U.S. patent application number 10/117932 was filed with the patent office on 2003-10-09 for pre-stretched film having improved edges.
Invention is credited to Smith, David J..
Application Number | 20030189118 10/117932 |
Document ID | / |
Family ID | 28674314 |
Filed Date | 2003-10-09 |
United States Patent
Application |
20030189118 |
Kind Code |
A1 |
Smith, David J. |
October 9, 2003 |
Pre-stretched film having improved edges
Abstract
Rolls of pre-stretched cling film are used to manually wrap and
unitize bulky loads such as boxes on a pallet. Using film that has
previously been plastically stretched simplifies the wrapping
operation. Unfortunately, however, the pre-stretched rolls of film
have edges which are prone to fail during use. The disclosed
invention concerns rolls of pre-stretched cling wrap having
improved edges that are less prone to fail, and the method and
apparatus for producing such rolls.
Inventors: |
Smith, David J.; (Topsfield,
MA) |
Correspondence
Address: |
Donald J. Shade
Battenfeld Gloucester Engineering Co., Inc.
P.O. Box 900
Gloucester
MA
01931
US
|
Family ID: |
28674314 |
Appl. No.: |
10/117932 |
Filed: |
April 8, 2002 |
Current U.S.
Class: |
242/160.4 ;
242/530; 242/530.4; 432/239 |
Current CPC
Class: |
B65H 2301/4148 20130101;
B65H 2301/5153 20130101; B65H 2301/5143 20130101; B65H 2301/41487
20130101; B65H 2701/1752 20130101; B65H 18/28 20130101; B65H
19/2284 20130101 |
Class at
Publication: |
242/160.4 ;
242/530; 242/530.4; 432/239 |
International
Class: |
B65H 018/08; B65H
018/28 |
Claims
I claim:
1. A process for producing a roll of pre-stretched film have
improved edges comprising; supplying a pre-stretched web of
thermoplastic material to slitting and annealing station, slitting
the pre-stretched web, thermally annealing the web along the slit
line, and winding the slit and annealed material into rolls.
2. A process according the claim 1 wherein the slitting and
annealing occurs by contacting the pre-stretched web with a heated
slitting and annealing blade, whereby slitting and annealing are
accomplished simultaneously.
3. A process according to claim 1 wherein the annealing step occurs
independently of the slitting step and the annealing step comprises
heating a narrow strip of web by means of a heating device.
4. A process according to claim 3, wherein the heating device is
adapted to conform closely to the surface of the pre-stretched
web.
5. A process according to claim 4 wherein the heating device is
arc-shaped and adapted to closely conform to the surface of the web
as it passes over a roll.
6. A process according to claim 3 wherein slitting is accomplished
by means of a heated blade.
7. Apparatus for slitting and edge annealing a pre-stretched web of
plastic film comprising: inlet guide means for directing a web of
pre-stretched plastic into a slitting and annealing station,
support means for said plastic web in said slitting and annealing
station, slitting means for slitting said plastic web and producing
a slit edge, annealing means for annealing said web adjacent said
slit edge, and discharge guide means for directing said slit and
edge annealed web away from said slitting and annealing
station.
8. Apparatus according to claim 7 wherein said slitting means and
said annealing means constitute a thermally heated blade means that
contacts said plastic web.
9. Apparatus according to claim 8 wherein said support means
comprises and arc-shaped shoe adapted to receive said slitting
means and said annealing means.
10. Apparatus according to claim 7 wherein said annealing means
comprises a narrow heating device adapted to closely conform to the
web.
11. Apparatus according to claim 10 wherein said heating device is
arc shaped and adapted to closely conform to the web as is passes
over a roller.
12. Apparatus according to claim 11 wherein said heating device
heats and anneals by applying hot air to the web.
13. Apparatus according to claim 7 further comprising a winder for
forming a roll of edge slit and annealed web.
14. A roll of pre-stretched film having slit and annealed
edges.
15. A roll of film according to claim 14 wherein the film comprises
a layer of material containing low density polyethylene or linear
low density polyethylene.
16. A roll of film according to claim 15 wherein said roll of film
is wound on a core.
Description
FIELD OF THE INVENTION
[0001] The current invention concerns a method, apparatus, and
product comprising a pre-stretched thermoplastic film having
improved edges.
BACKGROUND OF THE INVENTION
[0002] The use of thermoplastic stretch or cling films has become a
commonplace method of securing bulky load such as pallets filled
with boxes. Generally, there are two types of film and wrapping
methods, one referred to as machine wrap, the other as hand wrap.
Both types of these films are typically made largely from the
various polyethylene resins, and maybe made as single or multilayer
products. Frequently an additive known as a tackifier or cling
agent, e.g. polyisobutylene, will also be added to ensure that
adjacent layers of film will adhere to each other.
[0003] Machine wrap films are typically used in powered pallet wrap
machines, e.g. see U.S. Pat. No. 5,040,356 for an example. On the
other hand, hand wrap utilizes an operator to stretch the film
manually around the load. As the efficient use of the wrap requires
that it be plastically stretched around the load, various devices,
e.g. U.S. Pat. Nos. 4,600,163 and 4,752,045, have been devised to
help the operator in this task. More recently, however, various
methods of pre-stretching the film have been devised, e.g. U.S.
Pat. No. 5,458,841 and WO89/06594, which will simplify application
of the wrap to the load. With these pre-stretched hand wrap films,
the operator merely wraps the film around the load without
plastically stretching the film. As the elastic memory of the film
recovers, the film contracts about the load.
[0004] One problem, however, with these pre-stretched hand wraps is
that the edges of the film are subject to damage resulting in
tearing of the film during use. Typically, the edges of the
pre-stretched hand wrap film have been prepared by transversely
slitting individual roll widths of film from a wider width by means
of a conventional sharp edge slitter assembly. The film edges so
prepared are anything but uniform, and will contain numerous small
defects such as rips and tears. These rips and tears, plus the
relatively limited ductility remaining in the heavily pre-stretched
material leads to failure during application. One method of
reinforcing the edges of the pre-stretched film has been devised,
folding the edges of the material to form a hem, e.g. see U.S. Pat.
Nos. 5,565,222 and 5,531,393. These hems, however, cause
difficulties winding a uniform roll of film due to the essentially
doubled thickness of the hemmed edge as compared to the remainder
of the film. U.S. Pat. No. 5,531,393 discloses axially oscillating
the roll during winding to minimize piling up of the hemmed edges
on the roll.
OBJECTS OF THE INVENTION
[0005] It is an object of the present invention to provide a novel
roll of pre-stretched hand wrap film having edges resistant to
mechanical damage that results in tearing of the film during
application to the load. Additionally, the film will have edges of
uniform thickness that will simplify winding of uniform rolls.
[0006] A further object of the present invention is to provide a
new method and apparatus for manufacturing pre-stretched hand wrap
film having improved edges. A still further objective of the
present invention is to maximize the useful width of pre-stretched
hand wrap film manufactured by longitudinally slitting a greater
width of stretch film into individual narrower rolls by avoiding
the necessity of folding over or hemming the edges of the
individual rolls to prevent tearing when applied to a load.
SUMMARY OF THE INVENTION
[0007] According to the present invention, a roll of pre-stretched
hand wrap film having improved edges is produced by longitudinally
slitting and annealing a previously stretched width of
thermoplastic stretch wrap either by thermally slitting or by
slitting and applying heat and then winding. By thermally slitting
or slitting with the application of heat, the edges of the
resulting narrower rolls are thermally annealed, resulting in edges
of greater ductility and tear resistance than the remainder of the
width of the film.
[0008] According to another aspect of the invention, there is a
method for producing rolls of pre-stretched stretch wrap comprising
the steps of directing a moving web of previously stretched film to
a slitting means, slitting the web longitudinally to produce one or
more individual webs having a narrower width dimension than the
original web, and thermally annealing the slit edges of the web. In
the preferred method, there will be an additional step of winding
the slit and edge annealed web to produce the roll of improved
wrap.
[0009] The apparatus comprises a guide means arranged largely
transversely to the direction of motion of the previously stretched
film to support the film and direct it into contact with a slitting
blade and annealing means. Preferably, the guide means constitutes
a guiding and support surface over which the film passes, said
guiding and support surface having apertures into which a heated
blade assembly may pass to contact, sever and anneal the film
edges.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows a roll of pre-stretched film, including a
microscopic view of a slit edge of film that has been slit by a
conventional sharp edged blade and wound, all in accordance with
the prior art.
[0011] FIG. 2 shows a roll of film, including a microscopic view of
a slit edge of film, that has been slit by a thermal slitting and
annealing blade and then wound, all according to the present
invention.
[0012] FIG. 3 is a plan view of a thermal slitting arrangement in
accordance with the present invention.
[0013] FIG. 4 is an elevation view of a thermal slitting
arrangement in accordance with the present invention.
[0014] FIG. 5 is a drawing of the thermal slitting and annealing
blade used in the apparatus shown in FIGS. 3 and 4.
[0015] FIG. 6 is an elevation view of a thermal slitting and
annealing blade according to another embodiment of the present
invention.
[0016] FIG. 7 show a further embodiment of the present invention in
which the slitting and annealing means comprise separate means.
[0017] FIG. 8 is a detail on the construction of the annealing
means of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] FIG. 1 shows a roll of film 10, including a microscopic view
of a slit edge 13 and hemline 12 of a roll 10 of pre-stretched film
produced according to prior art methods. As shown, the roll 10,
which was wound on core 15, has tapered or conical ends 11
resulting from axial oscillation of the roll during winding.
Additionally, the microscopic view shows the fold 12 for the hem,
and the actual slit edge of the film 13. There are numerous defects
14 that can serve as initiation points for failure during use.
[0019] FIG. 2 shows a roll of pre-stretched film 55, including a
microscopic view of an edge 20', of pre-stretched film 20 produced
by slitting and annealing with a heater blade in accordance with
the present invention. As shown, the roll has remarkably square
edges 56, as there was no need to axially oscillate the roll during
winding to distribute hemmed material. Additionally, thermally slit
and annealed edge 20' is essentially uniform and defect fee.
[0020] FIG. 3. and FIG. 4 show the apparatus for producing an
improved film roll in accordance with the present invention. A
previously stretched film web 20 is directed into slitting and
annealing station 30 over guiding means 25 such as conventional
idler rolls, stretcher rolls or bowed rolls. Slit and annealed
individual webs, 20a through 20e in FIG. 3 are discharged from the
slitting and annealing station 30, over bowed roll 40 to winder 50
or winders 50a through 50e where the webs are wound into individual
rolls. Additionally, narrow strips of material 20z, which formed
the original edges of web 20, are either discarded or recycled.
[0021] As shown, slitting and annealing station 30 comprises two
main assemblies, a transversely oriented guide and support surface
31 and slitting and annealing knife assembly 33. Guide and support
surface 31 preferably has a convex surface over which pre-stretched
web 20 passes and one or more openings 32 in support surface 31.
Additionally, there will be at least one heated slitting and
annealing blade 33. One blade 33 is required for each longitudinal
slit. As shown in FIG. 3 and FIG. 4, there are six heated slitting
and annealing blades as pre-stretched web 20 is to be subdivided
into five final webs, 20a through 20e and two edge trims 20z.
Active surface 35 of heated slitting and annealing blade 33 is
brought into contact with web 20 and further recessed into openings
32 of support surface 31. As web 20 contacts and passes heated
slitting and annealing blade 34, blade 34 will heat and cut through
web 20 producing two edges, 20' and 20", as well as heat affected
zones, also referred to as annealed zones 21' and 21" adjacent to
the slit edge 20' and 20" respectively. As is well understood to
those familiar with the web handling art, heated slitting and
annealing blades 33 will be mounted to a support structure,
preferably one that will permit blades 33 to be moved from an
inactive position to an active position in contact with web 20. In
the interest of clarity, however, the support structure is not
shown in the Figures.
[0022] Also as shown in FIG. 3 and FIG. 4, a bowed roll or other
web spreading device 40 is adjacent to the discharge side 39 of
slitting and annealing station 30. Bowed roll 40 is used to
separate the slit edges 20' and 20" of web 20 to ensure that slit
edges 20' and 20" do not stick together in case of contact prior to
complete cooling. Following slitting, the now individual webs 20a
through 20e are directed to one or more winding machines 50. As
will be understood to those familiar with winding technology, many
different types of winding devices may be used. As shown in FIG. 3
and FIG. 4, however, individual staggered winders 50a through 50e
are shown. With this arrangement, each individual slit and annealed
web 20a through 20e will be wound on its own respective winder 50a
through 50e.
[0023] FIG. 5 shows a closer view of slitting and annealing blade
33. As previously indicated, slitting and annealing blade has an
active surface 35 that contacts web 20. Contact of web 20 with
active surface 35 produces slit edges 20' and 20" as well as
annealed zones 21' and 21" adjacent slit edges 20' and 20"
respectively. Body portion 34 of blade 33 contains one or more
cavities 36 containing electrical cartridge heaters 37 that are
used to heat blade 33 to its operating temperature. Operating
temperature will depend upon material thickness and the speed at
which web 20 passes blade 33. Preferably blade 33 will also contain
a temperature measuring device such as thermocouple 38, the output
of which will be directed to a temperature control device, as is
well known to those versed in the art.
[0024] An alternate type of heated slitting and annealing station
30' is shown in FIG. 6. In this instance the transverse guide means
31 takes the form of an upstream idler roll 31a and downstream
idler roll 31b. Web 20 passes over idler rolls 31a and 31b, and is
contacted by heated slitting and annealing blade 33 in the space
between rolls 31a and 31b. This blade is manufactured from an
electrically resistive material such as Chromel-A, and is directly
heated by passing electrical current through the blade. The blade
has an active edge 35' which will contact web 20, to produce slit
edges 20' and 20" along with the associated annealed zones 21' and
21". Temperature of blade 33' is controlled by varying the current
flowing through the blade 33'. Current in turn is controlled by
supplying power to blade 33' from a variable supply such as a
Variac.
[0025] FIG. 7 shows another configuration of a slitting and
annealing device useful in the practice of the current invention.
As shown, the device consists of a transverse web guiding and
support device shown generally as 31", a separate annealing device
70, and a slitting device 33". In operation, web 20 passes over the
first roll 31a' of the web guiding and support device 31", where a
narrow annealed zone 21 is produced in the web 20 by annealing
device 70. Annealing device 70 preferably takes the form of an arc
shaped shoe which closely conforms to the outside diameter of roll
31a' and which discharges heated air onto web 20. Alternately,
annealing device 70 could be an arc shaped shoe closely conforming
to the roll that is heated and which would heat web 20 by radiation
or convection. Web 20 then encounters slitter blade 33'" which
forms a longitudinal separation 21 of web 20. Slitter blade 33'" is
aligned with annealing device 70 so that the longitudinal
separation is centered within annealed band of web 20. Slitter
blade 33'" may be any device typically used for longitudinally
slitting a web, including a sharpened blade 33'" as shown in FIG.
7. Heated blades of the types shown in FIG. 3 and in FIG. 4 as 30
or if FIG. 5 as 30" may also be used. After slitter 33'", web 20
passes over a second roll 31b", and then to winders 50.
[0026] FIG. 8 shows the preferred form of annealing device 70. As
shown in FIG. 8, annealing device 70 will have a hollow body 71
having an air inlet 72, a heating chamber 73, and a heated air
distribution chamber 74, which will apply heated air to web 20.
Heating chamber 73 will contain one or more cartridge heaters 75 to
heat the flowing from inlet 72 to distribution chamber 74. As
previously indicated, heated air distribution chamber 74 is arc
shaped to conform closely to roll 31a'. Additionally, distribution
chamber 74 has a porous wall 76 that faces web 20. The actual
discharge of heated air from the distribution chamber 74 to web 20
is through porous wall 76. Web 20 is thoroughly heated by annealing
device 70, which anneals a narrow band 21 of web 20.
[0027] As can be seen in FIG. 3, the improved rolls of
pre-stretched cling film of the present invention are produced as
follows. The pre-stretched film web 20 is brought from a source of
supply into the slitting and annealing unit over a series of rolls
or other appropriate web guide devices. The source for web 20 may
be a master roll of pre-stretched and wound film, or it may be the
discharge from a pre-stretching unit such as a machine direction
orientation device or a cold pre-stretcher of the types identified
in U.S. Pat. No. 5,458,841 or WO89/06594. Within the slitting and
annealing unit 30 the film is brought across the surface of the
transverse film guide surface 31 and contacted by heated slitting
and annealing knife 33.
[0028] Under the influence of the heated blade 33, the film will be
separated longitudinally. Additionally, immediately adjacent to the
longitudinal separation the web will have seen sufficient heat to
anneal, i.e. reverse the effects of the prior stretching, the film.
The optimum temperature at which to operate the heated slitting and
annealing knife 33 will depend upon the material and thickness of
web 20 and the speed at which it passes through the slitting and
annealing unit 30. At the very least, however, the temperature of
the slitting and annealing knife 33 must exceed the melting
temperature of web 20. For the types of materials from which these
pre-stretched cling films are prepared, melting temperature are
frequently on the order of 120.degree. C.
[0029] The now longitudinally slit web 20 leaves the transverse
guide surface 31 over discharge bowed roll 40. Bowed roll 40 is
used to separate the slit edges 20'and 20" to prevent the
possibility of these edges sticking together in case of contact
with each other while sill tacky. After the bowed roll the
individual webs 20a through 20e are led over a series of nip rolls
and idler rolls to one or more winders 50. As is well known to
those involved with the web handling and winding arts, there are
many different ways in which the separate webs may be wound. As
shown in FIG. 3 and FIG. 4, however, each web goes to a separate
winder. Other possibilities include all webs going to individual
cores on a single winder shaft, or alternate webs being wound on
cores on alternate shafts, a process referred to as offset
winding.
[0030] It will be understood by those generally familiar with
handling plastic webs that the particular embodiments of the
invention disclosed in this document are illustrative and are in no
way meant to limit the invention. Numerous changes and
modifications may be made and the full use of equivalents made
without departing from the spirit or scope of the invention as
defined in the following claims.
* * * * *