EP1740769A1

EP1740769A1 - Method for the production of paper and cardboard, corresponding novel retention and draining agents, and paper and cardboard thus obtained

Info

Publication number: EP1740769A1
Application number: EP04805815A
Authority: EP
Inventors: Gatien Faucher; René Hund; Christian Jehn-Rendu
Original assignee: SNF SA
Current assignee: SPCM SA
Priority date: 2004-04-29
Filing date: 2004-11-08
Publication date: 2007-01-10
Anticipated expiration: 2024-11-08
Also published as: ES2523139T3; JP5053077B2; JP2007534858A; US7815771B2; EP1740769B1; FR2869626A3; US20090050282A1; WO2005116336A1

Abstract

The invention relates to a method for the production of cardboard or similar, consisting in initially adding at least one main retention agent consisting of a cationic co(polymer) to the fibrous suspension, then optionally shearing the flocks thus obtained, characterized in that at least one secondary retention agent selected from the group comprising silica derivatives and anionic or amphoteric organic polymers is added to the suspension, either separately or in a mixture, in one direction or in another, in addition to at least one tertiary retention agent consisting of a cross-linked anionic organic polymer whose size is greater than or equal to 1 micrometer and whose intrinsic viscosity is less than 3 dl/g.

Description

PROCESS FOR PRODUCING PAPER AND CARDBOARD. NEW CORRESPONDING RETENTION AND DRIP AGENTS AND THE PAPER AND CARDBOARD THUS OBTAINED

The invention relates to a process for the production of paper, cardboard or the like using at least three retention and draining agents, respectively a main agent, one or even two secondary agents and a tertiary agent. It also relates to the paper or cardboard obtained by this process. Finally, it relates to the use of specific crosslinked anionic organic polymers as a tertiary retention agent.

Microparticulate retention systems are well known in the papermaking process. Their function is to improve retention, drainage and training during the manufacture of the sheet.

We know in the prior art:

- US-A-3052595, where it is proposed to combine bentonite (inorganic microparticle) with a linear polyacrylamide (main retention agent), - EP-A-235893, which describes the addition of a high molecular weight cationic polymer (main retention agent), then a shearing step, then the addition of bentonite (secondary retention agent). According to this patent, the polymer must be essentially linear (without voluntary addition of branching agent), - US-A-5180473 and the article Watanabe & al. (Pulp Gijitsu Times, March 1989, pages 17 to 21) relate to the use in a “dual” type system of a polymer (main retention agent) and then an organic microparticle (secondary retention agent). It is specified (col. 3, 1.65) that the microparticles (anionic or cationic) must be as uniform as possible and as fine as possible. It may be noted that, as is the case for retention systems using mineral microparticles, those skilled in the art know, as early as 1989, that the size of the organic microparticles is a direct indication of the power of particle agglomeration and therefore of retention (by allowing, in particular, to increase the availability of loaded, anionic or canonical sites).

Following Watanabe's teaching, then come: - Patent EP-A-462365, which also relates to the use of a polymer (main retention agent) and an organic microparticle (secondary retention agent) , characterized in that the average size of the microparticle must be less than 750 nm, - the document WO 02/33171 proposes, in the same line as the patent cited above (p.7, 1.16+), the use in addition to the cationic organic polymer (main retention agent), an inorganic particle (secondary retention agent) and an anionic organic particle (tertiary retention agent) which must be less than 750 nm in size. This is a trial system, that is to say a system in which there are three types of retention agent, - the document WO 98/29604 describes the use of a cationic polymer ( main retention agent) followed by a branched anionic organic polymer entirely soluble in water and having an IV greater than 3 dl / g (secondary retention agent). According to this document, the use of a polymer Branched anionic as a secondary retention agent, in place of a linear polymer would improve both the formation and retention of the sheet. In addition, this document as well as EP-B-1 167 392 distinguishes the concept of branched polymer and that of crosslinked polymer. Thus, and taking into account the teachings of document EP-A-374 458, a polymer obtained by reverse phase polymerization of a water-soluble anionic monomer, in the presence of a crosslinking agent, the level of which is between approximately 6 and 25 ppm molar, in the absence of transfer agent, is necessarily reticle. As is apparent from document EP-B-1 167 392, this therefore means that at a crosslinking agent content of less than 6 ppm molar and in the absence of transfer agent, the anionic polymer obtained is branched, while in the range of 6 to 25 ppm molar, the presence of transfer agent is necessary to obtain a branched polymer. It follows that for higher levels of crosslinking agent, the polymer is necessarily crosslinked if there is no transfer agent. Another criterion allowing to distinguish the two branched / crosslinked notions would be the calculation of the delta tangent, parameter described in these documents. In practice, polymers whose delta tangent is less than 0.7 are crosslinked while they are branched in the opposite case. Thus the polymers disclosed in particular in Examples 57A to 59A of document EP-A-374 458, obtained in the presence of 6.9, 11.6 and 23.2 ppm molar of crosslinking agent respectively and in the absence of transfer agent, for which the tangent delta is respectively 0.54, 0.32 and 0.51 actually correspond to polymers that are not completely soluble in water, that is to say crosslinked polymers. It is also envisaged in document WO98 / 29604 to use the secondary retention agent in the form of a mixture of anionic polymers. In such a hypothesis, either each of the polymers reproduces the characteristics of the specific anionic polymer (branched, entirely soluble in water, viscosity greater than 3 dl / g and tangent delta greater than 0.7), or the overall mixture reproduces these characteristics. In this latter hypothesis, it is quite obvious that a globally branched mixture can only contain at least branched polymers and at most a mixture of branched polymers and linear polymers, which in turn means that a mixture of polymers crosslinked with linear polymers cannot lead to the production of a branched mixture, documents EP-A-1 228 273 and WO 01/34909 describe systems close to that mentioned in document EP-A-950 138 except that it is a trial system. More specifically, it is planned to introduce bentonite or a siliceous material, before or after the anionic polymer.

The Applicant has found that the use of a crosslinked polymer of standard size as a retention agent, optionally in admixture with an anionic or amphoteric polymer, in place of the other organic polymers of the prior art, gave very good results. at least in terms of training but also and in some cases, in terms of retention and drainage. The subject of the invention is therefore a process for manufacturing cardboard paper or the like which consists in: - firstly adding to the fibrous suspension at least one main retention agent consisting of a cationic (co) polymer, - then optionally shearing the flocs obtained, the process being characterized in that one then adds to the suspension, separately or as a mixture, in one direction or the other: at least one secondary retention agent chosen from the group comprising derivatives of silica and anionic or amphoteric organic polymers, at least one tertiary retention agent consisting of a crosslinked anionic organic polymer, of size greater than or equal to 1 micrometer and having an intrinsic viscosity less than 3 dl / g.

As we have seen from reading the prior art, those skilled in the art have long been completely dissuaded from using as a secondary retention agent a compound of large size and / or of low specific surface area because these characteristics are associated with low agglomeration power.

Those skilled in the art were dissuaded from using polymers of low molecular weight (low intrinsic viscosity) because these are known to exhibit poor performance in terms of retention and drainage. Because of this knowledge, which seems prohibitive, the risk of failure was therefore significant. This explains the fact that the technology of the invention, aiming to use in a “microparticulate” system, a crosslinked anionic organic polymer of size greater than or equal to 1 micron and of low intrinsic viscosity, was not used.

One of the merits of the invention is to have developed a process for manufacturing paper pulp, according to which there is no specific constraint linked to the process for preparing the tertiary agent, which is obtained by a conventional process for dispersion polymerization requiring no particular precaution with regard to the polymerization conditions.

For marketing reasons, it will be sought to provide the tertiary agent in its most concentrated form possible, preferably in dispersion, well known to those skilled in the art. This form having the advantage of not requiring the use of high amounts of surfactants. The tertiary agent is thus produced either in reverse or “water-in-oil” emulsion, or in aqueous dispersion also called “water-in-water emulsion”.

As already stated, the invention relates to an improved process which consists in adding, to the suspension or fibrous mass or pulp to be flocculated, as the main retention agent, at least one cationic polymer, followed by the addition, as a mixture or no, at least one secondary retention agent and at least one tertiary crosslinked anionic organic retention agent different from the secondary agent, of size greater than or equal to 1 micron and of low intrinsic viscosity (less than 3 dl / g).

The additions of the main retention agent and of the secondary and tertiary agents are separated or not by a shearing step, for example at the level of the so-called “fan pump” mixing pump. In this area, reference will be made to the description of patent USP 4, 753, 710 and to a very large prior art dealing with the point of addition of the retention agent with respect to the shearing stages existing on the machine, in particular USP 3,052,595, Unbehend, TAPPI Vol. 59, N ° 10, October 1976, Luner, 1984 Papermakers Conférence ou Tappi, April 1984, pp 95-99, Sharpe, Merck and Co Inc, Rahway, NJ, USA, around 1980, Chapter 5 "polyelectrolyte retention aids", Britt, Tappi Vol. 56, October 1973, p 46 ff. and Waech, Tappi, March 1983, pp 137, or the USP 4,388,150. The process of the invention makes it possible to obtain a markedly improved retention and this without reverse effect. Also improved, which is an additional feature of this improvement, the draining properties without deteriorating the quality of formation of the sheet.

This selection of an anionic organic particle of size greater than or equal to 1 micron, of low intrinsic and crosslinked viscosity makes it possible to achieve a level of performance unequaled until then in the paper application for the total retention and of fillers and the draining.

The process of the invention can take several embodiments.

In a first embodiment, a single secondary retention agent consisting of one or more silica derivatives, advantageously bentonite, is added to the suspension. In this case, the tertiary retention agent is added separately, at the same point or at a separate point, before or after the secondary agent.

In the following description and in the claims, the expression “a single secondary agent” means that said agent may contain several products provided that they are of the same nature. This is for example the case when the secondary agent consists of one or more silica derivatives. In a second embodiment, a single secondary retention agent consisting of one or more anionic or amphoteric organic polymers different from the tertiary retention agent is added to the suspension. In such a case, the secondary and tertiary retention agents can constitute a mixture, which is then injected at a point. This will generally be the case when the two products are in compatible physical forms.

In a third embodiment, two secondary retention agents are added to the suspension, respectively one or more silica derivatives and one or more anionic or amphoteric organic polymers different from the tertiary retention agent.

In this case and as above, essentially for reasons of simplification of the industrial process, when the tertiary agent and one of the secondary agents will be in a physical form making their mixture compatible, these will preferably be used as a mixture. Whatever solution is chosen, the objective is to reduce the number of injection pumps necessary for the process in order to simplify its implementation.

The main, secondary and tertiary retention agents will now be described in detail.

A / The main retention agent: the cationic polymer

Advantageously, in practice, the main cationic retention agent is a cationic polymer based on:

- At least one unsaturated cationic ethylene monomer, chosen from the group comprising the monomers of dialkylaminoalkyl (meth) acrylate, dialkylaminoalkyl (meth) acrylamide, diallylamine, methyldiallylamine and their quaternary ammonium or acid salts. Mention will be made in particular of dimethylaminoethyl acrylate (ADAME) and / or dimethylaminoethyl methacrylate (MADAME) quaternized or salified, dimethyldiallylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC) and / or acrylamidopropyltrimethylammonium chloride (MAPTAC).

optionally at least one nonionic monomer chosen from the group comprising acrylamide and / or methacrylamide and / or one of their substituted derivatives and or N-isopropylacrylamide and / or NN-dimethylacrylamide and / or N-vinylformamide and / or N-vinyl acetamide and / or N-vinylpyrrolidone,

- Optionally, at least one hydrophobic acrylic, allylic or vinyl monomer chosen from the group comprising racrylamide derivatives such as N-alkylacrylamide for example N-tert-butylacrylamide, octylacrylamide as well as N, N-dialkylacrylamides such as N, N-dihexylacrylamide and / or acrylic acid derivatives such as alkyl acrylates and methacrylates,

- possibly a branching / crosslinking agent.

Optionally, the main retention agent can also be of an amphoteric nature by comprising, in association with the cationic charges, anionic charges carried by anionic monomers, such as, for example, acid.

(meth) acrylic, acrylamidomethylpropane sulfonic acid, itaconic acid, maleic anhydride, maleic acid, vinyl sulfonic acid and their salts.

This polymer does not require the development of a particular polymerization process. D can be obtained by all the polymerization techniques well known to those skilled in the art: gel polymerization, precipitation polymerization, emulsion polymerization (aqueous or reverse) whether or not followed by a distillation and / or spray drying step, suspension polymerization, solution polymerization ... The branching and / or crosslinking may preferably be carried out during (or possibly after) the polymerization, in the presence of a branching / crosslinking agent and optionally a transfer agent. Below is a non-limiting list of branching agents / crosslinking agents: methylene bisacrylamide (MBA), ethylene glycol di-acrylate, polyethylene glycol dimethacrylate, diacrylamide, cyanomethylacrylate, vinyloxyethylacrylate or methacrylate, triallylamine, formaldehyde, glyoxal, glycidyl ether type compounds such as ethylene glycol diglycidyl ether, or epoxies or any other means well known to those skilled in the art allowing crosslinking.

As is well known, an optimization of the polymerization conditions (quantity of branching / crosslinking agent used, concentration of the active material in the polymerization, polymerization temperature, type and quantity of initiators, possible transfer agent) makes it possible to obtain depending on what is desired, either a branched polymer or a crosslinked polymer.

In practice, the branching / crosslinking agent is methylene bis acrylamide (MBA), introduced at a rate of five to ten thousand (5 to 10,000) parts per million by weight, preferably 5 to 1000.

Below is a non-limiting list of transfer agents: isopropyl alcohol, sodium hypophosphite, mercaptoethanol, etc.

Those skilled in the art will know how to choose the best combination based on their own knowledge and the present description, as well as the examples which follow.

The cationic polymer is characterized in that it has an IV greater than 2 dl / g and without maximum limitation. Advantageously, the quantity of cationic polymer introduced into the suspension to be flocculated is between thirty and one thousand grams of active polymer per tonne of dry paste (30 and 3000 g / t), or between 0.003 percent and 0.3 percent. It has been observed that if the amount is less than 0.003%, no significant retention is obtained. Likewise, if this amount exceeds 0.3%, no significant improvement is observed. Preferably, the quantity of main retention agent introduced is between 0.01 and 0.05 percent (0.01 and 0.05%) of the quantity of the dry paste, ie between 150 g / t and 500 g / t.

The injection or introduction of the main retention agent according to the invention is carried out before a possible shearing step, in the paper pulp (or fibrous mass to be flocculated) more or less diluted according to human practice of trade, and generally in diluted paper pulp or "thin stock", that is to say a pulp diluted to approximately 0.7 - 1.5% of solid materials such as cellulose fibers, possible fillers, and the various usual additives for papermaking.

A variant of the invention relates to the fractional introduction, part of the cationic polymer according to the invention will be introduced at the stage of preparation of the thick stock or “thick stock” at approx. 5% or more of solid matter, or even in the preparation of the thick paste before a shearing step.

B / The secondary retention agent

These agents preferably include, but are not limiting, alone or as a mixture:

- silica derivatives such as, for example, silica particles, including bentonites originating from hectorites, smectites, montmorillonites, nontronites, saponites, sauconites, hormites, attapulgites and sepiolite, derivatives of such as silicates, aluminosilicates or borosilicates, zeolites, kaolinites, or modified or unmodified colloidal silicas. This type of secondary agent is preferably introduced just upstream of the headbox, at a rate of 0.01 to 0.5 percent (0.01 to 0.5%) by dry weight relative to the weight dryness of the fibrous suspension, - anionic or amphoteric organic polymers, crosslinked, branched or linear and different from the tertiary retention agent. Advantageously, in practice, it is a (co) polymer, preferably linear, of at least one unsaturated anionic ethylenic monomer, chosen from the group comprising monomers such as, for example, (meth) acrylic acid. , tallow acrylarnidomethylpropane acid, itaconic acid, maleic anhydride, maleic acid, vinyl sulfonic acid and their salts and having a UL viscosity greater than 2, preferably greater than 4 and without maximum limitation .

This type of secondary agent is preferably introduced just upstream of the headbox, at a rate of 30 to 1000 g / t by weight of active material of the polymer relative to the dry weight of the fibrous slurry suspension. paper, preferably from 30 to 600 g / t.

C / The tertiary retention agent: the crosslinked anionic organic dispersion of size greater than or equal to 1 micron and of low intrinsic viscosity

In practice, the tertiary retention agent is an anionic organic polymer characterized in that it is crosslinked, of particle size greater than or equal to 1 micron and of low intrinsic viscosity less than 3 dl / g.

More particularly, the invention relates to dispersions of organic polymers with anionic units obtained in the form of a dispersion comprising for example from 10 to 80% by weight of at least one crosslinked anionic polymer of particle size greater than or equal to 1 micron and low intrinsic viscosity (less than 3 dl / g). By the term "dispersion" or similar terms relating to the polymer used according to the invention, the skilled person will understand that is meant either a composition comprising a continuous oil phase, a discontinuous aqueous phase and at least one emulsifier of water in oil type, or a composition comprising as a continuous phase a brine (water + salts) and at least one stabilizing agent.

The tertiary retention agents of the present invention are obtained by using, during the polymerization, a crosslinking agent, well known to those skilled in the art, and preferably in the absence of transfer agent.

More specifically, the tertiary retention agents are obtained by polymerization (or respectively copolymerization, together throughout the text and the claims: "polymerization") of at least one anionic monomer and optionally other nonionic or cationic monomers, in the presence of 'a crosslinking agent. They must have an overall anionic charge.

Those skilled in the art will be able to appreciate, from their own knowledge or using routine tests, the polymerization conditions to be used to obtain a final polymer having an intrinsic viscosity as required.

In addition, it is also possible to concentrate the polymer by all the known techniques, such as for example by azeotropic distillation, precipitation, spray drying ...

According to the present invention, it has been surprisingly discovered that a new family of anionic organic dispersions makes it possible to achieve a level of performance hitherto unequaled for retention and drainage.

According to a preferred embodiment, the copolymer is obtained from - 10-100 mol% of at least one monomer having an anionic charge, - 0-90 mol% of at least one monomer having a neutral and / or cationic charge, - the polymerization concentration is preferably between 20 and 50%, - and a crosslinking agent. Preferably the level of crosslinking agent is greater than 5 ppm, advantageously 15 ppm.

The following is a non-limiting list of the monomers which can be used: a / the unsaturated anionic ethylenic monomers having a carboxylic function (ex: acrylic acid, methacrylic acid, and their salts, etc.), having a sulphonic acid function (ex : 2-acrylamido-2- methylpropane sulfonic acid (AMPS) and their salts ...) ... b / non-ionic monomers: acrylamide, methacrylamide, N- isopropylacrylamide, NN dimethylacrylamide, N-vinylformamide, N-vinyl acetamide, N-vinyl pyrrolidone, vinylacetate, acrylate esters, allyl alcohol ... and or cationic monomers: mention will be made, in particular and without limitation, of dimethylaminoethyl acrylate (ADAME) and / or dimethylaminoethyl methacrylate (MADAME) quaternized or salified, dimethyldiallylammonium chloride (DADMAC), acrylamide-propyltrimethylammonium chloride (APTAC) and / or methacrylamidopropyltrimethylammonium chloride (MAPTAC).

It is important to note that, in combination with these monomers, it is also possible to use water-insoluble monomers such as acrylic, allylic or vinyl monomers comprising a hydrophobic group. When they are used, these monomers will be used in very small amounts, less than 20 mol%, preferably less than 10 mol%, and they will preferably be chosen from the group comprising acrylamide derivatives like N-alkylacrylamide for example N-tert-butylacrylamide, octylacrylamide as well as N, N-dialkylacrylamides like N, N-dihexylacrylamide ... acrylic acid derivatives like alkyl acrylates and methacrylates ...

The following is a non-limiting list of crosslinkers: methylene bisacrylamide (MBA), ethylene glycol di-acrylate, polyethylene glycol dimethacrylate, diacrylamide, cyanomethylacrylate, vinyloxyethylacrylate or methacrylate, triallylamine, formaldehyde, glyox compounds of the glycidyl ether type such as ethylene glycol diglycidyl ether, or epoxies or any other means well known to those skilled in the art allowing crosslinking.

The tertiary retention agent is introduced into the suspension, very preferably at a rate of 30 g / t to 10000 g by weight of active material (polymer) relative to the dry weight of the fibrous suspension, preferably 30g t at 600g / t.

As already indicated above, the polymer particle can be used either in the form of a dispersion, dissolved or "inverted" in water, or in the form of a solution in water of the powder obtained by drying. of said dispersion.

In an advantageous embodiment, a coagulant is added to the fibrous suspension, prior to the addition of the main retention agent.

As those skilled in the art are well aware, the use of this type of product makes it possible to improve the retention performance even more at dosages (in active ingredients) of 0.01 to 10 kg t and preferably between 0, 03 and 3 kg / t. Mention will be made in particular, and by way of examples, of the coagulants chosen from the group comprising mineral coagulants such as aluminum polychloride (PAC), alumina sulphate, aluminum polychlorosulphate, etc., or coagulants. organic including - polymers based on diallyldimethyl ammonium chloride (DADMAC), - quaternary polyamines manufactured by condensation of a primary or secondary amine on epichlorohydrin, polymers having vinylamine type functions or dicyandiamide type resins ... These coagulants can be used alone or as a mixture and are preferably added in thick paste .

It will be noted that the addition of the secondary and tertiary retention agents can be carried out in any order of introduction, mixed or not.

The invention also relates to the use of a crosslinked anionic organic polymer, of size greater than or equal to 1 micron and having an intrinsic viscosity of less than 3 dl / g optionally in mixture with one or more anionic or amphoteric organic polymers different from said polymer anionic organic crosslinked as a retention agent in a process for making paper, cardboard or the like.

In a particular case, it also relates to a tertiary or secondary retention agent consisting of at least one crosslinked anionic organic polymer, of size greater than or equal to 1 micrometer and having an intrinsic viscosity of less than 3 dl / g, possibly in blend with one or more linear anionic organic polymers.

The following examples illustrate the invention without, however, limiting its scope.

1. Method for measuring particle size and intrinsic viscosity:

a / The particle size measurements were carried out using a HORIBA LA-900 series device by laser light diffraction. b / The intrinsic viscosity measurements were carried out according to the method as defined in standard ISO 1628/1 - October 1988 "Guiding principles for the standardization of the methods for determining the viscosity index and the viscosity limit index polymers in dilute solution

c / UL viscosity measurement: the UL viscosity is measured using a Brookfield viscometer of LVT type fitted with a UL adapter whose module rotates at 60 revolutions / minute (0.1% of polymer by weight in a 1M sodium chloride saline).

d / Training measures: - Table 3: visual evaluation (Frm). Scale of leaf formation obtained: 1: excellent, homogeneous; 2: good, melted; 3: medium, cloudy; 4: bad, lumpy. - Table 6: measurement of the formation index (LT index) using a 2-dimensional epairmeter: the lower the value, the better the formation of the sheet.

2. Presentation of polymers

A The main retention agent: the cationic polymer

In the following examples, the following polymers are used:

With: - AM: acrylamide - ADC: dimethylaminoethyl acrylate quaternized by methyl chloride - APTAC: acrylamidopropyltrimethylammonium chloride - Branching / crosslinking agent: methylene Bis acrylamide - Ionic regain: RI = ((XY) / Y) x 100 with X: ionicity after shear in meq / g Y: ionicity before shear in meq / g.

B / The tertiary retention agent: the dispersion of crosslinked anionic organic polymer

With the exception of E3, all the particles were prepared by the reverse emulsion polymerization technique on a 30 mol% acrylamide and 70 mol% ammonium acrylate basis.

* E3 is produced in aqueous dispersion (“water in water” emulsion) 50 mol% of acrylamide and 50 mol% of acrylic acid.

Examples E relate to the tertiary retention agents of the invention. Examples X are counterexamples.

3. Emulsion test procedure

The various tests were carried out in a “Britt Jar” type container and with a paste consisting of a mixture of:

- 70% bleached hardwood kraft - 10% bleached softwood kraft

- 20% mechanical pulp - 20% natural calcium carbonate.

- bonding in a neutral medium with 2% of a dimeric ketene alkyl emulsion. The paste used is diluted to a consistency of 1.5%. 2.24g dry paste is taken, i.e. 149g 1.5% paste and then diluted to 0.4% with clear water. A volume of 560 ml of this diluted paste is introduced into the plexiglass cylinder of the automated form and the sequence is started.

Britt Jar sequence at 1000 rpm (revolutions per minute): T = 0s: Possible addition of the coagulant T = 70s: Addition of the main retention agent T = 80s: Addition of the secondary retention agent T = 85s: Addition of the tertiary retention officer

T = 90s: Elimination of the first 20 ml corresponding to the dead volume, then sampling of 100 ml exactly for filtration for the britt jar test. The following analyzes are then carried out:

-% FPAR: first pass ash retention in percentage -% FPR: first pass retention in percentage (total retention)

- CSF: measurement of the degree of drainability of the dough (TAPPI T 227OM-94 standard). For each of these analyzes, the highest values correspond to the best performance.

4. results

Tab.l: comparison of different retention systems

PL: linear anionic copolymer (30 mol% sodium acrylate, 70 mol% acrylamide): UL viscosity: 8.2 (IV = 25).

The coagulant used in Table 1 is a poly aluminum chloride (dosage: 1 kg / T).

Comments on the results: For a given main retention agent, the use in combination with a secondary retention agent of a tertiary retention agent of the invention improves the efficiency of the papermaking process overall and significantly, in retention and draining. We note in particular that: - the association of a tertiary agent of the invention with bentonite (test 8 / tests 2, 5, 6 and 7) makes it possible to obtain performances hitherto unequaled - likewise, l association of a tertiary agent of the invention with a colloidal silica (9/3) or with an organic microparticle such as Polyflex CP3 (10/4) results in higher retention and drainage levels than comparable systems . Tests 5, 6, 7 and 8 demonstrate the essential role played by the criteria of dispersion size and intrinsic viscosity.

Tab. 2: Comparative study linked to the nature of tertiary retention agents

Comments on the results: The tests demonstrate that the performance of the particles is not correlable to their size, which goes against the knowledge and expectations of those skilled in the art. Only the particles according to the invention, which combine both a size greater than 1 micron, a degree of crosslinking and an intrinsic viscosity less than 3, make it possible to exhibit greater efficiency with respect to the total retention and the retention of charges and to draining. Tab. 3: Comparative study linked to the dosage of secondary retention agents

Comments on the results: The use of an organic dispersion according to the invention as a tertiary retention agent makes it possible to reduce the dosage of the secondary retention agent without affecting the performance of the process.

In addition, and quite surprisingly, the formation of the sheet is not altered and is even in some cases improved, by the use of a tertiary agent of the invention, despite an increase in the performance of the sheet. 'draining (which most often occurs at the expense of leaf formation).

Tab. 4: Comparative study linked to the nature of the main retention agent

Comments on the results:

The organic particle according to the invention used as a tertiary retention agent is not significantly affected by the nature of the main retention agent (8, 21-23; 24-26; 27). The order of introduction of secondary and tertiary retention agents is also not a criterion for distinction (28).

In conclusion, despite a low intrinsic viscosity and a high particle size, greater than 1 micron, it can be seen that, in combination with another secondary retention agent, the combination according to the invention provides a net gain in charge retention and in total retention and turns out to be superior to preexisting systems.

Tab. 5: Comparative study linked to the nature of the coagulant

*: epichlorohydrin resin + dimethylamine #: DADMAC homopolymer Comments of the results: For a given retention system of the invention, the use of a coagulant improves the overall efficiency of the paper-making process. Tab. 6: Comparative study linked to the use of several secondary agents

We observe that :

- Only the use of the polymers of the invention makes it possible to obtain both high performance both in retention and in formation

the association of the crosslinked polymers of the invention with a second secondary retention agent of the linear anionic polymer type, in addition to bentonite, allows a significant improvement in the retention with the simple counterpart a very limited and industrially acceptable deterioration of the leaf formation.

This makes it possible to offer a flexible multi-component retention system that can be adjusted to the paper manufacturer's objectives (productivity performance and production quality).

It will be noted that the branched polymer (test 40) used as a tertiary agent exhibits, as indisputably demonstrated in the preamble to this application, characteristics different from those of a mixture of linear polymer + crosslinked polymer and leads to inferior results.

Claims

1 / Process for manufacturing cardboard paper or the like which consists: - first of all in adding to the fibrous suspension at least one main retention agent consisting of a cationic (co) polymer, - then optionally in shearing the flocs obtained, characterized in that the suspension is then added, separately or as a mixture, in one direction or the other: at least one secondary retention agent chosen from the group comprising silica derivatives and anionic or amphoteric organic polymers , at least one tertiary retention agent consisting of a crosslinked anionic organic polymer, of size greater than or equal to 1 micrometer and having an intrinsic viscosity of less than 3 dl / g.

2 / A method according to claim 1, characterized in that one adds to the suspension a single secondary retention agent consisting of one or more silica derivatives.

3 / A method according to claim 1, characterized in that added to the suspension a single secondary retention agent consisting of one or more anionic or amphoteric organic polymers, different from the tertiary retention agent.

4 / A method according to claim 1, characterized in that two secondary retention agents are added to the suspension, respectively one or more silica derivatives and one or more anionic or amphoteric organic polymers, different from the tertiary retention agent.

5 / Method according to one of claims 3 or 4, characterized in that the anionic or amphoteric organic polymers are injected in mixture with the tertiary retention agent. 6 / A method according to claim 1, characterized in that: - the tertiary retention agent is prepared in the form of a dispersion and is introduced into the paper pulp at a concentration of 30 to 1000 g / t by weight of active material of the polymer relative to the dry weight of the fibrous suspension of paper pulp, preferably from 30 to 600 g / t, and in that; the secondary retention agent is: a silica derivative chosen from the group comprising silica particles, including bentonites originating from hectorites, smectites, montmorillonites, nontronites, saponites, sauconites, hormites, attapulgites and sepiolites, derivatives of the silicate, aluminosilicate or borosilicate type, zeolites, kaolinites, and colloidal silicas, modified or not, and is introduced at a rate of 0.01 to 0.5 percent (0.01 to 0.5%) by dry weight relative to the dry weight of the fibrous suspension, - and / or an anionic or amphoteric organic polymer introduced, at a rate of 30 to 1000 g / t by weight of active material of the polymer relative to the weight dryness of the fibrous suspension, preferably from 30 to 600 g / t.

Il Method according to claim 1, characterized in that the second secondary retention agent is a linear anionic organic polymer.

8 / A method according to claim 7, characterized in that the linear anionic organic polymer is a (co) polymer of at least one unsaturated anionic ethylenic monomer, chosen from the group comprising monomers such as (meth) acrylic acid , acrylamidomethylpropane sulfonic acid, itaconic acid, maleic anhydride, maleic acid, vinyl sulfonic acid and their salts and having a UL viscosity greater than 2, preferably greater than 4.

9 / A method according to claim 1, characterized in that the main retention agent is a cationic polymer based: at least one cationic ethylenic unsaturated monomer, chosen from the group comprising monomers of dialkylaminoalkyl (meth) acrylate type , dialkylaminoalkyl (meth) acrylamide, diallylamine, methyldiallylamine and their quaternary ammonium or acid salts, and optionally, at least one nonionic monomer chosen from the group comprising acrylamide and / or methacrylamide and / or N-isopropylacrylamide and / or NN-dimethylacrylamide and / or N-vinylformamide and / or N-vinyl acetamide and / or N-vinylpyrrolidone, and / or anionic chosen from the group comprising (meth) acrylic acid, acrylamidomethylpropane sulfonic acid, itaconic acid, maleic anhydride, maleic acid, vinyl sulfonic acid and their salts; optionally, at least one acrylic, allylic or vinyl hydrophobic monomer chosen from the group comprising acrylamide derivatives such as N-alkylacrylamide for example N-tert-butylacrylamide, octylacrylamide as well as N, N-dialkylacrylamides such as N, N-dihexylacrylamide and / or acrylic acid derivatives such as alkyl acrylates and methacrylates, - and optionally a branching / crosslinking agent.

10 / A method according to claim 1, characterized in that the main retention agent has an IV greater than 2 dl / g.

11 / A method according to claim 1, characterized in that the tertiary retention agent is a polymer prepared based on: at least one unsaturated anionic ethylenic monomer, chosen from the group comprising the monomers having a carboxylic function and their salts, acrylic acid, methacrylic acid, and / or the monomers having a sulfonic acid function and their salts including 2-acrylamido-2-methylpropane sulfonic acid, optionally, of at least one nonionic monomer chosen from the group comprising acrylamide and / or methacrylamide and or N-isopropylacrylamide and / or NN-dimethylacrylamide and / or N-vinylformamide and / or N-vinyl acetamide and or N-vinylpyrrolidone. - and a crosslinking agent. 12 / A method according to any one of claims 9 or \, characterized in that the branching / crosslinking agent is chosen from the group comprising methylene bisacrylamide (MBA), ethylene glycol di-acrylate, polyethylene glycol dimethacrylate , diacrylamide, cyanomethylacrylate, vinyloxyethylacrylate or methacrylate, triallylamine, formaldehyde, glyoxal, glycidylether compounds such as ethylene glycol diglycidylether, or epoxies.

13 / A method according to claim 11, characterized in that the branching / crosslinking agent chosen is MBA and is introduced at a concentration greater than 5 ppm (parts per million) by weight of monomers and preferably greater than or equal to 15 ppm.

14 / A method according to claim 1, characterized in that the secondary retention agent is a semi-sodium bentonite, used in an amount of 0.1 to 0.5% by dry weight relative to the dry weight of the fibrous suspension.

15 / A method according to claim 1, characterized in that the amount of main retention agent introduced is between 0.003 and 0.3% by weight of active material of the polymer relative to the dry paste, preferably between 0.01 and 0.05%.

16 / A method according to claim 1, characterized in that prior to the addition of the main retention agent, a coagulant is added to the suspension.

17 / A method according to claim 16, characterized in that the coagulant is chosen from the group comprising poly aluminum chloride (PAC), alumina sulfate, poly aluminum chlorosulfate ..., or organic coagulants including: polymers based on diallyldimethyl ammonium chloride (DADMAC), quaternary polyamines manufactured by condensation of a primary or secondary amine on epichlorohydrin, polymers having functions of vinylamine type or resins of dicyandiamide type. 18 / Use of a crosslinked anionic organic polymer, of size greater than or equal to 1 micron and having an intrinsic viscosity of less than 3 dl / g optionally in mixture with one or more anionic organic polymers or amphoteric different from said crosslinked anionic organic polymer as agent retention in a process for manufacturing paper, cardboard or the like.

19 / Tertiary or secondary retention agent consisting of at least one crosslinked anionic organic polymer, of size greater than or equal to 1 micrometer and having an intrinsic viscosity of less than 3 dl / g, optionally in admixture with one or more linear anionic organic polymers .