EP0805234B1

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Info

Publication number: EP0805234B1
Application number: EP19970107188
Authority: EP
Inventors: Ramasubramanyam Nagarajan; Jane B. Wong Shing
Original assignee: Nalco Chemical Co
Current assignee: ChampionX LLC
Priority date: 1996-05-01
Filing date: 1997-04-30
Publication date: 2002-07-03
Anticipated expiration: 2017-04-30
Also published as: ID16844A; BR9701967A; MY123120A; AU729008B2; DE69713677D1; DE69713677T2; EP0805234A3; ES2176553T3; CA2204050A1; AU1915897A; EP0805234A2; NO326449B1; MX9703180A; NO972022D0; CA2204050C; NO972022L

Description

The present invention is in the technical field of papermaking and moreparticularly in the technical field of wet-end additives to papermaking furnish.
In the manufacture of paper an aqueous cellulosic suspension or slurry is formedinto a paper sheet. The cellulosic slurry is generally diluted to a consistency (percent dryweight of solids in the slurry) of less than 1 percent and often below 0.5 percent ahead ofthe paper machine, while the finished sheet must have less then 6 weight percent water.Hence the dewatering aspects of papermaking are extremely important to the efficiencyand cost of the manufacture.
The dewatering method of the least cost in the process is drainage, and thereaftermore expensive methods are used, for instance vacuum, pressing, evaporation and thelike, and in practice a combination of such methods are employed to dewater, or dry thesheet to the desired water content. Since drainage is both the first dewatering methodemployed and the least expensive, improvement in the efficiency of drainage willdecrease the amount of water required to be removed by other methods and henceimprove the overall efficiency of dewatering and reduce the cost thereof.
Another aspect of papermaking that is extremely important to the efficiency andcost of the manufacture is retention of furnish components on and within the fiber matbeing formed during papermaking. A papermaking furnish contains generally particles that range in size from about the 2 to 3 millimeter size of cellulosic fibers to fillers at afew microns, and to colloids. Within this range are cellulosic fines, mineral fillers(employed to increase opacity, brightness and other paper characteristics) and other smallparticles that generally, without the inclusion of one or more retention aids, would insignificant portion pass through the spaces (pores) between the cellulosic fibers in thefiber mat being formed during papermaking.
One method of improving the retention of cellulosic fines, mineral fillers andother furnish components on the fiber mat is the use of a coagulant/flocculant system,added ahead of the paper machine. In such a system there is first added a coagulant, forinstance a low molecular weight cationic synthetic polymer or a cationic starch to thefurnish, which coagulant generally reduces the negative surface charges present on theparticles in the furnish, particularly cellulosic fines and mineral fillers, and therebyaccomplishes a degree of agglomeration of such particles, followed by the addition of aflocculant. Such flocculant generally is a high molecular weight anionic syntheticpolymer which bridges the particles and/or agglomerates, from one surface to another,binding the particles into large agglomerates. The presence of such large agglomerates inthe furnish as the fiber mat of the paper sheet is being formed increases retention. Theagglomerates are filtered out of the water onto the fiber web, where unagglomeratedparticles would to a great extent pass through such paper web.
While a flocculated agglomerate generally does not interfere with the drainage ofthe fiber mat to the extent that would occur if the furnish were gelled or contained anamount of gelatinous material, when such flocs are filtered by the fiber web the pores thereof are to a degree reduced, reducing the drainage efficiency therefrom. Hence theretention is being increased with some degree of deleterious effect on the drainage.
Another system employed to provide an improved combination of retention anddewatering is described in United States Patent No. 4,753,710 and United States PatentNo. 4,913,775, inventors Langley et al., issued respectively June 28, 1988 and April 3,1990. In brief, such method adds to the aqueouscellulosic papermaking suspension first a high molecular weight linear cationic polymerbefore shearing the suspension, followed by the addition of bentonite after shearing. Theshearing generally is provided by one or more of the cleaning, mixing and pumpingstages of the papermaking process, and the shearing breaks down the large flocs formedby the high molecular weight polymer into microflocs, and further agglomeration thenensues with the addition of the bentonite clay particles.
Another system uses the combination of cationic starch followed by colloidalsilica to increase the amount of material retained on the web by the method of chargeneutralization and adsorption of smaller agglomerates. This system is described inUnited States Patent No. 4,388,150, inventors Sunden et al., issued June 14, 1983.
Dewatering generally, and particularly dewatering by drainage, is believedimproved when the pores of the paper web are less plugged, and it is believed thatretention by adsorption in comparison to retention by filtration reduces such poreplugging.
Greater retention of fines and fillers permits, for a given grade of paper, areduction in the cellulosic fiber content of such paper. As pulps of less quality are employed to reduce papermaking costs, the retention aspect of papermaking becomeseven more important because the fines content of such lower quality pulps is greatergenerally than that of pulps of higher quality.
Greater retention of fines, fillers and other slurry components reduces the amountof such substances lost to the white water and hence reduces the amount of materialwastes, the cost of waste disposal and the adverse environmental effects therefrom.
Another important characteristic of a given papermaking process is the formationof the paper sheet produced. Formation is determined by the variance in lighttransmission within a paper sheet, and a high variance is indicative of poor formation. Asretention increases to a high level, for instance a retention level of 80 to 90 percent, theformation parameter generally abruptly declines from good formation to poor formation.It is at least theoretically believed that as the retention mechanisms of a givenpapermaking process shift from filtration to adsorption, the deleterious effect onformation, as high retention levels are achieved, will diminish, and a good combination ofhigh retention with good formation is attributed to the use of bentonite in U. S. Patent No.4,913,775.
It is generally desirable to reduce the amount of material employed in apapermaking process for a given purpose, without diminishing the result sought. Suchadd-on reductions may realize both a material cost savings and handling and processingbenefits.
It is also desirable to use additives that can be delivered to the paper machinewithout undue problems. An additive that is difficult to dissolve, slurry or otherwise disperse in the aqueous medium may require expensive equipment to feed it to the papermachine.. When difficulties in delivery to the paper machine are encountered, the additiveis often maintained in aqueous slurry form by virtue of high energy input equipment. Incontrast, additives that are easily dissolved or dispersed in water require less energy andexpense and their uniformity of feed is more reliable.

Summary of the Invention

The claimed invention comprises a papermaking process comprising forming anaqueous cellulosic papermaking slurry, subjecting the slurry to one or more shear stages,adding to the slurry a mineral filler prior to at least one of the shear stages, adding to theslurry after the addition of the mineral filler and prior to at least one of the shear stagesfrom 0.5 to 100 ppm by weight of dry pulp contained in the slurry of a cationic dispersionpolymer obtainable by dispersion polymerization of a monomer mixture soluble in an aqueous solution of a polyvalent anionic salt saidpolymer being selected from the group consisting ofcopolymers of acrylamide and dimethylaminoethylacrylate methyl chloride quaternarysalt (DMAEA.MCQ), dimethylaminoethylmethacrylate methyl chloride quaternary salt(DMAEM.MCQ), dimethylaminoethylacrylate benzyl chloride quaternary salt(DMAEA.BCQ) and dimethylaminoethylmethacrylate benzyl chloride quaternary salt(DMAEM.BCQ) and wherein said polymer is insoluble in the aqueous solution, shearing the slurry, adding an amount ofmicroparticlesselected from the group consisting ofcopolymers of polyacrylic acid, bentonite and silica sol to the slurry, draining theslurry to form a sheet, and drying the sheet to form a paper sheet.

Description of the Preferred Embodiments

According to the invention, a water soluble polymer is added to a cellulosic slurrybefore the formation of a paper product. The water soluble polymer should become substantially dispersed within the slurry before formation of the paper product in anycase. The microparticle of the invention is added after shearing of the slurry. Theaddition of the polymer in an aqueous medium, for instance as a water solution ordispersing, facilitates the dispersion of the polymer of the slurry. In a preferredembodiment, the polymer is added to the cellulosic slurry before the processing steps ofdraining and forming the paper sheet.
The present process is believed applicable to all grades and types of paperproducts, and further applicable for use on all types of pulps including, withoutlimitation, chemical pulps, including sulfate and sulfite pulps from both hard and softwoods and acid pulps, thermo-mechanical pulps, mechanical pulps, recycle pulps andground wood pulps, although it is believed that the advantages of the process of thepresent invention are best achieved when the pulp employed is of the chemical pulp type,particularly alkaline chemical pulp.
In preferred embodiment the filler used in the cellulosic slurry is anionic, or atleast partially anionic. Other mineral, or inorganic, fillers may, however, be used, such ascalcium carbonate, clay, titanium dioxide, or talc or a combination may be present.
The amount of alkaline inorganic filler, such as one of the alkaline carbonates,generally employed in a papermaking stock is from 10 to 30 parts by weightof the filler, as CaCO₃, per hundred parts by weight of dry pulp in the slurry, but theamount of such filler may at times be as low as 5, or even 2, parts by weight,and as high as 40 or 50 parts by weight, same basis.
The reduced specific viscosities of the polymers and copolymers as reportedherein were determined in 0.125M sodium nitrate solution from published data.Similarly, all molecular weights of the polymers as reported herein are the approximateweight average molecular weights of the polymers.
The dispersion polymerization process used to manufacture the polymers of theinvention offer numerous advantages which have previously been unavailable. Since thepolymers of the invention are synthesized entirely in water, no oil solvent is required.This is significant since:
1) the polymers of the invention do not present a fire hazard;
2) oil is not added to the water which is to be treated (more environmental friendly);
3) dissolution of the polymers of the invention requires only the addition of water,no special activators are needed;
4) the ability of the polymers of the invention to dissolve/invert is superior to that ofoil dispersion latexes; and
5) the polymers of the invention may be diluted to virtually any concentration byusing appropriately concentrated salt water.
Another major advantage is that the bulk viscosity of the polymer is low, unlikesome oil dispersion latex polymers. This physical property enables any standardchemical pump to deliver the material at the injunction site.
A new class of water-soluble dispersion polymers have been discovered to bemore effective in increasing drainage and retention than currently available chemicaltreatments. As will be discussed in more detail below, the polymer dispersion is prepared in an aqueous solution of a polyvalent anionic salt. The polymerdispersion achieves fine particle sizes and aqueous solubilities notavailable with other polymers used for this application. Furthermore, there does notappear to be a problem with overfeeding the polymer dispersion which is a drawbackwith latex polymers.
According to the method, the dispersion polymer of the invention is added to acellulosic papermaking slurry. The polymer is added in an effective amount of from 0.5to 100 ppm. More preferably, the amount of the polymer added is from 2 to40 ppm; and most preferably from 4 to 25 ppm. It is believed, that there doesnot appear to be a maximum dosage at which the polymers adversely affect the system.At some higher doses the beneficial effect may plateau, and on a cost basis such higherdoses, probably above about 100 ppm, are not cost effective. The polymers of theinvention are preferably added to the system in neat form. However, in someapplications, the polymers can be added as an aqueous solution.
The preferred polymers of the invention are manufactured by Hymo Corporation,Japan. Methods for manufacturing the polymer dispersion used in the invention isdescribed in detail in U. S. Patent No. 5,006,590 and U. S. Patent No. 4,929,655, assignedto Kyoritsu Yuki Co., Ltd., Tokyo, Japan.
According to the invention, an organic or inorganicmicroparticle is added to the slurry after the introduction of shear. Preferably, the organicmicroparticle is a medium molecular weight anionic polymer such as the copolymers of acrylic acid described in U.S. Patent No. 5,098,520 or mediummolecular weight anionic sulfonated polymers such as thosedescribed in U.S. Patent No. 5,185,062. The inorganicmicroparticle may be preferably chosen from among bentoniteand silica sol.
According to the invention, the dispersion polymer used to treat the cellulosicpapermaking slurry may further be prepared from a water-soluble monomer mixturecontaining at least 5 mole % of a cationic monomer represented by the general formula(I):
wherein R₁ is H or CH₃; R₂ and R₃ are each an alkyl group having 1 to 2 carbon atoms;R₄ is benzyl or CH₃;
A₁ is an oxygen atom or NH; B₁ is an alkyl group having 2 to 4 carbon atoms or ahydroxypropyl group and X₁ is a counter anion.
The above water-soluble monomer mixture is soluble in the aqueous solution ofthe polyvalent anionic salt. The polymer generated from the monomer mixture is,however, insoluble in the aqueous polyvalent anionic salt solution. The polymer of the monomer mixture can also be used as the seed polymer. The seed polymer is describedin detail below.
The above cationic monomer represented by the general formula (I) preferably isa quaternary ammonium salt obtained by the reaction of methyl chloride or benzylchloride and dimethylaminoethyl acrylate, diethylaminoethyl acrylate,dimethylaminohydroxypropyl acrylate, dimethylaminopropyl acrylamide,dimethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethylmethacrylate and dimethylaminopropyl methacrylamide.
The concentration of the above-mentioned monomers in the polymerizationreaction mixture is suitably in the range of 1.0 to 30% by weight for the methyl chloridequaternary ammonium salt. Preferably, the concentration is from 10 to 20%by weight. For the benzyl chloride quaternary ammonium salts, the concentration in thepolymerization reaction mixture is suitably in the range of from 1.0 to 35%by weight. Preferably, the concentration is from 10 to 20% by weight.
Monomers preferably copolymerized with the cationic monomer as representedby the general formula (I) include acrylamide, methacrylamide and the cationicmonomers represented by the general formula (II):
wherein R₅ is H or CH₃; R₆ and R₇ are each an alkyl group having 1 to 2 carbon atoms;R₈ is H or an alkyl group having 1 to 2 carbon atoms; A₂ is an oxygen atom or NH; B₂ isan alkyl group having 2 to 4 carbon atoms or a hydroxypropyl group and X₂ is a counteranion.
Preferable monomers represented by the formula (II) include the ammonium saltsof dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropylacrylamide, diethylaminopropyl acrylamide and dimethylhydroxypropyl acrylate,dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropylmethacrylamide, diethylaminopropyl methacrylamide and dimethylhydroxypropylmethacrylate as well as the methylated and ethylated quaternary salts. Among the morepreferable cationic monomers represented by the general formula (II) are the salts andmethylated quaternary salts of dialkylaminoethyl acrylate and dialkylaminoethylmethacrylate.
The polyvalent anionic salt to be incorporated in the aqueous solutionis suitably a sulfate, a phosphate or a mixture thereof. Preferablesalts include ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate,ammonium hydrogen phosphate, sodium hydrogenphosphate and potassium hydrogenphosphate. In the present invention, these salts may be each used as an aqueoussolution thereof having a concentration of 15% or above.
A dispersant is present in the aqueous anionic salt solution in which thepolymerization of the above monomers occurs. The dispersant is a water-soluble highmolecular weight cationic polymer. The dispersant is soluble in the above-mentionedaqueous salt solution. The dispersant is preferably used in an amount of from 1 to 10%by weight based on the total weight of the monomers. The dispersant is composed of 20mole % or more of cationic monomer units represented by the formula (II). Preferablythe residual mole % is acrylamide or methacrylamide. The performance of the dispersantis not greatly affected by molecular weight. However, the molecular weight of thedispersant is preferably in the range of 10,000 to 10,000,000 g/mol (daltons). Amultifunctional alcohol such as glycerin or polyethylene glycol can be coexistent in thepolymerization system. The deposition of the fine particles is smoothly carried out in thepresence of these alcohols.
For the polymerizations a usual water-soluble radical-forming agent can beemployed, but preferably water-soluble azo compounds such as 2,2'-azobis(2-amidinopropane)hydrochloride and 2,2'-azobis(N,N'-dimethyleneisobutylamine)hydrochloride are used.
A seed polymer can be added beforethe beginning of the polymerization of the above monomers for the purpose of obtaininga fine dispersion. The seed polymer is a water-soluble cationic polymer insoluble in theaqueous solution of the polyvalent anionic salt. The seed polymer is preferably a polymer prepared from the above monomer mixture by the process described herein.Nevertheless, the monomer composition of the seed polymer need not always be equal tothat of the water-soluble cationic polymer formed during polymerization. However, likethe water-soluble polymer formed during polymerization, the seed polymer shouldcontain at least 5 mole percent of cationic monomer units represented by the generalformula (I). The seed polymer used in one polymerization reaction can be the water-solublepolymer prepared in a previous reaction which used the same monomer mixture.

Examples

The following examples are presented to describe preferred embodiments andutilities of the invention and are not meant to limit the invention unless otherwise statedin the claims appended hereto. In the following examples, common terms usedthroughout have the following meanings.

Microparticle A (colloidal silica)

Dispersed silica in water with a particle size of 4 nm.

Microparticle B

Copolymer of acrylic acid

Microparticle C (bentonite)

Hydrated suspension of powdered bentonite in water.
DispersionPolymers
Polymer A
10 mole% DMAEA.BCQ RSV 19.6 dl/g
Polymer B
10 Mole % DMAEA.MCQ RSV 21.4 dl/g
Polymer C 20 mole % DMAEA.MCQ RSV 27.6 dl/g
LatexPolymer
Polymer D
10 mole% DMAEA.MCQ RSV 19.7 dl/g
The Reduced Specific Viscosity (RSV) was measured at a concentration of0.045% polymer in a solution of 0.125M NaNO₃ solution.

Britt Jar Test

The Britt Jar Test employed in Examples 1 to 3 used a Britt CF DynamicDrainage Jar developed by K. W. Britt of New York State University, which generallyconsists of an upper chamber of about 1 liter capacity and a bottom drainage chamber, thechamber being separated by a support screen and a drainage screen. Below the drainagechamber is a downward extending flexible tube equipped with a clamp for closure. Theupper chamber is provided with a variable speed, high torquemotor equipped with a 51-mm (2-inch) 3-bladed propeller tocreate controlled shear conditions in the upper chamber. Thetest was conducted by placing the cellulosic stock in the upper chamber and thensubjecting the stock to the following sequence:

Time	Action
0 seconds	Commence shear stirring at 750 rpm, (add starch, if needed).
10 seconds	Add the cationic polymer, increase speed to 2000 rpm.
40 seconds	Reduce shear stirring to 750 rpm.
50 seconds	Add the microparticle.
60 seconds	Open the tube clamp to commence drainage, and continue drainage for 30 seconds.

The material so drained from the Britt jar (the "filtrate") is collected and dilutedwith water to one-fourth of its initial volume. The turbidity of such diluted filtrate,measured in Formazin Turbidity Units or FTU's, is then determined. The turbidity ofsuch a filtrate is inversely proportional to the papermaking retention performance; thelower the turbidity value, the higher is the retention of filler and/or fines. The turbidityvalues were determined using a Hach Spectrophotometer, model DR2000.
The turbidity values (in FTU) that were determined were converted to (PercentImprovement) values using the formula:Percent Improvement = 100 X(Turbidityu - Turbidityt)/TurbidityuwhereTurbidity_u is the turbidity reading result for the blank for which no polymer ormicroparticle, and whereinTurbidity_t is the turbidity reading result of the test usingpolymer, or polymer and microparticle.

Filtration Test

The filtration tests used in Examples 1 to 8 measured the drainage (waterremoval) rate of the test stock subjected to the various chemical treatments. A filtrationcell, mounted upright on a stand, was used. The capacity of this cell is about 220milliliters. A 200 mesh drainage screen (76µm screen with 8% opening) served as thefilter medium. The stock was filtered by gravity. The filtrate was collected in a cupplaced on a weighing balance below the cell. This balance was interfaced with acomputer so that the displayed weight was recorded continuously over time. Thecomputer automatically recorded the change of weight over time.
The cellulosic stock was treated in the aforementioned Britt jar. The treated stockwas transferred to the cell and filtered until completion. The rate of filtrate collection isan indication of the drainage performance; the higher the filtrate collection rate, thehigher is the improvement in drainage.

Test Stocks

Alkaline Test Stock

The cellulosic stock or slurry used in Examples 1 to 3 and 8 was comprised of 70weight percent fiber and 30 weight percent filler, diluted to an overall consistency of 0.5percent with formulation water. The fiber was a 60/40 blend by weight of bleachedhardwood Kraft and bleached softwood Kraft, separately beaten to a Canadian Freenessvalue range of from 320 to 360 C.F.S. The filler was a commercial calcium carbonate ,provided in dry form. The formulation water contained 60 ppm calcium hardness (added as CaCl₂), 18 ppm magnesium hardness (added as MgSO₄) and 134 ppm bicarbonatealkalinity ( added as NaHCO₃). The pH of the final thin stock was pH 7.2.

Acid Test Stock

The cellulosic stock or slurry used in Examples 4 to 5 was comprised of 93weight percent fiber and 7 weight percent filler, diluted to an overall consistency of 0.54percent with formulation water. The fiber was a 50/50 blend by weight of bleachedhardwood Kraft and bleached softwood Kraft, separately beaten to a Canadian Freenessvalue range of from 320 to 360 C.F.S. The fillers were clay as predispersed kaolin andtitanium dioxide, commercially provided in dry form. The pH was adjusted to pH 4.00using dilute sulfuric acid, following which alum (0.005% of final slurry) and sizing agentrosin (0.0025 wt% of final slurry) were added. The formulation water contained 60 ppmcalcium hardness (added as CaCl₂), 18 ppm magnesium hardness (added as MgSO₄) and134 ppm bicarbonate alkalinity ( added as NaHCO₃).

Corrugated Coated Test Stock

The stock used in Examples 6 and 7 was obtained as thick stock (consistency of4.11 %) from a paper mill. It was a mixture of OCC, newsprint, and boxboard. It wasdiluted to an overall consistency of 0.8% with formulation water containing 60 ppmcalcium hardness (added as CaCl₂), 18 ppm magnesium hardness (added as MgSO₄) and134 ppm bicarbonate alkalinity ( added as NaHCO₃). The final pH of the thin stock waspH 6.5. The percent ash of the thin stock was 7.3 wt%.

Example 1

Using the alkaline test stock described above, the Britt jar test, also describedabove was employed to determine the retention performances of dispersion Polymer A incomparison to the inverse emulsion Polymer D, with microparticle A as themicroparticle. In each test, cationic potato starch was charged to the test stock in theamount of 4.5 kg/1000 kg (10 lb/ton) of dry weight of slurrysolids. The various programs tested areshown below in Table 1. The test results are reported in Table 1 below as diluted filtrateturbidity values (FTU) and (Percent Improvement), as defined earlier, for each of theprograms tested.
The drainage performance of these programs was measured for the same alkalinefurnish using the filtration test described above. In each test starch was charged to thetest stock in the amount of 4.5 kg/1000 kg (10 lb/ton) of dryweight of slurry solids. The results are shownfor each of the programs tested in Figure 1 as graphs of collected filtrate weight versustime.

Example 2

Using the alkaline test stock described above, the Britt jar test, also describedabove was employed to determine the retention performances of dispersion Polymer B incomparison to the inverse emulsion Polymer D, with microparticle A as themicroparticle. In each test, cationic potato starch was charged to the test stock in the amount of 4.5 kg/1000 kg (10 lb/ton) of dry weight of slurry solids.The various programs tested are shown below in Table 2. The testresults are reported in Table 2 below as diluted filtrateturbidity values (FTU) and (Percent Improvement), as defined earlier, for each of theprograms tested.

The drainage performance of these programs was measured for the same alkalinefurnish using the filtration test described above. In each test starch was charged to thetest stock in the amount of 4.5 kg/1000 kg (10 lb/ton) of dryweight of slurry solids. The results are shownfor each of the programs tested in Figure 2 as graphs of collected filtrate weight versustime.

Britt Jar Retention Tests Alkaline Furnish
No.	Polymer	Polymer Dosage kg/1000 kg (lb/ton)	Microparticle A Dosage kg/1000 kg (lb/ton)	Turbidity (FTU)	Percent Improvement
	blank
	0	0	359.5	-
1	A	0.73 (1.6)	0	289	20
2	A	0.73 (1.6)	0.91 (2)	84	77
3	D	0.73 (1.6)	0	291	19
4	D	0.73 (1.6)	0.91 (2)	162	55

Britt Jar Retention Tests Alkaline Furnish
No.	Polymer	Polymer Dosage kg/1000 kg (lb/ton)	Microparticle A Dosage kg/1000 kg (lb/ton)	Turbidity (FTV)	Percent Improvement
	blank
	0	0	359.5
1	B	0.73 (1.6)	0	252	30
2	B	0.73 (1.6)	0.91 (2)	74	79
3	D	0.73 (1.6)	0	291	19
4	D	0.73 (1.6)	0.91 (2)	162	55

Example 3

Using the alkaline test stock described above, the Britt jar test, also describedabove was employed to determine the retention performances of dispersion Polymer C incomparison to the inverse emulsion Polymer D, with microparticle A as themicroparticle. In each test, cationic potato starch was charged to the test stock in theamount of 4.5 kg/1000 kg (10 lb/ton) of dry weight of slurrysolids. The various programs tested areshown below in Table 3. The test results are reported in Table 3 below as diluted filtrateturbidity values (FTU) and (Percent Improvement), as defined earlier, for each of theprograms tested.

Britt Jar Retention Tests Alkaline Furnish
No.	Polymer	Polymer Dosage kg/1000 kg (lb/ton)	Microparticle A Dosage kg/1000 kg (lb/ton)	Turbidity (PTU)	Percent Improvement
	blank
	0	0	359.5
1	C	0.73 (1.6)	0	266	26
2	C	0.73 (1.6)	0.91 (2)	120	67
3	D	0.73 (1.6)	0	291	19
4	D	0.73 (1.6)	0.91 (2)	162	55

Example 4

Using the acid test stock described above, the filtration test, also described abovewas employed to determine the drainage performances of dispersion Polymer A incomparison to the inverse emulsion Polymer D, with microparticle A as themicropanicle. The results are shown for each of the programs tested in Figure 3 asgraphs of collected filtrate weight versus time.

Example 5

Using the acid test stock described above, the filtration test, also described abovewas employed to determine the drainage performances of dispersion Polymer A incomparison to the inverse emulsion Polymer D, with microparticle B as the microparticle.The results are shown for each of the programs tested in Figure 4 as graphs of collectedfiltrate weight versus time.

Example 6

Using the corrugated coated test stock described above, the filtration test, alsodescribed above was employed to determine the drainage performances of dispersionPolymer A, with microparticle A as the microparticle. The results are shown for each ofthe programs tested in Figure 5 as graphs of collected filtrate weight versus time.

Example 7

Using the corrugated coated test stock described above, the filtration test, alsodescribed above was employed to determine the drainage performances of dispersionPolymer A, with microparticle B as the microparticle. The results are shown for each ofthe programs tested in Figure 6 as graphs of collected filtrate weight versus time.

Example 8

Using the alkaline test stock described above, the filtration test, also describedabove was employed to determine the drainage performances of dispersion Polymer A incomparison to the inverse emulsion Polymer D, with microparticle C as the microparticle.In each test, cationic potato starch was charged to the teststock in the amount of 4.5 kg/1000 kg (10 lb/ton)of dry weight of slurry solids. The results are shown for each of the programs tested inFigure 7 as graphs of collected filtrate weight versus time.

Claims

A papermaking process comprising forming an aqueouscellulosic papermaking slurry, subjecting the slurry to one ormore shear stages, adding to the slurry a mineral filler priorto at least one of the shear stages, adding to the slurryafter the addition of the mineral filler and prior to at leastone of the shear stages
from 0.5 to 100 ppm by weight of dry pulp contained in theslurry of a cationic dispersion polymer obtainable by dispersionpolymerization of a monomer mixture soluble in an aqueous solution of a polyvalent anionic saltsaid polymer being selected from the group consisting ofcopolymers of acrylamide and dimethylaminoethylacrylate methylchloride quaternary salt, dimethylaminoethylmethacrylatemethyl chloride quaternary salt, dimethylaminoethylacrylatebenzyl chloride quaternary salt anddimethylaminoethylmethacrylate benzyl chloride quaternarysalt and wherein said polymer is insoluble in the aqueous solution;
shearing the slurry;
adding an amount ofmicroparticles selected from the group consisting of acopolymer of acrylic acid, bentonite and silica sol to the slurry;
draining the slurry to form a sheet; and
drying the sheet to form a paper sheet.
The process of claim 1 wherein the slurry is drained on apapermaking screen and is pumped to the site of thepapermaking screen prior to draining.
The process of claim 1 wherein the slurry is selected fromthe group consisting of an acid pulp slurry, alkaline chemical pulp slurry, thermo-mechanical pulp slurry, mechanical pulpslurry, recycle pulp slurry and ground wood pulp slurry.
The process of claim 1 wherein the mineral filler isselected from the group consisting of titanium dioxide, clayand talc calcium alkaline carbonate.
The process of claim 1 wherein the mineral filler is addedto the slurry in an amount of from 2 to 50 parts per hundredparts by weight of dry pulp contained in the slurry.
The process of claim 1 wherein the dispersion polymer isadded to the slurry in an amount of from 2 to 40 ppm by weightof dry pulp contained in the slurry.
The process of claim 6 wherein the dispersion polymer isadded to the slurry in an amount of from 4 to 25 ppm by weightof dry pulp contained in the slurry.