Patent Publication Number: US-2010129614-A1

Title: Low-density structural panel made from used paper material, and process for making same

Description:
BACKGROUND OF THE INVENTION 
     The present disclosure relates generally to structural panels made of fibrous materials such as paper materials. 
     Paperboard containers made from corrugated or non-corrugated paperboard are widely used for shipping products from manufacturers or distributors to retailers and other destinations. Other paper materials such as newsprint for advertising flyers, paper used as cushioning in cartons, and the like, are also widely used in industry. Once the paper materials have been used for their intended purpose, they are generally regarded as waste. In some cases, the used paper materials are simply disposed of along with other waste. In other cases, the recipient of the used paper materials may send the used paper materials to a recycler, at which the used paper materials are shredded and/or baled and then shipped to a paper mill. The paper mill can repulp the used paper materials to make recycled paper, which can then be converted into products of various types. 
     However, these recycling steps add significant cost to a material that is already of relatively low commercial value. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The present disclosure concerns a process for making a low-density structural panel from used paper material such as corrugated paperboard material. In accordance with one aspect of the disclosure, a process is described for making a low-density structural panel, comprising the steps of:
         providing used paper material that has been divided into pieces;   distributing an adhesive through the pieces of used paper material such that substantially all of the pieces have at least some adhesive thereon;   forming a layer of the adhesive-covered pieces;   contacting the layer of adhesive-covered pieces with a compression device so as to compress the layer to a smaller thickness and increase the density of the layer; and   heating the layer to dry and harden the adhesive so as to form a low-density structural panel.       

     The process can be either a batch-type process in which one panel at a time is produced, or a continuous process in which a continuous low-density structural panel is produced and is subsequently cut into desired lengths. A batch process can entail using a mold configured to impart the desired shape to the panel. After the pieces of paper material have been mixed with the adhesive, the mixture is deposited into the mold. A suitable compression device is then used to compress the mixture in the mold. The compression step can be performed with or without heating. After compression, the mold is opened and the panel is removed. The panel can then be heated in an oven to dry and harden the adhesive. 
     The continuous process can entail a number of different embodiments. In one embodiment, the forming step comprises continuously depositing the adhesive-covered pieces onto a moving conveyor to form a continuous layer of the adhesive-covered pieces. The contacting step comprises contacting the layer of adhesive-covered pieces being advanced by the moving conveyor with a compression device so as to compress the layer to a smaller thickness and increase the density of the layer. The heating step comprises heating the layer to dry and harden the adhesive so as to form a continuous low-density structural panel. 
     In one embodiment, the distributing step comprises mixing the pieces with a silicate-based adhesive. 
     The continuously depositing step can comprise using a headbox to continuously discharge the pieces onto the moving conveyor. Additionally or alternatively, the continuously depositing step can comprise using a metering spreader to spread the pieces on the moving conveyor at a generally controlled volumetric rate. 
     In some embodiments, the moving conveyor comprises a moving perforated screen or belt arranged in a loop about rotating rollers, the screen or belt being backed up by a platen. The contacting step comprises contacting the layer with a second moving perforated screen or belt arranged in a loop about rotating rollers and backed up by a second platen, the second screen or belt with the second platen being urged against the layer to compress the layer on the moving conveyor. At least one of the platens can be perforated and vacuum can be applied therethrough for facilitating draining of liquid from the layer. 
     In another embodiment, the distributing step comprises carrying a layer of the pieces on the moving conveyor through a bath of the adhesive, the moving conveyor comprising a perforated screen or belt and the layer being retained between the moving conveyor and a second moving perforated screen or belt. 
     The process can also include adhering a continuous paper web to one surface of the continuous low-density structural panel. In one embodiment, the moving conveyor comprises the continuous paper web, the paper web becoming adhered to one surface of the layer and forming a first surface of the low-density structural panel. Alternatively, the paper web can be adhered to the layer after the layer has been heated to dry and substantially harden the adhesive. The process can also include adhering a second continuous paper web to the opposite surface of the continuous low-density structural panel. 
     In one variation, the paper web is adhered to the surface of the low-density structural panel using only the adhesive applied previously in the distributing step. Alternatively, the paper web can be adhered to the surface after an application of additional adhesive to the paper web or to the surface of the low-density structural panel. 
     In accordance with another aspect of the present disclosure, a low-density structural panel is described, comprising a network of individual pieces of corrugated cardboard material arranged in random orientations with respect to one another and bound together by an adhesive, the pieces being less than about 50 in 2  in size. By “panel” is meant a structural member in which at least one of a length and a width of the member substantially exceeds a thickness of the member. Thus, “panel” can include items such as boards, sheets, planks, and the like, having various cross-sections that may or may not be uniform along the length and/or width. 
     In some embodiments, at least a portion of the pieces making up the panel comprise strips of the corrugated cardboard material, the strips having an average length-to-width ratio (or “aspect ratio”) greater than about 5, in some cases greater than about 10, and in some cases greater than about 15. 
     In some embodiments, the strips are cut from corrugated cardboard material such that a length of each strip extends perpendicular to a direction in which flutes of the corrugated cardboard material extend, such that each strip has a plurality of cells defined by the flutes, the adhesive infiltrating into at least some of the cells of the strips. 
     In preferred embodiments, substantially all of the pieces making up the network comprise the strips. The strips can have an average width of about ⅛-inch to about ½-inch and an average length of about 2 inches to about 6 inches. 
    
    
     
       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 photograph of pieces of shredded paper material in which the pieces are randomly shaped and of a variety of sizes ranging from particles to about 1 in 2  in size, in accordance with one embodiment of the invention; 
         FIG. 2  is a photograph of a mold useful for practicing a batch process for making a panel in accordance with one embodiment of the invention; 
         FIG. 3  is a photograph of a grid device in which the panel, after being removed from the mold, is held for heating of the panel in an oven; 
         FIG. 4  is a photograph of the completed panel; 
         FIG. 5  is a close-up photograph of a portion of the panel of  FIG. 4 ; 
         FIGS. 6 through 8  are photographs of a panel made from a second type of paper material comprising long narrow strips of old corrugated containers; 
         FIG. 9  is a diagrammatic illustration of a continuous process for producing panels in accordance with one embodiment of the invention; 
         FIG. 10  is a diagrammatic illustration of a continuous process for producing panels in accordance with another embodiment of the invention; and 
         FIG. 11  is a diagrammatic illustration of a continuous process for producing panels in accordance with yet another embodiment of the invention. 
     
    
    
     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. 
     A batch process for making panels in accordance with the present invention is first described with reference to  FIGS. 1 through 8 . In  FIG. 1  is shown a quantity of shredded old corrugated container (OCC) material that can be used in accordance with the invention. A ruler having inch marks is depicted alongside the material for scale. The pieces of OCC range from small particles to pieces of about 1 in 2  size. In accordance with one batch process for making a panel in accordance with the invention, a quantity of this shredded material is thoroughly mixed with a suitable adhesive such that substantially all of the pieces are at least partially coated with the adhesive. Any of various adhesives can be used. Aqueous adhesives are a suitable choice because they are easy to work with and do not have the environmental hazard issues that are associated with some solvent-based adhesives. As one example, the adhesive can comprise a silicate-based adhesive such as a sodium silicate adhesive. A suitable solution, for example, has 4 parts of a 38 wt. % solids silicate solution of 42° Be (having a sodium/silicate ratio of 3.22) to one part water. This solution is approximately 30 wt. % solids. 
       FIGS. 2 through 5  illustrate the formation of a panel using the mixture of  FIG. 1  with the 30 wt. % solids silicate adhesive solution described above. After the pieces of OCC were thoroughly mixed with the adhesive solution, the mixture was poured into the bottom member  22  of a mold  20  depicted in  FIG. 2 . The mold was configured to produce a rectangular panel having a length of about 15 inches and a width of about 12 inches, and a thickness of about 1 inch. The bottom mold member  22  was configured with a series of spaced recesses  24  for forming a plurality of spaced “feet” on the panel&#39;s lower surface. The top mold member  26  comprised a flat plate having a plurality of protrusions  28  shaped to complement the recesses in the bottom mold member such that the upper surface of the panel is formed to have depressions at the locations of the feet. The protrusions  28  help to compress the material in the feet so that the feet have sufficient density and strength. 
     Once the bottom mold member  22  was filled with an appropriate quantity of the OCC/adhesive mixture and the mixture was spread out into a substantially uniform-thickness layer, the top mold member  26  was placed atop the layer. The mold was then placed into a hydraulic press and a pressure of about 10 tons was applied (without heating) for about 15 minutes. The mold was then removed from the press and was opened, and the partially hardened panel  30  was removed from the mold. As shown in  FIG. 3 , the partially hardened panel  30  was then placed on a metal grid  32 . Another grid  34  was placed atop the panel to reduce warping of the panel, and this assembly was placed into an oven to substantially fully harden the adhesive. The mold was removed from the oven and the panel  30  was removed from the mold.  FIG. 4  illustrates the feet  32  formed on the lower surface of the panel  30 .  FIG. 5  shows one of the feet  32  in close-up. 
       FIGS. 5 through 8  depict a second panel  130  formed by the same process described above, but using a mixture of long narrow strips of OCC mixed with the silicate adhesive solution previously described. The strips had an average width of about ⅛-inch and an average length of about 4 inches. The strips were cut such that their length direction was perpendicular to the direction in which the flutes of the OCC extended. Accordingly, each strip had a plurality of “cells” formed by the flutes, the cells being open at the opposite long edges of the strip. When the strips were mixed with the adhesive, some of the adhesive was able to penetrate into the cells of the strips, and it is theorized this provides a reinforcing effect after the adhesive hardens, enhancing the strength properties of the panel. The long narrow strips form a network or matrix similar to cellulose fibers in paper but on a larger scale. This matrix allows the panel to have a significantly lower density (½ to ⅓ that of the panel produced from shredded OCC) while still retaining structural strength and integrity. 
       FIGS. 7 and 8  are additional views of the panel  130 . The lower surface has feet  132  as in the previous embodiment. 
     The process of the invention can also be practiced as a continuous process.  FIG. 9  shows an apparatus  200  and process for producing a continuous low-density structural panel in accordance with an embodiment of the invention. The apparatus includes a shredder  202  or other device for dividing OCC or other used paper materials into pieces. The shredding is shown as being performed inline with the rest of the process, but alternatively shredding can be done offline at an adjacent or a remote location, and the shredded material can be held in a hopper (not shown) and dispensed from the hopper in any suitable fashion. The shredded material is mixed with adhesive in a mixing device  204 . This mixture is continuously discharged from a headbox  206  or similar device onto a moving conveyor  208  comprising a foraminous (perforated) belt or screen  210  formed as an endless loop and guided by a plurality of rollers  212  one or more of which is rotatably driven by a suitable motor (not shown) such that the belt  210  continuously rotates for transporting the mixture discharged from the headbox. The headbox meters the mixture being discharged so that the layer  214  of material on the belt  210  has a generally uniform thickness of a desired value. The belt  210  allows excess adhesive solution to drain through the belt as shown. 
     The layer  214  is carried on the conveyor belt  210  through a compression device  216  comprising the belt  210  cooperating with a foraminous second belt or screen  218  formed as an endless loop about rollers  220  at least one of which is rotatably driven so the second belt  218  travels with the same linear speed as the conveyor belt  210 . The compression device includes a first platen  222  that backs up the conveyor belt  210  and that is perforated, and a second perforated platen  224  that backs up the second belt  218 . The second belt  218  and second platen  224  are urged toward the conveyor belt  210  and first platen  222  by a suitable actuator (not shown) so as to compress the layer  214  of paper/adhesive on the conveyor belt. As shown, suction can be exerted through either or both platens to assist in removing excess adhesive solution from the layer. The compression device reduces the thickness and increases the density of the layer  214  on the conveyor belt. 
     After the compression device, the conveyor belt  210  carries the layer  214  through an oven  226  or other suitable heating device to hasten the drying and hardening of the adhesive. A continuous low-density structural panel  230  is discharged from the oven. If desired, a continuous paper web  232  can be applied to one surface of the panel  230  and a second continuous paper web  234  can be applied to the opposite surface of the panel. In some cases, the adhesive present at the surfaces of the panel may suffice for adhering the paper webs. In other cases, adhesive can be applied to the paper webs (or to the surfaces of the panel) by suitable adhesive applicators  236  as shown. The finished panel can then be cut into desired lengths by a suitable cutting device  238 . 
     An alternative apparatus  300  and process in accordance with another embodiment of the invention are shown in  FIG. 10 . A shredder  302  divides the OCC/paper material into pieces. A metering spreader  304  spreads the pieces in a substantially uniform-thickness layer  306  on a moving conveyor belt or screen  310 . The conveyor belt carries the layer  306  into a reservoir  311  of adhesive. The layer is retained between the conveyor belt  310  and a second belt or screen  313  that contacts the upper surface of the layer. The conveyor belt  310  carries the adhesive-impregnated layer through a series of nip rollers  316  that compress the layer and squeeze excess adhesive out of the layer. Excess adhesive drains through the foraminous conveyor belt  310  back into the reservoir  311 . The layer is then carried on the conveyor belt  310  through an oven  326  to hasten the hardening of the adhesive. Continuous paper webs  332 ,  334  are applied to the opposite surfaces of the continuous low-density structural panel  330  discharged from the oven, and the finished panel is cut into desired lengths as in the previous embodiment. 
     Yet another apparatus  400  and process in accordance with a further embodiment of the invention are shown in  FIG. 11 . A shredder  402  divides the OCC/paper material into pieces. The pieces are mixed with adhesive in a mixer  404  and the mixture is deposited onto a moving continuous paper web  434  that functions as a conveyor for moving the layer of the mixture through the various stages of the process. A metering spreader  406  spreads the mixture in a substantially uniform-thickness layer  408  on the paper web  434 . The paper web  434  carries the layer through a first oven  426   a , which partially dries and hardens the adhesive. The paper web then carriers the layer through a series of nip rollers  416  that compress the layer and increase its density. The layer is then carried on the paper web  434  through a second oven  426   a  to substantially complete the hardening of the adhesive. A continuous paper web  432  is applied to the top surface of the continuous panel  430  discharged from the second oven. If desired or needed, additional post-heating can be performed with a third oven  426   c  and further compression of the panel can be accomplished with nip rollers  440  to further densify the panel. The panel can then be cut into desired lengths. 
     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.