Method of forming flat bottoms on bags of creasable material

Abstract

This disclosure concerns a method for forming a flat bottom on a bag of flat tubular stock comprising a material which, when folded and pressed, is left with somewhat permanent creases. To practice the method, an unfinished bag is provided in the form of a section of the tubular stock flattened in a manner to provide opposite longitudinally-extending laterally-inwardly-folded pleats with the bag completely sealed across one end and being openable at the other end. Assuming the flattened bag in a generally horizontal plane, the upper edges of the pleats are gripped while the lower edges are held fast at areas of the bag spaced from the sealed end thereof at a distance equalling twice the depth of the pleats. Thereafter, the gripped areas are pulled toward the openable end to drag the intended flat bottom portion longitudinally over the underlying bag portion until taut. Then, the intended bottom portion is pressed against the underlying portion to form creases in the bag outlining its flat bottom.

Description

BACKGROUND OF THE INVENTION

In the use of bags provided in a flat condition, e.g., at the checkout counters of supermarkets, it is desirable to be able to unfold the bag from its flat condition into a box-like configuration and have the bag stand on its flat bottom in a self-supporting condition while merchandise is packed thereinto. Paper bags perform admirably in this respect but are subject to tearing on being exposed to any dampness as from rain, or wet food products.

Bags of plastic film offer great advantage in strength and weather resistance over the conventional paper bags in, e.g., food retailing, but have not been accepted because of a lack of rigidity which facilitates opening, handling, and self-support incidental to the placing of packages therein. While present experimental work indicates that the problem of film rigidity may be solved by the coextrusion of films having laminae of different densities, plastic films are not ideal for bag formation by methods used for paper bags.

According to present technology, a plastic bag may be formed most efficiently from a tube divided longitudinally into sections of which each is sealed across one end. Then the difficulty arises of bringing the resulting semi-finished bag into a desirable commercial form wherein it may be manually shaken into an open condition providing a flat bottom by which it can be seated and be self-supporting on a flat surface. Method and apparatus for forming a flat bottom to a pleated bag are known, e.g., from U.S. Pat. No. 3,606,822. In developing the present invention it has been discovered that a pleated tube section may be shaped with a flat bottom by simpler method and apparatus than heretofore known to the present inventor.

It is an object of this invention to provide a method for forming flat bottoms on flattened bag stock for which machinery may be readily designed to perform in a rapid manner on a series of such bags proceeding through a bag bottom shaping station.

An object ancillary to the above object is to provide a method that involves a minimum of manipulation of the bag material in shaping the flat bottom and advantageously utilizes a flattened air evacuated condition of bag sections as normally provided from machinery for processing a bag-making tubular material.

It is particularly an object to render plastic bag materials more useful and commercially practical in the retail merchandising fields.

In fulfilling these and other objects, the invention resides in a method of producing bags with flat bottoms from a creasable material, e.g., a plastic film comprising laminae of diverse compositions, in the form of a flattened tube having longitudinally extending pleats folded laterally inwardly to a predetermined depth. Assuming a semi-finished bag section having one end sealed along a transverse seal line and the other end openable to be oriented in a generally horizontal plane, each pleat forms two superimposed edges one above the other. To form the flat bottom, the bag is supported on a flat surface in a substantially deflated condition and the lower edges of both pleats next to the surface. In a fold plane located from the seal line at a distance equal to twice the depth of either pleat, the lower edges of the pleats are secured to prevent movement relative to the flat surface, and both upper edges of the pleats are gripped in a manner to maintain the material between the gripped areas in taut condition while the means for gripping is advanced toward the openable end to drag the taut material over the now underlying areas of the bag between said held lower edges until the longitudinally overlying advanced portion of the bag which consequently now extends between the gripped areas and the fold plane has a length of twice the depth of the pleats and assumes a taut condition. The overlying advanced bag portion is then pressed at sufficient pressure and/or temperature against the underlying bag portion to develop creases or fold lines which define and outline the flat bottom of the bag.

The holding of the bag to the flat surface and the gripping of the upper edges is carried out with merely such means as are necessary to provide adequate gripping of the areas involved without slipping and may consist of very thin members which may pass by each other without interference substantially changing the height of the flattened bag. The portion of the bag which is advanced toward the openable end is preferably lifted only slightly with respect to the underlying portion to pass thereover in light frictional contact. This is preferable since, to raise the advanced portion to any considerable degree would tend to introduce air into the portions of the bag undergoing relative movement and cause an undesirable crease pattern of the bag as a result of the bottom pressing operation. The advancement of the bottom forming portion of the bag is preferably done with as complete deflation of the bag material as possible.

According to one embodiment disclosed, gripping elements may be employed to grip the upper pleat edges on the side of the above indicated fold plane nearer the seal line and rotate it about 180.degree. on an axis approximately through its edge further from the fold line before or during advancement toward the openable end of the bag.

In the drawing with respect to which the invention is described:

FIG. 1 is a fragmentary perspective view of a bag being subjected to edge separation of its lateral pleats;

FIG. 2 is a cross sectional view of the bag shown in FIG. 1 as taken along plane A--A;

FIGS. 3 and 4 are fragmentary perspective and transverse cross sectional views respectively illustrating means for gripping the upper edges and means for holding the lower edges to a support in place before any relative longitudinal movement of bag portions has taken place;

FIGS. 5 and 6 are fragmentary perspective and longitudinal-diagrammatic views of a bag in association with apparatus having partially effected longitudinal shifting of the bottom forming bag portion relative to restrained portions of the bag;

FIGS. 7 and 8 are fragmentary perspective and diagrammatic-longitudinal elevation views respectively of the bag at completion of the bottom portion advancing stroke with gripping and holding means still in place;

FIGS. 9 and 10 are fragmentary diagrammatic elevation views of two stages of a pressing elevation and apparatus therefor;

FIGS. 11 - 14 are fragmentary diagrammatic elevation views of a modified process wherein the means for gripping the upper pleat edges of the bag may be rotated through 180.degree. at the beginning, or during, the advancement of the bottom portion of a bag to the position for being pressed; and

FIG. 15 is a perspective view of the bag of the other figures in expanded self-supporting condition.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 illustrates a bag 5 resting in flattened condition on a support 6, such as a section of an endless conveyor belt. The bag 5 typically originates as a section of a continuously extruded tube of film. The tube, after leaving an extruder, passes through machinery not shown for flattening the tube and forming longitudinal pleats 7a, 7b therein as shown in FIG. 2 as taken in cross section along plane A--A of FIG. 1. The bag 5 is open along end 8 but closed along end 9 by a seal line 10 along which all opposing surfaces of the bag including those of the pleats are sealed together. Assuming the bag to be flattened in a horizontal plane, it has upper edges 14,15 formed by the pleats and lower pleat edges 16,17 normally located against a flat surface such as that provided by the upper face of the support 6. FIGS. 1 and 2 illustrate air jets 18,19 which project air or other gas against the pleat edges to separate the upper edges 14,15 from the lower edges 16,17 in preparation for being engaged by gripping devices 21,22/ Fingers or clamp elements 21a,21b of device 21 grip one upper pleat edge 14 while fingers 22a, 22b of device 22 grip the other upper edge 15. It should be noted that devices 21,22 grip areas of the bag on the side of plane A--A or its line 24 of intersection with the bag that is nearer the seal line 10.

The bag 5 is held fast to the support 6 by fingers or clamp elements 25,26 which engage the upper sides of lower pleat edges 16,17 17 respectively and hold the bag against any movement relative to the support 6 during subsequent longitudinal shifting of the bottom forming area toward the openable end 8 of the bag. As shown in FIG. 3, the area 28 between line 24 and the end 9 of the bag constitutes about one-half of the bottom portion 30 of the bag as shown in FIG. 7 with the other half portion 29. The extreme end 9 of the bag as shown in FIG. 3 is shown located between bottom halves 28,29 in FIG. 7.

In FIG. 4, the support 6 is shown perforated to provide openings 31 which permit communication between the vacuum chamber 32 and the underside of the bag 5. The vacuum force or negative pressure applied to the underside of the bag 5 is in any case helpful in holding the bag in position while performing the bottom shaping opration. However, it is possible with sufficient vacuum force applied to the underside of the bag 5 in a selective manner to eliminate the fingers 25,26 as means for securing the bag to the support 6. As FIG. 4 illustrates, the fingers 25,26 are carried on devices 34,35, each of which comprises fluid cylinders 36,37 connected in right-angle series relationship with the fluid cylinder 37 directly supporting the fingrs 25 or 26.

FIGS. 5 and 6 illustrate an intermediate stage of traversing the bottom portion of the bag comprising areas 28,29 toward the openable end 8 of the bag.

FIGS. 7 and 8 illustrate the bottom portion 30 of the bag 5 completely advanced toward the openable end 8 with the bottom portion of the bag in a taut condition longitudinally as well as transversely.

As shown in FIG. 2, the devices 21,22 comprise fluid cylinders 38,39 connected in series-angle relationship to effect both lateral and vertical movements of jaws 21b,22b. Jaws 21a,22a are fixed with respect to the fluid cylinders 39 whereas jaws 21b,22b are moved by respective fluid cylinders 39 to effect clamping of the upper pleat edges 14,15. During gripped condition of the edges 14,15, the cylinders 38 are operable to shift each pair of fingers in a lateral outward direction to produce lateral tautness in the intervening wall of the bag. The devices 21,22 are shown movably supported on tracks 41,42 which extend parallel to the longitudinal direction of the bag 5 or the support 6. Mechanical means in variety are known for transversing the devices 21,22 longitudinally of the tracks 41,42 to accomplish any desired motion of the devices 21,22 in shifting the bottom bag portion comprising areas 28,29 from the condition of FIG. 3 to that of FIG. 7. Also readily available is controlling apparatus with cycling and timing mechanisms for programming the various power elements such as fluid cylinders 36,37,38,39 and means for propelling the devices 21,22 along tracks 41,42 to effect any desired movements of fingers or clamping components, such as described above for gripping and holding the bag 5.

Such apparatus will also cause release of such bag grippers at a proper instant during a pressing operation as illustrated in FIGS. 9 and 10. These figures illustrate an apparatus which may be used to press the bottom portion 30 of the bag. Schematically shown is a press unit 45 capable of movement in the direction of the arrows perpendicular to the plane of the bag 5 which comprises, e.g., a pair of plates 46,47 hinged together at an axis 48 with the other ends of the plates pivotally supported on lower slotted extensions 51,52 of the body 53. The plates 46,47 may be equipped with electrical cartridge heaters 49 as shown to heat the plastic material of the bag in promoting crease permanence. This construction allows hinged portions of the plates disposed centrally under the body 53 to sag downward and first contact a middle area of the bag bottom 30 in a pressing operation.

As the press member 45 is lowered and establishes engagement with the bag bottom, the holding clamps 25,26 and the gripping clamps 21a,21b, 22a,22b may be withdrawn as the pressing member while descending first engages the bag to prevent any relative movement of portions thereof and then further descends to the position of FIG. 10 wherein the plates 46,47 assume a planate condition and effect such pressing of the bag as to form somewhat permanent creases which outline and define the bottom area of the bag. The bag is now formed with the bottom area 30 and may be jerked out into its box configuration as shown in FIG. 15 and be self supporting on its bottom 30.

FIGS. 11 - 14 illustrate a mode of practicing the present invention wherein the bag is manipulated in a slightly different manner to achieve formation of the bottom 30 of FIG. 14. In this latter embodiment, the bag 5 may be secured or held to the support 6 by fingers 25,26 as effected in the earlier described embodiment. The upper pleat edges are gripped by two pairs of elements somewhat in the manner effected by devices 25 and 26, as shown in FIG. 3, but at a different location with respect to the fold line plane A--A. As shown, a pair of clamp elements or fingers 61,62 are shown gripping the upper pleat edge 14 immediately adjacent to the plane but on the side thereof nearer its open end and away from the closed end 9. It will be noted that the upper half of the bottom surface 28 extends from the plane A to the closed end of the bag 9.

As FIG. 12 indicates, the elements 61,62 may rotate together about an axis extending transversely of the bag 5 adjacent and parallel to the edges 61a,62a of the elements which were initially toward the openable end of the bag from the plane A--A, as shown in FIG. 13, but face toward the closed end of the bag after rotation as shown in FIG. 13 or completion of the advancement of the bottom portion of the bag toward the openable end as shown in FIG. 14. The rotation of the elements 61,62 may occur without appreciable advancement toward the open end of the bag, or occur during the advancement of the elements toward the position of FIG. 14 by suitable apparatus. The bottom 30 may be pressed as shown in FIGS. 9 and 10 to obtain a suitable crease pattern for maintaining the bag in an expanded condition as shown in FIG. 15.

Claims

I claim:

1. A method of producing a bag with a flat bottom from a bag-forming material provided as a flattened tube having symmetrically opposite longitudinally extending pleats folded laterally inwardly to a uniform predetermined depth to provide two superimposed edges at each side of the tube, said edges occurring as two laterally opposite upper edges and two laterally opposite lower edges when said flattened tube assumes a horizontal planate position, comprising the steps of:

providing in the form of a bag a section of said flattened tube continuously sealed in a straight seal line across one end of the bag, to band together all adjacent surfaces including those of said pleats, the other end of the bag being freely openable;

supporting said bag substantially in a plane on a flat surface with said lower edges next to said surface in a flat substantially deflated condition;

with reference to a fold plane in transverse perpendicular relation to the general plane of the bag located at an approximate distance from said seal line equal to twice the depth of either of said pleats, said plane having a near side and a far side in reference to said seal line, holding both lower edges at locations along said far side in juxtaposition to said plane in fixed adjacent relation to the plane of said flat surface;

gripping both upper edges along areas in juxtaposition to, and on the far side of, said plane in a manner maintaining said material between the gripped areas in taut condition, and advancing said gripped upper edges with the taut material therebetween over said held areas of the lower edges and other intermediate bag surface in close to slidable relation therewith toward said openable end to bring a longitudinally advanced portion of the bag theretofore extending between fold line and the gripped areas measuring twice said pleat depth into a taut condition;

rotating a means gripping said areas about its far side before completing its movement to place said longitudinally advanced portion of the bag in a taut condition; and

pressing the entire advanced bag portion against the underlying bag portion to develop fold lines which define and outline said flat bottom.