WO2001051707A1

WO2001051707A1 - The use of inorganic sols in the papermaking process

Info

Publication number: WO2001051707A1
Application number: PCT/US2000/034488
Authority: WO
Inventors: Jose M. Rodriguez; Craig W. Vaughan
Original assignee: Calgon Corporation
Priority date: 2000-01-12
Filing date: 2000-12-19
Publication date: 2001-07-19
Also published as: AU2001224398A1

Abstract

A method of producing paper which includes adding to a paper making stock or furnish a microparticle system as a retention and/or drainage aid which comprises a polymer selected from the group consisting of polyampholyte polymer, a coagulant polymer and a high molecular weight water soluble polymer, and an inorganic sol selected from the group consisting of zirconia sol, and alumina sol. Optionally, a cationic starch may be part of the microparticle system and added prior to the addition of the polymer. The method may involve the addition of the inorganic sol after the last shearing stage.

Description

THE USE OF INORGANIC SOLS IN THE PAPERMAKING PROCESS

BACKGROUND OF THE INVENTION 1. Field Of The Invention

The invention relates to an improved retention and dewatering system in the paper aking process. More particularly, the invention relates to the use of a microparticle system including an inorganic sol and one or more polymers, such as a coagulant polymer, a polyampholyte polymer, and a high molecular weight water soluble flocculant polymer, in the cellulosic paper slurry to bring about improvements in retention, drainage, and sheet formation.

2. Description Of The Background Art

In papermaking processes, a dilute aqueous composition known as a "furnish" or "stock" is sprayed onto a screen or moving mesh known as a "wire". Solid components of the composition, such as cellulose fibers and inorganic particulate filler material, such as titanium dioxide, kaolin clay, and calcium carbonate, 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 .

A related property of the papermaking process is drainage. Drainage is the rate of removal of water from the furnish as the paper sheet is formed. Drainage usually refers to water removal that takes place in the "drainage zone" (gravity and vacuum sections) of the Fourdrinier-.or twin wire paper machine primarily before any pressing of the wet paper web subsequent to formation of the sheet. Thus, drainage aids help to drain the water from the fibrous web in the papermaking process, and are used to improve the overall efficiency of dewatering in the production of paper products in the papermaking process. Retention aids function to increase the amount of fillers remaining in the fibrous web. 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.

Formation relates to the uniformity of the paper or paperboard sheet produced from the papermaking process. Formation is generally evaluated by the variance in light transmission through a paper sheet. A high variance is generally indicative of "poor" formation and a low variance is indicative of "good" formation. Generally, as the retention level increases, the level of formation generally decreases from good formation to poor formation . Retention, drainage, and formation properties of the final paper or paperboard sheet are particularly desirable to paper producers for several reasons, the most significant of which is productivity. Good retention and good drainage will 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.

Thus, retention and drainage aids are additives which are used to flocculate the fine solids present in the furnish to improve retention and drainage in the papermaking process. The use of such additives is limited by the effect of flocculation on the formation of the paper sheet. As more retention aid is added so the size of the aggregates of fine solid material is increased, a variation in density and visible non- uniformity of the paper sheet can result. Over- flocculation can also affect drainage as it may eventually lead to holes in the sheet and a subsequent loss of vacuum pressure in the later stages of dewatering.

Retention and drainage aids are generally added to the furnish as the furnish approaches the headbox of the paper machine and may be one of three types, viz.: (a) single polymers;

(b) dual polymers;

(c) microparticle systems.

The present invention relates to the use of a retention and drainage aid of the last type, i.e. a microparticle system. This type generally may give the best results. Microparticle systems generally comprise a polymeric flocculant and a fine inorganic particulate material. The inorganic material improves the efficiency of the flocculant and/or allows smaller, more uniform floes to be produced.

Microparticle systems have been described widely in the prior art. Examples of publications of microparticle systems include EP-B-235,893 wherein bentonite is used as the inorganic material in conjunction with a high molecular weight cationic polymer in a specified addition sequence; WO-A-94/26972 wherein a vinylamide polymer is described for use in conjunction with one of various inorganic materials; EP-O-748,897 wherein an aluminum compound, such as polyaluminum chlorides, and an anionic inorganic particle, such as silica sol, are mixed immediately prior to addition to the pulp suspension; and EP-O-355,816 wherein a colloidal alumina sol having a positive surface charge and a colloidal alumina concentration in the range between 0.1 to 1% is added to the furnish along with an anionic polymer flocculant. In this latter publication, the colloidal alumina has a particle size in the range between 1-50 nanometers and the colloidal alumina sol is added to the furnish in an amount between about 0.025 to 0.5% by weight.

Examples of microparticle systems are disclosed in several patents.

U.S. Patent No. 4,964,954 discloses the use of a three component system comprising a cationic polymeric synthetic retention agent, an anionic inorganic colloid and a polyaluminum compound. Examples of anionic inorganic colloids are colloidal montmorillonite and bentonite, titanyl sulphate sols, silica sols, aluminum modified silica sols or aluminum silicate sols. U.S. Patent Nos. 4,388,150 and 4,980,025 disclose the use of silica-based particles generally supplied in the form of aqueous sols. U.S. Patent No. 4,388,150 discloses in a process for making paper the use of colloidal silicic acid and cationic starch. The cationic starch has a degree of substitution of not less than 0.01 and the weight ratio of cationic starch to Si0₂ is between 1:1 and 25:1. U.S. Patent No. 4,980,025 discloses in a process for making paper the use of cationic polyacrylamide and an aluminum modified silicic acid for improving retention and drainage .

In U.S. Patent No. 4,385,961, Svending et al . disclose the use of colloidal silicic acid and a cationic starch which is added to the stock before the sheet is formed. The manner of addition involves first adding and intermixing in the stock a portion of the colloidal silicic acid and then the cationic starch and, then later adding and intermixing the remainder of the colloidal silicic acid prior to sheet formation. In U.S. Patent No. 4,643,801, Johnson discloses a papermaking process in which a cationic starch, a high molecular weight anionic polymer, and a dispersed silica having a particle size ranging from between about 1-50 nanometers are added to the cellulosic pulp prior to formation of the sheet.

In U.S. Patent No. 4,749,444, Lorz et al. disclose a method for draining a paper stock by using activated bentonite, a cationic polyelectrolyte, and a high molecular weight polymer based on acrylamide or methacrylamide .

In U.S. Patent No. 4,750,974, Johnson discloses the use of a cationic starch having a degree of substitution of at least 0.01, a high molecular weight anionic polymer, and a dispersed silica having a particle size ranging from between about 1-50 nanometers .

In U.S. Patent No. 4,755,259, Larsson discloses the use of colloidal silicic acid and either amphoteric or cationic guar gum that may form part of the binder complex in a mixture with cationic starch.

In U.S. Patent No. 4,795,531, Sofia et al . disclose a method of enhancing the dewatering of paper during the papermaking process which includes adding a low molecular weight cationic coagulant followed by colloidal silica, and a high molecular weight flocculant.

In U.S. Patent No. 4,798,653, Rushmere discloses a retention and dewatering aid comprising a two component combination of an anionic polyacrylamide and a cationic colloidal silica sol. In U.S. Patent No. 4,913,775, Langley et al . disclose a process of making paper or paperboard comprising:, a) passing an aqueous cellulosic suspension through one or more shear stages, b) draining the suspension to form a sheet, and c) drying the sheet. Retention, drainage, drying and formation are achieved by adding to the suspension an excess of high molecular weight linear synthetic cationic polymer before shearing the suspension and adding bentonite after shearing. In U.S. Patent No. 4,927,498, Rushmere discloses a papermaking process, whereby retention and drainage are improved by the addition of a water soluble polyaluminosilicate microgel and an organic cationic polymer. In U.S. Patent No. 4,954,220, Rushmere discloses the use of anionic polysilicate microgels with an organic polymer to flocculate pulp and filler fines such that water removal is easier and fines retention is greater. In U.S. Patent No. 4,961,825, Andersson et al . disclose the use of an anionic component consisting of an aluminum silicate or an aluminum-modified silicic acid such that the surface groups of the particles contain silicium and aluminum atoms in a ratio of from 9.5:0.5 to 7.5:2.5. A cationic component consists of cationic carbohydrate having a degree of substitution of 0.01-1.0. In U.S. Patent No. 4,964,954, Johansson discloses the use of a retention agent, aluminum modified silica, and polyaluminium compound in the production of paper. In U.S. Patent No. 4,969,976, Reed discloses a process for increasing productivity by adding a water soluble cationic polymer, such as a cationic starch or a substantially linear cationic polymer, before the shearing and an inorganic material such as a colloidal silica or a bentonite after the shearing. In U.S. Patent Nos. 5,015,334 and 5,571,379, Derrick discloses the use of colloidal siliceous material, such as swelling, clay, in intimate association with a low molecular weight water soluble high anionic charge density organic polymer, such a polyacrylic acid or polyamine. The colloidal siliceous material is preferably added to the aqueous pulp after the addition of a conventional high molecular weight flocculating agent . In U.S. Patent No. 5,032,227, Derrick et al . disclose the addition to the thin stock of bentonite clay in intimate association with a low molecular weight water soluble anionic charge polymer. A non-ionic high molecular polyelectrolyte is added after the last high shear point.

In U.S. Patent No. 5,071,512, Bixler et al . disclose that the addition of hectorite and cationic starch to the furnish in the papermaking operation improves retention of filler material and the quality of the paper. In U.S. Patent No. 5,126,914, Chung discloses a process by which retention and drainage are substantially improved by the addition of a cationic coagulant, an anionic flocculant, and an inorganic material which is either bentonite or colloidal silica. In U.S. Patent No. 5,127,994, Johansson discloses the formation of paper by dewatering a suspension of cellulose containing fibers. The forming and dewatering is carried out in the presence of a combination of an aluminum compound, a cationic retention agent, and a polymeric silicic acid.

In U.S. Patent No. 5,178,730, Bixler et al . disclose a process for improving the papermaking by the addition of a cationic polymer and natural hectorite to the furnish prior to the headbox. In U.S. Patent No. 5,185,062, Begala discloses a papermaking process that includes the addition to the papermaking cellulosic slurry first a high molecular weight cationic polymer and then a medium molecular weight anionic polymer such as an ionizable sulfonate. In U.S. Patent No. 5,185,206, Rushmere discloses the use of anionic polysilicate microgels with an organic polymer to flocculate pulp and filler fines, such that water removal is easier and fines retention is greater. In U.S. Patent No. 5,194,120, Peats et al . disclose a process for making paper wherein a cationic polymer and an amorphous metal silicate material are added to a paper furnish prior to the introduction of the furnish to the headbox of a paper making apparatus. In U.S. Patent No. 5,221,435, Smith, Jr. discloses a papermaking process were retention performance is provided by the addition of a cationic species, an anionic flocculant and then a microparticle that is an inorganic, cationic source of aluminum. In U.S. Patent No. 5,227,764, Johansson et al . disclose the production of pulp and paper sheets from a suspension of cellulose containing fibers, to which is added anionic inorganic particle, such as bentonite and silica based particles, and a cationic carbohydrate polymer containing aluminum.

In U.S. Patent No. 5,274,055, Honig et al . disclose that in the papermaking process, improved drainage and retention are obtained by a composition of matter comprised of an ionic organic microbead and a high molecular weight ionic polymer or a polysaccharide.

In U.S. Patent No. 5,234,548, Hatton discloses a process for the manufacture of paper or paperboard, which comprises adding an organic polymer and bentonite to the cellulosic suspension which is drained to form a sheet. In U.S. Patent No. 5,393,381, Hund et al . disclose a process for the manufacture of paper or cardboard having improved retention, in which a polyacrylamide and bentonite are added to the fibrous suspension. The polyacrylamide is a branched polyacrylamide, which is easily soluble in water.

In U.S. Patent No. 5,447,604, Johansson et al . disclose the production of alkali metal or ammonium silica sols and the use of this sol in combination with a cationic polymer in the papermaking process.

In U.S. Patent No. 5,470,435, Rushmere et al . disclose an improved method for the production of water soluble polyaluminosilicate microgels and their use in the papermaking process.

In U.S. Patent No. 5,473,033, Kuo et al . disclose a drainage aid comprised of a microparticle and a water soluble cationic polymer selected from a water soluble cationic copolymer composed of the polymerization reaction of an N-vinylamide with at least one cationic quaternary amine monomer.

In U.S. Patent No. 5,482,595, Harrington et al . disclose a method of improving the drainage characteristics of a pulp slurry in a papermaking operation utilizing the sequential steps of adding alum, ionic polyacrylamide, and cationic starch.

In U.S. Patent No. 5,501, 774, Burke discloses the use of a cationic coagulating agent, an anionic particulate such as bentonite, and a polymeric retention aid.

In U.S. Patent No. 5,505,819, De Witt et al . disclose a method of making paper from a furnish containing mechanical pulp, chalk, polyacrylamide, and bentonite . In U.S. Patent No. 5,514,249, Cauley et al. disclose the use of a nonionic or anionic polymeric retention aid with a high electrolyte content, and anionic bentonite, colloidal silicic acid, zeolite, silica gel or hectorites . In U.S. -Patent No. 5,532,308, Schuster et al. disclose a composition and method for improving the drainage and retention characteristics of a paper furnish consisting of a water soluble graft copolymer and bentonite clay.

In U.S. Patent No. 5;543,014, Rushmere et al . disclose a process for preparing water soluble polyaluminosilicate and their use in the papermaking process . In U.S. Patent No. 5,584,966, Moffett discloses an improved method of paper formation by using a combination of polysilicate microgel and anionic and cationic polymers with the optional utilization of an aluminum salt. In U.S. Patent No. 5,595,629, Begala discloses the use of a cationic and an anionic polymer where the anionic polymer comprises a formaldehyde condensate of a naphthalene sulfonic acid salt.

In U.S. Patent No. 5,595,630, Moffett uses a cationic aluminum compound and an anionic aluminum in conjunction with a cationic polymer and an anionic microparticle, such as a polysilicate microgel or a polyaluminosilicate microgel.

In U.S. Patent No. 5,603, 805, Kjell et al . disclose the formation of a new silica sol with a high content of microgel which are particularly suitable for use as additives in combination with cationic acrylamide based polymers .

In U.S. Patent No. 5,607,552, Andersson et al . disclose the preparation of a suspension of silica based anionic particles and hydrated clays of the smectite type and a process for the production of pulp and paper which comprises utilizing the aqueous suspension as a flocculating agent. -•^• In U.S. Patent No. 5,643,414, Johansson et al . disclose silica sols having a high content of microgel and aluminum modified particles. The sols are particularly suitable for use as additives, in combination with cationic polymers, in papermaking.

In U.S. Patent No. 5,647,956, Elliot et al . disclose a composition comprising aqueous cellulosic furnish, a high molecular weight polymer, and a modified lignin. In U.S. Patent No. 5,670,021, Owens discloses a process for the production of paper by dewatering the cellulose suspension in the presence of an alkali metal silicate and a phenolic resin added at the same point into the suspension, and polyethylene oxide added at a subsequent point into the suspension. In U.S. Patent No. 5,723,023 Tsa et al . disclose the use of a selected ether or ester modified with a cationic starch as an additive in the wet end of a paper machine which provides significant improvements in retention and drainage, especially in an alkaline microparticle containing system.

Although some inorganic sols, such as colloidal silica sols, colloidal aluminum sols, and aluminum silicate sols have been proposed for use in microparticle systems, the selection of specific inorganic sols as in the present invention to improve, unexpectedly and beneficially, the performance of the microparticle system has not been considered in the prior art.

SUMMARY OF THE INVENTION According to the present invention a method of producing paper includes adding to a paper making stock or furnish a microparticle system retention and/or drainage aid which comprises one or more polymers selected from the group consisting of a high molecular weight water soluble flocculant polymer, a polyampholyte polymer and a coagulant polymer, and an inorganic particulate material comprising an inorganic sol selected from the group consisting of zirconia sol and alumina sol. The zirconia sol can exist in an amorphous form and/or a crystalline form. The alumina sol preferably is an alumina hydrate sol. The microparticle system may also comprise a coagulant comprised of a cationic polymer, a polyampholyte polymer or a polysaccharide, which is added to the stock or furnish.

Therefore, it is an object of the invention to provide a microparticle system comprising a high molecular flocculant and an inorganic sol selected from the group consisting of zirconia sol and alumina sol to improve the retention, drainage and formation properties of a paper or paperboard sheet.

These and other objects of the invention will be more fully understood from the following description of the invention and the claims on reference to the illustrations appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the amorphous form of the zirconia sol of the invention in "A", and the crystalline form of the zirconia sol of the invention in "B" .

DETAILED DESCRIPTION OF THE INVENTION

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

A "microparticle system" refers to the combination of at least a high molecular weight water soluble polymer used as a flocculant and at least one inorganic sol as the inorganic particulate material. Optionally, the microparticle system of the invention may further comprise a coagulant that may be either a cationic polymer or a polyampholyte polymer, or a polysaccharide may be added. The components of the microparticle system of the invention may be added simultaneously or sequentially to the furnish at the same or different points of addition but, preferably, added separately in the manner and order described herein below. The present invention relates to a papermaking process in which paper is made by the steps of forming an aqueous cellulosic slurry, subjecting the slurry to at least one shear stage, and draining the slurry to form a paper sheet. The process can be further characterized by unique steps concerning the sequence and point of addition of the components of the microparticle system of the invention.

The microparticle system of the present invention has been found to be particularly effective in improving the retention and drainage properties of the cellulosic slurry.

If a coagulant is used, the coagulant may be a cationic polymer or a polyampholyte polymer.

The polyampholyte polymer is preferably a water soluble polymer having a weight average molecular weight of from about 5,000 to 20 million. The polyampholyte polymer may contain at least one cationic monomer selected from the group consisting of a quaternary dialkyldiallyl ammonium, methacryloyloxyethyl trimethyl ammonium chloride, methacryloyloxythyl trimethyl ammonium methosulfate, acrylamido propyl triethyl ammonium chloride, methacrylamido propyl triethyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride, quaternized derivatives of N, N-dimethyl amino ethyl methacrylate, dimethyl amino ethyl acrylate, diethyl amino ethyl acrylate, dibutyl amino ethyl methacrylate, dimethyl amino methyl acrylate, demethyl amino methyl . methacrylate, diethyl amino propyl acrylate, diethyl amino propyl methacrylate, acryloyloxyethyl trimethyl ammonium methosulfate, amino methylated polyacrylamide, and combinations thereof. As used herein, the term "dialkyldiallyl 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 from about 1 to about 18 carbon atoms, and preferably, from about 1 to about 4 carbon atoms, and wherein X^' is any suitable counterion. Preferably, the counterions are selected from the group consisting of conjugate bases of acids having an ionization greater than 10^~13 , 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 dimethyly diallyl ammonium chloride, diethyl diallyl ammonium chloride, dimethyl diallyl ammonium bromide, and diethyl diallyl ammonium bromide.

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

The vinyl alcohol monomer will most conveniently be generated as a monomer simply by hydrolysis of vinyl acetate. Similarly, acrylic acid and methacrylic acid may conveniently be introduced into the polymer by hydrolysis of acrylamide and methacrylamide, respectively.

If the polyampolyte is a copolymer, preferably, it is be derived from a cationic monomer that is selected from the group consisting of dialkyldiallyl ammonium monomer, methacryloxyethyl trimethyl ammonium chloride, acrylamido propyl trimethyl ammonium chloride, and methacrylamido propyl trimethyl ammonium chloride, and an anionic monomer that is selected from the group consisting of acrylic acid, methacrylic acid, 2- acrylamido-2-methylpropanesulfonic acid, sodium vinyl sulfonate, and acrylamidoglycolic acid.

If the polyampolyte is a terpolymer, preferably, it is derived from (a) a cationic monomer that is selected from the group consisting of dialkyldiallyl ammonium monomer, methacryloxyethyl trimethyl ammonium chloride, acrylamido propyl trimethylammonium chloride, and methacrylamido propyl trimethyl ammonium chloride; (b) an anionic monomer that is selected from the group consisting of acrylic acid, methacrylic acid, 2- crylamido-2-methyylpropanesulfonic acid, sodium vinyl sulfonate, and acrylamidoglycolic acid; and (c) a nonionic monomer selected from the group consisting of N- vinylamide, N-alkylacrylamide, vinyl acetate, acrylate esters, diacetone acrylamide, and N, -dimethylacrylamide . The cationic coagulant is preferably a low molecular weight water-soluble polymer positively charged species. The positively charged species may be inorganic or organic. The organic coagulant will be a charged polymer having a weight average molecular weight of at least 2,000, although polymers having weight average molecular weights of 2 million are acceptable. Preferred polymers include epichlohydrin/dimethylamine copolymers, ethylene dichloride/ammonia copolymers, diallyldimethylammonium halide polymers and copolymers, e.g. diallyldimethylammonium chloride polymers and diallyldimethylammonium chloride/acrylamide copolymers, and acrylamido N,N-dimethyl piperazine quaternary/acrylamide copolymers .

The polysaccharide may be cationic, amphoteric or anionic. The polysaccharide chain may include starch, modified starches, guar gum, modified guar gums, xanthan gum, alginates, gum agar, gum arabic, gum ghatti, gum karaya, locust beam gum, and tamarind gum. The preferred polysaccharides are modified starches.

The organic high molecular weight water-soluble flocculant polymer may be a cationic or an anionic high molecular weight water-soluble polymer having a weight average molecular weight of at least 500,000, and preferably greater than about 8 x 10⁵.

The cationic high molecular weight water-soluble flocculant polymer may be a copolymer derived from at least one cationic monomer selected from the group consisting of a quaternary dialkyldiallyl ammonium, methacryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium methosulfate, acrylamido propyl trimethyl ammonium chloride, methacrylamido propyl triethyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride, quaternized derivatives of N, N-dimethyl amino ethyl methacrylate, dimethyl amino ethyl acrylate, diethyl amino ethyl acrylate, dibutyl amino ethyl methacrylate, dimethyl amino methyl acrylate, dimethyl amino methyl methacrylate, diethyl amino propyl acrylate, diethyl amino propyl methacrylate, acryloyloxyethyl trimethyl ammonium methosulfate, and amino methylated polyacrylamide.

It is noted that the cationic component of the cationic high molecular weight flocculant polymer may contain one or more mer units without departing from the concept of this invention. Copolymers or terpolymers, such as, for example, polymers comprising dimethyl diallyl ammonium chloride and acryloyloxyethyl trimethyl ammonium chloride may be employed as the cationic polymer component of the composition of the invention. The cationic polymer may contain at least one of the nonionic monomers selected from the group consisting of acrylamide, methacrylamide, diacetone acrylamide, N, N- dimethyl acrylamide, N-vinylamide, N-alkylacrylamide, vinyl acetate, vinyl alcohol, and acrylate esters.

Preferably, if the high molecular weight polymer comprises a cationic charge polymer, it is a copolymer derived from a cationic monomer selected from the group consisting of a methacryloxyethyl trimethyl ammonium chloride, acrylamido propyl trimethyl ammonium chloride, and methacrylamido propyl trimethyl ammonium chloride, and a nonionic monomer that is acrylamide, and wherein the weight ratio of said cationic monomer to said nonionic monomer is from about 99:1 to 1:99.

The anionic high molecular weight water soluble polymer is derived from monomers from acrylic acid or its homologues, sodium acrylate, vinyl sulfonic acid, sodium vinyl sulfonate, itaconic acid, sodium itaconate, 2- acrylamido-2methylpropanesulfonic acid sodium salt, acrylamidoglycolic acid, 2-acrylamido-2-methylbutanoic acid, 2-acrylamido-2methylpropanephosphonic acid, sodium vinyl phosphate, allyl phosphonic acid and/or admixtures thereof. This polymer may also be either a hydrolyzed acrylamide polymer or a copolymer 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-vinylamide, N- alkylacrylamide, vinyl acetate, vinyl alcohol, acrylate esters, diacetone acrylamide, and N, N- dimethylacrylamide . Acrylic acid and methacrylic acid may conveniently be introduced into the polymer by hydrolysis of acrylamide and methacrylamide, respectively. The anionic polymer may be a homopolymer, copolymer, 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-acrylamido-2-methylpropane sulfonate/acrylamide; acrylamido methane sulfonate/acrylamide; 2-acrylamido ethane sulfonate/acrylamide; 2-hydroxy-3-acrylamide 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 acid/acrylamide/2-acrylamido ethane sulfonate; and acrylic acid/acrylamide/2-hydroxy-3-acrylamide propane sulfonate. Commonly accepted counter ions may be used for the salts, such as sodium ion and potassium ion. If the high molecular weight polymer i-s an anionic charge polymer, it is selected from the group consisting of a homopolymer of acrylic acid, a copolymer of acrylic acid/acrylamide, acrylic acid/2-acrylamido-2- methylpropane sulfonate/acrylamide, and a terpolymer of acrylic acid/acrylamide/2-acrylamido-2-methylpropane sulfonate.

Preferably, the inorganic sol used in the invention is selected from the group consisting of a zirconia sol (Zr0₂) and an alumina sol.

A zirconia sol generally is in both amorphous form and crystalline form, and preferably has a positive charge. These two forms are illustrated in Figures 1A and IB, respectively. In solution, these two forms generally are in equilibrium. The morphology and particle size of the sol can be controlled by manipulating the starting materials and conditions. The particle size of the zirconia sol may range between 5nm to about lOOOnm and, preferably, ranges between about 5nm to about lOOnm.

The preferred alumina sol is an alumina hydrate sol. The alumina hydrate sol forms a fibrous micro gel and has a positive charge.

The high molecular weight water soluble flocculant polymer employed in the microparticle system of the invention generally is an agent for aggregating the solids into floes in the paper making furnish. Here fines' means fine solid particles including fine fibers as defined in TAPPI Standard No. T261cm-90 entitled "Fines fraction of paper stock by wet screening".

According to the definition fines are those particles (including fibers) which will pass through a round hole of 76 micron diameter. In general, flocculation of -the fines of the furnish may be brought about by the high molecular weight water soluble polymer itself or in combination with another agent, e.g. a cationic coagulant such as a cationic polymer, a polyampholyte polymer, or a polysaccharide.

The degree of flocculation obtained may be measured indirectly by the improvement in retention and/or drainage obtained. Flocculation of fines gives better retention of the fines in the fiber structure of the forming paper sheet thereby giving improved dewatering or drainage.

The floes formed by the high molecular weight water soluble polymer may be subject to a shearing action before addition of the inorganic sol of the microparticle system of the invention. Although in some cases, e.g. for groundwood furnishes, the inorganic, sol may be added prior to or at the same stage as the flocculant polymer. A shearing stage may be applied prior to addition of the polymer, if added prior to the inorganic sol, and before or after addition of the inorganic sol.

The method of the invention can give an improved combination of drainage and retention and in some cases drying and formation properties, and it can be used to make a wide range of papers of good formation and strength at high rates of drainage and with good retention. The microparticle system of the method of the invention may also surprisingly and beneficially improve one or more optical properties, e.g. brightness of paper sheets formed using the system in a given cellulosic stock. The method can be operated to give a surprisingly good combination of high retention with good formation. Because of the good combination of drainage and drying it is possible to operate the method at high rates of production and with lower vacuum and/or drying energy than is normally required for papers having good formation. The method can be operated successfully at a wide range of pH values and with a wide variety of cellulosic stocks and pigments. Preferably, the pH range for the stock in the invention is from about 3 to about 10.

The method of the invention can be carried out using any conventional paper making apparatus. The furnish or ^λthin stock' that is drained to form the paper sheet is often made by diluting a thick stock which typically has been made in a mixing vessel by blending pigment or filler material, such as one or more of the filler materials conventionally used in the art, appropriate fiber, any desired strengthening agent or other additives, and water. Dilution of the thick stock can be by means of recycled water. The thick stock may be cleaned in a conventional manner, e.g. using a vortex cleaner. Usually the thick stock is cleaned by passage through a centriscreen or pressure screen. The thin stock is usually pumped along the apparatus employed to treat the furnish by one or more centrifugal pumps (transfer or fan pumps) . For instance the thick stock may be pumped to the centriscreen by a first fan pump. The thick stock can be diluted by water to the thin stock at the point of entry to this first fan pump or prior to the first fan pump, e.g. by passing the thick stock and dilution water through a mixing pump. The thick stock may be cleaned further, by passage through a further centriscreen. The thin stock that leaves the final centriscreen may be passed through a second fan pump and/or a head box prior to the sheet forming process.

The sheet forming process may be carried out by use of any conventional paper or paper board forming machine, for example, flat wire Fourdrinier, twin wire former or vat former or any combination of these.

In the method of the invention the high molecular weight water soluble polymer used as a flocculant may be added before the thin stock reaches the last point of high shear, i.e. which generally is a centriscreen, and the resultant stock is preferably sheared, e.g. at the last point of high shear, before adding the inorganic sol. Preferably, in this instance, the cationic coagulant or polyampholyte, or polysaccharide is added to the thick stock before its passage to the fan pump prior to the thick stock's passage through the centriscreen. As noted earlier, in some cases the inorganic sol may be. added prior to the thin stock, prior to or at the same stage as the high molecular weight flocculant polymer, and shearing may be applied after addition of the inorganic sol and prior to the high molecular weight flocculant polymer. Preferably, in this instance, again the cationic coagulant, polyampholyte, or polysaccharide is added to the thick stock before its passage to the fan pump and prior to the thick stock's passage through the centriscreen.

As stated hereinabove, preferably, the cationic coagulant, polyampholyte or polysaccharide is added to the thick stock prior to a fan pump, the high molecular weight flocculant polymer is added to the thin stock after the stock's passage through the fan pump, and the inorganic sol is added to the thin stock after the stock' s passage through the centriscreen or pressure screen.

Preferably, the high molecular weight flocculant polymer of the microparticle system is added to thin stock (i.e. stock having a solids content of desirably not more than 2% or, at the most, 3% by weight) rather than- to thick stock, whereas the cationic coagulant, polyampholyte or polysaccharide is added to the thick stock. Thus the high molecular weight polymer may be added directly to the thin stock or it may be added to the dilution water that is used to convert thick stock to thin stock.

The amount of flocculant polymer added to the stock in the method according to the invention may be any amount sufficient to give a substantial effect in flocculating the solids, especially the fines, present in the stock or furnish. The total amount of flocculant polymer added may be in the range 0.005% to 1% by weight (from about 0.10 to about 20 pounds per ton of furnish), more particularly in the range 0.01% to 0.5% by weight (dry weight of polymer based on the dry weight of solids present in the stock or furnish) or from about 0.2 to about 10 pounds per ton of furnish. The addition may be carried out in one or more doses at one or more addition sites . The total amount of cationic coagulant, polyampolyte, or polysaccharide added may be in the range 0.005 to 0.5% (from about 0.1 to about 10 pounds per ton of furnish), more particularly in the range 0.05% to 0.25% by weight (dry weight of polymer based on the dry weight of solids present in the stock or furnish) or from about 1 to about 5 pounds per ton of furnish.

The amount of inorganic sol added to the stock according to the present invention may be in the range 0.005% to 1.0% (from about 0.1 to about 20 pounds per ton of furnish), more particularly in the range 0.05% to 0.5% by dry weight based on the dry weight of solids in the furnish or from about 1 to about 10 pounds per ton of, furnish. The addition of the cationic coagulant, polyampolyte, or polysaccharide and the high molecular weight polymer may cause the formation of large floes of the suspended solids in the stock or furnish to which it is added and these are immediately or subsequently broken down by the high shear (usually in the fan pump and/or centriscreen) to very small floes that are known in the art as " icrofIocs" .

The resultant stock is a suspension of these microflocs and the inorganic sol may then be added to it when the microflocs have been formed. The stock is desirably stirred during addition of the inorganic sol sufficiently to distribute the inorganic particulate material uniformly throughout the stock to which it is added.

If the stock that has been treated with the inorganic sol of the microparticle system of the invention is subsequently subjected to substantial agitation or high shear this will tend to reduce the retention properties but improve still further the formation. For instance, the stock containing the inorganic sol could be passed through a centriscreen prior to dewatering and the paper sheet product will then have very good formation properties but possibly reduced retention compared to the results if the inorganic particulate material is added after that centriscreen. Because formation in the final sheet is usually good, in the method of the invention, if the inorganic sol is added just before sheet formation and because it is generally desired to optimize retention, it is usually preferred to add the inorganic sol after the last point of high shear. Preferably, as stated hereinabove, the high molecular weight flocculant polymer is added just before the final shearing stage, e.g. the final centriscreen and the stock with the high molecular weight flocculant polymer added is led from the final centriscreen to a headbox with the inorganic sol being added either to the headbox or between the centriscreen and the headbox, and the stock is then dewatered to form the paper sheet.

The inventors have found that an inorganic sol selected from the group consisting of a zirconium sol and an aluminum sol along with a high molecular weight flocculant polymer and either a cationic coagulant, a polyampholyte, or a polysaccharide can increase the drainage and retention, and improve sheet formation in a papermaking process.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Examples 1-6 are illustrative of the use of zirconia sols in amorphous and crystalline form, as illustrated in Figures 1A and IB, respectively. As stated hereinabove, these two forms in solution can exist in equilibrium. As stated hereinabove, the morphology and particle size of the sol can be controlled by manipulating the starting materials and conditions. Example 7 is illustrative of the use of an alumina hydrate sol. These sols generally form a fibrous microgel and are positively charged.

Examples

The following Examples 1-8 are not intended to limit the scope of the invention in any way. In Examples 1-8, the following products were used: Preparation Of The Polyampholyte Polymer Solution: Product A - polyampholyte copolymer consisting of 50/50 acrylamide/DMDAAC; having a reduced viscosity (dl/g) at 0.05 d/dl in 1 N (unit of concentration) NaCl of 5.6; and being 30.2% active emulsion.

Product B - polyampholyte copolymer consisting of 50/50 acrylamide/DMDAAC, the acrylamide portion being approximately 5% post-hydrolyzed to acrylic acid; having a reduced viscosity (dl/g) at 0.05 d/dl in 1 N NaCl of 7.9; and being 29.4% active.

Product C - polyampholyte copolymer consisting of 50/50 acrylamide/DMDAAC, the acylamide portion being approximately 20% post-hydrolyzed to acrylic acid; having a reduced viscosity (dl/g) at 0.05 d/dl in 1 N NaCl of 9.6; and being 29.1% active.

(Products A-C supplied by Calgon Corporation, Pittsburgh, PA. )

Product D - polyampholyte copolymer of acrylamide/DMDAAC which is 8% active and which is commercially available under the tradename ECCat^™777 from ECC International Inc., GA, U.S.A.

Product K - polyampholyte acrylamide/DMDAAC/acrylic acid terpolymer which is 8% active and commercially available under the tradename ECCat^™ 7951 from ECC International Inc., GA. U.S.A.

The polyampholyte polymer solution of at least Products B - D and Product K was prepared by adding 1 ml of the polyampholyte to 100 ml of tap water. The solution was stirred for 1 hour with a magnetic stirrer.

Preparation of a Cationic Coagulant Solution: Product E - polyDMDAAC - commercially available coagulant manufactured by ECC International Inc. under the tradename ECCat^™ 2020. A solution was prepared by adding 1 ml of the 40% active polymer to 100 ml of tap water. The mixture was stirred for 1 hour with a magnetic stirrer.

Preparation of the High Molecular Weight Water Soluble Flocculant Polymer Solution:

Product F - water soluble anionic emulsion polymer being 28% active - commercially available from Calgon Corporation, Pittsburgh, PA under the trademark Hydraid^® 8736 and having a molecular weight ranging between 5 and 15 million.

Product G - water soluble anionic emulsion polymer being 25% active - commercially available from Calgon Corporation, Pittsburgh, PA under the trademark Hydraid^® 7706 and having a molecular weight ranging between 5 and 15 million.

Product H - water soluble anionic emulsion polymer consisting of acrylamide and acrylic acid units and being 30% active - commercially available from Calgon Corporation, Pittsburgh, PA under the trademark Hydraid^® 7736 and having a molecular weight ranging between 5 and 15 million.

Product M - 100% polyacrylic polymer with a molecular weight of approximately 1 million - manufactured by Chemdal International, an AMCOL International Corporation and available under the trademark RMP^® 100. Product N- - water soluble cationic emulsion polymer being 25% active - AM/AETAC copolymer - commercially available from Calgon Corporation, Pittsburgh, PA under the trademark Hydraid^® 954 and having a molecular weight ranging between 5 and 15.

Product O -- a highly charged cationic copolymer - in an aqueous solution of a cationic copolymer of 50% dimethyl diallyl ammonium chloride and 50% acrylamide having a molecular weight of about 5 x 10⁶ - available from Calgon Corporation, Pittsburgh PA under the trademark Merquat® 550.

Product P - an amphoteric terpolymer - an aqueous solution of an amphoteric terpolymer consisting of acrylic acid, dimethyl diallyl ammonium chloride and acrylamide - high molecular weight terpolymer containing 25/50/25 weight percent ratio of AA/DMDAAC/AM and a molecular weight of about 4 x 10⁶ - available from Calgon Corporation under the trademark Merquat® Plus 3330. A solution was prepared by adding 2 grams of polymer to 98 ml of water. The polymer solution was stirred for 1 hours. Then 1 ml of the above solution was diluted to 100 ml with deionized water.

Preparation of Starch Solution:

Product I - cationic starch manufactured by Grain Processing Corporation and available under the tradename CHARGEMASTER R-630. Product J - cationic starch manufactured by A.E.Staley Manufacturing Co., Decatur, IL and available under the trademark STA-LOK^® 400.

A solution was prepared by adding 22 grams of starch to 97 ml of deionized water. The starch solution was boiled for one hour.

Example 1

Furnish Preparation

The following components were obtained: Cellulose fibers: 80/20wt% bleached hardwood kraft/bleached softwood kraft.

Filler: 100 wt % water washed kaolin-grade filler clay processed by ECC International Inc., U.S.A. under the tradename ACME. The amount of filler was 20 wt % based on fiber solids.

A dry lap pulp of the fibers was soaked in tepid water for about 10 minutes and then diluted to 2wt% solids in water and refined with a laboratory scale Valley Beater to a Canadian Standard Freeness of 250ml. The filler was added to the refined pulp slurry. The pulp slurry was diluted further with water to approximately 0.5% consistency to form thin stock for testing. The pH of the pulp slurry was 5.8 and then adjusted with caustic to raise the pH to 8.2.

Sol

A zirconia sol containing both amorphous and crystalline forms in equilibrium were used in this Example 1. The zirconia sol was obtained from NYACOL Products, Inc. a Company of PQ Corporation. The product characteristics are given in Table 1. The sols were used "as is" without any further dilution. ("Zr 10/20" refers to zirconia particles with a mean particle size of lOnm and 20wt % solids in the solution. "Zr 50/20 would be zirconia particles having a mean particle size of 50nm and a 20wt% solids in solution, etc.)

TABLE 1

Drainage Testing

Either a polyampholyte or a cationic coagulant polymer solution was added to one liter of thin stock at 0.5wt% consistency prepared as discussed above in this Example 1. The stock was poured into a (Britt) mixing jar. The contents of the jar were mixed for 10 seconds with a Lightning mixer at a constant speed of 1500 rpm. The slurry was then dosed with either a polyampholyte polymer solution prepared above or the high molecular weight polymer solution prepared above and then stirred for an additional minute. The mixer was then turned off and the slurry was allowed to stand for three minutes. The zirconia sol was added and the pulp slurry was poured back and forth five times between two beakers. The slurry was poured into a Britt drainage jar and shaken three times before allowing the slurry to drain. The drainage water was collected for 30 seconds and weighed by using a tarred beaker. The final pH of the slurry was the pH of the drained water.

Retention Testing

Either the polyampholyte or cationic coagulant polymer solution was added to one liter of thin stock with the 0.5 wt % consistency prepared above in this Example 1. This slurry was poured into a square (Britt) mixing jar and was mixed for 10 seconds with a Lightning mixer at a constant speed of 1500 rpm. The slurry was then dosed with either the polyampholyte polymer solution as prepared herein above or the high molecular weight flocculant polymer solution prepared above. Stirring was continued for an additional minute. The mixer was then turned off and the slurry was allowed to stand for three minutes. The zirconia sol was added to the slurry and the pulp slurry was poured back and forth five times between two. beakers. The slurry was poured into a Britt drainage jar and shaken three times before allowing it to drain. The first 20 ml were collected. This sample was used in the turbidity measurement. The sample_...turbidity in NTU' s was measured with a portable turbidity meter (Model 2100P) made by Hach Company.

The higher the turbidity, the less retention of the fillers and the fines. For drainage, the higher the milliliters, the better the drainage rate.

This example used the zirconia sol designated in Table 1 as "Zr 50/20" in the dosage indicated in Tables 2 - 8. All dosages are given in pounds of polymer/zirconia sol per ton of solids based on the dry weight of the solids in the slurry. The order of addition of the components of the microparticle system of the invention to the pulp slurry coincide with the listed order from left to right for each component in the following Tables 2-8, i.e. Product D (polyampholyte) was added first, followed by Product F (flocculant) , followed by a zirconia sol.

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

TABLE 8

From Tables 2 - 8, it can be seen from Item 1 of each table that the best turbidity (lowest NTU value) and drainage (highest ml value) occurred when the zirconia sol was used in conjunction with at least two additional components, i.e. either a polyampholyte (Tables 2,3,4,6 and 7) or a cationic coagulant (Table 8) with a high molecular weight anionic soluble polymer or two polyampholytes (Table 5) . This Table 5 which involves the use of zirconia sol with two polyampholytes (Item 5) also seems to indicate that an increase in the dosage of zirconia sol improves ^"retention and drainage (Compare Item 5 to Items 1-4 and 6 in Table 5) and that such an increase was necessary in order to be as effective as when the zirconia sol is used in conjunction with a polyampholyte or a cationic polymer and. a high molecular weight flocculant polymer. (Tables 2-4 and 6-8.)

Example 2

The pulp slurry of Example 2 was similar to that used in Example 1. For the drainage retention tests, the order of addition of the components was changed from that of Example 1 in that the zirconia sol was added before the polyampholyte polymer (Product C) was added to the slurry. The listed order of the components in Tables 9 and 10 represents the order of addition of these components of the microparticle system of the invention to the pulp slurry, i.e. zirconia sol was added first, followed by the polyampholyte polymer (Product C) . Two different zirconia sols, i.e. one contained particles having a mean particle size of 50 nm (Zr 10/20) and the other had particles having a mean particle size of 50 nm (Zr 50/20) , respectively, were used. The characteristics of these zirconia sols appear in Table 1 above.

TABLE 9

TABLE 10

The results of Example 2 show that again the best turbidity (lowest NTU) and the best drainage (higher ml value) occurred when zirconia sol and a polyampholyte polymer were used regardless of the sequence of addition of these two components of the microparticle system of the present invention (compared to the sequence in Example 1) . These results also show that for these zirconia sols, the sol having a mean particle size of 10 nm (Zr 10/20) was more effective than that having a mean particle size of 50 nm (Zr 50/20) in improving retention but that drainage was comparable.

Example 3 This Example 3 illustrates the effects of the use of a cationic starch with a high molecular weight flocculant polymer and the three zirconia sols of Table 1.

The pulp slurry was similar to that used in Example 1. The preparation of the high molecular anionic emulsion flocculant polymer solution and the preparation of the cationic starch were similar to that described herein above. The water-soluble flocculant polymers were Products F, G, and H, and the cationic starches were Products I and J, described herein above. The order of addition of the components was starch first, followed by the high molecular weight flocculant polymer and then, as in the previous two Examples 1 and 2, after the shearing (mixing) step, adding the zirconia sol. The results are given in Table 11.

TABLE 11

From the low turbidity values and high drainage values of Table 11, it can be seen that zirconia sols were effective with a cationic starch and a high molecular weight flocculant polymer compared to the samples containing no zirconia sol which have high turbidity values and low drainage values. Example 4

This Example 4 was similar to Example 3, except that instead of a high molecular weight anionic emulsion flocculant polymer, polyampholytes (Products D and K) were used. The order of addition was first cationic starch (Product J) , followed by polyampholyte (Product D or K) , and then after the shearing (mixing) step, a zirconia sol. The zirconia sols were those listed in Table 1.

The results are given in Table 12.

TABLE 12

From the low turbidity values and the high drainage values of Table 12, it can be seen that zirconia sols prove to be effective with a cationic starch and a polyampholyte compared to the samples containing no zirconia sol. Example 5

In this Example 5 a 100 % polyacrylic polymer solution with a molecular weight of approximately 1 million was used. This is Product M described herein above .

The order of addition was starch (Product J) first, followed by polyacrylic acid (Product M) , then, after the shearing (mixing) step, a zirconia sol listed in Table 1. The results are given in Table 13.

TABLE 13

Low turbidity (good retention) and high drainage occur when zirconia sols are used with a cationic starch and a polyacrylic polymer (Items 2-4) compared to when no zirconia sol is used (Item 1) .

Example 6

The water-soluble flocculant polymer used in this experiment was a cationic emulsion polymer, Hydraid^® 954 (Product N) , described herein above.

The order of addition was as follows : cationic starch (Product J) , polymer (Product N) and then after the shearing (mixing) stage, zirconia sol. The results are given in Table 14. TABLE 14

Table 14 shows that again the microparticle system of the invention comprising a zirconia sol, a cationic starch, and a cationic emulsion (flocculant) was effective. The best results occurred for ^λZr 100/20" which gave the lowest turbidity, i.e.- 18 NTU (best retention) and the highest drainage, i.e. 315 ml. Example 7

This Example 7 illustrates the effectiveness of using an alumina sol as the inorganic sol of the microparticle system of the invention. The alumina sol used was an alumina hydrate sol dispersed in water and manufactured by Nissa Chemical, and available under . the trademark ALUMINASOL® 100. The product properties are given in Table 15.

TABLE 15

The solutions for the cationic starches (Products I and J) and the high molecular weight flocculant polymers (Products G, H and M) were prepared as described herein above for these products. The retention and drainage tests were performed as described herein above for Examples 1-6. The alumina sol was added after the last shearing (mixing) stage. The results are given in Table 16.

TABLE 16

The results show that low turbidity and high drainage occurred when an alumina hydrate sol was used with a cationic starch and a high molecular weight polymer, and that its effectiveness of an alumina sol is comparable to that of zirconia sols.

Example 8

This Example 8 demonstrates the effectiveness of various formulations of the instant invention comprising a zirconia sol as the inorganic sol in improving drainage, retentions, and various sheet properties, including formation, brightness, and opacity, of a synthetic, aqueous cellulosic furnish. The composition of this furnish was designed to mimic a typical alkaline, wood-free furnish used to manufacture base sheet for coated and uncoated magazine or printing and writing grades .

Furnish Preparation

The synthetic furnish used for drainage and retention tests and for making handsheets was prepared with the following components :

Fiber: 50/50 wt % bleached hardwood kraft/bleached softwood kraft Filler: 50/50 wt % ground calcium carbonate

(Carbital 60) /precipitated calcium carbonate . Filler loading: 20 wt % based on fiber solids Starch: 0.5 wt % (Interbond C) based on fiber solids

Size: 0.25 wt % Hercon 70 (AKD)

The dry lap pulp was soaked in tepid water for 10 minutes and then diluted to 2 wt % solids in water and refined with a laboratory scale Valley Beater to a

Canadian Standard Freeness of 590 ml. The starch, size, and fillers, were subsequently added to the refined pulp in order. The pH of the pulp slurry was typically 7.5 + 0.3. The pulp slurry was diluted further with tap water to approximately 1.0 wt % consistency to form thin stock for testing.

The drainage and retention tests for Example 8 generally followed the sequence for standard tests under the following conditions, however, only a flocculant, i.e. a high molecular weight water soluble polymer (Product N) and a zirconia sol were used.

Drainage Test Procedure

1. Pour 200 ml (2g solids) of stock at 1.0 wt % headbox consistency into a square mixing jar and diluted to 500 ml with tap water.

2. Mix the contents using a standard Britt Jar style propeller mixer (1 inch diameter) under the following mixing time and speed conditions to simulate chemical addition to the secondary fan pump inlet, fan pump outlet, and pressure screen outlet:

Time Speed (rpm) Additive Feed Point to 1200 Coagulant Pre-fan tio 1200 Flocculant Pre-screen t₂o 600 D/R/F aid Post-screen t₃o stop

3. Transfer the contents of the mixing jar to a 500 ml graduated drainage tube fitted on the bottom with a 100 mesh screen. Invert the tube 5 times to ensure the stock is homogenous . Removed the bottom stopper and the elution times for 100, 200, and 300 ml elution volumes. The elution time at 300 ml for an untreated stock blank should be preferably >60 seconds.

4. The improvement in drainage provided by a treatment was calculated as follows based on the drainage time for an untreated, blank sample:

% Drainage Improvement = (Drain Time with No Treatment - Drain Time With Treatment') x 10Q Drain Time with No Treatment Retentions Test Procedure (FPR, FPAR, FPFR)

1. Pour 500 ml of stock at headbox consistency (1.0%) into a Britt Jar with a 70 mesh screen while stirring the stock at 1200 rpm.

2. Use the same mixing time / speed sequence as that used in the drainage test procedure to simulate chemical addition points and add the following steps:

Time Speed (rpm) Additive Feed Point to 1200 Coagulant Pre-fan tio 1200 Flocculant Pre-screen t₂₀ 600 D/R/F aid Post-screen t₃o open the bottom stop cock and collect the first ml of eluate

a. Filter this eluate through Whatman 4 filter paper and dry the pad at 105°C. Burn the pad at 500°C for 2 hours to determine ash retention.

Hand Sheet Preparation and Testing

Hand sheets were prepared at 70 gs basis weight using a Noble & Wood Hand Sheet Mold. This apparatus generates a 20cm x 20 cm square hand sheet. The mixing time / speed sequence used in preparing hand sheets was the same as the sequence used for the drainage test procedure. The treated furnish sample is poured into the deckle box of the Noble & Wood handsheet machine and the sheet is prepared employing standard techniques well known by those skilled in the art.

The results are shown in Table 17. In this example, as stated hereinabove, only a flocculant (Product N) and a zirconia sol were used. TABLE 17

Comparisons of the results for Test 4 versus _.Tests 5-16 of Table 17 show that the addition of zirconia sols with a cationic, high molecular weight polymer (Tests 5- 16) significantly improve stock drainage and retention, particularly filler retention. The results of Tests 9 and 13 demonstrate the effectiveness of zirconia sols to improve stock drainage, filler retention, and sheet brightness without sacrificing sheet formation. Increasing dosages of the zirconia sol (Tests 13-15) yield even greater improvements in stock drainage, retentions, sheet brightness and opacity without any loss in sheet formation.

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

Claims

WHAT IS CLAIMED IS:

1. A method of producing paper which includes the steps of adding to a paper making stock or furnish a microparticle system retention and/or drainage aid which comprises at least one polymer selected from the group consisting of polyampholyte polymer, a coagulant polymer, and a high molecular weight water soluble polymer, and an inorganic sol selected from the group consisting of zirconia sol, and alumina sol.

2. The method of Claim 1, wherein said polyampholyte is a copolymer derived from a cationic monomer that is selected from the group consisting of dialkyldiallyl ammonium monomer, methacryloxyethyl trimethyl ammonium chloride, acrylamido propyl trimethylammonium chloride, and methacrylamido propyl trimethyl ammonium chloride, and an anionic monomer that is selected from the group consisting of acrylic acid, methacrylic acid, 2- acrylamido-2-methylpropanesulfonic acid, sodium vinyl sulfonate, and acrylamidoglycolic acid.

3. The method of Claim 2 wherein said acrylic acid is introduced into said polymer by hydrolysis of acrylamide and said methacrylic acid is introduced into said polymer by hydrolysis of methacrylamide.

4. The method of Claim 1, wherein said polyampholyte is a terpolymer derived from (a) a cationic monomer that is selected from the group consisting of dialkyldiallyl ammonium monomer, methacryloxyethyl trimethyl ammonium chloride, acrylamido propyl trimethylammonium chloride, and methacrylamido propyl trimethyl ammonium chloride; (b) anionic monomer that is selected from the group consisting of acrylic acid, methacrylic acid, 2- crylamido-2-methylpropanesulfonic acid, sodium vinyl sulfonate, and acrylamidoglycolic acid; and (c) a nonionic monomer selected from the group consisting of N- vinylamide, N-alkylacrylamide, vinyl acetate, acrylate esters, diacetone acrylamide, and N, N- dimethylacrylamide .

5. The method of Claim 4 wherein said acrylic acid is introduced into the terpolymer by hydrolysis of acrylamide, and wherein said methacrylic acid is introduced into the terpolymer by hydrolysis of methacrylamide .

6. The method of Claim 1, wherein said coagulant polymer is a low molecular weight cationic organic polymer having a weight average molecular weight ranging from about 2,000 to 2,000,000, and being selected from the group consisting of diallyldimethylammonium chloride polymer, diallyldimethylammonium chloride/acrylamide copolymer, epichlorohydrin/dimethylamine copolymer, ethylene dichloride/ammonia copolymer, and acrylamido N,N-dimethyl-piperazine quaternary/acrylamide copolymer.

7. The method of Claim 1, wherein said high molecular weight water soluble polymer is a cationic charge polymer having a weight average molecular weight greater than about 8 x 10⁵.

8. The method of Claim 7, wherein said cationic charge polymer is a copolymer derived from a cationic monomer that is selected from the group consisting of a methacryloxyethyl trimethyl ammonium chloride, acrylamido propyl trimethyl ammonium chloride, and methacrylamido propyl trimethyl ammonium chloride, and a nonionic monomer that is acrylamide, and wherein the weight ratio of said cationic monomer to said nonionic monomer is from about 99:1 to 1:99.

9. The method of Claim 1, wherein said high molecular weight water soluble polymer is an anionic charge polymer having a weight average molecular weight equal to or greater than 8 x 10⁵.

10. The method of Claim 9, wherein said anionic charge polymer is selected from the group consisting of a homopolymer of acrylic acid, a copolymer of acrylic acid/acrylamide, acrylic acid/2-acrylamido-2- methylpropane sulfonate, 2-acrylamido-2-methylpropane sulfonate/acrylamide, and a terpolymer of acrylic acid/acrylamide/2-acrylamido-2-methylpropane sulfonate .

11. The method of Claim 1, wherein said aqueous paper furnish has a pH from about 3 to about 10.

12. The method of Claim 1, wherein said microparticle system further comprises a cationic starch added to the stock or furnish at least prior to said polymer.

13. The method of Claim 1 wherein said inorganic sol comprises zirconia sol having a particle size ranging from about 5nmm to about lOOnm and about 20 wt % solids in solution.

14. The method of Claim 13 wherein said zirconia sol is comprised of amorphous and crystalline forms in equilibrium.

15. The method of Claim 1 wherein said inorganic sol comprises aluminum sol having an average particle size of about lOOnm by lOnm and a specific surface area ranging from about 300 to about 500 m²/g.

16. A paper sheet made by the method according to Claim 1.