Process for producing super high bulk, light weight coated papers

Abstract

The present invention relates to a process of manufacturing a high bulk, low weight paper product produced by using a high level of groundwood containing sheet, blade coating with specifically formulated coatings then passing the paper web between two extended-nip calenders, one calender for each side of paper. As a result, densification of the resulting coated paper product is reduced, while maintaining stiffness and opacity comparable to heavier weight sheets.

1 . A process for manufacturing a lightweight, high bulk coated paper, comprising the steps of: 
 (a) creating a fiber furnish comprising mechanical pulp and chemical pulp;    (b) forming a paper web from the fiber furnish;    (c) removing water from said web;    (d) applying a coating having a weight of at least 2.0 pounds per 3300 square feet per side onto each surface of said web to form a coated web having a moisture content greater than 5.5%, and a caliper greater than 2.6 mils;    (e) passing the coated web through two extended-nip calenders, with each side of the paper facing a heated roll and treated with one of said calender nips, and wherein each calendering nip is formed by a calender roll having a surface temperature of at least 300° F. and a backing shoe having a width of at least 30 mm, the nip providing loading of at least 1000 pounds per linear inch; and whereby the calendered paper has a caliper preservation greater than 75%.    
     
     
         2 . A process as in  claim 1  wherein said paper is No. 5 offset lightweight coated paper.  
     
     
         3 . A process as in  claim 1  wherein said furnish comprises at least 40% mechanical pulp.  
     
     
         4 . A process as in  claim 3  wherein said furnish comprises about 60 to 80% mechanical pulp.  
     
     
         5 . A process as in  claim 1  wherein said coating has a weight of 2.0 to 6.0 pounds per 3300 square feet per side.  
     
     
         6 . A process as in  claim 1  wherein said coated web has a moisture content greater than 6.5%.  
     
     
         7 . A process as in  claim 1  wherein said coated web has a moisture content greater than 7.0%.  
     
     
         8 . A process as in  claim 1  wherein said coating comprises a hollow plastic pigment; a kaolin pigment; a calcined kaolin clay; a titanium dioxide pigment; a synthetic latex binder; and a synthetic thickener, or a co-binder including carboxymethylcellulose or acrylic acid based or associative based thickeners.  
     
     
         9 . A process as in  claim 8  wherein said coating also comprises precipitated calcium carbonate or ground calcium carbonate.  
     
     
         10 . A process as in  claim 8  wherein said hollow plastic pigment is present in an amount of at least about 2% by weight of the total amount of pigment.  
     
     
         12 . A process as in  claim 8 , wherein said hollow plastic pigment is present in an amount of about 3 to 5% by weight of the total amount of pigment.  
     
     
         13 . A process as in  claim 8  wherein said kaolin pigment has a fine particle size distribution characterized in that at least 85% of said particles are less than 2 microns and at least 50% of said particles are less than 0.5 microns, based upon particle counting using a Sedigraph particle size analyzer.  
     
     
         14 . A process as in  claim 8  wherein said kaolin pigment has a platy morphology characterized as both fine and coarse particles having a shape factor greater than 15.  
     
     
         15 . A process as in  claim 8  wherein said kaolin pigment has a platy morphology characterized as both fine and coarse particles having a shape factor of about 20 to 27.  
     
     
         16 . A process as in  claim 8  wherein said kaolin pigment is present in an amount of at least 70% by weight of the total amount of pigment.  
     
     
         17 . A process as in  claim 8  wherein said kaolin pigment is present in an amount of 80% to 100% by weight of the total amount of pigment.  
     
     
         18 . A process as in  claim 8  wherein said titanium dioxide is present in an amount of at least about 2%.  
     
     
         19 . A process as in  claim 12  wherein said titanium dioxide is present in an amount of about 3 to 5%.  
     
     
         20 . A process as  claim 1  wherein the coating is preferably applied using a blade coater or a metering size press.  
     
     
         21 . A process as  claim 1  wherein the calender is a shoe nip calender, said shoe nip width being in the range of from about 40 mm to about 80 mm, and calendering temperature is at least 300° F., and nip loading at 1700-2400 pli.  
     
     
         22 . A process as in  claim 1  wherein said calendered paper has a basis weight of 28 to 38 pounds per 3300 square feet and exhibits a 75 degree TAPPI gloss of 35% or above and a caliper of at least 2.15 mils.  
     
     
         23 . A process for manufacturing a super high bulk, offset lightweight coated paper, comprising 
 (a) creating a fiber furnish comprising at least 40% mechanical pulp;    (b) forming a paper web from the fiber furnish;    (c) removing water from said web;    (d) applying a coating using a blade coater at coat weights of at least 2.0 pounds per 3300 square feet, per side onto each surface of said web to form a coated web having a moisture content of at least 5.5%; and    (e) passing the coated web through two extended-nip calenders, with each side of paper facing a heated roll and treated with one of said calender nips; whereby each calendering nip is formed by a calender roll having a surface temperature of at least 300° F. and a backing shoe nip having a width of at least 30 mm, the nip providing loading of at least 1000 pounds per linear inch (pli), and whereby the calendered paper has a caliper preservation greater than 75%,    wherein the coating comprises:    (i) hollow plastic pigment, in an amount of at least about 2% by weight of the total amount of pigment;    (ii) kaolin pigment in an amount of at least about 70% by weight of the total amount of pigment, said kaolin pigment having a fine particle size distribution characterized by at least 85% of said particles are less than 2 microns and at least 50% of said particles are less than 0.5 microns, and a platy morphology characterized as both fine and coarse particles having a shape factor greater than 15, preferably 20-27;    (iii) titanium dioxide in an amount of at least about 2% by weight of the total amount of pigment;    (iv) calcined kaolin in an amount of at least 5% by weight of the total amount of pigment;    (v) synthetic latex in a concentration of at least about 12 or more parts by weight of the total amount of pigment;    (vi) synthetic thickener in a concentration of at least about 0.05 or more parts by weight of the total amount of pigment; and    wherein the finished coated paper has a basis weight of 28 to 38 pounds per 33 square feet, exhibits a 750 TAPPI gloss of 35% or above, has a caliper of at least 2.15 mils, gives a 17-27% higher caliper, has up to 22% bulk improvement relative to a supercalendered 30 pounds/3300 square feet LWC, and has improved brightness, opacity and printing gloss.