WO2013158811A1 - Controllable filler prefloculation using a dual polymer system - Google Patents

Abstract

A method of preparing a stable dispersion of flocculated filler particles for use in papermaking processes comprises sequential addition of a first flocculating agent to an aqueous dispersion of filler particles followed by shearing of the dispersion, followed by addition of a second flocculating agent to the dispersion and further shearing of the resultant filler flocs to the desired particle size resulting in shear resistant filler flocs with a defined and controllable size distribution. In addition, a neutralizing coagulant can be added to the dispersion to partially or completely neutralize the charge of the filler before the first flocculating agent is added.

Description

CONTROLLABLE FILLER PREFLOCULATION

USING A DUAL POLYMER SYSTEM Cross-Reference to Related Applications

This Application is a Continuation-in-part of pending US Patent Application serial number 1 .1/854,044 filed on September 12, 2007,

Statement Regarding Federally Sponsored Research or Development

Not Applicable,

Background of the Invention

This invention relates to the prefioceulation of fillers used in papermakmg, particularly, the production of shear resistant filler floes with a defined and controllable size distribution at high filler solids is disclosed.

increasing the filler content in printing and writing papers is of great interest for improving product quality as well as reducing raw material and energy costs. However, the substitution of cellulose fibers with fillers like calcium carbonate and clay reduces the strengtli of the finished sheet. Another problem when the filler content is increased is an increased difficulty of maintaining an even clistributioii of fillers across the three-dimensional sheet stracture. An approach to reduce these negative effects of increasing filler content is to prefiocculate fillers prior to their addition to the wet end approach system of the paper machine.

The definition of the term "prefioceulation" is the modification of filler particles into agglomerates through treatment with coagulants and/or flocculants prior their addition to the paper stock. The flocculation treatment and shear forces of the process determine the size distribution and stability of the floes prior to addition to the paper stock. The chemical environment and high fluid shear rates present in modem high-speed papermaking require filler floes to be stable and shear resistant. The floe size distribution provided by a prefioceulation ireatraent should minimize the reduciiors of sheet strength with increased filler content, minimize the loss of optical efficiency from ihe filler particles, and minimize negative impacts on sheet uniformity and printahility. Furthermore, the entire system must be economically feasible.

Therefore, the combination of high shear stability and sharp particle size distribution is vital to the success of filler preilocculation technology. However, filler floes formed by a low molecular weight coagulant alone, including commonly used starch, tend to have a relatively small particle size that breaks down under the high shear forces of a paper machine. Filler floes 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 preilocculation technologies.

The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37

C.F.R. § 1.56(a) exists.

Brief Summary of the Invention

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 comprising 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 wi thout causing significant flocculation of the filler particles; e) adding a 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; and d) optionally shearing the flocculated dispersion to provide a dispersion of filler floes having the desired particle size. At least one embodiment is directed towards a method of making paper products from pulp comprising forming an aqueous cellulosie papermaking furnish, adding an aqueous dispersion of filler floes prepared as described herein to the furnish, draining the furnish to form a sheet and drying the sheet. The steps of forming the papermaking furnish, draining and drying may be canied out in any conventional manner generally known to those skilled in the art.

At least one embodiment is directed towards a paper product incorporating the filler floes prepared as described herein.

Brief Description of the Drawings

A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:

FIG. I is an illustration of an MCL time resolution of a flocculating reaction.

Detailed Description of the Invention

The following definitions are provided to determine how terms used in this application, and in particular how the claims, are to he construed. The organization of the definitions is for convenience only and is not intended to limit any of the definitions to any particular category. For purposes of this application the definition of these terms is as follows:

Coagulant means a composition of matter having a higher charge density and lower molecular weight than a flocculani, which when added to a liquid containing finely divided suspended particles, destabilizes and aggregates the solids through the mechanism of ionic charge neutralization.

"Flocculanf 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 mterpariicle bridging.

"Flocculating Agent' means a composition of matter which when added to a liquid destabilizes, and aggregates colloidal and fineiy divided suspended particles in die liquid, flocculants and coagulants can be flocculating agents.

"GCC means ground calcium carbonate, which is manufactured by grinding naturally occurring calcium carbonate rock

"PCC means precipitated calcium carbonate which is synthetically produced. In the event thai the above definitions or a description stated elsewhere in this application is inconsistent with a meaning (explicit or implicit) which is commonly used, in a dictionary, or stated in a source incorporated by reference into this application, the application and the claim terms in particular are understood to be construed according to the definition or description in this application, and not according to the common definition, dictionary definition, or the definition that was incorporated by reference, in light of the above, in the event that a term can only be understood if it is construed by a dictionary, if the term is defined by the Kirk- Othmer Encyclopedia of Chemical Technology, 5th Edition, (2005), (Published by Wiley, John & Sons, inc.) this definition shall control how the term is to be defined in the claims.

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, tale, titanium dioxide, alumina irihydrate, 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. Some examples of GCC and PCC slurries are provided in co-pending US Patent Application Serial Number 12/323,976. The dispersed slurry forms of GCC or PCC are typically produced rising polyacryiic acid polymer dispersants or sodium polyphosphate dispersants. Each of these dispersants imparts a significant anionic charge to the calcium carbonate particles. Kaolin clay slumes may also be dispersed using polyacryJic acid polymers or sodium polyphosphate.

In an embodiment, the fillers are selected from calcium carbonate and kaolin clay and combinations thereof,

in an embodiment, the fillers are selected from precipitated calcium carbonate, ground calcium carbonate and kaolin clay, and mixtures thereof.

The first flocculating agent is preferably a cationic polymeric flocculant when used with cationieally charged fillers and anionic when used with anionically charged fillers. However, it can be anionic, nonionic, zwitterionic, or amphoteric as long as it will mix uniformly into a high solids slurry without causing significant fiocculation.

The definition of "without causing significant fiocculation" is no fiocculation of the filler in the presence of the first flocculating agent or the formation of floes which are smaller than those produced upon addition of the second flocculating agent and unstable under conditions of moderate shear. Moderate shear is defined as the shear provided by mixing a 300 ml sample in a 600 ml beaker using an IKA RE 16 stirring motor at 800 rpm with a 5 cm diameter, four- biaded, turbine impeller. This shear should be similar to that present in the approach system of a modem paper machine.

Suitable fiocculants 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 nonionie monomers to form a zwitterionic polymer. One or more zwitterionic monomers and optionally one or more nomonie monomers may also be eopolymerized with one or more anionic or catiomc monomers to impart cationic or anionic charge to the zwitterionic polymer. Suitable flocculants generally have a charg content of less than 80 mole percent and often less than 40 mole percent.

While cationic polymer flocculants may be formed using catiomc monomers, it is also possible to react certain nonionie 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.

Similarly, while anionic polymer flocculants may be formed using anionic monomers, it is also possible to modify certain nonionie vinyl addition polymers to form anionieally charged polymers. 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 (raeth)acrylamide with dimethylaminoethyl methacrylate (DMAEM), dimethylaminoethyl aerylate (DMAEA), diethylaminoethyl aerylate (DEAEA), diethylaminoethyl methacrylate (DEAEM) or their quaternary ammonium forms made with dimethyl sulfate, methyl chloride or benzyl chloride. Representative anionic polymers include copolymers of acryiamide with sodium aerylate and/or 2-acrylamido 2-methylpropane sulfonic acid (AMPS) or an acryiamide homopolymer that has been hydrolyzed to convert a portion of the acryiamide groups to acrylic acid,

in an embodiment, the flocculants have a RSV of at least 3 d^'L/g.

In an embodiment, the flocculants have a RSV of at least 10 dL/g.

In an embodiment, the flocculants have a RSV of at least 15 dL/g. As used herein, "RSV" stands for reduced specific viscosity. Within a series of polymer horaologs which are substantially linear and well solvated, "reduced specific viscosity (RSV)" measurements for dilute polymer solutions are an indication of polymer chain length and average moieciilar weight according to Determination of Molecular Weights, by Paul J. Flory, pages 266-31 , Principles of Polymer Chemistry, Cornell University Press, Ithaca, NY, Chapter VII (1953), The RSV is measured at a given polymer concentration and temperature and calculated as follows:

RS = [(n/rj₀)-l ]/e where η = viscosity of polymer solution, η₀ ^::: viscosity of solvent at the same temperature and c ^::: concentration of polymer in solution.

The units of concentration "c" are (grams/100 ml or g/decihter). 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 η and η₀ are measured using a Cannon Ubbeiohde semi-micro dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a constant temperature hath 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 homoiogs within a series have similar RSV's that is an indication that they have similar molecular wesghts.

As discussed above, the first flocculating agent is added in a amount sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler particles. In an embodiment, the first flocculating agent dose is between 0.2 and 6,0 lb/ton of filler treated. In an embodiment, the flocculant dose is between 0.4 and 3.0 lb/ton of filler treated. For purposes of this invention, "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. In an embodiment, the second flocculating agent is selected from microparticles, coagulants, flocculants and mixtures thereof. Suitable micro-particles include siliceous materials and polymeric microparticles. Representative siliceous materials include silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluniinosilicates, polyaiuminosiiicates, borosiiieates, polyborosiiicates, zeolites, and. synthetic or naturally occurring swelling clays. The swelling clays may be bentonite, hectorite, smectite, montmorillonite, nonironiie, saponiie, sauconite, monnite, attapulgite, and. sepiolite.

Polymeric microparticles useful in this invention include anionic, cationic, or amphoteric organic microparticles. These microparticles typically have limited solubility in water, may be erosslinked, 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 aerylamide polymer microparticies or by polymerizing anionic monomers as (meth)aerylic acid and its salts, 2-acrylamido-2-methylpropane sulfonate, sulfeethy!- (meth)acrylate, vinyisulfonic acid, styrene sulfonic acid, maieic or other dibasic acids or their salts or mixtures thereof These anionic monomers may also be copolymerized with nonionic monomers such as (meih)acrylamide, N-alkylaerylamides, Ν,Ν-dialkylaerylamides, 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 diaiiyldialkyiammonium hafides,

acryioxyaikyltrimethylammonium chloride, (meth)aciylates of dialkyiarninoaikyl compounds, and salts and quaternaries thereof and, monomers of ,N-dialkylaminoalkyl(meth)acrv'la.mides, (meth)aciylamidopropyltrimethyiaimnonium chloride and the acid or quaternary salts of N, ~ dimethylaminoethylacrylate and the like. These cationic monomers may also be copolymerized with nonionic monomers such as (meth)acrylamide, N-alkylacrylamides, N, - dialkylacrylatnides, methyl (meth)acrylate, acrylonitrile, N-vinyl methylacetamide, N-vinyl methyl formamide, vinyl acetate, N-vinyl pyrrolidone, and mixtures thereof. Amphoteric organic niieroparticles are made by polymerizing combinations of at least one of the anionic monomers listed above, at least one of the eationie 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 polyfunctions! cross!inking agent. These 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. Examples of these agents are N,N-methylenebis(meth)acrylamide,

polyethyleneglyeol di(meth)aerylate, N-vinyl acrylamide, divinylbenzeiie, Iriallylammormim salts, N-methylallylaciylamide glycidyl (meth)aerylate, acrolein, methylolacryi amide, dialdehydes like g!yoxal, diepoxy compounds, and epiehlorohydrm.

In an embodiment, the microparticle dose is between 0.5 and 8 lb/ton of filler treated, In an embodiment, the microparticle dose is between 1.0 and 4.0 lb/ton of filler treated.

Suitable coagulants generally have lower molecular weight than flocculants and have a high density of eationie 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 hydroxyehloride), sulfated polyaluminum chlorides, polyaluminum silica sulfate, ferric sulfate, ferric chloride, and the like and blends thereof.

Many organic coagulants are formed by condensation polymerization. Examples of polymers of this type include epichlorohydrin-dimethylamine (EPI-DMA) copolymers, and EPI-DMA copolymers crosslinked with ammonia.

Additional coagulants include polymers of ethylene dichioride and ammonia, or ethylene dichioride and dimethylamine, with or without the addition of ammonia, condensation polymers of multifunctional amines such as diethylenetriamine. tetraethyl enepeniamine, hexarnethylenediamine and the like with ethylenedichioride or polyfunctions! 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)aerylanride, diallyl-N,N~disubstituted ammonium halide, dimethylammoethyl methacrylate and its quaternary ammonium salts, dimethyiaminoethyl acrylate and its quaternary ammonium salts,

methacrylainidopropyltrimethyiamnionium chloride. diailylmethyl(beta- propionamido)axrmioniutn chloride, (beta-methacryloyloxyethyl)irimethyi ammonium methvlsulfate, quatetmzed polvvinyllactam, vinylamine, and acrylamide or methaerylamide that has been reacted to produce the Maxmieh or quatemaiy Mannich derivatives. 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.

Other polymers useful as the second flocculating agent include cationic. anionic, or amphoteric polymers whose chemistry is described above as a floceulant, The distinction between these polymers and floccuianis is primarily molecular weight.

The second flocculating agent may be used alone or in combination with one or more additional second flocculating agents, in an embodiment, one or more m croparticles 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 floccu!ation of the filler particles in the presence of the first flocculating agent, in an embodiment, 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. In an embodiment, one or more microparticies may be added to the flocculated dispersion prior to shearing to provide additional flocculation and/or narrow the particle size distribution.

In an embodiment, the second flocculating agent and first flocculating agent are oppositely charged.

In an embodiment, the first flocculating agent is cationic and the second flocculating agent is anionic.

In an embodiment, the first flocculating agent is selected from copolymers of acryiamide with dmiethylaminoethyl metbacrylaie (DMAEM) or diraethyiarainoethyl acrylate (DMAEA) and mixtures thereof,

In an embodiment, the first flocculating agent is an acryiamide and dimethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of 5-50 mole % and an RSV of > 15 dL/g.

In an embodiment, the second flocculating agent is selected from the group consisting of partially hydro lyzed acryiamide and copolymers of acryiamide and sodium acrylate.

In an embodiment, 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.

In an embodiment, the first flocculating agent is anionic and the second flocculating agent is cationic.

In an embodiment, the first flocculating agent is selected from the group consisting of partially hydrolyzed acryiamide and copolymers of acryiamide and sodium acrylate.

In an embodiment, the first flocculating agent is a copolymer of acryiamide and sodium acrylate having an anionic charge of 5-75 mole percent and an RSV of at least 15 dL/g.

in an embodiment, the second flocculating agent is selected from the group consisting of epichlorohydrin-dimethylamine (ΕΡΪ-DMA) copolymers, EPI-DMA copolymers crossiinked with ammonia, and homopolymers of diallyl-N JS-disubslituted ammonium halides. In an embodiment, the second flocculating agent is a homopolyrner of dialiyi dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.

In an. embodiment, the second flocculating agent is selected from copolymers of aerylamide with dimethylaimnoethyi raethacrylate (DMAEM) or diinethylaminoethyl acrylate (DMAEA) and mixtures thereof.

in an embodiment, the second flocculating agent is an aerylamide and diinethylaminoethyl acrylate (DMAEA) copolymer with a cationic charge content of 5-50 mole % and an RSV of > 15 dL/g.

Dispersions of filler fiocs 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 floeculant 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 Does with increasing mixing time typically from several seconds to several minutes, depending on the mixing energy used. Optionally, a microparticle is added as a third component to cause reflocculation and narrow the floe size distribution. When the appropriate size distribution of die filler floes is obtained, the mixing speed is lowered to a level at which the floes are stable. This batch of flocculated filler is then transferred to a larger mixing tank with sufficient mixing to keep the filler floes uniformly suspended in the dispersion. The flocculated filler is pumped from this mixing tank into the papermaking furnish. In a continuous process the desired amount of 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 inline static mixer, if necessary. Optionally, a niicroparticle is added as a third component to cause refloceuiation and narrow the floe size distribution. High speed mixing is then required to obtain the desired size distribution of the filler floes. Adjusting either the shear rate of the mixing device or the mixing time can control the floe size distribution. A continuous process would lend itself to the use of an adjustable shear rate in a fixed volume device. Que such device 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, Other 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 paperrnaking furnish.

In both the batch and continuous processes described above, the use of a filter or screen to remove oversize filler floes can be used. This eliminates potential machine runnability and paper quality problems resulting from the inclusion of large filler floes in the paper or board.

In an embodiment, the median particle size of the filler floes is at least 10 μηι. In an embodiment, the median particle size of the filler ilocs is between 10 and 100 μπι. In an embodiment, the median particle size of the filler ilocs is between 10 and 70 nm.

In at least one embodiment 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. EXAMPLES

The foregoing may be better understood by reference to the following Examples, which are presented for purposes of illustration and are not intended to limit the scope of the invention;

Examples 1-7

The filler used for each example was either undispersed or dispersed, scalenohedral PCC (available as Albacar HO from Specialty Minerals Inc., Bethlehem, PA USA). When undispersed PCC is used, the dry product was diluted to 10% solids using tap water. When dispersed PCC was used, it was obtained as 40% solids slurry and is diluted to 10% solids using tap water. The size distribution of the PCC was measured at three second intervals during floeculation using a Lasentec^ S400 FBRM (Focused Beam Reflectance Measurement) probe, manufactured by Lasentec, Redmond, WA. A description of the theory behind the operation of the FBRM can be found in US Patent 4,871,251. The mean chord length (MCI.) of the PCC fiocs is used as an overall measure of the extent of floeculation. The laser probe is inserted in a 600 mL beaker containing 300 mL of the 10% PCC slimy. The solution is stirred using an IKA RE 16 stirring motor at 800 rpm for at least 30 seconds prior to the addition of flocculating agents.

The first flocculating agent is added slowly over the course of 30 seconds to 60 seconds using a syringe. When a second flocculating agent is used, it is added in a similar manner to the first flocculating agent after waiting 10 seconds for the first flocculating agent to mix. Finally, when a micropartiele is added, it is added in a similar manner to the flocculating agents after waiting 10 seconds for the second flocculating agent to mix. Floccu!ants are diluted to a concentration of 0.3% based on solids, coagulants are diluted to a concentration of 0,7% based on solids, starch is diluted to a concentration of 5% based on solids, and microparticles are diluted to a concentration of 0,5% based on solids prior to use. A typical MCL time resolution profile is shown in FIG. 1.

The MCL time resolution profile of FIG. 1 was recorded by Lasentec^ S400

FBRM. At point one, the first flocculating agent is introduced into the slurry and the MCL increases then quickly decreases under 800 rpm mixing speed, indicating that the filler floes are not stable under the shear. At point two, the second flocculating agent is introduced, and the MCL also increases then decreases slightly under 800 rpm mixing. At point three, a microparticle is introduced and the MCL increases sharply then reaches a plateau, indicating that the filler floes are stable under 800 rpm mixing. Once the shear is raised to 1500 rpm, MCL starts to decrease.

For every filler flocculation experiment, the maximum MCL after addition of the flocculating agent is recorded and listed in Table Π. The maximum MCL indicates the extent of flocculation. The slurry is then stirred at 1500 rpm for 8 minutes to test the stability of the filler floes under high shear conditions. The MCL values at 4 minutes and 8 minutes are recorded and listed in Tables III and IV, respectively.

The particle size distribution of the filler floes is also characterized by laser light scattering using the Mastersizer Micro from Malvern Instruments Ltd., Southborough, MA USA. The analysis is conducted using a polydisperse model and presentation 4PAD. This presentation assumes a 1.60 refractive index of the filler and a refractive index of i .33 for water as the continuous phase. The quality of the distribution is indicated by the volume-weighted median iloc size, D(V,9.5), the span of the distribution, and the uniformity of the distribution. The span and uniformity are defined as: s an^■■·-·-■

/) V !

Here D(v, 0.1), Div.0.5) and D(v, 0.9} are defined as the diameters thai are equal or larger than 10%, 50% and 90% by volume of filler particles, respectively. Vj and Dj are the volume fraction and diameter of particles in size group i. Smaller span and uniformity values indicate a more uniform particle size distribution thai is generally believed to have better performance m papermaking. These characteristics of filler floes at maximum MCI,, 4 minutes and 8 minutes under 1500 rpm shear are listed in Tables li, 111 and IV for each example, The PCC type, flocculating agents, and doses of flocculating agents used in each example are listed in Table I, Example 8

This experiment demonstrates the feasibility of using a continuous process to flocculate the PCC slurry. A batch of 18 liters of 10% solids undispersed PCC (available as

Albacar HO from Specialty Minerals Inc., Bethlehem, PA USA) in tap water was pumped using a centrifugal pump at 7.6 L/miii into a five gallon bucket. A 1.0 lb/ton active dose of 0.3% solids flocculant A solution was fed into the PCC slurry at the centrifugal pump inlet using a progressive cavity pump. The PCC was then fed into a static mixer together with 1 .0 lb/ton active dose of a 0.7% solids solution of coagulant A. The size distribution of the filler floes was measured using the Mastersizer Micro and reported in Table II. 300 ml, of the resultant slurry was stirred in a beaker at 1500 rpm for 8 minutes in the same manner as in Examples 1-7. The characteristics of the filler floes at 4 minutes and 8 minutes are listed in Tables III and IV, respectively.

Example 9

The filler slurry and experimental procedure was the same as in Example 8, except that coagulant A v/as fed into the centrifugal pump and flocculant A was fed into the static mixer. The size characteristics of the filler floes are listed in Tables Π, ΠΙ and IV. Table I, PCC type, flocculating agent descriptions, and flocculating agent doses for examples 1 through 9,

I Napervilie, IL USA. Table II. Characteristics of filler floca at maximum MCL or 0 miri under 1500 rpm shear.

Table ill. Characteristics of filler floes after 4 minutes under 1500 rpm shear.

Table IV. Characteristics of filler floes after 8 minutes under 1500 rpm shear.

As shown in Tables II-IV, filler floes formed in Example 1, where only calionic starch was used, are not shear stable. On the other hand, filler floes formed by multiple polymers exhibit enhanced shear stability, as demonstrated in Examples 2 to 9. Examples 2, 4, 6 and 8 show filler floes prepared according to this invention and Examples 3, 5, 7 and 9 show filler floes prepared using existing methods. The filler floes prepared according to the invention generally have narrower particle size distributions after being sheared down (as shown by the smaller values of span and uniformity in Tables 111 and IV) compared with those formed by existing methods.

Examplejj)

The purpose of this example was to evaluate the effects of different sizes of PCC floes on the physical properties of handsheets. The PCC samples were obtained using the procedure described in Example 2, except that the PCC solids level was 2%. Four samples of prefloceulated filler floes ( i O-A, 10-B, 10-C and 10-D) were prepared with different particle sizes by shearing at 1500 rpm for different times, The shear times and resulting particle size characteristics are listed in Table V. Thick stock with a consistency of 2.5% was prepared from 80% hardwood dry lap pulp and 20% recycled fibers obtained from American Fiber Resources (AFR) LLC. Fairmont, WV, The hardwood was refined to a freeness of 300 mL Canadian Standard Freeness (TAPPI Test Method T 227 om-94) in a Valley Beater (from Voith Sulzer, Appleton, WI). The thick stock is diluted with tap water to 0.5% consistency.

Handsheets were prepared by mixing 650 mL of 0.5% consistency furnish at 800 rpm in a Dynamic Drainage Jar with the bottom screen covered by a solid sheet of plastic to prevent drainage. The Dynamic Drainage Jar and rnixer are available from Paper Chemistry Consulting Laboratory, inc., Carmei, NY. Mixing was started and 1 g of one of the PCC samples was added after 1 seconds, followed by 6 lb/ton (product based) of GC7503 polyaluminum chloride solution (available from Gulbrandsen Technologies, Clinton, NJ, USA) at 30 seconds, 1 lb/ton (product based) of a sodium acrylate-acrylarnide copolymer floccuiant with an RSV of about 32 dL/g and a charge content of 29 mole % (available from Nalco Company, Naperville, IL USA) at 45 seconds, and 3,5 lb/ton (active) of a borosilicate micioparticle (available from Nalco Company, Naperville, IL USA) at 60 seconds.

Mixing was stopped at 75 seconds and the furnish was transferred into the deckle box of Noble & Wood handsheet mold. The 8"x 8" handsheet was formed by drainage through a 100 mesh forming wire. The handsheet was couched from the sheet mold wire by placing two blotters and a metal plate on the wet handsheet and roll-pressing with six passes of a 25 lb metal roller. The forming wire and one blotter were removed and the handsheet was placed between two new blotters and the press felt and pressed at 50 psig using a roll press. All of the blotters were removed and the handsheet is dried for 60 seconds (top side facing the dryer surface) using a rotary drum drier set at 220°F. The average basis weight of a handsheet was 84 g/m , The handsheet mold, roll press, and rotary drum dryer are available from Adirondack Machine Company, Queensbury. NY. Five replicate handsheets are produced for each PCC sample tested. The finished handsheeis were stored overnight at TAPPI standard conditions of 50% relative humidit - and 23 °C. For each sheet, the basis weight was determined using TAPPI Test Method T 410 om-98, the ash content was determined using TAPPI Test Method T 21 1 om~ 93, brightness is determined using ISO Test Method 2470: 1999, and opacity was determined using ISO Test Method 2471 ; 1998. Sheet formatio , a measure of basis weight uniformity, was determined using a Kajaani* Formation Analyzer from Metso Automation, Helsinki, FX The results from these measurements are listed in Table VI. The tensile strength of the sheets as measured using TAPPI Test Method T 494 om-01, Scott. Bond was measured using TAPPI Test- Method T 569 pm-00, and z-directional tensile strength (ZDT) was measured using TAPPI Test Method T 541 om-89. These results are listed in Table VII.

z l Table V. Filler floe size characteristics for samples 10-A through 10-E. The 10-E sample is an untreated PCC slurry.

Table VI. The optical properties of sheets with different size filler floes.

Table VII. Mechanical strength properties of sheets with different size filler floes.

[Mechanical Strength Improvement (%)

[FCC fro mjZDT !Scott Bon<3fren$i!e IndexjTEA 1 jScott Tensile

|EX. NO, kPa) (psi) j(N-m/g) j N.cm/cm²) |ZDT [Bond index TEA

[Ϊ0-Λ [733.2 [226.3 182.9 [2.6 |I4 [26 3.8 44

|10-B [709.7 [254.8 pi .7 2.2 [10 [52 2.3 20

ji O-C [675.9 [217.2 [83.0 [2,5 .8 jz9 3.9 36

jl O-D 81.4 1219.6 185.5 [2.3 [5.7 ΐ 7.0 30

μ ο-Ε Ϊ644.9 [1 79,0 [79.9 [1.8 jO J) 0 0 As shown in Table V, the size of the filler floes decreases as the time under 1500 rpm shear increases, demonstrating the feasibility of controlling the size of filler floes by the time under high shear. Handsheets prepared from each of the four preflocculated fillers (10- A through I0-D) and the untreated filler (10-E) have roughly equivalent ash contents and basis weight, as listed in Table VI. Increasing the floe size did not hurt brightness, but decreased the formation and opacity of the sheets slightly. The mechanical strength of the sheets, as measured by z- direciional tensile strength, Scott Bond, tensile index, and tensile energy absorption (TEA) increased significantly with increasing filler floe size. This is shown in Table VII. In general, higher median PCC floe size lead to increased sheet strength. In practice, the slight loss of opacity could be compensated for by increasing the PCC content of the sheet at constant to improved sheet strength.

In at least one embodiment, a method of preflocculating filler particles for use in papermaking processes comprises: a) providing an aqueous slimy of filler particles; h) adding a first flocculating agent to the dispersion under conditions of high mixing; d) adding a second flocculating agent under conditions of high mixing in an amount sufficient to initiate flocculation of the filler particles in the presence of the first flocculating agen t; and e) optionally shearing the ^"flocculated dispersion to provide a dispersion of filler floes having the desired particle size. Preferably, the first flocculating agen t is one of the previously described anionic flocculants. Preferably, the second flocculating agent is one of the previously described cationic flocculants. The two flocculants may each have a high molecular weight and low to medium charge density.

Without being limited by theory or design it is believed that the first high molecular weight flocculating agent forms an evenly distributed mixture through the slurry before absorption. This evenly distributed mixture aids the cationic second flocculating agent in efficiently pulling together the mass to form the floe particles. As the following examples demonstrate, this embodiment's novel use of two high molecular weight flocculating agents to control the particle size distribution through the slurry produces unexpectedly efficient floe production. This embodiment can best be understood with reference to Examples 11 -16.

Sealenohedral FCC (available as Syncarb S NY from Omya) was diluted to 10% solids using tap water. The size distribution of the filler was measured at three second intervals during floeculation using a Lasentec^® S400 FBRM. The laser probe was inserted in a 600 mL beaker containing 300 mL of the 10% FCC slurry. The solution was stirred using an IK A RE 16 stirring motor at 800 rpm for at least 30 seconds prior to the addition of flocculating agents.

The first flocculating agent was added, as a dilute solution, slowly over the course of several minutes using a syringe. When a second flocculating agent is used, it was added in a similar manner to the first flocculating agent after waiting 10 seconds for the first flocculating agent to mix. The slum' is then stirred at 1500 rpm for 2-4 minutes to test the stability of the filler floes under high shear conditions. The PCC type, flocculating agents, and doses of flocculating agents used in these examples are listed in Table VIII, and the resulting

characterization of the particles is given in Table IX.

This experiment demonstrated the feasibility of using a continuous process to flocculate the PCC slurry, A batch of 18 liters of 1 0% solids undispersed PCC (available as Albacar HO from Specialty Minerals Inc., Bethlehem. PA USA) in tap water is pumped using a centrifugal pump at 7.2 kg PCC/min into a five gallon bucket. The appropriate dosage of the first flocculating agent solution is fed into the PCC slurry at the centrifugal pump inlet using a progressive cavity pump. The PCC is then fed into a static mixer together with the appropriate dosage of the second flocculating agent. The size distribution of the filler floes is measured using the Mastersizer Micro and reported in Table X. The resulting sample is exposed to additional shear by circulating the sample through a centrifugal pump; the results are also given in Table X. The results shown in Tables ΪΧ-Χ highlight the advantages of the dual floeculant treatment. Examples 12. 14-16 demonstrate improved shear stability as indicated by a lower volume percent of pariicles with size less than 10 micron, These samples were found to he superior to Examples 11 and 13 ,

Table VIII. Calcium carbonate type, flocculating agent descriptions, and flocculating agent doses for examples.

Table ίΧ, Characteristics of flocculated calcium carbonate samples in Examples 1 1 -12 as prepared at 800 rpm and upon subsequent shear under 1500 i m.

Table X. Characteristics of flocculated calcium carbonate samples in Exampl

At least one embodiment is a method of prefioceulating filler that has been dispersed using a high charge, low molecular weight, anionic dispersing agent. The method consists of a) providing an aqueous slurry of anionically dispersed filler particles; b) adding a low molecular weight coagulant to the dispersion in order to completely or partially neutralize the charge in the system; c) adding a first flocculating agent to the dispersion under conditions of high mixing; d) adding a second flocculating agent (can he a coagulant or floceulant) to the dispersion under conditions of high mixing; and e) optionally shearing the flocculated dispersion to pro vide a dispersion of filler floes having the desired particle size.

Preferably, the low molecular weight, charge-neutralizing component is a coagulant, as previously described. Preferably, the first flocculating agent is an anionic or eationie floceulant, as previously described. Preferably, the second flocculating agent is either a coagulant or a floceulant with the opposite charge of the first flocculating agent. This can best be understood with reference to the following Examples 17-20:

Examples 17-20

The dispersed ground calcium carbonate (GCC) used in the examples is either Hydrocarb HO G-ME or Omyaf^'ii 90 from Oroya. The dispersed GCC, obtained as a 65% solids slurry, is diluted to 10% solids using tap water. The size distribution of the filler is measured at three second intervals during fiocculation using a Lasentee^® S400 FBRM (Focused Beam

Reflectance Measurement) probe, as described in Examples 1 -7. The laser probe is inserted in a 600 mL beaker containing 300 ml, of the 10% PCC slurry. The solution is stirred using an IKA RE16 stirring motor at 800 rpm for at least 30 seconds prior to the addition of flocculating agents.

The neutralizing polymer is added slowly over the course of approximately a few minutes. The first flocculating agent is then added slowly over the course of several minutes using a syringe. When a second flocculating agent is used, it is added in a similar manner to the first flocculating agent after waiting 10 seconds for the first flocculating agent to mix. The sluny is then stirred at 1500 rpm for 2-4 minutes to test the stability of the filler floes under high shear conditions.

Table XI. Ground calcium carbonate source, flocculating agent descriptions, and flocculating agent doses for examples 17-20.

Table XII. Characteristics of flocculated ground calcium carbonate samples in Example 17-20, as prepared at 800 rpm and upon subsequent shear under 1500 rpm.

As shown in Table XI, Examples 18 and 20 demonstrate the invention disclosed, namely, an initial treatment with a charge-neutralizing polymer followed by two flocculating polymers. Examples 17 and 19 represent the use of a coagulant followed by a floceulani As shown in Table XII, the preflocculated GCC in Examples 18 and 20 sho improved shear stability indicated by larger median particle size D(v,0.5) at the same amount of shear. Examples 18 and 20 also have an iraproved particle size distribution, indicated by smaller span and lower percent by volume less than 10 microns.

Example 21

The purpose of these examples was to evaluate the impact of the preflocculated ground calcium carbonate on the physical properties of paper sheets. The preflocculated sample from Example 20 was used for this purpose, and compared against untreated Omyafil 90.

Thick stock with a consistency of 2.3% was prepared from 75% hardwood dry lap pulp and 25% softwood dry lap pulp. Both woods were refined to a freeness of 400 ml. Canadian Standard Freeness (TAPPI Test Method T 227 om-94) in a Valley Beater (from Voith Sulzer, Appleton, WI), The thick stock was diluted with tap water to 0.5% consistency.

Handsheets were prepared by mixing 650 mL of 0.5% consistency furnish at 800 rpm in a Dynamic Drainage Jar with the bottom screen covered by a solid sheet of plastic to prevent drainage. The Dynamic Drainage Jar and mixer are available from Paper Chemistry Consulting Laboratory, inc., Carmel, NY. Mixing was started and the GCC sample was added, followed by 1 1 lb/ton cationic starch and 3 lb/ton of alco 7542 sizing agent at 15 seconds, and finally 0.6 lb/ton (product based) of a sodium aciyiate-acrylamide copolymer fiocculant with an RSV of about 32 dL/g and a charge content of 29 mole % (available from Nalco Company, Naperville, IL).

Mixing was stopped at 45 seconds and the furnish was transferred into the deckle box of a Noble & Wood handsheet mold. The 8"x 8" handsheet was formed by drainage through a 100 mesh forming wire. The handsheet was couched from the sheet mold wire by placing two blotters and a metal plate on the wet handsheet and roll-pressing with six passes of a 25 lb metal roller. The forming wire and one blotter were removed and the handsheet was placed between two new blotters and the press felt and pressed at 50 psig using a fiat press. All of the blotters were removed and the handsheet was dried for 60 seconds (top side facing the dryer surface) using a rotary drum drier set at 220°F. The handsheet mold, roll press, and rotary dram dryer are available from Adirondack Machine Company, Glens Falls, NY. Five replicate handsheets were produced for each PCC sample tested.

The finished handsheets were stored overnight at TAPPI standard conditions of 50% relative humidity and 23°C. The basis weight (TAPPI Test Method T 410 om-98), ash content (TAPPI Test Method T 21 1 om-93) for determination of PCC content, brightness (ISO

Test Method 2470: 1999), opacity (ISO Test Method 2471 : 1998), formation, tensile strength

(TAPPI Test Method T 494 om-01), Scott Bond (TAPPI Test Method T 569 pm-00), and z- directional tensile strength. (ZDT, TAPPI Test Method T 541 om-89) of the handsheets were tested. The formation, a measure of basis weight uniformity, was determined using a Kajaani^w

Formation Analyzer from Metso Automation, Helsinki, FI.

Table XII. Properties of sheets containing untreated ground calcium carbonate or a prefloceulated sample as described in Example 20,

The mechanical strength data in Table XII indicates a 20% increase in tensile index and 10% increase in internal bond strength at a level 18% ash for the sheets containing the prefloceulated filler produced in Example 20, compared to the sheets containing untreated GCC.

While this invention may be embodied in many different forms, there described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. All patents, patent applications, scientific papers, and any other referenced materials mentioned herein are incorporated by reference in their entirety. Furthermore, the invention encompasses any possible combination of some or all of the various embodiments described herein and/or incorporated herein. In addition the invention

encompasses any possible combination that also specifically excludes any one or some of the various embodiments described herein and/or incorporated herein.

The above disclosure is intended to be illustrative and not exhaustive, This description will suggest many variations and alternatives to one of ordinaiy skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term "comprising" means "including, but not limited to", Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims,

All ranges and parameters disclosed herein are understood to encompass any and all subranges subsumed therein, and every number between the endpoints. For example, a stated range of "1 to 10" should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10: that is, all subranges beginning with a minimum value of 1 or more, (e.g. 1 to 6.1), and ending with a maximum value of 10 or less, (e.g, 2.3 to 9.4, 3 to 8, 4 to 7), and finally to each number 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10 contained within the range.

This completes the description of the preferred and alternate embodimen ts of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.

Claims

Claims

1. A method of preparing a stable dispersion of flocculated filler particles having a specific particle size distribution for use in papermaking processes comprising a) providing an aqueous dispersion of filler particles;

b) adding a first floccuiating agent to the dispersion in an amount sufficient to mix imiformly in the dispersion without causing significant flocculation of the filler particles, and the first flocculating agent being amphoteric; c) adding a second floccuiating agent to the dispersio 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 flocculating agent;

d) shearing the flocculated dispersion to provide a dispersion of filler floes having the desired particle size; and

e) flocculating the filler particles prior to adding them to a paper stock and wherein no paper stock is present during the flocculation.

2. The method of claim 1 wherein the filler floes have a median particle size of 10-100 um.

3. The method of claim 1 wherein the filler is 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.

4. The method of claim 1 wherein the first flocculating agent has net anionic charge.

5. The method of claim 4 wherein the second flocculating agent is cationic, selected from the group consisting of copolymers and terpolymers of (meth) acrylamide with

dimethylaminoeihyl rnethacrylate (DMAEM), dimethylaniinoetliyl aerylate (DMAEA), diethylaminoethyi acrvlate (DEAEA), diethylaminoethyl rnethacrylate (DEAEM) or their quaternary ammonium forms made with dimethyl sulfate, methyl chloride or benzyl chloride, and mixtures thereof.

6. The method of claim 5 wherein the second flocculating agent is acrylamide- dimethylaminoeihyl aerylate methyl chloride quaternary copolymer having a cationic charge of 10-50 mole percent and a RSV of at least 15 dL/g.

7. The method of claim 4 wherein the second flocculating agent is a homopolymer of diallyl dimethyl ammonium chloride having an RSV of 0.1-2 dL/g.

8. The method of claim 1 further comprising adding one or more microparticles to the flocculated dispersion after addition of the second flocculating agent.

9. The method of claim 1 wherein the filler is 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,

ίθ. A method of papermaking comprising the use of filler, the method comprising the steps of:

providing an aqueous dispersion of filler particles, at least one dry strength aid, and cellulose fiber stock,

treating the filler particles with a composition of matter,

combining the filler particles with the cellulose fiber stock,

treating the combination with at least one dry strength aid, and

forming a paper mat from the combination,

wherein at least 10% of the filler particles are in a dispersed form using a high anionically charged dispersant,

the cellulose fiber stock comprises a plurality of cellulose fibers and water, and the composition of matter enhances the performance of the dry strength aid in the paper mat.