EP1092064B1 - Method for making paper and cardboard and retention and dewatering agents - 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 manufacture of paper and polymers used in this context.

The invention relates to a method for the production of a paper or a retention cardboard, 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 to the paste of bentonite, this can possibly be added to other mineral products, such as aluminum sulphates, or even synthetic polymers, especially polyethyleneimine (see for example DE-A-2,262 906 and US-A-2,368,635).

In US-A-3,052,595 it has been proposed to associate the bentonite has a polyacrylamide of essential linear characteristic. This process has competed with systems that are easier to implement while still performing well. In addition, even with current linear polyacrylamides, the retention power still remains insufficient.

In EP-A-0017353, it was 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 EP-A-0 235 893, it has been proposed to use cationic polyacrylamides with a molecular weight greater than thirty million and more, essentially linear. In this way we obtain an effect certainly satisfactory, but still considered insufficient in the application paper, because the use of bentonite causes difficulties during the further treatment of the effluents at the output of the machine, the users select this system only in case of significant benefits.

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

Finally, EP 0 574 335 has achieved an important improvement in proposing the use of polymers (in particular polyacrylamides) branched under the shape of a powder.

The invention overcomes the disadvantages mentioned above.

It is aimed at an improved process of the type in question, consisting of add, to the suspension or fibrous mass or flocculant pulp, as primary retention agent, an agent that consists of, or includes, a branched polyacrylamide which is characterized in that it has been prepared in emulsion reverse or water-in-oil, and bentonite as the second agent of retention (so-called "dual" system, also called "microparticular").

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 the bentonite are separated by a shearing step, for example at the so-called mixing pump "Fan pump". Reference in this field to the description of the patent USP 4, 753, 710 and a very extensive prior art dealing with the point of addition of the retention agent with respect to the shearing steps existing on the machine, including 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 USP 4,388,150 (Eka Nobel)

Reference is also made to USP Patent 4,753,710, for all that generalities concerning the manufacture of paper, the additives used, and similar details.

It is possible to replace bentonite as a retention agent secondary, by a kaolin as described in the patent application FR 95 13051 of the Applicant, this kaolin being preferentially pretreated by 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 charges and this without any reverse effect. We also improve, which is a additional feature of this refinement, the properties drip.

Branched polyacrylamide (or more generally (co) polymer branched) is introduced into the suspension, very preferably, under the water-in-oil inverse emulsion form, at the 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) per relative to the dry weight of the fibrous suspension, preferably from 0.15 to 0.5 per thousand, ie 150 to 500 g / t.

In a manner known to those skilled in the art, the inverse emulsion of polymer 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 application paper for the retention of fillers and fines, to reach a level of performance unmatched until then. The use of branched polymers allows in addition to better retain the bentonite on the sheet, as described in the patent EP 574 335 cited above and thus to limit its negative effects on the treatment subsequent effluents from the machine. In addition, the choice of this branched polyacrylamide increases the binding power of bentonite on the sheet, therefore leads to a synergy, so a recoagulation that reduces the bentonite content in white waters.

It will be understood that it is essential according to the invention that the polymer is prepared by water-in-oil inverse emulsion polymerization. By against, 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 emulsion inverse after its dissolution in water, either in the form of a powder obtained by drying (in particular by spray drying or spray-drying ") Of the inverse emulsion of the polymerization, then redissolution of this powder in water, for example at a concentration of about 5 g of active polymer / liter, the solution thus obtained being then injected into the dough substantially at the same polymer dosages.

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

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

As is known, a branched polymer is a polymer which present on the chain branches, groups or ramifications arranged globally in one plane and not in the three directions, unlike a cross-linked polymer; such polymers branched, high molecular weight, are well known as flocculating agents. These branched polyacrylamides are distinguished from crosslinked polyacrylamides by the fact that in the latter groups are arranged three-dimensionally to lead to practically insoluble products and of infinite molecular weight.

We can carry out the branching preferably during (or optionally after) the polymerization, for example by reaction of two soluble polymers having counterions, or by reaction on formaldehyde or a polyvalent metal compound. Often, the branching takes place during the polymerisation by addition of an agent ramifiantt, and this solution will be clearly preferred according to the invention. These Branching polymerization methods are well known.

Branching agents that can be incorporated include ionic branching agents such as polyvalent metal salts, formaldehyde, glyoxal, or, preferably, covalent crosslinking which will copolymerize with the monomers, diethylenically unsaturated monomers (such as family of diacrylate esters such as polyethylene diacrylates PEG glycols) or polyethylene, of the type that is conventionally used for the crosslinking of polymers soluble in water, and in particular the 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 one wishes to obtain a branched and not cross-linked polymer, by optimizing the conditions such as concentration during polymerisation, type and amount of transfer agent, temperature, type and amount of initiators, and like.

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

Advantageously, the amount of branched polyacrylamide introduced into the suspension to flocculate is between thirty and thousand grams of active polymer / tonne of dry pulp (30 and 1000 g / t), ie between 0.03 per thousand and one per thousand, preferably 150 to 500 g / t; it has been observed that if amount is less than 0.03% o (0.03 per thousand), we do not get any significant retention; likewise, if this quantity exceeds 1% o (1 per thousand), no proportional improvement is observed; however, unlike linear cationic polyacrylamides, as described in documents EP-A-0 017 353 and EP 0 235 893 referred to in the preamble, does not observe an inverse effect of dispersion by recirculation in the circuits closed 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%) 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 is prepared under inverse emulsion form (water-in-oil) to achieve perfection of the invention. Such emulsions and their preparation process are well known to those skilled in the art.

This approach was condemned in the aforementioned patent EP 0 574 335, where it was indicated that if a branched emulsion polymer is used, the indispensable presence in these emulsions of surfactants promotes the formation of foams during paper making and the appearance of disparities in the physical properties of the finished paper (modification of the absorbance at places where 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 stay in the field of branched polymers and not to go into the crosslinked polymers. Now, we know that technically, especially scale of industrial production, the border between the two areas is very easily crossed, so irreversibly. As the zone of branching is very narrow, we measure the difficulty of developing the invention, and it is the Claimant's merit that he attacked the use of this technology in the field of paper making, which poses particular problems and has very stringent quality requirements.

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

Compared with linear polymers, branched polymers in powder form EP 0 574 335 had already made significant progress in relates to the properties and the paper manufacturing process. improvements was in the range of 20 to 40% depending on the properties.

With the present branched emulsions, an improvement of 50% to 60%, which was not predictable since it was known On the other hand, cross-linked 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 are compared.

According to the invention, use will preferably, but not exclusively, a "moderately branched" polymer, for example at 10 ppm branching compared to the active ingredient.

As already indicated above, the polymer can be used either under the form of its inverse synthesis emulsion, dissolved or "inverted" in water, either in the form of the solution in the water of the powder obtained by drying said synthetic emulsion, in particular by drying by spray. Spray drying is a method also known of the skilled person. We will refer to the tests below to verify that the results are comparable.

Bentonite, also called "swelling smectic clay", from 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 likely to retain water (see, for example, US-A-4,305,781, which corresponds to EP-A-0 017 353, mentioned above, and FR-A-2 283 102).

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

As load ("filler"), we can use the kaolins, the "GCC" or ground CaCO3, precipitated CaCO3 or "PCC", and the like.

Injection or introduction of the branched polymer in emulsion inverse according to the invention is carried out before a shearing step in the pulp (or fibrous mass to flocculate) more or less diluted according to the practice of those skilled in the art, and generally in the thin stock or thin stock, ie a paste diluted 0.7 - 1.5% solids such as cellulose fibers, fillers possible, and the various usual additives of papermaking.

According to a variant of the invention, with a fractional introduction, introduce a portion of the branched polymer emulsion, according to the invention, at the stage of preparing the thick paste or "thick stock »at approx. 5% or more solids, or even at the level of the preparation of the thick paste before a shearing step.

The following examples illustrate the invention without, however, limit the scope.

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

a) - Phase organique

• 252 g d'Exxsol D100
• 18 g de Span 80
• 4 g d'Hypermer 2296

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 entraíne 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.

a) - Organic phase

• 252 g of Exxsol D100
• 18 g of Span 80
• 4 g of Hypermer 2296

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 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 1M 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 (%) RIV (%) 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

We note that linear products do not develop a revival ionicRI and see their intrinsic viscosity IV decrease under the effect high shear (two of IV values are negative); the branched emulsion products develop ionic RI growth, but no IV (values <= 0); cross-linked products develop a strong Ionic regain and a very strong IV rush.

Definitions of ionic regains and regains of intrinsic viscosity:

Ionic Regain RI = (X-Y) / Y x 100

with X:

ionicity after shearing in meq / g.

Y:

ionicity before shearing in meq / g.

Intrinsic viscosity boost R IV = (V1 - V2) / V2 x 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 a study efficiency in draining retention on an "automatic form of retention "of the Technical Paper Center.

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 an alkyl emulsion ketene dimer.

The paste used is diluted to a consistency of 1.5%. 2.24 g is taken 150 g of 150% pulp and then diluted to 0.4% with clear waters.

• 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 connaítre 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)
• measurement of 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)

Ash% =% by weight of ash retained (= retention of loads) on the leaf / weight of the leaf. Comments of the results: cf. Tables (I) and (II) below relating to Example 1 and FIG. 1 to 10 which represent the histograms correspondents

The crosslinked polymers 1, 4, 9, 12 are not of interest as regards the flocculation and retention of fines and fillers despite the high rate of shear applied during the process on the fibrous mass (and not 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 charges and colloidal materials because no reduction in turbidity is observed.

The combination with bentonite does not improve so significant efficiency in retention and only slightly improves efficiency in draining.

For the linear polymer, its behavior follows the trend, improved retentions of charges and fines.

The combination according to the invention of a branched polymer in inverse emulsion and bentonite brings a net gain in retention of load and in full retention, and proves to be superior to the system known linear polymer / bentonite.

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

The test R 52 and the test R 102 show that the invention allows to obtain branched products with higher UL viscosities than those accessible by a gel polymerization as described in patent EP 0 574 335 (FO 4198). Any attempt to achieve such very advantageous values of UL viscosity by a route of gel polymerization with powder drying would lead to a product totally insoluble and therefore totally unusable in the industry.

The SD 102 test shows that the polymer used in the form of a solution in the water of the powder obtained by drying the the inverse emulsion of the polymer synthesis behaves like the polymer used in the form of the solution in the water of said reverse synthesis emulsion. In particular, we do not observe degradation of the polymer during the spray drying step.

R 52 can be usefully compared to FO 4198 (powder) because polymers have the same chemistry, so the same cationicity, and the same% MBA, while the R 52 of the invention is much higher than the powder in terms of dewatering and retention (96.3 to bring closer to 83.6); NTU turbidity will also be compared after min. , of 32 compared to 75 NTU units.

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

The invention thus also relates to a novel retention agent for the manufacture of a sheet of paper, cardboard or the like, which consists of a (co) acrylic 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 may be used either in inverted emulsion with water or in solution 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 water-in-oil inverse emulsion:

a) - Phase organique :

• 252 g d'exxsol D100
• 18 g de Span 80
• 4 g d'Hypermer 2296.

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.

a) - Organic phase:

• 252 g of exxsol D100
• 18 g of Span 80
• 4 g of Hypermer 2296.

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 of the phases, the emulsion is sheared for 1 minute in order to create the inverse emulsion. The emulsion is then degassed by bubbling of nitrogen and then after 20 minutes, the gradual addition of metabisulphite entails the initiation then the polymerization.

When the reaction is complete, a burn-out is made to reduce the free monomer content.

The emulsion is then incorporated with its reversing surfactant in order to subsequently 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 relative in example 2 and Figs. 11 to 20 which represent the histograms correspondents

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

The invention also relates to new retention agents described above, characterized in that they consist of, or include, the at least one (co) polymer of the type described, branched, prepared in inverse emulsion, intended to cooperate with a secondary retention agent after a step intermediate shearing of pulp, as well as the processes of manufacture of sheets of paper, cardboard or the like, using the agents according to the invention or the method according to the invention, and the sheets of paper, cardboard and analogs 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.

Claims (20)

1. Process for manufacturing a sheet of paper or cardboard or the like having improved retention and dewatering characteristics, which consists in using a dual system of branched acrylic polymer as primary retention agent and bentonite or an optionally treated kaolin as secondary retention agent, of which the introduction is separated by a stage of shearing 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 and 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 > than 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‰) 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‰), that is from 150 to 500 g/t.
3. Process according to claim 1 or 2, characterised in that the branched acrylic (co)polymer prepared as an invert emulsion is a cationic (co)polymer 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), acrylamidopropyltrimethylammonium chloride (APTAC) and methacrylamidopropyltrimethylammonium chloride (MAPTAC).
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 a polyfunctional compound containing at least two reactive groups selected from the group comprising double bonds, aldehyde bonds or epoxy bonds.
5. Process according to any of claims 1 to 4, characterised in that the branched acrylic (co)polymer as an invert emulsion is branched by a branching agent formed by methylenebisacrylamide (MBA).
6. Process according to claim 5, characterised in that the (MBA) is introduced in a concentration of 5 to 200 moles per million moles of monomers.
7. Process according to claim 5 or 6, 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.
8. Process according to claim 5, 6 or 7, 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.
9. Process according to claim 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 0.03 and 1‰, that is between thirty and a thousand grammes/tonne (30 and 1000 g/t) of dry pulp.
10. Process according to claim 8 or 9, 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‰ (that is between 150 and 500 g/t).
11. Process according to claim 8, 9 or 10, characterised in that the bentonite is replaced by kaolin, optionally pretreated with a polyelectrolyte as secondary retention agent.
12. Process according to any of claims 1 to 11, 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 approx 0.7 to 1.5% of solids such as cellulose fibres, possible fillers and the various additives conventional in paper manufacture.
13. Process according to any of claims 1 to 11, 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 approx 5% or more of solids, or even during preparation of the thick pulp prior to a shearing stage.
14. Retention agent for. the manufacture of a sheet of paper, cardboard or the like, characterised in that it comprises a branched polyacrylamide (or more generally a branched acrylic (co)polymer) as an invert (or water-in-oil) emulsion (either an invert emulsion dissolved or inverted with water, or as a solution of the powder obtained by drying the invert emulsion, in particular by spray drying), and in that its viscosity (UL) is > 3.
15. Retention agent for manufacturing a sheet of paper, cardboard or the like, according to claim 14, characterised in that the branching agent is 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, in particular methylenebisacrylamide (MBA).
16. Retention agent for manufacturing a sheet of paper, cardboard or the like, according to claim 15, characterised in that the branching agent is introduced in a proportion of five to two hundred (5 to 200) moles per million moles of monomers, preferably 5 to 50.
17. Retention agent for manufacturing a sheet of paper, cardboard or the like, according to claim 14, 15 or 16, characterised in that the branched polyacrylamide is a cationic (co)polymer 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), acrylamidopropyltrimethylammonium chloride (APTAC) and methacrylamidopropyltrimethylammonium chloride (MAPTAC).
18. Retention agent for manufacturing a sheet of paper, cardboard or the like, according to any of claims 14 to 17, characterised in that its viscosity (UL) is > 3.5.
19. Retention agent for manufacturing a sheet of paper, cardboard or the like, according to any of claims 14 to 18, characterised in that its viscosity (UL) is > 4.
20. Retention agent for manufacturing a sheet of paper, cardboard or the like, according to any of claims 14 to 19, characterised in that it is "averagely branched", for example with 10 ppm of branching agent based on the active substance.

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