Patent Publication Number: US-2003232213-A1

Title: Multilayer storage container

Description:
CROSS REFERENCE TO RELATED APPLICATION  
     [0001] This claims the benefit under 35 U.S.C. §119(e) of U.S. provisional patent application Serial No. 60/382,757, filed May 23, 2002, the disclosure of which, in its entirety, is hereby incorporated herein by reference. 
    
    
     
       BACKGROUND  
       [0002] 1. Technical Field  
       [0003] The invention relates generally to reusable plastic storage containers. More specifically, the invention relates to reusable plastic storage containers having a multiple layer structure. Still more specifically, the invention relates to reusable plastic storage containers having a multiple layer structure including a middle layer disposed between inner and outer layers. The middle layer is designed to provide structural integrity and stacking strength to the container and, accordingly, is fabricated from a polymeric material having a high stiffness. Further, because impact strength is not important to the middle layer, the middle layer may be fabricated from a material having a low impact strength. In contrast, the inner and outer layers are not designed to provide structural integrity to the container and, accordingly, can be fabricated from polymeric materials having a relatively low stiffness. Further, because the inner and outer layers provide the aesthetic look and feel of the container, they should have a high impact strength so that they are resistant to cracking and shattering. Further, the inner and outer layers can be designed to provide a soft feel, which is preferred by consumers.  
       [0004] 2. Description of Related Art  
       [0005] Reusable storage containers are known. One common type of reusable storage containers is fabricated from molded plastic in the form of an open-top box with a molded plastic lid. Such containers come in a variety of styles and colors.  
       [0006] One problem associated with currently available reusable storage containers relates to their single layer or single polymeric component structure. Specifically, it is desirable that the inner and outer surfaces of a reusable polymeric storage container be resistant to cracking and shattering (i.e., have high impact strength) so that they provide an appropriate aesthetic appearance, which is desired by consumers. However, reusable storage containers must also have sufficient structural integrity. Therefore, the single material chosen to fabricate the container must possess a high stiffness coefficient or characteristic in addition to high impact strength.  
       [0007] The problem arises from the competing characteristics of high impact strength and high stiffness. Specifically, commodity materials, such as polyethylenes, polypropylenes and polystyrenes, typically meet only one of these criteria. For example, low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) are noted for their high impact strength, but these materials do not provide sufficient stiffness at moderate thicknesses. Consequently, if these high impact strength commodity materials are used to manufacture reusable storage containers, the container must be fabricated with a sufficient thickness to provide the requisite stiffness or structural integrity, which increases the container weight and cost of fabrication. Accordingly, such single layer containers comprising high impact strength commodity material are undesirable because consumers prefer a low cost, lightweight container.  
       [0008] Commodity polymeric materials that provide high stiffness such as high density polyethylene (HDPE) can be used to fabricate reusable storage containers with a relatively thin wall thickness, which results in a low cost, lightweight container. However, high stiffness commodity materials are susceptible to scratching and cracking. Further, high stiffness commodity materials such as high density polyethylene have a relatively hard feel. Accordingly, such single layer containers comprising high stiffness commodity materials are undesirable because consumers prefer aesthetically appealing containers (that do not scratch or crack easily) having a soft feel.  
       [0009] To solve the problem of the competing requirements of high impact strength/soft feel and high stiffness, the use of high performance engineering resins such as nylons and polycarbonates has been proposed. However, the material costs of high performance resins are substantially higher than the various polyethylenes, polypropylenes, and polystyrenes that are readily available and known as “commodity” resins. Thus, the use of high performance engineering resins would substantially increase the cost of a reusable storage container, which would adversely affect the price point and competitiveness of such a product.  
       SUMMARY OF THE DISCLOSURE  
       [0010] An economical, reusable, three-dimensional storage container is disclosed.  
       [0011] In one refinement of the disclosed container, the container comprises a middle layer comprising a polymeric material selected from the group consisting of high density polyethylenes, high density polyethylenes filled with calcium carbonate, polypropylenes, filled polypropylenes, polyethyleneterepthalates, polyvinylchlorides, polycarbonates, and mixtures thereof. The container further comprises inner and outer layers which are tied to opposing sides of the middle layer. The inner and outer layers may be the same or different polymeric materials selected from the group consisting of low density polyethylenes, linear low density polyethylenes, polyolefin plastomers, polyolefin elastomers, thermoplastic elastomers, thermoplastic rubbers, thermoplastic vulcanizates, ethylene vinyl acetate copolymers, and mixtures thereof.  
       [0012] In a further refinement, the inner, middle, and outer layers are coextruded and blow molded.  
       [0013] In another refinement, one or both of the inner and outer layers further comprises a colorant.  
       [0014] In yet another refinement, the middle layer is thicker than either the inner or outer layers. In a further refinement, a ratio of the thickness of the middle layer to a combined thickness of the inner and outer layers ranges from about 1:1 to about 4:1.  
       [0015] In still a further refinement, the disclosed container is formed by co-extrusion blow molding using separate parisons for the inner, middle, and outer layers.  
       [0016] In yet a further refinement, the middle layer may comprise scrap polymeric material from the inner and outer layers. Specifically, scrap material from a co-extrusion blow molding process used to form the container can be recycled back into the middle layer. Obviously, scrap material from the middle layer may be used in the middle layer of a successive container. Additionally, scrap material from the inner and outer layers, although different polymeric material than the middle layer, can be blended with the material of the middle layer and used to fabricate a middle layer of another container.  
       [0017] An economical, reusable, three-dimensional storage container is disclosed which includes three layers, including a middle layer comprising a commodity polymeric material having a high stiffness characteristic. The polymeric material of the middle layer does not need superior high impact strength characteristics because it is disposed between inner and outer layers. In contrast, the inner and outer layers are fabricated from a commodity polymeric material having high impact strength characteristics. The inner and outer layers are thinner than the middle layer, and therefore, do not supply a great proportion of the structural integrity of the container. Thus, the inner and outer layers can be fabricated from a commodity polymeric material with a high impact strength characteristic, but a low stiffness characteristic.  
       [0018] In a further refinement, the inner and outer layers can be specifically fabricated from a commodity polymeric material having good impact strength, but low stiffness, which thereby provides the inner and outer layers with a soft feel desired by consumers. To satisfy this criterion, low density polyethylenes, linear low density polyethylenes, polyolefin plastomesr, polyolefin elastomers, thermoplastic elastomers, thermoplastic rubbers, thermoplastic vulcanizates, ethylene vinyl acetate copolymers, and mixtures thereof can be used for the inner and outer layers. To provide the needed structural integrity, the middle layer should be fabricated from a commodity polymeric material with a high stiffness characteristic such as high density polyethylenes, high polyethylenes filled with carbonate, polypropylenes, filled polypropylenes, polyethyleneterepthalates, polyvinylchlorides, polycarbonates, and mixtures thereof.  
       [0019] The container and a top or lid for the container can be fabricated in accordance with the three-layer structures described above. One method of fabrication is a co-extrusion blow molding process. However, the three-layer structure may be provided in a sheet form, and subsequently molded into the three-dimensional container and/or lid.  
       [0020] The outer layers may be colored or, in the alternative, the middle layer may be colored with the outer layers uncolored for certain visual effects. Additional layers may be added depending upon performance requirements. A clear “view strip” may be incorporated to enable the consumer to see inside the container.  
       [0021] The disclosed containers may be fabricated using a co-injection molding process, whereby an injection mold is used to form the container and/or lid and the materials are co-injected into the mold to form separate skins. Also, the container and/or lid can be fabricated using an overmolding process, whereby one of the layers is molded first and the other layers are molded over the previously molded structure. Conventional injection molding and thermal molding may also be utilized. Further, injection molding and blow molding techniques may be combined by injection molding a preform, which is transferred to a blow mold, and inflated to form an outer structure with inner structures or layers blown into the outer structure. The process can be repeated to form as many layers as desired.  
       [0022] Other advantages of the disclosed container and methods will be apparent to those skilled in the art from a review of the following figures and detailed description taken in conjunction with the appended claims. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023] The disclosed container is described diagrammatically in the following drawings wherein:  
     [0024]FIG. 1 is a sectional view of a multilayer material used to fabricate a reusable storage container made in accordance with the disclosure;  
     [0025]FIG. 2 is a front sectional view of a reusable storage container and lid combination made in accordance with the disclosure;  
     [0026]FIG. 3 is an end sectional view of the container shown in FIG. 2;  
     [0027]FIG. 4 is an enlarged partial end view of the container shown in FIG. 2;  
     [0028]FIG. 5 is a top plan view of the container shown in FIG. 2 with the lid removed;  
     [0029]FIG. 6 is a perspective view of the container shown in FIG. 2 with the lid removed;  
     [0030]FIG. 7 is a front sectional view of two reusable storage containers as shown in FIG. 3 stacked one on top of another; and  
     [0031]FIG. 8 is sectional view of three parisons used to fabricate a reusable container in accordance with the disclosure.  
     [0032] The drawings are not necessarily to scale and the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations, and fragmentary views. In certain instances, details which are not necessary for an understanding of the disclosed containers or which may render other details difficult to perceive may have been omitted. It should be understood, of course, that the disclosure and the claims are not necessarily limited to the particular embodiments illustrated herein. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS  
     [0033] An economical, reusable three-dimensional container is provided with inner and outer layers having high impact strength yet a soft feel and a middle layer with a high stiffness, for structural integrity. The disclosed container has the desired characteristics of crack resistance, scratch resistance, shatter resistance, and soft feel on the inner and outer surfaces yet superior structural integrity due to the use of a thicker middle layer, all without resorting to the use of high performance engineering resins such as polycarbonates or nylons which, would substantially increase the cost of the product. Instead, commodity materials such as polypropylenes, polyethylenes, and other low cost commodity polymers can be employed.  
     [0034]FIG. 1 illustrates a three-layer structure including a first layer  20  tied to a second layer  21  and a third layer  22  tied to the first layer  20  opposite the second layer  21 . For sake of clarity, the layer  20  will be referred to as the middle layer  20 , the layer  21  will be referred to as the inner layer  21 , and the layer  22  will be referred to as the outer layer  22 . The middle layer  20 , in a preferred embodiment, provides the structural integrity of the resulting container  25  (see FIG. 2). Thus, the middle layer  20  should be fabricated from a commodity resin with a high stiffness characteristic. Because the middle layer  20  is disposed between the inner layer  21  and outer layer  22 , high impact resistance is not essential for the middle layer  20  of this embodiment. Thus, while the resin or polymer used for the layer  20  should have a high stiffness characteristic, it can have a low impact strength characteristic. Suitable resins include, but are not limited to, high density polyethylene (HDPE), filled high density polyethylenes (HDPE), such as, for example, high density polyethylene filled with calcium carbonate, polypropylenes, filled polypropylenes, polyethyleneterepthalates, polyvinylchlorides, polystyrenes, polycarbonates, and mixtures thereof. HDPE and HDPE filled with calcium carbonate are preferred due to their low cost.  
     [0035] In contrast to the middle layer  20 , the inner and outer layers  21 ,  22  should provide good impact resistance qualities to prevent cracking, shattering, and scratch resistance. Suitable polymers include, but are not limited to, low density polyethylenes (LDPE), linear low density polyethylenes (LLDPE), polyolefin plastomers, polyolefin elastomers, thermoplastic elastomers (TPE), thermoplastic rubbers (TPR), thermoplastic vulcanizates (TPV), ethylene vinyl acetate copolymers, and mixtures thereof. Low density polyethylenes and linear low density polyethylenes are especially preferred because they provide a desirable soft feel to the inner and outer surfaces, which are engaged by the user.  
     [0036] Suitable colorants for the outer and inner layers  21 ,  22  include, but are not limited to, various organic and inorganic pigments dispersed in a polyolefin carrier. In the alternative, the middle layer  20  can be colored and the inner and outer layers  21 ,  22  left uncolored for a specific visual effect. Further, to reduce the weight of the overall structure formed, foaming agents can be used in the middle layer  20 . Suitable foaming agents include, but are not limited to, citric acid mixed with sodium bicarbonate. In addition, fillers may be added to the thicker middle layer  20  to reduce the cooling time of the molded part. One preferred filler is calcium carbonate. Other suitable fillers include, but are not limited to, talc, barium sulfate, mica, glass, clay, titanium dioxide, dolomite, wood flower, and flax.  
     [0037] Other functional properties may be incorporated into the inner and outer layers  22 ,  21 , such as stain resistance. If stain resistance is desired for either layer  22 ,  21 , the layers should incorporate a stain-resistant resin including, but not limited to, polysulphones, polymethylpentenes, polycarbonates, polyetherimides, nylons, polyacrylates, polyphenylsulphides, polyphenylene oxides, polyethersulphones, polyethyleneterephtalates, aromatic polyketones, liquid crystal polymers, and mixtures thereof.  
     [0038] Further, fragrance can be added to any of the layers  20 - 22 . Suitable fragrance include various fragrance oils dispersed in a polyolefin carrier. Further, odor fighting additives, such as sodium bicarbonate can be added to one or more of the resins utilized. Still further, a foaming agent may be incorporated into at least the middle layer  20 , and optionally into the outer layers  21 ,  22 , to increase the insulating properties of the resulting container. Also, an anti-microbial agent can be used in any of the layers  20 - 22 , preferably, the inner layer  22 .  
     [0039] In the alternative, the function of the middle layer  20  and inner and outer layers  21 ,  22  can be reversed. That is, the high stiffness characteristic can be incorporated into the inner and outer layers  21 ,  22 , and the impact resistance characteristic can reside in the middle layer  20 .  
     [0040]FIG. 2 is a partial elevational/sectional view of a container  25  that can be fabricated from the three-layer structure of FIG. 1. Container  25  includes a lid  26  secured to an open-top container  27 . Container  27  includes bottom panel  28  disposed between and connected to opposing end panels  29 ,  31  as well as side panels  32 ,  33  (see also FIG. 6). The container portion  27  typically includes handles  30 ,  34 . To enhance sealing, the handles  30 ,  34  may include a bead  35 ,  36  around which a lip  37 ,  38  of the lid  26  is secured to provide a secure engagement. The side panels  32 ,  33  may also include recessed sections  41 - 44  (see also FIG. 6). The recess sections  41 - 44  enhance the structural integrity of the container  27 . Further, as discussed below with respect to FIG. 8, the recess sections  41 - 44  may also serve as a transparent window to make it easy for the consumer to view the contents of the container  27 . Similarly, as shown in FIGS. 3 and 6, the end panels  29 ,  31  may also include recesses  45 ,  46 . As shown in FIG. 7, the recesses  41 - 46  also enhance the stackability of two light container portions  27   a,    27   b.    
     [0041] Turning to FIG. 8, a preferred method for fabricating the reusable containers disclosed above is a co-extrusion blow molding process. In such a process, a parison  60  as shown in FIG. 8 is co-extruded so that it has an inner layer  20  and outer layers  21 ,  22  (see FIG. 1). The parison  60  may then be blow molded into a three dimensional article such as the container portion  27  or lid portion  26  of the container assembly  25  shown in FIG. 2. In the embodiment shown in FIG. 8, clear resins are provided at  61 ,  62  to provide a window at one of the recesses  41 - 46  of either the side panels  32 ,  33  or end panels  29 ,  31 , as shown in FIGS. 2, 3, and  6 - 7 .  
     [0042] The thickness of the layers  20 - 22  can vary, depending upon the embodiment. Preferably, the thickness of the layer  20  is at least twice as thick as the layer  21  in a two layer structure or the layer  20  is at least twice as thick as the combined thicknesses of the layers  21 ,  22  in a three-layer structure. Suitable ratios of the thickness of the layer  20  to the combined thicknesses of the layers  21 ,  22  can range from about 1:1 to about 4:1, and more preferably, from about 3:2 to about 4:1.  
     [0043] As noted above, a preferred way to fabricate the container  25  is using a co-extrusion blow molding process with the parison  60  shown in FIG. 8. As the mold closes, capturing the parisons, the parisons are inflated with air to form either the container portion  27  or top portion  26 . Once the part  27  or  26  is formed, the resulting part wall structure is a sandwich of the three layers  21 ,  20 ,  22 . The same process can be used to form more or fewer layers based upon the desired physical requirements. Also, scrap from the co-extrusion blow molding process may be recycled into the middle layer  20  or whichever layer is the thicker of the three layers. Thus, the middle layer  20  or the thicker layer may include scrap material from the thinner layers  21 ,  22 . Such a recycling step, of course, reduces manufacturing costs, and waste.  
     [0044] In addition to the co-extrusion blow molding process described above, a co-injection molding process can be employed whereby an injection mold is used to form the part  26 ,  27  and two or more, preferably three, materials are injected into the mold to form separate skins.  
     [0045] The multilayer parts  26 ,  27  can also be fabricated using an overmolding process wherein one layer is injection molded and then transferred to a separate mold where another material layer is then injected over the originally molded layer. The process is repeated for the number of layers desired. Adhesives may be required between the layers if this process is employed.  
     [0046] In addition, the three-layer structure illustrated in FIG. 1 can be provided in sheet form and then thermally formed to provide part  26  and/or  27 .  
     [0047] Further, combinations of injection molding and blow molding techniques can be employed. For example, an injection molded preform could be transferred to a blow mold, and inflated to form an outer layer of the part  26 ,  27 , before a second preform is transferred to the same mold and inflated inside the previously molded layer to form an inner or middle layer. The process is then repeated for the number of layers desired.  
     [0048] The foregoing detailed description is given for clearness of understanding only, and no unnecessary limitation should be understood therefrom, as modifications within the scope of the invention may become apparent to those skilled in the art.