Abstract:
A substantially paper-based composite container for an off-gassing product includes a paperboard can body having a substantially gas-impervious liner attached to an inner surface thereof, and a pair of substantially paper-based end closures attached to the opposite ends of the can body, each end closure defining a generally cylindrical sealing panel in contact with an inner surface of the can body. Heat-sealable materials are disposed on opposing surfaces of the sealing panel and can body. The sealing panels of the end closures are attached to the can body by heat seals. The heat seal for at least one of the end closures is discontinuous such that at least one vent channel extends through the heat seal so as to establish fluid communication between an interior of the composite container and the environment outside the composite container. The at least one vent channel is operable to vent excess gas pressure from the interior of the container.

Description:
BACKGROUND OF THE INVENTION 
     The present disclosure relates generally to containers for products, and more particularly relates to paper-based composite containers for off-gassing products. 
     Paper-based composite containers for off-gassing products (e.g., refrigerated dough) have been in the marketplace for many years. A typical dough can has a can body formed of a paperboard body ply wrapped helically about an axis such that a butt joint is defined between the adjacent edges of successive helical turns of the body ply. An impervious liner is attached to the inner surface of the body ply, and a peelable label is attached to the outer surface of the body ply. The label holds the butt joint closed until the consumer is ready to open the container. The ends of the can body are closed by metal end closures that are seamed onto the ends of the can body. To open the container, the label is peeled off to expose the butt joint. Often, the pressure of the expanded dough in the container is sufficient to open the butt joint once the label is removed. Otherwise, the butt joint is pressed or rapped against an edge of a countertop to cause it to open. The dough product is removed through the opening created by the separated butt joint. 
     Paper-based composite containers for other off-gassing products (e.g., roasted coffee) may also be desirable as alternatives to metal-based and plastic-based containers. 
     Generally, containers for off-gassing products require some type of provision for dealing with the pressure increase that occurs in the container when the products give off gases. Various approaches to this problem have been tried. Some containers include vents to vent the excess gases to the outside of the container, so that the container will not become bulged or distorted by the internal gas pressure. Other containers are designed to have portions that can expand outwardly to reduce the internal pressure, but in a manner that is not aesthetically displeasing. 
     Heretofore, commercial composite dough containers have employed the venting approach. In some cases, the metal end closures have been seamed onto the can body in such a way that a vent passage is defined between the end closures and the can body. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The present disclosure relates to paper-based composite containers for off-gassing products, in which the end closures are not metal but rather are paper-based. Paper-based end closures are not readily attachable to the can body by the seaming technique used with metal end closures, and hence a new approach to their attachment had to be developed. The attachment technique described herein allows secure attachment of the end closures in a hermetic fashion, while also providing a venting function. 
     In one embodiment described herein, a substantially paper-based composite container for an off-gassing product comprises: a can body comprising a tubular wall constructed from paperboard wrapped about an axis, the can body having opposite ends each defining an opening, the can body further comprising a substantially gas-impervious liner attached to an inner surface of the paperboard of the can body; and a pair of substantially paper-based end closures attached to the opposite ends of the can body, each end closure defining a generally cylindrical sealing panel in contact with a surface of the can body, a heat seal material being disposed on a surface of the sealing panel and a heat seal material being disposed on the surface of the can body contacted by the sealing panel. 
     The sealing panels of the end closures are attached to the can body by heat seals. The heat seal for at least one of the end closures is discontinuous such that at least one vent channel extends through the heat seal so as to establish fluid communication between an interior of the composite container and the environment outside the composite container. The at least one vent channel is operable to vent excess gas pressure from the interior of the container. 
     In embodiments described herein, the heat seal having the at least one vent channel is formed by a plurality of separate, spaced heat seal regions where the heat seal materials on the sealing panel and can body have been heat sealed together, thereby forming the at least one vent channel between the spaced heat seal regions. 
     The spaced heat seal regions can be spaced apart in a circumferential direction about the can body, the at least one vent channel extending generally axially of the can body. 
     There can be a plurality of vent channels circumferentially spaced apart. 
     In a specific embodiment suitable for dough containers, the paperboard of the can body is wrapped helically about the axis and a helically extending butt joint is defined in the can body between adjacent edges of successive helical turns of the paperboard. The container includes a label secured about an outer surface of the paperboard of the can body, the label comprising a polymer film. The label is scored to define a helically extending peel strip that is located over the helically extending butt joint. The peel strip is removable from the can body to expose the butt joint while leaving the remainder of the label on the can body. 
     In embodiments described herein, the end closures comprise a paperboard layer and a barrier layer. The barrier layer can comprise at least one of polymer film and metal foil. 
     The present disclosure also describes a method for assembling a composite container for an off-gassing product. In one embodiment, the method comprises the steps of providing a can body and a pair of substantially paper-based end closures of the type described above, and positioning the end closures over the openings at the ends of the can body and attaching the sealing panels of the end closures to the can body by forming heat seals therebetween. The heat seal for at least one of the end closures is formed to be discontinuous such that at least one vent channel extends through the heat seal so as to establish fluid communication between an interior of the composite container and the environment outside the composite container, the at least one vent channel being operable to vent excess gas pressure from the interior of the container. 
     In one embodiment, the heat seal having the at least one vent channel is formed by a plurality of separate, spaced sealing elements that are heated so as to heat and soften the heat seal materials on the sealing panel and can body at a plurality of separate, spaced regions, thereby forming the at least one vent channel between the spaced regions. 
     The sealing elements can be part of an expandable chuck. In this case, the heat seal can be formed by the steps of: placing the chuck in an unexpanded condition within the opening at the respective end of the can body, the sealing panel of the end closure being located between the tubular wall of the can body and the chuck; disposing a support ring about the end of the can body, such that the tubular wall of the can body and the sealing panel of the end closure are disposed between the support ring and the chuck; and heating the sealing elements of the chuck and expanding the chuck by moving the sealing elements radially outwardly to compress the sealing panel and tubular wall of the can body between the sealing elements and the support ring, the heated sealing elements causing the heat seal materials on the sealing panel and can body to be softened and to seal together at the spaced regions. 
     In embodiments described herein, between two and ten sealing elements are moved radially outwardly to compress the sealing panel and tubular wall of the can body between the sealing elements and the support ring, thereby forming the heat seal to have between two and ten spaced regions. More preferably, there are between four and eight sealing elements. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  is a perspective view of a heat-sealing tool, generally from below, for heat-sealing a substantially paper-based end closure to a paperboard can body in accordance with one embodiment of the present invention; 
         FIG. 1A  is an end view of the heat-sealing tool of  FIG. 1 , from below, showing the sealing chuck of the tool in a retracted (unexpanded) condition; 
         FIG. 1B  is an end view of the heating-sealing tool, from below, showing the sealing chuck in an extended (expanded) condition; 
         FIG. 2  is a side view of the heat-sealing tool positioned above an assembly of a paperboard can body and substantially paper-based end closure, in preparation for heat-sealing the end closure to the can body; 
         FIG. 3  is a highly magnified detail view of a portion of  FIG. 2  as indicated; 
         FIG. 4  is a side view of the heat-sealing tool and the can body/end closure assembly, after the heat-sealing tool has been lowered into engagement with the can body/end closure assembly and the sealing chuck has been extended to expand the chuck and heat-seal the end closure to the can body; 
         FIG. 5  is a highly magnified detail view to illustrate the engagement of the can body and end closure between the expanded sealing chuck and the outer support ring of the heat-sealing tool; 
         FIG. 6  is a cross-sectional view along line  6 - 6  in  FIG. 4 ; 
         FIG. 7  is a highly magnified detail view of a portion of  FIG. 6  as indicated; 
         FIG. 8  is a cross-sectional view through the can body and end closure of the completed container after the end closure has been heat-sealed to the can body; and 
         FIG. 9  is a highly magnified detail view of a portion of  FIG. 8  as indicated. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings in which some but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
       FIGS. 1, 1A, and 1B  depict a heat-sealing tool  20  for use in heating sealing a substantially paper-based end closure to a paperboard can body in accordance with the present invention. The tool  20  includes an outer support ring  22  defining a central opening whose diameter is approximately equal to (or very slightly less than) the sum of the diameter of the paperboard can body and twice the thickness of the end closure, for reasons that will be made apparent below. The inner surface  24  of the support ring defines six longitudinally extending grooves  26  spaced uniformly about the circumference of the inner surface  24 . The inner surface  24  also has a conical or flared portion  24   a  ( FIG. 3 ) adjacent the lower end face  28  of the support ring  22  to help guide the can body and end closure into the central opening of the support ring during a heat-sealing operation, as further described below. 
     The heat-sealing tool  20  further includes an expandable and contractible sealing chuck  30  that consists of six wedge-shaped segments  32  each forming one-sixth)(60° of a 360° disk, such that the six segments  32  collectively form the 360° disk. Each segment  32  has two radially extending side edges  34  that are linear and a radially outer edge  36  that is part-cylindrical (i.e., one-sixth, or 60°, of a cylinder). The segments  32  are sized in outside diameter such that when the segments have their adjacent side edges  34  abutting each other (as in  FIG. 1A ), the radially outer edges  36  of the segments define a substantially cylindrical surface having an outside diameter that is slightly smaller than the inside diameter of a paperboard can body to be processed by the heat-sealing tool. 
     The tool  20  includes an arrangement for moving the segments  32  radially outwardly in unison so as to increase the outside diameter of the substantially cylindrical surface that the segments collectively form. In the illustrated tool  20 , this arrangement comprises a longitudinally movable ram  40  connected at its lower end to a cam arrangement (not visible in the drawings) that engages cam surfaces on the segments  32 . The ram  40  passes down the center of a hollow guide tube  42  affixed at its lower end to the support ring  22 . Moving the ram  40  downward relative to the segments  32  causes the cam arrangement to urge the segments  32  radially outwardly. The tool  20  also includes an upper plate  44  rigidly connected by connecting members  46  to the support ring  22 , and has means (not shown) for urging the upper plate  44 , and therefore the support ring  22 , downward independently of the movement of the ram  40 , for reasons that will be made apparent below. 
     Turning to  FIGS. 2 through 5 , a heat-sealing operation employing the tool  20  is now described.  FIGS. 2 and 3  depict the tool  20  positioned atop an assembly consisting of a paperboard can body  50  and a substantially paper-based end closure  60 . The can body  50  has a cylindrical or tubular form and is open at both ends. The can body  50  is formed substantially of paperboard and includes a heat-sealable material on its inner surface. The heat-sealable material can be part of a gas-impervious liner  52  attached to an inner surface of a tubular wall  54  ( FIG. 7 ) constructed from paperboard wrapped helically or convolutely about an axis of the tube. The end closure  60  can comprise a laminate of multiple layers, including a heat-sealable layer  62  and a paper layer  64  ( FIG. 7 ). The end closure  60  is formed (preferably prior to placing it atop the can body  50 ) so that it has a disk-shaped central portion  66 , a cylindrical sealing panel  67  that extends upwardly from the central portion and is sized to fit closely into the top end of the can body  50 , and an outer peripheral portion  68  that extends radially outwardly from the top end of the sealing panel  67  for a distance sufficient to provide enough material to be wiped down the outer surface of the top end of the can body  50 . 
     As shown in  FIG. 3 , the heat-sealing tool  20  initially is in a starting position in which the sealing chuck  30  is in its retracted (contracted) state and has its lower surface closely adjacent or abutting the top surface of the central portion  66  of the end closure. The tool  20  as a whole can be lowered, or the can body  50  and end closure  60  assembly can be raised relative to the tool  20 , to cause the contracted sealing chuck  30  to push the central portion  66  of the end closure down into the top end of the can body  50  until the outer peripheral portion  68  is abutting or nearly abutting the top edge of the can body  50 . In this condition, the support ring  22  of the tool  20  is in a raised position slightly spaced above the top edge of the can body  50  and the outer peripheral portion  68  of the end closure  60  as shown in  FIG. 3 . 
       FIGS. 4 and 5  illustrate the next step of the heat-sealing operation. The support ring  22  is moved downward so that the upper end of the can body  50  is received inside the central opening of the support ring, in the radial space between the inner surface  24  of the support ring and the outer surface of the sealing chuck  30 . Substantially concurrently, the ram  40  is moved downward to cause the sealing chuck  30  to be expanded in diameter so that the end closure&#39;s sealing panel  67 , the can body  50 , and the outer peripheral portion  68  of the end closure are radially compressed between the expanded chuck  30  and the support ring  22 . The sealing chuck  30  and the support ring  22  are heated sufficiently to cause softening or melting of the heat-sealable materials on the can body  50  and end closure  60 . Specifically, with reference to  FIG. 7 , the heat-sealable layer  52  on the can body and the heat-sealable layer  62  on the end closure  60  are softened or melted and fuse together (note: layers  52  and  62  are shown with spacing between them in  FIG. 7 , for clarity of illustration; in reality they are in contact with each other). The heating is then discontinued and the support ring  22  and ram  40  are retracted and the finished can/end closure assembly is removed from the tool  20  to complete the heat-sealing operation. An end closure can be attached to the opposite end of the can body in the same fashion as just described. 
     The tool  20  produces unique features in the completed can/end closure assembly, which are now described with reference to  FIGS. 6 through 9 . In particular, because there are circumferential gaps between adjacent segments  32  of the expanded sealing chuck (as best seen in  FIG. 1B ), the heated segments  32  produce spaced heat seal regions where the heat seal materials on the sealing panel  67  and can body  50  have been heat sealed together. The spaces between those heat seal regions are areas where the sealing panel  67  of the end closure is not heat-sealed to the can body  50 , since the heat-sealable layers  52 ,  62  of these components are not heated and fused together in these areas. The result, as seen in  FIGS. 7 and 9 , is a series of channels  70  between the sealing panel  67  and the can body  50 . These channels  70  act as vents that can allow excess gas pressure inside the container to be vented to the outside of the container. It should be noted that  FIGS. 7 and 9  depict the channels  70  as being open radial spaces, but this is mainly for clarity of illustration. In reality, the sealing panel  67  and can body  50  may contact each other in the region of the channels  70 , but are not sealed or otherwise attached together in the channels  70 , which is what allows excess gas pressure to escape through the channels. 
     This venting action is also aided by similar channels  72  defined between the outer peripheral portion  68  of the end closure and the outer surface of the can body  50 . The channels  72  are formed as a result of the grooves  26  in the inner surface of the support ring  22 , which are aligned with the gaps between sealing chuck segments  32  and allow the outer peripheral portion  68  of the end closure in the regions of the grooves to “flow” outwardly into the grooves. The channels  70  on the inner side of the can body can communicate with the channels  72  on the outer side because the end closure is not sealed to the very top edge of the can body, as best seen in  FIG. 5 . 
     A container assembled in accordance with the foregoing description can be used for containing a product that off-gases or causes increasing pressure within the container, such as refrigerated dough or roasted coffee. Excess pressure in the container is vented through the channels. The threshold pressure at which venting will occur can be controlled by suitably designing the number and sizes of the gaps between sealing chuck segments  32  and correspondingly the number and sizes of the grooves  26  in the support ring  22 , thereby controlling the number and dimensions of the channels  70 ,  72 . 
     As one non-limiting example, the sealing panel  67  can have a thickness of about 0.015″ to about 0.020″, and a circumference of about 9.5″. The collective circumferential width of the channels  70  (i.e., the sum of the circumferential widths of all channels) can be about 0.095″ to about 1.5″, or on a percentage basis, about 1% to about 16% of the circumference of the sealing panel. The collective circumferential width more preferably ranges from about 2% to about 10%, and still more preferably about 4% to about 6% of the circumference. As one example, there can be six channels  70  each 0.060″ in circumferential width, for a collective circumferential width of 0.36″, or 3.8% of the circumference. It will be understood that the circumferential widths of the channels  70  correspond to the circumferential widths of the gaps between sealing segments  32  at the radially outer surface  36  of the sealing chuck  30 , and the circumference of the sealing panel  67  is substantially equal to the circumference of the outer surface  36  of the sealing chuck  30 . Thus, another way of specifying the preferred channel/gap widths is to require that the collective circumferential width of the gaps between segments  32  at the radially outer surface  36  of the sealing chuck  30  ranges from about 1% to about 16% (more preferably about 2% to about 10%, and still more preferably about 4% to about 6%) of the circumference of the outer surface  36 . 
     Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.