U.S. patent application number 12/470207 was filed with the patent office on 2010-01-21 for oriented film produced in-process for use in the stretch film market.
This patent application is currently assigned to Paragon Films, Inc.. Invention is credited to Shaun Eugene Pirtle, Khurrum Shamsi.
Application Number | 20100015422 12/470207 |
Document ID | / |
Family ID | 41529435 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100015422 |
Kind Code |
A1 |
Pirtle; Shaun Eugene ; et
al. |
January 21, 2010 |
Oriented Film Produced In-Process for Use in the Stretch Film
Market
Abstract
Pre-stretched films may be used to increase the rate at which
loads can be wrapped and to minimize the exertion required when
using conventional stretch films. However, pre-stretched films must
generally be stretched in a separate step and stored for several
days in order for cling to fully develop. The present disclosure
describes compositions, devices, systems, and methods for producing
film that eliminate the stretching and storage steps. In
particular, the present disclosure relates to the use of selected
resins and an angled die to increase the level of orientation in
the film as it is formed, thus eliminating the need to stretch the
film in a separate step. The present disclosure also relates to the
use of a cling agent which eliminates the storage time
traditionally required to develop the film's cling properties.
Inventors: |
Pirtle; Shaun Eugene;
(Coweta, OK) ; Shamsi; Khurrum; (Tulsa,
OK) |
Correspondence
Address: |
DOERNER SAUNDERS DANIEL & ANDERSON, LLP
320 South Boston, Suite 500
Tulsa
OK
74103-3725
US
|
Assignee: |
Paragon Films, Inc.
Broken Arrow
OK
|
Family ID: |
41529435 |
Appl. No.: |
12/470207 |
Filed: |
May 21, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61082398 |
Jul 21, 2008 |
|
|
|
Current U.S.
Class: |
428/213 ;
425/461; 428/516; 525/240; 526/352.2 |
Current CPC
Class: |
B65H 18/10 20130101;
Y10T 428/2495 20150115; B65H 2301/4148 20130101; B31F 1/0016
20130101; Y10T 428/31913 20150401; B65H 2701/1752 20130101; B65H
2701/11234 20130101; Y10T 428/2419 20150115; B31F 7/006 20130101;
B65H 2301/414322 20130101 |
Class at
Publication: |
428/213 ;
428/516; 526/352.2; 525/240; 425/461 |
International
Class: |
B32B 27/08 20060101
B32B027/08; B32B 27/32 20060101 B32B027/32; C08L 23/04 20060101
C08L023/04; B32B 7/02 20060101 B32B007/02; B29C 47/12 20060101
B29C047/12 |
Claims
1. An oriented film produced in-process that mimics the properties
of pre-stretched handheld film.
2. The oriented film according to claim 1, wherein the oriented
film is comprised of a linear low density polyethylene (LLDPE)
copolymer resin.
3. The oriented film according to claim 2, wherein the LLDPE
copolymer resin is blended with other resins chosen from the group
consisting of polyethylenes, polyethylene copolymers, and
polypropylene copolymers.
4. The oriented film according to claim 1, wherein the oriented
film is comprised of a majority layer and a plurality of minority
layers, the oriented film having a total film thickness.
5. The oriented film according to claim 4, wherein the majority
layer is comprised of a LLDPE copolymer resin.
6. The oriented film according to claim 4, wherein the minority
layers are comprised of resins chosen from the group consisting of
polyethylene, polyethylene copolymers, and polypropylene
copolymers.
7. The oriented film according to claim 4, wherein the minority
layers have a thickness ranging from 0 to 49 percent of the total
film thickness.
8. The oriented film according to claim 7, wherein the minority
layers have a thickness of approximately 16 percent of the total
film thickness.
9. The oriented film according to claim 6, wherein the resins
comprising the minority layers have a melt index ranging from 0.5
to 12.
10. The oriented film according to claim 9, wherein the resins
comprising the minority layers have a melt index ranging from 3 to
5.
11. The oriented film according to claim 6, wherein the resins
comprising the minority layers have a density ranging from 0.850 to
0.969.
12. The oriented film according to claim 11, wherein the resins
comprising the minority layers have a density of approximately
0.917.
13. The oriented film according to claim 5, wherein the majority
layer is comprised of a higher alpha-olefin LLDPE resin.
14. The oriented film according to claim 5, wherein the resin
comprising the majority layer has a melt index ranging from 0.5 to
4.
15. The oriented film according to claim 14, wherein the resin
comprising the majority layer has a melt index ranging from 0.8 to
1.2.
16. The oriented film according to claim 5, wherein the resin
comprising the majority layer has a density ranging from 0.900 to
0.960.
17. The oriented film according to claim 16, wherein the resin
comprising the majority layer has a density of approximately
0.920.
18. An oriented film produced in-process that contains a cling
agent comprised of a polybutene polymer, the oriented film having a
total film structure.
19. The oriented film according to claim 18, wherein the polybutene
polymer has a Saybolt Universal Viscosity of 14,900 SUS at
99.degree. C. and a number average molecular weight of 2,060.
20. The oriented film according to claim 18, wherein the cling
agent is incorporated into the film at an incorporation rate.
21. The oriented film according to claim 20, wherein the
incorporation rate varies from 0 to 25 percent of the total film
structure on a weight-to-weight basis.
22. The oriented film according to claim 21, wherein the
incorporation rate is approximately 0.6 percent of the total film
structure on a weight-to-weight basis.
23. An oriented film produced in-process that contains a
non-migratory cling agent incorporated into one or more layers of
the film.
24. The oriented film according to claim 23, wherein the
non-migratory cling agent is incorporated into the layers of the
oriented film at an incorporation rate.
25. The oriented film according to claim 24, wherein the
incorporation rate varies from 0 to 25 percent of the total film
structure on a weight-to-weight basis.
26. The oriented film according to claim 25, wherein the
incorporation rate is approximately 1 percent of the total film
structure on a weight-to-weight basis.
27. An apparatus for producing oriented film, the apparatus
comprising: an extruder that receives a resin and melts the resin
to a selected temperature that allows the resin to melt; and an
angled die that delivers a layer of melted resin from the extruder
onto a casting roll to produce a film.
28. The apparatus according to claim 27, wherein the angled die has
an intercept angle that is less than 90.degree..
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/082398, filed on Jul. 21, 2008, the
contents of which are hereby incorporated by reference in their
entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure generally relates to compositions,
devices, systems, and methods for producing oriented film
in-process for use in the stretch film market. In particular, the
present disclosure relates to the use of selected resins and an
angled die to increase the level of orientation in the film as it
is formed, thus eliminating the need to stretch the film in a
separate step. The present disclosure also relates to the use of a
cling agent which eliminates the storage time traditionally
required to develop the film's cling properties.
BACKGROUND OF THE DISCLOSURE
[0003] Stretch films are widely used in a variety of bundling and
packaging applications. For example, manually applied stretch films
(i.e., handheld stretch films) have become a common method of
securing bulky loads such as boxes, merchandise, produce,
equipment, parts, and other similar items on pallets. Stretch films
may be stretched at the time of use, which requires the application
of force in order to stretch the film as much as 200 percent to
properly contain the load. In contrast, stretch films may be
"pre-stretched" by a film converter prior to delivery to the
end-user. Pre-stretched films are described as films that are taken
from master rolls of film that have already been produced,
stretched in a separate step, and re-wound onto film rolls for
later use. Many end-users have chosen to use pre-stretched films to
increase the rate at which loads can be wrapped and to minimize the
force required to wrap loads.
[0004] Pre-stretched films are typically made from various
polyethylene resins and may be single or multilayer products. An
additive known as a cling agent is frequently used to ensure that
adjacent layers of film will cling to each other. A cling agent
typically used in pre-stretched films is polybutene with a Saybolt
Universal Viscosity of 3,000 SUS at 99.degree. C. with a number
average molecular weight of 1,290. This cling agent requires time
to migrate or "bloom" to the film's surface after the film is
produced and typically starts to reach equilibrium in 12 to 24
hours under optimum storage conditions. If the film is stretched
before the cling agent has fully migrated, the resulting film will
have little or no appreciable cling. Films that are produced with
excessive winding tension or stored at low temperatures will also
have little or no cling due to the lack of migration of the cling
agent.
[0005] As a result, conventional pre-stretched films require that
master rolls of film be stored for several days before stretching
in order for the cling agent to migrate and the cling to fully
develop. This necessary delay between the time the film is produced
and the time the film is stretched increases the cost and decreases
the efficiency of making pre-stretched films.
[0006] After the cling has fully developed, pre-stretched films are
stretched in a separate operation. This process orients the
molecules in the film in a longitudinal direction, parallel to the
direction of the film's travel through the stretching machine. This
orientation in the machine direction removes most of the stretch in
the film. The resulting film is relatively stiff for its thickness
and has very little residual orientation or stretch remaining
before the film fails in the machine direction. These
characteristics are desirable because much less effort is required
to secure a load using pre-stretched film as compared to
conventional handheld stretch films. However, this separate
operation requires additional material handling, dedicated
converting equipment, increased warehouse space, and the manpower
needed to manage the operation. This process also results in
increased film scrap and higher raw material usage, further
increasing the cost and decreasing the efficiency of making
pre-stretched film.
[0007] As can be seen, there is a need for compositions, methods,
systems, and devices which can produce oriented film in a single,
continuous process. In addition, there is a need for compositions,
methods, systems, and devices which can simplify the production
process by eliminating the need to stretch the film. Eliminating
the stretching and storage steps makes oriented film simpler,
quicker, and less expensive to produce. In addition, the production
line may be configured so that the film, as initially produced,
meets the length and width specifications for the final
product.
SUMMARY OF THE DISCLOSURE
[0008] The present disclosure provides an oriented film that is
produced in-process and mimics the properties of pre-stretched
handheld film. The oriented film may be comprised of a linear low
density polyethylene (LLDPE) copolymer resin. The LLDPE copolymer
resin may be blended with resins chosen from the group consisting
of polyethylene, polyethylene copolymers, and polypropylene
copolymers. The oriented film may have a majority layer and a
plurality of minority layers. The majority layer may be comprised
of a LLDPE copolymer resin and the minority layers may be resins
chosen from the group consisting of polyethylene, polyethylene
copolymers, and polypropylene copolymers.
[0009] The present disclosure further provides an oriented film
that is produced in-process and contains a cling agent comprised of
a polybutene polymer. The selected cling agent may be a polybutene
polymer with a Saybolt Universal Viscosity of 14,900 SUS at
99.degree. C. with a number average molecular weight of 2,060.
[0010] The present disclosure further provides an oriented film
that is produced in-process and contains a non-migratory cling
agent. The non-migratory cling agent may be incorporated into one
or more layers of the oriented film.
[0011] The present disclosure further provides an apparatus for
producing oriented film. The apparatus comprises one or more
extruders that receive and melt the resins. The apparatus also
comprises an angled die that delivers a layer of melted resin from
the extruder onto a casting roll to produce a film.
[0012] These and other features, aspects, and advantages of the
present disclosure will become better understood with reference to
the following drawings, description, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The disclosure will be better understood from the following
description and the accompanying drawings given as non-limiting
examples, and in which:
[0014] FIG. 1 illustrates the steps for producing oriented cast
film in-process, according to an embodiment disclosed herein;
[0015] FIG. 2 illustrates the means for producing a film from
molten resins, according to an embodiment disclosed herein;
[0016] FIG. 3 illustrates the standard placement of a cast film die
according to the prior art; and
[0017] FIG. 4 illustrates the placement of a cast film die at an
angle, according to an embodiment disclosed herein.
DETAILED DESCRIPTION
[0018] The following detailed description is of the best currently
contemplated modes of carrying out the disclosure. The description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating the general principles of the disclosure,
since the scope of the present disclosure is best defined by the
appended claims.
[0019] Broadly, the current disclosure includes compositions,
systems, devices, and methods for producing oriented film
in-process for use in the stretch film market. More specifically,
according to one aspect of the disclosure, the film may be
comprised of higher molecular weight resins than are conventionally
used for stretch films. The inventive resins may increase the level
of orientation in the film as it is formed. In addition, the resins
may be extruded onto the casting roll through an angled die, which
may further increase the level of orientation in the film. As a
result of the increased level of orientation, the film does not
have to be stretched in a separate operation. Eliminating the
stretching step may make the film simpler, quicker, and less
expensive to produce.
[0020] In another aspect of the disclosure, a cling agent may be
provided to enable an oriented film to be produced without an
extensive storage time between steps in the manufacturing process.
The inventive cling agent does not require an extended period of
time to migrate to the surface of the film. As a result, the cling
properties of the film will be immediately apparent. Eliminating
the storage time may further reduce the time and cost associated
with producing stretch film.
[0021] The film of the present disclosure may be comprised of one
layer or multiple layers, and the composition of each layer may
vary. Materials that may be used to produce the film layers may
include, but are not limited to, Ziegler Natta (ZN) catalyzed
linear low density polyethylene (LLDPE), metallocene catalyzed
linear low density polyethylene (mLLDPE), polyethylenes,
polyethylene copolymers, polyethylene terpolymers, polyethylene
blends, polypropylenes, polypropylene copolymers, and blends
thereof. Cling agents may be used as discrete layers or as blends
to produce one-sided, differential, or two-sided cling structures.
Such cling agents may be migratory or non-migratory.
[0022] One embodiment of the present disclosure may be a
three-layer film with a majority layer sandwiched between two
minority layers. The thickness of the minority layers may range
from 0 to 49 percent of the total film thickness. The preferred
thickness for the minority layers may be approximately 16 percent
of the total film thickness.
[0023] The majority layer may consist of a LLPDE copolymer resin,
such as a higher alpha-olefin LLDPE resin. The melt index of the
LLDPE copolymer resin selected for the majority layer may range
from 0.5 to 4, with a preferred melt index ranging from 0.8 to 1.2.
The density of the LLDPE copolymer resin selected for the majority
layer may range from 0.900 to 0.960, with a preferred density of
approximately 0.920. Using a LLDPE copolymer resin with a higher
molecular weight than is conventionally used in stretch films may
increase the level of orientation when the film is extruded through
a die. The LLPDE copolymer resin may be also combined with other
resins, including, but not limited to, other polyethylenes,
polyethylene copolymers, and polypropylene copolymers.
[0024] The minority layers may be resins comprised of polyethylene,
polyethylene copolymers, polypropylene copolymers, or blends
thereof. Depending upon the desired properties of the film, the
minority layers may or may not have the same composition. The melt
index of the resins selected for the minority layers may range from
0.5 to 12, with a preferred melt index ranging from 3 to 5. The
density of the resins selected for the minority layers may range
from 0.850 to 0.969, with a preferred density of approximately
0.917.
[0025] To impart cling to the film, a cling agent may be
incorporated into the film. The cling agent may be a migratory or
non-migratory additive. For example, a migratory cling agent may be
metered into a three-layer film through one or both extruders for
the minority layers. As another example, if the film is composed of
a single layer, a migratory cling agent may be metered into the
film through the extruder for that layer. The rate at which the
migratory cling agent is metered into the film may range from 0 to
25 percent of the total film structure on a weight-to-weight basis,
with a preferred rate of approximately 0.6 percent of the total
film structure on a weight-by-weight basis. As an alternative, a
non-migratory cling agent may be added to the minority layers at a
rate of 0 to 25 percent of the total film structure on a
weight-to-weight basis, with a preferred rate of approximately 1
percent of the total film structure on a weight-to-weight
basis.
[0026] As an example, a polybutene polymer with a Saybolt Universal
Viscosity of 14,900 SUS at 99.degree. C. with a number average
molecular weight of 2,060 may be used as a cling agent. The
molecular weight of this cling agent is higher than the molecular
weight of a cling agent typically used in stretch films (which is
polybutene with a Saybolt Universal Viscosity of 3,000 SUS at
99.degree. C. with a number average molecular weight of 1,290).
Unlike the typical cling agent, the higher molecular weight
polybutene polymer may not require time to migrate to the film's
surface. As a result, the film's cling properties may develop
almost immediately. In addition, the higher molecular weight
polybutene polymer may be minimally affected over time or winding
tension. As a result, the oriented film may be produced in-process,
which is more cost-effective and efficient than the standard
practice of producing master rolls of film, storing the master
rolls for several days while the cling develops, and then
converting the master rolls into pre-stretched film.
[0027] Referring generally to FIG. 1, the steps 100 for producing
oriented cast film in-process, according to an embodiment of the
present disclosure, are illustrated. Specifically, the steps may
comprise producing a film from molten resins 110, gauging the film
120, longitudinally slitting the film into multiple sections 130,
folding the edges of the film 140, oscillating the film 150, and
winding the film onto a film roll 160 in a manner that prevents
stacking of the edge folds and entraps air between the layers of
film. All of the steps may be performed along a single production
line. The steps may be performed in a different order, and one or
more steps may be eliminated without departing from the scope of
the present disclosure.
[0028] As shown in FIG. 2, a means for producing a film from molten
resins 200 may comprise one or more extruders 210 connected by
transfer pipes 220 to a die 230. The number of extruders 210 used
in the apparatus may depend upon the desired composition of the
film. For example, if the film is desired to have a three-layer
composition, then three extruders 210 may be used. As another
example, if the film has only a single layer, then one extruder 210
may be used.
[0029] The extruders 210 may be connected to a source 240 of stock
resins. The extruders 210 may heat the stock resins to a molten
condition and deliver the molten resins through the transfer pipes
220 to the die 230. The film may be extruded through the die 230
onto a casting roll 250. The casting roll 250 may be a 30-inch
diameter matt casting roll with a set temperature. As an example,
the set temperature of the casting roll may range from 75.degree.
F. to 100.degree. F., with a preferred value of approximately
90.degree. F. The film may move from the casting roll to a
secondary chill roll 260. The secondary chill roll may be a 20-inch
diameter mirror finish secondary chill roll with a set temperature.
As an example, the set temperature of the secondary chill roll may
range from 65.degree. F. to 90.degree. F., with a preferred value
of approximately 85.degree. F.
[0030] Oriented film may be produced by a plurality of suitable
methods. While the present disclosure specifically relates to chill
roll casting techniques, it is to be understood that the present
disclosure is not to be limited to that type of film production
method. The disclosed compositions, systems, methods, and devices
can be successfully employed with other film production methods,
including, but not limited to, blown film techniques and tubular
bath extrusion.
[0031] As shown in FIG. 3, dies 310 in the cast stretch film
industry are generally positioned vertically. The placement of the
die 310 may affect the melt curtain 320, which is defined as the
distance between the end 330 of the die 310 through which the film
is extruded and the surface 340 of the casting roll 250. The
placement of the die 310 may also affect the intercept angle 360,
which is the angle at which the extruded film initially contacts
the surface 340 of the casting roll 250. For example, the intercept
angle 360 for a vertical die 310 may be approximately
90.degree..
[0032] Possible die configurations in the present disclosure may
include, but are not limited to, angled, vertical, and horizontal.
As shown in FIG. 4, the present disclosure may use an angled die
410. When compared to a vertical die 310, an angled die 410 may
reduce the length of the melt curtain 320 and the intercept angle
360 to the casting roll 250. As a result, the molten resins contact
the casting roll 250 more quickly, giving the molecules in the
resins less time to lose their orientation before they are quenched
and frozen in place by the temperature of the casting roll 250 and
the secondary chill roll 260. As a result, an angled die 410 may
produce thin layers of film with increased machine direction
orientation more efficiently than a vertical die 310. Due to the
increased machine direction orientation, films produced by the
present disclosure do not require stretching in a separate
step.
[0033] As shown in FIG. 1, the film may undergo additional
processing steps once formed. These steps may include, but are not
limited to, gauging the film, longitudinally slitting the film into
multiple sections, folding the edges of the film, oscillating the
film, and winding the film onto a film roll.
[0034] As discussed above, oriented film may be produced by a
plurality of suitable methods, including cast or blown film
processes. Films produced via the cast film process may be made and
processed in the manner previously described. The blown film
process may use low blow-up ratios and narrow die gaps to achieve
the required orientation. Blown film products may be comprised of
single or multiple layers. However, multiple layers may be
necessary if high melt index resins are to be used to prevent or
minimize melt fracture and interfacial instability. The use of high
molecular weight cling agents may also be required to achieve a
commercially viable product.
[0035] As can be seen, the present disclosure provides
compositions, methods, systems, and devices for producing oriented
film in-process for use in the stretch film market. In particular,
the present disclosure relates to the use of particular resins and
an angled die to increase the level of orientation in the film as
it is formed, thus eliminating the need to stretch the film in a
separate step. The present disclosure also relates to the use of a
cling agent which eliminates the storage time traditionally
required to develop the film's cling properties.
[0036] From the foregoing, it will be understood by persons skilled
in the art that compositions, devices, systems, and methods for
producing oriented film in-process for use in the stretch film
market have been provided. While the description contains many
specifics, these should not be construed as limitations on the
scope of the present disclosure, but rather as an exemplification
of the preferred embodiments thereof. The foregoing is considered
as illustrative only of the principles of the present disclosure.
Further, because numerous modifications and changes will readily
occur to those skilled in the art, it is not desired to limit the
present disclosure to the exact methodology shown and described,
and accordingly all suitable modifications and equivalents may be
resorted to, falling within the scope of the present disclosure.
Although this disclosure has been described in its preferred form
with a certain degree of particularity, it is understood that the
present disclosure of the preferred form has been made only by way
of example and numerous changes in the details of the method may be
resorted to without departing from the spirit and scope of the
present disclosure.
* * * * *