Patent Application
20080066880
The inventors hereof have unexpectedly discovered that in the manufacture of paper or paperboard products, flocculation is significantly improved by use of an organic, cationic or anionic, micropolymer salt solution in combination with a siliceous material. Use of this flocculation system provides improvements in retention, drainage, and formation compared to a system using the organic micropolymers alone, or the siliceous material in the absence of the organic micropolymers.
Thus, in accordance with the present disclosure, a process is provided for making paper or paperboard, comprising forming a cellulosic suspension, flocculating the cellulosic suspension, draining the cellulosic suspension on a screen to form a sheet, and then drying the sheet, wherein the cellulosic suspension is flocculated by adding a flocculation system comprising an organic, anionic or cationic, micropolymer in a salt solution and a siliceous material, added simultaneously or sequentially.
In an specific exemplary embodiment, the process by which paper or paperboard is made comprises forming an aqueous cellulosic suspension, passing the aqueous cellulosic suspension through one or more shear stages selected from cleaning, mixing, pumping, and combinations thereof, draining the cellulosic suspension to form a sheet, and drying the sheet. The drained cellulosic suspension used to form the sheet comprises a cellulosic suspension that is flocculated with an organic micropolymer and an inorganic siliceous material, which are added, simultaneously or sequentially, in an amount of at least about 0.01 percent by weight, based on the total weight of the dry cellulosic suspension, to the cellulosic suspension after one of the shear stages. In addition, the drained cellulosic suspension used to form the sheet comprises an organic polymeric retention aid or flocculant comprising a substantially linear synthetic cationic, non ionic, or anionic polymer having a molecular weight greater than or equal to about 500,000 atomic mass units that is added to the cellulosic suspension before the shear stage in an amount such that flocs are formed by the addition of the polymer, and the flocs are broken by the shearing to form microflocs that resist further degradation by the shearing and that carry sufficient anionic or cationic charge to interact with the siliceous material and organic micropolymer to give better retention than the retention that is obtainable when adding the organic micropolymer alone after the last point of high shear.
In some embodiments, one or more shear stages comprise a centriscreen. The polymer is added to the cellulosic suspension before the centriscreen, and the flocculation system (micropolymer/siliceous material) is added after the centriscreen.
At a minimum, the flocculation system disclosed herein comprises an organic, anionic or cationic, micropolymer salt solution in combination with a siliceous material. The organic micropolymer is in the form of an aqueous salt solution and is a mixture of linear polymers and/or long chain branched polymers. The aqueous salt solution of the organic micropolymer mixture has a reduced specific viscosity above 0.2 deciliters per gram (dl/g). Suitable micropolymers can be prepared by initiating polymerization of an aqueous mixture of monomers in a salt solution to form a organic micropolymer. The monomers are selected from the group consisting of acrylamide, methacrylamide, diallyldimethylammonium chloride, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, acrylamidopropyltrimethylammonium chloride, methacrylamidoproplytrimethylammonium chloride, acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, ammonium methacrylate, and the like, and a combination comprising at least one of the foregoing monomers.
In particular, a dispersion of the organic micropolymer is prepared by polymerizing the monomer mixture containing at least 2 mole percent of a cationic or anionic monomer in an aqueous solution of a polyvalent ionic salt. The polymerization is carried out in an aqueous solution comprising about 1 to about 10 percent by weight, based on the total weight of the monomers, of a dispersant polymer, the dispersant polymer being a water-soluble anionic or cationic polymer which is soluble in the aqueous solution of the polyvalent anionic salt. The polyvalent ionic salt comprises phosphates, sulfates, and combinations thereof. The organic micropolymers exhibit a solution viscosity of greater than or equal to about 0.5 centipoise (millipascal-second) and have an ionicity of greater than or equal to about 5.0 percent.
The siliceous material is an anionic microparticulate or nanoparticulate silica-based material. The siliceous material is selected from the group consisting of hectorite, smectites, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites, laponite, sepiolites, and the like. Combinations comprising at least one of the foregoing siliceous materials can be used. The siliceous material also can be any of the materials selected from the group consisting of silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites, swellable clay, and the like, and a combination of at least one of the foregoing siliceous materials. Bentonite-type clays can be used. The bentonite can be provided as an alkali metal bentonite, either in powder or slurry form. Bentonites occur naturally either as alkaline bentonites, such as sodium bentonite, or as the alkaline earth metal salt, such as the calcium or magnesium salt.
These components of the flocculation system are introduced into the cellulosic suspension either sequentially or simultaneously. Preferably, the siliceous material and the polymeric micropolymers are introduced simultaneously. When introduced simultaneously, the components can be kept separate before addition, or can be premixed. When introduced sequentially, the organic micropolymer is introduced into the cellulosic suspension before the siliceous material.
In another embodiment, the flocculation system comprises three components, wherein the cellulosic suspension is pretreated by inclusion of a flocculant prior to introducing the organic micropolymer and siliceous material. The pretreatment flocculant can be anionic, nonionic, or cationic. It can be a synthetic or natural polymer, specifically a water-soluble, substantially linear or branched, organic polymer. The water-soluble organic polymers can be a natural polymer, such as cationic starch or synthetic cationic polymers such as polyamines, poly(diallyldimethylammonium chloride), polyamido amines, and polyethyleneimine. The pretreatment flocculant can also be a crosslinked polymer, or a blend of a crosslinked polymer and a water-sol-uble polymer. The pretreatment flocculant can also be an inorganic material such as alum, aluminum sulfate, polyaluminum chloride, aluminum chloride trihydrate and aluminum chlorohydrate, and the like.
Thus, in a specific embodiment of the paper or paperboard manufacturing process, the cellulosic suspension is first flocculated by introducing the pretreatment flocculent, then optionally subjected to mechanical shear, and then reflocculated by introducing the organic micropolymer and siliceous material simultaneously. Alternatively, the cellulosic suspension is reflocculated by introducing the siliceous material and then the organic micropolymer, or by introducing the organic micropolymer and then the siliceous material.
The pretreatment comprises incorporating the pretreatment flocculant into the cellulosic suspension at any point prior to the addition of the organic micropolymer and siliceous material. It can be advantageous to add the pretreatment flocculent before one of the mixing, screening or cleaning stages, and in some instances before the stock cellulosic suspension is diluted. It can even be advantageous to add the pretreatment flocculant into the mixing chest or blend chest or even into one or more of the components of the cellulosic suspension, such as coated broke, or filler suspensions, such as precipitated calcium carbonate slurries.
In still another embodiment, the flocculation system comprises four flocculent components, the organic micropolymer and siliceous material, a flocculant as described above, for example a water-soluble cationic flocculent, and an additional flocculent/coagulant that is an nonionic, anionic, or cationic water soluble polymer.
In this embodiment, the water soluble cationic flocculant can be organic, for example, water-soluble, substantially linear or branched polymers, either natural (e.g., cationic starch) or synthetic (e.g., polyamines, poly(diallyldimethylammonium chloride)s, polyamido amines, and polyethyleneimines). The water-soluble cationic flocculant can alternatively be an inorganic material such as alum, aluminum sulfate, polyaluminum chloride, aluminum chloride trihydrate and aluminum chlorohydrate, and the like. The water-soluble cationic flocculant is advantageously a water-soluble polymer, which can, for instance, be a relatively low molecular weight polymer of relatively high cationicity.
The at least one additional flocculant/coagulant is a water soluble polymer. The additional flocculant/coagulant component is preferably added prior to either the siliceous material, polymeric micropolymer or flocculating material. Typically the additional flocculent is a natural or synthetic polymer or other material capable of causing flocculation/coagulation of the fibres and other components of the cellulosic suspension. The additional flocculant/coagulant may be a cationic, non-ionic, anionic or amphoteric natural or synthetic polymer. It may natural polymer such as natural starch, cationic starch, anionic starch or amphoteric starch. Alternatively it may be any water soluble synthetic polymer which preferably exhibits ionic character. The preferred ionic water soluble polymers have cationic or potentially cationic functionality. For instance the cationic polymer may comprise free amine groups which become cationic once introduced into a cellulosic suspension with a sufficiently low pH so as to protonate free amine groups. Preferably however, the cationic polymers carry a permanent cationic charge, such as quaternary ammonium groups. When anionic or cationic, the anionic or cationic polymer is formed from a water soluble ethylenically unsaturated monomer or water soluble blend of ethylenically unsaturated monomers comprising at least one anionic or cationic monomer. The cationic or anionic polymer is a branched or linear polymer which has an intrinsic viscosity above 2 dl/g. For instance, the polymer can be a homopolymer of any suitable ethylenically unsaturated cationic monomers
Cationic flocculant/coagulants are desirably a water soluble polymer, which can, for instance be a relatively low molecular weight polymer of relatively high cationicity. For instance, the polymer can be a homopolymer of diallyl dimethyl ammonium chloride are exemplary. The low molecular weight, high cationicity polymers can be addition polymers formed by condensation of amines with other suitable di- or trifunctional species. For example, the polymer can be formed by reacting one or more amines selected from dimethyl amine, trimethyl amine, ethylene diamine, epihalohydrin, epichlorohydrin, and the like, and a combination of at least one of the foregoing amines. It is advantageous for the cationic flocculant/coagulant to be a polymer that is formed from a water-soluble ethylenically unsaturated cationic monomer or blend of monomers wherein at least one of the monomers in the blend is cationic or potentially cationic. A water-soluble monomer is a monomer having a solubility of at least 5 grams per 100 cubic centimeters of water. The cationic monomer is advantageously selected from diallyl dialkyl ammonium chlorides, acid addition salts or quaternary ammonium salts of either dialkyl aminoalkyl (meth)acrylate or dialkyl amino alkyl (meth)acrylamides. The cationic monomer can be polymerized alone or copolymerized with water-soluble non-ionic, cationic, or anionic monomers. It is advantageous for such polymers to have an intrinsic viscosity of at least 3 deciliters per gram. Specifically, up to about 18 deciliters per gram. More specifically, from about 7 up to about 15 deciliters per gram. The water-soluble cationic polymer can also have a slightly branched structure by incorporating up to about 20 parts per million by weight of a branching agent.
The additional flocculant/coagulant component is preferably added prior to either the siliceous material, organic micropolymer, or water soluble cationic flocculant.
In use, all of the components of the flocculation system can be added prior to a shear stage. It is advantageous for the last component of the flocculation system to be added to the cellulosic suspension at a point in the process where there is no substantial shearing before draining to form the sheet. Thus it is advantageous that at least one component of the flocculation system is added to the cellulosic suspension, and the flocculated cellulosic suspension is then subjected to mechanical shear wherein the flocs are mechanically degraded and then at least one component of the flocculation system is added to reflocculate the cellulosic suspension prior to draining.
In an exemplary embodiment, the first water-soluble cationic flocculant polymer is added to the cellulosic suspension and then the cellulosic suspension is mechanically sheared. The additional, higher molecular weight coagulant/flocculant can then be added and then the cellulosic suspension is sheared through a second shear point. The siliceous material and the organic micropolymer are added last to the cellulosic suspension.
The organic micropolymer and siliceous material can be added either as a premixed composition or separately but simultaneously, but they are advantageously added sequentially. Thus, the cellulosic suspension can be reflocculated by addition of the organic micropolymers followed by the siliceous material, but preferably the cellulosic suspension is reflocculated by adding siliceous material, and then the organic micropolymers.
The first component of the flocculation system can be added to the cellulosic suspension and then the flocculated cellulosic suspension can be passed through one or more shear stages. The second component of the flocculation system can be added to reflocculate the cellulosic suspension, and then the reflocculated suspension can be subjected to further mechanical shearing. The sheared reflocculated cellulosic suspension can also be further flocculated by addition of a third component of the flocculation system. In the case where the addition of the components of the flocculation system is separated by shear stages, it is advantageous that the organic micropolymer and the siliceous material are the last components to be added, at a point in the process where there will no longer be any shear.
In another embodiment, the cellulosic suspension is not subjected to any substantial shearing after addition of any of the components of the flocculation system to the cellulosic suspension. The siliceous material, organic micropolymer, and optionally, the coagulating material, can all be introduced into the cellulosic suspension after the last shear stage prior to draining. In such embodiments, the organic micropolymer can be the first component followed by either the coagulating material (if included), and then the siliceous material. However, other orders of addition can also be used, with all the components or just the siliceous material and the organic micropolymer being added.
Suitable amounts of each of the components of the flocculation system will depend on the particular component, the composition of the paper or paperboard being manufactured, and like considerations, and are readily determined without undue experimentation in view of the following guidelines. In general, the amount of sileceous material is about 0.05 to about 5.0 kg per metric ton (kg/MT); the amount of organic micropolymer dispersion is about 0.05 to about 3.0 kg/MT; and the amount of any one of the coagulants and coagulant/dispersant is about 0.05 to about 10.0 kg/MT. It is to be understood that these amounts are guidelines, but are not limiting, due to different types and amounts of actives in the solutions or dispersions:
The process disclosed herein can be used for making filled paper. The paper making stock comprises any suitable amount of filler. In some embodiments, the cellulosic suspension comprises up to about 50 percent by weight of a filler, generally about 5 to about 50 percent by weight of filler, specifically about 10 to about 40 percent by weight of filler, based on the dry weight of the cellulosic suspension. Exemplary fillers include precipitated calcium carbonate, ground calcium carbonate, kaolin, calcium sulphite, titanium dioxide, and the like, and a combination comprising at least one of the foregoing fillers. Thus, according to this embodiment, a process is provided for making filled paper or paperboard; wherein a cellulosic suspension comprises a filler, and wherein the cellulosic suspension is flocculated by introducing a flocculation system comprising a siliceous material and an organic micropolymer as described previously. In other embodiments, the cellulosic suspension is free of a filler.
The invention is further illustrated by the following non-limiting examples. The components used in the examples are listed in Table 1.
The following example illustrates the advantages of using a combination of a siliceous material and a dispersion micropolymer in a salt solution in paper production. The siliceous material is ANNP, and the dispersion micropolymer in a salt solution is ANMP. The data is from a study done with a 100 percent wood-free uncoated free sheet furnish under alkaline conditions. The furnish contains precipitated calcium carbonate (PCC) filler at a level of 29 percent by weight, based on the total weight of the furnish. Table 1 displays a list of the abbreviations used below.
The retention data are expressed in
The following example illustrates the advantage of applying a dispersion micropolymer in a salt solution with colloidal silica, in the presence of anionic polyacrylamide over the application of an oil in water emulsion micropolymer with colloidal silica in the presence of anionic polyacrylamide per the application described by U.S. Pat. No. 6,524,439. The data is from a study done with a 100 percent wood-free, uncoated, free sheet furnish under alkaline conditions. The furnish contains PCC filler at a level of 13 percent by weight.
The data in
The following data is from a study done with a wood containing furnish comprising 70 percent by weight thermomechanical pulp (TMP), 15 percent by weight ground wood pulp, and 15 percent by weight bleached kraft pulp used for super calendered (SC) paper production in alkaline conditions. The furnish contains PCC filler at a level of 28 percent by weight.
The results of this study show both retention and drainage rate data. Retention data are displayed in
The retention data in
The following example illustrates the enhanced performance in the paper and board making process when the dispersion micropolymer in a salt solution is applied, alone or in combination with siliceous material, compared to when C-Pam is applied, alone or in combination with a siliceous material. The data is from a study done on wood containing furnish used for newsprint production under acidic conditions. The furnish comprises about 5 percent by weight ash, predominantly kaolin. The dispersion micropolymer in a salt solution is CatMP-SS.
The drainage response was measured with a modified Schopper Reigler drainage tester using a single pass, while the retention characteristics were determined using a dynamic drainage jar. The results of this study are depicted in
The data in
The following example illustrates the advantages gained when the siliceous material is used in combination with the dispersion micropolymer in salt solution under acidic conditions, when compared to the use of the siliceous material in combination with regular polymers used in the art under acidic conditions. The data is from a study done on wood containing furnish used for newsprint production under acidic conditions. The furnish comprises about 5 percent by weight ash, predominantly kaolin. The drainage retention and response were measured as discussed above.
The results are presented in
The terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.” The term “water-soluble” refers to a solubility of at least 5 grams per 100 cubic centimeters of water. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety as though set forth in full.
While the invention has been described with reference to some embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
