Low density paperboard articles

Abstract

The invention provides a low density paperboard material and associated method for use in producing an insulated container, and is especially well-suited for making cups. The paperboard material comprises a paperboard web including wood fibers and expanded microspheres, and has a relatively low density ranging from about 6 to about 10 lb/3MSF/mil, a relatively high caliper ranging from about 24 to about 35 mil, and an internal bond strength of at least about 80×10 −3 ft−lbf., preferably at least 100×10 −3 lft−lbf. For applications such as cups the material is also coated on one or both sides with a barrier coating, preferably low density polyethylene, to limit liquid penetration into the web. The low density paperboard material of the invention is convertible for manufacture of containers, particularly cups, and exhibits insulative properties comparable to higher cost materials conventionally used to make cups. Also, the surface of the low density board may have a Sheffield smoothness of 300 SU or greater compared with the surface smoothness of 160 to 200 SU for conventional cupstock, the latter having been thought necessary for adequate print quality. However, it has been found that the low density board exhibits good printability on flexo printing machines despite its relatively rough surface, which is surprising and bonus effect realized along with the insulative and other properties of the board.

1 . A paperboard material useful in the manufacture of paperboard containers such as paper cups comprising a paperboard web including wood fibers and expanded microspheres dispersed within the fibers and having an apparent density of from about 6.0 to about 10 lb/3MSF/mil and a caliper of from 24 to about 35 mil with an internal bond of at least about 80×10 −3  ft−lbf.  
     
     
         2 . The paperboard material of  claim 1  wherein the density of the web is at least about 6.5 lb/3MSF/mil and the caliper of the web is at least about 28 mil.  
     
     
         3 . The paperboard material of  claim 2  wherein the average bond of the web is at lest about 100×10 −3  ft−lbf.  
     
     
         4 . The paperboard of  claim 1  wherein the average internal bond of the web is at least about 100×10 −3  ft−lbf.  
     
     
         5 . The paperboard of  claim 1  wherein the average internal bond of the web is at least about 80×10 −3  ft−lbf.  
     
     
         6 . The paperboard material of  claim 1  further comprising a barrier coating on at least one of the surfaces of the web.  
     
     
         7 . The paperboard material of  claim 6  wherein the barrier coating is present only on a surface of the web to be placed interiorly of a cup.  
     
     
         8 . The paperboard material of  claim 6  wherein the barrier coating has an average thickness of from about 0.5 to about 3.5 mil.  
     
     
         9 . The paperboard material of  claim 6  wherein the barrier coating comprises a coating material selected from the group consisting of polyethylene, EVOH, and polyethylene terephthalate having an average thickness ranging from about 0.5 to about 3.5 mil.  
     
     
         10 . The paperboard material of  claim 6  wherein the barrier coating comprises a low density polyethylene having an average thickness of from about 1 to about 3 mil.  
     
     
         11 . The paperboard material of  claim 6  wherein a barrier coating is present on both surfaces of the web.  
     
     
         12 . The paperboard material of  claim 1  wherein the web has a Sheffield smoothness of at least about 300 SU.  
     
     
         13 . The paperboard material of  claim 1  wherein the web has a surface with a Sheffield smoothness of at least about 300 SU and the material contains printing directly on the surface.  
     
     
         14 . The paperboard material of  claim 1  wherein the web has a surface with a Sheffield smoothness of at least about 300 SU and a PPS10 smoothness of about 6.5 microns or less and carries printing on the surface.  
     
     
         15 . The paperboard material of  claim 1  wherein the cellulosic fibers in the web comprise from about 20 to about 40% by weight dry basis softwood fibers and from about 60 to about 80% by weight dry basis hardwood fibers.  
     
     
         16 . The paperboard material of  claim 1  wherein the expanded microspheres in the web comprise synthetic polymeric microspheres and comprise from about 0.25 to about 10 wt. % of the total weight of the web on a dry basis.  
     
     
         17 . The paperboard material of  claim 1  wherein the expanded microspheres in the web comprise synthetic polymeric microspheres and comprise from about 5 to about 7 wt. % of the total weight of the web on a dry basis.  
     
     
         18 . A paperboard material useful in the manufacture of insulated containers such as cups which comprises a paperboard web including wood fiber and from about 5 to about 10 wt. % dry basis expanded synthetic polymer microspheres based on the total weight of the web dispersed within the fibers, an apparent density of from about 6.0 to about 10 lb/3MSF/mil, a caliper of from about 24 to about 35 mil, an average internal bond of at least about 80×10 −3  ft−lbf, a Sheffield smoothness of about 300 SU or greater, and a barrier coating having a thickness of from about 0.5 to about 3.5 mil on at least one surface of the web.  
     
     
         19 . The paperboard material of  claim 16  further comprising printing applied directly to at least one surface of the web.  
     
     
         20 . An assembled paper container which comprises a sidewall and a bottom sealably joined together wherein the sidewall is provided by a paperboard material which comprises a paperboard web including wood fiber and from about 5 to about 10 wt. % dry basis expanded synthetic polymer microspheres based on the total weight of the web dispersed within the fibers, an apparent density of from about 6.0 to about 10 lb/3MSF/mil, a caliper of from about 24 to about 35 mil, an average internal bond of at least about 80×10 −3  ft−lbf, a Sheffield smoothness of about 300 SU or greater, and a barrier coating having a thickness of from about 0.5 to about 3.5 mil on at least one surface of the web.  
     
     
         21 . An assembled paper cup which comprises a sidewall and a bottom sealably joined together wherein the sidewall is provided by a paperboard material which comprises a paperboard web including wood fiber and from about 5 to about 10 wt. % dry basis expanded synthetic polymer microspheres based on the total weight of the web dispersed within the fibers, an apparent density of from about 6.0 to about 10 lb/3MSF/mil, a caliper of from about 24 to about 35 mil, an average internal bond of at least about 80×10 −3  ft−lbf, a Sheffield smoothness of about 300 SU or greater, and a barrier coating having a thickness of from about 0.5 to about 3.5 mil on at least one surface of the web.  
     
     
         22 . A method for making a low density paperboard material suitable for use in producing an insulated container such as a cup comprising providing a papermaking furnish containing cellulosic fibers and from about 0.25 to about 10% by weight dry basis expandable microspheres, forming a paperboard web from the papermaking furnish, drying the web, and calendaring the web to a caliper of from about 24 to about 35 mils and a density ranging from about 200 to about 220 lb/3MSF.  
     
     
         23 . The method of  claim 22  wherein the density of the web is at least about 6.5 lb/3MSF/mil and the caliper of the web is at least about 28 mil.  
     
     
         24 . The method of  claim 23  wherein the internal bond of the web is at least about 100×10 −3  ft−lbf.  
     
     
         25 . The method of  claim 22  wherein the internal bond of the web is at least about 100×10 −3  ft−lbf.  
     
     
         26 . The method of  claim 22  wherein the internal bond of the web is at least about 80×10 −3  ft−lbf.  
     
     
         27 . The method of  claim 22  further comprising applying a barrier coating on at least one of the surfaces of the calendered web.  
     
     
         28 . The method of  claim 27  wherein the barrier coating is present only on a surface of the web to be placed interiorly of a container.  
     
     
         29 . The method of  claim 27  wherein the barrier coating has an average thickness of from about 0.5 to about 3.5 mil.  
     
     
         30 . The method of  claim 27  wherein the barrier coating comprises a coating material selected from the group consisting of polyethylene, EVOH, and polyethylene terephthalate having an average thickness ranging from about 0.5 to about 3.5 mil.  
     
     
         31 . The method of  claim 30  wherein the barrier coating comprises a low density polyethylene having an average thickness of from about 1 to about 3 mil.  
     
     
         32 . The method of  claim 27  wherein a barrier coating is present on both surfaces of the web.  
     
     
         33 . The method of  claim 22  wherein the web exhibits a Sheffield smoothness of at least about 300 SU.  
     
     
         34 . The method of  claim 22  wherein the web is calendered so as to exhibit a Sheffield smoothness of at least about 300 SU and the method further comprises printing directly on the surface.  
     
     
         35 . The method of  claim 22  further comprising printing directly on a surface of the web to be positioned on the exterior of the container and wherein the surface that carries the printing exhibits a Sheffield smoothness of at least about 300 SU and a PPS10 smoothness of about 6.5 microns or less.  
     
     
         36 . The method of  claim 22  wherein the furnish comprises from about 5 to about 7 wt. % dry basis expandable microspheres.  
     
     
         37 . A method for making an insulated paperboard-based cup having a sidewall and a bottom which comprises providing a paperboard material comprising a paperboard web including from about 0.25 to about 10% by weight dry basis of expanded polymeric microspheres, a caliper of from about 24 to about 35 mils, an apparent density of from about 6.5 to about 10 lb/3MSF/mil, an internal bond of at least about 80×10− 3  ft−lbf, and a Sheffield smoothness of at least about 300 SU, and a barrier coating on at least one surface of the web having a thickness of from about 0.5 to about 3.5 mil, forming at least the sidewall of the cup from the web with a surface of the web containing the barrier coating facing interiorly of the cup and the other surface of the web facing exteriorly of the cup, and sealably joining the sidewall to the bottom.  
     
     
         38 . The method of  claim 37  wherein the web has barrier coatings on both of its surfaces facing interiorly and exteriorly of the cup.  
     
     
         39 . The method of  claim 38 , wherein the web has printing on the barrier coating on the surface positioned exteriorly of the cup.  
     
     
         40 . The method of  claim 37 , wherein the web has a barrier coating only on its surface facing interiorly of the cup and the web has printing on its surface facing exteriorly of the cup.