WO2009018659A1

WO2009018659A1 - Bag having structurally variant sides

Info

Publication number: WO2009018659A1
Application number: PCT/CA2008/001422
Authority: WO
Inventors: Anthony Chow; Nicholas Farkas; Larin Godfroy
Original assignee: Liqui-Box Canada Inc.
Priority date: 2007-08-03
Filing date: 2008-08-01
Publication date: 2009-02-12

Abstract

A bag for receipt of flowable material therein. The bag has a pair of flexible walls joined continuously along edges thereof to form a seal between the walls, and at least one of the walls including an opening for passage of the material into the bag, wherein each wall has a structure different from the structure of the other wall.

Description

BAG HAVING STRUCTURALLY VARIANT SIDES

Field of the Invention

This invention relates to a bag for flowable material, the bag being made up of flexible sheets joined to form the flexible bag container for receipt of the material therein.

Background of the Invention

Bags for flowable material are often manufactured of flexible web material. Bags related to this invention are manufactured by joining two halves together along their edges, as opposed to pouches that are typically made from one piece of film that is folded over on itself. Relevant here are bags having two walls in which the walls are formed separate from each other and joined in the manufacturing process to form the bag. Whether the bag is a small bag (e.g. 1-15 gallons) or a bulk bag (typically 25-400 gallons), the two walls of the bag are structurally the same. This being said, where the web material is composed of layers and/or plies which result in a lack of symmetry from face-to-face, e.g., a multi-layer film having layers A/B/A/C, then the web material(s) of each wall is oriented to have the opposite orientation of the other. This results in the outer surface of both walls being composed of the same layer (e.g., layer A of the A/B/A/C film) and the inner layer of both walls of the bag being the same (e.g., layer C of the A/B/A/C film). One can see then, that a bag is usually made to be symmetrical in cross-section, e.g. one wall of the bag is the mirror-image of the other side. The only difference from one side of the bag to the other is that one wall of the bag may have one or more fitments for filling or dispensing the flowable material contained in the bag. Methods for making bags have been known for a considerable length of time and are known to the skilled person.

By a flowable material is meant a material which is flowable under force of gravity or which may be pumped. Normally such a material is not gaseous. Food products or ingredients in liquid, powder, paste, oils, granular or the like forms are examples of flowable materials.

Materials used in manufacturing and medicine are also considered such materials. Liquids are considered to be materials that benefit especially from packaging in accordance with the present invention. In the context of this invention, "ply" refers to an independent film structure forming the wall of a bag. "Layer" refers to a single stratum of e.g., a multi-layer film where the adjacent strata are secured to each other across their adjoining faces. Layers are sometimes in direct contact with each, or may be secured to each other by an intervening adhesive. Adjacent plies, on the other hand, are generally secured to each other at discrete locations, usually along their edges and the fitment area but are otherwise separate from each other.

Particular aspects of this invention relate to "pillow" bags where the seam that joins the upper wall of the bag to the lower wall is parallel to the ground in relation to the way that the filled bag is positioned inside a shipping container. A pillow bag is a bag that looks like a pillow case when filled or blown up with air.

Monolayer films are often used for making bags which require a moisture barrier but not a high oxygen barrier. The inner plies of multi-ply bags, which are added to improve shipping and handling performance, are often monofilms. Multi-layer films are used to make bags in which a more sophisticated combination of properties is needed, for example, high barrier to oxygen. The outer ply of a multi-ply bag is often a multi- layer film. The middle or inner ply may also be a multi-layer film, and is often of different in composition than the outer ply.

Disclosure of the Invention

In one broad aspect, the invention is a bag for receipt of flowable material therein. The bag includes first and second flexible walls joined continuously along edges thereof to form a seal between the walls. At least one of the first and second walls has an opening for passage of the material into the bag. The first wall has a structure different from the structure of the second wall.

In the context of this invention, a wall has a structure different from that of another wall if the walls differ from each other in composition, or number of layers or plies, or thickness of layers or plies.

One aspect of the invention includes a bag in which the materials used in the walls are the same in both walls, but one or more of the materials in one wall is of increased thickness in comparison to the other wall. The difference may exist between one or more layers of a multilayer ply, or between a monolayer. Typical increases in thickness would be in the range of 10% to 300%, more typically in the range of 15% to 250%, and most typically in the range of 20% to 200%.

In another aspect, the invention includes a bag in which one or more materials used in one wall is different from that of the other wall. A particular example includes a wall having a different barrier laminate/ply functioning as an oxygen barrier. One wall contains a metallized polyester core, while the other wall contains a biax nylon/EVOH structure. The latter is more robust during shipping and distribution and better retains its oxygen barrier properties over time. In another example, the skins of the barrier laminate/ply, or the inner plies of one wall of the bag are made of more puncture-resistant, thermally resistant or flex- crack resistant materials than the corresponding element(s) of the other wall of the bag. In another example, one wall of the bag contains a barrier laminate (or ply) having at least one more layer than the barrier laminate (or ply) of the other wall of the bag.

"Flex cracking" can be caused by movement of liquid within the bag, and is most prone to occur at locations where a film is in close proximity to the upper surface of the liquid. Flex cracking can occur during shipping and handling of large bulk bags down to the smallest fluid-containing pouches and bags. Flex crack pinholes result in at least, loss of oxygen and moisture barrier, reducing the shelf life potential of the packaged product, and in more extreme cases, loss of the hermetic seal, rendering the product unsafe for consumption. Flex crack resistance is measured by Gelbo flex testing according to ASTM F392. Generally, a film with good flex crack resistance will develop no or very few pinholes when flexed for a large number of cycles with the Gelbo flex tester.

The Gelbo flex testing does not measure an abrasion component relating to flex failure. Physical holes completely through the structure are the only failures measured by the colored turpentine portion of this test, described further below.

The Gelbo flex tester is set up to test in accordance with ASTM F392. This apparatus consists essentially of a 3.5" (90 mm) diameter stationary mandrel and a 3.5" movable mandrel spaced a distance of 7" (180 mm) apart from face-to-face at the start position (that is, maximum distance) of the stroke. The sides of the film sample are taped around the circular mandrels so that it forms a hollow cylinder between them. The motion of the moving mandrel is controlled by a grooved shaft to which it is attached. The shaft is designed to give a twisting motion of 440 degrees and, at the same time, move toward the fixed mandrel to crush the film so that the facing mandrels end up 1" apart at minimum distance. The motion of the machine is reciprocal with a full cycle consisting of the forward and return stroke. The machine operates at 45 cycles per minute.

By means of this tester, specimens of flexible materials are typically flexed at standard atmospheric conditions (23°C and 50% relative humidity). The number of flexing cycles can be varied depending on the flex crack resistance of the film structure being tested. A pinhole resistant film will develop very few pinholes (less than 5) when flexed for a large number of cycles (at least 10,000).

The flexing action produced by the Gelbo flex tester consists of a twisting motion, thus, repeatedly twisting and crushing the film. Flex crack failure is determined by measuring pinholes formed in the film. These pinholes are determined by painting one side of the tested film sample (300 cm² in area) with colored turpentine and allowing it to stain through the holes onto a white backing paper or blotter. Pinhole formation is the standard criterion presented for measuring failure, but other tests such as gas-transmission rates can be used in place of, or in addition to, the pinhole test.

Thermal resistance of films is an important factor in aseptic packaging, in particular for aseptic steam sterilization filling processes for bags. Bags made from films with low thermal resistance tend to exhibit wrinkling or so called "crocodile skin" on the exterior of the bag after steam sterilization, resulting in poor aesthetics and bag properties. This wrinkling can often be accompanied by the inner and outer plies of a multi-ply bag sticking together, or even a bag or pouch made from a monolayer film sticking to itself. In a typical steam sterilization process for aseptic filling of liquid foods, the bag is first placed into a drum or bin and the fitment is then secured onto the fill head of the filling machine. Before the fitment on the bag is opened, the fitment (or spout) assembly is subjected to a steam flush ranging from 3 to 60 seconds. The fitment is then opened, and the product is pumped into the bag. At this stage, steam can enter the bag. Residual steam in the fill head keeps the temperature at about saturated steam conditions. Once the bag has been filled with product, a steam flush is employed before, or while the fitment is being closed. This post-fill steam flush can typically last from 2 to 8-1/2 seconds. During this step, steam often enters the bag. The higher the steam temperature used in these filling operations, the greater the chance of wrinkling of the bag and hence the need for a more thermally resistant film for the bag.

There are other situations in which robust thermal resistance is needed of a film, such as hot- fill applications, hi this type of operation, the product is hot as it is pumped into the bag, typically from 77 to 96°C. The heat from the product serves to sterilize the inside of the bag and fitment. The bag, once filled, slides down along an inclined chute and is flipped so that the fitment is facing down (with hot product above it). The bag then passes through a long heating tunnel for several minutes which is maintained at roughly the same temperature as the product fill temperature to keep the contents hot and to kill mold and bacteria. The bag subsequently enters and passes through a long cooling tunnel to cool down to almost room temperature. Films used in such bags require thermal resistance adequate for the films and seals to maintain their integrity while in contact with the hot product.

Thermal resistance of films is assessed in a number of ways. Generally, Hot Tack Initiation Temperature and Hot Tack Strength are the primary indicators of a film's thermal resistance. Hot Tack is the strength of the molten seal immediately after sealing before it has cooled down to ambient temperature and achieved its final strength. Hot Tack Initiation Temperature is the minimum temperature at which 2N/inch of Hot Tack Strength is achieved in the Hot Tack Test using e.g., a JB Instrument Hot Tack Tester. The Hot Tack Initiation Temperature, sometimes referred to as Seal Initiation Temperature, is the minimum temperature required to form a molten seal of significant strength. It generally cools to form a low strength seal that can be peeled apart without stretching or distorting the film. This property allows the prediction of molten seal strength and resistance to thermal deformation (wrinkling) and/or sticking.

The invention includes a bag in which walls have different numbers of plies. In one example, one wall of the bag contains at least one more ply than the other wall, e.g., one wall contains one ply, the other wall two plies, or one wall contains two plies, the other three plies, etc., as may be needed to provide suitable resistance to puncture, abrasion, thermal resistance, etc. according to the intended use of the bag. Of course these various aspects can be combined in various ways, i.e., one wall can have layers and/or plies of different thickness, layers and/or plies of different composition, and a different number of layers and/or plies relative to the other wall.

In a specific embodiment, the invention includes a pillow bag having upper and lower walls which structurally differ from each other.

It has now been found according to the present invention that it is possible to tailor the structure of the different walls of the bag to meet the needs of the bag in use. The requirements of the walls, most often where one wall is an upper wall and the other is a lower wall are different. A bag of the present invention thus has the advantage of having walls in which each wall has a structure which meets the needs of that wall as it is situated in the environment in which the bag is intended to be exposed, be this sterilization, a filling procedure, shipping, storage, etc.

There are situations where one side of a bag is exposed to greater stresses than the other side. For example, when a bulk bag, typically 55 gallons or more, is filled inside a circular drum (for 55 gallons) or rectangular bin (for typically greater than 200 gallons), the top wall of the bag can be subjected to one or more of the following elements to which the bottom wall of the bag is not subjected, or is at least subject to such elements to a lesser degree. (A) increased levels of heat can enter the bag (during aseptic filling when the filler uses steam to keep the fill chamber sterile) which can cause sticking and wrinkling of the bag. (B) Increased flexing of the bag at the liquid/air interface inside the bag can occur, typically around the top shoulder areas of the filled bag, during shipping and distribution. This can lead to increased flex-cracking and pinhole formation, which in turn could lead to loss of asepticity, leaking, or reduction in oxygen barrier. There may be (C) different transparency requirements, e.g. end-user desires to mask contents of bag visible from the top of a bin in which the bag is located, or alternatively highlight contents of package— leading to different levels of opacity/transparency. There can be (D) a greater level of abrasion, tear and puncture because of the lid that is used to close the container (in which the filled bag is stored) is rough or has sharp edges. This is somewhat counter-intuitive, since it is often taken that the bottom half of the bag— which sees most of the weight— would be the more critical area.

For smaller bag-in-box applications, some of the above effects can also be seen, particularly (B) and (D).

There are situations where the bottom part, as opposed to the top part of a bag contains higher-performing materials, e.g. if the floor of the container that holds the bag is rough or contains splinters that require a tougher, more puncture-resistant material.

The walls of a bag are usually joined to each other by one or more heat seals.

Where the bag is a pillow bag for receipt within a rigid container, and one wall of the pair of walls is an upper wall when received in the container, and the other wall is a lower wall, the opening is typically in the upper wall. An opening is often fitted with a fitment. Such a bag often has a volume of between about 0.5 and about 15 gallons.

One bag of the invention is for receipt of material in the presence of steam and the wall having the opening is more thermally resistant than the other wall.

If the bag is for use in a rigid container during filling and shipping, then the upper wall preferably has greater flex-crack resistance than the lower wall.

The wall having the opening can have greater puncture or abrasion resistance than the other wall.

In certain bags, the layered composition of the walls is the same for both walls and one wall has at least one layer or ply greater in thickness than the corresponding layer in the other wall.

In other bags, the layered composition of a first of the walls is different from the layered composition of the other of the walls. In a particular embodiment, the first wall contains a layer different in composition from any layer in the other wall. Optionally, the first and second walls have the same number of plies and at least one ply of the first wall differs in composition or thickness from the corresponding ply of the second wall. The first wall can contain at least one more ply than the second wall.

Bags of the invention can have a volume of between 0.5 and 25 gallons.

Bags of the invention can be use to package liquid foods such as tomato paste, diced tomato, fruit juice and concentrates, fruit purees, dairy products, wine or other alcohol, soft drink concentrates, water, donut glaze, donut icing, and the like.

According to a particular embodiment, the invention is a bag for use in a rigid container during filling and shipping in which its wall contains a flex-crack resistant ply or layer that has greater pinhole resistance than a corresponding ply or layer in the lower wall, as measured by the Gelbo Flex Test. Preferably, the ply or layer of the upper wall has less than 5 pinholes per 300 cm² as measured by the Gelbo Flex test after 10,000 cycles at room temperature, and said ply or layer of the lower wall has greater than 5 pinholes per 300 cm² as measured by the Gelbo Flex test after 10,000 cycles at room temperature.

In another embodiment, the invention is a bag in which each of the upper and lower walls includes a laminate having a met-PET core layer wherein the laminate of the upper wall differs in structure from that of the lower wall. The core layer of the upper wall can have a higher barrier resistance than that of the core layer of the lower wall. Alternatively, or additionally, the core layer of the upper wall can have a better flex-crack resistance than that of the core layer of the lower wall. Alternatively, or additionally, the core layer of the upper wall has a higher thermal resistance than that of the core layer of the lower wall. Preferably, the core layer of the upper wall has a higher resistance to metal etching than that of the core layer of the lower wall and/or is at least 10% thicker than the core layer of the lower wall.

In one embodiment, a bag of the invention is for use with a food product having a viscosity of from 1 to 500,000 centipoise measured at 20°C. A particular bag is for use with a flowable material having a viscosity of from 1 to 10,000 centipoise measured at 20⁰C, and the upper wall of the bag has greater flex-crack resistance than the lower wall.

Bags of the invention can be for use to package non-food liquid products such as cleaners, disinfectants, waxes, paints, pesticides and the like. A bag can also be for use to package a liquid. The invention includes a method of manufacturing a bag having two flexible walls, for receipt of flowable material therein. The method includes the following steps: providing first and second webs of flexible materials, wherein the material of each web is structurally different from that of the other; - installing a spout on one of the webs and forming a seal between said web and spout; sealing the webs to each other to form first and second sealed edges of the bag, parallel to each other in a first direction; and sealing the webs to each other to form third and fourth sealed edges of the bag, parallel to each other in a second direction, and to form a complete seal between the two webs and thereby form the walls of the bag in sealed engagement to each other.

Usually, the method is an in-line method in which the webs are moved in first direction generally parallel to the first direction. The third sealed edge is the trailing edge of a first bag and the leading edge of a second bag which follows the first bag as the webs are moved in the first direction, and the fourth sealed edge is the trailing edge of the second bag and the leading edge of a third bag which follows the second bag as the webs are moved in the first direction, and the third sealed edge is formed prior to the fourth sealed edge.

The method can be used to manufacture a pillow bag for receipt within a rigid container in which one wall of the pair of walls is an upper wall when received in the container, the other wall of the pair of walls is a lower wall, and the spout is on the upper wall.

When the manufactured bag is for receipt of the flowable material in the presence of steam, the wall having the spout installed thereon would generally be more thermally resistant than the other wall. When the bag is for use in a rigid container during filling and shipping, the wall having the spout installed thereon would generally have greater flex-crack resistance than the other wall.

According to another general method of manufacturing a bag of the invention, there are steps of: providing first and second webs of flexible materials, wherein the material of each web is structurally different from that of the other; installing a spout on one of the webs and forming a seal between said web and spout; sealing the webs to each other to form a peripheral seal between the two webs and thereby form the walls of the bag in sealed engagement to each other.

Other aspects and advantages of the invention are described below or will be apparent to the skilled person from the description of preferred embodiments.

Brief Description of Drawings

Specific embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates schematically the structure, or anatomy, of one wall of a typical bulk bag of the invention; and

Figure 2 is a block diagram of a sample process that may be used to produce a bag of the invention.

Description of Preferred Embodiments

A number of samples of bags are made in accordance with the present invention to illustrate properties thereof. A typical arrangement of layers and plies making up a wall of a bulk bag is illustrated in Figure 1. A smaller bag would typically have fewer plies than illustrated.

In each case, unless otherwise noted, a sample bag is manufactured using conventional processes that are known to the skilled person. Advantages of the invention are obtained through the selection of materials to obtain a bag having the structural features in accordance with the invention. Manufacturing processes are also disclosed, for example, in co-owned United States Patent Application No. 11/899,244, published under United States Patent

Publication No. 2008/0090062 on April 17, 2008, entitled "Polyethylene and Polypropylene Blends for Liquid Packaging Films", the specification of which is incorporated herein in its entirety, can be used in the context of this invention.

General steps of a typical manufacturing process are shown in Figure 2 which illustrates a line to make two-ply bags with a spout. Four rolls of film of the same width are mounted on unwind stands (1). The two outermost film rolls form the outer ply on the front and the back of the bag. The composition and/or thickness of the films is selected in accordance with this invention. The outer plies are usually the most complicated film layers in the bag structures. They are often laminates or coextrusions with a core layer of a barrier polymer such as nylon, polyester, or EVOH. Thin non-polymeric layers may also be included such as aluminum, aluminum oxide or silicon oxide, usually as coatings on the core layer of the laminate. The laminated core layer material is also often monaxially or biaxially oriented.

The two innermost film rolls form the inner ply on the front and the back of the bag, again selected in accordance with this invention. Inner films are often monofilms or coextrusions of polyethylene.

A time code is applied to the outer surface of one of the outer plies at station (2). A hole is punched through the outer and inner plies that will form one side of the bag at station (3). At station (4), a spout, the form of which is selected from any of the standard forms known in the bag making art, is inserted through the hole, and an enlarged flange of the spout is normally heat sealed to the inner and outer film plies. At station (5), a pair of heat seals is applied across the width of the films, forming the trailing seal of one bag and the leading seal of the next bag in the production line. A brush or other means for removing air trapped between the film plies is shown at station (6). The seals parallel to the length of the bag line are applied at either side of the films at station (7). Rollers, which pull the films through the bag line, are located at position (8).

At station (9), a knife or hot sealing bar may be used to completely separate the bags between the adjacent cross seals. Alternately, a sealing bar may be used to form a perforation between adjacent bags, so that they can be wound up as a continuous roll. Station (10) is a conveyor belt to push the bag, or strip of bags, to the end of the bag-making line. At the final station (11), the bags are packed into boxes. Many variations of this procedure are known and the person skilled in the art would select from those processes as necessary for the proposed application.

There are variations to this process when, for example, bulk bags are manufactured. In one variation, the long seal (along the machine-direction) can take place before the cross (transverse) seal is made. In another variation, the perforation can occur between the long and cross seal steps. These variations apply for a single spout placed on a bag. For some bags, two spouts may be inserted on each bag. In such instance, a second hole punch and spout insertion step (for the second spout) is included and usually after the hole punch and spout insertion for the first spout is concluded.

Example One

A bulk bag for use in aseptic applications was made. This example illustrates a pillow bag in which each of the upper and lower walls is made up of three plies, the two inner plies being monolayer, and the outer ply comprising a multilayer laminate with a core metallized- polyester barrier layer. The two inner plies of the upper wall are different in thickness from corresponding plies of the lower wall.

(1) met-PET = metallized polyester (polyethylene teraphthalate)

(2) LLDPE = linear low density polyethylene

The bags were irradiated to 1.5 mRAD minimum to sterilize the bags. Bag dimensions were as follows:

- Width = 81 inches

- Length = 85 inches

Size and location of fitment: 2 inch diameter, centered in upper wall of the bag Both bags were filled with sterile tomato paste in an aseptic filling operation as follows: Steam pressure in fill chamber of fill head between 0.5 and 1 psig; At end of fill, steam entered the bag for a few seconds before the fitment is capped to seal the bag; - Temperature of tomato paste entering bag was about 95° F;

- Bags were filled inside a wooden bin, with the seam of the bag running parallel to the floor, and the fitment facing upwards in the center of the top half of the bag.

At the end of fill cycle, when the tomato paste was finished being pumped into the bag, the fill tube was retracted from the fitment, and steam from the fill head chamber entered the bag until the cap was sealed over the top of the fitment. Ballooning up of the bag was visible as the steam pushed it upwardly from the inside.

After filling in the bin, each bag was visually examined visually for excessive wrinkling of the upper wall of the bag. Wrinkling, i.e. crocodile skin results from inner plies sticking to outer plies when exposed to excessive heat. Wrinkles are considered undesirable, both from an aesthetic as well as a functional view. In the latter case, wrinkling can lead to a loss of oxygen barrier. In the case of a food product such as tomato paste product, the resulting oxygen exposure can lead to browning of the paste.

The conventional reference bag showed excessive wrinkling near one of the top corners while the sample bag made in accordance with the invention showed no evidence of excessive wrinkling. The sample bag thus displayed enhanced thermal resistance over the conventional bag.

Example Two

A bulk bag with the outer ply of each wall comprising a metallized polyester core was manufactured in accordance with the present invention. This example illustrates a bulk bag having an upper wall with enhanced resistance to metal etching that can be caused by exposure to hot condensate or steam during the filling process.

(1) and (2) are two different blends of PE materials.

The upper wall material has a blend that can stand thermal cycle during the filling process. The lower wall is made from standard materials that can fail if used in the upper wall of the bag. This new structure resulted a more thermally resistance bag for the application with less penalty on the cost of the material.

Example 3

In this example, the product can be seen through the top transparent wall, useful for differentiating between different products. Also the nylon top layer is more resistance to flex crack resistance so that no dunnage is required to fill the head space of the box or drum that the bag goes into. This can result in cost savings to a user.

Bags of the invention may be irradiated prior to use in accordance with standard procedures well known in the packaging art. Aseptic packaging is also encompassed for bags of all types.

Films used to manufacture a bag of the invention can be made using film extrusion processes which are well known to the film manufacturing industry. Examples include a mono-extruder based film blowing or casting process with air cooling or other cooling media. The melt processing temperature may range from 150⁰C to 260⁰C. For a blown film process, the film blow-up-ratio (BUR) may range from 1.5 to 2.8 to have a stable process and good film quality. Processing additives can be incorporated into the resins as supplied or otherwise dry blended in the form of additive concentrates or melt-compounded into the resins via melt compounding processes.

One can form one or more layers of a multilayer coextruded film made in a blowing or casting process. Films can be also be combined with other layers in processes such as adhesive lamination, thermal lamination, extrusion lamination, extrusion coating and the like. The end use for the bag influences the selection of the material or materials used. For example, one or more plies can comprise multilayer films that contain an oxygen barrier layer such as metallized polyester, metallized nylon, foil, biaxially oriented EVOH, etc., and these can be used in combination with plies that comprise monlayer polyolefln film plies.

The mono film comprising one or more plies of the bag may have a film thickness of from about 20 to about 150 microns. Preferably, the mono film thickness may range from about 25 to about 140 microns and more preferably from about 30 to about 125 microns. Multi-layer films may be produced using the film, generally having thicknesses in the same ranges.

The inner plies of multi-ply bags, which might be added to improve shipping and handling performance, are normally mono films. Multi-layer films are used to make bags, which need a more sophisticated combination of properties, for example, higher barrier to oxygen. The outer ply of a multi-ply bag is often a multi-layer film. The middle or inner ply may also be a multi-layer film, and is often of different composition than the outer ply.

The bags which may be produced in accordance with this invention are pre-made and then usually filled through a fitment. They are often sterilized and may be, for example, irradiated in a batch process, employing standard radiation conditions, known in the art. The film may also be sterilized rather than the bags. Sterilization can be achieved in a variety of known ways. For example, by exposure of the film or bag to peroxide. Often of importance is that the films and bags can endure aseptic packaging conditions.

The capacity of the bags made in accordance with the present invention may vary considerably. Typically, bags can be sized from 1 to 400 gallons.

The bags of the present invention can also be printed by using techniques known in the art, e.g., use of corona treatment before printing.

The invention provides a bag making process comprising the steps of providing a multi-ply film structure, having inner and outer plies selected according to the invention as exemplified above, securing a spout to inner and outer plies of the film structure through a hole provided therein, sealing the plies together transversely across the width of the multi-ply film structure, to form a seal in the following end of one bag and a seal at the leading end of the adjacent following bag as they are manufactured, then sealing the plies together along edges parallel to the length of the bag line at either side of the films, and trapped air being removed prior to completely sealing the bag. The bags may be separated immediately or just prior to use.

Claims

1. A bag for receipt of flowable material therein, the bag comprising a pair of flexible walls joined continuously along edges thereof to form a seal between the walls, and at least one of the walls including an opening for passage of the material into the bag, wherein each wall has a structure different from the structure of the other wall.

2. The bag of claim 1, wherein each wall comprises a flexible polymer film.

3. The bag of claim 1 or claim 2, wherein the walls are joined to each other by a heat seal.

4. The bag of claim 1, 2 or 3, wherein the bag is a pillow bag for receipt within a rigid container, and one wall of the pair of walls is an upper wall when received in the container, the other wall of the pair of walls is a lower wall, and said opening is in the upper wall.

5. The bag of claim 1, 2, 3 or 4, wherein said opening is fitted with a fitment.

6. The bag of any of claims 1 to 5, wherein the bag is for receipt of the material in the presence of steam and said wall having said opening is more thermally resistant than the other wall.

7. The bag of any of claims 1 to 5, wherein the bag is for use in a rigid container during filling and shipping, said wall having said opening is the upper wall and the upper wall contains a flex-crack resistant ply or layer that has greater pinhole resistance than a corresponding ply or layer in the lower wall, as measured by the Gelbo Flex Test as disclosed herein.

8. The bag of any of claims 1 to 5, wherein said wall having said opening has greater puncture or abrasion resistance than the other wall.

9. The bag of any of claims 1 to 8, wherein the layered composition of the walls is the same for both walls and one wall has at least one layer or ply greater in thickness than the corresponding layer in the other wall.

10. The bag of any of claims 1 to 8, wherein the layered composition of a first wall of the pair of walls is different from the layered composition of a second wall of the pair of walls.

11. The bag of claim 10, wherein the first wall contains a layer different in composition from any layer in the second wall.

12. The bag of claim 10, wherein the first and second walls have the same number of plies and at least one ply of the first wall differs in composition or thickness from the corresponding ply of the second wall.

13. The bag of claim 10, wherein the first wall contains at least one more ply than the second wall.

14. The bag of claim 9, wherein the said at least one layer or ply is at least 10-300% / 15- 250% / 20-200% thicker than the corresponding layer or ply in the other wall.

15. The bag of any of claims 1 to 14, wherein the bag has volume of between 25 and 400 gallons when in expanded condition.

16. The bag of any of claims 1 to 14, where the bag has a volume of between 0.5 and 25 gallons.

17. The bag of any of claims 1 to 16, wherein the bag has been sterilized by irradiation.

18. The bag of any of claims 1 to 17, wherein the bag is for use to package liquid foods such as tomato paste, diced tomato, fruit juice and concentrates, fruit purees, dairy products, wine or other alcohol, soft drink concentrates, water, donut glaze, donut icing, and the like.

19. The bag of claim 4, wherein the volume of the bag is between 0.5 and 15 gallons.

20. The bag of any of claim 1 to 19, wherein the bag is for use to package non-food liquid products such as cleaners, disinfectants, waxes, paints, pesticides and the like.

21. The bag of any of claims 1 to 19, wherein the bag is for use to package a liquid.

22. The bag of any preceding claim wherein the bag is for use with a food product having a viscosity of from 1 to 500,000 centipoise measured at 2O⁰C.

23. The bag of claim 5, for use with a flowable material having a viscosity of from 1 to 10,000 centipoise measured at 20°C, wherein the upper wall has greater flex-crack resistance than the lower wall.

24. The bag of claim 7, wherein said ply or layer of the upper wall has less than 5 pinholes per 300 cm² as measured by the Gelbo Flex test after 10,000 cycles at room temperature, and said ply or layer of the lower wall has greater than 5 pinholes per 300 cm² as measured by the Gelbo Flex test after 10,000 cycles at room temperature.

25. The bag of any of claims 10-12, wherein the opening is in the upper wall and each of the upper and lower walls includes a laminate having a met-PET core layer wherein the laminate of the upper wall differs in structure from that of the lower wall.

26. The bag of claim 25, wherein said core layer of the upper wall has a higher barrier resistance than that of the core layer of the lower wall.

27. A bag of claim 25, wherein said core layer of the upper wall has a better flex-crack resistance than that of the core layer of the lower wall.

28. A bag of claim 25, wherein said core layer of the upper wall has a higher thermal resistance than that of the core layer of the lower wall.

29. A bag of claim 25, wherein said core layer of the upper wall has a higher resistance to metal etching than that of the core layer of the lower wall.

30. A bag of claim 25, wherein said core layer of the upper wall is at least 10% thicker than the core layer of the lower wall.

31. A method of manufacturing a bag having two flexible walls, for receipt of flowable material therein, the method comprising: providing first and second webs of flexible materials, wherein the material of each web is structurally different from that of the other; - installing a spout on one of the webs and forming a seal between said web and spout; sealing the webs to each other to form first and second sealed edges of the bag, parallel to each other in a first direction; and sealing the webs to each other to form third and fourth sealed edges of the bag, parallel to each other in a second direction, and to form a complete seal between the two webs and thereby form the walls of the bag in sealed engagement to each other.

32. The method of claim 31, wherein said method is an in-line method in which the webs are moved in first direction generally parallel to the first direction.

33. The method of claim 32, wherein the third sealed edge is the trailing edge of a first bag and the leading edge of a second bag which follows the first bag as the webs are moved in the first direction, and the fourth sealed edge is the trailing edge of the second bag and the leading edge of a third bag which follows the second bag as the webs are moved in the first direction, and the third sealed edge is formed prior to the fourth sealed edge.

34. The method of any one of claims 31 to 33, wherein each web comprises a flexible polymer film.

35. The method of any one of claims 31 to 34, wherein the bag is a pillow bag for receipt within a rigid container, and one wall of the pair of walls is an upper wall when received in the container, the other wall of the pair of walls is a lower wall, and the spout is on the upper wall.

36. The method of any one of claims 31 to 35, wherein the bag is for receipt of the flowable material in the presence of steam and the wall having the spout installed thereon is more thermally resistant than the other wall.

37. The method of any of claims 31 to 35, wherein the bag is for use in a rigid container during filling and shipping and said wall having the spout installed thereon has greater flex- crack resistance than the other wall.

38. The method of any of claims 31 to 35, wherein said wall having the spout installed thereon has greater puncture and/or abrasion resistance than the other wall.

39. The method of any one of claims 31 to 38, wherein the material of each web comprises a layered composition which is the same as the other, and one of the two materials has at least one layer or ply greater in thickness than the corresponding layer in the other material.

40. The method of any one of claims 31 to 38, wherein the material of each web comprises a layered composition which is different from the layered composition of the other.

41. The method of claim 40, wherein the first wall contains a layer different in composition from any layer in the second wall.

42. The method of claim 40, wherein the first and second walls have the same number of plies and at least one ply of the first wall differs in composition or thickness from the corresponding ply of the second wall.

43. The method of claim 40, wherein the first wall contains at least one more ply than the second wall.

44. The method of claim 39, wherein the said at least one layer or ply is at least 10-300% , or 15-250%, or 20-200% thicker than the corresponding layer or ply in the other wall.

45. The method of any one of claims 31 to 44, wherein the bag has volume of between 25 and 400 gallons when in expanded condition.

46. The method of any one of claims 31 to 44, where the bag has a volume of up to 55 gallons, preferably between 0.5 and 25 gallons.

47. The method of any one of claims 31 to 46, wherein the bag is for use to package liquid foods such as tomato paste, diced tomato, fruit juice and concentrates, fruit purees, dairy products, wine or other alcohol, soft drink concentrates, water and the like.

48. The method of claim 35, wherein the volume of the bag is between 1 and 15 gallons.

49. The method of any one of claim 31 to 48, wherein the bag is for use to package non-food liquid products such as cleaners, disinfectants, waxes, paints, pesticides and the like.

50. The method of any of claims 31 to 48, wherein the bag is for use to package a liquid.

51. A method of manufacturing a bag having two flexible walls, for receipt of flowable material therein, the method comprising: providing first and second webs of flexible materials, wherein the material of each web is structurally different from that of the other; installing a spout on one of the webs and forming a seal between said web and spout; - sealing the webs to each other to form a peripheral seal between the two webs and thereby form the walls of the bag in sealed engagement to each other.