DOUBLE-BOTTOM SIDE-WELDED BAG

The present invention relates generally to flexible bags designed to hold food products such as bread.

It is known to construct a plastic bag by folding a continuous sheet of a flexible material, such as thermoplastic, over on itself, then making an in-fold at the folded edge, to form a gusset, and then simultaneously cutting and heat sealing the folded sheet along spaced apart transverse lines that are perpendicular to the fold. Each individual bag formed in this manner has an “W” shaped cross section at the gusset. This type of bag is commonly referred to as a “bread bag” and is often used for packaging loaves of bread. The bread loaf is inserted into the bag through an open end that is opposite the gusset. The open end is then tied shut in an appropriate manner to often present what is called the “pony-tail” end of the bag.

When fresh warm bread and similar bakery products are packaged in plastic bags, the moisture from the bread is retained and often condenses on the inside of the package. This is a particular problem when bread is stored in bags formed from polyethylene where the bread contacts the bottom gusset of the bag. Typically, the bottom gusset faces the consumer and contains the product identifying information and the supplier's trade-marks and logos. Product information and logos are often printed directly on the bag or affixed using a label at this location. Because bread bags are usually transparent or translucent, any moisture that condenses on the inside of the polyethylene bottom gusset causes the package to have an unsightly appearance and decreases the visual quality of the food.

There is therefore a need for improved flexible bags which solves the above problems and can be efficiently manufactured.

The present invention is directed to a double-bottom bag comprising an outer web and an inner web having an open mouth and an opposing bottom, where the outer web has a first side edge, an opposing second side and is folded upon itself thereby defining a front panel having a length and a back panel having a length. The outer web further includes an inward-facing cross-sectional gusset opposite the open mouth of the bag and centered along the width of the bag which joins the front panel to the back panel and forms an outer bottom portion of the bag. The inner web has a first side edge, an opposing second side and is folded upon itself thereby defining a front panel having a length which is less than the length of the front panel of the outer web and a back panel having length which is less than the length of the back panel of the outer web. The inner web further includes an inward-facing cross-sectional gusset opposite the open mouth of the bag and centered along the width of the bag which joins the front panel to the back panel and forms an inner bottom portion of the bag. The bag further comprises a first side-seam affixing the first side edge of both the inner and outer webs together and affixing the front and back panels of the outer web together along the first side edge. The bag still further includes an opposing second side-seam affixing the opposing second side edge of both the inner and outer webs together and affixing the front and back panels of the outer web together along the second side edge. The bag of the present invention is designed such that the inward-facing cross-sectional gussets of both the inner and outer webs expand to form a square cross-sectional portion upon receiving a material to be packaged. One advantage of the present invention provides is a separate surface of an inner web where moisture from the bread or other bakery products may condense without affecting the appearance of product identifying information printed on an outer web of the bag. The present invention also provides the convenience of a square or rectangular bottom gusset cross sectional area where product information can be printed and viewed by the consumer.

In accordance with the practice of the present invention, a representative double-bottom bag as described herein is shown in FIGS. 1-3. Bag 10 of the present invention comprises an open mouth 11 and an opposing bottom 12. As shown in the exploded view of bag 10 of FIGS. 2 and 3, bag 10 further includes an outer web 20 (represented as a solid line) having a first side edge 21 and an opposing second side edge, 22, a front panel 23 and a back panel 25. Bag 10 also includes an inner web 30 (represented as a dotted line) having a first side edge 31 and an opposing second side edge, 32, a front panel 33 and a back panel 35. Outer and inner webs each include an inward-facing cross-sectional gusset, 27 and 37, respectively, opposite the open mouth 11 and centered along the width of the bag. As depicted in FIGS. 2 and 3, gussets 27 and 27 join the front panels, 23 and 33 to the back panels, 25 and 35, respectively. Inward-facing cross-sectional gusset 27 of outer web 20 forms an outer bottom portion 28 of bag 10 while inward-facing cross-sectional gusset 37 of inner web 30 forms an inner bottom portion 38 of bag 10. Referring back to FIG. 1, bag 10 further comprises a first side-seam 41 affixing first side edges 21 and 31 together, and affixing the front and back panels, 23 and 25 of the outer web 20 together along the first side edge 31. Bag 10 also includes opposing second side-seam 42 affixing second side edges 22 and 32 together, and affixing the front and back panels, 23 and 25 of the outer web 20 together along the opposing second side edge 32. First and second side-seams, 41 and 42, will generally extend the entire length of front and back panels 23 and 25 of the outer web 20. Side-seams 41 and 42 may be formed by application of an adhesive which may include, but not limited to cold-seal adhesives, pressure sensitive adhesive and the like, or by heat sealing. Preferably, side seams 41 and 42 are each heat seals formed by application of heat and pressure to outer and inner webs 20 and 30. The inward facing cross-sectional gussets 27 and 37 are each adapted to expand to form a square or rectangular cross-sectional bag bottom upon receiving a material to be packaged. Such a material may include, but is not limited to bakery products, such as bread loaves, hot dog and hamburger buns and the like. Non-food products may also be packed in the bags of the present invention.

In accordance with the present invention, the front panel 33 of inner web 30 has a length which is less than the length of the front panel 23 of outer web 20. Front panel 33 may have a length which is about 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10% or 5% of the length of front panel 23 of outer web 20. Preferably, as illustrated in FIGS. 2 and 3, front panel 33 of inner web 30 has a length which is less than 50%, more preferably, less than 25% and most preferably, about 15%, 10% or 5% of the length of front panel 23 of outer web 20. Similarly, the back panel 35 of inner web 30 has a length which is less than the length of the back panel 25 of outer web 20. Back panel 35 may have a length which is about 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10% or 5% of the length of front panel 25 of outer web 20. Preferably, as illustrated in FIGS. 2 and 3, back panel 35 of inner web 30 has a length which is less than 50%, more preferably, less than 25% and most preferably, about 15%, 10% or 5% of the length of back panel 25 of outer web 20. It is also contemplated that a substantial portion of each front panels 23 and 33 face each other and are unlaminated together, and a substantial portion of each back panels 25 and 35 face each other and are unlaminated together.

Optionally, the back panel 25 of outer web 20 may have a length which is greater than the length of the front panel 23 of outer web 20. Back panel 25 may have a length which is 5%, 10%, 15%, 20% greater than the length of front panel 23 of outer web 20. As illustrated in FIGS. 2 and 3, by extending the length of the back panel 25 of outer web 20 a lip is formed which provides an area for one or more apertures, perforations or holes, 43 located near the open mouth 11. Bags constructed with one or more apertures aids in handling and packaging of products in such a way that multiple bags can be placed on a wire “wicket” for ease of dispensing. Typically, there may be up to 250 bags mounted on a wicket pack. With this construction style, the bags can be mounted on a blower that will blow each individual bag open to allow products to be slid in easily. The bag can then be torn from the wicket and the next bag will blow open, ready for another packaging operation.

Any suitable packaging material may be used to formed outer and inner webs 20 and 30. Preferably, outer web 20 is formed from a heat-fusible material. In one embodiment, it is desirable to form outer web 20 from a flexible thermoplastic film which is heat-fusible. In another embodiment, it is desirable to from outer 20 from a flexible thermoplastic film which is heat-fusible and substantially transparent. Preferably, outer web 20 is fabricated from a polyolefin thermoplastic material, which may include, but not limited to polyethylene homopolymer and copolymers, polyethylene blends, polypropylene homopolymer and copolymers, and blends of polyethylene and other thermoplastic materials.

Preferably, outer web 20 comprises a blend of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE), a blend of 10% by weight of low density polyethylene (LDPE) and 90% by weight of linear low density polyethylene (LLDPE), a blend of 40% by weight of low density polyethylene (LDPE) and 60% by weight of linear low density polyethylene (LLDPE), or a blend of 60% by weight of low density polyethylene (LDPE) and 40% by weight of linear low density polyethylene (LLDPE). Outer web 20 may comprise a monolayer or multilayer structure. Referring now the FIG. 5, outer web 20 may comprise a three ply structure 200 having an interior layer 202 sandwiched between two exterior layers 201 and 203. In a preferred embodiment, layers 201, 202 and 203 each comprise polyethylene. In another preferred embodiment, interior layer 202 comprises a blend of about 50% by weight polyethylene and about 50% by weight polypropylene copolymer, and exterior layers 201 and 203 each comprise polyethylene. It is also desirable that outer web 20 has a thickness of between 18 and 50 microns (0.71-2.0 mil).

Inner web 30 may be formed from the same material as outer web 20 or a different material. Preferably, inner web 30 is formed from a heat-fusible material. In one embodiment, it is desirable to from inner web 30 from a flexible thermoplastic film which is heat-fusible. In another embodiment, it is desirable to form inner 30 from a flexible thermoplastic film which is heat-fusible and substantially transparent. It may also be desirable to emboss at least one surface of inner web 30. Embossing reduces the total surface area of inner web 30 that comes into contact with the moistened surface of a bread product. In another embodiment, inner web 30 is embossed and formed from a flexible thermoplastic film which is substantially opaque. Preferably, inner web 30 is fabricated from a polyolefin thermoplastic material, which may include, but not limited to polyethylene homopolymer and copolymers, polyethylene blends, polypropylene homopolymer and copolymers, and blends of polyethylene and other thermoplastic materials. Inner web 30 may comprise a monolayer or multilayer structure. Referring now the FIG. 6, outer web 20 may comprise a three ply structure 300 having an interior layer 302 sandwiched between two exterior layers 301 and 303. In a preferred embodiment, layers 301, 302 and 303 each comprise polyethylene. It is also desirable that inner web 30 has a thickness of between 9 and 50 microns (0.35 and 2.0 mil), preferably, between 20 and 30 microns (0.8-1.2 mil).

The above description and the following examples illustrate certain embodiments of the present invention and are not to be interpreted as limiting. Selection of particular embodiments, combinations thereof, modifications, and adaptations of the various embodiments, conditions and parameters normally encountered in the art will be apparent to those skilled in the art and are deemed to be within the spirit and scope of the present invention.

In all the following examples, the outer web 20 structures were produced using a blown film coextrusion apparatus and methods which are well known to those skilled in the art. The inner web 30 structures were produced using cast coextrusion film apparatus and methods which are well known to those skilled in the art. Inner web 30 was embossed by pressing and simultaneously cooling a melt-plastified film against an engraving cylinder.

Example 1 is one embodiment of an outer web 20 as illustrated in FIG. 3, and one embodiment of an inner web 30 as illustrated in FIG. 4 each having a structure and layer compositions as described below:

Layer 201 is a blend of 43% by weight of low density polyethylene (LDPE) having density of 0.922 g/cm³, 54% by weight of linear low density polyethylene (LLDPE) having density of 0.918 g/cm³, and about 3% by weight of processing additives. Exemplary of a commercially available LDPE is ExxonMobil™ LDPE LD 123.LN supplied by Exxon Mobil Chemical Company (Houston, Tex., USA). Exemplary of a commercially available LLDPE is ExxonMobil™ LLDPE LL 1002YB supplied by Exxon Mobil Chemical Company (Houston, Tex., USA).

Layer 202 is a blend of 60% by weight of linear low density polyethylene (LLDPE) having density of 0.919 g/cm³, 10% by weight of polyethylene regrind, 27.5% by weight of low density polyethylene (LDPE) having density of 0.922 g/cm³, and about 2.5% by weight processing additives. Exemplary of a commercially available LLDPE is DOWLEX™ TG 2085B supplied by Dow Chemical Company (Midland, Mich., USA).

Layer 203 has the same composition as Layer 201.

Layer 301 is a blend of 29.5% by weight of linear low density polyethylene (LLDPE) having a density of 0.941 g/cm³, 25% by weight of high density polyethylene (HDPE) having a density of 0.96 g/cm³, 23% by weight of low density polyethylene (LDPE) having density of 0.918 g/cm³. 21% by weight of linear low density polyethylene (LLDPE) having a density of 0.918 g/cm³, and about 1.5% by weight processing additives. Exemplary of a commercially available LLDPE having a density of 0.941 g/cm³is ExxonMobil™ LLDPE LL 3404.48 supplied by Exxon Mobil Chemical Company (Houston, Tex., USA).

Layer 302 is a blend of 25% by weight of high density polyethylene (HDPE) having a density of 0.96 g/cm³, 22% by weight of linear low density polyethylene (LLDPE) having a density of 0.918 g/cm³, 18% by weight of linear low density polyethylene (LLDPE) having a density of 0.941 g/cm³, 18% by weight of low density polyethylene (LDPE) having density of 0.918 g/cm³, 12% by weight of a white pigmented low density polyethylene masterbatch, 2% by weight of polyethylene regrind, and about 2% by weight processing additives. Exemplary of a commercially available white pigment masterbatch is POLYBATCH® 8000 AP supplied by A. Schulman, Inc. (Akron, Ohio, USA).

Layer 303 has the same composition as Layer 301.

Webs 20 and 30 of Example 1 were then evaluated for their physical and optical properties. The results are shown in TABLES 1 and 2 as follows:

To produce a bag as illustrated in FIGS. 1-3, an outer web is unwound from a feed roll and then passed through a high speed in-register printing press to produce a printed outer web. An inner web that has been embossed and slit into narrow strips is unwound from a feed roll and is overlaid and centered onto the printed outer web. The two webs are folded upon themselves using a triangular fold initiator so as to create a front and back panel in each web. The outer web is folded in a manner so that the one panel is longer than the opposing other panel. The longer panel serves as a lip of the bag. Upon leaving the folding means, the folded edge of each web are engaged with a tucking element composed of three shaping disks, two disks which contact the inside surface of the inner web and one disk which contacts the outside surface of the outer web, which forms a longitudinally extending inward-facing tuck or a “W” shaped gusset in the folded edge of each web. The folded and gusseted webs are then drawn between a pair of opposed draw rolls and at least one hole is punched into the lip of the bag along with a corresponding tear notch, located near the open mouth of the bag. The lateral edges of the outer and inner webs are then sealed together by application of heat and pressure to form the side-seams. Each bag is then individualized by cutting along the length of the side-seam between the bag and the leading edge of the succeeding bag. Completed bags are collected in piles or placed on wickets for filling.