TOOL PATTERN FOR SEALING FLEXIBLE MATERIALS IN TWO SEPARATE PLANES

FIELD OF THE INVENTION

[0001] The invention relates to ultrasonic welding or sealing, and more specifically to an ultrasonic sealing device with a tool pattern for sealing flexible materials.

BACKGROUND OF THE INVENTION

[0002] Ultrasonic sealing or welding is a process that generates frictional heat to bond thermoplastic materials together. In rigid plastic bonding, a sacrificial feature is typically molded in to one of the mating parts to focus the clamp force and concentrate the development of frictional heat, facilitating the process. This feature is called an energy director.

[0003] When using the ultrasonic sealing process to bond thin films, such as pouches, it is not possible to create features in the film as it is manufactured differently than injection molded parts. For this reason, the feature or features required to focus the friction must be incorporated into the tools. The simplest form of ultrasonic tooling for film sealing is a single raised bead in the anvil and a flat horn (sonotrode).

[0004] This concept has been used for decades and is effective in generating a leak free seal in films. This simple concept, however, does have some drawbacks. The resulting bond is extremely narrow which concerns some end consumers and limits the strength of the bond. The highly-focused bonding area causes almost all of the film's sealant layer to be forced out of the bond area. This results in a bond only on the edge of the seal bead. And because of the extremely small surface area of this design, the process operating window is very narrow, and is highly sensitive to either too much or too little weld force and duration. The excessive compression that results from such a focused bonding area sometimes damages film structures.

[0005] There have been modifications made in order to try to improve upon the simple bead design for added seal strength. One example is illustrated in U.S. Patent No. 9,278,481 to Hull. This designed disclosed in Hull uses an interlocking horn and anvil with a specific pattern. It consists of a typical 90-degree peak, 4-sided pyramid that has been truncated, producing V-shaped grooves that run at 45 degree angles to the width of the package. The truncated knurl results in a slight engagement when the tools are interlocked. This offers sealing of greater surface areas and the processing window is widened.

[0006] However, this design has several drawbacks. In particular, the tools are intended to interlock with just a few thousandths of engagement which results in alignment that is critical and difficult to maintain. The pattern also consists of many sharp corners which stress films and result in tensile and burst failures at the leading edge of the seal. It also incorporates pyramid shaped pockets to accommodate the sealant layer that is forced from the bond area. Because these pockets have a sharp angle at the peaks, the film often bursts at these points from the pressure of the sealant flow

overstretching the film in the peaks and valleys. This phenomenon, referred to as film fracturing, can result from the use of such designs.

[0007] U.S. Patent No. 5,076,040 to Davis discloses seal bars for a pouch packing machine having asymmetric sealing surfaces. There are two opposing sealing surfaces with wave patterns defining ridges and grooves. Apices of the ridges contact nadirs of the grooves and at points between each ridge apex and groove nadir a space is formed. However, because the ridges and grooves are each curved and the convex surfaces have a radius of curvature that is less than that of the concave surfaces, the contact surfaces are minimal, which could lead to localized stress and strain. [0008] Therefore, there is a need for improved ultrasonic sealing tools and processes.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the present invention to provide an ultrasonic tool with an improved seal pattern presented on each of the horn and the anvil.

[0010] In one embodiment, an ultrasonic sealing device is provided, including a horn having a sealing surface and an anvil having a sealing surface, at least one of the horn and the anvil being moveable to engage the sealing surface of the horn with the sealing surface of the anvil. The sealing surfaces of each of the horn and the anvil include a plurality of protrusions and a recess between each of the protrusions, each of the protrusions having a flat distal surface and sloped sidewalls with curved edges therebetween and each of the recesses includes a flat recess surface with curved edges. Upon engagement of the sealing surface of the horn with the sealing surface of the anvil, the flat distal surfaces of each of the protrusions on each of the sealing surfaces engage corresponding ones of the flat recess surfaces of each of the recesses on each of the sealing surfaces and define gaps between the sloped sidewalls of each adjacent protrusion. The plurality of protrusions may extend along an entire length of a corresponding one of the sealing surfaces.

[0011] The flat distal surfaces of the horn may be in a first plane and the flat recess surfaces of the horn in a second plane parallel to the first plane, and likewise on the anvil. In preferred embodiments, the curved edges between the flat distal surfaces have a first radius and the curved edges of the flat recess surfaces have a second radius greater than the first radius.

[0012] In some embodiments, each of the flat distal surfaces has a width less than a width of the flat recess surfaces. The width of each of the flat distal surfaces may be in the range of 0.004 in. to 0.020 in. The width of each of the flat recess surfaces may be in the range of 0.006 in. to 0.030 in.

[0013] Further provided is an ultrasonic sealing tool, including a first tool portion having a sealing surface and a second tool portion having a sealing surface engageable with the sealing surface of the first tool portion. The sealing surface of the first tool portion includes at least one protrusion extending a length of the sealing surface of the first tool portion with a flat distal surface and sloped sidewalls with curved edges therebetween. The sealing surface of the second tool portion includes at least two protrusions extending a length of the sealing surface of the second tool portion and a recess between the at least two protrusions, each of the at least two protrusions having a flat distal surface and a sloped sidewall with a curved edge therebetween and the recess including a flat recess surface with curved edges.

[0014] Upon engagement of the sealing surfaces of the first and second tool portions, the flat distal surface of the at least one protrusion of the first tool portion engages into the recess on the sealing surface of the second tool portion and defines gaps between the sloped sidewalls of the at least one protrusion of the first tool portion and the sloped side walls of the at least two protrusions of the second tool portion.

[0015] In one embodiment, the sealing surface of the first tool portion includes only one protrusion. In another embodiment, the sealing surface of the first tool portion has four protrusions and the sealing surface of the second tool portion has five protrusions.

[0016] Further provided is a tool for ultrasonic sealing, and an ultrasonic sealing device including such tool, including a horn having a sealing surface and an anvil having a sealing surface. The sealing surface of the horn including a plurality of protrusions and a recess between each of the protrusions, each of the protrusions having a flat distal surface and sloped sidewalls with curved edges therebetween and each of the recesses including a flat recess surface with curved edges. The sealing surface of the anvil includes a plurality of protrusions and a recess between each of the protrusions, each of the protrusions having a flat distal surface and sloped sidewalls with curved edges therebetween and each of the recesses including a flat recess surface with curved edges. On the sealing surfaces of each of the horn and the anvil, the curved edges between the flat distal surfaces have a first radius and the curved edges of the flat recess surfaces have a second radius greater than the first radius. On the sealing surfaces of each of the horn and the anvil, the flat distal surfaces have a width less than a width of the flat recess surfaces.

[0017] Further provided is an ultrasonic tool including a horn and an anvil, each of the horn and the anvil having a surface with a plurality of beads that create a wavy seal pattern. Each of the beads has a flat distal surface that engages a corresponding flat surface in a recess between opposing beads. The surfaces engage one another in two different planes to create seal points in two different planes. Between each of the seal points, there is a diagonally situated gap to accommodate a limited amount of molten sealant flow.

[0018] Other objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 illustrates an ultrasonic sealing device including a tool according to an embodiment of the present invention.

[0020] FIG. 2 further illustrates the tool of the device shown in FIG. 1 including a part being sealed.

[0021] FIGS. 3A-3B are schematic views of the tool shown in FIG. 2. [0022] FIG. 4 is a side view of the tool shown in FIG. 2 including the part being sealed.

[0023] FIG. 5 illustrates a sealing surface of a horn portion of the tool.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Figure 1 illustrates an ultrasonic sealing device 100 including a tool 1 10 with a horn 1 12 and an anvil 1 14 according to an exemplary embodiment of the present invention. One of the portions of the tool 1 10, e.g., the anvil 1 14, is moveable along a track 1 16 towards and away from the other portion of the tool 1 10, e.g., the horn 1 12. Embodiments of the present invention may also include or be used in other ultrasonic sealing devices and machines, such as the device shown in Figure 8 of commonly owned U.S. Publication 2017/0152064, the contents of which are incorporated herein by reference.

[0025] The tool 1 10 is further illustrated in Figure 2. As one skilled in the art will understand, a part 200 to be sealed is pressed between the horn 1 12 and anvil 1 14. The part 200 may be, for example, a pouch made of a flexible packaging material containing a product (e.g., food product). For example, the part 200 may be a retort pouch. Ultrasonic vibrations are emitted by the sealing device 100 to the part 200 via the horn 1 12 to create a seal. The frequency of the vibration may be, for example, 15 kHz or greater, such as 20 kHz, 30 kHz, 35 kHz, 40 kHz or 70 kHz.

[0026] Each of the horn 1 12 and the anvil 1 14 have a mating or sealing surface which interface with one another to create the seal on the part 200. For example, in the case of a pouch, a seal is created to close an end of the pouch after it is filled. The seal has a seal pattern corresponding to the contours of the sealing surfaces of the horn 1 12 and the anvil 1 14.

[0027] Figure 3A is a schematic view of the ultrasonic tool 1 10 according to an exemplary embodiment of the present invention. The tool 1 10 includes the horn 1 12 and the anvil 1 14 with adjacent surfaces which create the seal pattern. The seal pattern is innovative in that it incorporates the benefits of existing basic bead technology but alters it in significant ways that provide substantial benefits.

[0028] The seal pattern is formed by multiple seal beads 302/304 (e.g., protrusions or ridges) running along sealing surfaces of both the horn 1 12 and anvil 1 14, e.g., along their entire lengths or large parts thereof. The pattern includes rolling humps, with no sharp angles, defining peaks and valleys or recesses extending in a wavy pattern. The pattern is generally the same on each of the horn 1 12 and the anvil 1 14 however it is of course offset such that the peaks on the horn 1 12 engage into valleys on the anvil 1 14, and vice versa. In one embodiment, the horn 1 12 has five beads 302 and four recesses, and the anvil 1 14 has four beads 304 and five recesses. In another embodiment, the horn 1 12 has only one bead 302 with flat portions or recesses on either side, and the anvil 1 14 has two beads 304 with flat portions or recesses on either side.

[0029] Each of the peaks of the beads 302/304 and corresponding recesses has a flat surface or landing area where a seal is formed, i.e., seal initiation points. In particular, each recess has a flat area or surface 320 with a recess width. Each peak has a flat area or surface 322 with a peak width. In the exemplary embodiment, the flats 320 in the recesses are larger in width than the flats 322 on the peaks to which they engage. For example, in one embodiment, the flats 322 on the peaks have a width selected from the range of 0.004 in. to 0.020 in. (e.g., 0.008 in.) while the flats 320 in the recesses have a greater width selected from the range of 0.006 in. to 0.030 in. (e.g., 0.016 in.). In the exemplary embodiment, all the peak surfaces 322 have the same width as one another and all the recess surfaces 320 have the same width as one another. However, in some embodiments, the peak and recess widths could be larger on one portion of the tool 1 10 (e.g., the top) to create varying seal widths. [0030] The lengths of the flat areas 320/322 generally extend the lengths of the sealing surfaces of the horn 1 12 or anvil 1 14. As shown in Figure 3A, each the peaks of the beads 302/304 has a first radius 310 (on each side of the flat distal surface) and each of the recesses have a second radius 312 (on each side of the flat recess surface) being larger than the first radius 310.

[0031] The wavy surfaces of the horn 1 12 and the anvil 1 14 are precisely aligned and contact only on the flats 320/322. Due to the differences in the radiuses 310 and 312 and/or the differences in the sizes of the flats 320/322, gaps 330 remain between each of the peaks and the recesses when the horn 1 12 is engaged with the anvil 1 14. As discussed in more detail below, material flows into these gaps 330 during the ultrasonic sealing process.

[0032] Figure 3B further illustrates the tool 1 10 schematically and identifies seal initiation points 340 and sealant flow points 350. The horn 1 12 and the anvil 1 14 contact one another only on the flats 320/322 which define the seal initiation points 340. A pattern thus results in seals occurring in at least two different planes 400/402, being parallel to one another and/or the film barrier, producing a wavy appearance of the resulting seal (e.g., a series of linear waves that run parallel to the width of the package). The familiar appearance eliminates any issues of consumer acceptance that are common with other ultrasonic seals.

[0033] The two-plane 400/402 design produces a zigzag effect within the seal area that grips the part or film 200 more securely, eliminating sliding issues that occur with traditional ultrasonic bead tool. In the exemplary embodiment, the two planes 400/402 are 0.005 in. or more (e.g., 0.010 in.) apart depending on the film thickness. Further, due to the use of multiple tightly spaced beads or protrusions, the overall effective seal is wider than when a traditional single rounded bead is used. [0034] The specific height and spacing of the seal beads 302/304 in the seal pattern are well thought out. In an exemplary embodiment, the pattern is manufactured by grinding or wire EDM machining the pattern into the tools to provide for superior dimensional consistency. Due to the particular shape, the beads 302/304 are engineered such that the diagonally situated gap 330 is formed between each of the seal initiation points 340 and provides room for some, but not all, of the sealant flow 350. These gaps 330, which are slightly undersized, maintain hydraulic compression on the molten sealant that flows away from the focused seal points 340.

[0035] In the exemplary embodiment, the gaps 330 typically have a width ranging from 0.002 in. to 0.010 in. (e.g., 0.003 in.) and a length ranging from 0.002 in. to 0.010 in. (e.g., 0.004 in.) depending upon the film thickness. This zigzag design of the sealant channel restricts the flow of the molten sealant, slowing its evacuation from the bond area. This key concept reduces film stress and increases seal strength by preventing the majority of the sealant from flowing out of the joint.

[0036] This hydraulic compression / restricted sealant flow concept is one important part of what differentiates the seal pattern according to the present invention from others. Further, the design of the present invention causes melt to flow from the peaks and valleys into the side channels or gaps 330. Prior art designs that weld on the sides of the peaks generally force melt flow into the peaks and valleys rather than away.

[0037] The height of the beads 302/304 is specific and may vary depending upon the film specifications, but is typically between .005 in. and .025 in. tall, such as 0.005 in. , 0.010 in., 0.015 in., 0.020 in. , or 0.025 in. The spacing of the beads 302/304 is important in that it provides a location for some of sealant flow but prevents evacuation of the majority of sealant from the seal area. The multi-plane, multi-pocket design and the resulting hydraulic resistance that it produces hinders the flow of the molten sealant. This hydraulic resistance provides two primary benefits. It slows the collapse of the film layers, resulting in a wider operating window. And, it maintains greater quantities of sealant between the film layers which produces substantial increases in bond strength.

[0038] In a recent independent lab study, the seal pattern according to the present invention produced bond strength averages 40% stronger than the average best design competitive ultrasonic seals (e.g., Herrmann). Even more impressive, the inventive design produced bond strengths averaging nearly 20% stronger than heat seals that were twice as wide. Never before has ultrasonic sealing delivered such superior strength to heat sealing. The gentle radii 310/312 at the top and base of each bead have also been found to eliminate the stresses that result from sharp corners or the over- compression of modified single bead designs.

[0039] Figure 4 shows the horn 1 12 and anvil 1 14 with the part 200, such as a plastic pouch, being sealed therebetween. The seal pattern has been painstakingly designed with specific bead dimensions and spacing that provide the necessary frictional focus points to initiate the melt while also allowing slightly under-sized pockets to contain a portion of the film sealant layer and restrict its flow. As such, the part includes portions 210 that are sealed and portions 220 where sealant or material flow is captured. As illustrated, the sealed portions 210 reside in two different substantially parallel planes 400/402.

[0040] Figure 5 is a detail view of sealing surface of the horn 1 12. As shown, the surface has the plurality of beads or protrusions 302 and recesses therebetween. Each protrusion 302 has a flat distal surface 322 and sloped sidewalls with curved edges therebetween and each of the recesses has a flat recess surface 320 with curved edges leading to the sloped sidewalls. In a preferred embodiment, the curves adjacent to the flat recess surfaces are greater (e.g., larger radius) than the curves adjacent to the flat distal surfaces. The anvil 1 14 would have a complementary sealing surface with protrusions 302 to engage in recesses of the horn 1 12 and vice versa.

[0041] To achieve larger seal areas, the pattern can be repeated as needed. For example, the horn 1 12 may have one bead, five beads, seven beads, or more. The end result is an ultrasonic seal with unparalleled bond strength and no damage to the film. Further, the unique design provides ease of processing under a wide range of conditions. The design is a truly unique breakthrough in ultrasonic sealing and provides previously unattained bond strengths.

[0042] Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many modifications and variations will be ascertainable to those of skill in the art.