U.S. patent application number 10/236703 was filed with the patent office on 2003-03-20 for method of creating easy-open load carrying bags.
This patent application is currently assigned to Preco Laser Systems, LLC. Invention is credited to Chow, Chris, Hatella, Kurt A., Miller, Dan B..
Application Number | 20030051440 10/236703 |
Document ID | / |
Family ID | 26930036 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030051440 |
Kind Code |
A1 |
Chow, Chris ; et
al. |
March 20, 2003 |
Method of creating easy-open load carrying bags
Abstract
A system and method for producing a partially perforated tear
line on a substrate material uses an high energy beam to ablate the
substrate material at a depth less than full depth of the
substrate. By varying the output energy level of the high energy
beam for varying time intervals, a substrate material is weakened
to provide an easy open feature without significantly reducing the
tensile strength of the substrate material. The ratio of partial
perforated to unablated substrate material may vary according to
almost any ratio.
Inventors: |
Chow, Chris; (Lake Elmo,
MN) ; Miller, Dan B.; (New Richmond, WI) ;
Hatella, Kurt A.; (New Richmond, WI) |
Correspondence
Address: |
KINNEY & LANGE, P.A.
THE KINNEY & LANGE BUILDING
312 SOUTH THIRD STREET
MINNEAPOLIS
MN
55415-1002
US
|
Assignee: |
Preco Laser Systems, LLC
Somerset
WI
54025
|
Family ID: |
26930036 |
Appl. No.: |
10/236703 |
Filed: |
September 6, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60318893 |
Sep 13, 2001 |
|
|
|
Current U.S.
Class: |
53/412 ;
219/121.71; 383/207; 493/227; 493/369; 53/133.8; 53/141 |
Current CPC
Class: |
B29C 59/007 20130101;
B31B 70/14 20170801; B23K 26/389 20151001; B29C 2035/0838
20130101 |
Class at
Publication: |
53/412 ;
53/133.8; 53/141; 383/207; 219/121.71; 493/227; 493/369 |
International
Class: |
B65B 061/18 |
Claims
1. A method of forming an easy open feature on a packaging system
using a high energy beam, the method comprising: tracing a tear
pattern onto a surface of the substrate material; and varying an
output energy of the high energy beam at a time interval while
tracing the tear pattern so as to selectively ablate the substrate
material at various depths and spacings along the tear pattern.
2. The method of claim 1 wherein the various depths of the ablated
substrate material are each less than a full thickness of the
substrate material.
3. The method of claim 1, wherein the tear pattern is
discontinuous.
4. The method of claim 1, wherein the output energy of the high
energy beam varies from a minimum output energy to a maximum output
energy.
5. The method of claim 4, wherein the minimum output energy of the
high energy beam is modulated to a level lower than a minimum
energy level required to damage the substrate material.
6. The method of claim 4, wherein the maximum output energy of the
high energy beam is modulated to a level less than a minimum energy
level required to damage the substrate material to a full thickness
of the substrate material.
7. The method of claim 1, wherein the step of varying comprises:
modulating the output energy of the high energy beam between three
energy levels, the three energy levels comprising: a minimum energy
level that is below an energy level required to damage the
substrate material; a first energy level that is sufficient to
damage the substrate material to a first depth that less than a
full thickness of the substrate material; and a second energy level
that is sufficient to damage the substrate material to a second
depth less than a full thickness of the substrate material; and
cycling between each of the three energy levels according to a time
parameter.
8. The method of claim 7, wherein the first depth is greater than
the second depth.
9. The method of claim 7, wherein the time parameter varies between
each of the three energy levels.
10. The method of claim 7, wherein the tear pattern is comprised of
weakened segments on the substrate material, and wherein the
weakened segments are damaged to either the first depth or the
second depth.
11. The method of claim 9, wherein the heat treated segments are
separated by undamaged segments.
12. The method of claim 1, wherein the substrate material comprises
a single-layered material.
13. The method of claim 1 wherein the substrate material comprises
a polymeric material.
14. A method of laser processing partial perforations on a moving
web comprising: directing a focal point of a laser beam onto a
surface of the moving web; adjusting an energy level of the laser
beam at a frequency of adjustment in order to control a depth of
each partial perforation along a predetermined pattern; and varying
the frequency of adjustment to control a spacing between partial
perforations on the predetermined pattern.
15. The method of claim 14, wherein adjusting the energy level of
the laser beam produces at least two partial perforations having
different ablation depths.
16. The method of claim 14, wherein the depth of each partial
perforation is less than a thickness of the substrate material.
17. The method of claim 16, wherein adjusting and varying produces
an intermittently perforated tear pattern on the moving web.
18. A packaging system comprising: a substrate material having a
thickness; and a tear line for easy-open applications, the tear
line defined by a plurality of ablated regions disposed within the
substrate material, each ablated region having a selected depth,
wherein the selected depths of adjacent ablated regions change
relative to one another.
19. The packaging system of claim 18, wherein each selected depth
of each ablated region is less than the thickness of the substrate
material.
20. The packaging system of claim 18, wherein the selected depth of
each ablated region is different from the selected depth of
adjacent ablated regions.
21. The packaging system of claim 18, wherein the selected depth of
each ablated region is either a first selected depth or a second
selected depth, wherein the first selected depth is greater than
the second selected depth.
22. The packaging system of claim 18, wherein the substrate
material comprises a single layered material.
23. A method of forming patterns of weakness in a substrate
material comprising: tracing a tear pattern with a high energy beam
onto the substrate material; and varying an energy output of the
high energy beam at a time interval while tracing the tear
pattern.
24. The method of claim 23, wherein the step of tracing comprises:
moving a focal point of the laser beam on a surface of the
substrate material according to a predetermined pattern.
25. The method of claim 23, wherein varying the energy output
comprises: ablating the substrate material with a high energy beam
to one or more depths, each depth being less than a full thickness
of the substrate material.
26. The method of claim 25, wherein a first depth of the one or
more depths is at the surface of the substrate material.
27. The method of claim 26, wherein a second depth of the one or
more depths is below the surface of the substrate material.
28. The method of claim 27, wherein a third depth of the one or
more depths is greater than the second depth.
29. The method of claim 23, further comprising: varying the time
interval.
30. The method of claim 23, wherein the tear pattern is
discontinuous.
31. The method of claim 23, wherein the substrate material is
multi-layered.
32. The method of claim 23, wherein the step of varying produces
the tear pattern having ablated and unablated segments, and wherein
the ratio of ablated segments to unablated segments varies from
less than 10% to greater than 90%.
33. An intermittently heat-treated packaging system comprising: a
substrate material having a thickness, the substrate material
formed into a sealed package; and a tear pattern for easy-open
applications, the tear pattern defined by a plurality of heat
treated regions disposed on the sealed package; wherein a tensile
strength of the substrate material across the tear pattern is
greater than or equal to that of the substrate material in an
untreated area of the substrate material; and wherein a tear force
required to tear the substrate material at the tear pattern is less
than that required to tear the substrate material across an
untreated area of the substrate material.
34. The system of claim 33, wherein the ablated regions form a
discontinuous tear pattern.
35. The system of claim 33, wherein each ablated region extends to
a depth less than the thickness of the substrate material.
36. The system of claim 33, wherein the tear pattern extends
substantially in a straight line.
37. A method of creating an easy open feature on a web material
comprising: advancing the web material under a high energy beam;
treating localized areas of the web material at intermittent
intervals with the high energy beam as the web material is
advanced; and moving a focal point of the high energy beam while
treating the localized areas in order to trace a tear pattern on
the web material.
38. The method of claim 37, further comprising: applying a tension
to the web material while advancing the web material.
39. The method of claim 37, wherein the high energy beam is a laser
beam.
40. The method of claim 37, wherein the step of treating localized
areas comprises: directing a focal point of the high energy beam
onto a surface of the web material; and modulating a power level of
the high energy beam so as to selectively vaporize portions of the
web material.
41. The method of claim 37, wherein a tensile strength across the
heated localized areas is equal to or greater than that of
untreated areas of the web material.
42. The method of claim 37, wherein the step of treating forms a
plurality of perforations in the web material.
43. The method of claim 42, wherein each perforation extends to a
depth less than a full thickness of the web material.
44. The method of claim 42, wherein the plurality of perforations
extend to either a first depth or a second depth.
45. The method of claim 44, wherein the second depth is greater
than the first depth.
46. The method of claim 46, wherein the first depth less than a
full thickness of the web material and greater than a surface depth
of the web material.
47. The method of claim 37, wherein the step of treating chemical
alters the web material immediately adjacent to the localized
areas.
48. The method of claim 47, wherein the chemically altered web
material is heat treated.
49. A method of forming a pattern of weakness on a load bearing
package comprising: advancing a packaging material under a laser
beam; heat treating the packaging material intermittently in
selected areas according to a predetermined pattern as the
packaging material is advanced; and sealing the packaging material
around a substance having a weight to form the load bearing
package; wherein a tensile strength across the heat treated
packaging material is equal to or greater than that of untreated
areas of the packaging material.
50. The method of claim 49, wherein a tear strength along the heat
treated packaging material is less than that of untreated areas of
the packaging material.
51. The method of claim 49, wherein the step of heat treating
comprises: directing a high energy beam onto the packaging
material; modulating a power level of the high energy beam
intermittently so as to selectively heat treat the packaging
material.
52. The method of claim 51, wherein modulating further comprises:
adjusting the power level of the high energy beam between two or
more power levels according to a time parameter.
53. The method of claim 52, wherein adjusting the power level forms
perforations in the packaging material at varying depths relative
to a full thickness of the packaging material.
54. The method of claim 53, wherein the varying depths comprise: a
first depth extending to a surface depth of the packaging material;
and a second depth extending deeper than the surface depth and less
than a full thickness of the packaging material.
55. The method of claim 54, further comprising: a third depth
extending deeper than the second depth and less than a full
thickness of the packaging material.
56. The method of claim 55, wherein modulating further comprises:
alternating between the first depth, the second depth and the third
depth according to a time interval.
57. The method of claim 56, wherein the time interval varies so as
to vary a distance between perforations.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from Provisional
Application Serial No. 60/317,893 filed on Sep. 7, 2001, entitled
"Method of Creating Easy-Open Load Carrying Bag."
FIELD OF THE INVENTION
[0002] The present invention relates to laser scoring to create
lines of weakness in flexible packaging so as to allow for easy
opening of the packaging. More particularly, the present invention
relates to a method of scoring load carrying plastic bags to
provide an easy-open feature with a minimum reduction in the
tensile strength of the packaging, so that the package can be
transported and handled without fear of accidental bursting and yet
can be opened easily.
BACKGROUND OF THE INVENTION
[0003] Flexible film material is increasingly being used in
packaging. Generally, thin film materials have been used to package
various items, from potato chips to fertilizer. Such flexible film
materials often have multiple layers of material, and the layers
may have different characteristics. For example, one or more of the
layers may provide a vapor barrier, preventing contamination of the
contents of the packaging.
[0004] Due in part to the various uses of the flexible film
packaging, flexible film materials are continuously being improved.
With the continuous improvements in film properties, flexible
packaging can be made thinner than ever before and yet be stronger
and tougher than previous packaging. The strength and toughness of
the newer films presents a new problem for consumers, namely the
packages have become increasingly difficult to open.
[0005] To overcome the strength of the flexible packaging,
perforated tear lines have long been applied to flexible packages
for the purpose of easy tear/easy-open of the package. Perforated
tear lines typically involve a single line or pattern of uncut and
cut segments on the package material. However, mechanical
perforations generally cut through the material, allowing vapor to
access the package contents through the perforations. Vapor flow
into the bag can cause problems with some packaged materials. For
example, product in the bag such as fertilizer or powder detergent
often form solid crumbs when exposed to moisture. Second, if vapor
can enter the bag, then chemicals can sometimes leach out of the
bag, presenting potential environmental concerns.
[0006] Additionally, mechanically perforated tear lines tend to
weaken the uncut substrate material directly adjacent to the cut
segment. This weakening may be caused by the exposure of minute
surface defects in the substrate material or by the creation of
fractures in the substrate along the edges of the cut segments
during the cutting process. These weakened areas contribute to
accidental burst or rupture, in part, because the weakened areas
propagate tears between cut segments. In practice, when performing
cross-web cuts on a roll of web material, cross cuts can weaken the
web material so substantially that the tension of the web cannot be
maintained without tearing.
[0007] A laser system overcomes some of the disadvantages of a
mechanical perforation by providing a score line on the bag. The
technique for laser scoring was first suggested in U.S. Pat. No.
3,626,143, where it is suggested that a continuous groove or score
line with a precise depth can be made on a plastic bag material by
a well defined focus continuous beam of laser light. Bags scored
using laser scoring techniques can provide an easy open/easy tear
without puncturing the vapor barrier.
[0008] With some uses of flexible packaging, such as with "load
bearing" packaging, additional considerations arise. While it is
often still desirable to provide an easy open score line without
puncturing the vapor barrier, the score line must not weaken the
flexible material so much that the load bearing bag can no longer
withstand mishandling. Specifically, with the prior art, it is
difficult to balance the desire for easy opening with the need for
sufficient tensile strength of the material. The phrase "load
bearing packaging" refers to packaging wherein the sealed package
supports heavy loads relative to the overall surface area of the
packaging material. For example, salt pellets, top soil,
fertilizer, dog food, cattle feed, and the like, are generally
packaged in larger flexible bags than when filled can be quite
heavy and can be characterized as "load bearing". The packages are
then stored or shipped and may be handled multiple times. In order
to withstand the handling, the perforated bags must maintain
sufficient durability and toughness such that dropping or
mishandling of the bag does not cause the bag to burst at the
perforations. Thus, while laser scoring can be controlled to
provide an easy open score line while maintaining the integrity of
the vapor barrier, the desire for easy open/easy tear must be
balanced against the need for toughness to prevent an accidental
burst of the sealed packaging.
[0009] One prior art patent, U.S. Pat. No. 5,482,376 issued to
Moseley et al. (the "Moseley patent"), suggests variations in the
shape and location of the tear line on a load bear bag in order to
provide an easy-open capability without weakening the packaging to
a point where it bursts open when dropped. Additionally, the
Moseley patent discusses ratios of uncut to cut segment portions
along the tear line of about 80% uncut to 20% cut to about 50%
uncut to 50% cut. The Moseley patent discloses that a bag cut
according to their invention at a 90 to 10 ratio of uncut to cut
segments passed a "drop" test, but could not be tom open by hand.
Additionally, a bag cut according to their invention at an 80 to 20
ratio would tear properly in the machine direction, but not in the
cross-web direction. Finally, a bag cut according to the Moseley
disclosure at a 75 to 25 ratio in a straight line could be opened
easily, but failed the drop test, while an L-shaped cut line at the
same ratio passed both the drop test and the easy-open test.
[0010] While score lines can weaken the film material to allow for
easy open, with large, load-bearing bags, the score line can be
quite long. For continuous score lines on polymers, such as
metallocene doped polyethylene, the tear must be performed in a
continuous non-stop motion. If the tear is stopped momentarily,
upon restarting the tear, the material tends to stretch instead of
the tear propagating along the tear line. With load bearing bags,
this problem is sometimes amplified by the toughness of the
material and by the length of the score line, which may require the
end user to adjust his or her grip in order to complete the
tear.
[0011] Thus, a method is needed for providing an easy open/easy
tear on load bearing packages of many shapes, sizes and locations,
without jeopardizing the durability and toughness of the flexible
material and without damaging the vapor barrier. Moreover, a method
is needed for providing an easy open/easy tear on load bearing
packages, which will work even with a discontinuous tearing
motion.
SUMMARY OF THE INVENTION
[0012] A system and method for producing a partially perforated
tear line on a substrate material uses an high energy beam to score
the substrate material at a depth less than full depth of the
substrate and at varying intervals along the substrate. The system
includes a high energy beam and a substrate material. The high
energy beam is directed onto a surface of the substrate material
according to a predetermined pattern. The beam traces the
predetermined pattern onto the substrate while the energy level of
the output is varied at intermittent intervals, so as to produce a
discontinuous pattern on the substrate. By varying the output
energy level of the high energy beam for varying time intervals, a
substrate material is weakened at selected intervals to provide an
easy open feature without significantly reducing the tensile
strength of the substrate material. The ratio of partial perforated
to unablated substrate material may vary according to almost any
ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of a sealed packaging system
including an easy-open feature made in accordance with the present
inventive method.
[0014] FIG. 2 is a perspective view of a partially opened packaging
system including an easy-open feature made in accordance with the
present inventive method.
[0015] FIG. 3 is a perspective view of a laser beam selectively
ablating a substrate material in accordance with the present
inventive method.
[0016] FIG. 4a is a cross-sectional side view of the substrate
material taken along line 4-4 in FIG. 3 illustrating a uniformly
spaced and uniform depth, partially perforated score line made in
accordance with the present invention.
[0017] FIG. 4b is a cross-sectional side view of the substrate
material taken along line 4-4 in FIG. 3 illustrating a uniformly
spaced, variable depth, partially perforated score line made in
accordance with the present invention.
[0018] FIG. 4c is a cross-sectional side view of the substrate
material taken along line 4-4 in FIG. 3 illustrating variably
spaced perforations of variable length and depth made in accordance
with the present invention.
[0019] FIG. 4d is a cross-sectional side view of the substrate
material taken along line 4-4 in FIG. 3 illustrating uniformly
sized and spaced partial perforations positioned adjacent to each
other.
[0020] FIG. 5 includes cut away views of the substrate material
taken along lines 4-4 in FIG. 3 illustrating other various patterns
of partially perforated score lines of the present invention.
[0021] FIG. 6 illustrates the tensile strength of a substrate
material that has been laser processed with a multilevel partial
perforation tear line similar to those shown in FIG. 4a and FIG. 5,
example G.
[0022] FIG. 7 illustrates the tensile strength of a substrate
material that has been laser processed with a partial perforation
tear line similar to those described in FIG. 4b and FIG. 5, example
C.
[0023] FIG. 8 illustrates the tensile strength of the substrate
material of FIG. 7 that has been laser processed at a lower power
level than that of FIG. 7.
[0024] FIG. 9 is a side view of a sealed, load-bearing packaging
system including an alternative easy-open feature made in
accordance with the present inventive method.
DETAILED DESCRIPTION
[0025] As shown in FIGS. 1 and 2, an exemplary packaging system 10
manufactured by the present inventive method generally includes a
partially perforated tear line 12 disposed on a substrate material
14. Generally, a partially perforated tear line 12 is a line of
weakness formed by partial perforations 16 at selected intervals on
the substrate material 14, wherein the partial perforations 16 do
not extend entirely through the substrate material 14.
[0026] The phrase "partial perforation" refers to a selected region
on the substrate material 14 that has been ablated by a laser beam
18 to a depth that is less than the full thickness of the substrate
material 14. The partial perforation 16 is formed by selectively
ablating the substrate material 14 at various locations according
to a predetermined pattern. The term ablated (or ablation) refers
to any type of altering of the substrate material by a laser beam
18, including physical or chemical alteration, whether or not such
alteration is visible. Each partial perforation 16 extends less
than a full depth of the substrate material 14. The resulting
partially perforated tear line 12 provides a "line" or "pattern" of
weakness 12 on the substrate material 14 that can be utilized to
tear open the packaging system 10.
[0027] As shown, the perforations 16 are disposed on the substrate
material 14 at various locations to form a tear line 12 for use in
easy-open applications. The phrases "easy-open" and "easy tear"
refer to lines of weakness or other opening systems that easily
separate along the partially perforated tear line 12, thus opening
the packaging system 10 as illustrated in FIG. 2. Specifically,
when a user applies a shear force or a tensile force at specific
regions on the packaging system 10, the material 14 of the
packaging system 10 tears along the predetermined line of weakness
or tear line 12.
[0028] In accordance with present inventive method, a suitable
substrate material 14 is chosen to manufacture the packaging system
10. Suitable substrate materials 14 include, but are not limited
to, plastic or polymeric materials such as polyethylene (PE),
linear and low-density polyethylene (LLDPE and LDPE), linear and
high-density polyethylene, polyethyleneterephthalate (PET), and
oriented polypropylene (OPP). Similar polymers such as, for
example, metallocene doped polyethylene are also within the scope
of the present inventive method. In addition to laminates
containing the aforementioned compositions, the present inventive
method can be used in single-layered substrate materials of uniform
composition or multi-layered substrate materials of uniform or
heterogeneous composition.
[0029] Generally, the easy open/easy tear perforation 16 can be
produced on the substrate material 14 whether the substrate
material is presented as a sealed packaging system, a continuous
web, or even discrete workpieces. In a preferred embodiment, the
substrate material 14 is a continuous web material that is thin,
flexible, tough and durable. Generally, the substrate material 14
is advanced relative to the laser beam. The direction of the
advancement of the substrate material is commonly referred to as an
in-line machine direction, as opposed to a cross-web direction
which is substantially normal to the in-line machine direction in
the plane of the web or substrate material 14. Generally,
positioning the tear line 12 in either the in-line machine
direction or the cross-web direction effects both the tensile
strength of the packaging system 10 and the ease of opening the
scored packaging system 10.
[0030] The substrate material 14 is positioned under the laser beam
18 to produce the tear line 12. The area under the laser beam 16
where the scoring takes place can be referred to as a
"work-surface". The work-surface can be mobile, such as an X-Y
directional table; continuously moving, such as a conveyor belt; or
stationary with the laser beam 18 moving across the substrate
material 14 in a predetermined pattern or line. Alternatively, the
work-surface can refer to the substrate material 14, such as a
moving web of film material, on which the tear line 12 is produced
directly. Finally, the work-surface can include any combination of
movement of both the work-surface and the laser beam 12.
[0031] Generally, the tear line 12 and selective perforations 16
are produced using a laser beam 18 (as shown in FIG. 3).
Preferably, the laser beam 18 is either a continuous wave (CW) or a
pulsed carbon dioxide laser beam; however, other lasers including
Nd:YAG and Ultraviolet (UV) lasers would also be within the scope
of the present inventive method.
[0032] The substrate material 14 is positioned such that a laser
beam 18 can be directed thereon for laser processing. During the
laser process, the substrate material 14 advances in an in-line
direction, and the laser beam 18 is directed onto the advancing
substrate material 14 (or discrete target such as with a workpiece
on a conveyor belt). The laser beam 18 can be adjusted such that
the spot of the laser beam 18 contacts the substrate material 14 at
varying locations as the substrate material 14 is advanced.
Depending on the velocity of the substrate material 14 in the
in-line direction and on the specific score pattern, the spot size
of the laser beam 18 and the angle at which the laser beam 18
contacts the substrate material 14 may vary during each laser
process in order to achieve the desired laser process pattern.
Thus, the substrate material 14 and the laser beam 18 effectively
move at a relative velocity to one another.
[0033] As previously mentioned, particularly with respect to load
bearing package systems, the ease of opening must be balanced
against the need to maintain durability and strength of the package
material 14 so that the sealed package system 10 does not
unexpectedly burst open during transit or handling. By laser
scoring the substrate material 14 at selected intervals to a depth
less than a full thickness of the substrate material 14, both the
viability of the package seal (vapor barrier) and the tensile
strength of the substrate material 14 can be maintained.
[0034] Tensile strengths of substrate materials 14 containing
partially perforated tear lines 12 made with the present inventive
method were greater than tensile strengths of substrate materials
having continuous score lines, as are currently used in the art.
Tensile strengths of partially perforated substrate materials made
using the method of the present invention remained high relative to
the tensile strengths of unscored materials. In some instances, the
tensile strength of the substrate material 14 having a partially
perforated tear line 12 remained substantially the same as the
tensile strength of the same substrate material without any score
line.
[0035] The partially perforated tear line 12 is characterized by
several variables, including whether the perforations 16 are made
on top of a continuous score line. Specifically, the partially
perforated tear line 12 may vary according to the depth of the
perforations 16, the size of the perforations, the spacing between
perforations 16, the thickness of the substrate material 14, and so
on, across the tear line 12. In other words, each partial
perforation 16 of a plurality of perforations 16 which form a tear
line 12 may be of a different depth. Any combination of variables
can be adjusted according to the particular substrate material 14
and the use for which the partially perforated packaging system 10
is intended.
[0036] The selective arrangement of partial perforations 16 having
different depths, voids or levels provides several advantages.
First, as previously mentioned, the partially perforated tear line
12 on the substrate material 14 retains substantially the original
tensile strength of the substrate. Second, the partial perforations
16 extend less than a full depth of the substrate material 14,
making it possible to partially perforate the substrate material 14
without exposing the contents of the packaging system 10 to
contamination. Third, the partial perforations 16 weaken the
substrate material 14 sufficiently that a lesser force applied to
the partially perforated tear line 12 causes the bag to tear open
as compared with a much greater force applied to an "untreated"
packaging system. An "untreated" packaging system is one that has
no easy open tear line. Fourth, by varying the depth of the partial
perforations 16 across the partially perforated tear line 12, a
tear can be initiated, stopped and restarted easily. Specifically,
the partial perforations 16 assist in re-initiating the tear along
the tear line 12, which has the additional benefit of controlling
the resulting tear so that the bag does not tear open incorrectly.
Finally, the variable depth of the partial perforations allows the
partially perforated tear line 12 to be formed at almost any ratio
of cut to uncut segments.
[0037] In the prior art, particularly with respect to materials
such as metallocene doped polyethylene, the momentum of the tear
was important for maintaining the efficiency of the tear line 12
and the accuracy of the resulting tear relative to the tear line
12. Specifically, if the tear was started and stopped, restarting
the tear was difficult and sometimes would not work. Often, the
material would stretch instead of tearing, or the material would
tear away from the tear line 12, thereby defeating the intended
efficiency and control of the tear line 12. However, by generating
a tear line 12 with uneven or varying depth partial perforations
16, the tear does not require momentum in order to propagate across
the packaging system 10.
[0038] Generally, at a microscopic level, most materials have
surface defects. When testing the tensile strength of materials,
fractures tend to occur first where such a surface defect is
present, and then to propagate from the defect. Theoretically, the
laser beam 18 of the present invention can be thought of as
providing a pattern of defects across the surface of the substrate
material 14 that may or may not be of the same depth as other
surface defects. When a tensile stress is then applied to the
packaging system 10, the pattern of defects or partially perforated
tear line 12 of the present invention weakens the substrate
material 14 no more than any of the other surface defects. However,
when a shear force is applied to the partially perforated tear line
12, the substrate material 14 fractures easily, and the tear
propagates along the tear line 12.
[0039] The present invention works at a wider ratio of partially
perforated material to unablated material than the prior art. In a
preferred embodiment, the ratio of partially perforated material to
unablated material is approximately 1 to 7. In another embodiment,
the ratio is 1 to 2. In still another embodiment, the ration is
greater than 1 to 2. Depending on the material and the intended use
of the packaging system, by modulating the depth of the partial
perforations 16, it may be possible to perform the present
invention at almost any ratio. With respect to the present
invention, the term "ratio" in this context applies to the linear
ratio of partial perforations relative to the unablated substrate
material, not to the volume or surface area.
[0040] Referring to FIG. 3, which depicts the substrate material 14
traveling in an in-line machine direction relative to the laser
beam indicated by arrows A, the partially perforated tear line 12
is formed by selectively ablating or weakening selected regions of
the substrate material 14 by laser processing partial perforations
16. Generally, the partially perforated tear line 12 is
characterized by partial perforations 16 and unablated regions
20.
[0041] The substrate material 14 is passed at a relative velocity
under the laser beam 18, which ablates the substrate material 14 to
a selected depth when activated. To selectively ablate the
substrate material 14 to a desired depth, an output energy level of
the laser beam 18 is regulated by a computer (not shown) to
correspond with the composition of the substrate material 14 and
the desired depth of the partial perforation 12. Varying the output
energy level of the laser beam results in a variation of the
ablation depth of the partial perforation 16. This variation ranges
from zero when the laser beam is inactive, to a maximum which
ablates to a depth equal to the full thickness (.tau.) of the
substrate material 14. However, in applications where a
hermetically sealed packaging system is desired, it should be
understood that the depth of the partial perforation 16 will always
be less than the full thickness (.tau.) of the substrate material.
Additionally, in applications where a vapor barrier is included as
one of the layers of the substrate material 14, the maximum depth
would preferably be less than the depth of the vapor barrier layer.
Preferably, a minimum depth would be approximately about 10% of the
substrate thickness, while a maximum depth would be approximately
about 90% of the substrate thickness, each value dependent upon the
substrate material used.
[0042] FIGS. 4a-4d include four side views of exemplary partially
perforated score lines 12 taken along lines 4-4 in FIG. 3. All four
exemplary partially perforated score lines 4a-4d are disposed
within the substrate material 14, which has a thickness .tau.. The
exemplary partially perforated tear line 12 represented by FIG. 4a
includes intermittent ablated regions or partial perforations 16,
each having depth (d) and a length (L) disposed between unablated
regions 20.
[0043] For illustrative purposes, the substrate material 14 in FIG.
4a is depicted as being formed from multiple layers 22. One of the
layers 22 not reached by the partial perforations 18 is shown to be
a vapor barrier 24. The vapor barrier 24 could be formed from a
similar material as other layers 22 of the substrate material 14;
however, to distinguish the vapor barrier layer 24 from the other
layers 22, the vapor barrier layer 24 is stippled in the
illustration. For simplicity, the substrate material 14 shown in
FIGS. 4b, 4c and 4d are depicted as a single homogenous layer 22
with partial perforations extending less than a full depth of the
substrate material 14; however, it should be understood that the
partial perforations depicted in FIGS. 4b, 4c and 4d could also be
performed on a multi-layer substrate 14 of almost any
composition.
[0044] The exemplary partially perforated tear line 12 represented
by FIG. 4b includes a first ablated region 16a having depth d', and
a second ablated region 16b having depth d". Disposed between and
adjacent to each ablated region 16a and 16b are unablated regions
20. As previously discussed, variations in the depths d',d" of the
perforations 16a, 16b allow the tear to propagate across the
substrate material 14 even if the moment of the tear is stopped and
restarted. Moreover, by adjusting the depths d',d" of the partial
perforations 16a,16 allows the tear line to be produced at almost
any ratio of partial perforations to untreated substrate material.
Specifically, the ratio of partially perforated to unablated
segments can be adjusted to high or low ratios and the depth of the
perforations can be adjusted to maintain the same ease of tear and
the same tensile strength of the packaging material.
[0045] FIG. 4c illustrates another exemplary partially perforated
tear line 12 showing variations in the perforation depths d',d"; in
the lengths of the unablated regions 20 (l',l"); and in the lengths
(L',L") of the partial perforations 16a,16b. As shown, FIG. 4c
includes partial perforations 16a having a depth d' and a length
L', and partial perforation 16b having a depth d" and a length L".
Furthermore, the length l',l" is shown to vary between partial
perforations.
[0046] By controlling the spacings l',l" between partial
perforations 16a,16b, the lengths L',L" of the partial perforations
16a,16b, and the depths d',d" of the partial perforations 16a,16b,
the tensile strength of the laser processed substrate material 14
can be adjusted or maintained. Moreover, by controlling these
elements, the easy open tear line 12 can be created without
compromising the tensile strength or the toughness of the packaging
system 10. By controlling these three variables of the partially
perforated tear line 12, the tear line 12 can be laser processed at
almost any ratio of perforations to unablated material, depending
on the material properties and the intended use of the packaging
system. Moreover, the resulting tear line 12 still provides an easy
open capability.
[0047] As shown in FIG. 4d, the spacing between partial
perforations 16a,16b can be reduced to a magnitude of zero, such
that the partial perforations 16a,16b are positioned adjacent to
each other without intervening unablated regions 20. While it has
been shown that the spacing, the length and the depth of the
perforations can be adjusted as desired, it is also within the
scope of the present inventive method to increase the number of
different depths of the partial perforations 16 as well as to vary
the number of partial perforations 16 per linear distance in order
to decrease or increase the tensile strength of the substrate
material 14, relative to the tensile strength of unablated
material.
[0048] Alternatively, with some polymeric materials a visible score
line is not perceivable on the substrate material after laser
processing. In other words, an actual ablation in the sense that
material either melts or vaporizes does not occur. What has been
found more closely correlates to a breakdown of the actual
molecular structure of the polymeric material. This break down
reduces the strength or weakens the substrate material 14 along the
tear line 12, thus allowing for an easier separation in much the
same fashion as the partially perforated tear line 12 mentioned
above. With the breakdown of the molecular bonds, it appears that
the cross-linked bonds remain, resulting in a brittleness along the
tear line 12.
[0049] As in the partial perforation examples, it has been found
that areas with varying degrees of damage done along the tear line
12 enhances the desired properties of an easy-open application,
even if the resulting tear line 12 is not comprised of partial
perforations 16. In other words, laser processing areas along the
tear line 12 with varying degrees of damage to the molecular
structure of the polymeric substrate material enhances the benign
characteristics desired for easy-open applications, in the same
respect as partial perforations 16 adjacent to nonablated regions
20 (or adjacent partial perforations 16 having different depths
d',d" of ablation). In reference to FIGS. 4a-4d, the ablated
regions 16 could be considered as "damaged" regions, and the
unablated regions 20 could be considered as "undamaged" regions, or
regions 16a could be considered to have experienced less damage
than regions 16b.
[0050] FIG. 5 illustrates examples of different variations of
partially perforated tear lines 12. Table 1 lists the lengths of
the scored and unscored segments shown in examples A-G of FIG.
5.
1TABLE 1 .about.Dash .about.Spac .about.Perc. Score Between (%) of
Exam- Processing Length Scores Length ple: Material: Condition**:
(inches): (inches): Scored A 5 mil PET/PE in-line .0030 .022 13.6 B
5 mil PET/PE stationary .0046 .025 18.4 C 7 mil PE/PE stationary
0.19 0.38 50 D 3 mil LDPE crossweb .050 .100 50 shrink film E 4.5
mil 48 g stationary .007 .015 47 PET/Ink/PE/ 250 g LLDPE F 3 mil PE
stationary .030 .060 50 G 3 mil 90 g crossweb .048 .095 100/50
OPP/10 lb PE/ 70 g OPP
[0051] In FIG. 5, example A, the substrate material 14 has been
intermittently laser-processed at uniform intervals and at uniform
power levels to produce partial perforations 16 of a uniform depth
and spacing. As shown, the processed substrate material 14 was
produced using an in-line fixed beam system with the laser beam 18
split into four beams. The system controller was configured to
provide a 70 micro-second pulse every 0.022 inches on the substrate
material 14. In FIG. 5, example B, the uniform depth and spacing of
the partial perforations 16 on the substrate material 14 was
produced using a steered beam system on a stationary substrate
material 14. The system controller was configured to pulse the
laser beam 18 at 18.2% duty cycle at 8 kHz. The laser beam 18 was
steered at 200 inches per second.
[0052] In FIG. 5, example C, the uniform depth and spacing of the
partial perforations 16 on the substrate material 14 was produced
using a steered beam system on a stationary substrate material 14.
The system controller was set to pulse the laser beam 18 at 50%
duty cycle at 5 kHz. The laser beam 18 was steered 300 inches per
second.
[0053] In FIG. 5, example D, the partially perforated tear pattern
12 was produced using a steered beam system on a moving web of
substrate material 14. The partially perforated tear line 12 was
produced in a cross-web fashion. The system controller was set to
pulse the laser beam 18 at 50% duty cycle at 800 Hz. The laser beam
18 was steered at 80 inches per second with the web moving at a
rate of 38 feet per minute.
[0054] In FIG. 5, example E, the partially perforated tear pattern
12 was produced using a steered beam system on a stationary
substrate material 14. The system controller was set to pulse the
laser beam 18 at 10% duty cycle at 20 kHz. The laser beam 18 was
steered at 300 inches per second.
[0055] In FIG. 5, example F, the partially perforated tear pattern
12 was produced using a steered beam system on a stationary
substrate material 14. The system controller was set to pulse the
laser beam 18 at 50% duty cycle at 6667 Hz. The laser beam 18 was
steered at in a combination of a curved and straight pattern
segments at 400 inches per second.
[0056] In example G, the partially perforated tear pattern 12 was
produced using a dual steered beam system on a moving web of
substrate material 14. The tear pattern 12 was done in a cross-web
fashion. The system controller was set to pulse the laser beam 18
from a lower power level to a higher power level at 50% duty cycle
at 1052 Hz. The laser beam 18 was steered at 100 inches per second
with the substrate material moving at 47 feet per minute.
[0057] To further illustrate the advantages provided by the present
inventive method, a laser and a steered beam system were used to
create continuous score lines and partial perforation tear lines on
two different types of films (specifically the materials of
Examples C and G in Table 1). First, the tensile strength of the
unprocessed material was tested. Then, the laser power was set to
obtain an easy open feature on a portion of the substrate material
with a continuos score line, and the tensile strength of the
continuous-scored material was tested. Finally, same laser power
was used to generate partial perforations on a portion of the
substrate material. The score line and the partially perforated
tear lines exemplify the easy open feature of the present
invention. The data was collected utilizing an Omega Eng., Inc.
(model LCCA-50) 50 lb load cell on a MTS tensile testing machine
(type T5002) pulling at a rate of 50 mm/minute.
[0058] FIGS. 6-8 illustrate the examples of higher tensile
strengths per unit time obtained utilizing the partial perforation
score lines as previously described. Included for comparison is the
tensile strength from the non-scored material. FIG. 6 illustrates
the tensile strength of a substrate material 14 that has been laser
processed with a multilevel partial perforation score line similar
to those described in FIG. 4a and FIG. 5, example G. FIGS. 7 and 8
illustrate partial perforation score lines similar to those
described in FIG. 4b and FIG. 5, example C. FIG. 7 illustrates the
tensile strengths resulting from a higher laser energy than those
used in the graph of FIG. 8.
[0059] As illustrated by the FIGS. 6-8, the partial perforations
generated by the laser can maintain a higher level of tensile
strength than that generated from a continuous score. Under certain
conditions the partial perforations can maintain the tensile
strength over that of the non-scored material. Unexpectedly, under
certain conditions, the partially perforated score line actually
increased the tensile strength over that of the unprocessed or
non-scored material. It can be further noted that this is not
limited to one type of material. In fact, the benefits of laser
processing partial perforations at constant or uneven depths
appears to extend to any suitable substrate material, depending on
the specific parameters of the cut depth and the ratio of partially
perforated to unablated segments of the score pattern.
[0060] It has been found that the edges directly adjacent the laser
processed partial perforations 16 of the present invention are not
easy to rupture or tear, absent a shear force. Specifically, along
the partially perforated tear line, the tensile strength of the
substrate material remains equal to or greater than the tensile
strength of untreated substrate material, while the shear or
tearing force required to tear the substrate material along the
partially perforated tear line is substantially less than the
tearing force required to tear the substrate material along
untreated areas of the substrate material.
[0061] It is believed that the thermal interaction between the high
energy beam and the material chemically or physical alters the
adjacent substrate, in effect "heat treating" the substrate
material along the tear line, thereby rendering the adjacent
substrate harder and less susceptible to tear propagation as
compared with conventional perforating techniques, which may cause
additional fractures in the surrounding substrate material. In some
instances, the localized heat treatment may partially melt the
substrate material 14 directly adjacent to the vaporized partial
perforations 16. The melted substrate material may then flow
filling minute imperfections and improving the surface
characteristics of the substrate material adjacent the partial
perforations 16. Finally, the melted substrate material sometimes
forms minute ridges, which may also improve the surface
characteristics of the substrate material surrounding the partial
perforations 16. By filling minute imperfections and/or by forming
minute ridges, such melt flow may fill minute imperfections that
might otherwise assist in propagating a tear.
[0062] This increase in tensile strength of substrate materials
that are laser processed with partially perforations makes it
possible to partially perforate substrate materials at almost any
ratio of heat treated to untreated segments. In fact, it may be
possible to laser process a perforation to a depth equal to a full
thickness of the substrate material at ratios greater than 50% cut,
without exposing the packaging system to accidental burst.
[0063] Additionally, the improved tensile strength of the substrate
material across the partial perforation makes it possible to
perform cross-web laser processing while maintaining the requisite
tension on the web material. Cross-web scoring of web materials in
the prior art risked tearing and stretching of the web material
before it could be rewound. In particular, polyethelene and similar
materials were difficult to process cross-web without experiencing
stretching and tearing caused by tensioning the web material so
that it does not flap during the laser process. However, the
present inventive method may be performed on polyethelene and other
flexible web materials in a cross-web scoring process, and tension
can be maintained without stretching or tearing.
[0064] While the invention has thus far been described with respect
to partially perforated tear patterns 12 that are largely linear,
it is contemplated that other shapes and positions of the partially
perforated tear pattern 12 can also be applied. As shown in FIG. 9,
a load bearing packaging system 26 formed from substrate material
14 is provided with a partially perforated tear line 12 on an end
28 of the package system 26. As previously described, the partial
perforations 16 extend to a depth less than a full thickness of the
substrate material 14. In this example, by positioning the tear
pattern 12 on an end 28 of the packaging system 26, the depth of
the partial perforations 16 do not impact the tensile strength of
the sealed packaging system 26 to the same degree as other
embodiments because the end 28 does not bear as much of the load as
the sides 30.
[0065] The punch-out tear pattern 12 shown in FIG. 9 may have
varying depths and spacing of the perforations 16. Specifically,
several perforations 16 may be made deeper and closer together so
as to create a point or area 32 of significant weakness along the
tear line 12 that can be used to initiate the tear by pushing on
the point or area 32 of weakness. Once the tear is initiated, it
propagates along the partially perforated tear line 12.
[0066] In addition to the tear lines 12 depicted in the figures,
various other shapes are also contemplated. Additionally, the
location of the tear line 12 may be varied according to the desired
opening. For example, FIG. 9 depicts a curved shape on the end 28
of the packaging system 26. This particular embodiment may be used
to form a pour spout on the end 28 of the packaging system 26, so
as to provide for an easy open feature that provides an easy pour
opening.
[0067] Finally, while the method of the present invention has been
described with respect to laser beam ablation, the invention can be
performed using any high energy beam, such as a laser beam, an
electron beam, or the like.
[0068] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *