US20030051440A1

US20030051440A1 - Method of creating easy-open load carrying bags

Info

Publication number: US20030051440A1
Application number: US10/236,703
Authority: US
Inventors: Chris Chow; Dan Miller; Kurt Hatella
Original assignee: Preco Laser Systems LLC
Current assignee: Preco LLC
Priority date: 2001-09-13
Filing date: 2002-09-06
Publication date: 2003-03-20

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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.”[0001]

FIELD OF THE INVENTION

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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

FIG. 1 is a perspective view of a sealed packaging system including an easy-open feature made in accordance with the present inventive method. [0013]
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. [0014]
FIG. 3 is a perspective view of a laser beam selectively ablating a substrate material in accordance with the present inventive method. [0015]
FIG. 4[0016] a 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.
FIG. 4[0017] b 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.
FIG. 4[0018] c 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.
FIG. 4[0019] d 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.
FIG. 5 includes cut away views of the substrate material taken along lines [0020] 4-4 in FIG. 3 illustrating other various patterns of partially perforated score lines of the present invention.
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. 4[0021] a and FIG. 5, example G.
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. 4[0022] b and FIG. 5, example C.
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. [0023]
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.[0024]

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, an [0025] 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.
The phrase “partial perforation” refers to a selected region on the [0026] 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.
As shown, the [0027] 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.
In accordance with present inventive method, a [0028] 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.
Generally, the easy open/[0029] 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.
The [0030] 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.
Generally, the [0031] 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.
The [0032] 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.
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 [0033] 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.
Tensile strengths of [0034] 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.
The partially [0035] 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.
The selective arrangement of [0036] 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.
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 [0037] 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.
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 [0038] 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.
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 [0039] 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.
Referring to FIG. 3, which depicts the [0040] 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.
The [0041] 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 (τ) 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 (τ) 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.
FIGS. 4[0042] a-4 d 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 4 a-4 d are disposed within the substrate material 14, which has a thickness τ. 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.
For illustrative purposes, the [0043] 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, 4 c and 4 d 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, 4 c and 4 d could also be performed on a multi-layer substrate 14 of almost any composition.
The exemplary partially [0044] perforated tear line 12 represented by FIG. 4b includes a first ablated region 16 a having depth d′, and a second ablated region 16 b having depth d″. Disposed between and adjacent to each ablated region 16 a and 16 b are unablated regions 20. As previously discussed, variations in the depths d′,d″ of the perforations 16 a, 16 b 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 16 a, 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.
FIG. 4[0045] c 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 16 a, 16 b. As shown, FIG. 4c includes partial perforations 16 a having a depth d′ and a length L′, and partial perforation 16 b having a depth d″ and a length L″. Furthermore, the length l′,l″ is shown to vary between partial perforations.
By controlling the spacings l′,l″ between [0046] partial perforations 16 a,16 b, the lengths L′,L″ of the partial perforations 16 a, 16 b, and the depths d′,d″ of the partial perforations 16 a, 16 b, 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.
As shown in FIG. 4[0047] d, the spacing between partial perforations 16 a, 16 b can be reduced to a magnitude of zero, such that the partial perforations 16 a, 16 b 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.
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 [0048] 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.
As in the partial perforation examples, it has been found that areas with varying degrees of damage done along the [0049] 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-4 d, the ablated regions 16 could be considered as “damaged” regions, and the unablated regions 20 could be considered as “undamaged” regions, or regions 16 a could be considered to have experienced less damage than regions 16 b.

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.

TABLE 1


			˜Dash	˜Spac	˜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

In FIG. 5, example A, the [0051] 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.
In FIG. 5, example C, the uniform depth and spacing of the [0052] 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.
In FIG. 5, example D, the partially perforated [0053] 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.
In FIG. 5, example E, the partially perforated [0054] 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.
In FIG. 5, example F, the partially perforated [0055] 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.
In example G, the partially perforated [0056] 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.
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. [0057]
FIGS. [0058] 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.
As illustrated by the FIGS. [0059] 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.
It has been found that the edges directly adjacent the laser processed [0060] 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.
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 [0061] 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.
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. [0062]
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. [0063]
While the invention has thus far been described with respect to partially [0064] 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.
The punch-[0065] 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.
In addition to the tear lines [0066] 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.
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. [0067]
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. [0068]

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.