WO1997026131A1

WO1997026131A1 - Flat bottom plastic bag and method of making the same

Info

Publication number: WO1997026131A1
Application number: PCT/US1997/000418
Authority: WO
Inventors: Howard A. Darmer; David W. Bourke
Original assignee: Union Camp Corporation
Priority date: 1996-01-18
Filing date: 1997-01-16
Publication date: 1997-07-24

Abstract

A plastic bag (2) having a flat bottom surface and method of making the same in which the plastic bag is formed by sealing opposed walls (8a, 8b) of a tubular sheet together and then drawing the same over a flat surface such that the sealed end forms a bottom section having an extension which is folded and then sealed to the bottom section over at least a portion of its length.

Description

FLAT BOTTOM PLASTIC BAG AND METHOD OF MAKING THE SAME

FIELD OF THE INVENTION

The present invention is directed to a flat bottom bag made of a sealable plastic material which is particularly suited for storing materials in a stand alone upright position. The plastic bag is made from plastic sheet material which has been sealed, by applied energy such as heat, to form a tube and then sealed in a manner to form an integral flat bottom portion which is strong and leak proof.

BACKGROUND OF THE INVENTION

Flat bottom bags have been developed because they facilitate loading and unloading of stored materials. Such bags can serve as point of purchase displays while at the same time enabling the customer to readily remove the bag from the storage shelf. As used herein, the term "flat bottom bag" shall mean a bag which when opened and ready for loading with a storable material can stand alone without support by mechanical means or the user.

Flat bottom bags have been made out of paper and are exemplified by the typical modern grocery store bag. Such bags, while being able to stand alone, are disadvantageous because the flat bottom portion can be formed only through the use of glues and adhesives. While such bags are suitable for packaging protected goods such as canned goods and the like, they are unacceptable for storing loose fill materials and/or materials which can deteriorate when exposed to air and humidity. Materials such as animal feeds, fertilizers, and the like are advantageously stored in bags which prevent exposure to the atmosphere. In addition, such materials can adversely affect seals formed from glues and adhesives and therefore can not adequately be stored in flat bottom bags made out of paper. The storage bag industry has therefore moved to employing sealable materials such as polypropylene, polyethylene and the like to form atmosphere impervious bags with flat bottoms. Typical examples of such flat bottom bags are shown in T. Piazze, U.S. Patent No. 3,237,845; J. Shapiro et al., U.S. Patent No. 3,739,977 and V. Hanson, U.S. Patent No. 3,970,241.

Sealable plastic bags are generally made from a plastic sheet material which is formed into a tube having front and rear walls and gussetted sides. The flattened bottom section is formed by sealing a flat piece of plastic to the bottom of the bag. Alternatively, the bottom section is formed by folding plastic portions upon each other in a manner which forms a flat bottom, sealing the folds to each other and then removing extraneous plastic therefrom.

In the manufacture of flat bottom sealable bags, it is important that the manufacturing operation be efficient and cost effective, i.e. be performed in the least amount of process steps at the lowest possible cost. In this regard each ofthe prior art processes are disadvantageous because they require additional plastic material or process steps to form the flat bottom section.

T. Piazze, U.S. Patent No. 3,237,845 discloses the formation of a flat bottom heat sealable bag from a tubular blank having gussetted sides. In the process of making the bag, the gussetted tube is flattened out to the original pregussetted tube shape. The blank is then positioned onto a mandril where the bottom section is flattened in a manner such that the sides automatically form two triangular ears which extend outward from the bottom poπion ofthe bag. Heat sealing is then performed on the bottom section. The corner ears formed as the result of heat sealing end up as extraneous material and therefore must be cut off in a separate operation.

The heat sealable flat bottom bag formed by the '845 patent is disadvantageous because extra process steps are required to flatten the original blank and to remove the extraneous corner ears from the bottom section ofthe bag. J. Shapiro et al., U.S. Patent No. 3,739,977 disclose a heat sealable flat bottom bag formed from a seamless tube. The bottom section ofthe bag is sealed along line 40 leaving an extension or tab 58 to provide a tear or cutting area for separating the bag section length from a continuous roll of plastic film in the manufacture thereof.

The bag ofthe '977 patent is disadvantageous because the sealing process for forming the flat bottom section requires multiple seals. The bottom section is sealed to the comers of the sides as well as across the ends ofthe bottom. In addition, the tab 58 prevents the bag from having a universally flat profile since no provision is made to eliminate the tab.

V. Hanson et al., U.S. Patent No. 3,970,241 disclose a flat bottom bag in which a tubular blank has opposed faces and sides initially joined together through a closing seal at the bottom end of the bag leaving a tab extending from the closing seal as in U.S. Patent No. 3,739,977 discussed above. A plunger is then inserted into the opening ofthe bag and the seamed bottom is thereby pressed flat against a flat surface to form a flat bottom section. The flat bottom is then sealed along opposed sides and optionally diagonally across the bottom section.

While the bag disclosed in U.S. Patent No. 3,970,241 produces a flat bottom section in which the extension is heat sealed to the bottom, nonetheless, the extension can still protrude because the seals cross the extension only at selected points (i.e. at the opposed ends or at the midpoint ofthe extension). As a consequence, the extension does not remain flat against the bottom ofthe bag and stored materials, especially loose fill can leak therefrom if the seal forming the extension is compromised. In addition, the sealing of the extension is especially disadvantageous in the manufacture of heavy duty plastic bags having a material thickness on the order of at least about 5 mils.

It would therefore be a significant advance in the art of making plastic bags with a flat bottom if the bag can be constructed in a cost efficient and effective manner with minimal process steps especially if the bag is made of heavy duty plastic. SUMMARY OF THE INVENTION

The present invention is directed to a sealable plastic bag, in which the seals are formed by applied energy such as thermal energy, ultrasonics and the like. The sealable plastic bag is especially suited for storing loose fill materials such as animal feeds, fertilizers, and the like. In general, the plastic bag is formed by a process in which minimal process steps are employed to form the flat bottom portion yet provides a reinforced and sturdy flat bottom section which can withstand the rigors of commercial use and is especially suited for heavy duty plastic bags.

More specifically, the present invention is directed to a plastic bag formed of a sealable plastic material comprising:

a) a body portion having a longitudinally extending seal, a first end for receiving a storable material and an opposed end; and b) a bottom portion at the opposed end ofthe body portion having a substantially flat bottom surface to enable the bag to stand alone in an upright position, said bottom portion comprising a first seal transverse to the direction of the longitudinally extending seal ofthe body portion thereby defining an extension, and at least one second seal extending along at least a portion ofthe extension to thereby secure the extension to the bottom portion and form said flat bottom surface.

The method of forming the flat bottom plastic bags of the present invention generally comprise:

a) forming a sheet of plastic material into a tube having front and rear walls and opposed sides; b) forming a gusset in each of said opposed sides; c) providing a seal across the bottom ofthe bag to thereby seal the front and rear walls and sides together to form a sealed bottom section having an extension protruding therefrom; d) placing the bag over a flat surface so that the sealed bottom section comes into contact with the flat surface; e) drawing the sealed bottom section across the flat surface to form a flat bottom region so that the extension is folded along the flat bottom region; and f) sealing the flat bottom region across at least a portion ofthe length of the folded extension to form the flat bottom.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings in which like reference characters indicate like parts are illustrative of embodiments of the invention and are not intended to limit the invention as encompassed by the claims forming part ofthe application.

Figure 1 is a perspective view of a sealable plastic bag in accordance with the present invention;

Figure 2A is a bottom view ofthe sealable plastic bag shown in Figure 1 showing one embodiment of a sealed bottom section thereof,

Figure 2B is a bottom view ofthe bag similar to Figure 2A showing another embodiment of a sealed bottom section ofthe bag;

Figure 2C is a bottom view of the bag similar to Figure 2A showing still another embodiment of a sealed bottom section ofthe bag;

Figure 3 is a partial side view ofthe sealable plastic bag shown in Figure 1, Figure 4A is a top view of a plastic sheet formed into a cylinder for use in forming a plastic bag ofthe present invention;

Figure 4B is a partial side view of the cylinder shown in Figure 4A extended to an unfolded condition;

Figure 5 is a partial side view ofthe bag with a flat bottom section formed ready for sealing;

Figure 6 is a plan view ofthe inside ofthe bag in the condition shown in Figure 5;

Figure 7 is a side view of an apparatus for forming the flat bottom bag of the present invention; and

Figure 8A is a partial side view ofthe apparatus shown in Figure 7 with an optional pivot feature.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a sealable plastic bag in which the bottom portion, which provides the flat surface for stand alone operation, is uniquely formed from a tubular blank.

It will be understood that the term "tubular blank" shall mean a plastic material which is extruded in the shape of a cylinder or is formed into a cylinder or the like. In the former embodiment, the cylinder has no seams. In the latter embodiment, a flat sheet of plastic material may be rolled and seamed to assume a cylindrical shape. For illustrative purposes only, the following description ofthe invention will employ a flat sheet of plastic as the starting material. The plastic materials employed herein must be sealable through the use of apphed energy such as by heat sealing, ultrasonic sealing, impulse sealing, resistance sealing and the like Such plastics include low density and high density polyethylenes, linear low density polyethylenes, polyethylenes modified with ethyl vinyl acetate, metallocene linear low polyethylenes and polypropylene For purposes of illustration only, the plastic bag ofthe present invention will be described hereinafter as employing heat sealing to form the desired seals It will be understood that other forms of applied energy (e g ultrasonics) can be used to form the seals

Referring generally to Figures 1-3, details of a heat sealable plastic bag in accordance with the present invention will now be described Referring first to Figure 1, a heat sealable plastic bag 2 includes a body portion 4 having a first end 6 which is opened for receiving a storable mateπal such as loose fill (e g animal feed, fertilizer and the like) and then may be sealed through conventional means for shipping and stoπng ofthe storable mateπal

The body portion 4 includes front and rear walls 8a and 8b and side walls 10a and 10b Each ofthe side walls 10a and 10b has a crease line 12 (only side 10a is shown) dividing the side walls into gussetted portions 14a and 14b Towards the bottom ofthe side walls 10a and 10b, there is further provided a tπangle-shaped gussetted portion 16 which contπbutes to the formation ofthe flat bottom portion ofthe plastic bag 2 as hereinafter descπbed

In accordance with the present invention, the heat sealable plastic bag 2 includes a flat bottom portion 18 which is formed by sealing, through the application of a transverse seal 19, the front and rear walls 8a and 8b and the side walls 10a and 10b in a unique manner as descπbed hereinafter Referπng specifically to Figures 2A-2C and 3, the bottom portion 18 includes opposed base portions 20a and 20b, side gussetted portions 22a and 22b and an extension 24 which is formed at the end ofthe bag by the transverse seal 19 mentioned above The extension 24 is folded downwardly and sealed through heat seal 26 or sealing by other means to form the bottom portion 18 ofthe bag The manner in which the extension 24 is sealed to form the bottom portion 18 ofthe bag is an important aspect ofthe present invention. As shown specifically in Figures 2A-2C, the extension 24 is sealed by the heat seal 26 along a line extending at least a part ofthe length of the extension 24. The extension 24 is therefore secured to the bottom portion 18 ofthe bag along at least a portion of its length rather than at specific points as described in U. S. Patent No. 3,970,241.

More specifically, the heat seal 26 shown in Figure 2A is formed at opposed end portions 28a and 28b of the extension 24. The heat seal 26 is shown in this embodiment as having a width about equal to the width ofthe extension 24 in its folded condition. An unsealed portion ofthe extension 24 remains in the middle thereof and is identified by numeral 28c. For example, in a flat bottom bag having a flat bottom section measuring approximately 9 inches in length and 6 inches wide, the opposed sealed end portions 28a and 28b ofthe extension 24 each measure approximately 3 inches. The unsealed portion 28C ofthe extension 24 is likewise about 3 inches long. It will be understood, however, that the dimensions ofthe sealed portion may vary

In another embodiment ofthe invention as shown in Figure 2B, the heat seal 26 covers the end portions 28a and 28b as described in connection with Figure 2A but only to the extent of a portion of the width of the folded over extension 24 (e.g. about V. of the width in the embodiment shown in Figure 2B). In a still further embodiment as shown in Figure 2C, the heat seal 26 extends over the entire length ofthe folded over extension 24. As specifically shown in Figure 2C the heat seal 26 covers only a portion ofthe width ofthe folded over extension 24. Altematively, the seal can cover the entire folded over extension if desired.

As shown in the embodiments of Figures 2A and 2B, the folded over extension need not be sealed over its entire length. However, the seal should typically cover at least about 33% of the folded over extension, preferably at least about 50%, most preferably at least about 66% of the folded over extension to ensure protection against leakage, especially for heavy duty plastics having a thickness of at least about 5 mils thick. The process of making the heat sealable bag ofthe present invention can be observed with reference to Figures 4A-8B.

Roll stock of a plastic material or laminates comprised ofthe same is creased along the longitudinally axis of the sheet at opposed points to form crease lines which form the side gussets as described hereinafter. As shown in Figure 4 A the thus formed sheet 30 has a backseam 32 which is formed, for example, by using a molten plastic material (e.g. polyethylene) and a pressure roll to fuse opposed ends ofthe sheet together and thereby form a cylinder or tube 34. At this stage in the process, the tube 34 has an open top end 36 and an open bottom end 38.

As further shown in Figure 4 A, a heat seal 40, spaced apart from the bottom end 38, is provided across the width ofthe lower end ofthe bag and transverse to the longitudinal seal 32. The heat seal 40 serves to close the bottom end 38 ofthe bag.

In closing the bottom end 38 ofthe bag, the seal 40 traverses the front and rear walls 8a and 8b and the gussetted sides 10a and 10b (see Figure 1) so that the gussetted sides 10a and 10b are automatically secured and joined to the front and rear walls 8a and 8b to form gussetted portion 16. The tube 34 of Figure 4A thus becomes a closed end bag as shown in Figure 4B.

In a preferred form ofthe invention, a comer seal extending from the side ofthe bag to the bottom is made on each side thereof to assist in squaring out the bottom ofthe bag during future processing. As shown in Figure 4A, opposed co er seals 42 are provided by heat sealing along lines 44 extending from the side ofthe bag towards the end 38. The comer seals 42 are preferably provided in advance of applying the transverse seal 40.

As a result, when the gussetted portion ofthe bag is extended from a folded condition to an unfolded condition, the side ofthe bag takes on the appearance shown in Figure 4B. As shown in Figure 4B, the seal 40 seals the front and rear walls 8a and 8b together leaving an extension 24 extending from the seal 40. The sealed bag shown in Figure 4B is now ready to be placed over a mandrel for forming the flat bottom portion.

More specifically, the sealed bag shown in Figure 4B is placed around a mandrel so that the top surface ofthe mandrel contacts the bottom portion ofthe sealed bag shown in Figure 4B. This causes the gussetted portions 14a and 14b to straighten outwardly so that the sides are substantially flat and planar as shown in Figure 5. In addition, the gussetted portions 14a and 14b within the bag form opposed triangular portions 50 as shown in Figure 6.

Details of the device for forming the flat bottom section are shown in Figure 7. A forrning device 60 includes a sealing head 62, such as a sonic, impulse or resistance sealer and the like which is spaced apart from a shaft 64 including a device 66 for retaining the bag for sealing mounted on top of a mandrel 68. The retaining device 66, in addition to being a positioner also serves as the flat contact surface for the sealing head 62. The retaining device 66 will always provide the inside dimension ofthe finished bag. The mandrel 68 and the shaft 64 are of fixed dimensions that can accommodate different bag sizes. The retaining device 66 is activated by air cylinders 72 or similar devices after the mandrel 68 is in place under the sealing head 62.

The forming device 60 may be pivotable, as shown in Figures 8 A and 8B, to accommodate the loading ofthe bag and the removal ofthe finished bag from the shaft 64. In particular, the shaft 64 is pivotable so that it can be moved out of alignment with the sealing head 62 as shown specifically in Figure 8B.

In operation, the bag is placed over the shaft 64 in contact with the flat surface ofthe mandrel 68 and secured therein by the retaining device 66. As indicated specifically in Figure

7, the Gaining device 66 is activated by the air cylinders 72 and extended to full travel from the bottom ofthe bag. The sealing head 62 is automatically deployed to contact the extension 24. The force of the sealing head 62 forces the extension 24 down onto the retaining device 66 which is then sealed to the bottom ofthe bag. The sealing operation bonds the extension 24 to the triangle-shaped gussetted portion 16 which in turn seals the same to the body ofthe bag.

Claims

WHAT IS CLAIMED IS:

1. A plastic bag formed of a heat sealable plastic material comprising:

2. The plastic bag of claim 1 wherein the body portion comprises front and rear walls and opposed gussetted sides.

3. The plastic bag of claim 2 further comprising a third seal extending at an angle from the opposed gussetted sides to the bottom portion.

4. The plastic bag of claim 1 comprising two spaced apart second seals extending from an end of the bottom portion toward the middle thereof, said second seals defining an unsealed portion therebetween.

5. The plastic bag of claim 4 wherein the unsealed portion is about one-third ofthe total length ofthe extension.

6. The plastic bag of claim 1 wherein the second seal covers less than an entire width ofthe extension.

7. The plastic bag of claim 1 wherein the second seal covers an entire width of the extension.

8. The plastic bag of claim 1 comprising a single second seal extending an entire length of the extension.

9. The plastic bag of claim 1 wherein the first and second seals are independently formed by the application of energy.

10. The plastic bag of claim 1 wherein the first and second seals are independently formed by the application of thermal energy, ultrasonic energy or a combination thereof.

11. A method of forming a flat bottom plastic bag comprising:

a) forming a sheet of plastic material into a tube having front and rear walls and opposed sides; b) forming a gusset in each of said opposed sides; c) providing a seal across the bottom ofthe bag to thereby seal the front and rear walls and sides together and form a sealed bottom section having an extension protruding therefrom; d) placing the bag over a flat surface so that the sealed bottom section comes into contact with the flat surface; e) drawing the sealed bottom section across the flat surface to form a flat bottom region with the extension folded along the flat bottom region; and f) sealing the flat bottom region across at least a portion ofthe length of the folded extension to form the flat bottom.

12. The method of claim 11 wherein the step of sealing one ofthe opposed ends ofthe tube comprises forming a seal along the width ofthe end region at a preselected distance from an end ofthe tube to thereby form an extension.

13. The method of claim 12 comprising folding the extension and sealing the folded extension to the flat bottom region.

14. The method of claim 11 comprising sealing the extension over an entire length thereof to the flat bottom region.

15. The method of claim 11 comprising sealing the extension over an entire width thereof.

16. The method of claim 11 comprising sealing the extension over less than the entire width thereof.

17. The method of claim 11 further comprising forming opposed seals extending at an angle from the opposed side to the bottom section.

18. A flat bottom plastic bag produced in accordance with claim 11.