Paper mill core structure for improved winding and support of paper mill roll

Abstract

Paper mill cores of the invention are structured to allow winding and unwinding chucks to distort the interior diameter and shape of the interior body wall of the core while resisting distortion of the core exterior to prevent center burst failure. The paper mill cores of the invention include a multi-ply zone of high strength, but relatively compliant, paperboard plies within the outer 70% (based on the total body wall thickness) of the body wall having a thickness of at least about 4 mm. An interior zone constituting at least about 25% of the total thickness of the body wall is formed from extremely high strength, extremely high density paperboard plies. The overall wall thickness of the core is preferably at least about 15 mm, and is thus preferably increased, as compared to the wall thickness of conventional high strength wide paper mill cores formed entirely of extremely high strength, extremely high density, non-compliant paperboard plies.

That which is claimed:  
     
         1 . A multi-ply paperboard core for supporting a roll of wide, continuous paper mill sheet comprising: 
 a multi-ply paperboard core structure having a length exceeding about 100 in. (255 cm.), and being defined by a generally cylindrical body wall having a thickness of at least about 15 mm;    said body wall including a radially interior multi-ply zone constituting at least about 25% of the total thickness of the body wall and consisting essentially of paperboard plies, each having a density exceeding about 0.80 g/cc; and,    a second multi-ply zone within the radially outer 70% of the total thickness of the body wall consisting essentially of paperboard plies each having a density of between about 0.65 and about 0.75 g/cc, said second zone having a thickness of at least about 4.    
     
     
         2 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 1  wherein said paperboard plies in said interior multi-ply zone each have a density between about 0.82 and 0.90 g/cc.  
     
     
         3 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 1  wherein said paperboard plies in said second multi-ply zone each have a density of between about 0.67 and 0.73 g/cc.  
     
     
         4 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 2  wherein said paperboard plies in said second multi-ply zone each have a density of between about 0.67 and 0.73 g/cc.  
     
     
         5 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 1  wherein said interior multi-ply zone constitutes between about 30 and 35% of the total thickness of the body wall.  
     
     
         6 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 5  wherein said second multi-ply zone has a thickness of between about 30 and 35% of the total thickness of the body wall.  
     
     
         7 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 1  wherein said second multi-ply zone has a thickness of between about 40 and about 50% of the total thickness of the body wall.  
     
     
         8 . A multi-ply paperboard core for supporting a roll of wide, continuous paper mill sheet comprising: 
 a multi-ply paperboard core structure having a length exceeding about 100 in. (255 cm.), and being defined by a generally cylindrical body wall having a thickness of at least about 15 mm, and an inside diameter of about 6 in. (152 mm);    said body wall including a radially interior multi-ply zone constituting about 25% to about 35% of the total thickness of the body wall and consisting essentially of paperboard plies, each having a density exceeding about 0.80 g/cc;    a second multi-ply zone within a central portion of the body wall consisting essentially of paperboard plies each having a density between about 0.65 and 0.75 g/cc., said second zone constituting between about 35% and about 45% of the total thickness of the body wall, said second zone having a thickness of at least about 4 mm.; and    a third multi-ply zone within a radially outer portion of the body wall consisting essentially of paperboard plies each having a density exceeding about 0.80 g/cc., said third zone constituting between about 30% and about 35% of the total thickness of the body wall.    
     
     
         9 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 8  wherein said paperboard plies in said radially interior multi-ply zone each have a density between about 0.82 and 0.90 g/cc.  
     
     
         10 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 9  wherein said paperboard plies in said second multi-ply zone each have a density of between about 0.67 and 0.73 g/cc.  
     
     
         11 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 8  wherein said paperboard plies in said second multi-ply zone each have a density of between about 0.67 and 0.73 g/cc.  
     
     
         12 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 9  wherein said interior multi-ply zone constitutes about 33% of the total thickness of the body wall.  
     
     
         13 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 9  wherein said second multi-ply zone has a thickness of about 33% of the total thickness of the body wall.  
     
     
         14 . A multi-ply paperboard core for supporting a roll of wide, continuous paper mill sheet comprising: 
 a multi-ply paperboard core structure having a length exceeding about 100 in. (255 cm.), and being defined by a generally cylindrical body wall having a thickness of at least about 15 mm, and an inside diameter of about 3 in. (76.2 mm);    said body wall including a radially interior multi-ply zone constituting at least about 50% of the total thickness of the body wall and consisting essentially of paperboard plies each having a density exceeding about 0.80 g/cc; and    a second multi-ply zone within the radially outer 50% of the body wall thickness consisting essentially of paperboard plies each having a density between about 0.65 and 0.75 g/cc., said second zone having a thickness of at least about 5 mm.    
     
     
         15 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 14 , wherein said paperboard plies in said radially interior multi-ply zone each have a density between about 0.82 and 0.90 g/cc.  
     
     
         16 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 14 , wherein said paperboard plies in said second multi-ply zone each have a density of between about 0.67 and 0.73 g/cc.  
     
     
         17 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 15 , wherein said paperboard plies in said second multi-ply zone each have a density of between about 0.67 and 0.73 g/cc.  
     
     
         18 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 15 , wherein said interior multi-ply zone constitutes about 55 to about 65% of the total thickness of the body wall.  
     
     
         19 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 18 , wherein said second multi-ply zone has a thickness of between about 35 and about 45% of the total thickness of the body wall.  
     
     
         20 . The multi-ply paperboard core for supporting a roll of wide continuous paper mill sheet according to  claim 19 , wherein said body wall has a total thickness of about 16 mm or greater.  
     
     
         21 . A paperboard core for supporting a roll of wide continuous paper mill sheet, the paperboard core being constructed to have enhanced resistance to center burst, and comprising: 
 a cylindrical body wall formed of a plurality of paperboard plies, the body wall having a thickness of at least about 15 mm, the body wall having only two multi-ply zones, a radially interior one of the zones consisting essentially of paperboard plies each having a density exceeding about 0.8 g/cc, and a radially outer one of the zones consisting essentially of paperboard plies each having a density between about 0.65 g/cc and about 0.75 g/cc, said radially outer zone lying radially outward of the radially interior zone and having a thickness of at least about 5 mm.    
     
     
         22 . The paperboard core of  claim 21 , wherein the radially outer zone occupies about 35% to about 45% of the total thickness of the body wall.  
     
     
         23 . The paperboard core of  claim 22 , wherein the radially interior zone occupies about 55% to about 65% of the total thickness of the body wall.  
     
     
         24 . The paperboard core of  claim 21 , wherein the paperboard plies in the radially outer zone each has a density between about 0.67 g/cc and about 0.73 g/cc.  
     
     
         25 . The paperboard core of  claim 24 , wherein the paperboard plies in the radially interior zone each has a density between about 0.82 g/cc and about 0.90 g/cc.  
     
     
         26 . The paperboard core of  claim 21 , wherein the paperboard plies in the radially interior zone each has a density between about 0.82 g/cc and about 0.90 g/cc.  
     
     
         27 . The paperboard core of  claim 21 , wherein the body wall has an inside diameter of about 3 inches (76.2 mm).  
     
     
         28 . A paperboard core for supporting a roll of wide continuous paper mill sheet, the paperboard core being constructed to reduce changes in outside diameter size and shape caused by radially expanding a chuck against an inside diameter of the core, the core comprising: 
 a cylindrical body wall formed of a plurality of paperboard plies, the body wall having a thickness of at least about 15 mm, the plies consisting essentially of a plurality of relatively less-compliant plies each having a density exceeding about 0.80 g/cc and a plurality of relatively more-compliant plies each having a density from about 0.65 g/cc to about 0.75 g/cc, the relatively more-compliant plies being disposed in the radially outer 50% of the body wall thickness, and the relatively less-compliant plies being located only radially inward of the relatively more-compliant plies, whereby radially outward expansion of the inside diameter of the core caused by an expanding chuck is at least partially absorbed by the relatively more-compliant plies such that changes in outside diameter size and shape are reduced.    
     
     
         29 . The paperboard core of  claim 28 , wherein the less-compliant plies collectively make up from about 55% to about 65% of the total thickness of the body wall.  
     
     
         30 . The paperboard core of  claim 28 , wherein the more-compliant plies collectively make up from about 35% to about 45% of the total thickness of the body wall.