Process for making abrasion resistant paper and paper and paper products made by the process

Abstract

In this papermaking process, a first strength agent is added to a stock suspension containing pulp and optionally other additives prior to its being formed into a web at the wet end of a papermaking machine. The web is then formed and processed into paper. A second strength agent is then applied to the surface of the paper. The strength agents may be selected to have opposite charge.

1 . A process for making paper and paper products comprising: 
 a) a stock preparation stage wherein a stock suspension of cellulosic fibers is prepared,    b) adding a first strength agent selected from the group consisting of cationic dry-strength agents, amphoteric dry-strength agents and cationic wet-strength agents to the stock suspension,    c) a wet end stage wherein the cellulosic fibers are formed into a substantially uniform web, and    d) a dry end stage wherein the web is dried into paper and a second strength agent selected from the group consisting of anionic dry-strength agents and amphoteric strength agents is applied to the surface of the paper.    
     
     
         2 . The process of  claim 1  wherein the first strength agent is a cationic dry-strength agent.  
     
     
         3 . The process of  claim 2  wherein the cationic dry-strength agent is selected from the group consisting of cationic polyacrylamides, cationic natural polymers, cationic modified natural polymers, cationic synthetic polymers, starches modified to have quaternary ammonium functional groups, cationic celluloses, cationic natural gums, cationic polyvinyl alcohol adducts, and combinations thereof.  
     
     
         4 . The process of  claim 3  wherein the cationic dry-strength agent is a cationic polyacrylamide.  
     
     
         5 . The process of  claim 2  wherein the cationic dry-strength agent is added in an amount of from about 1 lb/t (0.5 kg/t) to about 20 lb/t (9.1 kg/t).  
     
     
         6 . The process of  claim 2  wherein the cationic dry-strength agent has a viscosity from about 1,000 cps (1 Pa-s) to about 15,000 cps (15 Pa-s).  
     
     
         7 . The process of  claim 2  wherein the cationic dry-strength agent has a specific gravity of from about 1.00 to about 1.20.  
     
     
         8 . The process of  claim 1  wherein the first strength agent is a cationic wet-strength agent.  
     
     
         9 . The process of  claim 8  wherein the cationic wet-strength agent is selected from the group consisting of cationic acid curing resins, cationic neutral to acid curing resins, and cationic neutral to alkaline curing resins.  
     
     
         10 . The process of  claim 8  wherein the cationic wet-strength agent is added in an amount of from about 1 lb/t (0.5 kg/t) to about 20 lb/t (9.1 kg/t).  
     
     
         11 . The process of  claim 1  wherein the second strength agent is an anionic dry-strength agent.  
     
     
         12 . The process of  claim 11  wherein the anionic dry-strength agent is selected from the group consisting of anionic polyacrylamides, anionic natural starches, and anionic carboxymethylcellulose.  
     
     
         13 . The process of  claim 12  wherein the anionic dry-strength agent is an anionic polyacrylamide.  
     
     
         14 . The process of  claim 11  wherein the anionic dry-strength agent is added in an amount of from about 5 lbs/t (2.3 kg/t) to about 25 lbs/t (11.3 kg/t).  
     
     
         15 . The process of  claim 11  wherein the anionic dry-strength agent has a specific gravity from about 1.00 to about 1.20.  
     
     
         16 . The process of  claim 11  wherein the anionic dry-strength agent has a viscosity from about 1,000 cps (1 Pa-s) to about 15,000 cps (15 Pa-s).  
     
     
         17 . The process of  claim 1  wherein the second strength agent is applied to the surface of the paper by a technique selected from the group consisting of: 
 a) immersing the paper in a solution of the second strength agent in a calender waterbox,    b) applying a solution of the second strength agent to the paper with a size press, and    c) spraying a solution of the second strength agent on the paper using a sprayboom.    
     
     
         18 . The process of  claim 17  wherein the solution of the second dry-strength agent is applied to the paper in a calender waterbox.  
     
     
         19 . The process of  claim 17  wherein the solution further contains at least one optical brightener.  
     
     
         20 . The process of  claim 19  wherein the at least one optical brightener is selected from the group consisting of azoles, biphenyls, chelating agents, coumarins, furans, ionic brighteners, naphthalimides, pyrazenes, stilbenes, tetrasulfonated stilbenes, hexasulfonated stilbenes, salts thereof, and combinations thereof.  
     
     
         21 . The process of  claim 19  wherein the at least one optical brightener is added in an amount of from about 0.1 lbs/MSF to about 0.5 lbs/1000 square feed.  
     
     
         22 . The process of  claim 19  wherein the paper product has an optical brightness with a lightness value, L*, greater than about 0.89 after application of the solution.  
     
     
         23 . The process of  claim 1  further comprising adding at least one biocide to the stock suspension.  
     
     
         24 . The process of  claim 17  wherein the solution further contains at least one hydrophobic organo-silicone.  
     
     
         25 . Paper made by the process of  claim 1 .  
     
     
         26 . The process of  claim 1  further comprising incorporating the paper into a paper product.  
     
     
         27 . A paper product made by the process of  claim 26 .  
     
     
         28 . A paper product of  claim 27  that is drywall (wallboard) facing paper applied to the drywall by a conventional gypsum wallboard industry manufacturing process or by lamination onto the drywall after it is manufactured.