Novel additives for improving the wet strength and dry strength of paper

Abstract

The invention relates to a process for the treatment of paper consisting of the application to the paper either of a cationic resin, PAE, and of a latex containing acid functional groups, the resin and the latex being applied simultaneously but separately, or of a stable mixture prepared beforehand containing the PAE and a latex stabilized by a nonionic surfactant.

1 . A process for the treatment of paper consisting of the application to the paper of a cationic resin and of an aqueous dispersion of a polymer dispersed in the form of particles having a diameter ranging from 30 to 500 nm, these particles being stabilized by a polymeric or nonpolymeric surfactant, wherein said dispersion contains: 
 from 0.5 to 10% by weight with respect to the total weight of the particles of units derived by the polymerization of at least one monomer (A) carrying at least one acid functional group; and    from 90 to 99.5% by weight with respect to the total weight of the particles of units derived from the polymerization of at least one monomer (B) which is emulsion polymerizable, and copolymerizable with A, such as vinyl, meth(acrylic), styrene and diene monomers, the monomers (A) being carried, partially or completely, either by the polymeric surfactant or by the dispersed polymer.    
     
     
         2 . The process as claimed in  claim 1 , wherein the dispersion contains from 0.5 to 5% by weight of units coming from the monomer (A).  
     
     
         3 . The process as claimed in  claim 1  or  2 , wherein (A) is chosen from the group containing unsaturated monocarboxylic or α, β-dicarboxylic acids, such as acrylic acid, methacrylic acid, maleic acid or derivatives thereof, such as maleic anhydride.  
     
     
         4 . The process as claimed in  claim 3 , wherein A is acrylic acid.  
     
     
         5 . The process as claimed in  claim 3 , wherein A is maleic anhydride.  
     
     
         6 . The process as claimed in any one of the preceding claims, wherein the surfactant is chosen from the group consisting of: 
 ionic surfactants, such as sodium dodecylbenzene sulfonate or ethoxylated fatty alcohol sulfates;    nonionic surfactants, such as ethoxylated fatty alcohols; and    polymeric surfactants, such as polymers having, on the one hand, a monomer A and, on the other hand, a monomer chosen from the family of styrene, vinyl or (meth)acrylic ester monomers, or modified natural polymers, such as oxidized starch.    
     
     
         7 . The process as claimed in  claim 6 , wherein the surfactant is a styrene/maleic anhydride copolymer.  
     
     
         8 . The process as claimed in  claim 6 , wherein the surfactant is a methyl methacrylate/acrylic acid copolymer.  
     
     
         9 . The process as claimed in  claim 6 , wherein the surfactant is a styrene/acrylic acid copolymer.  
     
     
         10 . The process as claimed in  claim 1 , wherein the surfactant is oxidized starch.  
     
     
         11 . The process as claimed in one of the preceding claims, in which the dispersed polymers of the aqueous composition come from the radical emulsion polymerization, within the surfactant solution, of an overall hydrophobic mixture of monomers, the composition of which may be adjusted so as to obtain a polymer having one or more glass transition temperatures Tg of between −20° C. and +100° C.  
     
     
         12 . The process as claimed in  claim 11 , wherein the monomers to be polymerized are chosen from vinyl, styrene, (meth)acrylic and diene monomers, and unsaturated α, β-dicarboxylic acids and derivatives thereof.  
     
     
         13 . The process as claimed in  claim 1 , in which the useful amounts of wet-strength agents, expressed by weight of dry matter with respect to the mass of dry fibers, are from 0.1 to 5%, preferably from 0.5 to 3%, of aqueous dispersion and from 0.1 to 5%, preferably from 0.5 to 4%, of PAE resin, respectively.  
     
     
         14 . An aqueous composition containing: 
 from 5 to 15% by weight of a cationic resin such as PAE and    from 5 to 15% by weight of a thermoplastic polymer dispersed in the form of particles having a diameter of between 30 and 500 nm wherein said polymer contains from 0.5 to 10% by weight of units derived from the polymerization of least one monomer (A) containing an acid functional group and wherein the particles are stabilized by a nonionic surfactant or by a mixture of ionic and nonionic surfactants.    
     
     
         15 . The composition as claimed in  claim 14 , wherein the monomer A is chosen from the group containing unsaturated monocarboxylic or α, β-dicarboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, maleic acid and derivatives thereof, such as maleic anhydride.  
     
     
         16 . The composition as claimed in  claim 15 , wherein the monomer A is acrylic acid.  
     
     
         17 . The composition as claimed in  claim 15 , wherein the monomer A is maleic anhydride.  
     
     
         18 . The composition as claimed in one of  claims 14  to  17 , wherein the nonionic surfactant is chosen from the group consisting of ethoxylated nonyl phenols and ethoxylated fatty alcohols.  
     
     
         19 . The composition as claimed in one of  claims 14  to  18 , wherein the thermoplastic polymer is obtained by the emulsion polymerization, within the surfactant solution, of a monomer mixture containing: 
 from 0.5 to 10% of at least one monomer A and  
 from 99.5 to 90% of at least one monomer B, the composition of the mixture being defined so as to obtain a thermoplastic polymer having one or more glass transition temperatures (Tg) of between −20° C. and 100° C.  
 
     
     
         20 . A process for the treatment of paper consisting of the application to the paper of the composition of  claims 14  to  19 , in which the useful amounts of the wet-strength agents, expressed by weight of dry matter with respect to the mass of dry fibers, is from 0.1 to 10% and preferably from 0.2 to 5%.  
     
     
         21 . A process for manufacturing paper having wet strength, in which a PAE resin and a promoter, consisting of a latex based on a very fine dispersion of styrene/butyl acrylate thermoplastic copolymers in an aqueous solution of a styrene/maleic anhydride copolymer, are introduced into a chemical cellulosic pulp consisting of plant fibers refined to a high degree Schopper-Riegler, especially cotton fibers, successively or simultaneously.  
     
     
         22 . A process for the manufacture of hydrophobic papers having wet strength, in which a PAE resin and a promoter consisting of a latex based on a very fine dispersion of styrene/butyl acrylate thermoplastic copolymers in an aqueous solution of a styrene/maleic anhydride copolymer, this latex having a minimum film-forming temperature of between 0 and +60° C. and having a glass transition temperature of between −20 and +60° C., are introduced into the cellulosic pulp, successively or simultaneously.  
     
     
         23 . The process for manufacturing paper having wet strength, in which a PAE resin and a promoter consisting of a very fine dispersion of thermoplastic polymers of a butyl acrylate/methyl methacrylate/methacrylic acid terpolymer of 58.3/38.7/3 composition are introduced into a chemical cellulosic pulp consisting of plant fibers refined to a high degree Schopper-Riegler, especially cotton fibers, successively or simultaneously.  
     
     
         24 . The process for manufacturing hydrophobic papers having wet strength, in which a PAE resin and a promoter, consisting of a very fine dispersion of thermoplastic polymers having a minimum film-forming temperature of between 0 and +60° C. and having a glass transition temperature of between −20 and +60° C, are introduced into the cellulosic pulp, successively or simultaneously.  
     
     
         25 . The process for manufacturing hydrophobic papers having wet strength, in which a composition, the dry matter of which is composed of 50% of PAE and 50% of a butyl acrylate/methyl methacrylate/acrylic acid terpolymer of 58.3/38.7/3 composition, is introduced into the cellulosic pulp.