Closure For Film Packages And Method Of Making Same

Abstract

A method of forming improved film packages of a type wherein one or more of the package ends or regions is gathered and tied closed by encircling metal bands, closure clips or other closure devices. The resultant closure of compressed film is made leak-proof by application of ultrasonic vibratory energy to the package in the vicinity of the gathered region of film. The invention in its modified embodiments further invisions elimination of present bands, closure clips or other closure devices by using instead a temporary film gathering and holding means, and then applying ultrasonic energy to the gathered region of film to form a permanent closure not requiring a band or clip.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally in the field of improved film packages of a type gathered and tied at an end portion or other region thereof such as by an encircling metal band, closure clip or other closure means, and to methods of fabricating such packages. More specifically, the invention relates to obtaining a substantially leak-proof closure underneath and/or adjacent such clip means, and in certain embodiments, advantageously to elimination of such clip means from the package.

2. Discussion of the Prior Art

The term "clip seals" as used in the prior art indicates a type seal or closure wherein one or more ends of a film package is tightly gathered and tied such as by an encircling metal band or closure clip. Examples of such closures are illustrated in U.S. Pat. Nos. 2,884,749 and 2,924,924.

Conventional clip seals, for example, rely principally upon the gathering together of the film and folding it such that the film is held under pressure to make a seal. Such seals tend to be erratic in that the film does not gather in any regular form such as would assist in air-tight bunching together of the film underneath the clip. Moreover, conventional packaging films, such as saran, frequently do not display adequate compressibility to assist in obtaining a hermetic pressure seal in the compressed region.

In any event, capillary action or wicking or seeping of product through the clipped area, in present day packaging, is largely dependent on clip pressure. Putting greater pressure on the gathered film can be effected such as by using larger clips and the like, but has the disadvantage that pressure alone may damage the film if applied in too great amounts. Heat sealing in the clip region such as by a hot bar or hot wire has been tried but found lacking in that minute voids remain in the gathered region which prevent achieving a hermetic closure.

Accordingly, it is among the objects of the present invention to provide:

An improved film package of a type having an end portion or region thereof gathered and tied closed such as by a clip closure or the like, and wherein such a closure is substantially leak-proof even as to liquid products, or to products such as hamburger or grease which tend to seep or wick;

Such a package wherein the clip closure can be eliminated while still obtaining a leak-proof closure of the film in the gathered region;

Such a package wherein the film adjacent and/or underneath the clip is swelled to an extent sufficient to "squeeze out" voids in the gathered film, such as to assist in obtaining a hermetic closure of the package;

A method of forming such packages wherein the film is gathered tightly by permanent means such as a closure clip, or by temporary means, and ultrasonic vibratory energy applied to the gathered region of film in an amount sufficient such that a substantially leakproof closure results;

Such a method wherein the packages are formed continuously in a connected series of the same and wherein ultrasonic vibratory energy is applied between adjacent gathered ends of adjacent packages, such energy being sufficient to cut the packages apart from each other, and simultaneously to hermetically close both such gathered ends; and

Such a method wherein ultrasonic vibratory energy is applied through such gathering and/or tieing means to tightly swell the film against such means, and into tight substantially void-free conformity therewith, whereby a hermetically tight, leak-proof closure of the film is obtained.

BRIEF SUMMARY OF THE INVENTION

Briefly then, the present invention contemplates an improved closure for packages of a type including gathered film, the closure being of hermetically tight quality, and being obtained by strategically applying ultrasonic vibratory energy to the package, such energy sometimes being referred to as ultrasonic oscillatory energy. Such a package, for example, can be formed from a continuous film tube such as where product is filled through one end of the tube, and the film tightly gathered and clipped at regular intervals so as to form a connected string of packages. An ultrasonic cut-off tool has been found useful as means to severe the film between the clips of adjacent packages such as to separate the same for packing. In addition, it has now been discovered that the application of such energy simultaneously causes oriented films to shrink back away from the cut or severed region, causing a swelling and tightening of the film underneath the clip, and to a degree that maximizes the air tightness of the closure. It has been further discovered that sufficient application of such energy fuses the film underneath and/or adjacent the clip into a substantially solid or semi-solid void-free mass, and to an extent that the closure is preserved even after removal of the clip. Accordingly, the invention further contemplates elimination of the clip by using certain temporary means to substitute for its function of tightly gathering the film during package forming. Hermetically tight closures of the type indicated surprisingly can also be obtained by transmitting such energy to the gathered region of film through the clip closure, or through such temporary gathering and holding means. Where the clips are retained, however, it has been found that the swelled mass of film in the clip region has the added beneficial function of preventing the clips from popping off such as, for example, if packages are carelessly or roughly handled resulting in their dropping on the floor or the like, thus adding additional toughness to the closure.

Various preferred embodiments of the present invention are shown in the accompanying drawing wherein wheresoever possible like reference numerals designate corresponding materials and parts throughout the several views thereof in which:

FIG. 1 is a schematic and diagrammatic representation of apparatus for applying ultrasonic vibratory energy to a string of connected film packages having clipped ends whereby improved closures are obtained in accordance with the teachings of the present invention;

FIG. 2 is a partial and enlarged view of a package manufactured according to the apparatus and method of FIG. 1, and shows more clearly the closure obtained at the package ends;

FIG. 3 is a schematic and diagrammatic representation of a modified form of the invention where ultrasonic vibratory energy is applied through the clip holding the film under pressure at the package ends;

FIG. 4 is a partial and enlarged view of the resultant package manufactured according to the apparatus and method of FIG. 1, except with the clip removed;

FIG. 5 is a schematic and diagrammatic representation of temporary film gathering means whereby clip closures and the like can be advantageously eliminated.

Referring now more particularly to the drawings, there is shown in FIG. 1 a string of connected film packages 10 of generally tubular shape, their opposite ends 12 and 14 being permanently gathered and closed by encircling metal bands or clips 16, respectively. Packages 10 can be manufactured from flat film or web stock, such as by over-lapping and sealing together the opposite edges of the film to form a hollow tube (not shown), filling a product 18 through one end of the tube, constricting the filled tube at regular intervals, and thereafter tieing closed the constricted film regions such as by encircling metal bands or clips as indicated. Conventional apparatus for forming such packages is illustrated in some detail, for example, in U.S. Pat. Nos. 2,831,302 and 3,214,883.

It has now been found that significant improvement in the air-tight quality of the closure at ends 12 and 14 can be obtained by applying ultrasonic vibratory energy to strategic regions of package 10, and specifically in the vicinity of clips 16. Such can be accomplished, for example, through use of an ultrasonic cut-off tool or assembly as denoted generally at 20 in FIG. 1.

Cut-off assembly 20 basically includes a striker or focusing horn 22 whose point or working tip 24 is positioned such as to generally normally or perpendicularly contact the film at region 26 defined between clips 16 of adjacent packages 10. Focusing horn 22 receives ultrasonic vibratory energy through fixed connection to a transducer element 28. Transducer 28, in turn, is operated by an energy source such as a radio frequency generator 30, the latter being an electronic device that converts 60 cycle house current, or a like low frequency out put, to the desired ultrasonic frequency. Ultrasonic vibration from transducer 28 is accordingly fed through focusing horn 22, and concentrated at tip 24 such as to cut the film apart at region 26, thereby separating packages 10. To assist such cutting, assembly 20 conventionally includes an anvil or back-up member 32 disposed opposite tip 24, and at a location such that film region 26 is positioned in contacting engagement therebetween.

Cut-off assemblage 20 can operate, for example, generally simultaneously with the gathering and clipping of packages 10, or can be disposed at a station remote from such operations. As to the former, cut-off tool 20 is readily adaptable for use in combination with the package forming apparatus of the above mentioned U.S. patents, such as for example, by locating cut-off tool 20 such that its tip 24 operates between adjacent gathering, constricting, clip applying or the like movable plates of the indicated patented apparatus. In any event, for applications such as presently disclosed, focusing horn 22 and anvil 32 can be suitably mounted so as to move reciprocally away from and toward each other as indicated generally by arrows 36 and 38, respectively. Such movement permits the thick body portion 40 of packages 10 to pass between horn 22 and anvil 32, thereby permitting forward indexed advancement of packages 10 such as is appropriate for mechanized continuous package forming operations.

A wide variety of thermoplastic films or sheet material are suitable for practice for the principles of the present invention. Optionally, such films are oriented films, preferably biaxially oriented films. Such oriented films have been found to swell considerably when ultrasonic energy is applied in the gathered regions of the film, or in other words, where film mass is maximum. Specifically such energy is transmitted up the film from the cut-off point causing the film to shrink backward toward the clip, simultaneously increasing in radius, thereby filling up the clip and essentially producing a solidified, fused mass of film 42 underneath and/or adjacent the clip (see FIG. 2). Evidently such swelling squeezes trapped air and the like from within the folds or gathered region of the film such that voids are substantially "squeezed out" to maximize the hermetic qualties of the closure.

Exemplary of such oriented films contemplated for use in the present invention are such packing films as vinylidene chloride-vinyl chloride copolymer films generally sold under the designation "saran films." Examples of such saran films are Saran Wrap film and Saran Wrap S shrinkable film available through The Dow Chemical Company of Midland, Michigan. Saran Wrap S shrinkable film comprises generally by weight 73 per cent vinylidene chloride, 27 per cent vinyl chloride. Saran Wrap film is generally of a proportion comprising 85 per cent vinylidene chloride, 15 per cent vinyl chloride. Other examples of suitable films can include structured films such as, for example, of a type as is disclosed in U.S. Pat. No. 3,387,640; or such other conventional packaging films as olefinic homopolymer and copolymer films such as polyethylene or ethylene/ethyl acrylate film and the like. Such materials or films may include pigments, stabilizers, plasticizers, or can be otherwise formulated to enhance their properties as is customary in film manufacture.

Appropriately high orientation of such films is normally achieved by the manufacturer such as where the film is extruded as a "bubble" or hollow tube, and air pressure provided internally, thereby stretching the tube to biaxially orientate the same.

A modification of the present invention is shown in FIG. 3 wherein ultrasonic energy is applied through clips 16a of a package 10a. Again, sufficient application of such energy can be applied so as to fuse the film underneath the clip into a substantially solid or semisolid, air-tight mass. The flow and fusing of the film is readily evidenced by the resultant dumbbell configuration or region 26a, as is best seen in FIG. 4, a view where slip 16a is removed. The narrow region denoted at 44 (the part formerly underneath the clip) is fused as indicated. Immediately adjacent region 44, a swelled or bulbous-shapped end 46a away from the body portion 40a of package 10a. The resultant closure comprising region 44 and end 46 is observed as being of sufficient toughness to remain intact, even subsequent to removal of clip 16a.

In the above described embodiments of the invention, the means employed to tightly gather and hold the film are illustrated as being of a permanent nature such as clips 16 and 16a. Temporary gathering and tieing means, however, can be employed. Thus, as illustrated in FIG. 5, matched jaws 50 and 52 are suitably mounted (by means not shown) to move reciprocally as indicated by arrows 54 and 56 toward and away from each other to rightly gather therebetween film region 26b, and thereafter to release the film such as to permit subsequent forward indexed movement of packages 10b. Sufficient ultrasonic energy can be applied such as to cut apart packages 10b, or can be transmitted through jaws 50 and 52, as described, thus forming a permanent closure comprising a swelled solid or semi-solid fused film mass of a type as generally indicated above. Accordingly, by practice of the principles of the present invention, where desired, clip closures can be eliminated, substituting therefore a fused film mass. Packages 10b have the advantage of being more convenient to open than those heretofore provided, i.e., those employing closure such as clips 16.

Generally, the optimum residence time of the film between the focusing horn 22 and anvil 32 will vary with the ultrasonic frequencies utilized and the amplitude of the striker. Further variations would be dependent on film type, thickness and the like. Appropriate residence times are normally in the range of approximately 1/2-2 seconds. In any event, tolerances are readily worked out quickly through trial and error procedure, and the requirements of the closure as contemplated herein have been found such that satisfactory closures can be obtained within a fairly liberal range of tolerances.

The focusing horn 22 can be constructed of a hard metalic material at tip 26, such as hardened steel, and is normally positioned in a direction generally normal to the plane of film region 26 and 26a. The excitation frequencies transmitted to focusing horn 24 is beneficially in the range of about 15 to 500 kilocycles per second, and preferably in a range of 20 to 50 kilocycles per second. The lower operating ranges are normally limited by objectionable audible noise. The horn may be excited electrically by means of a conventional magnetostrictive transducer such as described in U.S. Pat. No. 2,803,735, or a conventional piezoelectric transducer, such as described in the article entitled "A Barium Titanate Transducer Capable of Large Motion at an Ultrasonic Frequency" by Mason and Wich, printed in The Journal of the Acoustical Society of America, March 15, 1951.

Anvil or back-up plate 32 is normally manufactured of hardened steel. Customarily, such devices having industrial applications are constructed in the form of a wheel to prevent localized cutting or rutting through prolonged operation.

The following example is intended to illustrate the invention, but is not to be construed as limiting thereof.

EXAMPLE

Packages 10 are constructed as indicated with the exception that such packages are filled with air to assist in measuring leakage in the closure region of the package. Saran Wrap packaging film is used. The packages are sealed using a magnetostrictive type transducer powered by a 300 watt, 24 kilocycle generator. Cut off of packages 10 is accomplished using a generally rectangular, blunt ended anvil 32 of one-eighth inch thickness as represented by reference letter X in FIG. 1. Tip 24 is of circular cross-sectional configuration having a diameter of approximately three-eighths inch, and is positioned approximately one-eighth to three-sixteenths inch from each side clips 16, respectively. Residence time is approximately 1/2 to 2 seconds. Any contamination inadvertently introduced into the film is found not to prevent hermetic sealing in the gathered film region 26. After ultrasonic cut off, packages 10 are then compared to like packages except that the gathered film regions thereof are secured only by external pressure through use of conventional aluminum wire clips. To assist comparison, packages of each type are placed in separate tubs of water, and a weight of 40 pounds placed across the packages. After a given time, the volumetric displacement of the water is measured, whereby the leakage per hour is determined. The ultrasonically sealed package 10 displays a significant improvement in leakage rate over those of conventional construction. Examination of the ultrasonically sealed packages 10 in region 26 is accomplished by removing clips 16. The film underneath the clip is observed as being swelled and fused into a compact mass of sufficient toughness to maintain air-tightness subsequent to clip removal.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention. For example, the principles of the present invention are readily applied for obtaining leakproof closures on plastic bags of a type gathered and tied closed at one or more ends or other regions thereof.

Claims

What is claimed is:

1. A method of manufacturing a package comprising the steps of:

a. locating a product within a tubular film envelope, the film being of a type which is sensitive to shrinkage and accompanying swelling via application of ultrasonic vibratory energy thereto;

b. gathering the film to form a package end, and applying an encircling metal clip in compression about the gathered film;

c. applying ultrasonic energy to the package in the general vicinity of said clip, to swell the film underneath the clip into intimate conformity therewith, and to form a substantially hermetically tight closure of said end.

2. The method of claim 1 wherein said energy is transmitted to the film through the clip.

3. The method of claim 1 wherein successive packages are formed and are connected each to the other by a gathered region, and wherein step C comprises applying ultrasonic vibratory energy to the gathered region to cut the packages apart from each other, said energy being applied at an area remote from and between a pair of spaced apart clips associated with each said gathered region.