WO2000034582A1

WO2000034582A1 - Copolymer coagulant in the papermaking process

Info

Publication number: WO2000034582A1
Application number: PCT/US1999/029228
Authority: WO
Inventors: Kenneth F. Henderson; Christopher M. Lewis
Original assignee: Ecc International Inc.
Priority date: 1998-12-10
Filing date: 1999-12-09
Publication date: 2000-06-15
Also published as: AU3114900A; AU1937500A; WO2000034581A1

Abstract

An emulsion copolymer is used as a retention/drainage/formation aid in the papermaking process to improve dewatering, press solids and brightness. It is also used to treat coated broke where the white pitch or stickies and pigments are fixed to the long fibers and fiber fines. As a retention/drainage formation aid, the copolymer is a low molecular weight coagulant that is added to the papermaking cellulosic slurry prior to the first or after the last shearing stage, and, optionally, a flocculant may be added either before the addition of the copolymer or before the first or the last shearing stage. The copolymer ranges from 20 % to 50 %, preferably 40.0 % active in emulsion form and has a weight average molecular weight from 3 to 7 million. It is comprised of acrylamide (nonionic monomer) and diallyl dimethyl ammonium chloride (cationic monomer) in a weight percentage ratio range of from about 25:75 to about 75:25 based on the dry weight of the copolymer. The press solids ranges from 30 % to 65 % by dry weight solids and a Technidyne brightness level ranges from 50 to 95.

Description

COPOLYMER COAGULANT IN THE PAPERMAKING PROCESS

BACKGROUND OF THE INVENTION 1. Field Of The Invention

The present invention relates to the use of a copolymer coagulant in several areas of the papermaking process: 1) as a retention/drainage/formation aid to improve dewatering and increase the press solids; and 2) to treat coated broke where the white pitch or stickies and pigments are fixed to the long fibers and fiber fines .

2. Description Of The Background Art In the production of paper or paperboard, a dilute aqueous composition, known as "furnish" or "stock" is sprayed onto a moving mesh known as a "wire" . Solid components of this composition, such as cellulosic fibers, fines, and inorganic particulate mineral fillers are drained or filtered by the wire to form a paper sheet. The percentage of solid material retained on the wire is known as the "first pass retention" of the papermaking process.

Retention is believed to be a function of different mechanisms, such as filtration by mechanical entrainment, electrostatic attraction, and bridging between the fibers and the fillers in the furnish. Because both the cellulosic fibers and many common filler materials are negatively charged, they are mutually repellent. Generally, the only factor tending to enhance retention is mechanical entrainment. Therefore, a retention aid is generally used to improve retention of the fibers and fillers on the wire.

Drainage or dewatering relates to the rate of removal of water from the furnish as the paper sheet is formed. Drainage usually refers to water removal which takes place m the "drainage zone" (gravity and vacuum sections) of a Fourdπnier or twin wire paper machine primarily before any pressing of the wet paper web subsequent to drying of the sheet. Thus, drainage aids are used to improve the overall efficiency of dewatering in the production of paper or paperboard.

Formation relates to the uniformity of the paper or paperboard sheet produced from the papermaking process. Formation is generally evaluated by the variance of light transmission through a paper sheet. A high variance is indicative of "poor" formation and low variance is generally indicative of "good" formation. Generally, as the retention level increases, the level of formation generally decreases from good formation to poor formation It can be appreciated that improvements in retention, drainage and formation properties of the final paper or paperboard sheet are particularly desirable for several reasons, the most significant of which is productivity. Good retention and good drainage enable a paper machine to run faster and to increase production. Good sheet formation improves sheet quality. These improvements are realized by the use of retention and drainage aids. These retention and drainage aids are generally added to the furnish as the furnish approaches the head-box of the paper machine and may comprise a coagulant/flocculant system used in conjunction with one or more shearing stages. Generally, the coagulant is a low molecular weight cationic synthetic polymer that reduces the negative surface charges on the fiber, fines, and/or filler particles to accomplish a degree of agglomeration of sucn particles. The flocculant, which generally is a high molecular weight cationic, nonionic, or anionic synthetic polymer, bridges the particles and/or agglomerates, from one surface to another, thereby binding the particles into larger floes. The larger floes increase retention of the particles; however, as they are filtered out of the water onto the fiber web, the pores of the floes are covered, thereby reducing the drainage efficiency of the fiber web. The larger floes can be broken αown by shearing which is provided by one or more of the cleaning, mixing and pumping stages of the papermaking process .

Greater retention of fines and fillers permits, for a given grade of paper, a reduction n the content of cellulosic fiber of such paper. As pulps of less quality are employed to reduce papermaking costs, such as recycled pulp for newsprint or coated broke, the retention aspect of papermaking becomes even more important because the fines content of such lower quality pulps is greater generally tnan that of the pulps of higher quality.

Greater retention of fines, fillers, and other slurry components reduces the amount of such substances lost to the white water. This reduces the amount of material wastes, the cost of waste disposal, and the adverse environmental effects therefrom.

The wet paper web is created through the forming section and the vacuum water removal process of the paper machine before it passes through a pressing operation. The primary objectives of the pressing operation are to continue the water-removal process and to consolidate the web. With regard to the water-removal process m the pressing operation, it is generally more economical to remove water by mechanical means than by evaporation. A reduction in evaporative load of the web entering the dryer section is desirable. Therefore, the papermaker is continually seeking new methods n which to improve the pressing efficiency, either by chemical or mechanical means . The wet fiber web contains free water and bound water m the fiber floes. The retention chemistry can impact how easily the bound water is released from the web. In this way, the press solids and pressing efficiency can be improved by the retention chemistry. The pressing operation can be comprised of two, three, or four press nips (points where the sheet is compressed in a convergent zone) where the sheet is more consolidated in the last press than it is m the first press. In order to attain high economical efficiency, it is desirable for the paper web to have as high press solids as reasonably possible m order to reduce the amount of energy necessary to dry the sneet in the dryer section which generally follows the pressing section of the paper machine. There is a need in the art to provide an improved coagulant/flocculant system which not only provides the required retention and drainage properties m the paper furnish, but allows the bound water to be more easily released, thereby improving the pressing efficiency and giving improved sheet properties, such as formation and brightness. This may be particularly true for paper furnishes containing recycled de nked finer, groundwood, bleached fiber Imerboard and/or coated broke furnishes may also include either treated or untreated fillers for the production of coated free sheet paper and newsprint.

Coated broke may be used a portion of the furnish in certain grades of paper. Coated broke is the name given to coateα paper which has been repulped. The coated paper generally contains natural or synthetic pigments, binders, dispersants, water and other agents. These natural pigments may be titanium dioxide, clay, talc, or calcium carbonate. The binders act to adhere the pigment particles to each other and to the fiber and fines in the paper web. Generally, the primary components of the coated broke are pigments and binders. During repulpmg, the binders, i.e., starch, polyvinyl acetate (PVA), latex, styrene butadiene rubber (SBR), polyvinyl alcohol (PVOH) , and other synthetic organic cinders, are liberated from the coating. Left untreated, the binders (latex, SBR, PVA, and PVOH) agglomerate at shear points or precipitate out of solution, due to pH or temperature shock in the furnish depositing on tank walls, wires, boil blades, rolls, felts, dryer cans, or piping shear point. These deposits can break loose causing defects or breaks m the paper web. The deposition of binder agglomerates at the shear points is referred to as "white pitch" or "stickies". There is a further need to prevent the "white pitch" or "stickies" of the coated broke from forming and depositing in the sheet which can result in defects and/or breaks n the paper web.

SUMMARY OF THE INVENTION

The invention has met these needs . In a first aspect of the invention, a copolymer coagulant, particularly m emulsion form, is used in the papermaking process to improve retention of pigments and fiber fines and/or to improve drainage and formation of the sheet being formed. The percent solids within and exiting the pressing operation is increased, while a desirable level of brightness in the sheet is attained. Optionally, a water soluble flocculant polymer is used with this copolymer coagulant.

The paper may be produced by forming an aqueous cellulosic slurry comprising recycled deinked newsprint, bleached or unbleached chemical pulps (hardwood or softwood), pulp fibers, recycled fiber (bleached or unbleached) , coated broke, and ground or mechanical pulp which may or may not contain a mineral filler or pigment; passing the suspension through one or more shear stages; draining the suspension to form a wet web; pressing and drying the wee web to produce the final sheet. The copolymer coagulant, preferably, is added to the slurry prior to the first or after the last shearing stage, and the flocculant may be added either before the addition of the coagulant or before the first or after the last shearing stage before the headbox. The copolymer coagulant may also be added after the flocculant or can be combined with the flocculant and added to the aqueous cellulosic slurry ahead of the headbox. The copolymer may be added to the aqueous cellulose slurry without the flocculant. The copolymer coagulant preferably is supplied as an emulsion, and is added in emulsion form in a diluted aqueous form to the furnish slurry during the papermaking process.

In a second aspect of the invention, the copolymer of the invention is used to treat coated broke prior to or after the coated broke is added to the paper furnish. After the coated paper is repulped, the copolymer is added to the coated broke in order to attach the "white pitch" and the pigments to the longer fibers, thereby lessening the amount of "white pitch" being deposited onto sites throughout the paper making process. This treated coated broke can then be used as pulp in a papermaking process where the copolymer may be used as a retention/dramage/formation aid m accordance with the teachings of a first aspect of the invention.

The copolymer of the invention has a molecular weight ranging from about 3 to 7 million. The copolymer preferably comprises at least two monomers, i.e. a nonionic monomer and a cationic monomer, with a total weight percent ratio of a:b ranging from about 25:75 to 75:25 based on the dry weight of the solids in the copolymer .

Preferably, the copolymer of the invention s about 20.0 to about 50.00%, most preferably, about 40.0% active m emulsion form and preferably is comprised of 25% by weight acrylamide (AM) and about 75% by weight of diallyl dimethyl ammonium chloride (DADMAC) , based on the dry weight of the solids n the copolymer. The copolymer of the invention results m a furnish with: 1) a press solids m at least one pressing operation of the press in a paper making machine ranging from about 30% to about 65% by dry weight solids and a moisture content of the furnish ranging from about 70% to about 35% by weight of the furnish and 2) a Technidyne brightness level ranging from about 65 to about 90.

If a flocculant is used with the copolymer of the invention as a retention/dramage/formation system, preferably the flocculant is a high molecular weight anionic, nonionic, or cationic polymer with a molecular average molecular weight ranging from about 1 million to about 30 million. The preferred dosage for the copolymer when used as a coagulant may range from about 0.0025% to about 3.0%, and more preferably, from about 0.005% to about 1.5%, based on the αry weight of the solids. The preferred dosage for the flocculant would range from about 0.0025% to about 3.0%, and more preferably from about 0.005% to about 1.5%, based on the dry weight of the solids in the furnish .

BRIEF DESCRIPTION OF THE DRAWING

The single figure graphically demonstrates the press solids (%) and the Technidyne brightness levels for the several standard polymers, including terpolymers and copolymers, in comparison to the copolymer of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term "paper" includes products comprising a cellulosic sheet material including paper sheet, paperboard, and the like.

A first aspect of the invention relates to the use of a copolymer of the invention as a low molecular weight coagulant as a retention/dramage/formation aid and, optionally, a high molecular weight flocculant for particular use in the wet end of a paper machine in the papermaking process for both acid, neutral, and alkaline paper grades .

The copolymer of the invention comprises a nonionic monomer and a cationic monomer used as a coagulant. Preferably, the weight percent ratio of the nonionic monomer to the cationic monomer is 25% by weight acrylamide to 75% by weight diallyl dimethyl ammonium chloride based on the dry weight of the solids n the copolymer. Preferably, the copolymer is in emulsion form, but not exclusive to this form (i.e., solution, dry or dispersion) .

The components of the coagulant/flocculant system of the invention may be added simultaneously or sequentially to the furnish at the same or different points of addition but, preferably, are added in the manner and order described herembelow.

A conventional papermaking machine contains one or several shearing stages, i.e., mixing and cleaning of the furnish or stock as it passes from the stock preparation area through the papermaking machine. Thick stock generally comprises filler, fiber, strengthening agent and/or other additives and water. The thick stock generally is diluted with white water to form "thin stock" by passing the thick stock and dilution water through a mixing pump. It may be cleaned by passing it through a vortex cleaner or centriscreen and/or it may be pumped to the paper machine by one or more centrifugal pumps (transfer or fan pumps) . The thin stock may be pumped through a set of centrifugal cleaners. The thin stock may be cleaned further by passing it through a barrier or a slotted screen prior to it being passed into a headbox m preparation for the sheet forming process . In the first aspect of the invention, preferably, the copolymer coagulant is added to the thin stock before the fan pump or after the centriscreen and the flocculant is added to the thin stock either as the thin stock exits the fan pump or prior to the thin stock being passed through the centriscreen before, after, or simultaneously with the addition of the copolymer of the invention. The cationic monomer of the copolymer of the invention, in addition to diallyl dimethyl ammonium chloride (DADMAC) , may be selected from the group consisting of dialkyl diallyl ammonium monomer, quarternary dialkyl diallyl ammonium, methacryloxyethyl trimethyl ammonium chloride, acrylamido propyl trimethyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride (AETAC) , methacrylamido propyl trimethyl ammonium chloride, quatermzed derivatives of N,N- dimethyl ammo ethyl methacrylate, dimethyl ammo ethyl acrylate, and dibutyl ammo ethyl methacrylate. The nonionic monomer, in addition to the acrylamide (AM) , may be selected from the group consisting of N-vmylamide, N-alkylacrylamide, vinyl acetate, acrylate esters, diacetone acrylamide, and N, N-dialkylacrylamide, vinyl pyrrolidone, and vinyl alcohol.

The copolymer has a weight percent ratio, i.e., a) noionic monomer to b) cationic monomer, ranging from about 25:75 to about 75:25, more preferably, 25:75 for a:b, and has a low weight molecular weight of about 3 to 7 million. In emulsion form, the copolymer of the invention ranges from about 20% to 50% active and preferably, is about 40.0% active. It is theorized that the cationic moiety of the copolymer attaches positively charged anchor sites to the negatively charged pulp fines and fillers and the nonionic moiety bridges between the fines, fibers and fillers to form small uniformly spaced agglomerates. In this way, the copolymer maintains uniform spacing, thus enhancing brightness through a good distribution of the filler the paper web. The molecular weight and the charge of the copolymer enhance drainage by uniform spacing of the fibers/fines and allow the free and bound water to be more easily released n the pressing section. The high molecular weight flocculant polymer of the invention enhances the retention of fines and fioers the papermaking furnish, thereby giving better drainage along with retention. Combining the flocculant and copolymer of the invention enhances the uniformity of the paper web and water release in the press section.

An effective amount of a copolymer coagulant /flocculant system of the invention should be employed. The effective amount for a given cellulosic furnish being treated generally depends on the type of pulp, the amount of recycled fiber, the water chemistry, and the amount and type of filler. Preferably, the effective coagulant dosage will be in an amount of at least about 0.01 (active) pounds per ton (0.0005% by weight) based on the dry weight of the solids in the aqueous cellulosic furnish. The effective amount of flocculant dosage will be an amount of at least about 0.01 (active) pounds per ton (0.0005% by weight) of dry solids m the aqueous cellulosic furnish.

Preferably, the dosage of the copolymer coagulant is about 0.01 (active) pounds per ton, or about 0.0005 weight % to about 3 weight % of the total weight of the dry weight of solids in the aqueous cellulosic furnish and, most preferably, 0.005 weight % to 1.5 weight %. The dosage of the flocculant ranges from about 0.05 to about 30.0 (active) pounds per ton based on the dry weight of the solids in the aqueous celluxosic furnish, or 0.0025 weight % to 1.5 weight % of the total weight of the dry solids, and, preferably, 0.0025 weight % to 1.0 weight % .

The copolymer coagulant of the invention is preferably in emulsion form. This generally is made m a batch process where 75% by weight DADMAC and 25% acrylamide (AM) by weight of the total monomer charge is added to a reactor. The reaction catalyst and the chain transfer agent are added to the solution phase. The oil and emulsifying surfactant are added during the emulsification step. The emulsion s heated with stirring to polymerize the monomers. The final step is the addition of the inverting surfactant. The final product is 40% active water in oil emulsion. The amounts and types of catalyst, chain transfer agent, oil, and emulsifying surfactant are well known to those skilled in the art. An example of such a copolymer coagulant is available from Calgon Corporation under the trade name ECCat™5200.

The coagulant/flocculant system of the invention can generally be successfully added to aqueous cellulosic furnishes over the entire pH range customarily employed in the papermaking process. Preferably, the coagulant/flocculant system of the invention is aαded to aqueous cellulosic furnishes having a pH from about 3 to 10. Therefore, it will be appreciated by those skilled m the art that the system of the invention may be added to paper furnishes that are acid, alkaline, or neutral in character. Where generally an acid furnish has a pH range from about 3.8 to 6.5, an alkaline furnish has a pH range of about 7.2 to greater than about 10, and a neutral furnish has a pH range of from about 6.5 to 7.2.

As stated heremabove, preferably, the copolymer coagulant of the invention is added to the paper furnish either before or after the final shearing stage and the high molecular weight flocculant polymer is added before or after the coagulant and, which may or may not be before the last shearing stage so "good mixing" of the polymers occurs before the th n stock enters the headbox of the paper machine. The copolymer of the invention may be used alone without a flocculant.

Examples of high molecular weight polymer flocculants suitable for use herein are those having a weight average molecular weight of about 100,000 or more, especially 500,000 or more. Preferably, the molecular weight is about 1 million and often above about 5 million, for instance in the range 10 to 30 million or more. These polymers may be linear, branched, cationic, anionic, nonionic, amphoteπc, or hydrophobically modified polymers of acrylamide or other nonionic monomers .

If a cationic flocculant polymer is used, the polymer may contain at least one cationic monomer selected from the group of a quaternary dialkydiallyl ammonium, methacryloyloxyethyl trimethyl ammonium chloride, methacryloyloxeythyl trimethyl ammonium methosulfate, acrylamido propyl triethyl ammonium chloride, methacrylamido propyl triethyl ammonium chloride, acrylayloxethyl trimethyl ammonium chloride, quaternized derivatives of N, N-dimethyl ammo ethyl methacrylate, dimethyl ammo ethyl acrylate, diethyl ammo ethyl acrylate, dibutyl ammo ethyl methacrylate, dimethyl ammo methyl acrylate, demethyl ammo methyl methacrylate, diethyl ammo propyl acrylate, diethyl ammo propyl methacrylate, ammonium methosulfate, ammo methylated polyacrylamide and combinations thereof. As used herein, the term "dialkyldially ammonium monomer" refers to any water soluble monomer of the formula [DADAAX] , which represents dialkyldiallyl ammonium X, wherein each alkyl group is independently selected from an alkyl group of form about 1 to 18 carbon atoms, and preferably from about 1 to 4 carbon atoms, and wherein X is any suitable counteπon. Preferably, the counterions are selected from the group consisting of conjugate bases of acids having an lonization greater than 10¹³, and more preferably selected from the group consisting of a halide, hydroxide, nitrate, acetate, hydrogen sulfate, methyl sulfate, and primary phosphate. The halide may be any halide, and more preferably is selected from the group consisting of fluoride, bromide and chloride. Preferably, the quaternary dialkyldiallyl ammonium halide monomer is selected from the group consisting of dimethyl diallyl ammonium chloride, diethyl diallyl ammonium chloride, dimethyl diallyl ammonium bromide, and diethyl diallyl ammonium bromide.

Also, the cationic flocculant polymer may contain at least one anionic monomer selected from the group of acrylic acid, methacrylic acid, 2-acrylamιdo-2- methylpropanesulfonic acid, crotonic acid, sodium vinyl sulfonate, acrylamidoglycolic acid, 2-acrylamιdo-2- methylbutanoic acid, 2-acrylamιdo-2- methylpropanephosphonic acid, sodium vinyl phosphonate, allyl phosphonic acid. Derivatives of the above anionic monomers are well known and those are useful n the present invention. The polymer may contain nonionic portions and may contain at least one nonionic monomer from the group of N-vmylamide, N-alkylacrylamide, vinyl acetate, vinyl alcohol, acrylate esters, diacetone acrylamide, N, N-dimethyl acrylamide.

The cationic flocculant polymer may have a weight average molecular weight ranging from about 500,000 to about 20 million.

If an anionic high molecular weight water soluble flocculant polymer is used, the polymer is derived from monomers from the group of acrylic acid or its homologues, sodium acrylate, vinyl sulfonic acid, sodium vinyl sulfonate, ltaaconic acid, sodium itaconate, 2- acrylamιdo-2-methylpropanesulfonic acid sodium salt, acrylamidoglycolic acid, 2-acrylamιdo-2-methylbutanoιc acid, 2-acrylamιdo-2-methylpropanephosphonιc acid, sodium vinyl phosphonate, allyl phosphonic acid and/or admixtures thereof. It may also be either hydrolyzed acrylamide polymers or copolymers of its homologues, such as methacrylamide . The polymer may contain nonionic portions and may contain at least one nonionic monomer from the group of acrylamide, N-vmylamide, N- alkylacrylamide, vinyl acetate, vinyl alcohol, acrylate esters, diacetone acrylamide, N, N-dialkylacrylamide . Acrylic acid and methacrylic acid may conveniently be introduced into the polymer by hydrolysis of acrylamide and methacrylamide, respectively. The anionic polymer may be homopolymers , copolymers, or terpolymer. The most preferred high molecular weight homopolymer is polyacrylic acid or its salts. The most preferred high molecular weight copolymers are acrylic acid/acrylamide copolymer; and sulfonate containing polymers such as 2- acrylamιdo-2-methylpropane sulfonate/acrylamide; acrylamido methane sulfonate/acrylamide; 2-acrylamιdo ethane sulfonate/acrylamide; 2-hydroxy-3-acrylamιde propane sulfonate/acrylamide . The most preferred high molecular weight terpolymers are acrylic acid/acrylamide/2-acrylamido-2-methylpropane sulfonate; acrylic acid/acrylamide/acrylamido methane sulfonate; acrylic acιd/acrylamιde/2acrylamιdo ethane sulfonate; acrylic acιd/acrylamιde/2-hydroxy-3-acrylamιde propane sulfonate. Commonly accepted counter ions may be used for the salts such as sodium ion, potassium ion, etc. The anionic flocculant polymer may have a weight average molecular weight ranging from about 1 million to about 30 million.

If the high molecular weight flocculant comprises a nonionic polymer, preferably it would be a polyacrylamide having a weight average molecular weight of about 500,000 to about 20 million.

Preferably, the copolymer of the invention consists of at least two monomers comprising nonionic and cationic monomers which preferably in emulsion form has a weight % ratio based on the total dry weight of the copolymer ranging from 25:75 to 75:25 for AM:DADMAC. In emulsion form, the copolymer is about 25-50% active, and preferably about 40.0% active. The initial thick stock can be made from any conventional papermaking stock such as traditional chemical pulps, for instance bleached and unbleached sulphate or sulphite pulp, mechanical pulps, such as groundwood, thermochemical or chemi-thermochemical pulp, or recycled pulp such as deinked waste fiber filler composites, including coated broke and broke' from aggregating or recycling processes and any mixtures thereof .

The furnish employed in the final paper can be substantially unfilled, e.g., containing less than 10% and generally less than 5% by weight filler in the final paper, or the filler can be provided in an amount of up to 50% based on the dry weight of the solids of the stock or up to 40% based on the dry weight of the paper. When filler is used, any conventional white pigment filler, such as calcium carbonate, kaolin clay, calcined kaolin, titanium dioxide, chalk or talc or a combination thereof may be present. The filler is preferably incorporated into the stock in a conventional manner, prior to the addition of the coagulant/flocculant system of the invention. If the furnish is neutral, i.e., a pH range from about 6.5 to 7.2, such as that used in newsprint, lightweight coated or super calendar grades, an acid tolerant calcium carbonate filler of the prior art could be used such as that discussed in U.S. Patent Nos.

5,593,489; 5,599,388; 5,647,902; 5,685,900; and 5,711,799 which are owned by the same assignee of the present invention. For example, U.S. Patent No. 5,711,799 discloses a calcium carbonate treated with sodium alummate in order to make the carbonate acid resistant or tolerant to the acidic pulp.

The furnish employed in the invention may include other known optional additives, such as rosin, alum, neutral sizing agents, optical brightening agents, or a strengthening or binding agent which for example may comprise a starch, often a cationic starch or a guar gum.

The amounts of fiber, filler or pigment, and other additives such as strengthening agents or alum can all be conventional. Typically, the thin stock has a solids content from 0.1% to 5.0% by weight which consists mostly of fiber.

The total amount of the water soluble copolymer in the furnish may be m the range of about 0.0005 to 3.0 weight %, and more preferably m the range of about 0.005 weight % to about 1.5 weight % (dry weight based on the dry weight of the solids the stock or furnish) . The total amount of the water soluble high molecular weight flocculant polymer in the furnish may be m the range of about 0.0025 to 3.0 weight %, and more preferably, in the range of about 0.0025 weight % to about 1.5 weight % (dry weight based on the dry weight of the solids m the stock or furnish) .

The inventor has found that a low molecular weight copolymer which comprises a nonionic monomer and a cationic monomer, when used m emulsion form with a high molecular weight flocculant polymer can increase drainage and retention and percent press solids, i.e. the press solids ranging from about 30% to about 65% by dry weight solids and a moisture content of about 70% to about 35% of the furnish, and can improve sheet formation and brightness characteristics of the furnish, i.e. a Technidyne brightness level ranging from about 50 to about 95. In the following examples, the following polymers were useα:

Products A, B, C, E, F, G, J, K, L, M, N P, Q, R, S, T, U, V, and W are available from Calgon Corporation, Pittsburgh, PA. and/or ECC International Inc., Atlanta, GA. Product D is available from Nalco Chemical Company and Product H is available from BASF Corporation Dispersion and Paper Chemicals.

Product F is the preferred copolymer of the invention and Product L is the preferred flocculant for the present invention. The other polymers used m the examples are experimental chemistries.

Note: All dosages herein relating to the invention and m the following examples are expressed as active based on lb. /ton of dry pulp. Copolymer- Retention/Drainage/Formation The copolymer discussed herein was used as a retention/dramage/formation aid in the papermaking process : Example 1

A laboratory vacuum drainage test was conducted on newsprint stock to compare the preferred copolymer coagulant of the invention with some other types of polymer coagulant products, some of which are standard coagulant products, such as polyammes, polydadmacs, and polyethyleneimme, and some of which are available from Calgon Corporation. The furnish was obtained from a paper mill and comprised "5 to 80% fine TMP (thermomechanical pulp), 5% kraft, 5% PCW (Post Consumer Waste), and 10 to 15% broke. The paper machine was running at 4100 to 4300 feet per minute, and the conditions were as follows:

35.1% First Pass Retention (FPR)

13.9% Fines Retention 1.24% Headbox Consistency

0.81% Tray Consistency

-785 μ eq/1 HB Total Mutek Charge -253 μ eq/1 HB Filtered Mutek Charge 2900 Conductivity

Thin stock was taken from the paper machine before any polymers were added. An aliquot of stock was mixed in a Britt Jar with a sheet of plastic over the wire while the flocculants and coagulants were added. The mixing sequence was as follows : Time 0 Sec. 1200 RPM

10 Sec. Add Flocculant (pre-shearing stage)

18 Sec. 800 RPM (representing a shearing stage)

20 Sec. Add Coagulant (post shearing stage)

30 Sec. Stop Mixer

The vacuum drainage test (VDT) was conducted using the Buchner Funnel, a vacuum pump, 24.5" Hg, and a 500 ml glass vacuum flask. The Vac. 400, which represents time (seconds) in which 400 ml of stock is drained from the flask, was recorded. The flocculant (Products L and M) was used at 0.25 (active) lb./t., and the coagulants were used at 1.0 (active) lbs. /ton.

The results are shown in Table 1 where the drainage rate for the stock containing Product F (Item 6) of the invention was relatively comparable to the stock samples containing other types of polymer coagulants, such as Products D and E.

TABLE 1

A second test was done similar to that above where the coagulants were used at 0.5, 1.0, 1.5 and 2.0 (active) lbs. /ton. Table 2 shows these results were the samples for Items 19-22 with Products F and L, the coagulant/flocculant system of the invention, again show comparable drainage rates relative to the samples containing standard coagulants, such as Products D and E.

TABLE 2

Example 2 Laboratory testing for retention was conducted on recycled newsprint furnish containing about 75% deinked pulp (DIP) and about 25% thermomechanical pulp (TMP) . First pass retention (FPR) was tested using TAPPI

Test Method T269. Stock was collected from the discharge of the primary fan pump. 500 ml samples were poured into a Britt Jar with a 70 mesh screen while stirring the stock at 1500 rpm. The mixing time/speed sequence was similar to that used for the drainage test herein in order to simulate chemical addition points in a paper machine .

The results are shown in Table 3. TABLE 3 Retention

Product F, the coagulant of the invention, when combined with Product Q (flocculant), show high ash retention results which are comparable to the samples containing other types of coagulants, such as Products D and E. These retention and drainage results indicate that in the invention, filler retention should be realized along with increased drainage.

Example 3 Pilot Pressing Study (Fine Paper)

Furnish Description 13% Softwood Bleached Kraft

44% Hardwood Bleached Kraft

36% Coated Broke

7% Post Consumer Waste (Mixed Office Waste) Furnish Preparation:

Thick stock and white water from an alkaline fine paper mill was used for this lab study. Furnish of the above proportions was combined with mill white water to dilute the thick stock to 1.0 % consistency (pH = 7.5) . A 630 ml aliquot was used for the Control and 540 ml aliquot for the handsheets containing retention aid. The target sheet weight was 5.4g (= 100 lb/3000ft² coated or about 801b raw stock weight) per 8"x8" sheet. The starch was a cationic starch obtained under the trade name HiCat 142 from the National Starch Company. About 2ml of starch of a 1.9% solution (= 14 lbs/ton) were used m this example. The 1.0 % consistency stock was mixed with flocculant and coagulant using a Britt Jar type (variable speed mixer) according to the procedure below.

Handsheet Procedure : (Williams Sheet Mold) for Pilot Pressing Study

Elapsed Time

1. Measure out stock.

2. Set agitator speed to 700 rp .

3. Add starch to stock and mix. (Start timer) 0 sec.

4. Increase speed to 1200 rpm. 40 sec.

5. Add first polymer. 1 mm.

6. Reduce speed to 700 rpm. 1 mm. 10 sec.

7. Add second polymer and mix. 1 mm. 10 sec. 9. Shut off mixer 1 mm. 15 sec.

9. Pour stock into handsheet mold already filled with water . 10. Mix stock with hand agitator. Drain sheet mold. Place two blotters on top of sheet and press with 5 lb. Williams "rolling pin".

11. Place sheets from each set in air-tight plastic bag.

12. Handsheets were then individually weighted and run through pilot sheet press.

Pressing Conditions

Press Speed: 1750 fpm Press Load (pounds/linear inch- PLI)

1^st Press: 425 2^nd Press: 450 3^rd Press: 550 Handsheets were run in sets of five. The weight of each sheet was measured before the first press and after pressing through each nip. Oven dry weight was determined to calculate press solids. Handsheet brightness was measured on a Technidyne Color One Touch brightness meter according to TAPPI Test Method T-452. The results are shown in the single figure. The press solids (%) and brightness (Technidyne) for coagulants B, 0, E, F, H, K, and V with Product W being the flocculant are graphically demonstrated n the single figure for the dosages, i.e. 08, 1.6, and 2.4 lbs/ton active. All samples, except Blank, contained 0.28 lb/ton active anionic flocculant (Product W) . The conventional sequence of addition is to first add the coagulant and then add the flocculant. In all but the last three samples, designated "Conv. F", the flocculant was added first followed by the coagulant. In the samples labeled "Conv.F", the coagulant and flocculant were added in the conventional manner, i.e. copolymer of the invention, Product F, was added first followed by the addition of the flocculant (Product W) . For copolymers of the invention, Polymer F, the press solids increased with an increase in dosage and the handsheet brightness decreased. However, the brightness levels for the dosages of Product F are in an acceptable range to the papermaker. The press solids for Products K and V were equivalent to Product F. However, the brightness for Product F was significantly higher. A difference of one point in brightness for Products K and V and Product F is valuable economically to the paper maker in terms of reduced filler and lower pulp bleaching costs .

As described in Principles of Wet End Chemistry by William E. Scott, PhD., TAPPI Press, Atlanta, GA, 1996, Page 25, low molecular weight (100,000-1,000,000) cationic coagulants with high charge density (> 4 meq charge/gram) are mixed with anionic particles (aqueous cellulosic furnish) to form a positive patch charge on the surface of the anionic particles . After the cationic coagulant is adsorbed onto the surface of the anionic particles, collision of the positive patch with a negatively charged surface on another particle leads to agglomeration .

The inventor has found that m certain paper furnishes that the copolymer of the invention works comparable to the high charge density coagulants of the prior art in terms of retention, drainage, and press solids but much better than coagulation of the prior art in terms of brightness. The above Examples 1-3 exemplify this .

Copolymer As An Attachment Aid In Coated Broke And A Retention/Drainage Aid

Example 4

A second aspect of the invention involves using the copolymer of the invention for treating coated broke and then using the treated coated broke as a portion of the furnish in making paper and adding the copolymer of the invention as a retention and/or drainage aid in the papermaking process. Coated broke is used in many fine or other paper furnishes . The base sheet may contain this coated broke comprising pigments and binders, both of which can cause problems in the sheet forming process. As explained hereinabove, the binders can agglomerate to form sheet defects or deposits on the machine. The coating pigments in the coated broke are more difficult to retain than wet end pigments in view of their small size. The copolymer of the invention as disclosed hereinabove for treating coated broke has been found to be an effective way for significantly reducing white pitch deposits and poor coating pigment retention problems, whereby the pigments and the binders are attached to the fiber in the furnish.

The copolymer of the invention was used as an attachment aid for the white pitch or stickies and the mineral pigments from coated broke where the white pitch or stickies and the pigments are attached to the longer fibers instead of depositing on sites in the papermaking process .

Several samples of coated broke were obtained from a coated broke tank of a commercial paper machine. A turbidity test was done to quantify the performance of coagulants and their ability to fix the colloidal and fine particles of the coated broke to the fiber in the furnish. For this test, 100 grams of coated broke in slurry form was placed into small beakers and treated with the copolymer of the invention (Product F) and several other types of coagulants . Each sample was mixed for 1 minute and then filtered through a No . 4 Whatman Filter Paper using a standard (inverted cone) funnel. The turbidity of the filtrate was then measured using a Hach TR 2000 Turbidimeter which measures turbidity in National Turbidity Units (NTU) . The cationic demand was measured using a Mutek Particle Charge Detector.

The dosages for the coagulant were 2.75 (active) pounds per ton (dry weight of solids in furnish) , and 3.75 (active) pounds per ton (dry weight of solids in the furnish) .

The results of the turbidity (fixation) tests are shown m Table 4. The turbidity level for Product F, the copolymer of the invention, is comparable to other copolymers but not as gooα as standard coagulants, such as polyamme and polyDADMAC.

TABLE 4

The copolymer of the invention was then used as a retention/drainage aid m the papermaking process.

For the vacuum drainage tests, stock from the mix chest (tank) was diluted to headbox consistency (-1.0%) The headbox stock contains a portion of the coated broke used for the turbidity test.

The test procedure was similar to that used in Example 1, except that the coagulant was added during high shear mixing (simulated screening or shearing stage) and the flocculant was added during low shear mixing. The dosage of the coagulant was 1.0 (active) lb. /ton based on the dry solids in the aqueous cellulosic furnish and the dosage of the flocculant was 0.25 (active) lb. /ton based on the dry solids in the aqueous cellulosic furnish .

The results are shown in Table 5 for the different coagulant products tested with the same flocculant (Product L) . Product F, the copolymer of the invention, performed as well as if not better than some of the standard coagulants, (polyamine and DADMAC) i.e. the lower numbers representing a faster drainage time.

TABLE 5

From the above results, it can be seen that there is a possibility that coated broke treated with the copolymer (Product F) of the invention prior to its being added to the paper furnish can produce acceptable turbidity levels and drainage rates of the fiber mat on the wire the paper forming process.

Whereas particular embodiments of the present invention have been described for purposes of illustration, it will be evident to those skilled in the art that numerous variations and details of the invention may be made without departing from the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS

1. A paper or paperboard furnish containing a retention and drainage aid composition to improve dewatering, press solids and brightness of said composition, comprising: a copolymer comprising about 20.0% to about 50.0% active in emulsion form, a nonionic monomer and a cationic monomer in a weight percentage ratio ranging from about 25:75 to about 75:25, based on the weight of the solids in the copolymer.

2. The furnish of Claim 1 wherein said nonionic monomer of said copolymer is acrylamide and said cationic monomer is diallyl dimethyl ammonium chloride in a weight percentage ratio of 25:75 based on the dry weight of the solids in the copolymer.

3. The furnish of Claim 1 wherein said press solids ranges from about 30% to about 65% by dry weight solids.

. The furnish of Claim 1 wherein said copolymer has a weight average molecular weight ranging from about 3 to about 7 million.

5. The furnish of Claim 1 wherein said copolymer is used as a coagulant and is present in the paper furnish in an amount of at least 0.0025% by weight based on the dry weight of the solids in the furnish.

6. The furnish of Claim 1 wherein said retention and drainage aid composition further comprises a water- soluble flocculant.

7. A method for producing paper products, the steps comprising : prior to a first shearing stage or after the last shearing stage, adding a copolymer to the paper furnish m an amount of at least 0.0025% by weight based on the dry weight of the solids in the furnish to improve the retention/dramage properties of a paper web m producing said paper product, said copolymer comprising about 20.0% to about 50% active in emulsion form, a copolymer comprising a nonionic monomer and a cationic monomer in a weight percentage ratio of about 25:75 to about 75:25 based on the dry weight of the solids in the copolymer.

8. A method of Claim 7 wherein said nonionic monomer is acrylamide and said cationic monomer is diallyl dimethyl ammonium chloride m a weight percentage ratio of 25:75 based on the dry weight of the solids in the copolymer.

9. The method of Claim 7 wherein said copolymer has a weight average molecular weight ranging from about 3 to 7 million.

10. The method of Claim 7, the steps further comprising: before adding the copolymer to the paper furnish, adding a water soluble flocculant to the paper furnish.

11. The method of Claim 7, wherein the press solids in the paper furnish at least in one of the pressing operations ranges from about 30% to about 65% by dry weight solids .

12. A paper product made with the copolymer of Claim 1 and having a Technidyne brightness level ranging from about 55 to about 95.

13. A method for treating coated broke comprising white pitch, fillers, and fibers, the steps comprising: adding a copolymer to the coated broke to attach at least the wnite pitch and fillers to the fibers, said copolymer comprising about 20% to about 50% active in emulsion form a nonionic monomer and a cationic monomer in a weight percentage ratio of about 25:75 to about 75:25 based on the dry weight of the solids m the copolymer .

14. A method of Claim 13 wherein said nonionic monomer is acrylamide and said cationic monomer is diallyl dimethyl ammonium cnloπde in a weight percentage ratio of 25:75 based on the dry weight of the solids in the copolymer.

15. The method of Claim 13 wherein said copolymer has a weight average molecular weight ranging from about 3 to about 7 million.

16. The method of Claim 13 wherein said copolymer polymer is present in the paper furnish in an amount of at least 0.0025% by weight based on the dry weight of the solids m the furnish.

17. A method of producing paper products, the steps comprising : treating coated broke containing white pitch and pigments with a copolymer to attach at least the fines to the fibers of the coated broke; adding said coated broke to a paper furnish; prior to a first shearing stage or after the last shearing stage, adding said copolymer to said paper furnish to improve the retention and/or drainage properties of a paper web in producing said paper product; said copolymer comprising from about 20% to about 50% active in emulsion form a nonionic monomer and a cationic monomer in a weight percentage ratio of about 25:75 to about 75:25 based on the dry weight of the solids in the copolymer.

18. A method of Claim 17 wherein said nonionic monomer is acrylamide and said cationic monomer is diallyl dimethyl ammonium chloride in a weight percentage ratio of 25:75 based on the dry weight of the solids in the copolymer .

19. A method of Claim 17 wherein said copolymer improves the press solids and the brightness of the furnish, and wherein said press solids ranges from about 30% to about 65% by dry weight solids and a Technidyne brightness level ranges from about 65 to about 90.

20. A method of Claim 17 wherein said copolymer has weight average molecular weight from about 3 to 7 million .

21. A paper or paperboard furnish containing a retention and drainage aid composition comprising: a copolymer comprising about 20.0% to about 50.0% active in emulsion form, a nonioninc monomer and a cationic monomer.

22. A furnish of Claim 21 wherein said nonionic monomer and said cationic monomer have a weight percentage ratio ranging from about 25:75 to about 75:25 based on the weight of the solids in the copolymer.