Abstract:
A sheet material and construction method suitable for manufacturing boxes and other types of containment devices, and containers formed with such materials and methods. According to one aspect, the sheet material includes a kraft paper, a reflective film material laminated to a first surface of the kraft paper, a heat-activated first adhesive bonding the reflective film material to the kraft paper, a core material laminated to a second surface of the kraft paper opposite the first surface thereof, and a heat-activated second adhesive bonding the kraft paper to the core material. According to an additional aspect, a sheet material is configured to have certain geometric features that promote its conversion into a container, especially if constructed of the sheet material described above.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/222,501, filed Jul. 2, 2009, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention generally relates to boxes and various other types of containment devices, and more particularly to boxes suitable for transporting and/or handling temperature-sensitive and/or moisture-sensitive materials. 
         [0003]    Various types of boxes and containment devices have been developed for the purpose of transporting and handling temperature-sensitive and moisture-sensitive materials. Such boxes have been manufactured from sheet materials produced by lamination processes to have a reflective surface, which can then be converted by folding, gluing, etc., into a desired box configuration. The reflective surface may be a metallic film, for example, a low-emissivity film material joined to kraft paper with an adhesive. The manufacturing of such sheet materials and the construction of boxes from these materials can be difficult. As a particular example, adhesives used to bond the low-emissivity film material to the kraft paper have been prone to fail, resulting in sporadic product results in terms of the structural integrity of the boxes. Such previously unsuccessful attempts have indicated that different manufacturing processes, including modifications in the box configuration and the manufacture of the sheet material from which the box is converted, must be used to produce a viable product. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    The present invention provides a sheet material and construction method suitable for manufacturing boxes and other types of containment devices, and containers formed with such materials and methods. The sheet material is capable of being used to construct boxes in a variety of sizes and styles, and is particularly well suited for the transport or handling of temperature-sensitive and/or moisture-sensitive materials. 
         [0005]    According to a first aspect of the invention, the sheet material includes a kraft paper, a reflective film material laminated to a first surface of the kraft paper, a heat-activated first adhesive bonding the reflective film material to the kraft paper, a core material laminated to a second surface of the kraft paper opposite the first surface thereof, and a heat-activated second adhesive bonding the kraft paper to the core material. According to preferred aspects of the invention, the kraft paper has a grammage of about 60 to about 70 g/m 2 , the reflective film material comprises a metallized polyester film having a thickness of about 10 to about 15 micrometers, the first adhesive is a low-density polyethylene blended with ethylene methacrylic acid and is present on a weight basis of greater than 10 g/m 2  and less than 20 g/m 2 , the core material is a polystyrene foam having a thickness of about 4 to about 5 mm and a density of about 30 to 35 kg/m 3 , and the second adhesive is a polyester applied on a weight basis of greater than 10 g/m 2  and less than 20 g/m 2 . 
         [0006]    Other aspects of the invention include methods of producing containers (for example, boxes and other containment devices) from the sheet material described above, the containers formed thereby, and methods of using the containers. 
         [0007]    According to an additional aspect of the invention, a sheet material is configured to have certain geometric features that promote its conversion into a container, especially if constructed of the sheet material described above. 
         [0008]    Boxes, containers, and other containment devices constructed in accordance with this invention can be manufactured in a variety of sizes and styles for transporting and/or handling various different types of temperature- and/or moisture-sensitive materials, as well as for a variety of other applications. The invention is particularly well suited for the construction of boxes whose construction is capable of meeting various aesthetic objectives and/or whose use is capable of reducing the carbon footprint of shipping temperature- and moisture-sensitive materials. 
         [0009]    Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of a regular slotted carton (RSC) box that can be produced in accordance with an embodiment of this invention. 
           [0011]      FIG. 2  represents a plan view of a sheet material configured for constructing the box of  FIG. 1 . 
           [0012]      FIG. 3  schematically represents a cross-sectional view of the sheet material of  FIG. 2 . 
           [0013]      FIGS. 4 through 8  are detailed views of five regions in  FIG. 2  identified as  4  through  8 , and a comparison of these regions with prior art RSC boxes. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  represents a box  10  of a type that can be constructed from a blank of sheet material  20  represented in  FIG. 2 . The box  10  is represented as having the general configuration of an RSC box, characterized by an interior volume  12  defined by four side panels  14 A-D, four bottom flaps (not shown) that form the bottom  16  of the box  10 , and four top flaps  18 A-D that are adapted to be folded to enclose the interior volume  12 . To facilitate the descriptions of the box  10  and the sheet material  20  provided below, the terms “top,” “bottom,” “lateral,” etc., will be used in reference to the perspective of the orientation of the box  10  in  FIG. 1 , and therefore are relative terms and should not be otherwise interpreted as limitations to the construction and use of the box  10  or the sheet material  20 . 
         [0015]      FIG. 2  shows a surface  22  of the sheet material  20  that, when converted to form the box  10  of  FIG. 1 , defines the interior-facing surfaces surrounding the interior volume  12  of the box  10 . As evident from  FIG. 2 , the sheet material  20  has been cut, such as with a die, to define the panels of the box  10  in  FIG. 1 . In particular, the sheet material  20  comprises the four side panels  14 A-D, four bottom flaps  16 A-D that form the bottom  16  of the box  10 , and the four top flaps  18 A-D that define the closing flaps of the box  10 . An additional flap, referred to as a stitch tab  24 , extends from the side panel  14 D which, as evident from  FIG. 1 , enables the panel  14 D to be glued or otherwise attached to the side panel  14 A for closing the sides of the box  10 . The surface  22  of the sheet material  20  seen in  FIG. 2  is preferably reflective, such that thermal radiation emitted by the contents of the box  10  is reflected back into the interior volume  12  and its contents. For this purpose, the surface  22  of the sheet material  20  is defined by a reflective film material that exhibits low emissivity (preferably 0.05 or less). The film material is also preferably protected with a coating capable of inhibiting corrosion to maintain the high reflectance of the film material. 
         [0016]    The sheet material  20  is manufactured and configured in a manner that promotes more consistent results in terms of the structural integrity of the box  10  constructed (converted) from the sheet material  20 . In a preferred embodiment, the raw materials of the sheet material  20 , including the reflective film material and the substrate to which the film material is applied, are structured to promote the ability of the sheet material  20  to produce a box (such as the box  10  of  FIG. 1 ) and facilitate the process by which such a box can be made. The following describes raw materials and production processes that were determined to be optimal for consistently achieving desirable results. 
         [0017]    As represented in  FIG. 3 , the sheet material  20  generally comprises the reflective film material  26  laminated with an adhesive layer  28  to a kraft paper  30 , which in turn is bonded to a core material  32  with an adhesive  34 . The film material  26  preferably comprises a low-emissivity metallization  36  on a polymer film  38 . The core material  32  is preferably an extruded polystyrene (XPS) foam sheet, the metallization  36  is preferably aluminum, and the polymer film  38  is preferably a polyester material. Ultimately, various combinations of changes to the kraft paper  30 , core material  32 , adhesives  28  and  34 , polymer film  38  and lamination conditions were investigated prior to the eventual production of a durable box  10 . 
         [0018]    The following aspects of the invention were determined to particularly affect the propensity for failure of the adhesive bond between kraft papers and reflective film materials that were observed in the prior art. The weight of the kraft paper  30  was determined to affect the reliability of the adhesion between the kraft paper  30  and the reflective film material  26 , with lower-weight kraft paper  30  providing the greatest reliability. Furthermore, the reflective film material  26  was also determined to promote reliability of the bond if formed of a higher-blend metallized polyester, with a preferred material being metallized polyethylene terephthalate (MPET) film. Further optimization is achieved if the adhesive  28  is a heat-activated blend of a low-density polyethylene (LDPE) and ethylene methacrylic acid (EMAA), and the adhesive  34  is a heat-activated polyester (PE) blend. As discussed below, these particular materials for the adhesives  28  and  34  were determined to promote the lamination of the MPET film material  26  to the kraft paper  30  and then the subsequent lamination of the laminate to the polystyrene foam core material  32  at relative low temperatures and standard lamination speeds. 
         [0019]    Another challenge was to modify the extrusion and lamination processes for the core material  32  so that the lamination formed by the reflective film material  26  and kraft paper  30  could be laminated onto the core material  32 . For this purpose, the core material  32  was modified during the extrusion process to produce a relatively thin, low density polystyrene foam that promoted heat-activated adhesion of the lamination, which in turn facilitated the ability to laminate these materials at relatively low temperatures but at typical lamination speeds. 
         [0020]    The modifications mentioned above are described in more detail below, and evidence that a combination of specific characteristics for the above-noted variables was optimized to consistently produce a viable box product. 
         [0021]    Kraft paper having a basis weight of 40# (40 lbs/ream, or about 65 g/m 2 ), was found to be optimal for a viable box product (ream is used in its ordinary sense to mean a basis ream having a surface area of 3000 square feet). Kraft paper weights ranging from 15# to 50# (about 24 to about 81 g/m 2 ) were investigated by laminating reflective MPET films and extruded polystyrene foam materials. Paper weights below 40#, for example, 30# (about 49 g/m 2 ) and less, resulted in a less rigid product that promoted delamination between the paper and the MPET films. On the other hand, weights above 40#, for example, 50# (about 81 g/m 2 ) and higher, were determined to necessitate greater amounts of the adhesive  28  and higher temperatures during the lamination process, which was also determined to promote delamination between the kraft papers and MPET films, as well as cause heat marks on the finished lamination. On this basis, kraft paper  30  having a grammage of about 60 to about 70 g/m 2  is believed to be suitable. 
         [0022]    For the reflective film material  26 , an MPET film having a thickness of about 48 gauge (about 0.00048 inch; about 12 micrometers) as the polymer film  38  and bonded to the above-noted kraft paper  30  with LDPE blended with EMAA as the adhesive  28  was found to be optimal for producing a viable box product. During investigations, MPET films ranging from 30 gauge to 60 gauge (about 8 to about 15 micrometers) were tested by lamination to 40# kraft paper using LDPE adhesives applied at rates of about 5 to about 25 lbs/ream (about 8 to about 41 g/m 2 ) and having EMAA contents of about 5% to about 15% by weight. Lower gauge MPET films (below 48 gauge) were determined to have an adverse effect on the emissivity of the reflective film material  26 , whereas higher gauge MPET films (above 48 gauge) required greater amounts of adhesive, which during the lamination process tended to melt and then extrude from between the MPET film and kraft paper to promote delamination in addition to creating a mess. These problems were exacerbated with LDPE adhesives having a weight basis above and below 10 lbs/ream (about 16 g/m 2 ) and EMAA contents above and below about 9% by weight. On this basis, an MPET film having a thickness of about 12 micrometers, for example, about 10 to 15 micrometers, is believed to be suitable for the polymer film  38 . Furthermore, LDPE applied on a weight basis of about 10 lbs/ream (about 16 g/m 2 ), for example, greater than 10 g/m 2  and less than 20 g/m 2 , is believed to be suitable for the adhesive  28 , particularly if blended to contain about 9 weight percent EMAA. 
         [0023]    PE was found to be optimal as the adhesive  34  that adheres the above-noted kraft paper  30  to a polystyrene foam material. During investigations, PE applied at rates of about 5 to about 20 lbs/ream (about 8 to about 33 g/m 2 ) was tested between the 40# kraft paper and polystyrene foam material. Similar to the observations seen with the LDPE adhesive  28 , excessive melting, extrusion and delamination were observed with PE adhesives applied at rates above and below about 10 lbs/ream (about 16 g/m 2 ). On this basis, PE applied on a weight basis of about 10 lbs/ream (about 16 g/m 2 ), for example, greater than 10 g/m 2  and less than 20 g/m 2 , is believed to be suitable for the adhesive  34 . 
         [0024]    Lamination temperatures were also determined to be important. With the materials noted above for the reflective film material  26 , kraft paper  30  and adhesives  28  and  34 , a lamination temperature of about 400° F. (about 205° C.) was determined to be optimal following investigations employing multiple different temperatures in combination with various weights and types of adhesives used. Temperatures above 400° F. promoted excessive melting of the adhesives and delamination, and temperatures below 400° F. were determined to not provide sufficient heat to bond to a polystyrene foam material, thus promoting delamination during cooling. On this basis, lamination temperatures of greater than 375° F. and less than 425° F. (about 190 to about 220° C.) are believed to be suitable. 
         [0025]    Various thicknesses and densities were also investigated for the polystyrene foam core material  32 . The investigations determined that thicknesses below about 0.175 inch (about 4.5 mm) didn&#39;t provide the needed rigidity for the finished product, whereas thicknesses above 0.175 inch were too rigid for implementing a satisfactory box-making process, including bending of the foam core material  32 . In addition, foam densities of about 2.2 lbs/ft 3  to about 3.2 lbs/ft 3  (about 32 to about 51 kg/m 3 ) were investigated, by which it was determined that higher densities led to poorer control of foam thickness during the lamination process as a result of the higher temperatures necessary to achieve lamination, which caused the foam material to expand beyond the desired thickness. On this basis, extruded polystyrene foam having a thickness of about 0.175 inch (about 4.5 mm) and a density of about 2.2 lbs/ft 3  (about 32 kg/m 3 ) was concluded to be optimal, with a suitable thickness range believed to be about 4 to about 5 mm and a suitable density range of about 30 to 35 kg/m 3 . 
         [0026]    On the basis of the above, the resulting sheet material  20  can be described as a kraft paper  30  of a particular weight, laminated with a low-emissivity metallized polyethylene terephthalate (MPET) film material  26  using a heat-activated polyester-based adhesive  28 , which is then laminated onto a thin extruded low-density polystyrene foam core material  32  using a second heat-activated polyester-based adhesive  34 . Advantageously, this construction also allows for the fabrication of grooves and bends necessary to produce the box  10  of  FIG. 1  from the sheet material  20  of  FIG. 2 , as described below. 
         [0027]    For addressing the conversion of the sheet material  20  into a variety of box configurations, such as the box  10  of  FIG. 1 , a structural design was desired that would enable the box  10  to be manufactured on conventional converting equipment used in the corrugated packaging industry. The following features relating to the design (geometry) of the sheet material  20  were developed to enable the manufacture of an RSC box ( FIG. 1 ) that would be as close to airtight as possible after the conversion process. To do this, it was necessary to take into consideration the normal variations that would occur in the manufacturing operation, and then design the box  10  so that there would not be any openings around stitched joints or where the panels  14 A-D,  16 A-D and  18 A-D meet, including the top flaps  18 A-D that define the closing flaps of the box  10 . Specific features are described below and illustrated in the detailed views of  FIGS. 4 through 8  labeled as “Invention,” which are placed alongside corresponding detailed views of a blank of a “Prior Art” sheet material used to construct RSC boxes of the prior art. For convenience, consistent reference numbers are used throughout  FIGS. 4 through 8  to identify corresponding structures of the prior art sheet and the sheet material  20  of the invention, though differences between these materials will be evident from the figures and the following discussion. 
         [0028]    To reduce the gap normally found at the joint with an outside stitched box, the edge  40  of the panel  14 A between the bottom and top flaps  16 A and  18 A was offset by a distance d 1  of about 1/16 inch (about 1.5 mm) from the adjacent edges  42  of the flaps  16 A and  18 A. As more readily seen in  FIG. 4 , the offset  44  of the edge  40  preferably commences a distance d 2  from the flap score  46  between the side panel  14 A and top flap  18 A and terminates an equal distance from the flap score  48  between the side panel  14 A and bottom flap  16 A. This distance d 2  is preferably about ⅜ inch (about 10 mm). 
         [0029]    The offset distance d 1  shown in  FIG. 4  necessitated offsetting the stitch tab  24  from the adjacent edges  50  of the bottom and top flaps  16 D and  18 D, as shown in  FIG. 5 , so that the panels  14 A and  14  D and flaps  16 A,  16 D,  18 A and  18 D would properly meet and fold at their respective joints. The resulting extension  52  is identified by a distance d 3  in  FIG. 5 , and is greater than the offset distance d 1  of  FIG. 4 . This distance d 3  is preferably about ⅛ inch (about 3 mm). 
         [0030]    The Prior Art detailed view in  FIG. 6  shows conventional flap scores  46  and  54  separating two adjacent top flaps  18 B and  18 C from their adjacent side panels  14 B and  14 C, and the flaps  18 B and  18 C separated by a slot  58  that is collinear with a score  60  separating the panels  14 B and  14 C and terminates at the score  54 . As shown in  FIG. 6  and as also evident from  FIG. 2 , the scores  46  and  54  are offset a distance d 4  from each other so as not to be collinear in order to allow the top flaps  18 B and  18 C to compensate for the thickness of the sheet material as the flaps  18 B and  18 C are closed. As shown in  FIG. 2 , the scores  48  and  56  separating the bottom flaps  16 A and  16 B and top flaps  18 A and  18 B from their adjacent side panels  14 A and  14 B are similarly offset from each other for the same reason. In the detailed view showing the invention in  FIG. 6 , instead of terminating at the score  54 , the termination  62  of the slot  58  is located at the score  46 , which is nearer the distal edges of the flaps  18 B and  18 C than the more interior score  54 , so that when the flaps  18 B and  18 C are closed, their intersection point (coinciding with the termination  62 ) becomes a pinch point closing off the corners of the box  10 . 
         [0031]    To allow for scrap material to eject from a cutting die during the conversion process by which the box  10  is produced from the sheet material  20 , the tapers of the slots  58  were modified as shown in  FIG. 7 . In the Prior Art and Invention views of  FIG. 7 , a midline between the larger (major) and smaller (minor) flaps  18 B and  18 D is collinear with the panel scores  60 . In the Prior Art view, the taper distances d 5  from the midline to the lateral edges of the flaps  18 B and  18 D are equal. For the invention, a greater “offset” distance d 6  was provided for the larger flap  18 B, such that the lateral edge of the larger flap  18 B is farther from the midline than the lateral edge of the smaller flap  18 D. The same applies to each adjacent pair of larger flaps  16 A,  16 B,  18 A and  18 B and smaller flaps  16 C,  16 D,  18 C and  18 D. The benefit of this configuration is to avoid the creation of a gap along the edge of the smaller flap ( 18 D) as it is folded toward the inside of the box  10 . Exemplary values for these distances d 5  and d 6  are about 9/32 inch and about 7/32 inch (about 7 and about 5.5 mm), respectively. 
         [0032]    Unlike corrugated board conventionally used in the construction of boxes, the MPET/foam construction of the sheet material  20  has a resiliency after the scores  46 ,  48 ,  54 ,  56  and  60  are formed in the sheet material  20  with a cutting die. This resiliency resulted in the sheet material  20  being more difficult to fold for stitching. As represented in  FIG. 8 , the score  56  between the side panel  14 C and lower flap  16 C has a wider profile (for example, eight point) as compared to the narrower profile (for example, four point) of the prior art to reduce resiliency and improve folding. The wider profile is equally applicable to all of the scores  46 ,  48 ,  54 ,  56  and  60  in the sheet material  20 . 
         [0033]    As with corrugated board, allowances or an addition to dimensions are preferably added to compensate for sheet material  20  lost in the actual fold of the box  10 . In order to reduce the variation at the joint and create a tighter fit, the width of the panel  14 D from which the stitch tab  24  extends can be reduced to less than that of its opposing panel  14 C. This difference in width can be, for example, about 1/16 inch (about 1.5 mm). 
         [0034]    There are a variety of ways that changes might be made to produce variations of the sheet material  20  and box  10  described above, including the use of various other types of films and facers. For example, aluminum foil could be used in place of the metallization  36  of the reflective film material  26 , and a variety of other types of metallized plastic films and kraft paper could be used. In addition to extruded polystyrene foam, the core material  32  of the sheet material  20  could be made with, for example, expanded polystyrene, corrugated and/or fluted plastic, or standard corrugated kraft paper box material. Various box/container styles are also within the scope of the invention, including the RSC box  10  represented in  FIG. 1 , as well as mailers, catering boxes, FOL RSC boxes, CSSC RSC boxes, five panel folder boxes, lid style boxes, to-go boxes, and round catering boxes. 
         [0035]    In view of the above, while the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. Therefore, the scope of the invention is to be limited only by the following claims.