Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/37—Polymers of unsaturated acids or derivatives thereof, e.g. polyacrylates
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/28—Starch
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
  • D21H17/44—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups cationic
  • D21H17/45—Nitrogen-containing groups
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/06—Paper forming aids
  • D21H21/10—Retention agents or drainage improvers

Definitions

• This invention relates to the preflocculation of fillers used in papermaking, particularly, the production of shear resistant filler flocs with a defined and controllable size distribution at high filler solids is disclosed.
• preflocculation is the modification of filler particles into agglomerates through treatment with coagulants and/or flocculants prior their flocculation and addition to the paper stock.
• the flocculation treatment and shear forces of the process determine the size distribution and stability of the flocs prior to addition to the paper stock.
• the chemical environment and high fluid shear rates present in modern high-speed papermaking require filler flocs to be stable and shear resistant.
• the floc size distribution provided by a preflocculation treatment should minimize the reduction of sheet strength with increased filler content, minimize the loss of optical efficiency from the filler particles, and minimize negative impacts on sheet uniformity and printability. Furthermore, the entire system must be economically feasible.
• filler flocs formed by a low molecular weight coagulant alone tend to have a relatively small particle size that breaks down under the high shear forces of a paper machine.
• Filler flocs formed by a single high molecular weight flocculant tend to have a broad particle size distribution that is difficult to control, and the particle size distribution gets worse at higher filler solids levels, primarily due to the poor mixing of viscous flocculant solution into the slurry. Accordingly, there is an ongoing need for improved preflocculation technologies.
• US 2009 267 258 discloses a method of preparing a stable dispersion of flocculated filler particles having a specific particle size distribution for use in papermaking processes.
• At least one embodiment is directed towards a method of preparing a stable dispersion of flocculated filler particles having a specific particle size distribution for use in papermaking processes according to claim 1.
• the method comprises the steps of: a) providing an aqueous dispersion of filler particles; b) adding a first flocculating agent to the dispersion in an amount sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler particles, and the first flocculating agent being amphoteric; c) adding a microparticle to the dispersion in an amount insufficient cause significant flocculation of the filler particles before, simultaneous to, and/or after adding the first flocculating agent, and prior to adding a second flocculating agent; d) adding the second flocculating agent to the dispersion in an amount sufficient to initiate flocculation of the filler particles in the presence of the first flocculating agent wherein the second flocculating agent has opposite charge to the net charge of the first amphoteric
• the filler flocs may have a median particle size of 10-100 ⁇ m.
• the filler may be selected from the group consisting of precipitated calcium carbonate, ground calcium carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate, barium sulfate and magnesium hydroxide, and mixtures thereof.
• the first flocculating agent is amphoteric and has a net anionic charge.
• the second flocculating agent is cationic, and may be selected from the group consisting of copolymers and terpolymers of (meth) acrylamide with dimethylaminoethyl methacrylate (DMAEM), dimethylaminoethyl acrylate (DMAEA), diethylaminoethyl acrylate (DEAEA), diethylaminoethyl methacrylate (DEAEM) or their quaternary ammonium forms made with dimethyl sulfate, methyl chloride or benzyl chloride, and mixtures thereof.
• DMAEM dimethylaminoethyl methacrylate
• DAEA dimethylaminoethyl acrylate
• DEAEA diethylaminoethyl methacrylate
• DEAEM diethylaminoethyl methacrylate
• the second flocculating agent may be acrylamide-dimethylaminoethyl acrylate methyl chloride quaternary copolymer having a cationic charge of 10-50 mole percent and a RSV of at least 15 dL/g and/or may be a homopolymer of diallyl dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.
• the filler may be anionically dispersed and a low molecular weight, cationic coagulant is added to the dispersion to at least partially neutralize its anionic charge prior to the addition of the first flocculating agent or microparticle. Swollen starch may also be added to the dispersion of filler particles.
• the swollen starch may be cationic, anionic, amphoteric or noionic and/or may be a swollen-starch-latex composition.
• the microparticle may be one item selected from the list consisting of: siliceous materials, silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites, and synthetic or naturally occurring swelling clays, anionic polymeric microparticles, cationic polymeric microparticles, amphoteric organic polymeric microparticles, and any combination thereof.
• At least one embodiment is directed towards a method of preparing a stable dispersion of flocculated filler particles having a specific particle size distribution for use in a papermaking processes.
• a first flocculating agent is added to an aqueous dispersion of filler particles in an amount and under conditions such that it mixes uniformly with the dispersion but does not cause any significant flocculation of the filler particles.
• a microparticle is added to the dispersion.
• first and second agents are according to any and all of the methods and procedures described in US Patent 8,088,213 .
• the flocculated dispersion can be sheared to provide a dispersion of filler flocs having an optimal particle size.
• microparticles have previously been used in papermaking processes, their use in this manner is quite novel. In some prior art processes, microparticles were added in the wet end to prevent the loss of material from the fiber-filler mixture. In this invention however the microparticles are added to the dispersion of filler prior to the dispersion coming into contact with the fibers used to make the paper.
• This invention is also different than previous microparticle using methods of preparing filler dispersions aiming to have optimal degrees of high shear stability simultaneous to sharp particle size have used microparticles (such as that of US Published Patent Application 2009/0267258 ). Those previous methods used the microparticles after the second (flocculation initiating) flocculating agent. In this invention the microparticle is added to the dispersion before flocculation is initiated. This is because the invention makes use of a previously unknown property of these microparticles.
• Microparticles are known to facilitate flocculation by strongly interacting with the flocculating agents to strengthening the resulting particle agglomeration. Thus it was previously known that they assisted only one (shear strength) of the two prerogatives of concern (shear strength and particle size).
• microparticles can positively interact with the filler particles in the absence of any flocculation occurring. Without being limited by theory or design it is believed that the microparticles form very hard "anchor sites" on the surface of the filler particles. Because these anchor sites are much harder that the flocculating polymers, they resist bending and more firmly hold polymer agglomerations onto the filler particles than agglomerations anchored in place by flocculating agents. Thus the inventive method uses microparticles to facilitate the other of the two prerogatives, increasing agglomeration size.
• the microparticle is one selected from the list consisting of: siliceous materials silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites, and synthetic or naturally occurring swelling clays, anionic polymeric microparticles, cationic polymeric microparticles, or amphoteric organic polymeric microparticles, and any combination thereof.
• the swelling clays may be bentonite, hectorite, smectite, montmorillonite, nontronite, saponite, sauconite, mormite, attapulgite, and sepiolite.
• a suitable representative microparticle is product PosiTEK 8699 (produced by Nalco Company, Naperville IL).
• Polymeric microparticles useful in this invention typically have limited solubility in water, may be crosslinked, and have an unswollen particle size of less than 750 nm.
• Anionic organic microparticles include those described in US 6,524,439 and made by hydrolyzing acrylamide polymer microparticles or by polymerizing anionic monomers as (meth)acrylic acid and its salts, 2-acrylamido-2-methylpropane sulfonate, sulfoethyl-(meth)acrylate, vinylsulfonic acid, styrene sulfonic acid, maleic or other dibasic acids or their salts or mixtures thereof.
• anionic monomers may also be copolymerized with nonionic monomers such as (meth)acrylamide, N-alkylacrylamides, N,N-dialkylacrylamides, methyl (meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl methyl formamide, vinyl acetate, N-vinyl pyrrolidone, and mixtures thereof.
• nonionic monomers such as (meth)acrylamide, N-alkylacrylamides, N,N-dialkylacrylamides, methyl (meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl methyl formamide, vinyl acetate, N-vinyl pyrrolidone, and mixtures thereof.
• Cationic organic microparticles include those described in US 6,524,439 and made by polymerizing such monomers as diallyldialkylammonium halides, acryloxyalkyltrimethylammonium chloride, (meth)acrylates of dialkylaminoalkyl compounds, and salts and quaternaries thereof and, monomers of N,N-dialkylaminoalkyl(meth)acrylamides, (meth)acrylamidopropyltrimethylammonium chloride and the acid or quaternary salts of N,N-dimethylaminoethylacrylate and the like.
• cationic monomers may also be copolymerized with nonionic monomers such as (meth)acrylamide, N-alkylacrylamides, N,N-dialkylacrylamides, methyl (meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl methyl formamide, vinyl acetate, N-vinyl pyrrolidone, and mixtures thereof.
• nonionic monomers such as (meth)acrylamide, N-alkylacrylamides, N,N-dialkylacrylamides, methyl (meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl methyl formamide, vinyl acetate, N-vinyl pyrrolidone, and mixtures thereof.
• Amphoteric organic microparticles are made by polymerizing combinations of at least one of the anionic monomers listed above, at least one of the cationic monomers listed above, and, optionally, at least one of the nonionic monomers listed above.
• Polymerization of the monomers in an organic microparticle typically is done in the presence of a polyfunctional crosslinking agent.
• crosslinking agents are described in US 6,524,439 as having at least two double bonds, a double bond and a reactive group, or two reactive groups.
• these agents are N,N-methylenebis(meth)acrylamide, polyethyleneglycol di(meth)acrylate, N-vinyl acrylamide, divinylbenzene, triallylammonium salts, N-methylallylacrylamide glycidyl (meth)acrylate, acrolein, methylolacrylamide, dialdehydes like glyoxal, diepoxy compounds, and epichlorohydrin.
• the microparticle dose is between 0.2 and 8 lb/ton of filler treated. In an embodiment, the microparticle dose is between 0.5 and 4.0 lb/ton of filler treated. These dosages refer to the active pounds of microparticle per 2000 pounds of dry filler.
• the method also involves contacting the filler particles with swollen starch.
• swollen starch As described in US Patents 2,805,966 , 2,113,034 , 2,328,537 , and 5,620,510 when starch slurry is cooked in a steam cooker under controlled temperature (and optionally controlled pH) condition, the starch can absorb large amounts of water without rupturing. The addition of such swollen starches can also increase the size of the filler flocs used in this invention.
• the swollen starch is a cross-linked starch such as one or more of those described in US Patent 8,298,508 and International Patent Application WO/97/46591 .
• the swollen starch added to the filler particles and/or the method of its use is according to any one of the swollen starch-latex compositions and methods described in US Patent Application 2010/0078138 .
• the swollen starch-latex composition in the presence or absence of co-additives, is suitably prepared in batch or jet cookers or by mixing the suspension of starch and latex with hot water.
• the swelling is done under controlled conditions of temperature, pH, mixing and mixing time, in order to avoid rupture of the swollen starch granules.
• the composition is rapidly added to the filler suspension, which is then introduced to the paper furnish, at a point prior to or at the headbox of the paper machine.
• the retained swollen starch granules with filler particles will rupture, thereby liberating amylopectin and amylose macromolecules to bond the solid components of the sheet.
• the combination of swollen starch and latex can be used in filler treatments under acid, neutral or alkaline environments.
• the filler is treated with a swollen starch-latex composition, made with or without co-additives, and is then added to paper slurry.
• the filler particles agglomerate and the agglomerated filler particles adsorb on the surfaces of the fines and fibers causing their rapid flocculation in the furnish.
• the swollen starch-latex composition is made by adding latex to uncooked starch and is followed by partial cooking at temperatures slightly below the gel point to produce swollen starch.
• one or more swollen starch compositions is added to the filler dispersion before or simultaneous to when the microparticle is added, before or simultaneous to when the first flocculating agent is added, before or simultaneous to when the second flocculating agent is added, after the second flocculating agent is added, and any combination thereof.
• the fillers useful in this invention are well known and commercially available. They typically would include any inorganic or organic particle or pigment used to increase the opacity or brightness, increase the smoothness, or reduce the cost of the paper or paperboard sheet.
• Representative fillers include calcium carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate, barium sulfate, magnesium hydroxide, and the like.
• Calcium carbonate includes GCC in a dry or dispersed slurry form, chalk, PCC of any morphology, and PCC in a dispersed slurry form.
• the dispersed slurry forms of GCC or PCC are typically produced using polyacrylic acid polymer dispersants or sodium polyphosphate dispersants. Each of these dispersants imparts a significant anionic charge to the calcium carbonate particles.
• Kaolin clay slurries may also be dispersed using polyacrylic acid polymers or sodium polyphosphate.
• the fillers are selected from calcium carbonate and kaolin clay and combinations thereof.
• the fillers are selected from precipitated calcium carbonate, ground calcium carbonate and kaolin clay, and mixtures thereof.
• the first flocculating agent is amphoteric as long as it will mix uniformly into a high solids slurry without causing significant flocculation.
• Moderate shear is defined as the shear provided by mixing a 300 ml sample in a 600 ml beaker using an IKA RE16 stirring motor at 800 rpm with a 5 cm diameter, four-bladed, turbine impeller. This shear should be similar to that present in the approach system of a modern paper machine.
• Suitable flocculants generally have molecular weights in excess of 1,000,000 and often in excess of 5,000,000.
• the polymeric flocculant is typically prepared by vinyl addition polymerization of one or more cationic, anionic or nonionic monomers, by copolymerization of one or more cationic monomers with one or more nonionic monomers, by copolymerization of one or more anionic monomers with one or more nonionic monomers, by copolymerization of one or more cationic monomers with one or more anionic monomers and optionally one or more nonionic monomers to produce an amphoteric polymer or by polymerization of one or more zwitterionic monomers and optionally one or more nonionic monomers to form a zwitterionic polymer.
• One or more zwitterionic monomers and optionally one or more nonionic monomers may also be copolymerized with one or more anionic or cationic monomers to impart cationic or anionic charge to the zwitterionic polymer.
• Suitable flocculants generally have a charge content of less than 80 mole percent and often less than 40 mole percent.
• cationic polymer flocculants may be formed using cationic monomers
• nonionic vinyl addition polymers to produce cationically charged polymers.
• Polymers of this type include those prepared through the reaction of polyacrylamide with dimethylamine and formaldehyde to produce a Mannich derivative.
• anionic polymer flocculants may be formed using anionic monomers
• Polymers of this type include, for example, those prepared by the hydrolysis of polyacrylamide.
• the flocculant may be prepared in the solid form, as an aqueous solution, as a water-in-oil emulsion, or as a dispersion in water.
• Representative cationic polymers include copolymers and terpolymers of (meth)acrylamide with dimethylaminoethyl methacrylate (DMAEM), dimethylaminoethyl acrylate (DMAEA), diethylaminoethyl acrylate (DEAEA), diethylaminoethyl methacrylate (DEAEM) or their quaternary ammonium forms made with dimethyl sulfate, methyl chloride or benzyl chloride.
• DMAEM dimethylaminoethyl methacrylate
• DAEA dimethylaminoethyl acrylate
• DEAEA diethylaminoethyl methacrylate
• DEAEM diethylaminoethyl methacrylate
• anionic polymers include copolymers of acrylamide with sodium acrylate and/or 2-acrylamido 2-methylpropane sulfonic acid (AMPS) or an acrylamide homopolymer that has been hydrolyzed to convert a portion of the acrylamide groups to acrylic acid.
• AMPS 2-acrylamido 2-methylpropane sulfonic acid
• the flocculants have a RSV of at least 3 dL/g.
• the flocculants have a RSV of at least 10 dL/g.
• the flocculants have a RSV of at least 15 dL/g.
• RSV stands for reduced specific viscosity.
• RSV reduced specific viscosity
• the units of concentration "c" are (grams/100 ml or g/deciliter). Therefore, the units of RSV are dL/g. Unless otherwise specified, a 1.0 molar sodium nitrate solution is used for measuring RSV. The polymer concentration in this solvent is 0.045 g/dL. The RSV is measured at 30°C. The viscosities ⁇ and ⁇ o are measured using a Cannon Ubbelohde semi-micro dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a constant temperature bath adjusted to 30 ⁇ 0.02°C. The typical error inherent in the calculation of RSV for the polymers described herein is about 0.2 dL/g. When two polymer homologs within a series have similar RSV's that is an indication that they have similar molecular weights.
• the first flocculating agent is added in an amount sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler particles.
• the first flocculating agent dose is between 0.2 and 6.0 lb/ton of filler treated.
• the flocculant dose is between 0.4 and 3.0 lb/ton of filler treated.
• lb/ton is a unit of dosage that means pounds of active polymer (coagulant or flocculant) per 2,000 pounds of filler.
• the second flocculating agent can be any material that can initiate the flocculation of filler in the presence of the first flocculating agent.
• the second flocculating agent is selected from microparticles, coagulants, flocculants and mixtures thereof.
• Suitable coagulants generally have lower molecular weight than flocculants and have a high density of cationic charge groups.
• the coagulants useful in this invention are well known and commercially available. They may be inorganic or organic. Representative inorganic coagulants include alum, sodium aluminate, polyaluminum chlorides or PACs (which also may be under the names aluminum chlorohydroxide, aluminum hydroxide chloride, and polyaluminum hydroxychloride), sulfated polyaluminum chlorides, polyaluminum silica sulfate, ferric sulfate, ferric chloride, and the like and blends thereof.
• EPI-DMA epichlorohydrin-dimethylamine
• EPI-DMA copolymers crosslinked with ammonia.
• Additional coagulants include polymers of ethylene dichloride and ammonia, or ethylene dichloride and dimethylamine, with or without the addition of ammonia, condensation polymers of multifunctional amines such as diethylenetriamine, tetraethylenepentamine, hexamethylenediamine and the like with ethylenedichloride or polyfunctional acids like adipic acid and polymers made by condensation reactions such as melamine formaldehyde resins.
• Additional coagulants include cationically charged vinyl addition polymers such as polymers, copolymers, and terpolymers of (meth)acrylamide, diallyl-N,N-disubstituted ammonium halide, dimethylaminoethyl methacrylate and its quaternary ammonium salts, dimethylaminoethyl acrylate and its quaternary ammonium salts, methacrylamidopropyltrimethylammonium chloride, diallylmethyl(beta-propionamido)ammonium chloride, (beta-methacryloyloxyethyl)trimethyl ammonium methylsulfate, quaternized polyvinyllactam, vinylamine, and acrylamide or methacrylamide that has been reacted to produce the Mannich or quaternary Mannich derivatives.
• vinyl addition polymers such as polymers, copolymers, and terpolymers of (meth)acrylamide, diallyl-
• Suitable quaternary ammonium salts may be produced using methyl chloride, dimethyl sulfate, or benzyl chloride.
• the terpolymers may include anionic monomers such as acrylic acid or 2-acrylamido 2-methylpropane sulfonic acid as long as the overall charge on the polymer is cationic.
• the molecular weights of these polymers, both vinyl addition and condensation, range from as low as several hundred to as high as several million.
• polymers useful as the second flocculating agent include cationic, anionic, or amphoteric polymers whose chemistry is described above as a flocculant. The distinction between these polymers and flocculants is primarily molecular weight.
• the second flocculating agent may be used alone or in combination with one or more additional second flocculating agents.
• one or more microparticles are added to the flocculated filler slurry subsequent to addition of the second flocculating agent.
• the second flocculating agent is added to the dispersion in an amount sufficient to initiate flocculation of the filler particles in the presence of the first flocculating agent.
• the second flocculating agent dose is between 0.2 and 8.0 lb/ton of filler treated. In an embodiment, the second component dose is between 0.5 and 6.0 lb/ton of filler treated.
• one or more microparticles may be added to the flocculated dispersion prior to shearing to provide additional flocculation and/or narrow the particle size distribution.
• the second flocculating agent and first flocculating agent are oppositely charged.
• the first flocculating agent is cationic and the second flocculating agent is anionic.
• the first flocculating agent is selected from copolymers of acrylamide with dimethylaminoethyl methacrylate (DMAEM) or dimethylaminoethyl acrylate (DMAEA) and mixtures thereof.
• DMAEM dimethylaminoethyl methacrylate
• DAEA dimethylaminoethyl acrylate
• the first flocculating agent is an acrylamide and dimethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of 5-50 mole % and an RSV of > 15 dL/g.
• DAEA dimethylaminoethyl acrylate
• the second flocculating agent is selected from the group consisting of partially hydrolyzed acrylamide and copolymers of acrylamide and sodium acrylate.
• the second flocculating agent is acrylamide-sodium acrylate copolymer having an anionic charge of 5-40 mole percent and a RSV of 0.3-5 dL/g.
• the first flocculating agent is anionic and the second flocculating agent is cationic.
• the first flocculating agent is selected from the group consisting of partially hydrolyzed acrylamide and copolymers of acrylamide and sodium acrylate.
• the first flocculating agent is a copolymer of acrylamide and sodium acrylate having an anionic charge of 5-75 mole percent and an RSV of at least 15 dL/g.
• the second flocculating agent is selected from the group consisting of epichlorohydrin-dimethylamine (EPI-DMA) copolymers, EPI-DMA copolymers crosslinked with ammonia, and homopolymers of diallyl-N,N-disubstituted ammonium halides.
• EPI-DMA epichlorohydrin-dimethylamine
• the second flocculating agent is a homopolymer of diallyl dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.
• the second flocculating agent is selected from copolymers of acrylamide with dimethylaminoethyl methacrylate (DMAEM) or dimethylaminoethyl acrylate (DMAEA) and mixtures thereof.
• DMAEM dimethylaminoethyl methacrylate
• DAEA dimethylaminoethyl acrylate
• the second flocculating agent is an acrylamide and dimethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of 5-50 mole % and an RSV of > 15 dL/g.
• DAEA dimethylaminoethyl acrylate
• Dispersions of filler flocs according to this invention are prepared prior to their addition to the papermaking furnish. This can be done in a batch-wise or continuous fashion.
• the filler concentration in these slurries is typically less than 80% by mass. It is more typically between 5 and 65% by mass.
• a batch process can consist of a large mixing tank with an overhead, propeller mixer.
• the filler slurry is charged to the mix tank, and the desired amount of first flocculating agent is fed to the slurry under continuous mixing.
• the slurry and flocculant are mixed for an amount of time sufficient to distribute the first flocculating agent uniformly throughout the system, typically for about 10 to 60 seconds, depending on the mixing energy used.
• the desired amount of second flocculating agent is then added while stirring at a mixing speed sufficient to break down the filler flocs with increasing mixing time typically from several seconds to several minutes, depending on the mixing energy used.
• Microparticle is added to the filler slurry before, simultaneous to, and/or after adding the first flocculating agent, and prior to the second flocculant agent.
• a microparticle is added after the second flocculating agent.
• the addition of microparticle increases the shear stability of filler flocs and narrow down the particle size distribution of flocs.
• the mixing speed is lowered to a level at which the flocs are stable.
• This batch of flocculated filler is then transferred to a larger mixing tank with sufficient mixing to keep the filler flocs uniformly suspended in the dispersion.
• the flocculated filler is pumped from this mixing tank into the papermaking furnish.
• first flocculating agent is pumped into the pipe containing the filler and mixed with an in-line static mixer, if necessary.
• a length of pipe or a mixing vessel sufficient to permit adequate mixing of filler and flocculant may be included prior to the injection of the appropriate amount of second flocculating agent.
• the second flocculating agent is then pumped into the pipe containing the filler and mixed with an in-line static mixer, if necessary.
• Microparticle is pumped into the pipe containing the filler slurry and mixed with an in-line static mixer, if necessary.
• the addition point is before, simultaneous to, and/or after pumping the first flocculating agent, and prior to addition of the second flocculant agent.
• a microparticle is pumped after the second flocculating agent. Addition of microparticle increases the shear stability of filler flocs and narrow down the particle size distribution of flocs. High speed mixing is then required to obtain the desired size distribution of the filler flocs. Adjusting either the shear rate of the mixing device or the mixing time can control the floc size distribution.
• a continuous process would lend itself to the use of an adjustable shear rate in a fixed volume device.
• US Patent 4,799,964 is described in US Patent 4,799,964 . This device is an adjustable speed centrifugal pump that, when operated at a back pressure exceeding its shut off pressure, works as a mechanical shearing device with no pumping capacity.
• Suitable shearing devices include a nozzle with an adjustable pressure drop, a turbine-type emulsification device, or an adjustable speed, high intensity mixer in a fixed volume vessel. After shearing, the flocculated filler slurry is fed directly into the papermaking furnish.
• the median particle size of the filler flocs is at least 10 ⁇ m. In an embodiment, the median particle size of the filler flocs is between 10 and 100 ⁇ m. In an embodiment, the median particle size of the filler flocs is between 10 and 70 ⁇ m.
• the invention is practiced using at least one of the compositions and/or methods described in US Patent Application 12/975,596 . In at least one embodiment the invention is practiced using at least one of the compositions and/or methods described in US Patent 8,088,213 . In at least one embodiment the invention is practiced using at least one of the compositions and/or methods described in US Patent 8,172,983 .
• the filler slurry was diluted to 10% solids with tap water and 300 mL of this diluted slurry was placed in a 500 mL glass beaker. Stirring was conducted for at least 30 seconds prior to the addition of any chemical additives.
• the stirrer was an IKA ® EUROSTAR Digital overhead mixer with a R1342, 50 mm, four-blade propeller (both available from IKA ® Works, Inc., Wilmington, NC USA).
• the final floc size distribution was characterized by laser light scattering using the Malvern Mastersizer Micro from Malvern Instruments Ltd., Southborough, MA USA. The analysis was conducted using a polydisperse model and presentation 4PAD.
• D(V, 0.1), D(V, 0.5), and D(V, 0.9) are defined as the diameters that are equal or larger than 10%, 50%, and 90% in volume of filler flocs, respectively. Smaller span values indicate more uniform particle size distributions that are believed to have better performance in papermaking.
• the values of D(V, 0.5) and span for each example were listed in Table I and II.
• the filler used was scalenohedral, precipitated calcium carbonate (PCC) dry powder (available as Albacar HO from Specialty Minerals Inc., Bethlehem, PA, USA). This PCC powder was dispersed in tap water at 10% solid. The slurry was stirred under 800 rpm, and a small amount of the sample was taken to measure the particle size distribution using Malvern Mastersizer.
• PCC precipitated calcium carbonate
• flocculating agent DEV115 which is a commercially available anionic sodium acrylate-acrylamide copolymer with an RSV of about 32dL/g and a charge content of 29 mole percent, available from Nalco Company, Naperville, Ill., USA
• flocculating agent DEV125 which is a commercially available cationic acrylamide-dimethylaminoethyl acrylate-methyl chloride quaternary salt copolymer with an RSV of about 25 dL/g and a charge content of 10 mole percent, available from Nalco Company, Naperville, Ill., USA..
• microparticle Nalco-8699 which is a commercially available colloidal silica dispersion available from Nalco Company, Naperville, Ill., USA.
• Experiment 1 was repeated with microparticle as one of the component in the treatment program. 0.5 lb/ton Nalco-8699 was added before the addition of DEV115.
• Experiment 1 was repeated with microparticle as one of the component in the treatment program. 1.0 lb/ton Nalco-8699 was added before the addition of DEV115.
• Experiment 1 was repeated with microparticle as one of the component in the treatment program. 1.5 lb/ton Nalco-8699 was added before the addition of DEV115.
• Experiment 1 was repeated with microparticle as one of the component in the treatment program.
• 1.0 lb/ton Nalco-8699 was added after the addition of DEV115 but before DEV125.
• Experiment 1 was repeated with microparticle as one of the component in the treatment program. 1.0 lb/ton Nalco-8699 was added after the addition of DEV125.
• Experiment 1 was repeated with microparticle as one of the component in the treatment program.
• 1.0 lb/ton Nalco-8699 and 1.5 lb/ton DEV115 were premixed before adding into the filler slurry, followed by the addition of DEV125.
• Table I The particle size distribution characteristics of PCC (precipitated calcium carbonate) flocs formed by different chemical programs and sheared under 1500 rpm for various times.
• the filler used was ground calcium carbonate (GCC) slurry as 70% solids. This slurry was diluted to 10% solids with tap water. The slurry was stirred under 800 rpm, and a small amount of the sample was taken to measure the particle size distribution using Malvern Mastersizer.
• GCC ground calcium carbonate
• the results in Table II show that the untreated GCC had a monomodal particle size distribution with a median particle size of 1.51 ⁇ m and a span of 2.029.
• Experiment 8 was repeated with microparticle as one of the component in the treatment program. 1.0 lb/ton Nalco-8699 was added before the addition of DEV115.
• Experiment 8 was repeated with microparticle as one of the component in the treatment program.
• 1.0 lb/ton Nalco-8699 was added after the addition of DEV115 but before DEV125.
• Experiment 8 was repeated with microparticle as one of the component in the treatment program. 1.0 lb/ton Nalco-8699 was added after the addition of DEV125.

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