Patent Publication Number: US-2009238502-A1

Title: Perforated easy opening pouch

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/069,990 filed on Mar. 19, 2008. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to pouches. Specifically, the present invention relates to pouches which are easy to tear open. 
     BACKGROUND OF THE INVENTION 
     Pouches are typically formed of a laminate or a film and may be used for holding many types of items such as food, shampoos, detergents, medicines, etc. In order to make them easier to use, notches, laser cut score lines, and perforations are standard in the packaging industry. However it is always a challenge to balance the need for an easy opening functionality (e.g., tear lines, perforations, score lines, etc.) with pouch sturdiness and strength against bursting and leakage. Many packages such as, for example, laundry detergents do not have tearing lines because during shipment such pouches are often dropped, compressed, etc. which could cause unacceptable leakage. Instead, merely a notch or other slit is made to start the tearing, but no cost-effective technology has been found which can also control the propagation of the tear. Instead, often the pouches are cut open with scissors. 
     Small, e.g., less than 500 mL, pre-formed pouches and pouches formed from two layers are more easily customizable and they often possess notches, or perforated tearing lines. Specifically, while such pre-formed pouches are useful for smaller volumes, they become more difficult for larger volumes, where the volume : sealing area ratio becomes too large. The strength of a seal is directly proportional to the sealing area, and a seal is generally weaker than the film material itself. So, as the volume grows, the sealing area may need to grow proportionally, which leads to a large amount of wasted film material and/or a weak pouch which bursts too easily and/or which may leak during shipping, dropping, etc. in other words, when such pre-formed pouch technologies are scaled up to, for example 1-2 liter or larger bags, known methods for forming tearing lines (laser cutting, etc.) tend to unacceptably expensive to complicate, and/or may weaken the pouch integrity, causing undesirable leakage, breaking and/or bursting during manufacturing, filling, shipping, etc. 
     Accordingly, the need exists for an improved pouch and easy-opening system which is both easy to tear, and strong against unintentional breakage, especially for larger pouches. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a perforated large-size easy opening pouch is formed from a single sheet containing at least one layer of a film material, and the sheet forms a volume. The pouch also contains a seal containing a perforation. The perforation is completely surrounded by the seal. When a tear is initiated along the perforation, the tear propagates to a non-sealed portion of the pouch. 
     A sealing jaw contains a sealing arm with a profiled sealing area further containing a cut blade. The cut blade is completely surrounded by the profiled sealing area. The sealing jaw also contains a receiving jaw containing a profiled sealing area further containing a cut channel to receive the cut blade. 
     The pouch sealing method herein includes the steps of providing a sheet, forming a tube having a leading edge, sealing the leading edge to form a first seal, filling the tube with a predetermined amount of a product, and simultaneously sealing the tube to form a second seal and cutting the tube to form a pouch filled with the product. At least one of the first seal or the second seal comprises a perforation which is completely surrounded by the respective first or second seal. When a tear is formed along the perforation, the tear propagates to a non-sealed portion of the pouch. 
     It has now been found that the invention can balance easy opening via a tearing line combined with profiled sealing while also maintaining the robustness and strength of a complete seal. Also described herein is a method of and a sealing jaw for sealing and creating the easy opening portion simultaneously with the bag formation and packing. Since the sealing jaw combines the sealing profile with the perforator, it further reduces misalignment of the perforation, optional notch, sealing portions, etc. which could happen if they were formed on different machines, or in different processes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the invention, it is believed that the invention will be better understood from the following description of the accompanying figures in which like reference numerals identify like elements, and wherein: 
         FIG. 1  is a front view of an existing comparative pouch having a tear notch; 
         FIG. 2  is a front view of an embodiment of the pouch herein; 
         FIG. 3  is a cut-away view of the embodiment of  FIG. 2 , as seen along line  3 - 3 ; 
         FIG. 4  is a close-up front view of an embodiment herein; 
         FIG. 5  is a front view of an embodiment of the sealing arm according to the invention herein; 
         FIG. 6  is a front view of an embodiment of the receiving arm according to the invention herein; 
         FIG. 7  is a front view of an embodiment showing multiple perforations; 
         FIG. 8  is a close-up front view of an alternate perforation; 
         FIG. 9  is a close-up front view of an alternate perforation; and 
         FIG. 10  is a close-up front view of an alternate perforation. 
     
    
    
     The figures herein are not necessarily drawn to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
     All temperatures herein are in degrees Celsius (° C.) unless otherwise indicated. As used herein, the term “comprising” means that other steps, ingredients, elements, etc. which do not adversely affect the end result can be added. This term encompasses the terms “consisting of” and “consisting essentially of”. 
     This disclosure relates to a perforated large-size easy opening pouch formed of a single sheet of film material. The pouch contains a perforation which is completely surrounded by a seal, and when a tear is formed along the perforation, the tear propagates to at least one non-sealed portion of the pouch. This disclosure also relates to methods and equipment for making such a pouch. 
     Referring to the Figures herein,  FIG. 1  is a front view of an existing comparative pouch,  10 , having seals,  12 , on four sides. The seals form a volume,  14 , for containing a product. The pouch,  10 , is typically a pre-formed pouch which is formed from two sheets of film material. Pre-formed pouches are typically made by sealing all except for 1 side of the pouch, and either sequentially or concurrently cutting the shape. The product is then filled into the pouch, and the remaining side sealed. Such pre-formed pouches are typically used for small volumes of from &lt;1 mL up to about 500 mL, but tend not to be used for larger volumes. Occasionally pre-formed standing pouches may be used for larger volumes, such as liquid detergents. 
     The comparative pouch in  FIG. 1  contains a tear-notch,  16 , which provides a starting point and indicator for the user to tear the pouch, and the tear will propagate to a non-sealed portion, such as the spout,  18 , and then to somewhere on the sealed side,  12 ′. However, such a tear is not easy to control, and in fact the tear will often times go to very different places on the sealed side,  12 ′. In other words, it is difficult to reproducibly tear such a pouch. Once the pouch is tom open, the product can be used and/or taken out. 
       FIG. 2  is a front view of an embodiment of the pouch,  20 , herein which is formed from a single sheet of film material which contains seals,  12  at the top,  22 , and bottom,  24 . The pouch,  20 , also has sides,  26 , which do not have any seals. The pouch,  20 , contains a tear-notch,  16 , formed in the seal,  12 , at the top,  22  which points towards a perforation,  28 . The perforation,  28 , is completely surrounded by the seal,  12 ″ in the X and Y planes parallel to the pouch surface. It is the fact that the perforation,  28 , is completely surrounded by the seal,  12 ′, which allows the pouch to tear easily and controllably and yet still have the structural stability and also high bursting resistance. A longitudinal seal,  12 ′″ completes the pouch and forms what is commonly known in the art as a “pillow bag”. 
     The pouch is formed of sheet which is in turn formed from at least one film material typically selected from the group consisting of polyamide (nylon), polyethylene, polypropylene, ethyl-vinyl-acetate, poly-4-methylpentene-1, a microporous membrane, and a combination thereof; or polyamide (nylon), linear low-density polyethylene, an oriented polypropylene, polyethylene terephthalate, and a combination thereof. The film material may also be affixed to and/or contain a metal therein, and/or be a metallized film. Film materials are well known in the art and may further contain resins, laminates, printed artwork, additives (i.e., UV blockers, antimicrobials, dyes, pigments, etc.), etc. Suitable film materials are available from various suppliers worldwide such as 3M Company (St. Paul, Minn., USA), Du Pont Co. (Wilmington, Del., USA), Toppan Insatsu Co. (Tokyo, Japan), and Gelman Sciences Company (Ann Arbor, Mich., USA). The sheet herein may contain either a single layer or contain multiple layers of film material, so long as it remains sealable. The sheet is from about 15μ to about 220μ, or from about 20μ to about 200μ, or from about 25μ to about 160μ thick. Each individual film material may be oriented, or random. 
     Multiple layers of film materials may be joined together to form a sheet with multiple properties and/or benefits. In such cases, it is known in the art to join the multiple layers together by, for example, lamination, heat sealing, ultrasonic sealing, gluing, pressure sealing, etc. The sheet may then be formed into a pouch by pulling and/or stretching the sheet around a forming tube and sealing the edges in any direction such as the machine direction at any point or the cross direction at either the top and/or the bottom. In an embodiment herein the pouch is sealed in the machine direction to form a tube. The leading edge is then sealed by a sealing jaw in the cross direction, the product to be contained in the tube is then filled into the tube, pulled to advance the sheet, and the sealing jaw simultaneously seals and cuts the trailing portion in the cross direction, thereby releasing the filled bag and forming a new leading edge at the same time. Machinery and techniques for forming such filled pouches are often referred to as autopacking machines and are well known in the art and available from multiple suppliers around the world. 
     As noted above, small preformed pouches (see  FIG. 1 ) may easily possess sufficient strength to hold small amounts of product, and/or low density products without bursting even when perforations are made in the film and/or sheet. So, the pouch herein is typically intended to hold large amounts of bulky products, as that is where the benefits of the invention are especially evident. Thus, in an embodiment herein the pouch comprises a volume (when sealed) of at least 500 mL, or from about 500 mL to about 100 L, or from about 800 mL to about 60 L, or from about 1 L to about 30 L, or from about 1.5 L to about 20 L. The product (not shown) to be filled into the pouch typically has a bulk density of at least 250 g/L, or from about 300 g/L to about 1.3 kg/L, or from about 450 g/L to about 1.1 kg/L. Non-limiting examples of the product include a solid product, a granular product, a liquid product, and/or a gel product. In an embodiment herein, the product is a granular detergent, a liquid detergent, a food item, a drink item, a fabric softener, a fabric conditioner, a fertilizer, or a chemical, as such items may be easily packed and stored in such a pouch which may be easily opened by hand tearing. In an embodiment herein, the food item is a human food item or an animal food item such as a pet food. 
       FIG. 3  shows a cut-way view of the embodiment in  FIG. 2 , as seen along lines  3 - 3 . The pouch,  20 , is formed of a single sheet of film material,  30 , which is connected to itself at seals  12 ″ and  12 ′″ so as to define an internal volume,  14 . As will be understood by one skilled in the art when comparing  FIG. 2  and  FIG. 3 , the volume  14  and the volume  14 ′ are actually connected to each other and the same. Similarly, the seals  12 ″ are actually connected to each other and are the same. In  FIG. 3 , the perforation,  28 , (actually a cut,  34 , as per  FIG. 4 ) is the only thing which separates the seals  12 ″ from each other, and in fact where the perforation,  28 , ends it can be seen that the seals  12 ″ are part of the same seal,  12 ″. See also  FIG. 2 . 
       FIG. 4  shows a close-up view of an embodiment herein focusing on the top,  22 , where the perforation,  28  is located. Here, the perforation,  28 , is shown as a line of cuts,  32 , and in  FIG. 4  these cuts,  32 , are intended to be microdots leading in a straight line from the corner of the tear-notch,  16 , diagonally downwards towards the side,  26 . Typically, it is important that the cut,  32 , goes substantially through both layers of the sheet,  30 , present at the seal,  12 ″ so as to allow easy hand tearing. The perforation,  28 , herein typically is composed of a line or other pre-determined arrangement of a plurality of cuts,  32 , in the sheet,  30  with the shape of each cut,  32 , being selected from the group consisting of a line, a dot, a triangle, a diamond, a circle, a rectangular, an oval, and a combination thereof, or a line, a dot and a combination thereof, that can enhance directional propagation of the tear. Typically, each cut,  32 , should generally lead in the same direction, so as to be able to guide the propagation of the tear towards the side,  26 , and more specifically towards the target tear destination,  34 . Such guiding of the propagation of the tear is especially effective if at least one film material is in the sheet at least partially oriented, and/or contains an oriented sheet which encourages the tear to propagate in the desired direction. 
     To further encourage the tear to propagate towards the side,  26 , rather than the bottom,  24 , it can be seen in  FIG. 4  that the top,  22  forms a line A-A and the perforation,  28 , forms a line B-B. A-A and B-B intersect to form an angle, α, that is typically of from about 90° to about 180°; or from about 110° to about 160°, or from about 120° to about 150°. In an embodiment herein, the cuts forming the perforation are arranged in a line, a curve, an angle, and a combination thereof (see,  FIGS. 8-10 ). 
       FIG. 4 , indicates a certain perforation distance, PD, which is measured from the beginning of the first cut,  32 , along the pattern, often a line, formed by the other cuts,  32 , to the farthest portion of the last cut,  32 ′. In many cases the dimensions of each cut,  32 , will be difficult to measure by the naked eye; however, regardless of the shape of the cut, each cut typically measures less than about 1 cm, or from about 1 cm to about 0.01 mm, or about 5 mm to about 0.05 mm, or from about 3 mm to about 0.1 mm in their longest direction. 
     In  FIG. 4 , the torn portion,  36 , is the triangular corner which is removed from the pouch,  20 , after the tear propagates along line B-B to reach the target tear destination,  34 . Once the torn portion,  36 , is removed, a spout,  18 , remains. In  FIG. 4 , the spout,  18 , would have a circumference of two (2) times the spout distance, SD, which is measured from the edge of the seal,  12 , to the tear target destination,  34  along the line B-B. 
       FIG. 4  also indicates the tear distance, TD, which is the distance as measured from the end of the last cut, to the target tear destination,  34 . For convenience&#39;s sake, the target tear destination in  FIG. 4  is defined as the point at which a hypothetical line extended from the end of the last cut,  32 ′ touches the side,  26 . In other embodiments, such as seen in  FIG. 7 , for example, one skilled in the art would understand that the target tear destination is oppositely oriented, with the tear propagating from the side,  26  to a target tear destination,  34 , at the top,  22 . One skilled in the art understands that other variations are possible and encompassed herein. The ratio of the perforation distance, PD, to the tear distance, TD, is typically more than 1:10, or from about 1:10 to about 3:1, or from about 1:5 to about 2:1, or from about 1:3 to about 1:1. Without intending to be limited by theory, it is believed that ratios where the tear distance is too much larger than the perforation distance result in a less controllable tear which may then propagate in too many undesirable directions such as towards the bottom,  24 , instead of towards the target tear destination. Conversely, if the tear distance is too much smaller than the perforation distance, then the spout formed may be too small to efficiently dispense the product. 
       FIG. 5  is a front view of an embodiment of a sealing arm,  50 , of the present invention. The sealing arm,  50 , and the receiving arm (see  FIG. 6 , at  70 ), are opposed to each other, and often joined together to form a sealing jaw (not shown). The sealing arm,  50 , contains a profiled sealing area,  52 , for forming the seal (see  FIG. 4  at  12 ″). The profiled sealing area,  52 , further contains a plurality of cut blades,  54 , for forming the cuts,  32 . As can be seen in  FIG. 5 , the profiled sealing area,  52 , completely surrounds the cut blades,  54  in the X and Y planes parallel to the sealing arm surface. The cut blades,  54 , directly correspond to and form the cuts, (see  FIG. 4  at  32 ). As one skilled in the art would appreciate, the shape and number of the cut blades,  54 , should correspond to the shape and number of the desired cuts (see  FIG. 4  at  32 ), and thus may also encompass needles, and/or other shapes. Furthermore, as one skilled in the art would realize, the cut blades should be of sufficient structural integrity, and durability to both penetrate both layers of the sheet (see  FIG. 4 , at  30 ) completely, and also be oriented to easily release the sheet and/or the finished pouch after the seal and perforation is made. In an embodiment herein, the cut blade is from about 1 cm to about 10μ, or from about 5 mm to about 20μ, or from about 2 mm to about 40μ in height, as measured perpendicularly from the surface of the sealing arm,  50 . In an embodiment herein, a plurality of sealing jaws may be used such that, for example, sealing jaw may be present to seal the top of the pouch, while a separate sealing jaw may seal the bottom of the pouch. In an embodiment herein the cut blade may be perpendicular to the surface of the sealing arm, or may be angled in the machine direction. Without intending to be limited by theory, it is believed that if the cut blade is perpendicular to the surface of the sealing arm, then at slower autopacking machine speeds the cut blade will more effectively form the cuts. However, it is believed that at faster autopacking machine speeds, a cut blade that is angled in the direction of the package flow may more quickly release the finished pouch, so as to reducing jamming of the autopacking machine caused by a failure of the finished pouch to drop away from the sealing arm. 
     In  FIG. 5 , the sealing arm,  50 , further contains an optional cutting edge,  56 , for cutting the pouch,  20 , after filling, and also a slit blade,  58 , for cutting a slit (see, e.g.,  FIG. 9  at  38 ). The cutting edge,  56 , may be present on either the sealing arm,  50 , or the receiving arm (see  FIG. 6  at  70 ), as desired. However placing the cutting edge,  56 , and the cut blade,  54 , on the same part of the sealing jaw may avoid problems caused by misalignment of the sealing arm,  50 , and the receiving arm (see  FIG. 6 , at  70 ). The cutting edge,  56 , may be straight, jagged, curved, etc. as desired. The slit blade,  58 , is typically located next to the first cut blade,  54 , so as to enhance the propagation of the tear in the desired direction. One skilled in the art recognizes that the slit blade may be easily replaced by, for example, a notch blade to form a notch, etc. In an embodiment herein, the sealing arm or the receiving arm contains a slit blade, a notch blade, or a combination thereof. 
     The sealing arm,  50 , contains a top seal portion,  60 , which forms the seal at the top of the pouch (see  12 , at  22  in  FIG. 4 ). On the other side of the cutting edge,  56 , from the top seal portion,  60 , lies the bottom seal portion,  62 , which forms the seal at the bottom (see  12 , at  24  in  FIG. 2 ) of the next pouch in the series. The sealing arm,  50 , also contains optional sealing ridges,  64 , which provide textured seals, which may be desirable in some instances to produce, for example, an easier to grip seal, to enhance seal strength, aesthetic reasons, etc. In an embodiment herein, the sealing jaw is designed so that it can cut a handle in the seal,  12 . 
       FIG. 6  is a front view of an embodiment of a receiving arm,  70 , of the present invention. The receiving arm,  70 , complements the sealing arm ( FIG. 5  at  50 ), and is a mirror image thereof, containing a complementary profiled sealing area,  52 , which matches with the sealing arm&#39;s profiled sealing area,  52  ( FIG. 5 ). The receiving arm,  70 , contains a cut channel,  74 , which is typically a concave indentation or depression in the surface of the receiving arm,  70 , that allows the cut blade ( FIG. 5  at  54 ), the slit blade ( FIG. 5  at  58 ), the notch blade (not shown), etc. to punch through the sheets and form the respective cuts, slit, notch, etc. In  FIG. 6 , the cut channel,  74 , is surrounded by the profiled sealing area,  52  in the X and Y planes parallel to the receiving arm surface. It is essential that the cut channel be deep enough and aligned correctly so that the closing of the sealing jaw during use does not damage the cut blades. In an embodiment herein, the cut blades are releasably attached to the sealing arm, so that when thee cut blades wear out they may be sharpened and/or replaced without having to make an entire new sealing arm. 
     The sealing arm,  50 , the receiving arm,  70 , or both actively interact to form the seal by, for example, heat sealing, ultrasonic sealing, pressure sealing, etc. as desired, and therefore contains the appropriate sealing technology therein or thereupon, such as, for example, a heater, an ultrasonic generator, a pressure clamp, etc. The sealing arm and the receiving arm are each independently formed of an appropriate durable material for their uses herein, such as, for example, a metal, a ceramic, a plastic, and a combination thereof. A sealing jaw intended for heat sealing should be both strong and conduct heat well, such as copper, brass, steel, or iron, aluminum, etc. since it has a heating element therein, such as a heating coil. Impulse and induction sealing methods are useful herein. Based on this disclosure, a sealing arm and a receiving arm according to the present invention may be custom made by various suppliers and/or machine shops around the world. 
     One skilled in the art will recognize that the sealing jaw herein may be used to simultaneously seal and form a perforation completely surrounded by the seal on, for example, a pre-formed bag, a pillow bag, and/or a gusset bag. In an embodiment herein the sealing jaw is used on an autopacking machine. 
       FIG. 7  shows a front view of an embodiment showing a plurality of perforations,  28 ,  28 ′, and  28 ″ in parallel lines which help to ensure propagation of the tear towards the target tear destination,  34  approximately located in the top,  22 , seal,  12 . In  FIG. 7 , the seal,  12 ″ starts on the side,  26 , and completely surrounds the plurality of perforations,  28 ,  28 ′, and  28 ″. In an embodiment herein, the pouch contains at least  1  perforation, or from about 1 to about 10, or form about 1 to about 5, or from about 2 to about 4 perforations. In an embodiment herein the plurality of perforations are aligned to follow each other, such as to be in parallel lines. In an alternate embodiment herein, the plurality of perforations may start from different areas, such as from the side, and the top, and be aligned so as to propagate one or more tears that join up in a non-sealed portion of the pouch. From this disclosure, one skilled in the art will also understand how to form a sealing jaw to form pouches, such as seen in  FIG. 7 . 
       FIG. 8  shows an alternate embodiment of the pouch,  20 , herein having a top,  22 , with a larger seal,  12 ′. The top,  22 , contains a notch,  16 , that leads to a perforation,  28 , forming an angle, β. The perforation is completely surrounded by the seal,  12 ′. When torn, the perforation propagates a tear through a non-sealed portion such to form a spout,  18 , and towards the target tear destination,  34 , which in this case is on the side,  26 . 
       FIG. 9  shows an alternate embodiment of the pouch,  20 , herein having a top,  22 , with a seal,  12 , and a slit,  38 , cut into the seal,  12 . The slit,  38 , functions the same as a notch to allow the user to easily initiate propagation of the tear through the perforation,  28 , and towards the target tear destination,  34 , on the side,  26 , to form a spout,  18 . The perforation,  28 , is surrounded by the seal,  12 ′. 
       FIG. 10  shows an alternate embodiment of the pouch,  20 , herein having a side,  26 , which contains a slit,  38 , which allows the user to easily initiate a tear through the perforation,  28 . Since the perforation contains an angle, β, the tear will not continue to the other side (not shown), but will instead angle towards the top,  22 , at the target tear destination,  34 . One skilled in the art may adjust the seal,  12 , strength by varying the sealing method, and/or conditions, to allow the tear to completely propagate through the seal,  12 , or to allow the seal,  12 , to have a higher tearing resistance. 
     In an embodiment herein the invention is combined with additional techniques known in the art, such as a laser-cut, a half-cut, a score line, embossing, etc. and the known methods and machinery therefor. In an embodiment herein, a reclosing technology is combined with the invention herein, to allow easy and efficient re-closing of the pouch after opening. Such reclosing technologies are also especially beneficial with larger-sized pouches. Typical reclosing technologies are known in the art and include plastic pressure-sensitive zippers, hook and loop fastening systems, zipper systems, adhesive strips and patches, clips and snaps, locking systems, etc. For additional technologies useful in combination with the present invention, see, EP Patent No. 1 409 366 B1 to Camargo-Parodi, et al., granted on Jun. 21, 2006; and EP Patent Application No. 07119454.2 To Rogers, filed on Oct. 29, 2007. 
     EXAMPLE 1 
     Pouches according to  FIG. 2 ,  FIG. 4 , and  FIG. 7 , are formed on an autopacking machine from a sheet using the sealing jaw of  FIGS. 5-6 . The autopacking machine creates all seals by heating to create thermal bonding between the separate sheets. The sheet is a three layer laminate of the film materials polyethylene terepthalate, a metallic film (like MYLAR®), and polyethylene. The sheet is provided on a roll which feeds into the autopacking machine and is stretched onto an area where the tube is formed by sealing a line in the machine direction. The tube has a leading edge which is sealed to form a first seal using the sealing jaws according to  FIGS. 5-6 . A predetermined weight (2 kg) of laundry detergent is filled into and flows down the tube and the tube is sealed using the sealing jaws of  FIGS. 5-6  to form a filled pillow bag containing 2 kg of granular laundry detergent. The process then repeats itself for the next pouch. 
     The pouch formed above substantially corresponds to the pouch of  FIG. 2 , except that the notch is replaced with a slit. The seal,  12 ′, is the same width on each side of the perforation,  28 , as the seal,  12 , on the top of the bag. When tested by a mechanical tester, the seal around the perforation does not decrease the bursting strength of the pouch at all, as compared to an identical bag which lacks the perforation. The pouch is easily opened via hand tearing to form a spout from which to easily pour the laundry detergent. 
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.” 
     All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.