JPH093794A - Method for manufacturing of paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a profitable method for producing paper, improved in water drainage and filler holdability. SOLUTION: This method for producing the paper from a suspension comprises adding an aluminum compound and anionic inorganic particles to the suspension containing cellulose-containing fibers and an arbitrary filler and subsequently spreading the suspension on wires to produce the paper and drain the water. Therein, the aluminum compound and the anionic inorganic particles are mixed with each other just before added to the suspension, and the anionic inorganic particles are selected from among colloidal silica, polysilicate, colloid aluminum-modified silica having a specific surface area of up to 1,000m<2> /g, colloid aluminum silicate having a specific surface area of up to 1,000m<2> /g, smectite type clay, and their mixtures.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of making paper, and more particularly to a method of adding a freshly prepared mixture of aluminum compounds and anionic inorganic particles to a papermaking feedstock to improve drainage and retention. .

[0002]

BACKGROUND OF THE INVENTION A drainage and retention aid consisting of two or more components added to a raw material in order to promote drainage and increase adsorption of fine particles to cellulosic fibers. It is known in the paper industry that additive systems are used so that they are retained by the fibers. Systems containing aluminum compounds and anionic inorganic particles are known and these components are usually used in combination with organic polymers, especially cationic polymers. Examples of anionic inorganic particles widely used for drainage and retention purposes include silica-based particles and smectite clay, which have been found to be very effective.

The components of the drainage aid system and the retention aid system are usually added separately to the raw materials. It is further known to use drainage aids and retention aids containing the reaction product of an aluminum compound and anionic inorganic particles. U.S. Pat. Nos. 4,927,498 and 5,368,833 disclose aluminum modified silica particles obtained by reacting silica particles with an aluminate. The latter patent shows that when the effect of drainage aids and retention aids containing cationic polymers and aluminum-modified silica particles is added to the raw materials as well as additional aluminum compounds, such as those commonly used in papermaking. It discloses that it will be promoted.

[0004]

According to the present invention, it is possible to improve drainage and / or retention during papermaking by mixing an aluminum compound with anionic inorganic particles immediately before addition to the raw material. It has been found to be possible. More particularly, the present invention relates to a method of making paper from an aqueous suspension of cellulose-containing fibers and optional fillers, the method comprising adding an aluminum compound and anionic inorganic particles to the suspension. , Producing a suspension on the wire and draining, where the aluminum compound and the anionic inorganic particles are mixed just prior to addition to the suspension. Accordingly, the present invention is directed to a method as further specified in the claims.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention provides a method for making paper which is different from the method in which the components are added to the raw materials separately as well as the method in which the components are reacted or mixed at some time prior to the addition. Provides improved drainage and / or retention. Thus
By applying the method of the present invention, the speed of the paper machine can be increased, and even lower application amounts of the components can produce corresponding effects, thereby leading to economic benefits and improved papermaking processes.

The method of the invention is characterized in that the aluminum compound and the anionic inorganic particles are mixed just before addition to the raw materials. This means that the contact time, ie the time between mixing these components and adding the resulting mixture to the raw materials, should be as short as possible.
This time period is preferably less than 4 minutes, 2
It is preferably less than minutes. This rapidly mixes the aqueous phase of the aluminum compound with the aqueous phase of the anionic inorganic particles,
Then, the obtained aqueous mixture can be mixed with the raw materials.

According to a preferred embodiment of the invention, an aqueous stream of aluminum compound is contacted with an aqueous stream of anionic inorganic particles and the resulting aqueous stream is then introduced into a suspension. This can be done by directing separate streams of the components to be mixed towards each other, impinging them on one another and introducing the mixture thus produced into the feed. The mixing is preferably carried out under turbulent flow conditions which promote more intensive and rapid mixing of the streams. These streams are provided by any mixing device having at least two inlets to which separate streams of the components to be mixed are fed and at least one outlet through which the resulting mixture is passed and subsequently introduced into the feedstock. Can be mixed. By applying a flow mixing process, especially when using a mixing device of the type described above, the components of the resulting stream are intimately contacted for less than a minute before incorporation into the feedstock, which is especially It has been found to be very effective with contact times of less than about 30 seconds, preferably less than about 15 seconds. The stream mixing embodiment is more advantageous from a practical point of view and offers operational advantages. Mixing devices that can be used to practice the method of the present invention are known in the art, although they are intended for other types of ingredients and for other purposes. For example, mixing pipes that are substantially Y-shaped or T-shaped can be used whereby separate streams of the components are passed in substantially opposite directions to impinge upon one another, after which the resulting mixture is a raw material. Is flowed in. Also, differently shaped mixture pipes as well as static mixers can be used.

Anionic inorganic particles that can be used in accordance with the present invention include silica-based particles, smectite type clays, and mixtures thereof. The particle size is preferably in the range of colloidal particle size. Particles based on silica, ie SiO ₂ based particles, comprising colloidal silica, different types of polysilicic acid, colloidal aluminum modified silica, colloidal aluminum silicate, and mixtures thereof, alone,
Alternatively, it is preferably used in combination with other types of anionic inorganic particles. Suitable silica-based particles and methods for their preparation are described in US Pat. No. 4,388,150.
No. 4,954,220, No. 4,961,825, No. 4,980,
No. 025, No. 5,127,994, No. 5,368,833, and No. 5,447,604, and International Patent Publication WO 94/0559
6 and WO 95/23021, all of which are incorporated herein by reference.

The silica-based particles are less than about 50 nm, preferably less than about 20 nm, and more preferably about 1 nm.
It is preferred to have a particle size in the range of about 10 nm. The specific surface area of the silica-based particles is about 50 m ^2.
/ G or more, preferably about 100 m ² / g or more. Generally, one silica-based particle
It can have a specific surface area of up to 700 m ² / g.
Colloidal silica up to 1000 m ² / g, preferably 9
It is preferred to have a specific surface area of up to 50 m ² / g. Further, it is suitable that the colloidal aluminum-modified silica and the colloidal aluminum silicate have a specific surface area of up to 1000 m ² / g, preferably up to 950 m ² / g. Specific surface area is determined by Analytical Chemistr
y) 28 (1956): 12, 1981-1983 in Sears (Sears
), And can be measured by titration with NaOH.

According to a preferred embodiment of the invention, the anionic inorganic particles are therefore particles based on silica having a specific surface area in the range 50 to 1000 m ² / g, preferably 100 to 950 m ² / g. Is. Suitable silica-based particles of this type are generally provided in the form of an aqueous sol as disclosed, for example, in US Pat. Nos. 4,388,150 and 4,980,025. The latter patent discloses a sol comprising particles having at least a surface layer of aluminum silicate or aluminum modified silicic acid containing silicon and aluminum atoms in a ratio of 9.5: 0.5 to 7.5: 2.5. ing.

According to another preferred embodiment of the invention,
Have an S value in the range of 8 to 45%, preferably 10 to 30%, and 750 to 1000 m ² / g, preferably 800 to 9
Silica particles having a specific surface area in the range of 50 m ² / g (these are surface-modified with aluminum with a degree of substitution of silicon atoms of 2 to 25% as disclosed in US Pat. No. 5,368,833). A silica sol containing is used. The S value can be measured and calculated as described by Iler and Dalton in J. Phys. Chem. 60 (1956), 955-957. The S value indicates the degree of formation of aggregates or microgels, and the low S value is an indicator of the high degree of aggregation.

According to another preferred embodiment of the invention,
Polysilicic acid having a high specific surface area of about 1000 m ² / g or more is preferably used. Polysilicic acid is also referred to in the art as polymeric silicic acid, polysilicic acid microgels and polysilicate microgels, all of which are included in the term polysilicic acid. Polysilicic acid is 1000-1
700m ² / g, preferably 1050~1600m ² / g
It is preferable to have a specific surface area within the range. Polysilicic acid which can be used according to the present invention includes U.S. Pat.
150, No. 4,954,220, and No. 5,127,994.

The polysilicic acid is preferably an alkali metal silicate, for example containing from about 0.1 to 6% by weight of SiO ₂ , eg
It can be prepared by acidifying a dilute aqueous solution of potassium water glass or sodium water glass. Acidification can be accomplished in a number of ways, including acidic ion exchange resins, mineral acids such as
This can be done by using sulfuric acid, hydrochloric acid and phosphoric acid, acid salts or acid gases, preferably ion exchange resins or mineral acids or combinations thereof. If a more stable polysilicic acid is desired, it is preferred to use an acidic ion exchange resin. Suitably the acidification is carried out to a pH in the range 1 to 11, preferably to a pH in the acidic range 2 to 4. According to another preferred aspect of the present invention, partial acidification is carried out to a pH of about 7-10, thereby producing a polysilicic acid, commonly referred to as activated silica. Aqueous polysilicic acids are usually not very stable compared to sols containing low specific surface area silica based particles. For this reason, polysilicic acids should not be stored for too long, but some aging for one or two days, for example at concentrations of about 4-5% by weight or less, may lead to improved effects. According to another preferred embodiment of the invention, the aqueous polysilicic acid used is produced at the place of use. Even when using polysilicic acid, which is usually less stable in the pH range of 4-7, which gels rapidly, the mode of operation is all acidified p's of 1-11.
Applicable in the H range.

Clays of the smectite type that can be used in the process of the present invention are known in the art and include naturally occurring materials,
Includes synthetic and chemically treated substances. Examples of suitable smectite clays include montmorillonite / bentonite, hectorite, beidellite, nontronite and saponite, preferably bentonite, especially those having a specific surface area of preferably 400-800 m ² / g after swelling. To be

Suitable bentonites and hectorites are disclosed in US Pat. Nos. 4,753,710 and 5,071,512, respectively, which are incorporated herein by reference.
Suitable mixtures of silica-based particles and smectite clay, preferably natural bentonite, are disclosed in International Patent Publication WO 94/05595, which is also included herein by reference, where silica-based The weight ratio of particles to clay particles may be in the range of 20: 1 to 1:10, preferably 6: 1 to 1: 3. Aluminum compounds that can be used in the method of the present invention are known in the art and include alum, aluminates, aluminum chloride, aluminum nitrate and polyaluminium compounds such as polyaluminum chloride, polyaluminum sulfate,
Includes polyaluminum compounds containing both chloride and sulfate ions, polyaluminum silicate sulfate, and mixtures thereof. The polyaluminum compound may also contain other anions, such as those from phosphoric acid, organic acids such as citric acid and oxalic acid. A preferred aluminum compound is US Pat. No. 5,127,994.
Are disclosed in the specification. According to a preferred embodiment of the present invention, the aluminum compound is an aluminate, such as sodium or potassium aluminate,
Preferred is sodium aluminate. According to another preferred embodiment of the invention, an acidic aluminum compound is thus used, which can be selected from alum, aluminum chloride, polyaluminium compounds and mixtures thereof.

The premix used in the method of the present invention comprises 10 anionic inorganic particles to an aluminum compound.
It can be produced by mixing the anionic inorganic particles with the aluminum compound in a weight ratio within the range of 0: 1 to 1: 1. The weight ratio of the anionic inorganic particles to the aluminum compound is 50: 1 to 1.5: 1, preferably 20: 1 to 2: 1.
It is preferred that it is within the range.

The amount of anionic inorganic particles added to the suspension may vary within wide limits, depending, for example, on the type of particles used. The amount is usually at least 0.01 k, calculated as dry particles for dry fiber and any filler.
g / ton, often at least 0.05 kg / ton. The upper limit may be 10 kg / ton, preferably 5
It is kg / ton. When silica-based particles are used, their amount is in the range of 0.05 to 5 kg / ton, preferably 0.1 to 0.1, calculated as SiO ₂ with respect to the dry raw material system.
It is preferably in the range of 2 kg / ton.

The amount of aluminum compound added to the suspension may depend on the type of aluminum compound used and other effects desired from it. For example, it is known in the art to use aluminum compounds as precipitants for rosin-based sizes. Mixed with anionic inorganic particles to form a premix, followed amount of aluminum compound added to the raw material, compared dry fibers and optional filler, calculated as Al ₂ O ₃ of at least 0.001 kg / It is preferably ton. The amount is in the range of 0.01 to 1 kg / ton, preferably 0.
It is preferably in the range of 05 to 0.5 kg / ton. If required, additional aluminum compounds can be added to the feedstock at any location prior to drainage. Examples of suitable additional aluminum compounds include those mentioned above.

The concentration of the aqueous phase of the aluminum compound and the anionic inorganic particles mixed according to the invention can vary within wide limits and can depend on the type of components used. The solution of aluminum compound can have a concentration of at least 0.01% by weight, calculated as Al ₂ O ₃ , the upper limit of which is usually about 25% by weight. Suitably the concentration is in the range 0.1 to 10% by weight, preferably 0.2 to 5% by weight. The aqueous phase of the anionic inorganic particles used in the mixing can have a concentration of at least 0.01% by weight, the upper limit of which is usually about 20% by weight. Suitably the amount is in the range 0.1 to 15% by weight, preferably 0.5 to 10% by weight. The freshly prepared mixture, the premix, can have a dry content of at least 0.01% by weight, the upper limit of which is usually about 20% by weight. Suitably the dry content is in the range 0.05 to 10% by weight, preferably 0.1 to 5% by weight.

The freshly prepared mixture of aluminum compound and anionic inorganic particles of the present invention comprises a drainage aid which can be selected from anionic polymers, amphoteric polymers, nonionic polymers and cationic polymers and mixtures thereof. And / or at least one organic polymer which acts as a retention aid. The use of such polymers as drainage aids and / or retention aids is known in the art. Suitably at least one cationic or amphoteric polymer is used, preferably a cationic polymer. These polymers can be derived from natural or synthetic sources, and they can be linear or branched. Examples of suitable polymers include anionic starch, amphoteric and cationic starch, guar gum and acrylamide-based polymers, and poly (diallyldimethylammonium chloride), polyethyleneimine, polyamines, polyamidoamines, melamine-formaldehyde resins. And urea-formaldehyde resins. Cationic starch and cationic polyacrylamide are particularly preferred polymers. When using the premix of the present invention in combination with the above organic polymers, at least one anionic scavenger (Anionic T
It is further preferred to use Rash Catcher = ATC). ATC is known in the art as a neutralizing agent for harmful anionic substances present in the feedstock. Here, AT
C may enhance the effectiveness of the ingredients used in the method of the invention. Thus, as a more preferred combination of polymers that can be co-used with the premix of the present invention, high molecular weight polymers such as cationic starch and / or cationic polyacrylamide, ATC in combination with anionic polyacrylamide, and Mention may be made of cationic starch and / or cationic polyacrylamide in combination with anionic polyacrylamide. Suitable ATCs include cationic polyelectrolytes, especially low molecular weight, highly charged cationic organic polymers such as polyamines.
Homopolymers and copolymers based on polyethyleneimine, diallyldimethylammonium chloride, (meth) acrylamide and (meth) acrylate are mentioned. Even if the order of addition is arbitrary, it is preferable to add one or more polymers to the raw material before the mixture of the aluminum compound and the anionic inorganic particles. Usually ATC is added to the feedstock before the other polymers.

The amount of organic polymer can vary over a wide range depending, inter alia, on the type of polymer (s) used and other effects desired from it. Generally, at least 0.005 kg of polymer is used per ton of dry fiber and optional filler. For synthetic cationic polymers, such as cationic polyacrylamides, amounts of at least 0.005 kg / ton are commonly used, calculated as dry matter for dry fibers and optional fillers, preferably 0.01-3 kg. / Ton, preferably 0.03 to 2 kg / ton is used. For carbohydrate-based cationic polymers, such as cationic starch and cationic guar gum, an amount of at least 0.05 kg / ton calculated as dry matter to dry fiber and optional fillers is typically used. . For these polymers, the amount is suitably 0.1 to 30 kg / ton, preferably 1 to 15 kg / ton.

The improved retention and dehydration effects of the system of the present invention are obtained over a wide pH range of the feedstock. p
H may be in the range of about 3 to about 10. pH is 3.
It is preferably above 5, and is preferably in the range of 4 to 9.

The method of the invention is in sheet or web form,
For example, it may be used to make products containing cellulosic fibers of pulp sheets and paper. The method of the invention is preferably used in the production of paper. The term "paper" as used herein, of course, includes not only paper and its products, but also other sheet or web-like products, such as board and paperboard, and their products.

The process according to the invention can be used for the production of sheet or web-like products from different types of suspensions containing cellulosic fibres, the suspension being at least 50% by weight, based on dry matter, of such fibres. Is preferably included. Suspensions can be based on fibers from chemical pulps, such as sulfate and sulfite pulps, thermomechanical pulps, chemo-thermomechanical pulps, refiner pulps or groundwood pulps from both hardwood and softwood, and It may be used with suspensions based on recycled fibers. The suspension may also contain mineral fillers of the usual type, such as kaolin, titanium dioxide, gypsum, talc and both natural and synthetic calcium carbonate. The raw materials can, of course, also include the usual types of papermaking additives, such as wet strength enhancers, rosins, ketene dimers or raw material sizing agents based on alkenyl succinic anhydride. The invention makes it possible to improve the retention of such additives, which means that further advantages are obtained, for example improved sizing and wet strength of the paper.

The invention is further described in the following examples, which are not intended to limit the invention. Parts and% relate to parts by weight and% by weight, respectively, unless otherwise stated.

[0026]

EXAMPLES Example 1 In the following test, the dehydration effect was evaluated by the Canadian standard freeness (C
SF) tester, which is SCAN-C21:
Standard method for characterizing dehydration or drainage according to 65.

The raw material used was 0.3 g / l Na ₂ S.
60:40 Bleached Hippopotamus with O ₄ · 10H ₂ O added /
It was based on pine sulfates. The raw material consistency was 0.3% and pH 7.0. Add chemical 1
Performed on a blit dynamic drain jar with baffle, with blocked outlet at a stirring speed of 000 rpm. If no chemicals are added, the raw material is 280 ml
The freeness was shown. In the test, the cationic polymer Raisamyl 142 was used. This is a normal intermediate-highly cationized starch (hereinafter referred to as CS) having a degree of substitution of 0.042, which is added to the raw material in an amount of 10 kg / ton calculated as the dry matter of the dry raw material system. did. 280m when only CS is added to the raw material
A freeness of 1 was obtained. The aluminum compound used was sodium aluminate (hereinafter referred to as NaAl), which was calculated as Al ₂ O ₃ per ton of dry raw material system and added to the raw material in the amount specified below. The anionic organic material used was a silica sol of the type disclosed in US Pat. No. 4,388,150. About 40 sol
Alkali stabilization up to the SiO ₂ : Na ₂ O molar ratio of
It contains silica particles having a specific surface area of about 500 m ² / g, which is hereinafter referred to as P1. The anionic inorganic particles are calculated as dry matter per ton of dry raw material system,
It was added to the raw materials in the amounts specified below.

The method of the present invention was carried out by adding the cationic polymer to the raw material, followed by stirring for 30 seconds, adding the premix to the raw material, followed by stirring for 15 seconds, and then transferring the raw material to the CSF tester. I went. 0.5% by weight of Al ₂ O
Aqueous stream of aluminum compound containing ₃ and 0.5% by weight
The premix used was prepared by feeding an aqueous stream of anionic inorganic particles containing the above particles to a mixing device with two inlets and one outlet. In the mixing device,
The separate streams were intimately mixed, after which the resulting stream was introduced into the feed. The premix stream was contacted for less than about 5 seconds prior to addition to the feedstock. First component + Second component +
A comparative test was conducted by adding the third / last component to the raw material for 45 seconds with stirring after each and then 15 seconds after the final addition, and then transferring the raw material to the CSF tester. The ingredients are specified in Table 1.

[0029]

[Table 1] As is apparent from Table 1, the method of using a premix of particles based on sodium aluminate and silica according to the present invention improved dehydration relative to tests 1 to 4 in which the ingredients were added separately to the raw material. .

Example 2 In this example, the procedure described in Example 1 was followed to test a sol of silica-based particles of the type disclosed in US Pat. No. 5,368,833. The sol contained silica particles having an S value of about 25% and having a specific surface area of about 900 m ² / g surface-modified with aluminum to the extent of 5%. This type of particle is called P2.

[0031]

[Table 2] As can be seen from Table 2, the dehydration effect was improved when the premix method of the present invention was applied.

Example 3 In this example, Example 1 was used to test a suspension of the type disclosed in WO 94/05595.
Followed the procedure described in. The suspension contained particles of type P2 silica-based particles described in Example 2 and natural bentonite in a weight ratio of 2: 1. This type of particle is called P3.

[0033]

[Table 3] The method of the present invention comprises the following steps:
3 showed improved drainage.

Example 4 In this example, polyaluminum chloride (referred to as PAC) was used as the aluminum compound and polysilicic acid was used as the anionic inorganic particles.
The comparison was performed in the same manner as. The polysilicic acid was treated with a cation exchange resin saturated with hydrogen ions to obtain 3.5: 1 Si.
Prepared by acidifying a sodium silicate solution having a molar ratio of O ₂ : Na ₂ O and a SiO ₂ content of 5.5% by weight to a pH of about 2.5. The resulting polysilicic acid was aged for about 30 hours and then 0.5 with deionized water.
Diluted to a concentration of SiO ₂ by weight. The polysilicic acid thus produced has a specific surface area of 1200 m ² / g and is hereinafter referred to as P4.

The raw material used in this example was prepared from the raw material described in Example 1 with chalk added in an amount of 30% based on dry fiber. The raw material thus obtained is 7.
It had a pH of 5 and exhibited a freeness of 330 ml. The solution of the aluminum compound contained 0.25% by weight of Al ₂ O ₃ , and the amount of the aluminum compound added to the raw material was calculated as Al ₂ O ₃ per ton of dry raw material system.

[0036]

[Table 4] The premix method of the present invention showed improved effectiveness over the method with separate additions.

Example 5 In this example, the procedure described in Example 4 was followed except that the aluminum compound used was alum.

[0038]

[Table 5] As is apparent from the table, the premix method resulted in improved dehydration.

Example 6 In this example, the procedure described in Example 4 was substantially followed except that the aluminum compound used was sodium aluminate. The method of the present invention is described in US Pat. Nos. 4,927,498 and 5,17 using polyaluminosilicates.
Further comparison was made with the method disclosed in 6,891. 2.
A sodium aluminate solution containing 5% by weight Al ₂ O ₃ was added to 1% by weight aged aqueous polysilicic acid prepared as described in Example 4 and added 13:
A polyaluminosilicate was prepared by obtaining a molar ratio of Al ₂ O ₃ to SiO ₂ of 87, after which the product was added to 0.5
Diluted to a concentration of% by weight. This product is called PAS. The time from the point of contact of the sodium aluminate solution and the aqueous polysilicate to the subsequent dilution and introduction of the product thus produced into the raw material was 10 minutes. In Table 6, the molar ratio represents the molar ratio of Al ₂ O ₃ to SiO ₂ .

[0040]

[Table 6] Premixing sodium aluminate and polysilicic acid according to the present invention resulted in improved dehydration compared to the method using separate additions and the method using polyaluminosilicate.

Claims (10)

[Claims] 1. Paper from an aluminum compound and anionic inorganic particles, which is added to a suspension of cellulose-containing fibers and optional fillers, which suspension is produced on a wire and drained. A method of producing a mixture of an aluminum compound and anionic inorganic particles immediately before addition to a suspension, wherein the anionic inorganic particles are colloidal silica, polysilicic acid, a ratio of up to 1000 m ² / g. Surface-modified colloidal aluminum-modified silica, 1000 m ² /
A process for producing paper, characterized in that it is selected from colloidal aluminum silicates having a specific surface area up to g, smectite type clay, or mixtures thereof. 2. A process according to claim 1, characterized in that the aluminum compound is mixed with the anionic inorganic particles and, within 1 minute, the resulting mixture is added to the suspension. 3. A process according to claim 1, characterized in that the aqueous stream of aluminum compound is contacted with the aqueous stream of anionic inorganic particles and the aqueous stream obtained thereby is introduced into the suspension. . 4. The aluminum compound is alum, aluminate, aluminum chloride, aluminum nitrate, polyaluminum chloride, polyaluminum sulfate, sulfate-containing polyaluminum chloride or polyaluminum silicate sulfate. The method according to any one of 3 above. 5. The anionic inorganic particles are colloidal silica,
The method according to claim 1, wherein the method is polysilicic acid or colloidal aluminum-modified silica. 6. The method according to claim 1, wherein the anionic inorganic particles are silica-based particles and bentonite. 7. The method according to claim 1, wherein the weight ratio of the anionic inorganic particles to the aluminum compound is in the range of 100: 1 to 1: 1. 8. A method according to any of claims 1 to 7, characterized in that the method further comprises adding at least one organic polymer to the suspension. 9. The method of claim 8 wherein the polymer is a cationic or amphoteric polymer. 10. Process according to claim 8 or 9, characterized in that the polymer is a polymer based on cationic starch and / or cationic acrylamide.