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
  • D21H17/41—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
  • D21H17/20—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
  • D21H17/375—Poly(meth)acrylamide
• • 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
  • D21H21/14—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 characterised by function or properties in or on the paper
  • D21H21/18—Reinforcing agents
• • 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
  • D21H17/675—Oxides, hydroxides or carbonates

Definitions

• This invention relates to a method of increasing the strength of a paper mat of fibers produced in a papermaking process.
• Paper mat comprises water and solids and is commonly 4 to 8% water.
• the solid portion of the paper mat includes fibers (typically cellulose based fibers) and can also include filler.
• Increasing the strength of the paper mat would allow one to increase the proportion of the solids that is filler content. This is desirable because it reduces raw materials costs, reduces energy needed in the papermaking process, and increases the optical properties of the paper.
• Prior Art discloses paper mat having a solid portion of between 10% and 40% filler. The Prior Art however also discloses that increasing the filler content coincides with a loss in strength in the resulting paper.
• Fillers are mineral particles that are added to paper mat during the papermaking process to enhance the resulting paper's opacity and light reflecting properties. Some examples of fillers are described in US Patent Number 7,211,608. Fillers include inorganic and organic particles or pigments used to increase the opacity or brightness, or reduce the cost of the paper or paperboard sheet. Some examples of fillers include one or more of: kaolin clay, talc, titanium dioxide, alumina trihydrate, barium sulfate, magnesium hydroxide, pigments such as calcium carbonate, and the like.
• Paper strength is a function of the number and the strength of the bonds formed between interweaved fibers of the paper mat. Filler particles with greater surface area are more likely to become engaged to those fibers and interfere with the number and strength of those bonds. Because of its greater surface area, PCC filler interferes with those bonds more than GCC.
• At least one embodiment of the invention is directed towards a method of papermaking having an increased filler content.
• the method comprises the steps of: adding a first flocculating agent to an aqueous dispersion in an amount sufficient to mix uniformly in the dispersion without causing significant fTocculation of the filler particles,
• the paper fiber stock comprises a plurality of fibers and water, and the initiated flocculation enhances the performance of the strength additive in the paper mat.
• At least one embodiment of the invention is directed towards this method in which the strength of the paper made by the papermaking process is increased by an amount greater than the sum of: the strength enhancement provided by the preflocculation process using the first and second flocculating agents and the strength enhancement provided by the strength additive by itself.
• the filler may be selected from the group consisting of calcium carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate, barium sulfate, and magnesium hydroxide.
• the paper fiber may be cellulose fiber.
• the method may further comprise the step of shearing the dispersion to obtain a pre determined floc size.
• the filler floes may have a median particle size of 10-100 ⁇ m.
• the first and second flocculating agents may have an RSV of at least 2 dL/g.
• the first flocculating agent may be anionic.
• the strength additive may be glyoxylated
• the ratio of strength additive relative to the solid portion of the paper mat may be 0.3 to 5 kg of strength additive per ton of paper mat.
• the first flocculating agent may be a copolymer of acrylamide and sodium acrylate.
• the strength additive may be a cationic starch.
• the strength additive and the second flocculating agent may carry the same charge.
• the second flocculating agent may be selected from the list consisting of copolymers of acrylamide with DMAEM, DMAEA, DEAEA, DEAEM.
• the second flocculating agent may be in quaternary ammonium salt form made with a salt selected from the list consisting of dimethyl sulfate, methyl chloride, benzyl chloride, and any combination thereof.
• 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.
• the second flocculating agent may have a charge, which is opposite to the charge of the first flocculating agent.
• the filler floes may have a median particle size of 10-100 ⁇ .
• the filler may be selected from the group consisting of calcium carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate, barium sulfate and magnesium hydroxide.
• the low molecular weight composition may be a cationic coagulant
• the first flocculating agent may be an anionic flocculent
• the second flocculating agent may be a cationic flocculent
• both flocculants may have a molecular weight of at least 1,000,000
• FIG. 1 is a graph showing the improved strength of paper made according to the invention.
• Coagulant means a composition of matter having a higher charge density and lower molecular weight than a flocculant, which when added to a liquid containing finely divided suspended particles, destabilizes and aggregates the solids through the mechanism of ionic charge neutralization.
• DMAEM dimethylaminoethylmethacrylate as described and defined in US Patent 5,338,816.
• DAEA dimethylaminoethylacrylate as described and defined in US Patent 5,338,816.
• DEAEM diethylaminoethyl methacrylate as described and defined in US Patent 6,733,674.
• Flocculant means a composition of matter having a low charge density and a high molecular weight (in excess of 1 ,000,000) which when added to a liquid containing finely divided suspended particles, destabilizes and aggregates the solids through the mechanism of interparticle bridging.
• Flocculating Agent means composition of matter that when added to a liquid, destabilizes and aggregates colloidal and finely divided suspended particles in liquid into floes.
• GCC ground calcium carbonate, which is manufactured by grinding naturally occurring calcium carbonate rock
• PCC precipitated calcium carbonate which is synthetically produced.
• Preflocculation means the modification of filler particles into agglomerates through treatment with a particular flocculating agent selected on the basis of the size distribution and stability of the floe that the flocculating agent will form.
• At least one embodiment of the invention is a method of making paper, which is strong, has a high filler content, and has superior optical properties.
• the method of papermaking comprises the steps of: providing filler material, pre- treating at least some of the filler material by preflocculation leading to a decrease in the adsorption of a strength additive on the filler material, and adding both the preflocculated filler blend and the strength additive to the paper mat.
• Preflocculation is a process in which, material is treated by two flocculating agents in a manner that optimizes the size distribution and stability of the floes under a particular shear force prior to its addition to the paper stock.
• the particular chemical environment and high fluid shear rates present in modern high-speed papermaking require filler fiocs to be stable and shear resistant.
• the floe 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. Examples of preflocculation methods applicable to this invention are described in US Published Application 2009/0065162 Al and US Application 12/431356.
• strength additives it has been known for some time that adding strength additives to paper mat increases the strength of the resulting paper.
• Some examples of strength additives are described in US Patent Number 4,605,702.
• Some examples of strength additives are cationic starches, which adhere to the cellulose fibers and tightly bind them together.
• filler to the paper mat reduces the effectiveness of the strength additive. Because filler has a much higher specific surface area than fiber, most of the strength additives added into the papermaking slurry go to filler surfaces, and therefore there is less strength additive available to bind the cellulose fibers together. This effect is more acute with PCC compared to GCC because PCC has a much higher surface area and is able to adsorb more strength additive.
• One method of addressing this situation is by pre-treating the filler material with a coagulant as described in US Application 12/323976. Another method involves using preflocculation instead of a coagulant.
• the filler content in the paper is increased by the following method: An aqueous dispersion of filler materials is formed and the filler materials are preflocculated before being added to a paper fiber stock. A first flocculating agent is added to the dispersion in an amount sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler particles. A second flocculating agent is then added following the first flocculating agent, in an amount sufficient to initiate flocculation of the filler material in the presence of the first flocculating agent, the second flocculating agent being of opposite charge to the first flocculating agent. A paper mat is formed by combining the preflocculated filler material with the fiber stock and treating this combination with the strength additive. The preflocculation of the filler material enhances the performance of the strength additive.
• the fiber stock comprises fibers, fillers, and water.
• the fibers are predominantly cellulose based. In at least one embodiment the flocculated dispersion is sheared to obtain a particularly desired particle size.
• FIG. 1 illustrates that a paper produced from a paper mat that includes PCC filler tends to become weaker as more PCC filler is added.
• a strength additive adds little strength to the paper.
• Paper made from preflocculated PCC filler combined with a strength additive however increases the strength of the paper to a degree that it is stronger than paper having 10% less PCC that is not preflocculated. Even more surprising was the fact that paper containing preflocculated PCC without a strength additive was almost as strong as the paper with the strength additive.
• the strength agent is more effective in increasing sheet strength with preflocculated filler than with untreated filler and 2) there is a synergistic effect from the combination of strength agent and filler preflocculation which makes it superior to the additive effects of the sum of the strength agent alone plus the filler preflocculation alone.
• preflocculation of the PCC filler material leads to the production of paper that is unexpectedly strong.
• fillers encompassed by this invention are well known and commercially available. They include any inorganic or organic particle or pigment used to increase the opacity or brightness, reduce the porosity, or reduce the cost of the paper or paperboard sheet.
• the most common fillers are calcium carbonate and clay. However, talc, titanium dioxide, alumina trihydrate, barium sulfate, and magnesium hydroxide are also suitable fillers.
• Calcium carbonate includes ground calcium carbonate (GCC) in a dry or dispersed slurry form, chalk, precipitated calcium carbonate (PCC) of any morphology, and precipitated calcium carbonate 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 also are dispersed using polyacrylic acid polymers or sodium polyphosphate.
• the strength additive carries the same charge as the second flocculating agent.
• Strength additives encompassed by the invention include any one of the compositions of matter described in US Patent 4,605,702 and US Patent Application 2005/0161181 Al and in particular the various glyoxylated Acrylamide/DADMAC copolymer compositions described therein.
• An example of a glyoxylated Acrylamide/DADMAC copolymer composition is product ⁇ Nalco 64170 (made by Nalco Company, Naperville, Illinois).
• the fillers used are PCC, GCC, and/or kaolin clay. In at least one embodiment, the fillers used are PCC, GCC, and/or kaolin clay with polyacrylic acid polymer dispersants or their blends.
• the ratio of strength additive relative to solid paper mat can be 3kg of additive per ton of paper mat.
• the effectiveness of the synthetic strength additive is independent of or despite the presence of some, low amounts, or no amount of starch in the paper mat.
• the addition of materials in such large amounts however is cumbersome and less than ideal.
• the use of synthetic strength additives in contrast allows similar strength performance to be achieved while requiring the addition of far less strength additive material to the paper mat.
• the synthetic strength additive is cationic or anionic or contains both cationic and anionic functional groups.
• a furnish was produced containing 25% pine softwood and 75%
• eucalyptus hardwood Both the softwood and hardwood were reslushed from dry lap.
• the filler used was Albacar HO PCC obtained from Specialty Minerals Inc.
• the filler material preflocculation was performed with the dual flocculant approach described in example 14 of US Application 12/431356.
• 6 lb/ton strength additive Naco 64114, a glyoxalated Acrylamide/DADMAC copolymer

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Paper (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (2)

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Cited By (4)

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• 2010
  • 2010-03-19 US US12/727,299 patent/US8647472B2/en active Active
• 2011
  • 2011-03-18 WO PCT/US2011/028917 patent/WO2011116253A2/en not_active Ceased
  • 2011-03-18 CN CN201180002456.6A patent/CN103038419B/zh active Active
  • 2011-03-18 BR BR112012022861-7A patent/BR112012022861B1/pt active IP Right Grant
  • 2011-03-18 KR KR1020127023009A patent/KR101767460B1/ko active Active
  • 2011-03-18 CA CA2793849A patent/CA2793849C/en active Active
  • 2011-03-18 JP JP2013500223A patent/JP5828883B2/ja active Active

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