Method of making a smooth low density paperboard

Abstract

A paperboard product has at least two or three plies. One of the plies has at least 25% by weight bulky cellulosic fibers. Another of the plies is an outer ply and has an outer surface having a Parker PrintSurf measurement of between 3 and 6μ when measured at 10 kg/cm 2 using a soft backing surface. The paperboard product has a density no greater than 0.5 grams per cubic centimeter. An embodiment has a caliper in the range of 0.4 and 1.2 mm. An embodiment has a basis weight in the range of 200 to 500 grams per square meter. A method for making the paperboard product by passing the web through a soft nip calender and an extended nip calender which can be a shoe calender under conditions which provide the surface and density properties.

1 . A method of manufacturing a paperboard product comprising the steps of: 
 wet laying at least two plies of pulp to form a web,    one of said plies comprising a least 25% by weight bulky cellulosic fibers,    another of said plies being an outer ply of said paperboard product and having an outer surface,    removing water from said web,    passing said web through a soft nip calender, said calender providing a temperature in the range of 120° C. to 160° C. to the web surface and a linear load in the range of 40 to 150 Newtons per millimeter, and    thereafter passing said web through an extended nip calender having an extended nip in the range of 6 to 12 cm., a temperature in the range of 180° C. to 250° C. on the web surface and a linear load of 100 to 300 Newtons per millimeter    to provide a paperboard product having a density no greater than 0.5 grams per cubic centimeter and    said outer surface of said another ply having a Parker PrintSurf measurement of between 3 and 6μ when measured using a clamping pressure of 10 kg/cm 2  and a soft backing surface.    
   
   
       2 . The method of  claim 1  in which said method provides a paperboard product having a caliper in the range of 0.4 and 1.2 mm.  
   
   
       3 . The method of  claim 1  in which said method provides a paperboard product having a basis weight of 200 to 500 grams per square meter.  
   
   
       4 . The method of  claim 1  in which said method provides a paperboard product having a density of between 0.3 and 0.45 grams per cubic centimeter.  
   
   
       5 . The method of  claim 4  in which said method provides a paperboard product having a caliper in the range of 0.4 and 1.2 mm.  
   
   
       6 . The method of  claim 4  in which said method provides a paperboard product having a basis weight of 200 to 500 grams per square meter.  
   
   
       7 . The method of  claim 1  in which said method provides a paperboard product having a density of between 0.35 and 0.4 grams per cubic centimeter.  
   
   
       8 . The method of  claim 7  in which said finished web has a caliper in the range of 0.4 and 1.2 mm.  
   
   
       9 . The method of  claim 7  in which said method provides a paperboard product having a basis weight of 200 to 500 grams per square meter.  
   
   
       10 . The method of  claim 1  in which there is a drying step between said soft nip calendar and said extended nip calender.  
   
   
       11 . The method of  claim 1  in which said extended nip calendar is a shoe calender.