Abstract:
A plastic bag comprising a first face and a second face, at least a portion of each being 2-ply and having an intermediate space therebetween, the 2-ply portion of the first face having an inner layer of air-impervious plastic material having openings therein; the 2-ply portion of the second face having an outer layer of air-impervious plastic material, the outer layer having openings therein permitting air to pass therethrough, the openings of the outer layer having a smaller average opening area than an average opening area of the openings of the inner layer of the first face; and a filtering chamber formed between the inner layer and the outer layer such that air in an interior of the bag may egress the bag by passing through the filtering chamber, the air being at least partially filtered of particulate matter as it egresses the bag.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention claims priority to U.S. Provisional Patent Application Nos. 60/864,589 filed Nov. 6, 2006 and 60/954,145 filed Aug. 6, 2007, both entitled “Plastic Bag with Improved Air Evacuation Structure”. The entirety of each of these documents is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to plastic bags such as those that may be used for packaging bulk products. 
       BACKGROUND OF THE INVENTION 
       [0003]    Bulk products, such as concrete, plaster, foodstuffs, pet foods and litters, lawn care products, salt, and many others, are conventionally transported, distributed, and sold in bags. Depending on the application, these bags are typically made of paper or plastic, both of which have their advantages and drawbacks, which may either be inherent and/or dependent on the particular product being packaged. 
         [0004]    Most bags used with cement and concrete products and other heavy flowable contents are large multi-wall paper bags with fill valves, like those commonly seen palletized in home improvement centers throughout the U.S. They typically contain products, such as 60# mortar and concrete mix and 94# cement and concrete mix, sold to consumers for use in home, garden and yard applications. The chief reason paper valve bags are used for these applications is primarily due to per unit costs and productivity factors. Paper valve bags cost more than standard, top-loading plastic bags, but the paper bags are much faster to fill, thus substantially improving productivity and output. 
         [0005]    Nonetheless, as anyone experienced in the art knows, there are several problems associated with conventional paper bags. In addition to the high cost, other disadvantages of paper packaging include the consumption of five times the storage space of plastic, the vulnerability of cement and concrete products stored in paper to weather conditions (especially rain and moisture), and the vulnerability of paper to pest infestations. Another significant disadvantage of paper packaging is that it often rips or breaks, spilling out its contents. Indeed, this occurs so often that in some home improvement centers, an employee is assigned the full-time task of cleaning up bulk materials spilled from ripped or broken paper bags. Both the wasted material and the time spent cleaning it up are a significant wasted expense. 
         [0006]    To improve this situation, one prior art solution was to use a plastic bag for packaging such materials. International Patent Publication No. WO 03/000005 entitled “Flowing Bag Filling System and Bag Therefor” published on Jan. 3, 2003 (herein incorporated by reference in its entirety) describes a bag particularly adapted for this purpose. It provides a bag having an inwardly disposed seam manufactured from a sheet of plastic bag material having two major surfaces and two parallel side edges. A first seam seals the two parallel side edges together at the same major surface with the side edges disposed inwardly of the tube to form the sheet of plastic bag material into a tube with internal flap portions extending interiorly of the tube. At least one seal across the tube is provided for forming at least a three-sided bag structure (and preferably two seals across the tube for forming a closed four-sided bag structure) whereby pressure in the interior of the bag acts against the internal flap portions disposed inwardly of the tube to enhance the sealing of the seam. The bag is filled at an opening defined along the opposite side edges of the seam facing inwardly of the tube. 
         [0007]    The bag of the &#39;005 publication was an improvement over the then conventional paper bags. Being made of plastic, it was lightweight, took up less storage space, and was significantly less prone to ripping or breaking. Moreover, these bags were not subject pest infestation. They were impervious to fluids, meaning that rain water could not cause the bags to deteriorate; nor could unwanted moisture pass through the bags and into the contents thereof (it being particularly important to keep contents such as cement or concrete moisture-free). 
         [0008]    However, fluid-imperviousness, while clearly helpful in some ways, is a major problem in others, particularly in the filling of the bag with its contents. In order to fill the bag with its contents, the bulk material to be put into the bag (such as cement or concrete) must be fluidized by being mixed with and suspended in moving air to form a flowing stream of material/air mixture. The more fine the particles of the material, the more air that is required to fluidize them and create the flowing material/air stream. Fine materials in powder form require a significant amount of air to be fluidized and moved. 
         [0009]    Once the flowing fluidized mixture is created it is directed into the bag, wherein the material is deposited and the air must be withdrawn. Given the plastic material of the bag, the plastic material being impervious to fluids, some means for removing the air must be provided. The means described in the &#39;005 publication (at paragraph 54 and in FIG. 15) is an air evacuation system combined with the filling system to withdraw air from the bag during filling operations. While adequate for its intended purpose, that system is not optimal. The difficultly is that its does not completely “defluidize” the air/material mixture, and leaves some air entrapped in the bag. This makes these bags unwieldy and difficult (and in some instances very difficult or nearly impossible) to stack. This situation is undesirable for bags that are destined to be palletized for transportation and/or distribution, as stackablity of the bags is extremely desirable. Simple and economical means for allowing air entrapped in the bag after the bag has been filled would be desirable. 
         [0010]    One such means for allowing air to escape from a plastic bag is described in European Patent No. 0,444,261, entitled “Flexibles Verpackungsbehältnis in Form eines Sackesoder Beutels aus Kunststoffolle” (“Flexible Packaging Container in the Form of a Bag or Pouch, Made from Plastic Film”) published on Aug. 11, 1993 (herein incorporated by reference in its entirety). The &#39;261 patent provides a flexible packaging container in the form of a bag or pouch made from plastic film or similar material which is impermeable to air, which has in the bag wall an air outlet region in which the bag material as an outside wall part is provided with perforations for passage of air from the filling space of the bag. The perforated bag material is covered on the inside by an air-permeable inside wall part. The inside wall part consists, in turn, of material, such as plastic film, which is impermeable to air and, for its air-permeable construction, is likewise provided with perforations which, however, although being the same size, have a construction and arrangement for a greater air passage than the perforations of the outside wall part in the air outlet region of the bag wall, the inside wall part and the outside wall part jointly bounding an air chamber which is closed all round at the edge. The difficulty with the bag described in the &#39;261 patent is that, while air is indeed permitted to escape from the interior, so is the material that the bag is supposed to contain unless some kind of external filter is added. This escape of material is undesirable where the material is a fine power such as cement or plaster; and external filters are expensive and needlessly complicate the manufacture process. 
         [0011]    There is thus a need in the art for a fluid-impervious bag made from a plastic material having structure allowing for air entrapped in the interior of the bag to escape therefrom, while at the same time preventing an undesirable quantity of material contained within the bag from escaping. 
       STATEMENT OF THE INVENTION 
       [0012]    It is therefore an object of the present invention to provide a plastic bag with an improved air evacuation structure over plastic bags of the prior art. 
         [0013]    Thus, in one aspect, as embodied and broadly described herein, the present invention provides a plastic bag comprising a first face, at least a portion thereof being 2-ply and having a first intermediate space therebetween, the 2-ply portion of the first face having an inner layer of air-impervious plastic material having openings therein permitting air to pass therethrough; a second face, at least a portion thereof being 2-ply and having a second intermediate space therebetween, the 2-ply portion of the second face having an outer layer of air-impervious plastic material, the outer layer having openings therein permitting air to pass therethrough, the openings of the outer layer having a smaller average opening area than an average opening area of the openings of the inner layer of the first face, the first intermediate space and the second intermediate space being fluidly interconnected; whereby a first filtering chamber is formed between the inner layer and the outer layer such that air in an interior of the bag may egress the bag by passing through the openings of the inner layer and through the openings of the outer layer, the air being at least partially filtered of particulate matter as it egresses the bag. 
         [0014]    Although many different bag constructions are contemplated (some of which are described hereinbelow), it is preferred for most embodiments of the present invention that the bag simply be of a two-layer construction (i.e. 2-ply) in order to simplify manufacturing and to avoid increasing costs. In bags of a two-layer construction there will be an inner layer (i.e. the layer to be in contact with the contents of the bag), an outer layer (i.e. the layer surrounding the inner layer and in contact with the environment), and an intermediate space therebetween. The term “intermediate space” should be understood as encompassing the situation where the inner layer and the outer layer are in direct contact, and thus there is no actual space between them (i.e. bags of the present invention should be understood to have an intermediate space even if situations exist during the course of their use during which there is no actual space between the relevant layers). 
         [0015]    Typically bags of the present invention (when filled with material) will be three-dimensional rectilinear bodies, most commonly rectangular parallelepipeds. As would be apparent to those of ordinary skill in the art, in such cases the bags will have  6  faces: a front face, a rear face, a left side face, a right side face, a bottom face and a top face. The front face and the rear face will typically be the two parallel rectangular faces with the greatest surface area, and the remainder of the faces will be defined to be consistent with the front face and the rear face. In cases where the bags are cubes, the same 6 faces will be present, however, any two parallel faces may be the front face and the rear face, with the remainder of the faces being consistently defined therewith. Where the bag is a three-dimensional curvilinear body, for example, a right circular cylinder, the front face and the rear face may be opposing portions of an appropriate exterior surface. 
         [0016]    For greater certainty it should be understood that a “face” of a bag of the present invention includes all of the layers comprising the face and not just the outer layer. Thus for example for 2-ply bags the front face includes both the front face outer layer and the front face inner layer. The front face inner layer is termed “front face” even though it actually faces the front face outer layer. 
         [0017]    An “opening” in a layer of material should be understood to mean an absence of material, however caused or formed, that allows air to pass through the layer. For example openings may be formed by needle perforation (the preferred method for forming the openings in the outer layer) or by a slicing with spinning blade (the preferred method for forming the openings in the inner layer). The average opening area of the openings of a face is calculated by determining the effective cross-sectional open area of each of the openings of a face, and averaging them. 
         [0018]    Bags of the present invention provide a filtering chamber between the inner layer of the first face and the outer layer of the second face such that air in an interior of the bag may egress the bag by passing through the openings of the inner layer into the filtering chamber and then through the openings of the outer layer, such that the air is at least partially filtered of particulate matter as it egresses the bag. Preferably, what occurs is that the inner and outer layers act as a progressive sieve. Thus, the inner layer will allow air to escape but will filter out all particles over a certain size allowing only (generally) very fine particles to pass therethrough entrained with the air. The openings in the outer layer are however smaller and will again allow to air to pass therethrough while filtering out particles over a certain size even smaller than that of the inner layer. Ideally, if possible, the size of the outer layer is such that no particles will be allowed to pass therethrough, only air. If not possible, the size is calculated to keep particle passage below a desired maximum. 
         [0019]    This construction is beneficial in that because the particles capable of reaching the outer layer of are a much smaller size than those filtered out by the inner layer; clogging of the openings of the outer layer is less likely to occur than if the bag consisted of a single layer equivalent to the outer layer. 
         [0020]    In should be understood that merely because the average opening area of the openings of the outer layer is smaller than the average opening area of the openings of the inner layer, it does not mean that the total opening area of the openings (i.e. the sum of the opening area of each of the openings) of the outer layer is smaller than the total opening area of the openings of the inner layer. Indeed, preferably, it is larger (i. e. the total opening area of the openings of outer layer is greater than the total opening area of the openings of the inner layer). In this manner, control of the air flow through the filtering chamber and out of the bag is controlled by the total opening area of the openings of the inner layer. Thus depending on the application of the bag, a desired airflow can be created or controlled by increasing or decreasing the size and/or number of openings in the inner layer. 
         [0021]    It is not required that the inner-layer openings and the outer-layer openings be on the same face of the bag. They may be on different faces. For example, it may be that the left side face inner layer has openings and the front face outer layer has openings. What is important is that there be some pathway for air to egress the interior of the bag passing through both the openings of the inner layer and the openings of the outer layer; the intermediate spaces of 2-ply areas (of the left side inner layer and the front face outer layer - from the previous example) thus must be fluidly connected. It may be that in such situations no other faces of the bag have layers with openings. Alternatively, it may that there are other faces that do have openings, but that their intermediate spaces are not in fluid communication with the faces in question (the left side inner layer and the front face outer layer—from the previous example), and thus they provide for filtering chambers that are fluidly distinct from others on the bag. 
         [0022]    Nonetheless, for most applications it is preferred that the first face and the second face are the same face of the bag and that the first intermediate space and the second intermediate space are the same intermediate space. I.e. it is the inner layer and the outer layer of the same face that have openings and a filtering chamber is formed directly therebetween. 
         [0023]    In such cases, it is highly preferred that the openings of the outer layer be offset from the openings of the inner layer. This will discourage the openings of the outer layer from becoming clogged with particles or having particles become lodged therein. Particles travelling through the openings of the inner layer will impact on the material of the outer layer itself and will (hopefully) ricochet back into the filter chamber where they will harmlessly remain trapped. This is contrasts with the situation where particles travelling through the inner layer would be directed (with some force) directly towards an opening in the outer layer, greatly increasing the chances that the outer-layer opening will become clogged. 
         [0024]    It is further preferred that in the absence of air and particulate matter in the filtering chamber the outer layer of the second face and the inner layer of the first face lie flat against one another. 
         [0025]    It is also highly preferred that the plastic bag further comprises: a third face, at least a portion thereof being 2-ply and having a third intermediate space therebetween, the 2-ply portion of the third face having an inner layer of air-impervious plastic material having openings therein permitting air to pass therethrough; a fourth face, at least a portion thereof being 2-ply and having a fourth intermediate space therebetween, the 2-ply portion of the fourth face having an outer layer of air-impervious plastic material, the outer layer having openings therein permitting air to pass therethrough, the openings of the outer layer having a smaller average opening area than an average opening area of the openings of the inner layer of the third face, the third intermediate space and the fourth intermediate space being fluidly interconnected; whereby a second filtering chamber is formed between the inner layer and the outer layer such that air in an interior of the bag may egress the bag by passing through the openings of the inner layer and through the openings of the outer layer, the air being at least partially filtered of particulate matter as it egresses the bag. 
         [0026]    As was previously described hereinabove with respect to the first and second faces, it is not required that the third-face inner-layer openings and the fourth-face outer-layer openings be on the same face of the bag. They may be on different faces. Nonetheless, for most applications it is preferred that the third face and the fourth face are the same face of the bag and that the third intermediate space and the fourth intermediate space are the same intermediate space. I.e. it is the inner layer and the outer layer of the same face that have openings and a filtering chamber is formed directly therebetween. In such cases, it is highly preferred that the openings of the outer layer be offset from the openings of the inner layer as was also described hereinabove. 
         [0027]    It should be understood that there may or may not be any correlation between the first, second, third and fourth faces. That is to say that none, some or all of the faces may be the same face. Further, their intermediate spaces may or may not be fluidly connected (provided at least one pathway for air to egress the interior of the bag is provided). Thus, many different constructions within the scope of the present invention are possible. 
         [0028]    By way of non-limiting example, it may be that all of the faces are the same face, yet the first and second intermediate spaces are not fluidly connected with the third and fourth intermediate space. Thus two independent filtering chambers would be formed on the same face. Alternatively, it may be that only the second and third face are the same face. In such as case, the first and second intermediate spaces may or may not be fluidly connected with the third and fourth intermediate spaces such that one or more than one filtering chamber will be formed. 
         [0029]    For most applications it is preferred that the first intermediate space, the second intermediate space, the third intermediate space, and the fourth intermediate space are all fluidly interconnected forming such that the first filtering chamber and the second filtering chamber are the same filtering chamber. This will maximize the chances of air egressing the interior of the bag as many pathways will be formed. 
         [0030]    It is highly preferred that the layers with openings therein be the front face and rear face inner layer and the front face and the rear face outer layer. Where such is the case, it is also preferred that no other layer of any other face have openings. Bags of the present invention are likely destined to be palletized for transport and distribution. Where this is the case, they will be laid on the pallet (or on another bag lower down on the pallet) either on their front face or on their rear face, such that the material in the bag will lie on the face of the bag facing the pallet (or the bag below as the case may be) and the air will rise to the above and be permitted to egress the bag through the filter chamber described hereinabove. If both the front faces and rear faces of all layers of the bag having openings, it is not necessary for the person placing the bag to ensure that a particular face is oriented in a particular direction; either face may be face-up, simplifying packing operations. 
         [0031]    In such cases, it is highly preferred that the bag have no structure that would keep the layers of the faces in a spaced-apart relationship, i.e. in the absence of air and/or particulate matter in the filter chamber, the outer layer and the inner layer should lie flat against one another (i.e. be touching such that there is no volume therebetween). The openings of the outer layer being misaligned with the openings of the inner layer will cause the openings of the inner layer to be blocked by the outer layer when the two layers are in contact. This is desirable to occur in the scenario described above for the face-down face of the bag. In this manner, the face-down face of the bag is sealed by the weight of the material in the bag, and the air will have to pass through the openings in the face-up face of the bag (the overpressure of air will force the inner and outer layers to separate and create the filter chamber). When the next bag is placed on top of the bag on the pallet, the weight of material in the second bag will then seal (at least until that bag is removed) both its own face-down face and the face-up face of the bag on which it was placed. This will have the effect of sealing the first bag (ideally completely) so as to prevent moisture from re-entering the bag through any of the openings. In situations where this described occurrence is desired, it is preferred that none of the other faces of the bags have openings so that the bags may be completely sealed once stacked on one another. 
         [0032]    It is also preferred the openings of the inner layer (of whatever face) have a jagged edge (i.e. a jagged-edge that opens inward toward the interior or outward away from the interior of the bag). It has been found that this structure will discourage particles from clogging the openings of the inner layer. Jagged edges may be formed by any suitable method. 
         [0033]    It should be understood that bags of other physical constructions are within the scope of the present invention. In this respect, it is not necessary that bags of the present invention be completely 2-ply (i.e. that each and every one of their faces is 2-ply). Also possible is a construction where only a portion or portions of the bags are 2-ply. The portion or portions may be on a single face or may be on multiple faces. Where the later is the case, it is not necessary that the portion of the inner layer having openings and the portion of the outer layer having openings be on the same face. It may be that these portions are remote from one another and it also may be that they are on different faces. What is important is that there be some pathway for air to egress the interior of the bag; the intermediate spaces of 2-ply areas must be fluidly connected. 
         [0034]    For some applications (particularly those requiring cleanliness), it may be preferred that the openings of the outer layer are arranged with respect to each other such that the outer layer of the bag may be ripped apart (and removed from the bag) along a tear line including such openings. In such cases, the openings of the outer layer are preferably serrations (that may be easily torn) running across the length of the bag. In this manner, it may not be necessary to ship and store the bag in any particular fashion. The outer layer will be exposed to the environment but the inner layer will not. At an appropriate time, the outer layer may be removed and the clean inner layer and its contents may be used as desired. 
         [0035]    In another aspect, as embodied and broadly described herein, the present invention also provides a multi-ply plastic bag comprising: an inner layer of air-impervious plastic material, at least a portion of which has openings therein permitting air to pass therethrough; an intermediate layer of air-impervious plastic material, at least a portion of which has openings therein permitting air to pass therethrough; and an outer layer of air-impervious plastic material, at least a portion of which has openings therein permitting air to pass therethrough. 
         [0036]    It is preferred that the openings of the outer layer have an average opening area that is smaller than an average opening area of the openings of the intermediate layer; and the average opening area of the openings of the intermediate layer is smaller than an average opening area of the openings of the inner layer, whereby a filtering chamber is formed such that air in an interior of the bag may egress the bag by passing through the openings of the inner layer, through the openings of the intermediate layer, and through the openings of the outer layer, the air being at least partially filtered of particulate matter as it egresses the bag. 
         [0037]    It is further preferred that the openings of the outer layer are offset from the openings of the intermediate layer; and the openings of the intermediate layer are offset from the openings of the inner layer. It also preferred that in the absence of air and particulate matter in the filtering chamber, the outer layer, the intermediate layer and the inner layer lie flat against one another. It is still also preferred that the total opening area of the openings of outer layer and the total opening area of the openings of the intermediate layer are each individually greater than the total opening area of the openings of the inner layer. 
         [0038]    Preferably, as described herein above in relation to other aspects of the invention, the plastic bag has a plurality of faces including a front face and a rear face, and the openings are located solely on the front face and the rear face of the bag. Further, the inner-layer openings have a jagged edge and the outer-layer openings have a non-jagged edge. 
         [0039]    Embodiments of the present invention each have at least one of the above-mentioned objects and/or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present invention that have resulted from attempting to attain the above-mentioned objects may not satisfy these objects and/or may satisfy other objects not specifically recited herein. 
         [0040]    Additional and/or alternative features, aspects, and advantages of the embodiments of the present invention will become apparent from the following description, the accompanying drawings, and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0041]    For a better understanding of the present invention, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where: 
           [0042]      FIG. 1  is a front elevation view of an unfilled bag of a first embodiment of the present invention; 
           [0043]      FIG. 2  is cross-sectional view of the bag of  FIG. 1  taken along the line  2 - 2  therein; 
           [0044]      FIG. 3  is a rear left perspective view of a filled bag of  FIG. 1 ; 
           [0045]      FIG. 4  is a close-up top plan view of the front surface of the inner layer of the bag of  FIG. 1 ; 
           [0046]      FIG. 5  is a close-up top plan view of an opening on the front surface of the inner layer of the bag of  FIG. 1 ; 
           [0047]      FIG. 6  is a cross-sectional view of the opening of  FIG. 5 ; 
           [0048]      FIG. 7  is a close-up top plan view of the front surface of the outer layer of the bag of  FIG. 1 ; 
           [0049]      FIG. 8  is a close-up top plan view of an opening on the front surface of the outer layer of the bag of  FIG. 1 ; 
           [0050]      FIG. 9  is a cross-sectional view of the opening of  FIG. 8 ; 
           [0051]      FIG. 10  is top plan view showing a comparison of the openings of  FIGS. 5 and 8 ; 
           [0052]      FIG. 11  is close-up cross sectional view of the front surfaces of the inner and outer layers of the bag of  FIG. 1 , showing the offset of the openings therein; 
           [0053]      FIG. 12  is a schematic cross-sectional view of a filled bag of the present invention on a pallet; 
           [0054]      FIG. 13  is a close-up cross sectional view of the front surfaces of the inner and outer layers of the bag of  FIG. 12 , showing the action of the filtering chamber therebetween; 
           [0055]      FIG. 14  is a close-up cross sectional view of the rear surfaces of the inner and outer layers of the bag of  FIG. 12 ; 
           [0056]      FIG. 15  is a close-up cross sectional view of the front surfaces of the inner and outer layers of the bag of  FIG. 12  as well the rear surfaces of the inner and outer layers of a second bag of similar construction placed on top of the bag of  FIG. 12  on the pallet; 
           [0057]      FIG. 16  is a front elevation view of a bag of a second embodiment of the present invention; 
           [0058]      FIG. 17  is cross-sectional view of a bag of a third embodiment of the present invention; 
           [0059]      FIG. 18  is close-up cross sectional view of the bag of  FIG. 17 ; 
           [0060]      FIG. 19  a top plan view showing a comparison of the openings of  FIG. 18 ; 
           [0061]      FIG. 20  is a front elevation view of an unfilled bag of a fourth embodiment of the present invention; and 
           [0062]      FIG. 21  is a close-up top plan view of the front surface of the inner layer of the bag of  FIG. 20 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0063]    In  FIG. 1  of the present invention there is shown a bag  10  similar (albeit constructed according to the teachings of the present invention) to one described in the &#39;005 publication. It should be understood that this bag is described herein only as a preferred embodiment. Other embodiments are possible in accordance with the teachings of the present invention. 
         [0064]    In  FIG. 1 , bag  10  (collapsed) has a top face  12  and a bottom face  14 , left- and right side gussets  16 ′ and  16 , respectively, with left- and right-side center gusset creases  18 ′ and  18  respectively. (For ease of understanding, it should be noted that the left side of the bag is closer to the right edge of the drawing page (and vice versa), as it is the bag&#39;s left, and not the viewer of the drawing&#39;s left, that is being referred to.) Extending inward from the right-side center gusset crease  18  are internal flap edges  20  and  22  (the latter not shown in  FIG. 1  as it lies directly underneath internal flap edge  20 ). Internal lap sealed portion  24  (the shaded strip) is the narrow strip of material in between right-side center gusset crease  18  and internal flap edges  20  and  22 , and runs continuously from bag top  12  to bottom  14 . As viewed, the lap sealed portion  24  lies inside of the bag  10  adjacent to the right-side center gusset crease  18 , and the lap seal defining right-side center gusset crease  18 . With the lap seal facing inward, inside the bag, the outer surface of the bag has no ridges or seals pointed outward. 
         [0065]    As can be seen in  FIG. 2 , bag  10  is of a 2-ply construction, having an outer layer  40  and an inner layer  42 . (The 2-ply nature of the bag  10  is not shown in  FIG. 1  simply for ease of understanding.) The outer layer and the inner layer may be of plastic material suitable for the intended use of the bag. Thermoplastic resins blends such as polyolefin resin blends and polyethylene resin blends are non-limiting examples of preferred materials. 
         [0066]    The bag  10  has front face  26  and a rear face  28 . The front face  26  has an outer layer  26   o  (being a portion of the outer layer  40 ) and an inner layer  26   i  (being a portion of the inner layer  42 ). Similarly, the rear face  28  has an outer layer  28   o  (being a portion of the outer layer  40 ) and an inner layer  28   i  (being a portion of the inner layer  42 ). 
         [0067]    The bag  10  also has a right side face  31  and a left side face  35 . The right side face  31  has an outer layer  31   o  (being a portion of the outer layer  40 ) and an inner layer  31   i  (being a portion of the inner layer  42 ). The right side face outer layer  31  o is formed from a right side front gusset outer layer  30   o , a right side rear gusset outer layer  32   o , and a right side center gusset crease  18 . The right side face inner layer  31   i  is formed from a right side front gusset inner layer  30   i , a right side rear gusset inner  32   i , and the right side center gusset crease  18 . The left side face  35  has an outer layer  35   o  (being a portion of the outer layer  40 ) and an inner layer  35   i  (being a portion of the inner layer  42 ). The left side face outer layer  35   o  is formed from a left side front gusset outer layer  34   o  and a left side rear gusset outer layer  36   o . The left side face inner layer  35   i  is formed from a left side front gusset inner layer  34   i  and a left side rear gusset inner  36   i . (For ease of understanding there is a gap shown in  FIG. 2  between the inner layer  42  and the outer layer  40  layers of the bag  10 . It should be understood however, that ideally there is no such gap when the bag  10  is flat and unfilled. The gap illustrates intermediate spaces associated with of the various layers of the faces. For example, there is an intermediate space  46   o  associated with the front face outer layer  26   o , an intermediate space  46   i  associated with the front face inner layer  26   i , an intermediate space  48   o  associated with the rear face outer layer  28   o , and an intermediate space  48   i  associated with the rear face inner layer  28   i . These intermediate spaces will form part of the filtering chamber  44 , best shown in  FIG. 13 .) 
         [0068]    In between the right side center gusset crease  18  and internal flap edges  20  and  22  is internal lap-sealed portion  24 . (The lap-sealed portion sealing the inner layer  42  and outer layer  40  together, each of these portions of the bag is labelled as a single common portion.) This lap-sealed portion may be a strip as narrow as 3 mm or may be wider. 
         [0069]    In  FIG. 3  bag  10  has been filled with a flowable material (air and material mixture under pressure) and sealed at the top edge  12 . Right side center gusset crease  18  is one continuous crease formed by the internal lap-sealed portion  24  (the latter not shown since it is inside bag  10 ). The outer appearance of center gusset crease  18  looks much like that of any other side gusset crease commonly seen in standard tube-type bags, that is, one clean, continuous fold. 
         [0070]    Referring still to  FIGS. 1 to 3 , there are marked areas ( 27  in  FIGS. 1 &amp; 3 ) on the front face outer layer  26   o  (marked area being  27   o  in  FIG. 2 ), front face inner layer  26   i  (marked area being  27   i  in  FIG. 2 ), rear face outer layer  28   o  (marked area being  29   o  in  FIG. 2 ), and rear face inner layer  28   i  (marked area  29   i  in  FIG. 2 ). These areas have openings therein (described hereinbelow), although the openings have been omitted in these figures for ease of illustration. 
         [0071]      FIG. 4  shows a close-up view of the marked area  27   i  of front surface inner layer  26   i . Openings  25   i  can be seen. The openings are preferably slits being 500 microns long and 100 microns wide. The openings  25   i  are shown at a regularly-spaced intervals (which is preferably along a grid 1.25 cm apart in both directions), but this is merely a preferred configuration.  FIG. 5  shows a close-up view of single opening  25   i  shown in  FIG. 4 . The opening  25   i  is irregular in shape, again this being a preferred configuration. Finally,  FIG. 6  shows a cross-sectional view of the opening  25   i  of  FIG. 5 . The opening  25   i  has an (outwardly) jagged edge  33   i . The marked area  29   i  of the rear surface inner layer  28   i  has similar openings. 
         [0072]      FIG. 7  shows a close-up view of the marked area  27   o  of front surface outer layer  26   o . Openings  25   o  can be seen. The opening are preferably circular and have a diameter of between  20  and 100 microns, with 50 microns being most preferred. The openings  25   o  are shown at a regularly-spaced intervals (which is preferably along a grid 5 mm apart in both directions), but this is merely a preferred configuration.  FIG. 8  shows a close-up view of single opening  25   o  shown in  FIG. 7 . The opening  25   o  is regular in shape, again this being a preferred configuration. Finally,  FIG. 9  shows a cross-sectional view of the opening  25   o  of  FIG. 8 . The opening  25   o  has a smooth edge  33   o . The marked area  29   o  of the rear surface outer layer  28   o  has similar openings. 
         [0073]      FIG. 10  shows the relative size difference between the openings  25   i  of the inner layer  26   i / 28   i  and the openings  25   o  of the outer layer  26   o / 28   o.    
         [0074]      FIG. 11  shows the relative positioning of the openings  25   i  of the rear face inner layer  28   i  and the openings  25   o  of the rear face outer layer  28   o . As can be seen, the openings  25   i  are offset from the openings  25   o.    
         [0075]      FIG. 12  shows a bag  10  that has been filled with particulate material  37  and has been placed on a palette rear face  28  down. (The filling of the bag could have been by any conventional means, including those described in the &#39;005 publication.). Air is entrapped within the particulate matter  37 .  FIG. 13  shows a close-up of the front face of the bag. As can be seen, particulate matter  37  is made up a particles of different sizes, for ease of illustration shown as large particles  37   a , medium particles  37   b , and small particles  37   c . Air under pressure inside the bag a result of the filling of the bag, will flow out of the bag in the path shown, first through an opening  25   i  of the front face inner layer  26   i  and into filter chamber  44  between the front face inner layer  26   i  and the front face outer layer  26   o  (the air will force the inner layer  26   i  and the outer layers  26   o  apart to create the filter chamber  44 ) and then from the filter chamber  44  through an opening  25   o  of the front face outer layer  26   o  to the environment. As can be seen, the opening  25   i  is of such as size so as to prevent large particles  37   a  from entering the filter chamber  44 . Further, opening  25   o  is of such as size so as to prevent medium particles  37   b  from exiting the filter chamber. (Those particles will remain in the filter chamber  44  or flow back into the interior of the bag  10  through an opening  25   i .) Only small particles  37   c  are of a size that can exit the bag  10  through the opening  25   o  (and only then if they actually reach the opening  25   o . Some will impact the outer layer  26   o  and be deflected into the filter chamber  44  to a point where they cannot reach an opening  25   o ). In this manner, air is filtered as it exists the bag  10 . 
         [0076]      FIG. 14  shows a close-up of the rear face  28  of the bag  10  of  FIG. 12 . The weight of the particles  37  maintains the rear face outer layer  28   o  and rear face inner layer  28   i  together such the openings  25   i  and  25   o  are effectively sealed on that face  28 . (The edge  33   i  of the opening  25   i  of the rear face inner layer  28   i  has collapsed into the opening  25   i .) No filter chamber is formed and no air can escape the bag through the rear face  28  of the bag. 
         [0077]      FIG. 15  shows a close up of the front face  28  of the bag  10  after a second bag  10 ′ has been placed on top. In this case, the weight of the second bag  10 ′ helps to seal and discourage moisture from entering the first bag  10  as it forces the front face of the outer layer  28   o  of the first bag  10  against the front face inner layer  28   i  of the first bag  10 , sealing off the openings  25   i / 25   o . (Some small  37   c  and medium particles  37   b  remain trapped between the layers.) In addition, adding to this effect, the rear face outer layer  28   o ′ of the second bag  10 ′ blocks off the openings  25   o  of the front surface the outer layer  28   o  of the first bag  10 . 
         [0078]      FIG. 16  shows a second embodiment of the present invention, a gusset valve bag  210 . Valve bag  210  is similar to the previously described first embodiment of the present invention gusset bag  10 , with the exception of the presence of a valve portion similar to that found on conventional paper valve bags. In valve bag  210 , internal lap-sealed portion  224  (shaded portion) is a narrow sealed strip that lies adjacent to side center gusset crease  218  and spaced from internal flap edges  250 , but runs continuously only from bag bottom face  214  up to a point  256  where it stops. Valve opening  258  is the unsealed portion that lies along the center gusset crease  218  in between point  256  and bag top face  212 , and is suitable for allowing entry of a fill nozzle much like those used to fill standard paper valve bags. With valve opening  258  positioned at the center gusset crease, it is easy and natural for the user to find the valve opening  258  of bag  210  and mount it on a fill nozzle. In between lap-sealed portion  254  and valve opening  258 , and internal flap edges  250 , lie internal flap portions  260  that run continuously from bag top face  212  to bag bottom face  214 . Typically flap portions  260  may extend inward, inside bag  210 , about 5 cm to 7.5 cm depending on bag size, but could be more or less. Horizontal seal  264  begins at point  256  and runs approximately horizontally into internal flap portions  260 . The area in between horizontal seal  264  and sealed bag top  212  forms a valve sleeve  265 , which sleeve, along with valve opening  258 , typically measure about the same overall circumference, or slightly greater, as an existing prior art fill nozzle. Thus, valve opening  258  and valve sleeve  265  may be mounted onto a fill nozzle with a reasonably snug fit, preventing leakage as the bag is filled, and subsequently collapsing upon itself after filling, so that the flowable material contained inside will not leak out. In other respect, for instance the presence of openings in area  227 , the bag  210  is similar to bag  10  of the first embodiment. 
         [0079]      FIG. 17  shows a third embodiment of the present invention, multi-ply bag  310 . As can be seen in  FIG. 17 , bag  310  is of a 3-ply construction, having an outer layer  340 , an inner layer  342 , and an intermediate layer  341  therebetween. The bag  310  has front face  326  and a rear face  328 . The front face  326  has an outer layer  326   o  (being a portion of the outer layer  340 ), an intermediate layer  326   m  (being a portion of the intermediate layer  341 ) and an inner layer  326   i  (being a portion of the inner layer  342 ). Similarly, the rear face  328  has an outer layer  328   o  (being a portion of the outer layer  240 ), an intermediate layer  328   m  (being a portion of the intermediate layer  341 ) and an inner layer  328   i  (being a portion of the inner layer  342 ). 
         [0080]    The bag  310  also has a right side face  331  and a left side face  335 . The right side face  331  has an outer layer  331   o  (being a portion of the outer layer  340 ), an intermediate layer  331   m  (being a portion of the intermediate layer  341 ) and an inner layer  331   i  (being a portion of the inner layer  342 ). The right side face outer layer  331   o  is formed from a right side front gusset outer layer  330   o,  a right side rear gusset outer layer  332   o , and a right side center gusset crease  318 . The right side face intermediate layer  331   m  is formed from a right side front gusset intermediate layer  330   m , a right side rear gusset intermediate layer  332   m , and a right side center gusset crease  318 . The right side face inner layer  331   i  is formed from a right side front gusset inner layer  330   i , a right side rear gusset inner  332   i , and the right side center gusset crease  318 . The left side face  335  has an outer layer  335   o  (being a portion of the outer layer  340 ), an intermediate layer  335   m  (being a portion of the intermediate layer  341 ) and an inner layer  335   i  (being a portion of the inner layer  342 ). The left side face outer layer  335   o  is formed from a left side front gusset outer layer  334   o  and a left side rear gusset outer layer  336   o . The left side face intermediate layer  335   m  is formed from a left side front gusset intermediate layer  334   m  and a left side rear gusset intermediate layer  336   m . The left side face inner layer  335   i  is formed from a left side front gusset inner layer  334   i  and a left side rear gusset inner  336   i . (In  FIG. 17  the layers are shown as flat and lying together with no gap therebetween. This is the preferred state before the bag is filed. 
         [0081]    In between the right side center gusset crease  318  and internal flap edges  320  and  322  is internal lap-sealed portion  324 . The lap-sealed portion sealing the inner layer  342 , intermediate layer  341 , and outer layer  340  together. This lap-sealed portion may be a strip as narrow as 3 mm or may be wider. 
         [0082]    As shown in  FIG. 18 , when the bag  310  is filled and has air entrapped therein, the inner layer  342  and the intermediate layer  341  will separate from each other forming an inner filter chamber  344   i . Similarly the intermediate layer  341  and the outer layer  342  will separate from each other forming an outer filter chamber  344   o . Air will egress the bag by flowing from the interior into the inner filter chamber  344   i , then into the outer filter chamber  344   o , and finally to the environment.  FIG. 18  also shows the relative positioning of the openings  325   i  of the front face inner layer  326   i , the openings  325   m  of the front face intermediate layer  326   m , and the openings  325   o  of the front face outer layer  326   o . As can be seen, the openings  325   o  are offset from the openings  325   m  and the openings  325   m  are offset from the openings  325   i.    
         [0083]      FIG. 19  shows the relative size difference between the openings  325   i  of the inner layer  342 , the openings  325   m  of the intermediate layer  341 , and the openings  325   o  of the outer layer  340 . The openings  325   i  of the inner layer  342  are preferably irregularly-shaped slits being 500 microns long and 100 microns wide, being formed by slicing with a spinning blade. They preferably have an (outwardly) jagged edge  333   i  ( FIG. 18 ). The openings  325   o  of the outer layer  340  and the openings  325   m  of the intermediate layer  341  are preferably circular and have a diameter of between 20 and 100 microns (with openings  325   m  of the intermediate layer  341  being larger than those  325   o  of the outer lawyer  340 ), preferably being formed by needle perforation. They preferably have an (outwardly) smooth edge  333   o / 333   m . In this manner the inner filter chamber  344   i  and outer filer chamber  344   o  progressively filter air egressing the bag therethrough. 
         [0084]    In  FIG. 20 , There is shown a bag  400  (collapsed) of a 2-ply construction in accordance with a fourth embodiment. Bag  400  has a top face  402  and a bottom face  404 , a front face  401  and a rear face  403  (not shown) which is identical to the front face  401 , Bag also has right- and left side gussets  406  and  406 ′, respectively, with right- and left-side center gusset creases  408  and  408 ′ respectively. Bag  400  has an outer layer  410  and an inner layer  412  ( FIG. 21 ). The 2-ply nature of the bag  400  is not shown in  FIG. 20  for ease of understanding. The inner layer  412  of the bag  400  is micro-perforated with openings  414  having a diameter of between 20 and 100 microns, with 50 to 75 microns being the most preferred. The outer layer  410  is not perforated but includes four serrations. Each serration extending substantially the entire length of the bag  400  from the top face  402  to the bottom face  404 . Specifically, there is a first serration  416   a  extending the length of bag  400  on the right side of the front face  401 , a second serration  416   b  extending the length of bag  400  on the left side of the front face  401 , and two similarly positioned serrations on the right side and the left side of the rear face  403  of the bag  400 . 
         [0085]    Bag  400  is destined to be used in a food application, where a virtually impermeable (although not quite) outer layer  410  is required to prevent dust from entering into the bag  400  at all. Air evacuation is slower than previous embodiments since the inner layer  412  includes micro-openings  414  of between 20 and 100 microns and air can only evacuate through the serrations  416  of the outer layer  410 . The serrations  416  are preferably larger in size than the openings  414 . However, the openings  414  of the inner layer  412  could be larger than the serrations  416  for food products that are not powdery such as grains and flakes. 
         [0086]    The serrations  416  are designed so that the outer layer  410  can be removed just before the bag  400  is emptied. For example bags  400  is filled with a food product such as batter mix, then shipped to a user and stored. When the bag  400  is ready to be used, it is placed in a clean room where it is opened and the product is dumped into the batch mix. Just before going into the clean room, an operator rips the outer layer  410  of the front face  401  and the rear face  403  along a tear line including the serrations  416 , removes outer layer  410  from the bag and discards it. The bag  400  is now clean since the inner layer  412  remains and it was never exposed to the outside environment. The bag  400  is then brought into the clean room, cut open and the product is dispensed into an appropriate processor for processing. 
         [0087]    A bag  400  provided with outer layer  410  including serrations that allow removal of the outer layer  410  may be, for example, either an open-mouth bag which is sealed after being filled or a valve bag as previously described. 
         [0088]    Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims