Stand-up plastic bag and method of making same

A stand-up plastic bag has a pair of front and rear side walls defining an open bag mouth at upper edges thereof, and a pair of front and rear bottom gusset walls being disposed between the side walls. The walls are composed of a multi-layered film of different, heat-sealable, coextruded thermoplastics, such as polyethylene and Nylon. Polyethylene is on the interior surfaces and Nylon is on the exterior surfaces of the walls. The gusset walls have upper portions interconnected together to form a bottom wall extending between the front and rear side walls. The gusset walls also have lower portions joined by heat seals to lower portions of the front and rear side walls at contiguous portions of polyethylene material on their interior surfaces to form a support band which connects to and extends below the bottom wall. The front and rear gusset walls also have opposite longitudinal edges joined together by heat seals at contiguous portions of Nylon material on the exterior surfaces thereof which complete formation of the support band as a continuous self-standing structure that defines with the bottom wall a stand-up base on the bag.

BACKGROUND OF THE INVENTION 
The present invention generally relates to plastic bags and, more 
particularly, to a plastic bag capable of standing up by itself before, 
during and after being filled and to a method of making the bag. 
So-called stand-up, free-standing or self-standing plastic bags are 
well-known in the prior art. Representative of the prior art are the 
plastic bags disclosed in U.S. patents to Knuetter U.S. Pat. No. 
2,265,075, Doyen et al U.S. Pat. No. 3,380,646, Kugler U.S. Pat. No. 
3,437,258, Michel U.S. Pat. No. 3,715,074 and Bustin U.S. Pat. No. 
4,353,497. Also, well-known in the prior art are plastic bags 
incorporating a zipper-type closure device along the top opening or mouth 
of the bags. Representative of the prior art are the plastic bags 
disclosed in a U.S. patent to Ausnit U.S. Pat. No. 4,601,694 and a U.K. 
Patent Application No. to Kirkpatrick (2,047,199). Further, U.S. patents 
to Kan U.S. Pat. Nos. 3,980,225 and 4,055,109 disclose a self-standing 
plastic bag which also incorporates a zipper-type closure device along its 
mouth. 
Market research has shown that consumers greatly desire a stand-up, 
reclosable plastic bag because of the convenience of filling and storing 
highly liquid foods and of microwave heating of foods directly in the bag. 
Some known stand-up bags attempt to provide the stand-up capability merely 
by use of a simple bottom gusset alone or supplemented with seals added in 
the gusset structure. A simple bottom gusset sealed at its sides does not 
provide a normal consumer plastic bag with a sufficient stand-up feature. 
Such plastic bag typically made from polyethylene film, for example of 
under 1.0 mil thickness, is too limp to stand up from the gusseted bottom. 
Other plastic films of greater thickness and higher modules can be 
fabricated into a bag that will stand up from a simple bottom gusset. One 
plastic bag currently available uses a very deep bottom gusset design to 
provide certain advantages in food storage and microwave heating, but some 
difficulty has been experienced in filling and emptying this bag. The bag 
does not stand up easily when empty, and the zipper-type closure is 
difficult to maintain open when filling and emptying this bag. Other 
currently-available stand-up bags seal the bottom gusset into a stand-up 
base that is much more stable than the simple bottom gusset. The 
self-standing bag of the above-cited U.S. patents to Kan is an example of 
a bag having such stand-up base. 
It is perceived that additional improvements need to be made before 
consumers will be provided with a stand-up reclosable plastic bag that 
fully meets their needs. These improvements must relate to the provision 
of a bag with a stronger, sturdier and more stable stand-up base, one 
which will faithfully support the bag when empty as well as during and 
after filling, and a bag with a more reliable, leak-proof side seam. Also, 
the improvements must allow a simpler and less costly method of making the 
bag. 
SUMMARY OF THE INVENTION 
The present invention provides a stand-up plastic bag and method of making 
same designed to satisfy the aforementioned needs. 
The stand-up plastic bag of the present invention comprises a pair of front 
and rear side walls which define an open mouth at upper edges of the side 
walls, and a pair of front and rear bottom gusset walls disposed between 
the side walls. The front and rear side walls and the front and rear 
bottom gusset walls are composed of a multi-layered film of first and 
second heat-sealable thermoplastic materials. The first material is on 
interior surfaces of the walls and heat-sealable at a temperature within a 
first temperature range. The second material is on exterior surfaces of 
walls and heat-sealable at a temperature within a second temperature range 
greater than the first temperature range. 
The bottom gusset walls have upper portions that are interconnected 
together to define a bottom wall extending between the front and rear side 
walls. The bottom gusset walls also have lower portions joined by heat 
seals to lower portions of the front and rear side walls at contiguous 
portions of the first material on the interior surfaces thereof to form a 
support band connected to and extending below the periphery of the bottom 
wall. The bottom gusset walls further have opposite longitudinal edges 
joined together by heat seals at contiguous portions of the second 
material on the exterior surfaces thereof which complete formation of the 
support band as a continuous self-standing structure and define with the 
bottom wall a stand-up base on the bag. 
Further, the front and rear side walls and the front and rear bottom gusset 
walls along opposite longitudinal edges of the walls are joined together 
by heat seals at contiguous portions of the first material on interior 
surfaces thereof. Also, an openable and closable closure device is defined 
on the front and rear side walls below and adjacent to the bag mouth 
defined at the upper edges of the side walls. 
The method of the present invention for making the stand-up plastic bag 
comprises the steps of: supplying a multi-layered film of the first and 
second heat-sealable thermoplastic materials; folding the film to form the 
front and rear side walls and the front and rear bottom gusset walls 
disposed between the side walls with interior surfaces of the walls having 
the first material thereon and exterior surfaces of the walls having the 
second material thereon; forming heat seals which join lower portions of 
the front and rear bottom gusset walls with corresponding lower portions 
of the front and rear side walls at contiguous regions of the first 
material on the interior surfaces thereof and thereby form a support band 
being connected to and extending below the periphery of a bottom wall 
formed by connected upper portions of the front and rear bottom gusset 
walls which extend between the front and rear side walls; forming heat 
seals which join the front and rear side walls with the front and rear 
bottom gusset walls along opposite longitudinal edges thereof at 
contiguous portions of the first material on interior surface of the 
longitudinal edges of the walls; forming heat seals which join the front 
and rear bottom gusset walls together along their opposite longitudinal 
edges at contiguous portions of the second material on the exterior 
surfaces thereof and thereby complete formation of the support band as a 
continuous self-standing structure to define with the bottom wall a 
stand-up base on a bag; and separating the film into completed plastic 
bags by severing the film through at each of the heat seals at each of the 
longitudinal edges of the walls. 
Accordingly, it is an object of the present invention to provide a stand-up 
plastic bag that has a stronger, sturdier and more stable stand-up base 
capable of supporting the bag whether empty or full; to provide a stand-up 
plastic bag that has more reliable, leak-proof side seams; and to provide 
a stand-up plastic bag that is simplier and less costly to make because of 
its employment of heat seals between materials on the interior surfaces 
and a heat seal between materials on the exterior surfaces of the 
longitudinal ends of the gusset walls which eliminate the necessity of 
punching holes or cutouts through the gusset walls, as done in prior art 
bags, in order to seal the opposite side walls of the bag together in the 
region of the gusset wall longitudinal ends; and to provide a method of 
making such a stand-up plastic bag. Other objects and advantages of the 
invention will be apparent from the following description, the 
accompanying drawings and the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference is made to FIGS. 1-5 of the drawings which illustrate a stand-up 
plastic bag, generally designated 10 and comprising one embodiment of the 
present invention. In its basic components, the bag 10 includes a pair of 
front and rear side walls 12, 14 and a pair of front and rear bottom 
gusset walls 16, 18 (see FIGS. 2-5). The side walls 12, 14 define an open 
mouth 20 for the bag 10 between upper edges 12A, 14A of the walls 12, 14. 
The front and rear bottom gusset walls 16, 18 are disposed between the 
side walls 12, 14 and each have respective upper and lower portions 22, 24 
and 26, 28. The upper portions 22, 26 of the gusset walls 16, 18 are 
integrally connected and foldable relative to one another about a center 
fold line 30. The upper portions 22, 26 of the gusset walls 16, 18 are 
integrally connected and foldable relative to the respective lower 
portions 24, 28 thereof about front and rear fold lines 32A, 32B. Also, 
the lower portions 24, 28 of the gusset walls 16, 18 at their lower edges 
16A, 18A are integrally connected and folded relative to the lower edges 
12B, 14B of the side walls 12, 14. 
Referring specifically to FIG. 2, there is illustrated a cross-section 
taken through lower portions 34, 36 of the front and rear side walls 12, 
14 corresponding to the lower portions 24, 28 of the front and rear bottom 
gusset walls 16, 18. The composition of the film of which each of the 
walls 12-18 is formed is depicted most clearly in FIG. 2 wherein it is 
illustrated that the film is multi-layered, being composed of two 
different heat-sealable thermoplastic materials 38 and 40 and an adhesive 
or glue material 42 there between bonding the two thermoplastic materials 
together. It is important that the thermoplastic materials selected be 
heat-sealable at different ranges of temperatures. Particularly, the 
material 38 which ultimately will be on the interior surfaces of the walls 
12-18 must be heat-sealable within a temperature range which is lower than 
the temperature range at which the material 40 on the exterior surfaces of 
the walls 12-18 will be heat sealable. Maintenance of this difference in 
heat sealing temperature ranges between the exterior and interior surfaces 
of the walls 12-18 is important in order to avoid heat sealing together 
the facing exterior surfaces 44, 46 of the front and rear bottom gusset 
walls 16, 18, shown in FIG. 2, at the same time that the interior surfaces 
48, 50 of their lower portions 24, 28 which face interior surfaces 52, 54 
of the lower portions 34, 36 of the front and rear side walls 12, 14 are 
heat sealed thereto to form a support band 56 of a stand-up base 58 for 
the bag 10, as will be described in detail below. 
By way of example, the preferred composition of the film is a multi-layer 
coextrusion of Nylon (polyamide)/glue/PE (polyethylene) in thicknesses of 
about 0.1-1.0 mils, 0.1-0.5 mils and 0.5-5.0 mils respectively. Bag 
stability has been found to increase with film modulus (stiffness). The 
heat sealing temperature range of the polyethylene material 38 is from 
about 125.degree. to 190.degree. C. The preferred temperature for heat 
sealing the material 38 on the interior surfaces of the walls 12-18 is 
approximately 130.degree. to 150.degree. C. The heat sealing temperature 
range of the Nylon material 40 is from about 190.degree. to 280.degree. C. 
The preferred temperature range for heat sealing the material 40 on the 
exterior surfaces of the walls 12-18 is approximately 210.degree. to 
250.degree. C. Other materials, thicknesses and heat sealing temperature 
ranges are possible. For example, thermoplastics like polycarbonate, 
polyester, polyvinylidene chloride, poly-4-methyl-1-pentene, polyphenylene 
sulfide and other higher temperature sealing thermoplastics may be 
substituted for the Nylon and other polyolefins, polyvinylchloride, 
ethylene vinyl acetate, polystyrene, polyisoprene, and other lower 
temperature sealing thermoplastics may be substituted for the 
polyethylene. 
The preferred composition of the film is particularly well suited for a 
stand-up bag to hold hot liquids--i.e. it may be used for boiling water 
temperature liquids in either microwave or in boiling water heating. The 
Nylon layer has high modulus and high heat distortion features which add 
to hot liquid stand up stability and boiling water performance. 
The preferred composition of the film is also particularly well suited for 
freezer use. The relatively thick polyethylene layer provides toughness 
and flexibility even at freezer temperatures. 
Referring still to FIG. 2 as well as FIG. 1, it will be seen that the upper 
portions 22, 26 of the front and rear bottom gusset walls 16, 18 are 
interconnected together to define a bottom wall 60 which extends between 
the front and rear side walls 12, 14 and which, because of the other 
feature of the bag of the present invention, will present a relatively 
flat support base when the bag is in use. Thus, the lower portions 24, 28 
of the front and rear bottom gusset walls 16, 18 are joined by heat seals 
62, 64 to lower portions 34, 36 of the front and rear side walls 12, 14 at 
contiguous portions of the thermoplastic material 38 on their respective 
interior surfaces 48-54. By such heat seals 62, 64, the gusset and side 
wall lower portions 24, 28 and 34, 36 cooperate to form the upright 
support band 56 which is connected to and extends below the periphery of 
the bottom wall 60. The configuration of the bottom wall 60 preferably 
either is concave-shaped, as shown in the first embodiment of FIG. 1, or 
has a shape wherein the opposite end portions of the bottom wall are 
oppositely inclined at about forty-five degrees and then interconnected by 
a generally flat or planar intermediate portion, as shown in the second 
(and preferred) embodiment of FIGS. 7-8, discussed in more detail below. 
Also, preferably, several limited regions 65 between the respective 
interior surfaces 48-54 of the gusset and side wall lower portions 24, 28, 
34, 36 as outlined in FIGS. 1, 6B, 7 and 8 are left unsealed to minimize 
the amount of distortion of the material in the band 56 which ordinarily 
results from the heat sealing process. Regions 65 also provide a "cool 
corner" for the user to hold onto when emptying hot contents from the bag. 
As shown in FIGS. 4 and 5, the formation of the band 56 (see FIG. 1) of the 
stand-up base 58 is completed by joining together the opposite right 
longitudinal edges 66, 68 and left longitudinal edges of the front and 
rear bottom gusset walls 16, 18 of FIG. 1 by the formation of respective 
heat seals 70. Only the right longitudinal edges 66, 68 of the gusset 
walls 16, 18 and the right heat seal 70 are shown in detail in FIG. 5. The 
heat seals 70 are formed at contiguous portions of the thermoplastic 
material 40 on the facing exterior surfaces 44, 46 (see FIG. 2) thereof at 
the longitudinal edges 66, 68 adjacent the gussetted portion of the bag 
10. The upright support band 56 now constitutes a continuous self-standing 
structure which along with the bottom wall 60 provides a sturdy and stable 
stand-up base 58 for the bag 10 which renders the bag capable of standing 
up by itself before, during and after being filled. The interaction of 
support band 56 with the film stiffness and other structural features 
permits the bag to stand up when empty or even when filled with boiling 
water. 
Additionally, the opposite right longitudinal edges 72 and left 
longitudinal edges 74 of the front and rear side walls 12, 14 are joined 
with the aforementioned right longitudinal edges 66, 68 and left 
longitudinal edges of the gusset walls 16, 18 by heat seals 76 formed at 
contiguous portions of the thermoplastic material 38 on interior surfaces 
thereof, as shown both in FIGS. 3 and 4. These heat seals 76 provide a 
reliable, leak-proof seal along the opposite longitudinal edges adjacent 
the non-gussetted portion of the bag 10. As seen in FIG. 3, an additional 
end seal 78 can be provided between the thermoplastic material 40 on the 
exterior surfaces of the longitudinal edges 72, 74 of the side walls 12, 
14 if the bags 10 are severed from one another by using a hot wire or hot 
knife severing technique. However, this additional seal is not essential. 
A guillotine knife cut at the center of the bar seal is preferred for the 
sake of process simplicity. 
As seen in FIG. 1, the bag 10 also may preferably include an openable and 
closable closure device 80 of any suitable conventional design although a 
zipper-type closure device is preferred. The device 80 is defined on the 
front and rear side walls 12, 14 just below and adjacent to the bag mouth 
20 defined at the upper edges 12A, 14A, thereof. The components 80A, 80B 
of the closure device 80, as seen schematically in FIG. 6, can be 
integrally formed on the film 82 or laminated thereon. 
In the bag of the first embodiment shown in FIGS. 1-5, a bag with an 
approximate 6 cup capacity (6.2 cups) would have a preferred height of 
approximately 7.0 inches, a preferred width of approximately 9.5 inches, 
and a preferred gusset height of approximately 2.0 inches. For a smaller 
bag, such as one having a 3.4 cup capacity, it would preferrably have a 
height of 5.5 inches a width of 8.0 inches, and a gusset height of 2.0 
inches. 
Turning now to FIGS. 6 and 6A-6C, the steps involved in the method of the 
present invention for making the stand-up reclosable plastic bag 10 are 
shown in block form and the states of a bag at the various stages in its 
formation are illustrated. The process may be a continuous, a 
semi-continous or a multi-step batch process. The components used in the 
method are individually well-known in the art and to illustrate them in 
detail herein would not make it easier to understand the method of the 
present invention. The components used in the method herein are generally 
the same as components schematically illustrated in the afore-cited U.S. 
patents to Doyen et al and Kan. The differences reside not in the 
components per se but the steps they are employed to carry out in the 
method of the present invention. 
Block 84 represents the supplying of a web of the multi-layered film 82 
from a roll thereof. Alternatively a web of multi-layered film 82 may be 
supplied directly, as fabricated, from an extrusion and/or laminating 
line. As described above, the film 82 has the two different thermoplastic 
materials 38, 40 (FIG. 2), for instance polyethylene and Nylon, which are 
heat-sealable upon applying of heat at temperatures within different 
ranges, as described previously. 
Block 86 represents performance of the steps of folding the film 82 to form 
the front and rear side walls 12, 14 and to form the front and rear bottom 
gusset walls 16, 18 (FIGS. 1 and 2) being disposed and folded inwardly 
between the side walls so that the Nylon and polyethylene materials are 
respective on the interior and exterior surfaces of the side and gusset 
walls, as was described previously. Also, block 86 represents the locking 
or closing of the components 80A, 80B of the closure device 80. The state 
or condition of a partially completed bag after leaving block 86 would 
resemble that depicted in FIG. 6A. All heat sealing steps can be 
interchanged, reversed in order or combined into a single sealing step 
containing differential temperature zones. 
Next, block 88 represents the applying of heat, by use of shoe or bar-like 
members, to the lower portions 24, 28 of the gusset walls and lower 
portions 34, 36 of the side walls 12, 14 (FIG. 2). The application of heat 
within the lower one of the two aforementioned temperature ranges causes 
joining of the lower portions at their interior surfaces, but not at their 
exterior surfaces, by forming the above-described heat seals 62, 64 in 
FIG. 2 and as represented by the dotted regions in FIG. 6B. That figure 
shows the condition of the partially completed bag after leaving block 88. 
Partial formation of the support band 56 has now taken place. 
The next successive blocks 90 and 92 can be arranged as shown or reversed. 
Block 90 represents forming heat seals 76 (FIG. 4 and 5) as depicted by 
the dotted regions in FIG. 6C, to join the front and rear side walls 12, 
14 with the front and rear bottom gusset walls 16, 18 along the opposite 
longitudinal edges thereof at contiguous portions of the polyethylene 
material 38 on their interior surfaces. Heat seals 76 are formed by 
applying heat t the lower temperature range as before using conventional 
sealing bars. 
Block 92 represents forming heat seals 70 (FIG. 5) to join the front and 
rear bottom gusset walls together along their opposite longitudinal edges 
at contiguous portions of the Nylon material 40 on the exterior surfaces 
thereof and thereby complete formation of the upright support band 56, as 
described above. To form the heat seals 70, heat is now applied to the 
gusset wall edges at a temperature within the higher temperature range 
using conventional sealing bars. 
Block 92 can also represent a combined or separate step of separating the 
film 82 through into completed plastic bags by severing the film through 
at each of the heat seals at each of the longitudinal edges of the walls. 
If the sealing and severing are combined, then a conventional hot wire or 
hot knife is used. However, if they are performed successively, then a tab 
sealing bar is used to seal the gusset edges followed by an unheated 
conventional severing knife. 
Referring now to FIGS. 7-8, there is shown a second and preferred 
embodiment of bag 10. The preferred stand-up, reclosable bag shown in 
FIGS. 7-8 is made by the same procedure shown in FIG. 6 and utilizes the 
same materials and structural elements described with reference to FIGS. 
1-5 and, therefore like reference numerals have been used. 
However, unlike the bag illustrated in the first embodiment of FIGS. 1-5 
wherein a concave-shaped bottom wall 60 is used, the bag of FIGS. 7-8 has 
a bottom wall with end portions oppositely inclined at about forty-five 
degrees. This is best seen in FIG. 8 where center fold line 30 is 
horizontal in the middle portion thereof, but has an approximate 
45.degree. incline at the ends 30A and 30B, thereof. 
That approximate 45 degree incline is essentially the same as straight 45 
degree heat seal of support band 56 at the opposite ends 56A and 56B 
thereof, as best seen in FIG. 7. The use of approximate 45.degree. angles 
at ends 30A and 30B of center fold line 30 and at ends 56A and 56B of 
support band 56 results in flat bottom with an essentially rectangular 
base. That design has been found to be the most stable. In particular it 
optimizes hot liquid stability with the bag either open or closed. This is 
because the bag design of FIGS. 7-8 has a lower center of gravity which is 
especially important with hot liquids. A hot liquid softens the bag film 
and the softened bag tends to "sag" more than an unheated bag. The lower 
center of gravity better accommodates the "sag" and prevents the bag from 
tipping over under those conditions. 
In the preferred bag design, of the second embodiment shown in FIGS. 7-8 a 
bag with an approximate 6 cup capacity (6.1 cups) would have a preferred 
height of approximately 6.0 inches, a preferred width of approximately 
10.0 inches and a preferred gusset height of approximately 2.0 inches. For 
a smaller bag, such as having an approximate 2 cup capacity, a smaller 
gusset height of approximately 1.5 inches may be used; although, a 2.0 
inch gusset length is still preferred for process simplicity. For example, 
a bag with a 2.9 cup capacity having 5 inch height, an 8 inch width, and a 
gussett height of 2.0 inches was found to be particularly stable. 
Having thus described the stand-up plastic bag and method of making same of 
the present invention in detail and by reference to a preferred embodiment 
thereof, it will be apparent that certain modifications and variations are 
possible without departing from the scope of the invention defined in the 
appended claims.