EP1092064B2 - Method for making paper and cardboard - Google Patents

Abstract

The invention concerns an improved method for making paper which consists in using as main retention agent a branched polymer prepared in invert emulsion and bentonite as secondary retention agent (dual type system). The two additions are separated by a step for shearing the fibrous suspension (or mass). The invention enables to obtain a highly improved retention and also highly improved dewatering. Moreover, it enables to reduce the bentonite content in the white water.

Description

The present invention relates to the technical sector of papermaking.

The invention relates to a method for the production of paper or cardboard retention, and other properties, improved.

• l'augmentation de la production et la diminution des coûts de fabrication : économie énergétique, marche plus régulière de la machine, rendement plus élevé en fibres, fines, charges et de produits d'ennoblissement anioniques, plus faible acidité dans le circuit liée a une diminution de l'utilisation de sulfate d'alumine et donc amoindrissement des problèmes de corrosion ;
• l'amélioration de la qualité : meilleure formation et meilleur épair ; amélioration du taux d'humidité de la feuille, de l'opacité, du lisse, du pouvoir absorbant et diminution de la porosité du papier.

In the manufacture of paper, cardboard or the like, it is well known to introduce into the paste retention agents whose function is to retain a maximum of fines and fillers in the sheet. The beneficial effects that result from the use of a retention agent are essentially:

• increased production and lower manufacturing costs: energy saving, more regular machine operation, higher yield of fibers, fines, fillers and anionic finishing products, lower acidity in the circuit related to reduction in the use of alumina sulphate and thus lessening of corrosion problems;
• quality improvement: better training and better looking; improvement of the leaf moisture content, opacity, smoothness, absorbency and decrease of paper porosity.

For a long time, it has been proposed to add bentonite to the paste, which may optionally be added to other mineral products, such as aluminum sulphates, or even synthetic polymers, in particular polyethylene imine (see for example documents DE-A-2,262,906 and US-A-2,368,635 ).

In the document US-A-3,052,595 it has been proposed to associate bentonite with a polyacrylamide of essential linear characteristic. This process has been in competition with systems that are easier to implement while being equally efficient. In addition, even with current linear polyacrylamides, the retention capacity is still insufficient.

In the document EP-A-0 017 353 It has been proposed, for the retention of slightly loaded pastes (at most 5% fillers) to associate with the bentonite a nonionic linear copolyacrylamide weakly anionic. This process has hardly developed, because these polymers are relatively poor in retention, especially filled pasta, probably as a result of insufficient synergy between these copolymers and bentonite which has little tendency to recoaguler.

In the document EP-A-0 235 893 it has been proposed to use cationic polyacrylamides with a molecular weight greater than one million, of thirty million or more, essentially linear. In this way we obtain a retention effect certainly satisfactory, but still considered insufficient in the paper application, because, the use of bentonite causing difficulties during the subsequent treatment of the effluents at the output of the machine, the users do not select this system that 'in case of significant benefits.

In notes presented at the course of lectures in Seattle, October 11-13, 1989, and published under the title "Supercoagulation in the control of wet end polymer by polymer and activated bentonite", R. Kajasvirta described the mechanism of the supercoagulation of the activated bentonite in the presence of a cationic copolyacrylamide, without specifying the exact nature thereof. This process has the same disadvantages as before.

Finally, EP 0 574 335 a a major improvement by proposing the use of polymers (especially polyacrylamides) branched in the form of a powder.

The invention overcomes the disadvantages mentioned above.

It relates to an improved process of the type in question, which consists in adding, to the suspension or fibrous mass or paper stock to be flocculated, as main retention agent, an agent which consists of, or comprises, a branched polyacrylamide according to claim 1 and as described has been prepared in inverse emulsion or water-in-oil, and bentonite as second retention agent (so-called "dual" system, also called "microparticulate").

By the term "is in inverse emulsion" or similar terms, referring to the polymer used (ie as injected or introduced into the flocculant paste) according to the invention, the skilled person will understand that we designate the water-in-oil inverse emulsion which is dissolved in the water before its injection or its introduction into the mass or paste to be flocculated (this dissolution in the water causes what is called the "inversion" of the initial water-in-oil emulsion, these processes are well known to those skilled in the art).

The additions of the polymer and of the bentonite are separated by a shearing step, for example at the so-called fan pump. In this area reference will be made to the description of the USP Patent 4, 753, 710 as well as a very wide prior art dealing with the point of addition of the retention agent with respect to the shearing steps existing on the machine, in particular USP 3,052,595 , Unbehend, TAPPI Vol. 59, No. 10, October 1976 , Luner, 1984 Papermakers Conference or 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 (Eka Nobel)

We will also refer to USP Patent 4,753,710 , for all that relates to the generalities concerning the manufacture of paper, the usual additives used, and similar details.

It is possible to replace the bentonite, as a secondary retention agent, with a kaolin as described in the application for patent FR 95 13051 of the Applicant, this kaolin being preferentially pretreated with a polyelectrolyte. The skilled person can refer to this patent FR 95 13051 .

This method makes it possible to obtain a markedly improved retention of fines and fillers without any reverse effect. An additional feature of this improvement is also improved the dewatering properties.

The branched polyacrylamide (or more generally the branched (co) polymer) is introduced into the suspension, very preferably, in the form of a water-in-oil inverse emulsion, at a rate of 0.03 to one per thousand. (0.03 to 1% o, ie 30 to 1000 g / t) by weight of active ingredient (polymer) relative to the dry weight of the fibrous suspension, preferably from 0.15 to 0.5 per thousand, ie 150 at 500 g / t.

In a manner known to those skilled in the art, the inverse polymer emulsion is diluted with water and inverted (solubilized) by this dilution before its introduction, as described above.

This selection of the inverse emulsion form allows, in the paper application for the retention of fillers and fines, to reach a level of performance unequaled until now. The use of branched polymers makes it possible to better retain the bentonite on the sheet, as described in the patent. EP 574,335 above mentioned and thereby limit its negative effects on the subsequent treatment of the machine outlet effluents. In addition, the choice of this branched polyacrylamide increases the binding power of the bentonite on the sheet, therefore results in synergy, thus recoagulation that reduces the content of bentonite in white water.

It will be understood that it is essential according to the invention that the polymer is prepared by water-in-oil inverse emulsion polymerization. On the other hand, this polymer can then be used (ie injected or introduced into the mass or paste to be flocculated) either in the form - preferably - of this inverse emulsion after its dissolution in water, or in the form of a powder obtained by drying (in particular by spray-drying or "spray-drying") of the inverse emulsion of the polymerization, and then redissolving this powder in water, for example at a concentration of the order of 5 g of active polymer / liter, the solution thus obtained being then injected into the dough at substantially the same polymer dosages.

The branched (co) polyacrylamide is a cationic copolymer of acrylamide and an unsaturated cationic ethylenic monomer selected from the group comprising dimethylaminoethyl acrylate (ADAME), dimethylaminoethyl methacrylate (MADAME), quaternized or salified by different quaternizing acids and agents, benzyl chloride, methyl chloride, alkyl- or aryl chlorides, dimethyl sulphate, dimethyldiallylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC), and methacrylamidopropyltrimethylammonium chloride (MAPTAC),

In known manner, this copolymer is branched by a branching agent consisting of a compound having at least two reactive groups selected from the group comprising double bonds, aldehyde bonds or epoxy bonds. These compounds are well known and are described for example in the document EP-A-0 374 458 (see also the document FR-A-2,589,145 of the Applicant).

As is known, a branched polymer is a polymer which has branches, groups or branches on the chain which are generally arranged in a plane and not in the three directions, unlike a crosslinked polymer ( "Cross-linked"); such branched, high molecular weight polymers are well known as flocculants. These branched polyacrylamides are distinguished from the crosslinked polyacrylamides in that in the latter, the groups are arranged three-dimensionally to give substantially insoluble products of infinite molecular weight.

The branching may preferably be carried out during (or possibly after) the polymerization, for example by reaction of two soluble polymers having counterions, or by reaction with formaldehyde or a polyvalent metal compound. Often, the branching takes place during the polymerization by addition of a branching agent, and this solution will be clearly preferred according to the invention. These branching polymerization processes are well known.

Branching agents which can be incorporated include ionic branching agents such as polyvalent metal salts, formaldehyde, glyoxal, or preferably covalent crosslinking agents which will copolymerize with the monomers, preferably diethylenically unsaturated monomers (such as the family of diacrylate esters such as PEG polyethylene glycol diacrylates) or polyethylene, of the type conventionally used for the crosslinking of water-soluble polymers, and in particular methylenebisacrylamide (MBA) or any of the other known acrylic branching agents.

These agents are often identical to the crosslinking agents, but the crosslinking can be avoided, when it is desired to obtain a branched and not crosslinked polymer, by an optimization of the polymerization conditions such as concentration during the polymerization, type and amount of polymerization. transfer agent, temperature, type and amount of initiators, and the like.

In practice, the branching agent is methylenebisacrylamide (MBA), introduced at a rate of five to two hundred (5 to 200) moles per million moles of monomers, preferably 5 to 50 moles.

Advantageously, the amount of branched polyacrylamide introduced into the suspension to be flocculated is between thirty and thousand grams of active polymer / tonne of dry pulp (30 and 1000 g / t), or between 0.03 per thousand and one per thousand, of preferably from 150 to 500 g / t; it has been observed that if the amount is less than 0.03% o (0.03 per thousand), no significant retention is obtained; likewise, if this quantity exceeds 1% o (1 per thousand), no proportional improvement is observed; however, unlike linear cationic polyacrylamides, as described in the documents EP-A-0 017 353 and EP 0 235 893 referred to in the preamble, there is no reverse effect of dispersion by recirculation in the closed circuits of the excess polymer not retained on the sheet. Preferably, the amount of branched polyacrylamide introduced is between 0.15 and 0.5 per thousand (0.15 and 0.5% o) of the quantity of the dry pulp, ie between 150 g / t and 500 g / t.

As already stated, it is important that the branched polymer be prepared as an inverse emulsion (water-in-oil) to achieve the improvement of the invention. Such emulsions and their method of preparation are well known to those skilled in the art.

This approach was doomed in the EP 0 574 335 mentioned above, where it was stated that if a branched emulsion polymer is used, the essential presence in these emulsions of surfactants promotes the formation of foams during the manufacture of the paper and the appearance of disparities physical properties of the finished paper (modification of the absorbance at places where a part of the oil phase of the emulsion is retained on the sheet).

It was therefore not obvious to consider a fortiori the inverse emulsions water in oil whose oil content is obviously high.

The invention was all the more difficult to realize that it is important to remain in the field of branched polymers and not to go into the field of crosslinked polymers. However, we know that technically, especially at the scale of industrial production, the border between the two zones is very easily crossed, in fact irreversibly. As the branching zone is very narrow, the difficulty of developing the invention is measured, and it is the Claimant's merit that it has tackled the use of this technology in the field of manufacturing the paper, which poses particular problems and presents very stringent quality requirements.

The risk of failure was all the more important, which may explain the fact that this technology has not been used, that cross-linked emulsions are not known to provide a particular advantage in paper.

Compared with linear polymers, the branched powdered polymers of the aforementioned EP 0 574 335 had already made significant progress with regard to the properties and the papermaking process. The improvement was of the order of 20 to 40% depending on the properties.

With the present branched emulsions, an improvement of the order of 50 to 60% is reached, which was not foreseeable since it was known, on the other hand, that the crosslinked products did not work.

In this regard, the tests 11 (R52) - according to the invention and 13 (FO 4198) - according to the patent EP 0 574 335 .

According to the invention, a "moderately branched" polymer, for example 10 ppm branching with respect to the active material, will be used in a preferred manner, but not limited to.

As already indicated above, it is possible to use the polymer either in the form of its synthetic inverse emulsion, dissolved or "inverted" in water, or in the form of the solution in the water of the powder obtained by drying the said synthetic emulsion, in particular by spray drying. Spray drying is a method also known to those skilled in the art. Refer to the tests below to verify that the results are comparable.

Bentonite, also called "swelling smectic clay", of the montmorillonite family, is well known and there is no need to describe it here in detail; these compounds, formed of microcrystallites, have on the surface sites with a high cation exchange capacity that can retain water (see for example document US-A-4,305,781 , which corresponds to the document EP-A-0 017 353 , mentioned above, and the FR-A-2,283,102 ).

A semi-sodium bentonite, which is introduced just upstream of the headbox, is preferably used at a rate of 0.1 to 0.5 percent (0.1 to 0.5%) of the dry weight of the fibrous suspension.

As filler, use may be kaolins, ground "GCC" or CaCO3, precipitated CaCO3 or "PCC", and the like.

Injection or introduction of the branched polymer in inverse emulsion is carried out before a shearing step in the paper pulp (or fibrous mass to be flocculated) more or less diluted according to the practice of the person skilled in the art, and generally in the pulp. thin paper, ie a pulp diluted to about 0.7 - 1.5% solids such as cellulose fibers, optional fillers, and the various conventional papermaking additives.

According to a variant of the invention, fractionally introduced, will be introduced a portion of the emulsion branched polymer, according to the invention, at the stage of preparation of the thick paste or "thick stock" to approx. 5% or more solids, or even in the preparation of the thick slurry before a shear step.

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

EXAMPLE 1 Manufacture of a branched polymer in the form of a water-in-oil inverse emulsion

1. a) - Phase organique
   • 252 g d'Exxsol D100
   • 18 g de Span 80
   • 4 g d'Hypermer 2296
2. b) - Dans un bêcher B, on prépare la phase aqueuse de l'émulsion à réaliser en mélangeant :
   • 385 g d'acrylamide à 50 %
   • 73 g de chlorure d'acrylate éthyl triméthyl ammonium 80 %
   • 268 g d'eau
   • 0,5 g de méthylène bis acrylamide à 0,25 %
   • 0,75 ml du bromate de sodium à 50 g l^-1
   • 20 ppm d'hypophosphite de sodium par rapport à la matière active
   • 0,29 ml de Versenex à 200 g l^-1

On mélange le contenu de B dans A sans agitation. Après le mélange des phases, on cisaille l'émulsion au mixer (mélangeur) pendant 1 minute afin de créer l'émulsion inverse. L'émulsion est alors dégazée par un bullage d'azote puis après 20 minutes, l'addition progressive du métabisulfite entraîne l'initiation puis la polymérisation.
La réaction terminée, on effectue un « burn out » (traitement au métabisulfite) afin de diminuer la teneur en monomère libre.
L'émulsion est alors incorporée avec son tensio-actif inverse afin de libérer par la suite le polymère en phase aqueuse. Il sera nécessaire d'introduire de 2 à 2,4 % d'alcool éthoxylé. La viscosité Brookfield standard dudit polymère sera de 4,36 cps (viscosité prise à 0,1 % dans une solution 1 M NaCl à 25°C à soixante tours par minute)In a reactor A, the constituents of the organic phase of the emulsion to be synthesized are mixed at ambient temperature.

1. a) - Organic phase
   • 252 g of Exxsol D100
   • 18 g of Span 80
   • 4 g of Hypermer 2296
2. b) - In a beaker B, the aqueous phase of the emulsion to be prepared is prepared by mixing:
   • 385 g of 50% acrylamide
   • 73 g of acrylate ethyl trimethyl ammonium chloride 80%
   • 268 g of water
   • 0.5 g of 0.25% methylenebisacrylamide
   • 0.75 ml of sodium bromate at 50 gl ^-1
   • 20 ppm sodium hypophosphite relative to the active ingredient
   • 0.29 ml of Versenex at 200 gl ^-1

The contents of B are mixed in A without stirring. After the mixing of the phases, the emulsion is shredded (mixer) for 1 minute in order to create the inverse emulsion. The emulsion is then degassed by bubbling nitrogen and after 20 minutes, the gradual addition of metabisulfite leads to initiation and then polymerization.
When the reaction is complete, a "burn out" (metabisulphite treatment) is performed in order to reduce the content of free monomer.
The emulsion is then incorporated with its inverse surfactant in order subsequently to release the polymer in the aqueous phase. It will be necessary to introduce 2 to 2.4% ethoxylated alcohol. The standard Brookfield viscosity of said polymer will be 4.36 cps (viscosity taken at 0.1% in a 1 M NaCl solution at 25 ° C. at sixty revolutions per minute).

According to a variation of the MBA content of 5 to 20 ppm, the UL viscosity results are as follows:

Table of Example 1:

Trial MBA ppm NaH2PO2 ppm (*) UL [mPa · s] Viscosity RI (1) (%) RIV (2) (%) State R 52 5 20 4.56 12.8 0 ramified R 102 10 20 3.74 28.9 0 ramified SD 102 10 20 3.70 26 0 ramified X 104 10 40 2.31 45 50 Reticle X 204 20 40 2.61 54.8 50 Reticle EM 140 CT 0 15 4.5 0 <0 Linear EM 140 L 0 30 3.82 0 0 Linear EM 140 LH 0 40 3.16 0 <0 Linear EM 140 BD 5 0 1.85 80 100 Reticle FO 4198 5 20 3.2 5 <0 ramified FO 4198: branched powder containing 20 ppm transfer agent and 5 ppm branching agent (according to EP 0 574 335 ).
(*): sodium hypophosphite, transfer agent. (1): ionic increase in%. (2): intrinsic viscosity increase in%.
EM140CT: standard emulsion of very high molecular weight containing no branching agent. EM140L: standard high molecular weight emulsion containing no branching agent.
EM140LH: Medium molecular weight emulsion containing no branching agent.
EM140BD: crosslinked emulsion containing no transfer agent and 5 ppm crosslinking agent.
SD 102: spray-dried emulsion R 102, and powder obtained dissolved in water at 5 g of active polymer / liter.

It is noted that the linear products do not develop an ionic surgeI and their intrinsic viscosity IV decrease under the effect of a high shear (two of the values of IV are negative); branched emulsion products develop ionic RI but not IV (values <= 0); cross-linked products develop a strong ionic surge and a very strong IV boost.

Definitions of ionic regains and regains of intrinsic viscosity:

$$\mathrm{Ionic\; Regain\; RI}=\left(\mathrm{X}-\mathrm{Y}\right)/\mathrm{Y}\times 100$$

with X:

ionicity after shearing in meq / g.

Y:

ionicity before shearing in meq / g.

$$\mathrm{R\; IV\; intrinsic\; viscosity\; boost}=\left(\mathrm{V}1-\mathrm{V}2\right)/\mathrm{V}2\times 100$$

with V1:

intrinsic viscosity after shear in dl / g

V2:

intrinsic viscosity before shear in dl / g

Some of the emulsions mentioned above will be the subject of an efficiency study in draining retention on an "automatic retention form" of the Center Technique du Papier.

Procedure for testing emulsions Paste used :

70% Bleached Hardwood Kraft Blend KF 10% bleached softwood kraft KR 20% of mechanical pulp PM 20% natural calcium carbonate.

Bonding in a neutral medium with 2% of a ketene dimeric emulsion.

The paste used is diluted to a consistency of 1.5%. 2.24 g of pulp are taken, ie 149 g of pulp at 150% and then diluted to 0.4% with clear water.

• t = 0 s, démarrage agitation à 1500 rpm.
• t = 10 s, addition du polymère.
• t = 60 s, réduction automatique à 1000 rpm et addition si nécessaire de la bentonite.
• t = 75 s, arrêt de l'agitation, formation de la feuille avec le vide sous toile puis récupération des eaux blanches.

The volume of 560 ml is introduced into the plexiglass cylinder of the automated form and the sequence is started.

• t = 0 s, starting agitation at 1500 rpm.
• t = 10 s, addition of the polymer.
• t = 60 s, automatic reduction to 1000 rpm and addition of bentonite if necessary.
• t = 75 s, stopping the agitation, forming the sheet with the vacuum under canvas then recovery of white water.

• mesure de la turbidité des eaux sans toile.
• dilution d'un bêcher de pâte épaisse pour une nouvelle feuille avec les eaux sous toiles recueillies.
• séchage de la feuille dite 1 ère passe.
• démarrage d'une nouvelle séquence afin de réaliser la feuille dite 2nde passe.

The following operations are then performed:

• measurement of the turbidity of water without canvas.
• dilution of a beaker of thick paste for a new leaf with the collected underwater.
• drying of the so-called first pass sheet.
• starting a new sequence in order to make the sheet known as the 2nd pass.

After 3 passes, we change products to test.

• mesure des matières en suspension des eaux sous toile (Norme TAPPI : T 656 cm / 83 )
• mesure des cendres des feuilles, (Norme TAPPI : T 211 om - 93 )
• mesure de la turbidité 30' après que les fibres soient déposées afin de connaître l'état du milieu ionique.
• mesure du degré d'égouttabilité de la pâte avec un Canadian Standard Freeness (CSF; Norme TAPPI T 227 om - 94).

The following analyzes are then carried out:

• measurement of suspended solids under canvas (TAPPI standard: T 656 cm / 83)
• measurement of leaf ash, (TAPPI standard: T 211 om - 93)
• measuring the turbidity 30 'after the fibers are deposited in order to know the state of the ionic medium.
• measuring the degree of drainability of the pulp with a Canadian Standard Freeness (CSF TAPPI Standard T 227 om - 94).

Notes for Tables (I) and (II) below:

X =

measure said to the first pass.

R1 =

measured in the second pass (1st recycling)

R2 =

measure said to the third pass (2nd recycling)

$$\mathrm{Ashes}\mathrm{\%}\mathrm{=}\mathrm{\%}\mathrm{by\; weight\; of\; retained\; ash}\left(\mathrm{=}\mathrm{retention\; of\; charges}\right)\mathrm{on\; the\; paper}\mathrm{/}\mathrm{leaf\; weight}\mathrm{.}$$

Comments of the results: cf. Tables (I) and (II) below relating to Example 1 and FIG. 1 to 10 which represent the corresponding histograms

The crosslinked polymers 1, 4, 9, 12 are not of interest for the flocculation and retention of fines and fillers despite the high rate of shear applied during processing on the fibrous mass (and not applied to the polymer itself), here 1500 rpm, which is characteristic of this type of microparticulate retention system. They show a low capture of the charges and colloidal materials because no reduction of turbidity is observed.

The combination with bentonite does not significantly improve retention efficiency and only slightly improves drainage efficiency.

For the linear polymer, its behavior follows the trend, improving the retention of charges and fines.

The combination according to the invention of a branched polymer in inverse emulsion and bentonite provides a net gain in charge retention and total retention, and is found to be superior to the known linear polymer / bentonite system.

The coagulation power is higher for a branched polymer in emulsion, which results in an excellent reduction of the turbidity at 30 '(30 min.).

The R 52 test and the R 102 test show that the invention makes it possible to obtain branched products having higher UL viscosities than those accessible by a gel polymerization as described in US Pat. EP 0 574 335 (FO 4198). Any attempt to achieve such highly advantageous UL viscosity values by a powdered gel polymerization route would result in a product that is completely insoluble and therefore totally unusable in the industry.

Test SD 102 shows that the polymer used in the form of a solution in the water of the powder obtained by drying the inverse emulsion of the synthesis of the polymer behaves as the polymer used in the form of the solution in the water of said synthesis inverse emulsion. In particular, there is no degradation of the polymer during the spray drying step.

The test R 52 can be usefully compared to the test FO 4198 (powder) because the polymers have the same chemistry, therefore the same cationicity, and the same% MBA, while the R 52 used according to the invention is very higher than the powder in terms of dripping and retention (96.3 to be closer to 83.6); the NTU turbidity will also be compared after 30 minutes. , of 32 compared to 75 NTU units.

Such values of UL viscosity lead in particular to a very improved drainage.

The invention therefore relates to a method for producing a sheet of paper or cardboard or the like, using a retention agent, which consists of an acrylic (co) polymer as described above, branched, in inverse emulsion, and which is characterized in that its UL viscosity is> 3, or> 3.5 or> 4. Said agent can be used either in inverted emulsion with water, or in solution of the powder obtained by drying the emulsion, as described above.

EXAMPLE 2 Manufacture of a branched polymer based on acrylamido propyl tri-methyl ammonium chloride (APTAC) in the form of a water-in-oil inverse emulsion:

1. a) - Phase organique :
   • 252 g d'exxsol D100
   • 18 g de Span 80
   • 4 g d'Hypermer 2296.
2. b) - Dans un bécher B, on prépare la phase de l'émulsion à réaliser en mélangeant
   • 378 g d'acrylamide à 50 %
   • 102,2 g de chlorure d'acrylamido-propyl triméthyl ammonium (60 %)
   • 245,7 g d'eau
   • 0,5 g de méthylène bis acrylamide à 0,25 %
   • 0,75 ml de bromate de sodium à 50 g/l
   • 20 ppm d'hypophosphite de sodium par rapport à la matière active
   • 0,29 ml de Versenex à 200 g/l

In a reactor A, the constituents of the organic phase of the emulsion to be synthesized are mixed at ambient temperature.

1. a) - Organic phase:
   • 252 g of exxsol D100
   • 18 g of Span 80
   • 4 g of Hypermer 2296.
2. b) - In a beaker B, the phase of the emulsion to be prepared is prepared by mixing
   • 378 g of 50% acrylamide
   • 102.2 g of acrylamido-propyltrimethylammonium chloride (60%)
   • 245.7 g of water
   • 0.5 g of 0.25% methylenebisacrylamide
   • 0.75 ml of sodium bromate at 50 g / l
   • 20 ppm sodium hypophosphite relative to the active ingredient
   • 0.29 ml of Versenex at 200 g / l

The contents of B are mixed in A with stirring. After mixing the phases, the emulsion is sheared for 1 minute in order to create the inverse emulsion. The emulsion is then degassed by bubbling nitrogen and after 20 minutes, the gradual addition of metabisulfite leads to initiation and then polymerization.

When the reaction is complete, a "burn out" is performed in order to reduce the content of free monomer.

The emulsion is then incorporated with its reversing surfactant in order subsequently to release the polymer in the aqueous phase.

Table of Example 2 :

Trial MBA ppm NaH2PO2 ppm (*) UL Viscosity RI (1) (%) RIV (2) (%) State M 52 5 20 4.20 14.2 0 ramified M 102 10 20 3.34 21.3 0 ramified XM 104 10 40 2.11 37 50 Reticle XM 204 20 40 1.94 58 55 Reticle EK 190 0 15 4.35 0 0 Linear EK 190 BD 5 0 1.85 78 60 Reticle EK 190: standard emulsion of acrylamide co-polymer and acrylamido-propyltrimethylammonium chloride, linear.

Procedure for testing emulsions (identical to that of example 1) Comments of the results: cf. Table (III) below relating to Example 2 and FIGS. 11 to 20 which represent the corresponding histograms

The results call for the same comments as those of Example 1 and confirm the great interest of the present invention.

The invention relates to a method for producing a sheet of paper or cardboard or the like employing retention agents described above, characterized in that they consist of, or comprise, at least one (co) polymer of the type described, branched, prepared in inverse emulsion, intended to cooperate with a secondary retention agent after an intermediate step of shearing the paper pulp, as well as processes for producing sheets of paper, cardboard or the like, using the agents described above in the process according to the invention, and the sheets of paper, cardboard and the like thus obtained.

Said agent may be used either in inversion emulsion with water, or in solution of the powder obtained by drying the emulsion, as described above. <b><u> Table (I): comparative table of the results of Example 1 (polymer only) </ u></b> No. Trial % bentonite % Turbidity Turbidity Turbidity % Retry % Retry % ash % ash Turbidity Turbidity CSF X R1 R2 X R2 X R2 30 'X 30 'R2 (Ml) 0 White 0 0 0 > 4000 > 4000 > 4000 71.2 62.2 70.9 19.8 3558 3714 365 1 (X) EM 140BD 0.05 CPB1 0 > 4000 3761 3647 79.0 70.1 41.1 53.7 1383 > 4000 390 2 (/) EM 140CT 0.05 CPB1 0 1090 1494 1609 85.4 84.6 67.1 84.2 145 161 405 3 (Y) R 52 0.05 CPB1 0 791 1059 1236 88.2 90.3 73.6 91.3 50 55 415 4 (X) X 204 0.05 CPB1 0 3700 > 4000 > 4000 72.5 64.0 49.1 51.0 1482 > 4000 385 5 (Y) FO 4198 0.05 CPB1 0 1553 2730 3204 86.1 83.8 74 82.8 160 205 402 6 (Y) R 102 0.05 CPB1 0 1100 1705 1860 86.3 88.25 70.3 90.09 56 53 410 7 (Y) SD 102 0.05 CPB1 0 1050 1690 1780 93.4 92.35 71.5 91.2 55 53 410 8 (/) EM 140 L 0.05 CPB1 0 1245 2035 2563 83.3 87.8 66.1 80.2 180 190 400 (in italics: branched polymer) (FO 4198 is also a powder, obtained by a gel polymerization)
(X) = crosslinked; (Y) branched; (/) = linear No. Trial % bentonite % Turbidity Turbidity Turbidity % Retry % Retry % ash % ash Turbidity Turbidity CSF X R1 R2 X R2 X R2 30 'X 30 'R2 (Ml) 0 White 0 0 0 > 4000 > 4000 > 4000 71.2 62.2 10.9 19.8 3558 3714 365 9 (X) EM 140BD 0.05 CPB1 0.2 > 4000 > 4000 > 4000 80.0 72.6 50.7 52.7 846 > 4000 395 10 (/) EM 140CT 0.05 CPB1 0.2 362 523 834 90.6 91.3 80.5 86.9 38 45 435 11 (Y) R 52 0.05 CPB1 0.2 147 250 285 96.7 95.1 94.1 96.3 16 32 440 12 (X) X 204 0.05 CPB1 0.2 3000 3350 > 4000 81.0 73.0 53.2 54.1 750 > 4000 390 13 (Y) FO 4198 0.05 CPB1 0.2 188 1135 2103 95.1 92.0 93.2 83.6 25 75 422 14 (Y) R102 0.05 CPB1 0.2 300 500 780 94 93.2 92.1 93.3 25 40 430 15 (Y) SD102 0.05 CPB1 0.2 385 480 760 94.1 93.3 92.3 93.8 27 41 427 16 (/) EM 140 L 0.05 CPB1 0.2 899 1025 1400 86.1 90 78.0 85 48 54 420 (in italics: branched polymer) (FO 4198 is also a powder, obtained by a gel polymerization)
(X) = crosslinked; (Y) = branched; (/) = linear No. Trial % bentonite % Turbidity Turbidity Turbidity % Retry % Retry % ash % ash Turbidity Turbidity CSF X R1 R2 X R2 X R2 30 'X 30 'R2 (Ml) 0 White 0 0 0 > 4000 > 4000 > 4000 71.2 62.2 10.9 19.8 3558 3714 365 1 (X) EK 190BD 0.05 CPB1 0 > 4000 3526 3703 78.1 71.2 42.1 51.6 1425 > 4000 386 2 (/) EK 190 0.05 CPB1 0 969 1340 1592 84.3 84.9 66.2 82.1 163 172 410 3 (Y) M 52 0.05 CPS1 0 731 926 1134 87.9 89.0 75.2 92.5 47 49 416 4 (X) XM204 0.05 CPB1 0 3598 > 4000 > 4000 73.1 65.2 49.5 52.8 1510 > 4000 390 5 (X) EK 1908D 0.05 CP91 0.2 3280 > 4000 > 4000 81.1 75.3 55.0 57.9 769 > 4000 390 6 (/) EK 190 0.05 CPB1 0.2 301 486 710 92.1 91.9 83.4 88.5 27 55 435 7 (Y) M 52 0.05 CPB1 0.2 125 198 265 95.9 96.0 95.7 96.1 12 21 449 8 (X) XM 204 0.05 CPB1 0.2 3110 3281 3862 82.4 72.0 56.1 53.6 719 3924 394 (X) = crosslinked; (Y) = branched: (/) = linear

Claims (12)

1. Process for manufacturing a sheet of paper or cardboard or the like having improved retention and dewatering characteristics, of the type using a dual system of branched acrylic polymer and bentonite or a kaolin optionally treated as primary retention agent an as secondary retention agent, the introductions of which are separated by a shearing stage of the fibrous suspension or mass or wood pulp, characterised in that said polymer is a branched acrylic (co)polymer prepared in the form of an invert water-in-oil emulsion which is a cationic copolymer of acrylamide and of an unsaturated cationic ethylenic monomer, selected from the group comprising dimethylaminoethyl acrylate (ADAME), dimethylaminoethyl methacrylate (MADAME), which are quaternised or salified by various acids and quaternising agents, benzyl chloride, methyl chloride, alkyl or aryl chlorides, dimethyl sulphate, dimethyldiallylammonium chloride (DADMAC), acrylamidopropyl- trimethylammonium chloride (APTAC) and methacrylamidopropyl-trimethylammonium chloride (MAPTAC), used either as an emulsion inverted with water or as a solution of the powder obtained by drying the emulsion, and in that its viscosity (UL) is > 3, preferably > 3.5 and preferably > 4.
2. Process according to claim 1, characterised in that the branched acrylic (co)polymer prepared as an invert emulsion is introduced into the wood pulp in a concentration from 0.03 to one per thousand (0.03 to 1%o) by weight, that is from 30 to 1000 g/t, of the dry weight of the fibrous wood pulp suspension, preferably from 0.15 to 0.5 per thousand (0.15 to 0.5%o), that is from 150 to 500 g/t.
3. Process according to any one of claims 1 to 2, characterised in that the branched acrylic (co)polymer as an invert emulsion is branched by a branching agent formed by a polyfunctional compound containing at least two reactive groups selected from the group comprising double bonds, aldehyde bonds or epoxy bonds.
4. Process according to any of claims 1 to 3, characterised in that the branched acrylic (co)polymer as an invert emulsion is branched by a branching agent formed by methylenebisacrylamide (MBA).
5. Process according to claim 4, characterised in that the MBA is introduced in a concentration of 5 to 200 moles per million moles of monomers.
6. Process according to claim 4 or 5, characterised in that the bentonite is a semi-sodium bentonite used in a proportion of 0.1 to 0.5 per cent (0.1 to 0.5%) of the dry weight of the fibrous suspension.
7. Process according to claim 4, 5 or 6, characterised in that the filler-containing pulp used is diluted, then the polymer is added as main retention agent, a shearing stage is carried out, for example in the mixing pump or fan pump, then the bentonite is added as secondary retention agent.
8. Process according to claim 7, characterised in that the amount of branched polyacrylamide (or more generally of branched acrylic (co)polymer) introduced either as an invert water-in-oil emulsion inverted with water, or as a solution of the powder obtained by drying the emulsion, is between 0.03 and 1‰, that is between thirty and a thousand grammes/tonne (30 and 1000 g/ t) of dry pulp.
9. Process according to claim 7 or 8, characterised in that the amount of branched polyacrylamide (or more generally of branched acrylic (co)polymer) introduced either as an invert water-in-oil emulsion inverted with water, or as a solution of the powder obtained by drying the emulsion, is between 0.15 and 0.5%o (that is between 150 and 500 g/t).
10. Process according to claim 7, 8 or 9, characterised in that the bentonite is replaced by kaolin, optionally pretreated with a polyelectrolyte, as secondary retention agent.
11. Process according to any of claims 1 to 10, characterised in that the branched polymer prepared as an invert emulsion is injected or introduced (either as an emulsion inverted with water or as a solution of the powder obtained by drying the emulsion) prior to a shearing stage into the more or less dilute wood pulp (or fibrous mass to be flocculated) according to the practice of the person skilled in the art, and generally into the dilute wood pulp or thin stock, in other words a pulp diluted to approximately 0.7 to 1.5% of solid matter, such as cellulose fibres, optional fillers, and the various additives conventional in paper manufacture.
12. Process according to any of claims 1 to 10, characterised in that a portion of the branched polymer is introduced as an emulsion during the stage of preparation of the thick pulp or thick stock containing approximately 5% or more of solid matter, or even during the preparation of the thick pulp prior to a shearing stage.