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POLY ERIC PACKAGE OPENING STRUCTURE

Field of the Invention The present invention relates to opening structures for sealed packages, and in particular relates to an opening structure for a sealed package formed of a polymer, and for which sterile conditions must be initiated and maintained until the bag is opened.

Background of the Invention Packages, specifically in the forms of pouches or bags, are used in a variety of commercial and industrial applications. Many such applications are in the medical industry, where such polymer (plastic) pouches are often used to carry instruments, devices, and materials ("kits") used in medical procedures. As might be expected, in order to prevent contamination and infection of a patient when the medical device or instruments are used, such devices and materials are typically often sterilized either during manufacture or by post-manufacture sterilization. Accordingly, the polymers used to form such bags are desirably selected according to their ability to withstand various sterilization techniques such as radiation, steam, other high-temperature or electromagnetic treatments, or other techniques. Furthermore, in many circumstances, the materials carried in the bag need to be sterilized, and thus not all plastics or polymers can be appropriately used for such sterile medical applications.

Certain thermoplastic polymers, particularly polyolefins, are one set of materials that are useful for such bags. Thermoplastic polymers can be subjected to commonly-used sterilization techniques, are generally very durable, provide a biological barrier to

prevent instruments after sterilization, and can often be made into transparent films that permit the contents of the bags to remain visible, particularly to the personnel that are going to use them. In logical sequence, the purpose of packaging medical instruments and supplies in sterile bags is that of later using them in medical procedures. Thus, once formed and sterilized, the bags must be relatively easy to open, in terms of both speed and convenience, by medical personnel during the course of medical procedures. One typical method of providing an opening system for such a bag is to provide a score line across the bag, i.e., a line of weakness in the polymer. A score line represents an attempt to give medical personnel a means for easily opening the bag by pulling on opposite sides of the score line.

Score lines, however, must meet conflicting standards. They need to be weak enough to allow the package to be opened easily when desired, but strong enough to prevent the bag from opening unintentionally during normal handling. Thus, the task of producing a successful score line is one of making a highly predictable strength value. As might be expected, because of the stringent requirements of medical packaging, attempting to get such a perfect score line can tend to result in a fair amount of manufacturing waste. Forming score lines of a desired strength has also been made more difficult by the generally increasing strength of the polymers used to form the bags. Additionally, score lines are particularly disadvantageous for bags that contain sterile liquids because of their potential for undesired and unintentional leakage.

Another typical opening structure for sterile packaging is referred to as a "peelable header." Such a structure is formed of a portion of paper or other similar material that is welded over an opening in the

polymer that forms the remainder of the sterile package. Although generally useful, the extra materials and steps required to produce peelable headers tends to raise their cost and manufacturing complexity. Additionally, peelable headers tend to be vulnerable to premature--i.e. , undesired--opening during sterilization and handling.

As an additional factor, the strength of polymers used to form sterile packages has continued to increase. As might be expected, the increased polymer strength offers a number of advantages in the resulting package: larger kits can be packaged, and shorter, but more severe, sterilization techniques can be used. The stronger polymers also provide higher resistance to cuts, punctures, and overall impact. Nevertheless, the stronger polymers are more difficult to open, and balancing structural integrity against ease of opening becomes more difficult.

Object and Summary of the Invention

Therefore, it is an object of the present invention to provide an opening structure for a polymeric package which provides ease of opening when opening is desired, but which has a better strength and integrity in keeping the package closed during manufacture, packaging, sterilization, storage, and handling.

The invention meets this object with an opening structure for a polymeric sheet material such as those used to form sealed packages, including sealed sterile packages for medical applications. The opening structure comprises a polymer sheet formed of a plurality of linearly extending adjacent ribs in which the polymer is highly oriented along the linear direction defined by the ribs. The ribs include portions that are generally weaker in tear strength along the direction of orientation than the remaining

portions of the ribs to thereby form a more easily tearable, and thus more easily opened, portion of the polymer sheet. The opening feature can be used in the absence of other mechanical features such as scoring that would otherwise weaken the mechanical integrity of the sheet.

In another aspect, the invention comprises an opening structure for a polymeric sheet material such as those used to form sealed packages, in which the opening structure comprises a first polymer sheet having an opening precursor structure; and a second polymer sheet superimposed on the first polymer sheet and covering the opening precursor structure. The second sheet has a tear strength that is greater than the tear strength of the opening precursor structure and less than the tear strength of the remainder of the first polymer sheet.

The foregoing and other objects, advantages, and features of the invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments, and wherein:

Description of the Drawings

Figure 1 is a perspective view of an opened bag with an opening structure according to the present invention;

Figure 2 is a perspective view of a sealed bag with the opening feature of the present inven ion; Figure 3 is a view showing the manner in which the opening features works;

Figure 4 is a cross-sectional view taken along lines 4-4 of Figure 1; and

Figure 5 is a view of the interior face of a polymer sheet with an opening structure according to a further embodiment of the invention.

Detailed Description

The present invention is an opening structure for a polymeric sheet material such as those used to form sealed packages, including sealed sterile packages for medical applications. The opening structure is usually incorporated in conjunction with a bag structure, although it will be understood that the invention is not limited to bags per se. Figures 1 and 2 illustrate perspective views of a bag broadly designated at 10 that incorporates the opening structure according to the invention. As illustrated, the bag is formed of two substantially transparent polymer sheet portions 11 and 12. Although illustrated as being transparent, such is a preference rather than a requirement. In other cases, the sheets are preferably translucent or opaque as may be desired or necessary for a given application. It will thus be understood that the transparency or opacity of the sheets is unrelated to the invention or to the scope of the claims herein. The bag 10 also includes four edges 13, 14,

15, and 16 respectively that together form and define the bag 10. As illustrated in Figures 1 and 2, the bag edges can comprise seals or folds depending upon the manner in which the bag is made. In Figure 2, sides 14 and 16 are perhaps most clearly illustrated as seals, while edges 13 and 15 are illustrated as folds. It will be understood, however, that the various combinations of seals and folds that can be used to make a plastic bag are not in themselves limiting of, or dependent upon, the opening feature of the present invention.

The opening structure is a polymer sheet broadly designated in the drawings at 17. The sheet is formed of a plurality of linearly extending adjacent ribs 20 (Figure 4) in which the polymer is highly oriented along the linear direction defined by the ribs. The ribs include portions that are generally weaker in tear strength along the direction of orientation than are the remaining portions of the ribs 20 to thereby form a more easily tearable, and thus more easily opened, portion of the polymer sheet.

Generally, the weaker portions are the thin portions between the ribs 20.

The term "orientation" is used herein in its usual sense to express the degree of parallelism of the chain molecules that form the polymer. The more parallel the molecules, the more highly oriented the polymer is said to be.

The drawings illustrate the ribbed polymer sheet as a substantially planar strip 17, but in other embodiments, the ribbed polymer sheet can comprise a tube. The ribbed polymer strip 17 can be incorporated into a side seal bag format or a bottom seal bag format as may be desired or necessary.

The ribbed polymer sheet is preferably formed of a thermoplastic polymer, as these tend to be the most easily oriented and thus most useful for the present invention. For medical applications, where strength and sterilizability are required, polyolefins (e.g., polyethylene, polystyrene, polypropylene) are often preferred, along with various ionomers. For other applications, such as food packaging, where properties such as moisture and oxygen transmission characteristics (or barrier characteristics) are required, the polymer can comprise nylon, ethylene vinyl alcohol (EVOH) polymers and other polymers with similar or related properties.

It will be understood that if desired, the entire bag 10 could be formed of the ribbed sheet 17. Nevertheless, for most applications, some greater or lesser amount of non-ribbed surface portions are useful for printing, labeling, and overall visibility, particularly when the polymer sheets 11 and 12 are transparent. Additionally, the non-ribbed sheet portions tend to be more amenable to the blowing steps often used in the manufacture of polymer tubes and bags. Stated differently, the blow-up ratios of the ribbed portions tend to be lower than those of the non- ribbed portions.

Thus, the opening structure 17 according to the present invention can be welded to a transparent sheet of thermoplastic polymer, as illustrated by the weld lines 21 and 22 in Figure 3. Alternatively, the opening structure 17 can comprise a single sheet that includes both ribbed portions and non-ribbed portions. In the embodiment illustrated in Figures 1 and 4, the ribbed sheet 17 is welded over a portion of the sheet material 11 that forms the overall bag 10. In a preferred embodiment, at least one of the polymer sheets 11 or 12 can comprise a score line (not shown) , and the ribbed polymer strip 17 can cover the score line, a perforated line, or even a slit. Because the ribbed polymer strip 17 is welded to the sheets 11 and 12, the score line is sealed from exposure, and thus can be formed to be easily tearable _. without sacrificing the overall integrity of the bag 10 and without concern for opening unintentionally.

Alternatively, the sheet 11 or 12 can be replaced by the strip 17 for a portion of the bag equivalent to the width of the strip. In either case, the strip 17 is preferably welded to the sheets 11 and 12. In yet another embodiment, the ribbed polymer strip 17 can be integral with the remainder of one or both of the polymer sheets 11 and 12. If desired, the

opening structure can be used in the absence of other mechanical features such as scoring, perforations, or slits, that could otherwise weaken the mechanical integrity of the sheets 11 and 12 and the overall bag 10.

As used herein, the term "welded" refers to any appropriate method of securing polymer sheets to one another and can include heat sealing, radio frequency sealing, and other techniques that will provide the appropriate integrity required for such a sterilizable structure. As noted earlier, in many embodiments, the polymer sheets 11 and 12 are transparent and form an overall transparent bag structure. In another aspect, the invention comprises a method of forming an opening structure for a polymeric sheet such as the sheets used to form sealed packages including sealed sterile packages for medical applications such as the bag 10 illustrated in the drawings. The method comprises extruding a fluid polymer through a plurality of adjacent capillaries that provide sufficient drag flow to the fluid polymer to force the fluid polymer into linear orientation along the direction of extrusion. Thereafter, the extruded liquid polymer is solidified quickly enough to prevent the extruded liquid polymer from returning to a more random orientation during solidification.

As used herein, the term "extrusion" is used in its usual sense; i.e., a processing operation in which the material--here the polymer--is forced through a forming die, followed by some sort of cooling or other hardening. When polymers are extruded, they can be solidified in several fashions. The usual techniques include cooling a liquid polymer to a temperature lower than its melting point; e.g. by contact with air, water, or a cool- surface such as a chill roller.

In a preferred method of the invention, the step of extruding the fluid polymer through the plurality of adjacent capillaries comprises extruding the polymer through adjacent capillaries that together form a substantially planar opening, or alternatively a substantially circular opening. It will be understood, of course, that a circular (round die) opening or a planar (slot die) opening are not the only geometric shapes that are appropriate, but are the most straightforward and logical for a large number of applications. In either case, the step of solidifying the extruded liquid polymer comprises solidifying the liquid polymer either in the substantially planar shape of the opening, or the substantially circular shape of the opening. The solidifying step is preferably a conventional cooling step such as exposure to air, a water bath, or a chill roller.

As set forth earlier, the step of extruding the polymer preferably comprises extruding a thermoplastic polymer selected from the group consisting of polyethylene, polypropylene, other polyolefins, and polystyrene. The term "thermoplastic" is used in its usual sense herein and refers to those polymers that soften when exposed to heat, and return to their original condition when cooled to room temperature. Natural thermoplastic substances include rubber and certain waxes, but the term is more typically applied to synthetics such as polyvinyl chloride (PVC) , nylons, fluorocarbons, polyolefins, polyurethane prepolymers, polystyrene, and certain of the cellulosic and acrylic resins. In certain circumstances, however, a thermosetting polymer may be selected, the term "thermosetting" being used in its usual sense to define a polymer that solidifies or sets irreversibly when heated or chemically cured.

Figure 5 is a view of the interior face of a bag, and illustrates another embodiment of the present

invention. In Figure 5, the interior face 25 of one of the sheets that forms the bag includes an opening precursor structure shown as the perforated line 26. As noted earlier, the opening precursor structure could also comprise structures such as slits or score lines. A second polymer sheet 27 is superimposed on the first polymer sheet 25 and covers the perforated line 26 on the exterior of the first sheet 25 and thus on the exterior of a bag structure that includes the first sheet 25. The second sheet 27 has a tear strength that is greater than the tear strength of the perforated line 26, and less than the tear strength of the remainder of the first sheet 25. In that manner, the second sheet 27 provides both an appropriate sealing structure over the perforated line 26, as well as a structure that is easier to open than would be a bag structure formed entirely of the material of the first sheet 25.

In summary, the invention provides an easily openable package that can be formed of stronger polymers that would otherwise be difficult to open. If necessary, the structure provides for sterilization and physical integrity of the package that is much higher than when other opening systems are incorporated. As noted with respect to the structural aspects of the invention, the ribbed and non-ribbed portions of a sheet (or bag precursor tube) could be extruded from a common opening.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms have been employed, they have been used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.