. C. After being cooled, the film layer can
then be stretched in either one direction or in both the
longitudinal direction and the lateral direction. In one
embodiment, for instance, the film layer after being cooled can be
first stretched in the longitudinal direction, which is sometimes
referred to as the machine direction. The film can be stretched in
the machine direction using, for instance, one or more draw
rollers. The film layer, in one embodiment, can be stretched in the
longitudinal direction while at a temperature that is within about
30% of the glass transition temperature. For instance, the film
layer can be stretched while at a temperature that is within at
least about 25%, such as at least about 20%, such as within about
15% of the glass transition temperature of the polymer.
[0052] Alternatively, the film layer can be stretched within a
particular temperature range without reference to the glass
transition temperature. For instance, the film layer can be
stretched in the machine direction while at a temperature of from
about 55.degree. C. to about 120.degree. C., such as from about
70.degree. C. to about 110.degree. C.
[0053] Stretching the film in the longitudinal direction will
generally increase the crystallinity of the film and therefore
increase the glass transition temperature (such as to about
80.degree. C.). In one embodiment, after being stretched in the
longitudinal direction, the film can then be stretched in the
lateral direction. For instance, in one particular embodiment, the
film can be reheated while on a tenter frame to a temperature that
is within about 30% of the new glass transition temperature of the
polymer, such as within about 25% of the new glass transition
temperature, such as within about 20% of the new glass transition
temperature, such as within about 15% of the new glass transition
temperature. When heated on a tenter frame, the tenter frame
generally travels through an oven during or prior to stretching.
While on the tenter frame, the film typically enters a
crystallizing zone. According to the present disclosure, the
temperature within the crystallizing zone, in one embodiment, can
be from about the dew point to about 70.degree. C., such as from
about the dew point to about 50.degree. C.
[0054] As explained above, in one embodiment, the film can be
stretched in only a single direction. The single direction can be
the longitudinal direction or the lateral direction. When only
stretching the film in the lateral direction, for instance, the
film may be immediately placed on the tenter frame after formation
and stretched as opposed to being reheated as described above.
[0055] Regardless of the glass transition temperature, the
temperature of the film layer during stretching in the transverse
direction, in one embodiment, can vary from about 60.degree. C. to
about 120.degree. C., such as from about 70.degree. C. to about
100.degree. C. Stretching can be primarily carried out using a
mechanical force as opposed to heating the polymer to a temperature
sufficient for the polymer to flow.
[0056] Stretching the film as described above has been found to
increase the latent stretch properties of the polymer. In addition,
stretching the film also imparts strength and toughness to the
film. As explained above, films made according to the present
disclosure also have great stiffness properties making the films
easier to handle. For instance, the films generally are stiffer
than many comparative films allowing for higher application speeds
and for lower thicknesses.
[0057] The amount the film is stretched can depend upon various
factors. When uniaxially stretched, the film can be stretched in
one direction (such as the machine direction or the cross machine
direction) in an amount from about 1 time to about 5 times its
original length, such as from about 3 times to about 4 times its
original length. When biaxially stretched, the film can be
stretched in a perpendicular direction in an amount from about 1
time to about 5 times its original length, such as from about 3
times to about 4 times its original length. In general, the greater
the amount the film is stretched, the greater amount of latent
shrink is incorporated into the product.
[0058] The final thickness of the film layer can vary depending
upon the amount the film layer is stretched and the particular
application for which the film layer is to be used. In general, the
film layer can have a thickness of from about 10 microns to about
500 microns or greater. In one embodiment, for instance, the film
layer can have a thickness of less than about 150 microns, such as
from about 35 microns to about 55 microns.
[0059] In some applications, it may be desirable to control the
amount of haze that is contained in the film layer after being
formed. The present inventors have discovered that by carefully
controlling the temperature of the film during stretching and the
amount the film is stretched, the amount of haze incorporated into
the film layer can be minimized while also dramatically increasing
the stretch properties of the film. In general, stretching the film
at temperatures much lower than the glass transition temperature of
the polymer may increase the haze of the film. Thus, when haze is
an important attribute of the resulting product, stretching may
occur while the temperature of the film layer is not more than
about 10.degree. C., such as not more than about 5.degree. C. lower
than the glass transition temperature. Film layers made according
to the present disclosure can have less than about 8% haze, such as
less than about 5% haze, such as even less than about 3% haze. Haze
is determined according to ASTM Test Method D-1003.
[0060] When incorporating the shrinkable film layer of the present
disclosure into a usable product, the film layer may be used alone
or in combination with other layers. For instance, the film layer
may be coextruded with other polymer layers or may be adhesively
secured to other layers after the film layer has been formed.
[0061] When coextruding the shrinkable film layer with other
layers, the other layers may comprise the same polymer or a
different polymer. For instance, in one embodiment, two or more
film layers may be extruded together all comprising the same
polyester polymer. Different additives, such as an anti-slip agent
or pigment particles, may be included in each of the layers in
different amounts for a desired result.
[0062] In an alternative embodiment, different polymers may be
incorporated into the different film layers. The different polymer
may comprise, for instance, a polyolefin polymer, such as
polyethylene or polypropylene or another type of polyester polymer.
For instance, in one embodiment, a film product can be produced
containing a shrinkable film layer comprising an non-modified
polyester polymer that is coextruded with at least one other film
layer containing a modified polyester polymer.
[0063] If desired, a composite film can be produced having multiple
layers in which each layer has different shrink properties. For
instance, one film layer may shrink greater than 10%, such as
greater than 20%, such as greater than 30%, such as greater than
40%, such as even greater than 50% in one direction as opposed to
another layer contained within the composite film.
[0064] As described above, the film layer of the present disclosure
may be used in numerous applications. In one embodiment, for
instance, the shrinkable film layer can be incorporated into a
label for application to a container, such as a beverage container.
When incorporated into a label, the shrink properties of the film
layer may be utilized in different ways. For instance, in one
embodiment, the shrinkable film layer may be used to shrink wrap
the label onto the container. In an alternative embodiment, the
shrink layer can be used to remove the label from the container,
once the container has been used.
[0065] Referring to FIGS. 1 through 3, various embodiments of
labels made in accordance with the present disclosure are shown.
For instance, a label 10 is shown in FIG. 1. As illustrated, the
label includes a film layer 12 made in accordance with the present
disclosure. In particular, film layer 12 is made from a polyester
polymer that is shrinkable when exposed to heat. The film layer 12
may comprise a monolayer film or may comprise multi-layers of film
that have been coextruded together. For instance, in one
embodiment, three layers all made from a polyester polymer are
coextruded together to form the composite layer 12.
[0066] Adjacent to one surface of the film layer 12 is a print
layer 14. The print layer 14 is intended to be visible through the
shrinkable film layer 12. Thus, in this embodiment, the film layer
12 is transparent or at least translucent. The print layer 14 may
comprise, for instance, any suitable printed design or wording as
may be necessary or desired for the particular application.
[0067] Opposite the print layer 14 is an adhesive layer 16 for
adhering the label 10 to a container or adjacent surface. The
adhesive layer 16 may comprise any suitable adhesive. The adhesive
used to produce the adhesive layer 16 may be selected, for
instance, based upon whether or not the label is intended to be
shrunk and washed off later and depending upon the type of surface
that the label is to be adhered to.
[0068] In one embodiment, for instance, the adhesive layer may
contain a hot melt adhesive, a glue, a radiation curing adhesive,
or a thermally melting adhesive.
[0069] When label 10 comprises a wash-off label, for instance, the
adhesive may comprise an aqueous acrylate dispersion. Still other
adhesives include water-soluble adhesives, water-swellable
adhesives, adhesives that include water-soluble or water-swellable
backbone binders, and the like. For instance, the adhesive may be
based upon an acrylate, polyvinyl alcohol, polyglycolic acid, a
polylactide, and the like.
[0070] In an alternative embodiment, the adhesive may comprise a
pressure sensitive adhesive or a thermally sensitive adhesive.
Solvent adhesives are also suitable for use in the present
disclosure. Solvent adhesives may contain, for instance, natural or
synthetic rubber, such as styrene-butadiene-styrene block
copolymers, styrene-isoprene-styrene block copolymers, and the
like.
[0071] When used in a wash-off label application, the label 10 as
shown in FIG. 1 is applied to a container. Once the container has
been used and it is desirable to remove the label, the container is
then immersed in a hot aqueous bath. The bath may contain, for
instance, water combined with a base, such as sodium hydroxide. The
temperature of the water may be from about 70.degree. C. to about
90.degree. C. Once submerged in the hot water, the film layer 12
shrinks causing the entire label to detach from the container.
[0072] Another embodiment of a label 10 made in accordance with the
present disclosure is shown in FIG. 2. Like reference numerals have
been used to indicate similar elements. In this embodiment, the
shrinkable film layer 12 is positioned in between the adhesive
layer 16 and a print layer 14. As shown, in this embodiment, the
print layer 14 is no longer protected by the film layer 12. Thus,
the label 10 may further include a protective layer 18. The
protective layer 18 may comprise, for instance, a lacquer or a
protective film layer.
[0073] Referring to FIG. 3, still another embodiment of a label 10
made in accordance with the present disclosure is shown. Again,
like reference numerals have been used to indicate similar
elements. In the embodiment illustrated in FIG. 3, the label 10 is
in the form of a tube that is intended to be shrink wrapped onto a
container.
[0074] As shown, the label 10 includes a film layer 12 made in
accordance with the present disclosure. In particular, the film
layer 12 is comprised of a polyester polymer and is shrinkable when
exposed to energy, such as heat.
[0075] The label 10 further includes a seam 22 formed by bonding
together the two ends of the composite film. In order to facilitate
bonding, the label 10 further includes a skin layer 20. The skin
layer 20 can be, for instance, coextruded with the film layer 12
and can be made from a material that allows for the ends of the
composite film to bond together.
[0076] For example, in one embodiment, the ends of the composite
film can be bonded together using a solvent. More particularly, a
solvent is contacted with the skin layer 20 which causes the skin
layer to bond to the film layer 12 and form the seam 22.
[0077] Examples of skin layers that may be used in accordance with
the present disclosure are disclosed, for instance, in U.S. Pat.
No. 5,407,752 and in U.S. Pat. No. 6,765,070. For instance, in one
embodiment, the skin layer comprises a polyester polymer comprised
of a dicarboxylic acid component composed mainly of an aromatic
dicarboxylic acid or its ester forming derivative and a diol
component composed mainly of ethylene glycol and an ethylene oxide
adduct of a bisphenol compound or its derivative. The dicarboxylic
acid component may include, for instance, terephthalic acid and
isophthalic acid or their ester forming derivatives.
[0078] In an alternative embodiment, the skin layer may comprise a
copolymerized polyester resin comprising a polyethylene
terephthalate resin and a polybutylene terephthalate resin, wherein
the polyethylene terephthalate resin is present in an amount from
about 50% to about 95% by weight based on the total amount of the
resin present. In this embodiment, the polyethylene terephthalate
resin may be produced by reacting terephthalic acid and isophthalic
acid with ethylene glycol. The isophthalic acid may be present in
an amount from about 3 to about 30 mol percent based upon the total
amount of dicarboxylic acids present. In addition, the ethylene
glycol may be present in conjunction with cyclohexan dimethanol in
an amount from about 3 to about 40 mol percent based upon the total
diols present.
[0079] In addition to the above, any suitable skin layer may also
be used.
[0080] When bonding the skin layer 20 to the film layer 12, a
solvent, such as tetrahydrofuran or 1,4 dioxylene are contacted
with the skin layer at the desired area and the skin layer is then
brought into contact with the film layer 12.
[0081] The present disclosure may be better understood with
reference to the following Example.
EXAMPLES
Example 1
[0082] Two different film samples made in accordance with the
present disclosure were produced and tested for their shrinkage
characteristics.
[0083] The film samples were made from a polyethylene terephthalate
(PET) homopolymer. In order to produce the film samples, the PET
resin was melted and extruded to form a molten film layer. In
particular, the molten polymeric material was extruded into a sheet
onto a polished revolving casting drum to form a cast film. The
film was formed at a temperature of from about 280.degree. C. to
about 290.degree. C. The film was quickly quenched by contacting
the film with a chilled roller at a temperature of about 19.degree.
C. The residence time on the chilled roller was from about 5
seconds to about 6 seconds.
[0084] After being quenched, the film was fed through a plurality
of rollers and drawn or stretched in the machine direction. An
infrared heater heated the film during stretching. The film
temperature during stretching was from about 70.degree. C. to about
110.degree. C. The film was stretched in the machine direction from
about 2.5 times to about 4 times its original length.
[0085] After being stretched in the machine direction or
longitudinal direction, the film was once again quenched by
contacting the film with a chilled roller at a temperature of about
20.degree. C. After quenching, the film was placed on a tenter
frame, reheated in an oven and coated with a print receptive
coating. The film was then stretched in the transverse direction
from about 3 times to about 5 times its original length. After
being stretched, the film was then allowed to cool.
[0086] Two different film samples were produced. The first sample,
Sample No. 1, was heated to lower temperatures after being
stretched in the machine direction. In particular, the first sample
was preheated in an oven at a temperature of 70.degree.-90.degree.
C. and then stretched in the transverse direction at a temperature
of from about 70.degree. C. to about 85.degree. C.
[0087] The second sample, Sample No. 2, on the other hand, was
preheated in an oven at a temperature of about
90.degree.-110.degree. C. and then stretched in the transverse
direction at a temperature of from about 85.degree. C. to about
100.degree. C.
[0088] All of the film samples had a thickness of 45 microns.
[0089] The two film samples were then tested for their stretch
characteristics. In particular, each film sample was cut into
sample specimens having dimensions of about 4 inches.times.4
inches. The films were then submerged in agitated water baths at
different temperatures. Once in the water baths for 5 minutes, the
dimensions of the specimens were once again measured to determine
the amount of shrinkage. The results are illustrated in FIG. 4.
[0090] As shown in FIG. 4, Sample No. 1 tended to shrink in greater
amounts at lower temperatures.
[0091] As also shown in FIG. 4, the amount of shrinkage in the
machine direction is comparable to the amount of shrinkage that
occurred in the transverse direction.
[0092] As shown, films can be made according to the present
disclosure that shrink at least 2%, such as at least 5% at a
temperature of 60.degree. C. The film samples also shrunk at least
10%, such as from about 10% to about 20% at 70.degree. C. At
80.degree. C., the film samples shrunk in an amount from about 15%
to about 25%.
Example 2
[0093] Ten different film samples were made generally according to
the process described in Example No. 1. In this example, the film
samples were tested for shrink force, which refers to the amount of
force the film exhibits during shrinking.
[0094] As described in Example No. 1 above, PET homopolymer resin
was melted and extruded to form a molten film layer. The film was
quickly quenched by contacting the film with a chilled roller at a
temperature of from about 18.degree. C. to about 20.degree. C.
After being quenched, the film was fed through a plurality of
rollers and stretched in the machine direction. The temperature of
the film during machine direction stretching was from about
70.degree. C. to about 110.degree. C. The draw ratio in the machine
direction was from about 2.5 to about 4.
[0095] After being stretched in the machine direction, the film was
once again quenched by contacting the film with a chilled roller.
After quenching, the film was placed on a tenter frame, coated with
a print receptive coating, and reheated in an oven. The film was
stretched in the transverse direction at a draw ratio of from about
3 to about 5. The temperature of the film during stretching in the
transverse direction varied from about 73.degree. C. to about
90.degree. C. In particular, the temperature of the film was
measured during initial stretching and during final stretching.
During initial stretching in the transverse direction, the
temperature of the film was from about 73.degree. C. to about
85.degree. C. The temperature of the film at the end of the
transverse stretch, on the other hand, was from about 82.degree. C.
to about 90.degree. C. All of the film samples had a thickness of
45 microns.
[0096] Once the film samples were produced, shrink force
measurements were taken using an AR1000-N rheometer produced by TA
Instruments. In order to heat the film during testing, an
environmental test chamber clamshell-type oven was used. Film
samples were placed between two opposing chucks on the rheometer
and heated in the oven. The starting temperature of the film was
15.degree. C. The temperature was then increased at a rate of
1.degree. C. per minute until the oven reached a temperature of
100.degree. C. The inter-grip distance used was 37.5 mm. All of the
test specimens had a width of 15 mm.
[0097] During testing, the torsional movement of the rheometer was
nulled or zeroed. After each sample was clamped into place, the
clamshell-type oven was closed around the sample. The temperature
in the oven was then increased and the force exerted between the
clamps during shrinkage of the film was recorded. Results were
recorded in Newtons per 15 mm width. The following results were
obtained:
TABLE-US-00001 Maximum Shrinkage Force in Newtons/15 mm Width
Machine Transverse Sample No. Direction Direction Sample 1 8.0 11.2
Sample 2 6.7 9.3 Sample 3 6.0 8.1 Sample 4 8.0 10.1 Sample 5 7.5
9.4 Sample 6 6.3 9.1 Sample 7 8.0 10.0 Sample 8 7.8 10.2 Sample 9
7.8 9.5 Sample 10 7.1 9.2
TABLE-US-00002 Minutes From Shrinkage Onset to Shrinkage Maximum
Machine Transverse Sample No. Direction Direction Sample 1 9.5 13.5
Sample 2 9.1 14.1 Sample 3 9.6 16.8 Sample 4 7.8 9.5 Sample 5 8.6
12.7 Sample 6 9.0 14.5 Sample 7 9.7 12.6 Sample 8 9.0 13.2 Sample 9
9.2 12.1 Sample 10 9.1 11.8
TABLE-US-00003 Temperature (.degree. C.) of Shrinkage Onset Machine
Transverse Sample No. Direction Direction Sample 1 63.3 64.1 Sample
2 65.3 64.8 Sample 3 65.7 65.4 Sample 4 60.6 61.3 Sample 5 61.6
60.9 Sample 6 64.8 66.4 Sample 7 62.9 62.9 Sample 8 65.1 63.6
Sample 9 64.0 63.8 Sample 10 63.8 64.3
TABLE-US-00004 Temperature (.degree. C.) at Maximum Shrinkage Force
Machine Transverse Sample No. Direction Direction Sample 1 72.8
77.6 Sample 2 74.4 78.9 Sample 3 75.3 82.2 Sample 4 68.4 70.8
Sample 5 70.2 73.6 Sample 6 73.8 80.9 Sample 7 72.6 75.5 Sample 8
74.1 76.8 Sample 9 73.2 75.9 Sample 10 72.0 76.1
[0098] The results are also illustrated in FIGS. 5 and 6. In
particular, FIG. 5 illustrates shrink force in the machine
direction, while FIG. 6 illustrates shrink force in the transverse
direction for all ten samples.
[0099] These and other modifications and variations to the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention, which is more particularly set forth in the appended
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims.
* * * * *