EP0336842A1 - Process for producing a paper pulp for fiduciary use - Google Patents

Abstract

Process for the manufacture of a paper pulp for fiduciary use from a raw material consisting of textile fibres is characterised in that the operations of laundering, bleaching, shredding, unstringing, cutting and washing of the textile fibres are carried out in at least one processing machine (10, 40) of the type with two screws rotating together, in a number of stages following each other continuously. To this end the operations comprise a stage of feeding and mixing the raw material and water, at least one compression stage, at least one stage of shearing the textile fibres, at least one processing stage with the introduction of the laundering and bleaching reactants, at least one stage of washing of the bleached pulp with introduction of the washing water, and a stage of transfer and removal of the bleached and washed pulp. <IMAGE>

Description

The present invention relates to a process for the manufacture of paper pulp for fiduciary use. The invention applies more particularly to the manufacture of a paper pulp obtained from textile fibers such as, for example, cotton, ramie, or linen, intended for the production of very high quality paper such as that used for the production of banknotes.

It is known that this type of paper must in particular have determined mechanical characteristics, that is to say a high breaking load and resistance to folding, as well as a uniformity and a texture suitable for the formation of a watermark. In addition, this paper must meet very strict criteria, particularly in terms of its dimensional stability, its optical whiteness and its cleanliness.

The traditional preparation of a paper pulp intended for the manufacture of fiduciary paper is carried out in several distinct stages.

First of all, the raw material generally consisting of cotton fibers coming either from waste from combing machines, or also in the form of textile waste, or from other textile fibers such as ramie, linen, is first subjected to coarse shredding and, is stored in a silo. The fibers and / or fiber bundles are then compacted using a pestle in a rotating tank, therefore at the outlet of this device the raw material is in the form of annular rings.

The annular crowns, also called "cakes", are then admitted into a digester where the operations of joint are carried out leaching and bleaching using an aqueous solution of sodium hydroxide and hydrogen peroxide. This operation is carried out under a pressure close to atmospheric pressure and at a temperature of the order of 90 ° to 95 ° C. The blanched cakes are always placed in the digester, washing is carried out with clear water in order to remove the leaching and bleaching reagents.

The purpose of the compacting operation using the pestle, before introduction into the digester, is essentially to increase the density of the raw material in order to best use the volume of said digester.

The cakes, bleached and washed after extraction from the digester, are shredded using a special machine of the milling type.

The material is then treated in stacking stacks or using another system adapted to this fibrous material. This operation carried out in water, allows in addition to the separation of the textile fibers, to cut them uniformly to a length of 3 to 4 mm.

The fibers thus obtained, always accompanied by water, are introduced into a vat and constitute the raw dough or half-dough.

The raw pulp is then passed through a disc refiner, where the fibers are refined. This operation modifies the physical structure of the fibers and gives the paper the physical and mechanical characteristics required by fiduciary use.

The refined pulp then arrives in a mixing vat in which is added pulp from the recycling of winder trimmings or trimmers and defective paper waste. This the mixing vat then feeds a vat located at the head of the paper machine proper.

It can therefore be seen that the traditional manufacture of fiduciary paper corresponds to a discontinuous process, and includes numerous handling operations for loading and unloading of the apparatuses, more particularly for the pounding of the cakes, the leaching and the milling of the bleached cakes .

The subject of the present invention is a method avoiding the aforementioned drawbacks and making it possible to continuously prepare the paper pulp, without breaking the load in the line for preparing said pulp, from the distribution silo after shredding the raw material to obtaining the semi-dough or raw dough before refining.

In addition, the method according to the invention makes it possible to considerably reduce the energy consumption usually required to produce such a paste.

The subject of the invention is therefore a process for the preparation of a paper pulp for fiduciary use, in particular banknotes, from a raw material constituted by textile fibers such as, for example, cotton, ramie or linen, comprising successively:
- a raw material shredding operation,
- a leaching and bleaching operation,
- a shredding operation for washed and bleached textile fibers,
- a scrolling and washing operation for the separation, cutting and washing of the fibers textiles,
- a kneading operation in a vat room to obtain a raw dough or half-dough, and
- a refining operation to obtain a refined paste,
characterized in that the operations of leaching, bleaching, shredding, defibering, cutting and washing of the textile fibers are carried out continuously in at least one treatment machine of the type with two co-rotating screws.

According to an essential characteristic of the invention, the operations which take place continuously in the processing machine include:
- at least one phase of feeding and mixing the raw material and water, or recycling water,
- at least one compression phase,
- at least one shearing phase of the textile fibers,
- at least one treatment phase with the introduction of leaching and bleaching reagents,
at least one phase of washing the bleached pulp with the introduction of washing water, and
- at least one phase of transfer and evacuation of the bleached and washed pulp.

According to another characteristic of the invention, the operations of leaching, bleaching and shredding of the textile fibers are carried out in a first processing machine of the type with two co-rotating screws for obtaining a bleached pulp, and the scrolling, cutting and washing operations are carried out in a second processing machine of the type with two co-rotating screws for obtaining a bleached and washed pulp, the bleaching operation being continued in a retention tank equipped with means for transporting the pulp and interposed between the two processing machines.

• - La figure 1 représente de manière schéma­tique une installation correspondant au procédé traditionnel de fabrication de pâte à papier à usage fiduciaire,
• - la figure 2 représente de manière schéma­tique les diverses phases et les appareils mis en oeuvre dans le procédé conforme à la présente inven­tion,
• - la figure 3 est une vue schématique de l'agencement général des machines de traitement utilisées dans le procédé,
• - la figure 4 est une vue en coupe dans un plan vertical passant par l'axe d'une vis de la première machine de traitement,
• - la figure 5 est une vue en coupe selon la ligne 5-5 de la figure 4,
• - la figure 6 est une vue en coupe par un plan vertical passant par l'axe d'une vis de la seconde machine de traitement,
• - la figure 7 est une vue en coupe selon la ligne 7-7 de la figure 6.

Other characteristics and advantages of the present invention will appear during the description which follows, given with reference to the appended drawings in which:

• FIG. 1 schematically represents an installation corresponding to the traditional method of manufacturing paper pulp for fiduciary use,
• FIG. 2 schematically represents the various phases and the apparatuses used in the process according to the present invention,
• FIG. 3 is a schematic view of the general arrangement of the processing machines used in the process,
• FIG. 4 is a sectional view in a vertical plane passing through the axis of a screw of the first treatment machine,
• FIG. 5 is a sectional view along line 5-5 of FIG. 4,
• FIG. 6 is a sectional view through a vertical plane passing through the axis of a screw of the second processing machine,
• - Figure 7 is a sectional view along line 7-7 of Figure 6.

In the description which follows, it has been assumed by way of example that the raw material consists of cotton fibers originating either from combing waste, or even in the form of rags, but other textile fibers such as, for example, ramie and linen can be used.

In the traditional installation shown in Figure 1, the raw material in the form of bales 1 of textile fibers is first coarsely shredded in a bale opener 2 and introduced into a distribution silo 3. The fibers are then compacted to using a pestle in a rotating tank 4 and therefore leaving this device the raw material is in the form of annular rings.

The annular rings are then admitted into a digester 5 where the leaching and bleaching operations are carried out jointly using an aqueous solution of sodium hydroxide and hydrogen peroxide. The bleached crowns are still placed in the digester 5, washing is carried out with clear water in order to remove the leaching and bleaching reagents.

Bleached crowns washed after extraction from the digester 5 are shredded using an apparatus of the milling type 6.

The material is then treated in a runner 7. This operation, carried out in water, makes it possible, in addition to the separation of the textile fibers, to cut them uniformly. The fibers thus obtained, always accompanied by water, are introduced into a vat 8 and constitute the raw dough or half-dough.

The raw pulp then passes through a refiner 9, and the pulp thus refined is then admitted into a mixing vat 9a into which is added pulp originating from the recycling of the trimmers of winders or guillotines and waste paper defective. This mixing vat then feeds a vat, not shown, located at the head of the actual paper machine.

In the installation for implementing the method according to the present invention, shown in FIG. 2, at the outlet of the distribution silo 3, the textile fibers accompanied by water are then introduced into a first treatment machine 10 of the type to two co-rotating screws.

As shown in FIGS. 3, 4 and 5, the first treatment machine 10 comprises at least two screws 11 and 12 driven in rotation around their axes by a motor 13 and a reduction gear 14 (FIG. 3) inside an elongated enclosure forming a sheath 15 which envelops them. The screws 11 and 12 are provided with helical threads which mesh with one another and the internal wall of the sheath forms two intersecting cylindrical lobes, with an inside diameter slightly greater than the outside diameter of the threads. These threads are nested one inside the other, and the two screws are driven at the same speed of rotation and in the same direction so that the two screws are identical, the threads being simply offset with respect to each other.

The screws 11 and 12 are advantageously made up of splined shafts 16 and 17 respectively on which are stacked sections of screws made up of sleeves. The internal bore of these sleeves is provided with grooves corresponding to those of the shaft and the external part is provided with helical threads whose pitch differs according to the section considered for the treatment and transport of the material. It is thus possible to have a fairly large number of sections making it possible to vary the pitch, the depth, the number of nets and the length of each zone.

Thus, the first processing machine 10 is made up of several successive zones, each corresponding to a particular function:
a first zone A for feeding and mixing the material and the water,
- a second compression zone B,
- a third shear zone C,
- a fourth zone D for conveying and processing,
- a fifth shear zone E,
- And a sixth zone F for transferring and discharging the bleached pulp.

In the first zone A for feeding and mixing the textile fibers, as obtained after shredding the bales, and water, the sheath is pierced with a feeding orifice 18 surmounted by a hopper 19, d brought products. In this zone, the screws 11 and 12 are provided with threads 20 with a wide pitch and a reduced section, in order to ensure the transfer of the products introduced through this orifice 18 which opens widely on the two screws 11 and 12 in order to distribute the material in the threads 20.

The textile fibers and water, or possibly the effluents from the second treatment machine 40, are therefore immediately transported downstream of the treatment machine and mixed by the effect of rotation and meshing of the screws 11 and 12.

In zone B, the screws have threads 21 with a tight pitch and a thicker section, so that when the products are mixed, they will be compressed.

The material then passes through a shear zone C.

To this end, the zone C is provided with helical threads 22 whose winding direction is reversed with respect to that ensuring the transfer of the material in the processing machine 10. In these threads 22 are formed openings 23 which extend radially from the core of each screw 11 and 12 to the periphery of the threads and which are also regularly distributed around the axis. The screws 11 and 12 are fixed so that two openings 23 periodically coincide in the central meshing zone. This controls the passage of the material flow downstream, which determines braking in this zone C, and a compression effect upstream. In addition, it follows a significant shearing of the material which homogenizes the mixture, improves the impregnation of the textile fibers by water, and which also constitutes a first phase of unwinding and cutting of the threads. In addition, these shearing and kneading operations, in zone C as well as elsewhere, although to a lesser degree, in zone B, causes the material to heat up, a significant part of the mechanical work being converted into thermal energy. Therefore at the end of its passage in zone C, without external heat input, the material is at a temperature of the order of 95 ° C which makes it suitable for undergoing the treatment operation in the following zone .

Zone D, conveying and processing zone, is provided with threads 24 whose pitch and thickness have characteristics close to those of zone B. At the upstream part of zone D, the sheath is provided with a opening 25, connected to a pipe rie 26 of arrival of the leaching and bleaching reagents consisting, in particular, of an aqueous sodium hydroxide solution, water, and oxygenated water optionally accompanied by sequestering and stabilizing agents. These reagents come from a dosing and injection station which includes a tank 27 for storing the aqueous sodium hydroxide solution, pipes 28 for supplying water and a tank 29 for storing hydrogen peroxide (FIG. 2) . Therefore, all along this zone D, the textile material will be stirred and mixed with these reagents in order to ensure this essential leaching and bleaching step in the manufacture of paper pulp.

The treatment machine of the type with two co-rotating screws is particularly well suited for carrying out this operation. Indeed, due to the rotation of the screws in the same direction, there is a reversal of the material in the interpenetration zone of the threads which is particularly effective as regards its kneading, which allows an intimate mixing of the reagents and textile fibers that have been in the upstream areas impregnated with water. In this way, a better use of the reagents is obtained, which results on the one hand in an economy of these and on the other hand by a reduction, in the subsequent phases, of the clear washing water and therefore effluents from the installation.

In addition, this mixing work is accompanied by an internal heating of the material, and without external heat input, the temperature thereof will be maintained at a value of 90 ° or 95 ° C compatible with good kinetics reactions, without thermal alteration of the paper pulp.

The zone D of conveying and processing is followed by a zone E which is a braking zone constituted, like the zone C of helical threads 30 of winding opposite to that in advance of the material, or counter-threads, and also comprising passage windows 31. Physical and thermal phenomena, as well as the functions carried out in this zone E, are similar to what is carried out there in zone C, that is to say significant shearing and mixing , as well as scrolling and cutting the fibers.

The last section of the treatment machine 10 constituted by zone F, comprises threads 32 whose pitch and thickness are similar to those of zone D. The leaching and bleaching reactions continue during the flow of the material, in this zone which, moreover, ensures the transfer to the outlet orifice 33 constituted by a simple opening at the downstream end of the sleeve 15.

At the outlet of this first treatment machine 10, there is thus a flow at atmospheric pressure at a temperature of the order of 80 ° C. to 100 ° C. of a bleached paste, but which still contains the residual reagents and the products resulting from the action of these reagents on the raw material.

This paste is admitted by a simple flow chute, not shown, in a retention capacity 34 (Figures 2 and 3). This capacity 34 which has the essential role of completing the bleaching reaction comprises a screw conveyor system 34a, in order to transport the dough to the second treatment machine 40.

This retention capacity 34 is dimensioned to obtain a relatively long residence time. weak between 10 min and 30 min.

The second treatment machine 40 (FIGS. 6, 7) is in its general design similar to the first treatment machine 10. It comprises at least two screws 41 and 42 driven in rotation around their axes by a motor 43 and a reduction gear 44 (Figure 3) inside an elongated enclosure forming a sheath 45 which envelops them. The screws 41 and 42 are provided with helical threads which mesh with one another and the inner wall of the sheath forms two intersecting cylindrical lobes, with an inside diameter slightly greater than the outside diameter of the threads. The threads are nested inside each other, and the two screws are driven at the same speed of rotation and in the same direction so that the two screws are identical, the threads being simply offset from each other.

This treatment machine 40 is made up of several successive zones, each corresponding to a particular function:
a first zone G for feeding and mixing the bleached pulp and the washing water,
a plurality of zones H for compression, shearing and washing of the dough,
- And a downstream zone J for transferring and discharging the bleached and washed pulp.

In the first zone G for feeding and mixing the bleached pulp coming from the retention capacity 34, at a temperature of the order of 65 ° to 70 ° C, with a fraction of the washing water, the sheath is pierced with an introduction orifice 46 surmounted by a hopper 46a for supplying the products. In this zone G, the screws 41 and 42 are provided with threads 47 to not wide and of reduced section to ensure the transfer of the products introduced by this orifice 45 which opens widely on the two screws 41 and 42 in order to distribute the material in the threads.

The bleached pulp and this first fraction of the washing water are therefore immediately transported downstream of the treatment machine 40, and mixed by the effect of rotation and meshing of the screws 41 and 42.

Thus, the dough passes through a succession of zones H1, H2 ... similar in their construction and in their function. In the example shown, the processing machine 40 has four H-type zones, which constitutes an interesting compromise as regards the production of the processing machine and the characteristics of the dough obtained. It is obvious that the process which is the subject of the present invention also applies to constructive solutions comprising a greater number of these sections H by modifying the geometrical characteristics of the threads.

Each zone H, for example zone H1, comprises a first element of compression and washing zone H11, and a second element of braking and shearing zone H12.

In the zone element H11, the screws have threads 48 with a tight pitch and a cross section thicker than that of the thread 47 of zone G. In this way, to the mixture of products will be added compression of the fibrous material . Therefore, all along the element H11, the bleached pulp is stirred and mixed with the washing water introduced into the feed hopper 46a in order to remove the residual reagents and the products resulting from the action of the reagents on the paste. Downstream of the H11 zone, where the compression is maximum, the washing effluents are discharged by means of filters 53 judiciously placed in the sheath 45.

The zone element H12 is provided with threads 49 whose winding direction is reversed with respect to that ensuring the transfer of the material in the processing machine 40. In these threads 49 are provided openings 50 which extend radially from the core of each screw 41 and 42 to the periphery of the threads and are also regularly distributed around the axis. The screws 41 and 42 are set so that two openings 50 periodically coincide in the central meshing zone. This controls the passage of the pulp flow downstream, which determines braking in this zone H12 and a compression effect upstream. Furthermore, it follows a significant shearing of the dough, which in addition to the homogenization thereof constitutes a phase of unthreading and cutting the fibers.

In addition, as in the first processing machine, these shearing and kneading operations in the braking zones as well as elsewhere, although to a lesser degree, in the other zones, cause the dough to heat up, part important mechanical work being converted into thermal energy. Therefore the dough is brought to a temperature of about 90 ° C which improves the efficiency of the washing operation.

At the upstream part of the element H21, the sleeve 45 is connected to a pipe 52 for supplying clean washing water. Therefore, all along element H21, the bleached pulp is stirred and mixed with the washing water in order to remove the reagents residuals and products from the action of the reactants on the pulp.

It should be noted that the treatment machine of the type with two co-rotating screws is particularly suitable for carrying out this washing operation efficiently and economically as regards the volume of water used. Indeed due to the rotation of the screws 41 and 42 in the same direction, there is a reversal of the dough in the interpenetration zone of the threads which is particularly effective for achieving an intimate mixture of the dough and the water of washing, which thus translates into a saving thereof.

The dough thus passes successively into zones H1, H2, H3 and H4 where the washing and unrolling operations for the dough take place in an identical manner.

The outflows from the washing effluents are produced by means of filters 53 in the downstream parts of the elements of zones H11, H21, H31 and H41.

In the example shown, it has been assumed that the three injections 52 of clear water in the zones H2, H3 and H4, as well as those at the level of the arrival of the bleached pulp in the zone G were carried out in parallel by report to a general collector, not shown. It is obvious that another arrangement of the series type can be made without departing from the scope of the present invention. In this case, the total flow of the washing water is injected into zone H41, the effluents from zone H41 are introduced into zone H31, and so on, as far as zone G. that is to say against the current with respect to the general flow of the dough in the processing machine 40.

Part of these effluents, containing the chemical reagents not consumed, can optionally be recovered in order to be recycled in the first treatment machine 10.

Zone J, which constitutes the downstream outlet section of the dough, is similar to the elements H11, H21, H31 and H41 and comprises threads 51 similar to the threads 48. It essentially ensures the transfer function of the bleached and washed dough, which leaves the processing machine 40 through an orifice 54 and is then admitted directly into the half-pulp vat 8, upstream from the refiner 9 (FIG. 2) and from the paper machine.

The method according to the present invention can also be implemented by a single processing machine of the type with two co-rotating screws ensuring in an upstream part all the functions of the first treatment machine and in a downstream part all of the functions of the second processing machine.

The paper pulp obtained with the method according to the present invention makes it possible to produce a paper entirely in accordance with what is required in traditional manufacture of fiduciary paper.

The tables below make it possible to compare the characteristics of the papers obtained by the traditional process and the process according to the present invention.

Mass concentration of reagents used relative to the mass of dry cotton

Traditional process Method according to the present invention Welded 4% 1% Hydrogen peroxide 4.8% 4% Stabilizing 0.002% 0%

Physical and mechanical characteristics Measurement conditions

- The paper samples were conditioned according to standard NF Q03-010 (23 ° C 50% RH)
- Folding, according to standard NF Q03-001
unglued paper: LHOMARGY plyograph equipped with a weight of 16 N
glued paper: LHOMARGY plyograph equipped with a weight of 20 N
- Traction, according to standard NF Q03-004
INSTROM dynamometer type 1026
- Whiteness, according to standard NF Q03-039
ELREPHO photometer equipped with a bright trap
- Paper background opacity, according to standard NF Q03-040
ELREPHO photometer
- Satin finish or smoothed, according to standard NF Q03-012
Smoothness meter BEKK Type 131 ED

Physical and mechanical characteristics of the papers obtained

Traditional process Method according to the present invention Dough refining index, Shopper-Riegler degree 81 80 Unglued paper weight, g / m2 53.1 53.8 Bonded paper weight, g / m2 61.5 62.6 Folding not glued sense walking 175 330 cross direction 17 21 Folding glued paper sense walking 1177 1783 cross direction 151 284 Whiteness% 86.2 84.1 Opacity% 75.6 75.1 Satiny s 22-40 20-37 Breaking load in da.N sense walking 6.8 7.8 cross direction 3.4 3.9 Breaking length in m sense walking 7371 8470 cross direction 3686 4240 Elongation at break, in% sense walking 4.7 4.9 cross direction 5.3 4.8

These results were obtained with a pulp production line in accordance with FIG. 2, the refining and the paper machine obviously being identical to the traditional comparison process illustrated in FIG. 1.

At the outlet of the second treatment machine, the measurements carried out on the residual soda content give an efficiency of 85 to 90% for washing.

Another advantage of the process according to the present invention lies in the savings in energy consumption and washing water. The results below clearly show the savings made.

- A consumption of 900 to 1100 kwh / ton of dry pulp by the process according to the present invention, instead of 2200 to 2400 kwh / ton of pulp in the traditional process.

- A washing water consumption of 8 to 10 tonnes / ton of dry pulp by the process according to the present invention, instead of 100 tonnes / ton of dry pulp in the traditional process.

Thus, the process according to the present invention makes it possible to obtain a paper pulp for fiduciary use with the same characteristics as the traditional process, with a continuous production line, and lower energy and water consumption.

In addition, the savings in washing water thus produced mean that the volume of effluents generated in the manufacture of this paper is lower and that consequently the treatment of these effluents is less costly and the nuisances are lower.

Finally, the method according to the present invention This eliminates handling operations for loading and unloading of the devices, as well as the pestle, the digester, the milling machine and the stackers which are necessary in the traditional process.

Claims (9)

1. Process for the production of paper pulp for fiduciary use, in particular banknotes, from a raw material constituted by textile fibers such as, for example, cotton, ramie or linen, successively comprising:
- a raw material shredding operation,
- a leaching and bleaching operation,
- a shredding operation for textile fibers, leached and bleached,
- a scrolling and washing operation for the separation, cutting and washing of textile fibers,
- a kneading operation in a vat room to obtain a raw dough or half-dough,
- a refining operation to obtain a refined paste,
characterized in that the operations of leaching, bleaching, shredding, scrolling, cutting and washing of the textile fibers are carried out continuously in at least one extrusion machine (10, 40) of the twin screw type - rotary. 2. Method according to claim 1, characterized in that the operations which take place continuously in the treatment machine (10-40) include:
- a phase A for supplying and mixing the raw material and water, or recycling water,
- at least one compression phase B,
- at least one phase (C, E, H12, H22 ...) of shearing of textile fibers,
- at least one treatment phase D with the introduction of leaching and bleaching reagents,
- at least one phase (H11, H12 ...) of washing the bleached pulp with the introduction of washing water,
- And a phase J of transfer and evacuation of the bleached and washed pulp. 3. Method according to claims 1 and 2, characterized in that, in the shearing phases (C, E, H12, H22 ...) and the processing phases (D), the material is at a temperature of range from 90 ° to 95 ° C. 4. Method according to claim 1, characterized in that the operations of leaching, bleaching and shredding of the textile fibers are carried out in a first treatment machine (10) of the type with two co-rotating screws (11, 12) for obtaining a bleached dough, and the operations of scrolling, cutting and washing are carried out in a second processing machine (40) of the type with two co-rotating screws (41, 42) for obtaining a bleached and washed dough, the bleaching operation being completed in a retention capacity (34) equipped with means (34a) for transporting the dough and interposed between the two treatment machines (10, 40). 5. Method according to claim 4, characterized in that the first treatment machine (10) comprises continuously, from upstream to downstream in the direction of transport, respectively:
- a phase A for supplying and mixing the raw material and the water,
- a compression phase B,
- a shear phase C,
a phase D of conveying and treatment with the introduction, at the start of this phase, of leaching and bleaching reagents constituted in particular by an aqueous solution of soda and hydrogen peroxide,
- a new phase E of shearing,
- And a last phase F of transport and evacuation of the bleached pulp in the retention capacity 34. 6. Method according to claim 5, characterized in that at the exit of phase F of transfer and evacuation, the bleached pulp is at a temperature of the order of 80 ° C. 7. Method according to claim 4, characterized in that the second treatment machine (40) comprises continuously, from upstream to downstream in the direction of transport respectively:
a phase G of feeding and mixing the bleached pulp coming from the retention capacity (34) and the washing water,
- a succession of phases (H1, H2 ...) of compression, shearing and washing of the dough,
- And a last phase J of transfer and evacuation of the bleached and washed pulp. 8. Method according to claim 7, characterized in that each phase (H1, H2 ...) consists of a first phase (H11, H21 ...) of kneading with introduction (46, 52), at the start of this first phase, of washing water, and with evacuation (53), at the end of said first phase, of the effluents, and of a second phase (H12, H22 ...) of shearing. 9. Method according to claim 7, characterized in that in phase G of supply and mixture of the bleached pulp and washing water, said bleached pulp is at a temperature of the order of 65 ° to 70 ° C.

Images