Paper and paperboard production process and corresponding novel retention and drainage aids, and papers and paperboards thus obtained

Abstract

The invention relates to an improved paper production process, according to which a branched polymer prepared in reverse phase emulsion is used as the main retention aid, and then bentonite is used as the secondary retention aid (a dual type system). The two additions are separated by a stage for shearing the fibrous suspension (or mass). A distinctly improved retention of the fines is obtained, and also a distinct improvement in drainage. Moreover, the bentonite content in the white water is reduced.

1 . Process for producing a sheet of paper, paperboard or the like having improved retention and drainage properties, of the type which uses a dual system of an acrylic polymer and bentonite or a possibly treated kaolin as the primary and secondary retention aids, respectively, the introductions of which are separated by a stage for shearing the suspension or fibrous mass or paper pulp, characterized in that said polymer is a branched acrylic (co)polymer prepared in the form of a reverse phase water-in-oil emulsion, used either in emulsion inverted in water, or in a solution of the powder obtained by drying the emulsion.  
     
     
         2 . Process according to  claim 1 , characterized in that the branched acrylic (co)polymer prepared in reverse phase emulsion is introduced into the paper pulp at a concentration of 0.03 to one per mill (0.03 to 1% o) by weight, or 30 to 1,000 g/t, of the dry weight of the fibrous suspension of paper pulp, preferably 0.15 to 0.5 per mill (0.15 to 0.5% o), or 150 to 500 g/t.  
     
     
         3 . Process according to  claim 1  or  2 , characterized in that the branched acrylic (co)polymer prepared in reverse phase emulsion is a cationic copolymer of acrylamide and of an unsaturated cationic ethylenic monomer chosen from the group comprising dimethylaminoethyl acrylate (ADAME), dimethylaminoethyl methacrylate (MADAME), quaternized or salified by different acids and quaternizing agents, benzyl chloride, methyl chloride, alkyl or aryl chlorides, dimethyl sulfate, diallyldimethylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC), and methacrylamidopropyltrimethylammonium chloride (MAPTAC).  
     
     
         4 . Process according to any of claims  1  through  3 , characterized in that the branched acrylic (co)polymer in reverse phase emulsion is branched by means of a branching agent constituted by a polyfunctional compound having at least two reagent groups chosen from the group comprising the double bonds, the aldehyde bonds or the epoxy bonds.  
     
     
         5 . Process according to any of claims  1  through  4 , characterized in that the branched acrylic (co)polymer in reverse phase emulsion is branched by means of a branching agent constituted by methylenebisacrylamide (MBA).  
     
     
         6 . Process according to  claim 5 , characterized in that the MBA is introduced at a concentration of 5 to 200 moles per million moles of monomers.  
     
     
         7 . Process according to  claim 5  or  6 , characterized in that the bentonite is a semisodic bentonite, used at a rate of 0.1 to 0.5 percent (0.1 to 0.5%) of the dry weight of the fibrous suspension.  
     
     
         8 . Process according to  claim 5 ,  6  or  7 , characterized in that the pulp used, which contains the filler, is diluted, after which the polymer is added as the main retention aid a shearing stage is carried out, for example in the mixing pump or “fan pump,” then the bentonite is added as the secondary retention aid.  
     
     
         9 . Process according to  claim 8 , characterized in that the quantity of branched polyacrylamide (or more generally of branched acrylic (co)polymer), introduced either in reverse phase water-in-oil emulsion inverted in water, or in a solution of the powder obtained by drying the emulsion, is between 0.03 and 1% o, or between thirty and one thousand grams per ton (30 and 1,000 g/t) of dry pulp.  
     
     
         10 . Process according to  claim 8  or  9 , characterized in that the quantity of branched polyacrylamide (or more generally of branched acrylic (co)polymer), introduced either in reverse phase water-in-oil emulsion inverted in water, or in a solution of the powder obtained by drying the emulsion, is between 0.15 and 0.5% o (or between 150 and 500 g/t).  
     
     
         11 . Process according to  claim 8 ,  9  of  10 , characterized in that the bentonite is replaced by kaolin, possibly pretreated with an electrolyte, as the secondary retention aid.  
     
     
         12 . Process according to any of claims  1  through  11 , characterized in that the branched polymer prepared in reverse phase emulsion is injected or introduced (either in emulsion inverted in water, or in a solution of the powder obtained by drying the emulsion), before a shearing stage, into the paper pulp (or fibrous mass to be flocculated), which is more or less diluted according to the experience of one skilled in the art, and generally into the diluted paper pulp or “thin stock,” i.e. a pulp diluted to about 0.7-1.5% solid matter such as cellulose fibers, possible fillers, and the various additives common in papermaking.  
     
     
         13 . Process according to any of claims  1  through  12 , characterized in that some of the branched polymer in emulsion is introduced at the level of the stage for preparing the “thick stock” with about 5% or more solid matter, or even at the level of the preparation of the thick stock before a shearing stage.  
     
     
         14 . Novel retention aid for the production of a sheet of paper, paperboard or the like, characterized in that it comprises a branched polyacrylamide (or more generally a branched acrylic (co)polymer) in reverse phase (or oil-in-water) emulsion (either in reverse phase emulsion dissolved or “inverted” in water, or in a solution of the powder obtained by drying the reverse phase emulsion, especially by means of spray-drying).  
     
     
         15 . Novel retention aid for the productions of a sheet of paper, paperboard or the like according to  claim 14 , characterized in that the branching agent is a branching agent constituted by a polyfunctional compound having at least two reagent groups chosen from the group comprising the double bonds, the aldehyde bonds or the epoxy bonds, particularly methylenebisacrylamide (MBA).  
     
     
         16 . Novel retention aid for the production of a sheet of paper, paperboard or the like according to  claim 15 , characterized in that the branching agent is introduced at a rate of five to two hundred (5 to 200) moles per million moles of monomers, preferably 5 to 50.  
     
     
         17 . Novel retention aid for the production of a sheet of paper, paperboard or the like according to  claim 14 ,  15  or  16 , characterized in that the branched polyacrylamide is a cationic copolymer of acrylamide and of an unsaturated cationic ethylenic monomer, chosen from the group comprising dimethylaminoethyl acrylate (ADAME), dimethylaminoethyl methacrylate (MADAME), quaternized or salified by different acids and quaternizing agents, benzyl chloride, methyl chloride, alkyl or aryl chlorides, dimethyl sulfate, diallyldimethylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC), and methacrylamidopropyltrimethylammonium chloride (MAPTAC).  
     
     
         18 . Novel retention aid for the production-of a sheet of paper, paperboard or the like according to any of claims  14  through  17 , characterized in that its UL viscosity is >3.  
     
     
         19 . Novel retention aid for the production of a sheet of paper, paperboard or the like according to any of claims  14  through  18 , characterized in that its UL viscosity is >3.5.  
     
     
         20 . Novel retention aid for the production of a sheet of paper, paperboard or the like according to any of claims  14  through  19 , characterized in that its UL viscosity is >4.  
     
     
         21 . Novel retention aid for the production of a sheet of paper, paperboard or the like according to any of claims  14  through  20 , characterized in that it is “moderately branched,” for example with 10 ppm of branching agent relative to the active material.  
     
     
         22 . Sheet of paper, paperboard or the like, characterized in that it is obtained with the use of a retention aid according to any of claims  14  through  21 .  
     
     
         23 . Sheet of paper, paperboard or the like, characterized in that it is obtained with the use of a process according to any of claims  1  through  13 .