In particular, the invention relates to the use of microparticle systems including a water soluble flocculant polymer and an inorganic particulate material to bring about such improvements.

In papermaking processes, a dilute aqueous composition known as a furnish'or stock'is sprayed onto a moving mesh known as a wire'. Solid components of the composition, such as cellulose fibres and inorganic particulate filler material, 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 process.

A related property of the papermaking process is the so-called drainage'. This is the rate of removal of water from the furnish as the paper sheet is formed.

It usually refers only to water removal which takes place before any pressing of the paper sheet subsequent to. formation of the sheet.

Retention and drainage of a papermaking process are related parameters which are important to paper producers for several reasons, the most significant of which is that these parameters have a strong influence on productivity. Good retention and drainage will enable a paper machine to run faster and will reduce machine stoppages.

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

process. The use of such additives is limited by the effect of flocculation on the so-called paper sheet formation'. As more retention aid is added so the size of the aggregates of fine solid material is increased and this can cause a variation in density and visible non-uniformity of the paper sheet. 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 of three types, viz: (a) single polymers; (b) dual polymers; (c) microparticle systems.

The present invention relates to use of retention and drainage aids of the last type which is the type which has given the best results in the prior art.

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 flocs 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 and WO-A-97/16598 wherein kaolin is proposed

for use in conjunction with one of various cationic polymers.

Although kaolin has been proposed for use in microparticle systems, the selection of specific kaolin types as in the present invention to improve unexpectedly and beneficially the performance of the microparticle system has not been considered in the prior art.

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 a hydrophilic polymer and an inorganic particulate material, wherein the inorganic particulate material comprises a kaolinite- rich inorganic particulate material having a mean particle size of less than 1pm, desirably between 0. lpm and 1. Opm.

By a kaolinite-rich'material is one wherein at least 50% by weight, desirably at least about 60% weight, of the material is kaolinite, ie hydrated aluminosilicate obtained from a kaolin clay such as china clay or ball clay. The kaolinite content may be at least 70% by weight.

In this specification paper'includes products comprising a cellulosic sheet material including paper sheet, paper board and the like.

In this specification microparticle system' refers to the combination of at least one hydrophilic polymer and at least one inorganic particulate material. The components of the combination may be added together to the stock or furnish to be treated but are preferably added separately in the manner and order described later.

Particle size properties of an inorganic particulate material, such as mean particle size and equivalent spherical diameter, as referred to herein, are well known properties as measured using the standard method, well known to those familiar with the characterisation of particulate materials, of sedimentation of the particles of the material in a fully dispersed form in an aqueous medium using a SEDIGRAPHE 5100 machine supplied by Micromeritics Corporation, United States of America.

The mean particle size may also be measured optically by an instrument sold under the trade name Malvern Mastersizer by Malvern Instruments Ltd, Malvern, England.

The kaolinite-rich inorganic particulate material employed in the method according to the present invention may be obtained by particle size classification of a suitable kaolin obtained from a mineral source, eg obtained from china clay. The material may be refined and processed in a known manner prior to, during or after the particle size classification, eg by one or more of screening, grinding, magnetic impurity separation, and selective flocculation. The particle size classification may be carried out in a known manner using a known particle size classifier, eg an air classifier or a centrifuge, eg a decanter centrifuge operating on an aqueous suspension of the mineral. Refinement, processing and particle size classification, eg classification using a centrifuge, may be carried out on an aqueous suspension of the material.

The kaolinite-rich inorganic particulate material may alternatively be obtained from a naturally fine

mineral source. For example, the material may be obtained from ball clays which are kaolin-containing minerals obtained from secondary deposits. Such deposits are found in Devon and Dorset in England.

Processed ball clays are produced and commercially available and may be used in the method according to the present invention. Examples of suitable processed ball clays are those produced and sold by ECC International Ltd, England under the trade names HYMOD, OGB and NTA.

Preferably, the inorganic particulate material in the method of the invention comprises a material obtained from a kaolinite-rich mineral containing a so- called three layer aluminosilicate mineral impurity (ie a mineral having a three layer unit cell structure, as distinct from the two layer unit cell structure of kaolinite). For example, the impurity may be a smectite clay impurity, a mixed layer mineral impurity or both. The three layer mineral impurity may be present in the inorganic particulate material in an amount of from 0.1% to 50% by weight, eg from 0.5% to 35% by weight, eg from 1% to 25% by weight based on the total weight of the inorganic particulate material.

The inorganic particulate material may thus comprise a clay material from an English deposit, eg a ball clay from South West England, or a material obtained by fractionating a clay material, eg china clay, obtained from an English deposit, eg from Cornwall, England.

The mean particle size (on a weight averaged basis) of the inorganic particulate material in the method of the invention may be from O. lum (lOOnm) to 0.9um (900nm) especially from 0.2um to 0.6pm) as

measured by a Malvern Mastersizer instrument available from Malvern Instruments Ltd, Malvern, UK.

Although use of kaolin has been suggested, eg as in WO-A-97/16598, for use in a microparticle system for retention assistance in papermaking, use of a kaolin specially selected from the many forms of kaolin minerals available in the world to have naturally or by treatment the particular properties as specified herein has not been suggested for use in such systems. As demonstrated later, such selection unexpectedly and beneficially provides significant improvement in retention and drainage performance compared with material which may be regarded as representative of a conventional paper grade kaolin.

The inorganic particulate material of the microparticle system may be physically and/or chemically treated in a known manner prior to use in a microparticle system in paper making. For example, a physical treatment which may be applied to the inorganic particulate material in the form of a suspension in an aqueous medium comprises high speed stirring to disperse the colloidal particles of the material homogeneously in the aqueous medium.

Alternatively or in addition an aqueous suspension of the material may be treated by a known dewatering process to thicken the suspension.

An example of a suitable chemical treatment comprises addition of a chemical dispersing agent.

Suitable dispersing agents include soluble inorganic salts such as carbonates, phosphates and silicates and organic polyelectrolytes, eg water soluble polymers obtained from olefinic carboxylic acids and salts thereof. Polyelectrolytes containing acrylate units

optionally together with other units in a copolymer system, eg methacrylate units or maleate units are preferred. The dispersing agent where employed may be one of the anionic agents currently employed in the processing of inorganic particulate materials, although it is possible also to use cationic non-ionic or amphoteric dispersant chemicals.

The dispersing agent is typically used in an amount of at least 0.05% by weight, based on the weight of the particulate inorganic material, although the optimum amount to achieve dispersion of the inorganic material can be determined by the skilled person without difficulty. Where the dispersing agent is a polyelectrolyte it preferably has a weight average molecular weight of not more than 20,000, as determined by gel permeation chromatography using a low angle laser light scattering detector. The polyelectrolyte dispersing agent may, for example, be a salt either of an alkali metal (for example sodium) or an ammonium salt of a poly (acrylic acid) or a poly (methacrylic acid). Sodium polyacrylate having a weight average molecular weight in the range from 1,000 to 10,000 is especially suitable. The amount of the dispersing agent used may be in the range of from 0.1 to 2.0% by weight, based on the dry weight of the particulate inorganic material.

The polyelectrolyte where employed as a dispersing agent may be fully neutralised salt of a polymeric acid. However, the polyelectrolyte where employed may alternatively be acidic or only partially neutralised.

The hydrophilic polymer employed in the microparticle system in the method according to the invention may comprise a flocculant, ie an agent for

aggregating the solids into flocs, in the paper making furnish. Here fines'means fine solid particles including fine fibres 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 fibres) which will pass through a round hole of 76um diameter.

Flocculation of the fines of the furnish may be brought about by the hydrophilic polymer itself or by the hydrophilic polymer in combination with another agent, eg a cationic inorganic agent, such as aluminium sulphate (alum). The hydrophilic polymer is preferably cationic, although it can be anionic, eg weakly anionic, amphoteric or non-ionic.

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 fibre structure of the forming paper sheet thereby giving improved dewatering or drainage.

The flocs formed by the hydrophilic polymer may be subject to a shearing action before addition of the inorganic particulate material of the microparticle system, although in some cases, eg for groundwood furnishes, the inorganic particulate material may be added prior to or at the same stage as the polymer or some of the polymer. A shearing stage may be applied prior to addition of polymer, if added prior to inorganic particulate material, and before or after addition of inorganic particulate material.

Whereas the hydrophilic polymer of the microparticle system preferably comprises a cationic

flocculant polymer the inorganic particulate material generally will comprise an anionic material.

A coagulant polymer, typically a medium molecular weight polymer, eg a cationic polymer, may optionally be added to the treated furnish, eg at a stage earlier than that at which the flocculant polymer is added.

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, eg 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.

The method of the invention can be carried out using any conventional paper making apparatus. The furnish or thin 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 fibre, 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, eg using a vortex cleaner. Usually the thin stock is cleaned by passage through a centriscreen. The thin stock is usually pumped along the apparatus employed to treat the furnish by one or more centrifugal pumps known as fan pumps. For instance the thin 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, eg by passing the thick stock and dilution water through a mixing pump. The thin 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 hydrophilic flocculant polymer of the microparticle system may be added before the stock reaches the last point of high shear and the resultant stock is preferably sheared, eg at the last point of high shear, before adding the inorganic particulate material of the microparticle system. However, as noted earlier, in some cases the inorganic particulate material may be added prior to or at the same stage as the polymer and shearing may be applied after addition of the inorganic particulate material and prior to the polymer addition.

It is possible to insert in the apparatus employed a shear mixer or other added shear stage for the

purpose of shearing the suspension contained in the stock between adding the hydrophilic polymer and the inorganic material of the microparticle system but it is preferred to use a shearing device that is already included for other reasons in the apparatus. This device may be one that acts centrifugally. It can be a mixing pump or a fan pump or a centriscreen. The hydrophilic polymer of the microparticle system may be added just before the shear stage that precedes the addition of the inorganic particulate material or it may be added earlier and may be carried by the stock through one or more stages to the final shear stage, prior to the addition of the inorganic particulate material. If there are two centriscreens then the hydrophilic polymer can for example be added after the first but before the second. When there is a fan pump prior to the centriscreen the hydrophilic polymer can be added between the fan pump and the centriscreen or into or ahead of the fan pump. If thick stock is being diluted by the fan pump then the hydrophilic polymer may be added with the dilution water or it may be added directly into the fan pump.

Preferably, the hydrophilic flocculant polymer of the microparticle system is added to thin stock (ie stock having a solids content of desirably not more than 2% or, at the most, 3% by weight) rather than to thick stock. Thus the 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 hydrophilic flocculant polymer of the microparticle system added to the stock or furnish in the method according to the present 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 water soluble polymer added may be in the range 0.01% to 1%, more particularly in the range 0.02% to 0.2% by weight (dry weight of polymer based on the dry weight of solids present in the stock or furnish). The addition may be carried out in one or more doses at one or more addition sites.

The amount of inorganic particulate material of the microparticle system added to the stock or furnish in the method according to the present invention may be in the range 0.001% to 1.0%, more particularly in the range 0.01% to 0.5% by dry weight (based on the dry weight of solids present).

The amount required to be added will depend upon the mean particle size of the inorganic particulate material. For example, for a material having a mean particle size of 700nm to lOOOnm (0.7pm to lpm), the amount added may be from 100 to 50,000ppm by weight.

For a material having a mean particle size of lOOnm to 700nm, the amount added may be from 50 to 10,000ppm by weight.

The amount added in the method of the invention may unexpectedly and beneficially be substantially less than the amount specified for the kaolin addition in the microparticle system described in W097/16598. The addition in the method of the invention may be carried out in one or more doses at one or more addition sites.

The inorganic particulate material may be added in dry form or in the form of a slurry in water.

The particulate material when added to the stock may conveniently be added in the form of a dilute suspension eg having a solids concentration of less

than 1% by weight, eg from 0.05% to 0.5% by weight, to facilitate uniform mixing of the particles thereof with the existing solids of the stock.

The addition of the hydrophilic polymer may cause the formation of large flocs 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 flocs that are known in the art as microflocs'.

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

The effectiveness of the inorganic particulate material may be enhanced by shearing of the material, eg in the form of an aqueous suspension, prior to addition. Such a treatment may be carried out by vigorous mixing of the particles using a conventional mixer or blender device.

If the stock that has been treated with the inorganic particulate material of the microparticle system 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 inorganic particulate material 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 particulate material is added just before sheet formation and because it is generally desired to optimise retention it is usually preferred to add the inorganic particulate material after the last point of high shear. Preferably the hydrophilic polymer is added just before the final fan pump and/or final centriscreen and the stock with the hydrophilic polymer added is led, without applying shear from the final centriscreen or fan pump, to a headbox, the inorganic particulate material is added either to the headbox or between the centriscreen and the headbox, and the stock is then dewatered to form the paper sheet.

In some forms of the method of the invention it may be desirable to add some of the inorganic particulate material at one point and the remainder of the inorganic particulate material at a later point (eg part immediately after the centriscreen and part immediately before dewatering, or part before the centriscreen or other device for applying the shear and part after).

The thick stock is usually brought to its desired final solids concentration by dilution with water, before the addition of the inorganic particulate material of the microparticle system and generally before (or simultaneously with) the addition of the cationic hydrophilic polymer of the microparticle system but in some instances it is convenient to add further dilution water to the thin stock after the

addition of the polymer or even after the addition of the inorganic particulate material.

The initial thick stock can be made from any conventional paper making stock such as traditional chemical pulps, for instance bleached and unbleached sulphate or sulphite pulp, mechanical pumps such as groundwood, thermomechanical or chemi-thermochemical pulp or recycled pulp such as deinked waste, fibre- filler composites from aggregating or recycling processes and any mixtures thereof.

The stock employed in the method of the invention, and the final paper, can be substantially unfilled (eg containing less than 10% and generally less than 5% by weight filler in the final paper) or filler can be provided in an amount of up to 50% based on the dry weight of the solids of the stock or up to 40% based on the dry weight of paper. When filler is used any conventional white pigment filler such as calcium carbonate, kaolin clay, calcined kaolin, titanium dioxide or talc or a combination thereof may be present. The filler (if present) is preferably incorporated into the stock in conventional manner, before addition of the components of the microparticle system.

The stock employed in the method of the invention may include other known optional additives such as rosin, alum, neutral sizes, optical brightening agent or coagulant. The coagulant may comprise a medium molecular weight (eg 10,000 to 100,000) cationic polymer eg in a dose of from 50 to 500ppm (0.005 to 0.05% by weight) based on the dry weight of solids. It may include a strengthening or binding agent and this can for example comprise a starch, often a cationic

starch. The pH of the stock is generally in the range 4 to 9 and a particular advantage of the method of the invention is that it functions effectively at low pH values, for instance below pH 7.

The amounts of fibre, filler, and other additives such as strengthening agents or alum or size can all be conventional. Typically the thin stock has a solids content of 0.2% to 3% by weight or a fibre content of 0.1% to 2% by weight. The thin stock will usually have a solids content of from 0.5% to 1.5% by weight.

In the method of the present invention, the water soluble polymer of the microparticle system may suitably comprise a synthetic cationic polymer which has a weight average molecular weight of 100,000 or more especially 500,000 or more. Preferably the molecular weight is above about 1 million and often above about 5 million, for instance in the range 10 to 30 million or more. Polymers having these properties which are flocculants in paper making are well known.

Thus, the cationic polymer of the microparticle system may be made by copolymerising one or more ethylenically unsaturated monomers, generally acrylic monomers, that consist of or include at least one cationic monomer.

Suitable cationic monomers are dialkylaminoalkyl- (meth) acrylates or -meth) acrylamides, either as acid salts or preferably, quaternary ammonium salts. The alkyl groups may each independently contain 1 to 4 carbon atoms and the aminoalkyl group may contain 1 to 8 carbon atoms.

Particularly suitable are dialkylaminoethyl (meth) acrylates, dialkylaminomethyl (meth) acrylamides and dialkylamino-

1,3-propyl (meth) acrylamides. These cationic monomers may be copolymerised with a non-ionic monomer, preferably acrylamide and preferably have an intrinsic viscosity above 4 dl/g. Other suitable cationic polymers include polyethylene imines, polyamine epichlorhydrin polymers and homopolymers or copolymers, generally with acrylamide, of monomers such as diallyl dimethyl ammonium chloride. Any conventional synthetic linear polymeric flocculant suitable for use as a retention aid in papermaking can be used.

The flocculant polymer can be linear or it can be cross linked and/or branched.

The hydrophilic polymer may have a relatively high charge density. For instance if the polymer is a nitrogen-containing cationic polymer it may have a charge density of above 0.2 preferably at least 0.35, most preferably 0.4 to 2.5 or more, equivalents of nitrogen per kilogram of polymer. When the polymer is formed by polymerisation of cationic, ethylenically unsaturated, monomer optionally with other monomers the amount of cationic monomer will normally be above 2% and usually above 5% and preferably at least about 10% molar based on the total amount of monomers used for forming the polymer.

The inorganic particulate material employed in the microparticle system in the method of the invention may optionally include other materials in addition to the kaolinite-rich inorganic particulate material. The said kaolinite-rich material may form at least 20%, eg at least 50%, by dry weight of the total inorganic particulate material employed in the microparticle system. Examples of other known materials which may be employed in addition to the kaolinite material include

known inorganic particles especially those having a net overall negative surface charge (which may be contributed to by both negative and positive sites, the negative sites being greater in number). Such additive particles include, but are not limited to, particles of siliceous materials, clay materials, colloidal silica, alumina, oxides of other metals such as titanium or zirconium or tin, and mixtures thereof. The clay material added may be bentonite or another swellable mineral, eg saponite. If water swellability is not a natural property of the mineral, it may be activated before being used, ie converted to its water-swellable sodium, lithium, ammonium or hydroxonium form.

Suitable inorganic particles for use as additives together with fine kaolinitic material in the microparticle system used in the method of the invention also include"modified"inorganic particles wherein the ionicity of the inorganic particles is modified by contacting the particles with low molecular weight (eg below 100,000), high charge density (eg at least 4 mEq/g) cationic or anionic polymers. An example of such a modified inorganic particle for use in this way in the method of this invention is a modified bentonite material which has been modified with an acrylic or methacrylic polymer.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figures 1 to 6 and Figures 8 and 9 are graphs (vertical scale linear, horizontal scale logarithmic) of percentage improvement in drainage obtained versus mineral dose added for various minerals employed in a

microparticle system to enhance drainage of a papermaking furnish in a method to be described.

Figure 7 is a graph (vertical scale linear, horizontal scale logarithmic) of retention versus mineral dose for two microparticle systems illustrating respectively an embodiment of the invention and the prior art.

Figure 10 is a graph (vertical scale linear, horizontal scale logarithmic) of mineral dose to give a specified improvement in drainage versus mineral particle size for various mineral samples.

Figure 11 is a graph of the specified mineral dose as plotted in Figure 10 versus non-kaolinite impurity clay content for the mineral samples the subject of Figure 10.

In the following Examples 1 to 7, various kaolinite-containing inorganic particulate materials were investigated for their effectiveness in a microparticle system, together with a cationic polymer flocculant, in improving drainage of a cellulose paper making furnish.

The furnish employed in each Example below, which is representative of a typical alkaline, wood-free filled furnish employed in the paper making industry to manufacture base sheets for coated and uncoated grade papers, was prepared as in Method A as follows.

Method A: Furnish preparation The following components were obtained: Cellulose fibres: 50/50wt% bleached hardwood kraft/bleached softwood kraft

Filler: 50/50wt% ground calcium carbonate (CARBITAL 60)/precipitated calcium carbonate; the amount of filler was 20wt% based on fibre solids Starch: (INTERBOND C) 0.5wt% based on fibre solids Size : HERCON 70 (AKD) 0.25wt% based on fibre solids A dry lap pulp of the fibres was soaked in tepid water for 10 minutes and then diluted to 2wt% solids in water and refined with a laboratory scale Valley Beater to a Canadian Standard Freeness of 590ml. The starch, size and fillers, in that order were added to the refined pulp slurry. The pH of the pulp slurry was typically 7.50.3. The pulp slurry was diluted further with tap water to approximately l. Owt% consistency to form thin stock for testing.

Performance of a given microparticle system was then determined by (a) first measuring the drainage of the furnish prepared as in Method A using only a flocculant and no subsequent mineral addition then (b) measuring drainage using the same flocculant in the same amount with the mineral forming, together with the flocculant, the microparticle system and (c) calculating the % change in drainage obtained by use of the mineral. These measurements were carried out by Method B as follows.

Method B: Drainage Test Procedure 1.200ml (2g solids) of thin stock at lwt% consistency prepared in Method A described above was poured into a (Britt) mixing jar and diluted to 500ml with tap water.

2. The contents of the jar using a standard Britt Jar type propeller mixer (2.5cm diameter) were mixed 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 in a paper making operation: Time Speed (rpm) Additive Feed Point Start 1200 10 secs 1200 Flocculant Pre-screen 20 secs 600 Mineral Post-screen 30 secs stop 3. The contents of the mixing jar were transferred to a 500ml graduated drainage tube fitted on the bottom with a 100 mesh (-150pm) screen and a stopper to allow contents to drain through the screen. The tube was inverted five times to ensure the stock contained therein was homogenous. The bottom stopper was removed and elution times were measured for 100ml, 200ml, and 300ml elution volumes. The elution time at 300ml for an untreated stock blank should be preferably >60 seconds.

4. The percentage improvement I in drainage provided by a treatment was calculated as follows from the drainage time Tt following the treatment and the drainage time Tu for the corresponding untreated sample in which no mineral was added after the flocculant: I Tu-Tt Tu Equation 1

In each case the flocculant employed was the product commercially available under the trade name TRP 954 from ECC International Inc at Calgon Corporation, Pittsburgh PA, United States of America. This product is representative of the retention aid cationic polymers employed in the paper industry. It consists of a 25wt% active high molecular weight acrylamide/acryloyloxyethyltrimethylammonium chloride copolymer comprising about 90mole% acrylamide. In each case, the flocculant was added in an amount of 375ppm based on the dry weight of the solids content of the furnish. The mineral in each case was a selected processed kaolin-containing material. In each of the Examples below, the mineral was added in different dose amounts in different experiments each in the same Example and the effectiveness of the mineral was thereby determined by plotting percentage improvement in drainage obtained (compared with that obtained by use of the flocculant with no subsequent mineral addition) versus dose of mineral added. For comparison purposes, an industry standard material of a different, more expensive class of inorganic particulate materials was subjected to exactly the same test procedure using the same furnish as for the material under test. Also for comparison purposes, a coarse kaolin representing the closest published prior art was first investigated in Example 1. In subsequent Examples below, the kaolin selected was a selected processed material having a mean particle size less than lm, ie representing a kaolin for use in methods embodying the invention.

Example 1 (Prior art for comparison) The mineral employed in Method B in this Example was the processed kaolin sold by ECC International Ltd, St Austell, England under the trade name INTRAFILL C.

This has been widely used as a filler material in paper making. It has the following properties: Percentage by weight of particles smaller than 5pm: 25 Percentage by weight of particles smaller than 2pm : 52 mean particle size = 2. 6pm kaolinite content = >80% by weight The results obtained are shown in Figure 1. In Figure 1 and subsequent Figures, the bold line shown represents the results obtained for the material under test and the dashed line shown represents the results obtained for an industry standard material of another (more expensive) family investigated under the same conditions.

Example 2 The mineral employed in Method B in this Example was a fines fraction obtained by fractionating by centrifugation a processed kaolin obtained from china clay in Cornwall, England. The fines fraction had the following properties:

mean particle size (measured by Malvern Mastersizer): 0.535pm kaolinite content: 96% by weight mica content: 2% by weight feldspar content: 1% by weight quartz content: <0.1% by weight The results obtained are shown in Figure 2. By comparing Figure 2 with Figure 1, it can be seen that unexpectedly and beneficially much lower doses of the fine kaolin material employed in this Example 2 than the coarse kaolin material employed in Example 1 are required to obtain the same levels of drainage improvement.

Example 3 The mineral employed in Method B in this Example was a processed kaolin obtained from china clay in Cornwall, England. The fines fraction had the following properties: mean particle size (measured by Malvern Mastersizer): 0.682won kaolinite content: 96% by weight mica content: 3% by weight feldspar content: <0.1% by weight quartz content: <0.5% by weight The results obtained are shown in Figure 3. By comparing Figure 3 with Figure 1, it can be seen that unexpectedly and beneficially much lower doses of the

fine kaolin material employed in this Example 3 than the coarse kaolin material employed in Example 1 are required to obtain the same levels of drainage improvement.

Example 4 The mineral employed in Method B in this Example was a processed ball clay obtained from Dorset, England. The ball clay used has the following properties: Mineral content by weight: Kaolinite 93% Mica 4% Feldspar 1% Other minor constituents 2% 92% by weight of the particles have a size less than 2pm. 87% by weight have a size less than lpm.

The mean particle size is 0.4pm.

The results obtained are shown in Figure 4. By comparing Figure 4 with Figure 1, it can be seen that unexpectedly and beneficially much lower doses of the fine kaolin material employed in this Example 4 than the coarse kaolin material employed in Example 1 are required to obtain the same levels of drainage improvement.

Example 5 The mineral employed in Method B in this Example was a processed ball clay obtained from Devon, England.

The ball clay used has the following properties: mean particle size (measured by Malvern Mastersizer): 0.509pm % by weight kaolinite content: 60% % by weight mica content: 35% % by weight quartz content: 5% The results obtained are shown in Figure 5. By comparing Figure 5 with Figure 1, it can be seen that unexpectedly and beneficially much lower doses of the fine kaolin material employed in this Example 5 than the coarse kaolin material employed in Example 1 are required to obtain the same levels of drainage improvement.

Example 6 The mineral employed in Method B in this Example was a processed ball clay obtained from Devon, England.

The ball clay used has the following properties: mean particle size (measured by Malvern Mastersizer): 0.625zm % by weight kaolinite content: 95% % by weight mica content: 3% % by weight quartz content: 2%

The results obtained are shown in Figure 6. By comparing Figure 6 with Figure 1, it can be seen that unexpectedly and beneficially much lower doses of the fine kaolin material employed in this Example 6 than the coarse kaolin material employed in Example 1 are required to obtain the same levels of drainage improvement.

An improvement in drainage obtained by a given microparticle system is generally associated with a similar improvement in retention. In order to illustrate this, comparative first pass retention was measured for the furnish prepared as described in Method A and treated as described in Method B using in Method B firstly the mineral described in Example 1 and secondly the mineral described in Example 4. The retention measurements were carried out as in Example 7 as follows.

Example 7 A fixed volume of each suspension formed as in Method B was filtered through a Buchner filter holding a separate Whatman No 50 filter paper of diameter 5.5cm simulating a paper making wire (because it is a coarse filter paper giving a clear filtrate). Each filter paper had been accurately weighed prior to use. The filter paper plus solids deposited thereon was in each case carefully removed from the filter and was dried in an oven at a temperature of about 105°C. The paper plus solids was cooled and reweighed. The weight of solids deposited was calculated (and expressed as a percentage of the theoretical maximum possible).

As can be seen in Figure 7, the amount in the microparticle system of mineral required to give a particular % retention level, say 60%, is much greater where the mineral is coarse kaolin as described in Example 1, curve A in Figure 7, than when the mineral is fine kaolin in the form of ball clay as described in Example 4, curve B in Figure 7.

The following further Examples are embodiments illustrating the invention. In these Examples, the following products were used: Polymer A is a high molecular weight, cationic, acrylamide/acryloyloxyethyltrimethylammonium chloride copolymer, comprising 10 mole% cationic monomer and available from Calgon Corporation, Pittsburgh, USA.

Polymer B is a high molecular weight, anionic acrylamide/acrylic acid copolymer available from Calgon Corporation, Pittsburgh, USA, comprising about 30 mole% acrylic acid.

Polymer C is a medium molecular weight homopolymer of diallyldimethylammonium chloride available from Calgon Corporation, Pittsburgh, USA.

Polymer D is a medium molecular weight, cationic copolymer of acrylamide and diallyldimethylammonium chloride available from Calgon Corporation, Pittsburgh, USA.

Polymer E is a medium molecular weight, terpolymer of acrylamide, acrylic acid and diallyldimethylammonium chloride available from Calgon Corporation, Pittsburgh, USA.

Kaolin A is a processed kaolin obtained from china clay and as described in Example 2 earlier.

Nalco 8671 is a colloidal silica product available from Nalco Chemical, Naperville, IL, USA.

Examples 8 to 77 Examples 8 to 77 in Table 1 as follows further demonstrate the effectiveness of various formulations for use in the method of the instant invention 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. In these Examples, the following procedures were employed: (a) Furnish preparation The synthetic furnish used for drainage and retention tests and for making handsheets was prepared as in Method A described earlier.

(b) Drainage Test Procedure The drainage test procedure as in Method B described earlier was employed. In some cases a coagulant polymer was added pre-fan at time to in the Britt jar.

(c) Retentions Test Procedure (FPR, FPAR) 1. Pour 500ml of stock at headbox consistency (1.0%) into a Britt Jar with a 70 mesh screen while stirring at 1200rpm.

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 tic 1200 Flocculant Pre-screen t20 600 D/R/F aid Post-screen t30 open the bottom stop cock and collect the first 100ml of eluate (a) Filter this eluate through Whatman 4 filter paper and dry the pad at 105°C. Measure the first pass retention (FPR) as described in Example 7.

Burn the pad at 500°C for 2 hours to determine first pass ash retention.

(d) Hand Sheet Preparation and Testing Paper handsheets were prepared at 70gsm basis weight using a Noble & Wood Hand Sheet Mold. This apparatus generates a 20cm x 20cm square handsheet.

The mixing time/speed sequence used in preparing handsheets is 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. Brightness and opacity were measured by standard TAPPI specified procedures.

The results obtained for these Examples 8 to 77 using the test procedures described (a) to (d) above are listed in Table 1 as follows.

Table 1 Pre-Fan Pump Pre-Screen Post Screen Examp 1st Lb/T Produ lb/T 2nd lb/T Drain FPR FPAR MK Brigh Opaci le No Produ ct No Produ age (%) (%) Forma tness ty ct 2 ct Impro tion added added vemen Index t (t) *1Polym0.10****n77.031.120.085.787.1 er A 1 9 - - " 0.25 - - 28 79.6 40.5 17.0 84.9 88.1 10 0. 50--43 84. 2 56. 0 15. 7 84. 8 BB. 7 11 - - " 0.50 Kaoli 2 51 88.9 75.2 15.3 85.1 88.5 n A 12 272.515.785.588.4 T3'"'""*"6489.177.714.485.888.5 14 - - " " " 8 64 88.9 75.8 13.6 86.1 89.2 15 - - " " " 10 65 89.6 78.7 15.7 85.9 89.1 16 Polym 0. 1 Polym 0. 50 Kaoli 10 66 91. 4 83. 0 12. 5 85. 7 88.8 er C er A n A *n'0.25'?692.083.411.985.489.5 *T0.50*'*6T91.482.712.265.289.9 T5fo"*"*90.279.313.285.090.2 20 0. 50 0. 50 5 45 88. 9 78. 3 13. 4 84. 8 90.5 21 1. 0 0. 50-19 85. 9 72. 3 13. 0 84. 3 89.5 22 1. 0 0. 25 5 18 82. 2 59. 7 18. 2 1 84. 5 89.6 *1.0*0.10*T*} 78.9 47. 4 20. 7 84. 3 89.4 'IT*TTo0.10T77.242.219.2*6T*667.5 '?"0.5*0.10*"*?I76.848.719.985.468.5 "*"0.10*T5'76.938.322.886.766.8 T?*0.25*"7681.448.217.686.488.4 *?8Polym0.50Polym0.25Kaoli*582.050.317.385.589.6 erCerAnA 29 0. 50 0. 25 10 53 83. 9 55. 3 17. 1 85. 6 89. 5 30 " 0.50 " 0.25 - - 20 82.0 50.9 16.9 84.7 88.9 "nPolym0.10"0.50Kaoli15"7584.963.114.8857986.5 er D n A **0.25****"7587.068.213.265.886.1 "0.50"'""787.569.6'TT'Y*6?*486.4 *?T'O'*'"'*7T90.676.09.385.186.6 "?50.50*''*87.670.611.665.066.1 36 1. 0-42 86. 4 68. 3 15. 1 84. 7 85.9 37 " " " 0.25 Kaoli 5 54 84.3 59.9 17.5 85.0 86.4 n A 8**'"0.10*T5*82.450.423.185.585.7 39 29 80. 4 44. 8 20. 9 84. 8 84. 1 "75'*0.50*'"Kaoli*M79.942.321.385.985.3 n A TI""****TT*876.921.122.386.363.7 42 0. 25 5 51 79. 2 32. 8 24. 2 1 85. 9 84.9 43 Polym 0. 50 0. 25 57 82.4 47. 2 17. 2 85. 4 85.9 er D 44 10 62 83. 6 50. 3 16. 3 85. 6 86.3 45 " " " " - - 39 83.4 47.9 18.7 85.1 85.2 46 Polym 0.10 Polym 0.50 Kaoli 10 72 86.0 64.6 14.8 85.86.8 er E er A n A T?"0.25"""""7386.365.611.785.7B6.7 *T8*0.50""""7488.270.010.385.567.1 *T9"1.0"""""7489.875.510.884.287.7 "5'5"0.50"""5"6689.174.814.783.567.5 "5T"1.0"***"T486.767.720.383.366.5 '*2"""0.25Kaoli"5"E584.156.620.684.067.4 nA "53""'0.1'*T5'7678.844.923.484.667.0 54 32 79. 9 45. 5 34. 5 83. 9 84. 4 "'0.50**KaoliT880.446.323.585.265.7 n A *6'To"n77.430.427.685.884.8 *'"0.25"5*B79.439.126.485.766.5 *?8Polym0.50""""i82.550.924.085.166.3 er E 9''''"'TS"SB'8?"351.118.0''<nn87.4 "60*'''"'*? 81.6 47. 4 26. 4 84. 3 86.3 Polym0.10Polym 0.25--6 76. 2 18. 3 21. 0 85. 0 89.8 er C er B "f*'0.375**i76.719.117.985.090.0 "6"*0.50""76.821.419.084.969.5 "6T0.25"'Kaoli**I76.529.021.185.290.4 n A "6"0.50*'79.139.918.265.090.9 *6*1.0'*?681.248.517.283.691.5 "6"0.50*'578.237.316.284.690.6 "M*1.00.50"**'*?!79.545.419.084.290.7 " 0.375 Kaoli 5 36 79.1 41. 2 18. 8 83. 9 91.2 n A 70 " " " 0.25 " 10 41 79.3 41.3 19.0 83.9 92.4 "71'"*"*77.232.919.484.490.5 710.50Kaoli**?578.236.417.364.990.8 n A "750.10"0.25To-1776.527.222.565.090.0 "74"*0.375*-2275.524.921.48S.489.6 *7*0.50*"'"5"77.130.718.085.390.6 T"'*"'"*"ni"76.032.415.585.290.6 77 " " " " - - 27 77.0 28.3 18.3 85.1 90.5

Examples 78 to 103 Examples 78 to 103 in Table 2 as follows demonstrate the effectiveness and improved performance of the instant invention, as compared to a silica microparticle system of the prior art, in improving drainage, retentions, sheet brightness, and sheet opacity of a synthetic, aqueous cellulosic furnish.

The composition of this furnish and the test procedures employed were the same as used for Examples 8 to 77.

Properties as measured for earlier Examples 8 to 77 were measured in a similar manner.

Table 2 Pre-FanPump Prt-SoreenPoatScM'M Exampl 1st lb/T 2nd lb/T 3rd lb/T Draina FPR FPAR Bright Opacit attoProduoproduoProduoge()(t)nM* ness Y t t t Improv added added added @m@nt (t) 78 Stalok 5 Polyme 0. 125 Nalco 0. 50 22 78. 4 22. 8 84. 3 86.7 400-r B 8671 "F9"T5***'"*81.135.383.687.2 'T5"'*0.50**84.046.983.388.3 *8T"S''*?480.438.083.387.8 *8*0.250.75*78.631.683.887.4 '"6*"1*0125*'TT81.139.383.786.9 84 " " " 0.25 " " 33 81.3 40.5 83.5 87.8 T''*7''182.850.8*8?'87.1 86 25'*'Ti81.847.083.1"s774 *0.125'1.0TS81.946.883.685.9 '?8*'*0.50"'TI85.159.184.185.8 "8*''"380.943.284.486.4 "550.12579.436.084.286.0 91 - - Polyme 0. 25 Kolin 5 37 83.1 42.8 85.2 85.1 r A A *'**0.50"*82.942.785.066.6 i"'*"*T5"n82.743.685.686.2 "?4*0.25*"78.724.085.783.6 95 Polyme 0. 25 7. 5 43 82. 3 41. 7 85. 3 85.9 r E ***0.375*"'82.442.085.186.1 'T?***7.584.550.885.386.2 98 543.985.486.2 *'0.50'*7.5"S886.055.385.287.0 1000.50Hi"788.463.5C5.187.3 101 5 70 88. 8 65. 4 84. 9 87.5 102*'**0.25**T5i80.836.585.386.4 103 5 58 80. 5 34. 4 85. 2 86.5 Example 104 In this Example 104, further various fine clay fractions were employed separately in drainage studies in Method B described earlier. These fine fractions were obtained by particle size classification of processed china clay from the St Austell area of England. The classification was carried out in a known manner using decanter centrifuging operating on an

aqueous slurry of the china clay. The particle size cut point between the coarse fraction and the fine fraction obtained in this way may be selected in a known manner by adjusting the slurry flow rate through the centrifuge. Eight fine clay fraction samples S1 to S8, were obtained in this manner. The properties of Sl to S8 are summarised in Table 3 as follows.

Table 3 Sample Identity Mean particle Non-kaolinite size (nm) impurity clay content (wt%) S1 878 0 S2 535 2 S3 335 12 S4 264 23 S5 456 2 S6 377 8 S7 275 12 S8 244 25 The percentage change in drainage versus dose of the mineral (fine clay fraction) as measured in earlier Examples is plotted in Figure 8 for the fine clay fractions samples Sl to S4. The curves in Figure 8 labelled S1, S2, S3 and S4 represent the corresponding samples S1, S2, S3 and S4. The percentage change in drainage versus dose of mineral (fine clay fraction sample) as measured in earlier Examples 1 to 6 is plotted in Figure 8 for the fine clay fraction samples S5 to S8. The curves in Figure 8 labelled S5, S6, S7 and S8 represent the corresponding samples S5, S6, S7

and S8. For reference purposes, the percentage change in drainage versus dose of mineral for the commercially available material employed in earlier examples was used in Method B under the same conditions as Sample S1 to S8 is shown as curve A in Figures 8 and 9.

A graph of the microparticle mineral dose obtained from the results of Figures 8 and 9 and required to match the drainage lift obtained for a given dose (200ppm) of the commercially available mineral represented in curve A versus mean particle size of each sample is plotted in Figure 10. The specified dose in each case is a measure of microparticle mineral efficiency, the less the required dose the greater the efficiency. As seen in Figure 10, microparticle mineral efficiency of the fine clay fraction samples increases with decreasing mean particle size. By making the mean particle size of the clay fraction in samples S1 to S8 finer it can be shown that the non- kaolinite impurity clay content of the (three layer aluminosilicate mineral content) fraction is increased by the centrifugation. This in turn increases the sample microparticle efficiency.

The microparticle mineral dose for samples S1 to S8 as plotted against particle size in Figure 10 is plotted in Figure 11 against non-kaolinite impurity clay content. The increase in efficiency is seen by the fall in required dose with increasing non-kaolinite impurity (three layer aluminosilicate) clay content.