NZ245689A - Method of controlling pitch in pulp by sequentially adding a low molecular weight high cationic charge, water soluble polymer, and montmorillonite clay - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £45689 245689 Patents Form 5 - V »I 1 ^ « J K. w . r ; • P2.lrt.o\-i3, . . . , HpZ-y Kal <o^ (a^Uif-. X^J .HZ.I I S'v N.Z. No.

NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION METHOD FOR CONTROLLING PITCH 2,6 AUG TO f=e_i £ /V /• 18 ^£8/993 SJ We, VININGS INDUSTRIES INC., a United States Corporation of 3950 Cumberland Parkway, Atlanta, Georgia 30339-4501, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - -1 - (Followed by 1A) \k 1730 u9 Method for controlling pitch This invention concerns a method of controlling pitch in pulps br use m making paper. More particularly, this invention concerns a method o controlling the buildup of pitch on equipment used for pulping and the improved diversion of pitch in pulps.

Pitch, carried over from wood or bark pulped to make papermaking furnishes, is formed of a complex mixture of oleophilic, water insoluble, low molecular weight, essentially non-polar resins comprising fatty and resin aoas with ionisable hydrophiilic groups, fatty and resin acid esters, sterols, c> and tri-giycerides, terpenes and waxes and various alcohols, nyorocarDons and neutral compounds associated with these resins. The resms ieno to agglomerate to form sticky films or pitch balls, which in turn can give nse to spotting in the final paper product, wire spots, localised stcxv spots on rolls, holes in the paper sheet, poor paper formation, felt pugging or sticking on dryer and calender rolls.

Effective pitch control, particularly in paper mills which produce paper trom groundwood, thermo-mechanical and semi-chemical pulps, has traditionally been difficult. The important parameters for pitch control are elegantly summarised in US-A-4964953 as follows: "To control pitch effectively it is not necessary to remove all of the pucn from the pulp. Different types of pulp mills have different tolerance levels for pitch panicles which must be exceeded before piteh caused propiems occur. What is necessary, however, is that the pitch be d'spersed as tmy non-harmful aggregated or agglomerated panicles and retained in - i i i' this fine pamculateform rather than as larger harmful globs in the paper , 1 sneet. Simply flocculating pitch will not give good pitch control; !ho pitch/' must be made to attach to eitner the celluiosic fibres or to any paniculate IdFEgm matter used as filler m the paper sheet, or preferably to both. Pitch retair in large floes causes breaks and undesirable dark specks in the finished paper sheet, while pitch not retained but m small floes tends to accumulate in the papermaking facility's white water system".

Efforts to control pitch deposit problems by dispersing or precipitating the pitch have traditionally involved the use of alum salts; ultrafine crystalline talc; anionic, canonic and non-ionic dispersants, polymeric retention aids and mixtures of these materials. More recently, water soluble zirconium salt complexes and organotitanium chemicals have been suggested as pitch control agents.

Papermakers alum (Al2(S04)3.14H20), liquid sodium aluminate (20- .5% AI2O3) and polyaluminium chloride are the primary alumina sources 2 2AhUHU used for pitch control. Above pH 3 hydrolysis of the salts occur and a variety of hydroxy-aluminium complexes are formed depending upon the hydroxide ion concentration. Hydroxy! bridging occurs forming dimers and higher order polymer species (ligands). The formation of these desirable short chain relatively low molecular weight polymer species is primarily influenced by the system pH, temperature (the higher the better), the concentration of aluminium ions and The cationic demand of The stock. In pitch control, the optimum pH is preferably around 4.5 although in practice an operating range of 4.0-5.5 is f/airly typical. It is believed that pitch control with aluminium salts is a combination of a flocculation mechanism, where the pitch panicles are entrapped by the polymeric aluminostructure, and the formation of a cationic complex with the resin and fatty acid components of the pitch, which in turn is then adsorbed onto the pulp fibres. A sodium aluminate/alum combination is generally preferred because tnere is no need for caustic soda to be used to control pH, it minimises suiDnate ion build up in closed white water systems and it limits iron contamination thus making it easier to meet brightness specifications. Typical consumption figures are: alum 5-25 Kg/tonne and 45% sodium aiummate 5-10 Kg/tonne.

Uitrafme talc with a surface area of from 10 to 15m2/gm has been used for puch control in pulp paper mills and in panicular in those mills that are processing Kraft or sulphite pulps, i.e. where the pitch is present in a pamaiiy saponified state. The dispersed pitch panicles are adsorbed on to the hydrophobic talc platelets and then retained in the paper. Typically, a use rate of 10-40 Kg/tonne is required.

A wide range of surfactants and shon chain polymeric dispersants have been used to maintain pitch m a dispersed state within the paper ; making circuit. These dispersants function by charge and/or steric 1 hmderance mechanisms. Anionic dispersants. such as lignin sulphonates, polynaphthalene sulphonates and polyacryiates, increase the electro^' negative charge on the pitch panicles, i.e. they peptize the pitch panTcle-s :• and inhibit agglomeration. Noniomc surfactants result in steric repulsion of the pitch and depending on the type and concentration can soften and emulsify pitch deposits already formed. Since dispersants do not artach the pitch to the pulp fibres, they have limited use in controlling severe pitch problems such as is generated in TMP mills. An excess of dispersant can result m a substantial build up in the concentration of pitch in closed white T86%'ti water systems. Usage rates for pitch dispersants are typically in the range of 5-100 ppm on the stock.

The use of polyquaternary ammonium polymers for pitch control has been promoted in recent years. The control mechanism is described by T Hassler, Tappi Journal, June 1988, p 195 onwards. The low moiecular weight cationic polymers which are commercially available are believed to be linear and/or partially crosslinked polydiallyldimethyl ammonium chloride (polyDADMAC) and copolymers of epichlorohydrin and short chain aliphatic secondary amines. A typical use rate would be from 1.25- 2.3 Kg/tonne.

The use of current retention and drainage aid technologies e.g. "Lapotam" (laporte Industries Limited), "Composil" (Eka-Nobel) and "Positek" (Nalco Chemical Co) etc, give significant improvements in pitch control on the machines, but reliance on this type of technology however is only possible when the mill can justify a retention and drainage aid programme.

More recently, a method of reducing pitch in pulping and papermaking operations by a process which comprises (1) adding to a pitch-containing furnish a particulate composite substance comprising (a) a water soluble canonic polymer adsorbed onto (b) an essentially water insoluble particulate substrate carrying an anionic charge, and (2) adsorbing pitch onto said composite to form discrete, finely dispersed pitch-containg aggregates in the furmsh, is disclosed in US-A-4964955. On Column 8, line 67, to Column 9, line 1 5, of the US patent, it is disclosed that any essentially water-insoluble paniculate organic or inorganic substance may be employed as the substrate, including phyllosilicate minerals, kaolin, talc, mica, montmonlionite. chlorite and pseudolayer silicates, though Kaolin is particularly preferred. Indeed, this preference is clearly demonstrated in the examples m that Kaolin is the only substrate exemplified. It is demonstrated in Examples IV to VI, IX and X that improved pitch control may be achieved by pre-treatmg a groundwood pulp with alum prior to treatment with a cationic kaolin. In Example XII, on Column 19. lines 12 to 16. it is disclosed that using 60-80 lbs/ton of cationic kaolin slurry with 35 lbs/ton of alum will essentially eliminate all pitch. From a practical point of view, however, the amount of cationic kaolin required in the process tends to make a papermaking process uneconomic. A similar method is disclosed in EP-A-0349311. ,/• Japanese patent application No 62-245908 discloses a method reinforcing paper strength by adding bentonite to a pulp after a cationi lu- paper strength reinforcing agent has been mixed in the pulp. It is noted in the patent application that the process, apart from improving the paper strength, also solves pitch troubles. It is disclosed in Example 1 and Example 2 that a minimum of 10 Kg/tonne (1% relative to pulp) of bentonite ' was added to a pulp which had been previously treated with reinforcing agent and alum. Whilst this method appears suitable for improving paper strength, retention and pitch problems, as a method for controlling pitch alone, this process would tend to be uneconomic.

It is an object of the present invention to provide a process for controlling pitch in pulps, which process is technically at least as efficient at eliminating or reducing pitch in pulps as the process described in US-A-4964955 but which is economically more acceptable.

In accordance with the present invention, there is provided a method tor the control of pitch in a pulp and is characterised in that the method comprises sequentially adding to and mixing with the pulp (1) 1- 10 Kg'tonne of pulp dry solids of a low molecular weight, high cationic charge, polymeric, water-soluble species and (2) 0.5- < 10 Kg/tonne of pulp dry solids of montmorillonite clay panicles, which clay particles do not have a water-soluble cationic polymer adsorbed thereon.

The low molecular weight, high cationic charge, polymeric, water-soluble species may be organic but is preferably inorganic and is preferably present in an amount of 2 to 6 Kg/Tonne of pulp. The polymeric species has a low molecular weight, preferably below 1 million and more pfeferably below 0.5 million.

If an organic species is used, it is preferably a polymer of the tyoe disclosed on column 9. line 50, to column 10, line 34, of US-A-4964955. The polymer preferably has a cationic charge density of at least 5 m.eq/gm, preferably a charge density of from 6 to 7 m.eq./g or more. Preferably, the polymer is not a Mannich polymer.

\ If an inorganic species is used, it is preferably papermakers atum, sodium alummate, poly aluminium chloride, poly aluminium silicate.br an other inorganic water soluble salt of aluminium. Preferably sodium aluminate is used in the present invention.

Montmorillonite clays are distinguished by their ability to be water swellable. Synthetic water swellable clays, such as Laponite (Laporte Industries Limited) , are understood to have similar properties to montmorillonite clays and are therefore included within the scope of the present invention. Bentonite is the preferred montmorillonite. Preferably, the amount of montmorillonite added to the pulp is from about 1 Kg / Tonne to less than 10 Kg / Tonne, more preferably from about 2 Kg / Tonne to about 5 Kg / Tonne.

Whilst for cost purposes it is preferred to use bentonite which has not been chemically modified in any way, in some instances it may be technically preferrable to employ a bentonite which has been chemically modified, e.g. by alkali treatment to conven calcium bentonite substantially to alkali (e.g. sodium, potassium or ammonium) bentonite, or a bentonite in intimate association with a water soluble, highly charged anionic polymer, e.g. Lapotain available from Lap one Industries Limited.

Preferably, the pulp contains less than 0.15% poiyacrylamide which has been submitted to a Mannich reaction and preferably the. pulp contains no such polymer.

The order of addition of the components to the pulp is not imponant in achieving the advantages of the present invention; component (1) may be added after component (2), though it is preferred to add component (1) before component (2). It is imponant, however, that in any event, the first component added to the pulp must be thoroughly mixed into the pulp before the second component is added. Mixing may be achieved by subjecting the pulp to high shear conditions, such as by passing the pulp through a centriscreen or through mixing pumps or fan pumps, though simple turbulence mixing obtainable by passing the pulp along a length of pipeline may be just as effective.

The process of the present invention has a number of advantages over the the process described in US-A-4964955, including the surprising fact that the process of the present invention has improved pitch control over the process of the prior an. Other advantages, including the obvious cost advantage, will be immediately apparent to a person skilled in the an.

The invention will now be funher described, without limitation, by reference to the examples set foinn below. / v\<.

/ Examples Samples of a virgmTMP pulp, obtained from a major pulp/paper manufacturer located in the south east of U.S.A., were used in the following examples. The pulp was selected on the basis that southern pine pulps from this pan of U.S.A. may contain significant concentrations of troublesome pitch. <lt should be appreciated that comparison of one series of results lo 24!>U8:; obtained from one pulp sample cannot be compared with the series of results obtained from a different pulp sample) In each evaluation, the thick stpck samples, taken from either the refiner or the latency stock chest, were diluted and aged at 180°F with tap water processed through a laboratory scale disintegrator and adjusted to 1 % consistency.

The samples were subjected to the colloidal dispersed solids test (CDS) the procedure of which involves 1. Pulp stock samples (after treatment) are sieved through a 60 mesh screen, the resulting low solids soiution is placed in 50 ml or TOO ml centrifuge tubes and spun for 30 mins at 4000rpm. 2. The supernatent is carefully removed by syringe and transferred into a small bottle (need approx 60mls of supernatent) 3. A suitable aliquot is then transferred to tared beaker. It is recommended that a minimum of 25gms of liquid should be filtered. Care is necessary to prevent any extraneous material contaminating the beaker. 4. Record the weight of the sample taken using a 2 decimal place balance.

The liquid sample is then filtered through a previously dried, oessicated and weighed 0.45 micron millipore filter using maximum vacuum. The filter is previously "wet out" with distilled water. 6 After the fluid has completely drained, remove the filter pad, dry at 50°C for 15 mins, dessicate and reweigh using 4 decimal place balance. 7. Record this weight.

The weight of the filter and solids minus the weight of the filter is eauai to the weight of colloidal dispersed solids (CDS) WeiQht of colloidal dispersed solids x 10® = ppm CDS Weight of supernatent liquid taken This test procedure has good correlation with the prediction of pitch problems in operating newsprint and linerboard mills. CDS measurements also correlate well with microscopic pitch counting procedures as described in Pitch Panicle Concentration: an Important Parameter in Pitch Problems by L.H. Allen. Pulp & PaperResearch Institute of Canada, Pointe Claire, Que, p1 -9.

PITCH ADSORPTION RESULTS Optimisation Series I Stock consistency pH Blank C.D.S Chemical j Alum (17% AItOj) I System adjusted to i pK 5.3 'Prose!' 1820 Poiymin SK Selected Components 0.62% 4.8 98 ppm Dose Rate kg/tonne 1 2 4 1 2 4 % Reduction In CDS (Pitch) 27 88 16 35 57 31 53 g Chemical ' Dose Rate % Reduction in CDS kq/tonne .

(Pitch) PoiyDADMAC - ... 1 m --- _ .2 : 47 ■ 4 61 Southern Clay 3 43 SCPX572 " 63 • 92 • 96 Fulgel 300/2 3 61 • 78 • 80 • 84 • • <£s\ >/'v ll q|», i:l8 5£B}993 *jj V"£*. rv J' rO JI •0.^ Optimisation Series II Stock-Consistency 0.65% pH 4.9 Blank CDS 121 ppm Activity of Simple Components A. Cationic Components Chemical Dose Rate kg/tonne % Reduction In CDS (Pitch) VSA 45 - pH of System adjusted tc 5.3 O w 34 • 42 Alum (17% AhOa) pH adjustment to 5.3 3 22 ■ 27 PAC (17% AliOi) pH adjustment to 5.3 3 22 • 'Prose:' 2830 0.5 21 m 1.0 51 B. BentQnite Subsjrate ComDon^nts f^ftrrorf} Chemical Dose Rate .... " kg/tonrie" i % Reduction in CDS (Pitch) "Gadorgel" X 2 13 m 3 n 23 "Fulgel" 300 2 16 " 3 29 • 43 i SCPX 590 i 2 - 3 26 i 36 SCPX 592 2 14 • 3 22 • 27.

Chemical Dose Rate — -kg/tonne %Reduction In CDS ' • • (PItchJ .

SCPX 590/2 : -."3 ■ - 29 m 37 SCPX 59212 3 m ....... 5 42 Note: SCPX-/2 Substrates are the basic bentonite modified with 2% "AvAccumer 9000 (available from Rohm and Haas Co) in solids 12 Optimisation Series HI Stock Consistency 0.65% pH 4.8 ' Blank CDS 133 - 134 ppm Chemical Programme Dose rate of % Reduction in CDS Components (Pitch) ka/tonne VSA 45/*Fuiger 300 3/2 pH to 5.3 After VSA acriition VSA 45/"Fulgel" 300 /2 90 p.H to 5.2 After VSA addition " 3/3 23 /3 87 vSA 45 Alone 74 pH to 5.3 VSA 45/Fulgel 300/2 3/2 12 pH to 5.3 After VSA addition m /2 45 - 3/3 17 1 ~ 5/3 73 Fuigel 300/2/VSA 45 2/3 27 ie Reverse Addition /% * \ 18 FEB 1995 'PI* 13 24 Chemical Dose Rate of Components kg/tonne I- % Reduction In CDS | (Pitch) j. r 'Proset' 2830/,Fulgel' 300 - 0.5/2 24 • 1/2 43 ■ 0.5/3 31 ■ 1/3 46 1/5 49 'Prosef 2830 Alone 0.5 - 1.0 33 'Prose:' 2S30/Tulgel' 3 CO/2 • 0.5/2 1/2 22 33 • 0.5/3 • 1/3 32 14- Chemical Programme • Dose Rate of Components kg/tonne % Reduction in CDS • - (Pitch) ~ Alum Alone (17%Al20a) pH adjusted to 5.3 " ' 22 Alurn/FulgeP 300 /3 31 • /5 42 Alum/Fulgel' 300/2 /3 28 AlunVFulgel' 300/2 /5 16 Alum @ Equivalent Al»0> to VSA 45 - SCPX572 7.5/5 55 Chemical D0SQ Rate of Components kg/tonne - • Reduction in CDS • (Pitch) VSA 45 Alone pH to 5.3 72 VSA 45/SCPX 572 /3 83 ■ /5 87 VSA 45/SCPX 572/2 /3 67 VSA 45/SCPX 572/2 /5 73 Chemical Dose Rate of Components kg/tonne % Reduction in COS (Pitch) 'Preset' 2830/SCPX 572 1/3 53 • 1/5 57 •Proset'2830/SCPX 572/2 1/3 • 1/5 38 # SrocK Ssmole Consistency pH Blank CDS concentration - 0.9% 4.8 158 ppm Chemical Dose Rate of Components kg/tonne % Reduction in CDS (Pitch) VSA 45 (alone) 43 VSA 45/SCPX 590 /5 71 'Prose:' 2S30 (alone) 1 29 'Proset' 2B30 (alone) 1.5 75 'Prosef 2330/SCPX 590 1/5 77 j 'Proser 2830/SCPX 590 1 1.5/5 94 • • PITCH ADSORPTION ACTIVITY: ro PAC / PAC &c ACCOFLOC HCX @ 5Kg/l ACCOfLOC IICX / IICX & PROSET 2830 §j X R«du<tlon In COS (■prior) PAC e flKfl/l 44 PAC O IOKg/1 44 PAC O 25Kg/l 97 PAC © 5Kg/l & HCX 60 PAC O 10Kg/l A HCX 72 PAC O 25Kg/l & HCX 98 K .< . ,3'-' CO ^ ii <«: Co :' i •• SO '.v % ^ • V Q * .J '''V-''' X Reduction In CDS ( PfTCII ) HCX O JKg/l HCX O 5Kg/l 45 HCX O IOKg/1 54 HCX O 20Kg/l 73 HCX O 3Kg/l St P28JO 68 HCX O 5Kg/l St P28JO 9 t HCX O 10Kg/l St P2BJ0 96 HCX 020»<g/l 6t P20JO 95 D 7T o o (/) X3 CO T « -1- O O 7T n O ZJ W M ri n> 3 o ■< NJ -J CO "O T3 3 *>■ 00 ID cn • • PITCH ADSORPTION ACTIVITY: PROSET 2830/ P2830 Sc IICX/ P2830 & GADORCCL X (HCX 6e GADORCCL & 5Kcj/l) ( I AY SUHSIRAIfS @ IOKg/1 ?S Radudion In CDS (•pncir) PROSCf 2 ft JO O JKq/l Ml PROSTt 2630 O 7Kg/l 82 PROSTT 2630 O 4Kg/| 96 P2BJO O IKq/l S, IICX 77 P28J0 O 2Kg/l A IICX 87 P2BJO O 4Kg/« it IICX 97 P26JOO 1Kg/l\CAOORCEL 60 P2630O2Kg/l\CAD0RCEl . 66 ; P28JO<HKg/l\GA£»ORCEl. > " 95 % REDUCTION IN CDS ('PITCH') FULBOND X • 53 GADORGEL X 60 AX SAPONIIE 59 ACCOrLOC IICX 59 rULGCL 300 59 ...

• • • • PITCH ADSORPTION ACTIVIT V • PROSET 2830 @ 2Kg/t PROSCf 2830 © IKy/t &c CLAY SUBSTRATES @ 5Kg/t & CI.AY SUDS1RA1ES <0> 5Kg/t X R»du<t>on of CDS (Tilth') P2830 only 02 P2830 6c HCX 87 P2830 6c GADORGCL X 88 P2830 6c GADORGEL X /2 91 P2830 Sc TULGEL 300 100 • P2830 6c FULGEL 300, '2 97 X ftadudion of CDS (Pilch*) P2830 only 38 P2830 &c HCX JJ P2830 Sc GADORGEL X so P2B30 6c GADORGEL X/; 94 P2830 6c FULGEL 300 »4 P2830 6c FULGEL 300/2 SI O r\j J 4b{ 2\ The performance of the process of the present invention was compared with the process described in US-A4964955. A 2gm per litre dispersion of SCPX 572 bentonire was modified by reacting with a dilute solution (2%) of a polyDADMAC product. The Zeta potential of the composite material was measured at 40 mv on a Matec Applied Sciences Electrokinetic Sonic Analysis System. The ratio of cationic polymer to bentonite was used to produce a 7g/l total actives dispersion for testing. The results were as follows.

Stock Sample Consistency - 0.9% (100% TMP) pH - 4.8 Blank CDS Concentration - 158 ppm P"?cr5mrne Dose Rate of % Reduction IP CDS Components ka/tonne (Pitch) SCPX 572 Bentonrte 10 67 Cation Modified SCPX572 Bemomte 10 68 Cation Modified SCPX572 Bentonrte 14 82 - Poly DADMAC @ 4kgAonne followed by SCOX572 Bentonite @ 10kg. tonne 4/10 81 Note AJI concentrations are expressed as 100% Active Materials AJum (17% AJ2O3) System adjusted to pH 5.3 5 37 AJum followed by SCPX572 Bentonite 5/10 85 AJum followed by Cation modified SCPX572 Bentonite 5/10 90 22 24r>ll8!) As can be seen from the results, the cation modified bentonite demonstrates substantially no advantage over the normal anionic charge bentonite at equivalent use rates. This result is technically most surprising and clearly demonstrates the commercial advantage of the present invention.

The following trade marks, which may be registered trade marks, have been used in the Examples: PROSET T820 is an epichlorohydrindimethylamine polymer available from Vin/ngs Industries Inc.

POLYMIN s« is a poiyamidoamine available from BASF SCPX 572 is a high swelling bentonite clay available from Southern Clay Products Fulge! 300/2 is an anionically modified bentonite available from Laoone Industries Limited VSA 45 is a 45% sodium aluminate solution available from Vinings Industries Inc PAC is polyaluminium chloride PROSET 2830 is an epichlorohydrindimethylamine crosslinked with a short cnain aliphatic amine available from Vinings Industries Inc GADORGEL is a high swelling bentonite clay available from Laporre Industries Ltd FULGEL 300 id a high swelling bentonite clay available from Laporte Industries Ltd SCPX 590 is a high swelling bentonite clay available from Southern Clay Products SCPX 592 is a high swelling bentonite clay modified with a low molecular weight anionic polymer available from Southern Clay Products SCPX 590/2 is a bentonite clay modified with anionic polymer available from Southern Clay Products SCPX 592/2 is a bentonite clay modified with an anionic polymer available from Southern Clay Products ACCOFLOC HCX is an hectorite clay available from American CollpfSfi"ty"p- Inc. -lOSiu 23 ! i

Claims (10)

WHAT WE CLAIM IS:

1. A method for the control of pitch in a pulp, characterised in that the method comprises sequentially adding to and mixing with the pulp (1) 1- 10 kg/tonne of pulp dry solids of a low molecular weight, high cationic charge, polymeric, water-soluble species and (2) 0.5 to less than 10 kg/tonne of pulp dry solids of montmorillonite clay particles, which clay particles do not have a water-soluble cationic polymer adsorbed thereon.

2. A method as claimed in claim 1, wherein the montmorillonite clay is bentonite.

3. A method as claimed in claim 1 or claim 2, wherein the amount of montmorillonite added to the pulp is from 1 kg/tonne to 5 kg/tonne.

4. A method as claimed in any one of the preceding claims, wherein the montmorillonite clay is bentonite which has been chemically modified by alkali treatment to convert calcium bentonite substantially to a member selected from the group consisting of sodium, potassium and ammonium bentonite.

5. A method as claimed in claim 4 wherein the montmorillonite clay is bentonite in intimate association with a water soluble, highly charged anionic polymer.

6. A method as claimed in any one of the preceding claims, wherein the amount of component (1) added to the pulp is from 2 kg/tonne to 6 kg/tonne, more preferably from 2 kg/tonne to 5 kg/tonne.

7. A method as claimed in any one of the preceding claims wherein, component (1) is an organic polymer having a charge density of at least 5 m.eq./g.

8. A method as claimed in any one of claims 1 to 6, wherein component (1) is an inorganic polymer selected from one or more of papermakers alum, sodium aluminate, polyaluminium chloride, r L J 24 polyaluminium silicate and another inorganic water soluble salt of aluminium.

9. A method as claimed in any one of the preceding claims, wherein component (1) is added and mixed with the pulp before component (2) is added and mixed to the pulp.

10. A method as claimed in claim 1 and substantially as hereinbefore described with reference to the examples. VIIMINGS INDUSTRIES INC. By their attorneys HEIMRY Per: