Plastic Bag Having Reinforced Closure

Abstract

A plastic bag having formed integrally therewith cooperating male and female pressure fastenable releasable interlocking elements for selectively closing the open end of the bag and a pair of stiffener ribs also formed integrally with the bag but of a thermoplastic material more rigid than that from which the remainder of the bag is formed to provide increased lateral rigidity along the open end of the bag to prevent inadvertent separation of the interlocking elements.

Description

This invention pertains generally to the field of plastic containers such as bags, pouches or the like and more particularly to such containers which include a pair of superimposed plastic sheets joined together along the edges thereof except for a portion forming the open side of the bag and which further include cooperating male and female pressure fastenable releasable interlocking elements made of plastic and formed integrally with the sheets along the openside of the bag.

Such containers are known in the prior art as having utility in a wide variety of applications. For example, such containers are used as inexpensive, light briefcases. They are also used as packages for a wide variety of goods. Such diverse products as handkerchiefs, fishhooks and nuts and bolts are all packaged in such plastic containers.

Examples of early prior art plastic bags having releasable fasteners are generally formed in two parts, i.e., a pair of superimposed plastic sheets bonded together along their corresponding edges except for the edge along which is formed the open end of the bag, and a pair of plastic strips on which are formed the interlocking profiles or the cooperating male and female elements of the releasable fastener. The two strips are usually heat-sealed to the sheets along the open side of the bag.

In other examples of the prior art a single sheet of plastic material is folded over itself to form the opposite walls of the bag but in other respects the construction of the bag is similar to the first-mentioned example.

With respect to either of these two bag constructions it is essential that the plastic sheets be of sufficient thickness to allow the efficient heat-sealing operation of the fastener strips to the sheets. As a consequence the sheets which form the sides of the bag are often thicker than the particular packaging application requires. For example, assume that a plastic bag in which a handkerchief is intended to be packaged requires a wall thickness of only 0.2 mils. Nevertheless, it may often be necessary to increase the wall thickness by 50 to 100 percent of the thickness required by the goods in order to allow the sheets to be sealed quickly and adequately to the fastener strips.

The interlocking male and female elements of the releasable fastener were and are relatively small and quite flexible so that the releasable fastener can be opened and closed quite easily and with only light finger pressure.

More recently it was determined that plastic bags can be formed from an extruded tubular plastic film, the operating male and female elements of the fastener being formed integrally with the film. In this operation the tubular film is slit longitudinally, generally between the male and female fastener elements or profiles, and then the film is cut along its length into sections of predetermined length and bonded generally at the same time as the cutting, along the cut edges to form a plurality of individual containers. As a result of the integral formation of the fastener profiles or male and female interlocking elements the thickness of the sheets which comprise the walls of the bag can usually be reduced to the thickness that is required or dictated by the product or goods which are to be contained within the bag.

All of these prior art plastic bags, however, because of the low range of thicknesses of the plastic sheets which comprise the walls of the bag, have been found to be susceptible to inadvertent opening of the releasable fastener. This susceptibility arises from the lack of sufficient lateral rigidity of the bag along the open end when subjected to side forces which occur, for example, when the bag is squeezed laterally along the open end or when the bag is dropped on its side.

Such lateral forces tend to wrinkle (in more or less a serpentine fashion) or "double up" the releasable plastic fastener. At each curved portion of the fastener one of the male and female elements of which it is comprised must assume a curve which is larger than the curve of the adjacent portion of the other element, and since the elements are of the same length under normal conditions, the result of this curvature or doubling-up is that the elements become separated from one another. This separation of the two elements of the fastener has the effect, of course, of inadvertently opening the bag.

In light of the foregoing it is an object of the present invention to provide a plastic bag in which the plastic fastener attached to the walls of the bag whether integrally at extrusion or later by sealing, is reinforced in a manner so as to increase the lateral rigidity of the bag along the closeable end and to decrease the likelihood of inadvertent opening of the releasable fastener when the bag is subjected to side forces.

To this end the invention may be summarized as comprising a plastic bag (and a method of and apparatus for producing the same) which comprises a pair of superimposed plastic sheets which form the walls of the bag and a plastic releasable fastener formed of cooperating interlocking male and female elements made either separately or integrally with the sheets and extending continuously along the open side of the bag. A stiffener rib or beam is also formed integrally with one or both of the plastic fasteners or sheets and extends along the open end of the bag to provide lateral rigidity and to reduce the likelihood of inadvertent opening of the releasable fastener when the bag is subjected to lateral or side forces tending to wrinkle or double-up the fastener.

The rib (or ribs) is also formed of plastic material but in the preferred embodiment the plastic of which the rib is made is considerably physically stiffer than is the plastic of which the sheets and the fastener are made.

In the preferred embodiment the bag is formed from an extruded tubular film, though it may also be formed from an extruded sheet, the male and female fastener elements as well as the stiffener rib being extruded along with the film. The sheet-form film, which forms the walls of the bag, as well as the male and female fastener elements are made of highly flexible plastic while the stiffener rib is made, in the preferred form of the invention, of very stiff plastic.

As a consequence of the stiffener rib or ribs, a plastic bag constructed in accordance with the principles of the present invention is more reliable in use as a container because of the reduced likelihood of inadvertent opening of the fastener when subjected to lateral forces acting on the bag along a line parallel to the longitudinal axes of the male and female fastener elements.

Another object of the present invention is to provide an improved plastic bag at substantially the same cost as is required in the production of prior art plastic bags.

Another object of the invention is to rigidify the bag in the area of the releasable fastener for reducing the likelihood of inadvertent opening of the fastener when the bag is subjected to side forces.

Another object is to provide a bag with a reinforcing or rigidifying rib or beam in an inexpensive manner through the utilization of a plastic material of greater stiffness than the plastic material of which the walls of the bag and the releasable fastener are formed.

Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheets of drawings, in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example only.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an isometric view of a plastic container such as a bag, pouch or the like constructed in accordance with the principles of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along lines II-II of FIG. 1.

FIGS. 3 and 4 are similar to FIG. 2 but illustrate other forms of the invention.

FIG. 5 comprises a plastic extruder assembly constructed in accordance with the principles of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of the invention the same reference numerals are used throughout in designating the various parts or features of the invention which are common to the several illustrated forms thereof.

Referring to the drawing and particularly to FIGS. 1 and 2, reference numeral 10 indicates generally a plastic bag or similar container such as a briefcase, pouch or the like constructed in accordance with the principles of the present invention. The bag 10 generally comprises a pair of plastic sheets 11 and 12 which are superimposed one on the other or otherwise arranged in substantially parallel side-by-side relation. In the illustrated embodiment sheets 11 and 12 are rectangularly shaped although it will be understood as the description of the invention develops herein that the sheets 11 and 12, which comprise opposite walls of the bag 10, may assume configurations other than the rectangular.

The adjacent or corresponding edges of the sheets 11 and 12 are joined together along the lines indicated at reference numerals 13, 14 and 15 but are separated along a top open end of the bag indicated at 16. The edges 13 and 14 may be bonded together by means of a heat seal, adhesive or the like. The bottom edge 15 may also comprise a bond between sheets 11 and 12 but in the illustrated embodiment of the invention as in FIG. 2 the sheets 11 and 12 actually comprise a single larger sheet which is folded back over itself to provide an integral bottom wall at the lower edge 15.

The bag 10 may be further characterized as comprising a pressure releasable fastener indicated generally at reference numeral 17 which is formed parallel and close to the top open end 16. The fastener 17 comprises a pair of cooperating interlocking profiles or rib and groove members, one of which may be referred to as a male element and which is indicated at reference numeral 18 and the other of which may be referred to as a female element and which is indicated at reference numeral 19. The male and female elements 18 and 19 as shown in their preferred embodiment are formed integrally with sheets 11 and 12 and project perpendicularly thereto. In addition the male and female elements 18 and 19 extend in straight lines substantially across the entire width of the sheets 11 and 12.

Sheets 11 and 12 and the male and female elements 18 and 19 are formed of the same thermoplastic material which may be characterized as being quite flexible. This flexibility enables the fastener 17 to be opened and closed easily without any appreciable force.

Thus in order to close the fastener 17 a slight pressure is applied to the male and female elements 18 and 19 to force the same together along the length of the fastener 17. This pressure causes a tapered arrowhead portion 18' of the male element 18 to spread a pair of arms 20 and 21 formed on the female element 19. After the arrowhead portion 18' is completely inserted into a recess 22 formed between the arms 20 and 21, the inherent resiliency of the thermoplastic causes the arms to inturn over and become interlocked with the arrowhead portion 18'.

To open the fastener 17 it is merely necessary to apply a slight separating force to marginal portions 23 and 24 of the sheets 11 and 12 which extend adjacent the open end 16. The application of this force causes the arm 20 to spread and allow the separation of the arrowhead portion 18' of the male element 18 from the female element 19, thus opening the top end 16 of the bag 10.

As a result of the high flexibility of the thermoplastic of which the sheets 11 and 12 and the fastener 17 are constructed the upper portion of the bag 10 adjacent the top open end 16 may be easily collapsed or squeezed together in serpentine fashion by the application of a lateral force acting along the longitudinal axes of the male and female elements 18 and 19. The application of such a lateral force may be inadvertent, such as may occur, for example, if the bag were to fall to the ground on edges 13 or 14. In addition, however, the normal use of the bag 10 in the performance of its function as a container may involve inadvertent or unavoidable lateral contraction of the bag along its top end 16.

The resultant "doubled up" or curved configuration of the fastener 17 causes separation of the male and female elements 18 and 19. Since the male and female elements 18 and 19 are of the same length and are continuous across the entire width of the sheets 11 and 12, a curvature of the fastener 17 will produce different radii of corresponding longitudinal portions of the male and female elements 18 and 19. Since the plastic of which the sheets 11 and 12 and the male and female elements 18 and 19 are constituted has virtually no stretch capability the result of this difference in curvature of the male and female elements is the separation of the two and opening of the fastener 17.

This problem could perhaps be overcome by forming the male and female elements 18 and 19 of very rigid thermoplastic material. While this would provide the lateral rigidity to the fastener 17 necessary to reduce or substantially eliminate bending of the fastener upon the application of moderate side forces, nevertheless as a result of this increased rigidity it then would be extremely difficult to lock and unlock the male and female elements. A compressive force substantially greater than moderate finger force would be required and for many applications of the bag 10 this additional force required to open and close the bag would be prohibitively undesirable.

In accordance with the present invention, the lateral rigidity of the bag 10 (at least along that portion thereof which may effect the inadvertent opening of the fastener 17) is increased by the utilization of a reinforcement beam or stiffener rib extending substantially across the width of the bag 10. In FIG. 2 a stiffener rib is indicated at reference numeral 25, the same being constructed integrally with the sheet 12 and formed of thermoplastic material which is much stiffer and more rigid than the thermoplastic material of which the sheets 11 and 12 and the male and female elements 18 and 19 are constructed. As indicated another stiffener rib 26 may be formed on the sheets 11, and both ribs 25 and 26 project perpendicularly for m the sheets 11 and 12 and extend in spaced parallel relation to the male and female elements 18 and 19 of the fastener 17. The stiffener ridges or ribs 25 and 26 are shown in their preferred embodiment on the inside of the bag. They may however also be located on the outside of the bag 10.

With the provision of the stiffener ribs 25 and 26, assume that a lateral force were applied to the bag 10 against the edges 13 and 14. While the bag may become contracted or doubled up in the central or lower portions thereof, that portion of the bag which is adjacent the top end 16 and which includes the fastener 17 and the stiffener ribs 25 and 26 is maintained in a stiff or rigid position, or at least in a broad curved position, so as to reduce or entirely eliminate doubling-up of the upper portion in a serpentine fashion to a degree sufficient to separate the male and female elements 18 and 19.

In the embodiment illustrated in FIG. 2 the stiffener ribs 25 and 26 are substantially rectangularly shaped in transverse cross section, that is, a cross-sectional view through the bag 10 in a direction normal to the sheets 11 and 12. The ribs 25 and 26 are also slightly offset from one another in a direction parallel to the sheets 11 and 12 and, in the closed position of the fastener 17, are arranged in mutually overlapping relation.

In the embodiment illustrated in FIG. 3 the stiffener ribs 25a and 26a are hook-shaped and are arranged in mutually inverted relation to provide an interlocking connection therebetween when they are pressed together in a direction normal to the sheets 11 and 12, which is the same direction in which the force is applied to close the fastener 17.

In the embodiment illustrated in FIG. 4, the ribs 25b and 26b each comprise in transverse cross section a first portion 27 which projects laterally from its corresponding sheet 11 and 12 and a second portion 28 which extends from the distal end of the first portion 27 in a direction parallel to its corresponding sheet. In this embodiment as in the embodiment illustrated in FIG. 3, the ribs 25b and 26b are arranged in mutually inverted relation with portions 28a and 28b overlapping one another to provide an interlocking connection therebetween when they are pressed together in a direction normal to the sheets 11 and 12. Depending on the length of the portions 28a and 28b and as these portions are rigid, it may be necessary to interhook them rather than press them into position.

The present invention also encompasses a method of making the bag 10 and an apparatus useful in the practice of that method.

In the preferred method a circumferentially continuous tubular film of thermoplastic is extruded from a die. Formed in the walls of the die plate which form the annular aperture through which the tubular film is extruded are a plurality of recesses which are shaped to correspond to the male and female elements 18 and 19 and to the stiffener ribs 25 and 26. The continuously extruded tubular film is subsequently cut along its length into plural sections. The longitudinal length of each section corresponds to a predetermined width of a plastic bag, that is, the distance between edges 13 and 14 of the bag 10. The film is first flattened and then cut longitudinally between the male and female elements 18 and 19 so that one half of the slit film overlies the other half in a manner so that sheet 11 is superimposed on sheet 12 as in FIGS. 2--4. The cut edges of each section are then bonded to complete the bags.

Illustrated in FIG. 5 is a die assembly indicated generally at reference numeral 29 which is constructed in accordance with the preferred method of the present invention of forming a tubular film having the male and female elements 18 and 19 and the stiffener ribs 25 and 26 integral therewith. The extrusion die assembly 29 may be more particularly characterized as comprising a die plate 30 in which an annular aperture 31 is formed. Although the die plate 30 is illustrated in FIG. 5 as being two-dimensional it will be understood that it does have a dimension perpendicular to the plane of the drawing and the aperture 31 extends longitudinally into the die plate 30.

The aperture 31 is formed between a pair of circular walls 32 and 33, and formed in the wall 32 are a plurality of recesses indicated at reference characters 18", 19", 25", and 26". These recesses, of course, conform to and correspond with the male and female elements 18 and 19 and the stiffener ribs 25 and 26. All of the recesses are at a specific point in open communication with the aperture 31.

The assembly 29 also comprises a conduit indicated somewhat schematically at reference numeral 34 adapted for connection to a source of thermoplastic for delivering the thermoplastic continuously in the direction of the arrow 35 to the annular aperture 31. The resultant tubular film is extruded form the aperture 31 in a direction perpendicular to the plane of the drawing.

The thermoplastic being delivered through conduit 34 will enter the recesses 18" and 19" opening into the aperture 31 thereby causing the male and female elements 18 and 19 to be extruded integrally with the tubular film and of the same thermoplastic of which the film is made. Another conduit indicated generally schematically at reference numeral 36 is also adapted for connection to a source of thermoplastic for delivery thereof in the direction of the arrow indicated at reference 37. The thermoplastic being delivered by conduit 36, however, is not the same as that which is delivered by conduit 34 and in fact is much more rigid or stiff when cooled to its solid state. Preferably the thermoplastic being delivered through conduit 36 is the most rigid or stiff polyethylene which is capable of being extruded through the recesses 25" and 26".

Passages 38 and 39 interconnect the conduit 36 with the recesses 25" and 26" so that the thermoplastic from conduit 34 will form that portion of the tubular film immediately adjacent ribs 25 and 16 and will join with the more rigid plastic coming from conduits 38 and 39 to form the ribs 25 and 26 in overlying relation on the film.

It will be appreciated that after the tubular film emerges from the extrusion die plate 30 and the temperature thereof has fallen to a sufficient degree, the film has been slit longitudinally between the male and female elements 18 and 19, cut into sections along the length thereof and bonded along the cut edges, it will form a plurality of bags similar to those indicated at reference numeral 10.

Although minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably come within the scope of my contribution to the art.

Claims

I claim:

1. A plastic bag including a pair of superimposed sheet portions the corresponding edges of which are bonded together to form sealed sides and an open side, means forming longitudinally continuous cooperating male and female interlocking elements on said sheets along the open side of the bag to provide a releasable fastener, and a stiffener rib formed on one of said sheets extending along the open side of said bag, said male and female elements being formed of a first thermoplastic material and said stiffener rib being formed of a second thermoplastic material, said second thermoplastic material being substantially more rigid than said first thermoplastic material to provide lateral rigidity to said bag along the open side to reduce the likelihood of inadvertent opening of said releasable fastener.

2. The plastic bag as defined in claim 1, wherein said cooperating male and female elements and said stiffener rib are formed integrally with said plastic sheets.

3. The plastic bag as defined in claim 2, wherein said stiffener rib is disposed in spaced parallel relation with respect to said cooperating male and female elements.

4. The plastic bag as defined in claim 3, and including another stiffener rib formed on the other of said sheet and extending along the open side of said bag in parallel relation to said first mentioned stiffener rib, said ribs being slightly offset from one another in a direction parallel to said sheets and arranged in mutually overlapping relation in the closed position of said fastener.

5. The plastic bag as defined in claim 4, said ribs being substantially rectangularly shaped in transverse cross section.

6. The plastic bag as defined in claim 1, and including another stiffener rib of said second thermoplastic material formed on the other of said sheets and extending along the open side of said bag in parallel relation to said first-mentioned stiffener rib, said ribs being hook-shaped in transverse cross section and arranged in mutually inverted relation to provide an interlocking connection therebetween when joined together.

7. The plastic bag as defined in claim 1, and including another stiffener rib of said second thermoplastic material formed on the other of said sheets and extending along the open side of said bag in parallel relation to said first mentioned rib, said ribs each comprising in transverse cross section a first portion projecting laterally of its corresponding sheet and a second portion extending from the distal end of said first portion in a direction parallel to its corresponding sheet, said ribs being arranged in mutually inverted relation and said second portions overlapping one another to provide an interlocking connection therebetween when joined together.

8. In a bag having sides made of plastic sheet-form material and an elongated plastic releasable fastener joined along corresponding marginal portions of the bag sides to provide a closable opening in the bag, the improvement comprising stiffening means formed adjacent said releasable fastener to impart lateral rigidity to the marginal portions beyond that afforded by the inherent rigidity of the sides of the bag and by the releasable fastener, said stiffening means comprising a rib formed on the marginal portion of one of the bag sides and extending in parallel relation to the releasable fastener and projecting toward the marginal portion of the other of the bag sides, said rib being made of plastic having a stiffness value which is greater than the stiffness value of the plastic of which the bag sides and the releasable fastener are made.