US3362302A

US3362302A - Bag closure

Info

Publication number: US3362302A
Application number: US479148A
Authority: US
Inventors: Friedman Abraham
Original assignee: Studley Paper Co Inc
Current assignee: Studley Paper Co Inc
Priority date: 1965-08-12
Filing date: 1965-08-12
Publication date: 1968-01-09
Anticipated expiration: 1985-01-09

Description

Jan. 9, 1958 A FRlEDMAN 3,362,302

BAG CLOSURE Filed Aug. l2, 1965 F/af.

IN VEN TOR. 45e/www /e/.f @M4/M United States Patent Office 3,362,302 Patented Jan." 9, 1968 3,362,302 BAG CLOSURE Abraham Friedman, Brooklyn, N.Y., assigner to Studley Paper Company, Inc., a corporation of New York Filed Aug. 12, 1965, Ser. No. 479,148 12 Claims. (Cl. 93-35) This invention relates to manufacture of paper and plastic bags and the like. In particular, this application relates to methods of closing an end of a tubular structure of sheet material to lform a bag thereof.

In the usual methods for manufacture, su-ch as grocery bags, shopping bags, vacuum-cleaner filter bags and the like, as well as envelopes and the like, it is common practice to prepare a tubular member of sheet material, for example by folding the side edges of a flat blank inwardly and gluing them together, and then close an end of the resulting iiat tubular structure in any of a variety of Ways. The most common methods of closing the end have involved folding an end one or more times to provide a hem-like closure, and either gluing or stitching, or both, to hold the end of the bag in the resulting folded and closed configuration. Conventional grocery bags are folded in a somewhat dilferent manner, to provide the feature of exhibiting a fiat rectangular bottom when the bag is opened up for use, but are also made in much the same manner, i.e., by a combination of folding and gluing.

Although satisfactory and highly successful for many purposes, the methods of closing bag ends which involve folding and gluing are subject to certain disadvantages. For one thing, the machinery required for producing the folded configuration is complicated and expensive. Moreover, where a leakproof closure is required, it is diicult to achieve by such methods, because of diiiiculties encountered in the precise control of the amount of glue applied and its flow characteristcis. If the amount of glue applied is relatively small, there is danger that some points along the glued surface will be devoid of glue and hence constitute leakage points. On the other hand, if this danger is to be avoided, it is necessary to apply an excess of glue, which tends to smear outside the glued surfaces, fouling the apparatus and causing sticking together of stacked bags, etc.

When a bag is stitched, rather than being glued, these diiiiculties are not encountered. However, stitching is more expensive than gluing, and produces a multiplicity of perforations in the bag material. To avoid leakage through these perforations, it is generally necessary to provide a double or triple fold in the end, rather than a single fold, and this is wasteful of material.

In the case of bags madefrom plastic materials such as polyethylene film, for example, the characteristics of the sheet materials used have led to the development of certain other techniques for manufacture of bags. One such technique is to fold a continuous flat sheet of material in half, thus forming a U-shaped web, and to heatseal the two layers of material thus formed at intervals by a double line` of heat-sealing running transversely of the long axis of the web. The web is subsequently cut apart by transverse cuts running between each pair of heatsealed lines, resulting in the formation of a series of bags, each of which is closed at the bottom by the U-shaped configuration of the material of the web, and at the sides by a heat-sealed seam. In a variation of this method, a web of plastic material is bent to a U-fold, as just described,` and the open' side of the web is heat-sealed to form a dat, tubular structure. Alternatively, a pair of webs are laid one atop the other, and heat-sealed along both edges, again forming a at, tubular structure. In either event, the tubular web is then heat-sealed transversely at intervals along its length, and also perforated by transverse perforations adjacent each transverse heatsealed region, so that when the web is torn at the line of perforations, the torn-off portion is a bag, heat-sealed at the bottom and along one lor both sides, and open at the top line corresponding to the line of perforations. Such heat-sealed plastic bags have found wide usage in a variety of applications, for example as garment bags for drycleaned articles, packagings for dry goods offered for sale, etc. However, they are suitable only for inherently heatscalable materials such as films of thermoplastic materials and the like. Such materials are unsuitable for many applications, in which the physical characteristics of plastic films are unsatisfactory `for the use for which the bag is intended. Also, even where plastic films are suitable as the construction material for the body of the` bag, the heatsealing method is frequently unsuitable because it is dilii-V cult in this manner to achieve a strong, continuous, leakproof closure without either bringing `about'a deterioration in the physical characteristics of that portion of the web which is actually heat-sealed, or a degradation in the properties of adjacent portions of the web.

An object of this invention, therefore, is to provide improved methods and apparatus for closing the ends of bags.

Another object is to provide bag-closing methods and apparatus which eliminate the necessity for folding portions of the material of the bag.

Still another object is to as aforesaid, which do not necessitate the control of application rates and iiowcharacteristics of a glue to effect closure of the bag.

Yet another object is to for closing the ends of bags, which do not involve stitching the end of the bag.

A further object is to provide methods and apparatus for closing the ends of bags, which are not essentially limited to use with any particular class of bag-construction materials. n

A still further object is to provide methods and apparatus for closing the ends of bags, which do not result iu degradation of the properties of the sealed portion or adjacent portions of the bag material.

A feature of the invention is the provision of a mold adapted to form a plastic bead over the end of a bag to be closed. Another feature resides in the deposition of a 4bead of plastic over and around the adjacent edges constituting the end of a bag to be closed.

Other objects, features and advantages will become ap-` parent from the following more complete description and claims, and by reference to the accompanying drawings.

In one particularly desirable embodiment, this invention contemplates a method of closing an end of a fiat tube of sheet material to form a bag thereof, said method comprising in combination the steps of molding a bead of thermoplastic material about a pair of juxtaposed edges of an end of said fiat tube, said bead extending at least from one side to the other side of said flat tube, and hardening said thermoplastic material.

In another particularly desirable embodiment, this invention contemplates an apparatus for closing an end of a fiat tube of sheet material to form a bag thereof, said apparatus comprising in combination a mold having a mold cavity therein, said mold cavity having a cross-sectional shape corresponding to the cross-sectional shape of a bead of plastic adapted to surround and seal together a pair of juxtaposed edges of one end of said flat tube, a passage communicating between said mold cavity and the atmosphere, said passage being of a size and shape to snugly receive a double thickness of the material of the walls of said fiat tube adjacent an end thereof, and

means for supplying molten thermoplastic material to the interior of said mold cavity.

provide methods and apparatus provide methods and apparatus Although adapted to the manufacture of bags of a wide variety of types, construction materials, and intended uses, this inventionis particularly adapted to the manufacture of dust-receiving filter bags for vacuum cleaners, and will be described at least in part, with particular respect thereto.

Referring now to the figures:

FIGURE l is a medial cross-section of one embodiment of the invention together with the end portion of a bag to be sealed, just prior to the sealing operation;

FIGURE 2 is a medial cross-section similar to FIG- URE 1 but on a somewhat larger scale, showing the apparatus of the invention in the process of sealing the end of a bag;

FIGURE 3 is a medial cross-section of the end portion of a bag after sealing by the process of this invention;

FIGURE 4 is a perspective View of one type of sealed bag, which may be produced according to the invention;

FIGURE 5 is a medial cross-section similar to FIG- URE 2, depicting the operation of an apparatus according to another embodiment of the invention adapted to provide the upper or open end of a bag with a stilfening rib and/or a carrying handle;

FIGURE 6 is a transverse cross-section taken along line `6 6 of FIGURE 5;

FIGURE 7 is a perspective view of a finished bag provided with a bottom closure and a top rib, both produced according to the presentrinvention; and

FIGURE 8 is a cross-section similar to FIGURE 5, showing a modified embodiment of the invention adapted t to provide the upper, open end of a bag with a carrying handle and a stiffening rib along the inside top margin of the bag.

Referring now more particularly to FIGURE l, the apparatus comprises a mold It), which is preferably made in two mating halves, 12 and 12. Each of the mating halves defines one-half of an internal mold cavity, the cavity halves being respectively designated 14 and 14. Communicating with the cavity halves are

passageway halves

16 and 16 which, when the mold is in closed position, define between them a passageway just sufficiently wide to accommodate a pair of juxtaposed end portions 18 of a bag to be closed.

Also communicating with the mold cavity halves are a pair of sprues 2li, serving to feed molten thermoplastic material into the mold cavity from appropriate external supplies thereof 22.

In the operation of this embodiment of the invention, the bag end to be closed is inserted between mold halves `12, 12 and the latter are brought together as illustrated in FIGURE 2. Molten plastic is then injected from plastic supplies 22 through sprues 20 into the mold cavity, forming a bead of plastic around the juxtaposed edges of the bag end. The mold may then be left in place until the plastic solidifies and reopened, as shown in FIG- URE l, and the sealed bag end Withdrawn, or the process may be continuous, by providing a continuous connected train of bag ends which are continuously withdrawn in a direction perpendicular to the plane of the paper, as molten thermoplastic material is continuously fed into the cavity through sprues 2t?. In either case, the bag end closure, in cross-section, is as illustrated in FIG- URE 3, with a solidified bead of thermoplastic material 24 completely surrounding and sealing the end of the bag.

FIGURE 4 illustrates a bag made in this manner. The bag of FIGURE 4 is made as first described above, i.e. by closing the mold over the bag end, injecting the plastic material, allowing the same to solidify, and then opening the mold. The extrusion-type process described above would produce a similar bag, except that instead of the sidewall pleats 26, there would be merely a straight heatsealed seam resulting from the transverse heat-sealing at intervals of a continuous double web of bag wall material.

FIGURES 5-7 illustrate another embodiment of the invention which may be used to apply a stilfening top rib and/or a carrying handle or the like to the upper, open end of a bag.

In .this embodiment of the invention, it is desired not to close the end of the bag by sealing the juxtaposed edges together, but rather to form a separate rib on each of the two edges, while leaving them separate and unconnected (except at their respective ends). Also, in the illustrated embodiment, the mold cavity is shaped to provide simultaneously a rib along each top margin of the bag, and a carrying handle integral with the rib.

To provide the necessary separation between the bag ends and prevent their beingfused together, there is provided a spacing member 28 in the form of a blade of f sheet metal or the like. If the top rib is formed before the bottom of the bag is closed, spacing member 28 may conveniently be inserted through the bottom of the bag and extend all the way through the bag from below the bottom to a position even with the top edges. Otherwise, it may be as shown, a short piece, separately inserted for each molding cycle, extending from the top edges a short distance into the interior of the bag.

The stiffening rib 30, which runs entirely around the upper edges of the bag, is formed by thermoplastic material supplied to the mold cavity through sprues 32 (FIG- URE 5). Thermoplastic material for the formation of handles 34, which are integral with rib 30, may be supplied through the same sprues, but is preferably provided for separately by way of sprues 36.

, At the sides of the flat tube 38 forming the body of the bag, the spacer 28 extends to the inside of the fiat tube, and the mold cavity extends slightly beyond the corner of tube 3S, so as to provide for the formation of a connecting portion 40 of rib 30, which goes around the side of the bag and unites the two major portions of rib 3G on the two at sides of the tube.

It will 'be appreciated that the embodiment of the apparatus and the mode of operation described in connection with FIGURES 5-7 are essentially an injection-molding operation, and cannot readily be converted to an extrusion type of operation, as described in connection with FIGURES 1-3, owing to the necessity of maintaining a separation between the opposed edges of the top of the bag, while at the same time providing for the formation of portion 4t) of the rib, encircling the side corners of the top.

The mold assembly shown in FIGURE 8 may be used to form a stilfening rib and carrying handle similar to those shown in FIGURE 7, except that the rib is inside the top edge of the bag instead of outside. As shown in FIGURE 8, spacer 28a is shaped to form a portion of the mold cavity, and also grooved as at 40 to form feed channels communicating with sprues 20. As molten thermoplastic material is injected through sprues 20, its iiows in both directions through feed channels 40 to form stilfening rib 30a and handles 34. Alternatively, an internal rib may be produced by the expedient of using the apparatus as shown in FIGURES 5 and 6, and subsequently turning the bag inside-out. This, however, involves an extra handling step which is not required when the rib is produced using the apparatus shown in FIGURE 8. Moreover, it would necessitate a reversal of the sharp bends in the rib at the side corners of the bag, which is usually precluded by the stiffness of the molded plastic.

The apparatus and method of this invention provide an improved solution to the problem of closing and sealing an end of a tubular body of sheet material to form a bag thereof. It eliminates the need for complicated and expensive folding apparatus, and avoids the disadvantages heretofore experienced from the use of. glued or stitched closures. The method of this invention is simple, inexpensive, and easily carried out without demanding unusual skill on the part of the operator. The apparatus of the invention is simple and inexpensive in construction,`

virtually maintenance-free, and is readily operated, even by relatively unskilled personnel.

While this invention has been described in terms of certain preferred embodiments and illustrated by way of certain drawings, these are illustrative only, as many alternatives and equivalents will readily occur to those skilled in the art, without departing from the spirit or proper scope of the invention. The invention is therefore not to be construed as limited, except as set forth in the appended claims.

I claim:

1. A method of closing an end of a at tube of sheet material to form a bag thereof, said method comprising in combination the steps of molding a bead of thermoplastic material about a pair of juxtaposed edges of an end of said flat tube, said bead extending at least from one side to the other side of said iiat tube, and hardening said thermoplastic material.

2. A method according to claim 1, wherein said molding is accomplished by clamping said juxtaposed edges between mold portions, said mold portions defining a cavity surrounding said juxtaposed edges, injecting a molten thermoplastic material into said mold cavity, and hardening said molten thermoplastic material.

3. A method according to claim 1, wherein said molding is accomplished by drawing said juxtaposed edges longitudinally through a molding zone, providing a supply of molten thermosplastic material in said molding zone, longitudinally withdrawing said juxtaposed edges together with molten thermoplastic material from said molding Zone, and hardening said thermoplastic material.

4. A method of forming a stilening rib on the end of a flat tube of sheet material, comprising in combination the steps of separating opposed edges of said end of said tube by a spacer inserted between said opposed edges, containing said edges with said spacer in an enclosed molding zone, surrounding said edges with molten thermoplastic material, hardening said thermoplastic material, removing said edges and said spacer from said molding zone, and removing said spacer from between said edges.

5. A method according to claim 4, wherein said spacer is positioned to project beyond said opposed edges, and said molten thermoplastic material is supplied to said molding zone in amount to form on either side of said spacer a pair of opposed carrying handles integral with said rib and projecting beyond said opposed edges.

6. A method according to claim 4, wherein said molten thermoplastic material is applied to the outer margins of said opposed edges, thereby forming an external stilening rib on said edges.

7. A method according to claim 4, wherein said molten thermoplastic material is applied to the inner margins of said opposed edges, thereby forming an internal stiiening rib on said edges.

8. Apparatus for closing an end of a flat tu-be of sheet material to form a bag thereof, said apparatus comprising in combination a mold having a mold cavity therein, said mold cavity having a cross-sectional shape corresponding to the cross-sectional shape of a bead of plastic adapted to surround and seal together a pair of juxtaposed edges of one end of said at tube, a passage communicating between said mold cavity and the atmosphere, said passage being of a size and shape to snugly receive a double thickness of the material of the walls of said flat tube adjacent an end thereof, and means for supplying molten thermoplastic material to the interior of said mold cavity.

9. Apparatus for forming a stiiening rib on the end of a flat tube of sheet material, said apparatus comprising in combination separator means for maintaining a separation between said opposed edges, injection means for supplying molten thermoplastic material to said edges, and mold means for shaping said molten thermoplastic material to the configuration of a rib generally coinciding with said edges.

1). Apparatus according to claim 9, wherein said mold means is shaped to provide `a pair of opposed carrying handles integral with said rib and projecting beyond said opposed edges.

11. Apparatus according to claim 9, wherein said means for supplying molten thermoplastic material comprises a conduit communicating between a supply of molten thermoplastic material and the external faces of said opposed edges.

12. Apparatus according to claim 9, wherein said means for supplying molten thermoplastic material comprises a conduit communicating between a supply of molten thermoplastic material and the internal faces of said opposed edges.

References Cited UNITED STATES PATENTS 2,471,258 5/1949 Bolten 18-36 2,488,212 11/1'949 Lloyd. 3,081,213 3/1963 Chin.

BERNARD STICKNEY, Primary Examiner.

Claims

1. A METHOD OF CLOSING AN END OF A FLAT TUBE OF SHEET MATERIAL TO FORM A BAG THEREOF, SAID METHOD COMPRISING IN COMBINATION THE STEPS OF MOLDING A BEAD OF THERMOPLASTIC MATERIAL ABOUT A PAIR OF JUXTAPOSED EDGES OF AN END OF SAID FLAT TUBE, SAID BEAD EXTENDING AT LEAST FROM ONE SIDE TO THE OTHER SIDE OF SAID FLAT TUBE, AND HARDENING SAID THERMOPLASTIC MATERIAL.