Adhesive Closure Having Enhanced Burst Strength for Flexible Bag

This invention relates to a closure for a thermoplastic bag and more specifically, this invention relates to an adhesive closure arrangement for a flexible thermoplastic bag.

Adhesive type closure arrangements have been used to seal and/or close plastic bags such as those used for sandwiches, garbage containers, and other household uses. For example, U.S. Pat. No. 4,519,095 describes an adhesive channel closure suitable for use with flexible bags, such as thermoplastic bags, especially those made from polyethylene, wherein the closure comprises at least one female channel member or strip-affixed to the bag and having a pressure sensitive adhesive layer on an internal portion of the channel strip such that the thickness of the adhesive layer is less than the interior depth of the walls of the channel strip. During shipment and storage the walls of the channel hold the pressure sensitive adhesive layer away from adjacent surfaces to prevent inadvertent sticking. Sealing of the bag is achieved by contacting the channel strip with a surface of the bag and exerting pressure along the strip whereby the pressure sensitive adhesive is contacted with a substantially flat portion of the surface and adhered thereto.

U.S. Pat. No. 4,519,095 shows a channel with the adhesive layer positioned on a flap of the bag; a channel with the adhesive positioned on the body of the bag over which the flap will fold; and two female channel strips positioned on opposite sides of a bag opening to affect a double seal by pressing the two channels into contact such that one wall or bead of each channel is contacted by the adhesive layer in the opposing channel.

One problem with the adhesive closures having rigid channel strip ribs described in U.S. Pat. No. 4,519,095 is that the closures are not easy to close. A sufficient amount of pressure applied to the rigid channel strip ribs is required to overcome the rigidity of the ribs to effectuate a closure. In addition, the closure requires restricting the width between the ribs to a predetermined width in order to avoid premature contact of the pressure sensitive adhesive with the opposite contact surface wall during processing and shipping of the bag, i.e., to avoid premature closure. The channels are also too small to accommodate the thumb of a user. Also, there is less surface contact between wall and adhesive because of the height and width of the channel. In addition, the bag surface adjacent the adhesive wrinkles easy causing an inadequate closure and leakage of liquids through the closure. Furthermore, there is no tactility indication on the closure described in U.S. Pat. No. 4,519,095.

Another problem with the closure described in U.S. Pat. No. 4,519,095 is that the external opening force is the same as the internal opening force of the closure. Thus, the contents of the bag will tend to fall out of the bag since the closure is easily opened from the inside and the closure does not have sufficient closure force to hold the contents in the bag when the bag is placed upside down or horizontally where pressure is exerted against the closure by the contents. On the other hand, if the adhesive is made strong enough to hold the contents, then the bag will be difficult to open.

It is desired to avoid the problems with the prior art closures and provide closures suitable for use with plastic bags wherein the closures are able to effect a satisfactory seal as needed.

It is also desired to provide a flexible bag with an easy external openable and resealable closure and yet have a stronger internal sealing force to prevent the opening of the bag from the inside due to the pressure of the contents when the bag is undesirably placed in a non-upright position.

One aspect of the present invention is directed to an adhesive closure useful for a flexible thermoplastic bag including:

an adhesive strip affixed transversely across the longitudinal width of a first inner surface of one of a front wall or rear wall of a bag at a preselected distance from the opening of the bag; and

a flap member strip affixed transversely across the longitudinal width of a second inner surface of one of a front wall or rear wall of the bag, and aligned on the wall opposite from the adhesive strip on the first inner surface, at a preselected distance from the opening of the bag;

said flap member of said bag being pressable against and into said adhesive strip on said first inner surface, whereby a seal is formed by contacting said adhesive strip with said flap member of said second inner surface, providing an enhanced burst strength to the internal opening of the bag.

Another aspect of the present invention is directed to a resealable flexible thermoplastic bag including a front wall and a back wall, said walls being joined along the major portions of their opposite longitudinal edges and bottom; an open mouth adjacent to the top edge of said bag; and the aforementioned adhesive closure near the open mouth of said bag.

In one embodiment of the closure of the present invention, a female channel strip is affixed to a surface of one of said front wall or said back wall at a preselected distance from said opening; and a flap member is affixed to the other of said front or back wall opposite of the female channel; said channel strip having a trough between two channel ribs; and an adhesive layer in said trough, such that the flap member portion of said bag is pressable into said trough between said channel ribs, whereby a seal is formed by contacting said adhesive layer with said flap member portion of said second surface.

In another embodiment of the closure of the present invention, a self-alignment guidance rib member is positioned adjacent the flap member surface on the opposite wall from the channel strip and which contacts one of the channel rib members.

In still another embodiment, a tactility surface is provided on the outer surface of the wall on which the flap member portion is attached.

FIG. 1 is an elevational view of a thermoplastic bag having one embodiment of a closure constructed in accordance with the present invention.

FIG. 2 is an enlarged cross-sectional view of one embodiment of the closure of the present invention.

FIGS. 3 to 8 are enlarged cross-sectional views of various embodiments of the closure of the present invention.

FIGS. 9 to 13 are partly cross-sectional and partly front view of various embodiments of the roughened surface portion of the closure of the present invention.

FIG. 14 is an elevational view of a thermoplastic bag having another embodiment of a closure constructed in accordance with the present invention.

FIG. 15 is an enlarged cross-sectional view of another embodiment of the closure of the present invention.

FIG. 16 is a portion of the bag of FIG. 15 showing the closure portion partly opened and partly closed.

FIG. 17 is an enlarged cross-sectional view of the closure shown in FIG. 16 in a closed position.

FIG. 18 is an enlarged cross-section view of the closure shown in FIG. 17 in a closed position and showing the opening and closure forces therein.

FIG. 19 is another embodiment of the closure of the present invention showing a portion of a bag with the closure portion partly opened and partly closed.

FIG. 1 shows a thermoplastic bag having a closure constructed in accordance with the present invention. A bag or bag body 20 comprises a front wall 21 overlying a back wall 22. Front wall 21 is attached to back wall 22 along opposite longitudinal heat seal edges 23 and bottom fold line 24, thereby forming an open mouth adjacent to the top edge of the bag. The open mouth provides access to the interior of the bag. The bag is preferably made out of a plastic film such as polyethylene. Adjacent the top edge opening of the bag 20 is positioned a closure arrangement generally indicated as numeral 25, the various embodiments shown in more detail in FIGS. 2 to 8.

With reference to FIG. 2, and in its broadest scope, the closure arrangement 25 is made up of an adhesive member 30 mounted on and positioned on the inside surface of one wall, for example the back wall 22, and a flap member 40 mounted on and positioned on the inside surface of one wall, for example the front wall 21 which is opposite of the adhesive strip 30. The adhesive member and flap member are provided in the form of strips that extend transversely across the full longitudinal width of the opening and are mounted to the bag generally near respectively longitudinal edges 26 and 27 closest to the opening of the bag. The flap member 40 is attached to the wall 21 at point 29 along one edge of the flap member. A surface space 28 between the upper edges 26 and 27 and closure members on walls 21 and 22 provide for gripping by a user.

Closure of the bag 20 is effected by contacting the front wall 21 to the back wall 22 and applying pressure along the area where adhesive strip 30 is contacted with the front wall member 21 thereby contacting the adhesive 30 with the flap member 40 of front member 21. Thus, the adhesive strip and flap member mesh together and join the front wall 21 to the back wall 22 of the bag to enclose the opening of the bag. It is one of the features of the present invention that the bag may be easily closed by contacting at least a portion of the flap member across the width of the bag without the closure strips being precisely aligned. During use, the adhesive and flap member are pressed together and secured together to join the front wall 21 to the back wall 22 and enclose the opening. When desired to open the bag, the front wall and the back wall may be grasped at the gripping surface 28 and pulled apart. The closure may be pressed and pulled apart many times to easily open (and reopen) and close the bag opening. The flap member 40 provides a means for enhancing the burst strength of the bag as described below.

The adhesive 30 of the present invention may be made of, for example, pressure-sensitive adhesive material or contact adhesive material. Preferably, the closures of the present invention are useful with adhesive systems such as pressure-sensitive adhesive materials including acrylic, natural and synthetic rubber types. Adhesives having good peel strength are also preferred.

With reference to FIG. 3, there is shown another embodiment of the closure of the present invention including a first inside toughened surface 50 on the flap member 40 inside surface which is to contact the adhesive strip 30.

The inside roughened surface portion 50 of the flap member 40 of the front wall 21 in contact with adhesive 30 is preferably roughened to advantageously provide a means for substantially preventing wrinkling of the contact surface upon closing of the bag. The roughened surface 50 also provides more surface area for adhesive contact and, thus, greater adhesion. The roughened surface 40 can be any type of surface to provide a wrinkle-free closure, for example, a uniform outwardly facing structured surface such as vertical or horizontal ridges or an embossing pattern.

In FIGS. 9 to 13 there is shown various embodiments of a plurality of protuberances 51 of various shapes which can be used as the roughened surface 50. For example, the protuberances 51 used in the present invention may be triangular in shape (FIG. 9), spherical in shape (FIG. 10), honey-combed in shape (FIG. 11), pyramidal in shape (FIG. 12), or conical in shape (FIG. 13). Other protuberances useful in the present invention and their manufacture are described in U.S. Pat. No. 5,113,555 incorporated herein by reference.

Generally, the roughened surface 50 may be extruded or embossed. More particularly, the roughened surface may be extruded as an integral portion of the bag itself, or embossed directly on the surfaces of the bag, rather than constructed as a separate member that is mounted on the bag.

In an optional embodiment, the roughened surface area 50 may contain a layer or coating of another adhesive (not shown) such as an adhesive of the same material or of different material than the adhesive 30 for contact adhesion provided that the other second adhesive adheres only to the adhesive 30. The second adhesive would readily attach to and detach from the adhesive 30 to provide the resealable feature of the present invention.

With reference to FIG. 4, there is shown another embodiment of the closure of the present invention including a second toughened outer surface 60 located on the outer surface of wall member 21 opposite the flap member 40 and the first roughened surface 50. The outer roughened contact surface 60 is used as a contact surface for contacting with a thumb or finger to provide tactility to a user.

The outside roughened surface portion 60 to be contacted with a thumb or finger by a user upon closing the bag is preferably toughened to advantageously provide a means for tactility when closing the bag. The roughened surface 60 can be any type of surface to provide tactility, for example, ridges or an embossing pattern with protuberances 61. The roughened surface 60 can be of the same type of surface as described with reference to roughened surface 50 for example, the embossing patterns with protuberances 51 shown in FIGS. 9 to 13. Examples of other types of outer roughened surfaces for the closure members which can be used in the present invention are described in U.S. Pat. No. 4,479,247; and in Canadian Patent No. 2,018,390 both which are incorporated herein by reference.

In a preferred embodiment, the inner and outer toughened surfaces, 50 and 60, respectively, are created substantially simultaneously in one step by impressing or embossing the outside surface of wall 21 with sufficient pressure using for example a pressure roller with conical protuberances to create a plurality of protuberances 62 on the inside surface of wall 21 and a series of indentions or recesses 63 on the outside surface of wall 21 which transfer through the thickness of the wall 21 to form protuberances 52 on the inside surface of flap member 50 and a series of indentions or recesses 53 on the outside surface of flap member 50 as shown in FIG. 15.

Generally, the depth "d" of the recess 53 or 63 is up to about the thickness of the film and the height "h" of the protuberance 52 or 62 is from a ratio of "h/d" of about 1.1 to about 1.9. The spacing "s" between protuberances 52 or 62 is from about 1/64 inch to about 1/4 inch. A sufficient surface portion of the front wall 21 is embossed to cover substantially the entire distance "x" of the adhesive strip 30. The embossing pattern can be formed by any conventional roller means having protuberances of the desired shape.

With reference to FIG. 5, there is shown a more preferred embodiment of closure 25 of the present invention including a female channel strip 70 positioned on the inside surface of one wall, for example the back wall 22, at a preselected distance from the opening. The adhesive 30 is positioned inside the channel strip 70.

The channel strip 70 has walls or ribs 71 and 72 and a base 73 which comprise a trough. Rib 71 will herein be referred to as upper rib 71 because it is nearest the top edge opening of the bag 20 and rib 72 will herein be referred to as lower rib 72 because it is below rib 71 relative to the top edge opening of the bag, when the bag is in an upright position as shown in FIG. 1. Preferably, base 73 is a layer formed integrally with ribs 71 and 72. Channel 70 may be fabricated in a separate step and applied to the wall 22 or it may be formed as an integral part of wall 22, e.g., by a heat deformation process such as well known post-applied extrusion or lamination processes. Interior to channel 70 is a layer of pressure sensitive adhesive 30, uniformly layered between the ribs 71 or 72 of channel 70 and which should preferably be applied to the bottom or base portion 73 of channel 70. Preferably the adhesive layer 30 is continuous or uninterrupted. The adhesive 30 may be applied as a hot melt, coating or any of a number of conventional adhesive application methods.

Closure of the bag 20 is effected by contacting the front wall 21 to the back wall 22 and applying pressure along the area where channel strip 70 is contacted with front wall member 21 thereby contacting the adhesive 30 with the flap member 40 of front wall member 21.

With reference to FIG. 6, there is shown an even more preferred embodiment wherein the front wall 21 of the bag 20 preferably contains a self-aligning and guidance means for the closure 25, in this instance, an aligning or guidance rib member 80 located adjacent the flap member 40 for contacting the channel strip 70. The rib 80 is on the inside surface of front wall 21 opposite the rib member 71 and off set slightly from rib 71, just above the upper rib 71, to provide a mating surface 81 with the surface 75 of rib 71. The guidance rib 80 provides a tactile guide for the thumb or finger of a user as the thumb or finger travels on the surface 60 and the front wall 21 is pressed against the back wall 22 for closure. The guidance rib 80 also provides a guide to align the flap member 40 of the front wall 21 for contacting with the channel 70.

In an optional embodiment the front and/or rear walls 21 and 22, respectively, at near the upper edges 26 and 27, respectively, on the gripping surface 28 can contain "grip strips" or gripping surfaces made up of ribs 90 as described in U.S. Pat. Nos. 5,009,828 and 5,167,454 incorporated herein by reference. In the alternative, the gripping surface 90 may be a toughened surface or embossed surface as described in European Patent No. 0 089 680, incorporated herein by reference.

FIG. 8 shows an enlarged cross-section views of an embodiment of closure 25 constructed in accordance with this invention in which the rib members 71a and 72a, the alignment rib member 80a, and the grip strips 90 have a key-hole type shape as described in U.S. Pat. Nos. 5,167,454 and 5,192,135, incorporated herein by reference. Any of one of the rib members, guidance rib or grip strips alone, or in combination with each other, may be key-hole shaped. In the alternate embodiment shown in FIG. 8, the guidance rib 80a with bulbous head 80b advantageously slides off the bulbous head 71b of rib 71a for ease of closure.

Any of the rib members 71 and 72 or guidance member 80 may be formed by extruding two extruded beads or ribs 71 and 72 onto a film web member to form a channel strip 70. The channel strip 70 of such an embodiment would have a base 73 comprising a portion of the film surface between the two beads 71 and 72, and a layer of adhesive 30 would be positioned on the surface within the area defined by the beads 71 and 72.

In FIGS. 14 to 18, there is shown a most preferred embodiment of the present invention wherein the guidance rib member 80 and the rib member 71 and 72 of the closure 25 includes a bulbous portion as shown in FIG. 15.

As shown in FIG. 16, as the bag is closed by pressing the front wall 21 against the back wall 22 at the channel 70 and embossed surface area 60, the guidance rib 80 rides on rib 71 while the flap member 40 is contacted with adhesive 30.

FIG. 17 shows a sectional view of an enlarged cross-section of the closure 25 of the present invention in a sealed position in which female channel strip 70 with adhesive layer 30 on an internal portion of the channel strip 70 in the trough, is positioned against the flap member 40 contacted with the adhesive layer 30 contained in channel strip 70 and has been pressed into the trough of the channel and into intimate contact with the adhesive layer, thus effecting sealing of the closure 25. The portion of flap member 40 of the front wall 21 that is contacted with adhesive layer 30 is deformed as may be seen in FIG. 17 to provide a seal.

FIG. 18 shows the forces acting on the closure 25. Opening of the bag from the outside shown by arrows 101 is by a peel force shown by arrow 102 while opening of the bag from the inside shown by arrows 103 is by a shear force shown by arrow 104. The maximum adhesion strength of the adhesive is when a shear force is applied to the adhesive strip 30. Thus, the opening force is small when compared to the burst force.

The amount of adhesive 30 contained in the channel structure 70 between the ribs 71 and 72 of channel structure 70 may be varied as desired. Generally, the amount of adhesive used or the thickness of the adhesive layer is up to a height sufficient to provide a uniform deformable surface to accommodate the height of the protuberances and to maintain contact with the surface area of the film wall at the base of the protuberances and the area between the protuberances to obtain the desired adhesion. The layer of adhesive 30 may be coated into channel structure 70 either as a continuous layer or as an interrupted layer, but is preferably applied at the bottom or base 73 as a continuous layer.

The dimension of ribs 71 and 72, including height and width, are selected such that each rib can be about 50 times thicker than the thickness of the film. The spacing between the ribs is selected to fit an average size thumb comfortably. A variety of dimensions may be used for the exterior height "r" and thickness "t" of channel ribs 71 and 72, interior width "w" of channel structure 70, and thickness "a" of adhesive layer 30. In a particularly preferred embodiment an extruded strip comprising polyethylene is applied to a polyethylene bag surface by means of a hot melt technique. A ribbon of pressure sensitive adhesive is positioned between the walls or ribs of the strip. The channel or ribbon structure is constructed so that the height "r" of the ribs 71 and 72 of the channel is from about 50 mils to about 70 mils high and the distance "w" between channel ribs 71 and 72 is from about 3/8 inch to about 5/8 inch apart. The thickness "t" of each channel ribs 71 and 72 is constructed to be from about 10 mils to about 50 mils, the thickness a of pressure sensitive adhesive layer 30 is a coating from about less than 2 mils or a height to provide a uniform deformable surface, and the layer of polyethylene is from about 0.5 mil to about 4 mils thick.

Pluralities of the closures of the present invention may also be used so that a bag may have two or more closure structures.

The channel strip 70 may optionally be colored in order to more easily locate their position on the bag. In another embodiment, the adhesive and/or the flap member surface may also be colored with different colors initially which change into a third color upon closing to provide for closure indication. For example, the adhesive may be yellow and the flap member surface may be blue to make green upon attaching the two closure members together; or other color combinations to make a third color can be used.

In another embodiment useful for closure indication, the closure members may be uncolored initially and upon closing form a color to provide closure indication. For example, when the closure members are made from polarized film such that when the closure members are superimposed upon each other, the closed or contacted closure changes to a certain color such as from clear to dark.

In still another embodiment shown in FIG. 19, the closure members may be colored at certain intermittent or interrupted portions 111a, 112a to form a series of uncolored spaces 111b, 112b between colored portions of the closure member to form a "dashed" line along the closure strip. The dashed lines are offset such that when the two dashed lines are contacted, the uncolored spaces and colored portions of the closure members interdigitate and mesh together to form a single solid line of a particular color to provide an indication to the user that the bag is closed.

In carrying out the process of manufacturing the thermoplastic bags containing the closure of the present invention, a film web is formed, for example, by an extrusion process. The flap member 40 may be extruded separately and then post applied to the film web or extruded integrally with the film web. The flap member of the bag may also be formed by inserting a fold in the film web thereby forming a flap. The adhesive strip 30 may be post applied to the film web in a separate step or applied to the film web simultaneously during extrusion of the film web. Various conventional methods can be used to affix the adhesive on the film web including, for example, the process described in U.S. Pat. No. 4,392,497, incorporated herein by reference. Substantially simultaneous or in a separate step, the film web is embossed to form the toughened surface 50 and the embossed surface 60. Preferably, the film web is embossed on one side of the film web with enough force to substantially simultaneously form the roughened surface 50 and the toughened surface 60. After the web has been embossed, the web is folded and heat sealed by techniques well known in the art to form the final bag structure.

Although specific embodiments of the present invention have been described it is to be understood that modifications and variations may be found by those skilled in the art which are within the spirit and scope of the invention.