EP0580529A1 - Process for making paper or cardboard having improved retention - Google Patents

Abstract

Process for making paper or cardboard having improved retention, in which a polyacrylamide and bentonite are added to the fibrous suspension, characterised in that the polyacrylamide is an amphoteric linear terpolymer and is introduced into the fibrous suspension in the form of a dissolved powder, in a proportion of 0.03 to 1.0 per thousand (0.03 to 1.0 %o), by weight, of the dry weight of the fibrous suspension.

Description

The invention relates to a method for manufacturing paper or cardboard with improved retention.

• 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 à une diminution de l'utilisation de sulfate d'alumine et donc amoindrissement des problèmes de corrosion;
• l'amélioration de la qualité : meilleure formation et épair ; amélioration du taux d'humidité sur feuille, de l'opacité, du lissé, du pouvoir absorbant et diminution de la porosité du papier.

During the production of paper, cardboard or the like, it is well known to introduce retention agents into the pulp, the function of which 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:

• the increase in production and the decrease in manufacturing costs: energy saving, smoother running of the machine, higher yield of fibers, fines, fillers and anionic finishing products, lower acidity in the circuit linked to a reduction in the use of alumina sulphate and therefore lessening of corrosion problems;
• quality improvement: better training and awareness; improvement of the humidity on the sheet, opacity, smoothness, absorbency and reduction of the porosity of the paper.

It has been proposed for a long time to add bentonite to the pulp, which can optionally be added to other mineral products, such as aluminum sulphates, or even synthetic polymers, in particular polyethyleneimine (see for example documents US-A-2,368,630 and DE-A-2,262,906).

In US-A-3,052,595 and 4,305,781, it has been proposed to combine bentonite with a linear polyacrylamide. This process has hardly developed, because it has found itself in competition with systems that are easier to implement while also being efficient. In addition, even with current linear polyacrylamides, the retention power is still insufficient.

In document EP-A-0 017 353, it has been proposed for the retention of lightly loaded pastes (at most 5% of fillers) to combine with bentonite a weakly anionic nonionic copolyacrylamide. This process has hardly been developed, since these polymers are relatively ineffective in terms of retention, no doubt as a result of insufficient synergy between these copolymers and bentonite, which has little tendency to recoagulate.

In document EP-A-0 235 893, it has been proposed to use cationic polyacrylamides of molecular weight greater than one million, preferably thirty million and more, essentially linear, even partially crosslinked. In this way we obtain a retention effect that is certainly satisfactory, but still considered insufficient in the paper application, because the use of bentonite causing water treatment difficulties, users only select this system in the event of advantages significant.

The invention overcomes these drawbacks.

It relates to an improved process of the type in question in which a polyacrylamide and bentonite are added to the fibrous suspension, and which makes it possible to obtain a clearly improved retention of fines and fillers, and this without reverse effect.

This improvement is characterized in that the polyacrylamide is a linear amphoteric terpolymer based on acrylamide, and is introduced into the suspension in the form of powder dissolved, at a rate of 0.03 to 1 per thousand (0.03 to 1 ‰) by weight, of the dry weight of the fibrous suspension.

In other words, the invention consists, among all of the polyacrylamides, in using a particular polyacrylamide in the form of an amphoteric terpolymer in the form of powder dissolved. Unexpectedly, this selection allows, in the paper application for the retention of fillers and fines, to reach a level of performance unmatched before. The use of these terpolymers also makes it possible to better retain the bentonite on the sheet, and therefore to limit its negative effects on the subsequent water treatment. In addition, the choice of this terpolyacrylamide increases the binding power of the bentonite on the sheet, and thereby causes synergy, therefore recoagulation, which reduces the content of bentonite in white waters.

In practice, the characteristic amphoteric terpolymer is a high molecular weight amphoteric polyelectrolyte formed of acrylamide and at least two other monomers, respectively an anionic, the other cationic, but with a predominant cationic nature.

Advantageously, the anionic monomer is chosen from the group consisting of acrylic acid, acrylamidomethylpropylsulfonic acid, known by the abbreviation "AMPS", while the cationic monomer is chosen from the group consisting of acrylamidopropyltrimethylammonium chloride (APTAC ); methacrylamidopropyltrimethylammonium chloride (MAPTAC), dimethylaminoethyl acrylate (ADAME) and quaternized or salified dimethylaminoethyl methacrylate, trimethylaminoethylacrylate chloride, trimethylaminoethylacrylmethylethyltrimethyl chloride, trimethyl chloride

• au moins 40 moles pourcent d'acrylamide ;
• de 5 à 15 moles pourcent de monomère anionique ;
• et de 10 à 50 moles pourcent de monomère cationique,

et dans lequel la charge anionique est au plus égale à la charge cationique, à défaut de quoi le composé obtenu est peu ou pas soluble.In a preferred embodiment, the characteristic copolymer is a terpolymer containing in molar ratio:

• at least 40 mole percent acrylamide;
• from 5 to 15 mole percent of anionic monomer;
• and from 10 to 50 mole percent of cationic monomer,

and in which the anionic charge is at most equal to the cationic charge, failing which the compound obtained is little or not soluble.

The amphoteric terpolymers characteristic of the invention are described in the literature and known for water treatment, and for the retention of fines and fillers (see for example patent 1 265 496 from CALGON).

• la quantité de polyacrylamide amphotère introduite, est comprise entre 0,05 et 0,5 pour mille ( ‰) de la quantité de pâte fibreuse sèche ;
• comme déjà dit, il importe que le polymère amphotère soit utilisé sous forme de poudre diluée; en effet, si l'on fait appel à un polymère en émulsion, la présence indispensable dans ces émulsions d'agents tensioactifs , favorise la formation de mousses lors de la fabricaton du papier et par là l'apparition de disparités des propriétés physiques du papier fini (modification de l'absorbance aux endroits où une partie de la phase huile de l'émulsion est retenue sur la feuille).

Advantageously, in practice:

• the amount of amphoteric polyacrylamide introduced is between 0.05 and 0.5 per thousand (‰) of the amount of dry fibrous pulp;
• as already said, it is important that the amphoteric polymer be used in the form of a diluted powder; in fact, if an emulsion polymer is used, the essential presence in these emulsions of surfactants, promotes the formation of foams during the manufacture of paper and thereby the appearance of disparities in the physical properties of the paper. finished (modification of the absorbance at the places where part of the oil phase of the emulsion is retained on the sheet).

Bentonite, also known as "swecting smectic clay", from the montmorillonite family, is well known and does not need to be described here in detail; these compounds, formed from microcrystallites, have sites on the surface with a high cation exchange capacity capable of retaining water (see for example document US-A-4,305,781 and FR-A-2,283,102).

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

In an advantageous embodiment, the powdered amphoteric ternary polyacrylamide is first dissolved in water, then this solution is introduced into the paste castle of the fibrous suspension circuit, at a rate of 0.05 to 0 , 5 per thousand (0.05 to 0.5 ‰) by dry weight of the dry weight of this fibrous suspension, then the mixture is then stirred and sheared, and finally we always add with stirring, upstream of the headbox, bentonite in an amount of 0.1 to 0.5 percent (0.1 to 0.5%) of the dry weight of the fibrous suspension. The amphoteric polymer previously dissolved is introduced at a concentration of between 0.1 and 3 g / liter in front of the pulp feed pump in the pulp circuit, preferably in the pulp castle, and the bentonite is introduced just upstream of the headbox.

The manner in which the invention can be implemented and the advantages which result therefrom will emerge more clearly from the examples of implementation which follow.

A - Manufacture of an amphoteric perpolymer :

• 11802 kilogrammes d'acrylamide 30 % dans l'eau ;
• 2590,5 kilogrammes de chlorure de méthacrylamidopropyltriméthylammonium (MAPTAC) à 50 % en solution dans l'eau ;
• 607,5 kilogrammes d'acide acrylamidométhylpropylsulfonique (AMPS).

In a reactor, the following are mixed at ambient temperature:

• 11802 kilograms of 30% acrylamide in water;
• 2590.5 kilograms of methacrylamidopropyltrimethylammonium chloride (MAPTAC) at 50% in solution in water;
• 607.5 kilograms of acrylamidomethylpropylsulfonic acid (AMPS).

A solution is obtained whose pH is 3.6. Cool to 0 ° C, add (1000) thousand ppm of catalyst: isobutyronitrile (AZDN) (or 15 kg) and degas by bubbling nitrogen for 30 minutes. A transfer agent (sodium formate) is then added at the rate of three thousand (3000) ppm relative to the load, ie (45 kilograms).

Then added 13.3 ppm of ammonium persulfate (20 grams) and 3.2 ppm of iron in the form of Mohr salt (22 ppm of Mohr salt, or 33.45 grams). The exothermic reaction is allowed to continue for approximately one hour, until the temperature of 90 ° C. is reached.

A gel is then obtained which is left to age for two hours, then which is ground, dried with hot air and re-embossed again, until a particle size of less than one millimeter is obtained.

A perfectly and easily soluble white powder is then obtained up to 40 grams per liter at room temperature, having an insoluble content of less than 0.02 percent (0.02%). This amphoteric terpolymer powder A has a Brookfield viscosity close to 1.9 cps (0.1% UL in a 1M Nacl solution at 25 ° C at sixty revolutions per minute (60 rpm).

• acrylamide :   85 %
• AMPS :   5 %
• MAPTAC :   10 %

The polymer obtained has the following molar composition:

• acrylamide: 85%
• AMPS: 5%
• MAPTAC: 10%

Example 1 :

In a known manner, a paper pulp is prepared comprising 85% of pulp proper at the rate of forty percent (40%) of bleached hardwood, ten percent (10%) of broken-coated and thirty five percent (35%) of kraft bleached, and fifteen percent (15%) calcium carbonate.

In neutral medium, bonding is done with 2.0% dimeric ketene alkyl.

The fibrous suspension is dissolved in water at the rate of 40 grams / liter. The pH of this suspension is 7.5.

650 cm3 of this fibrous suspension are introduced into the bowl of an automated CTP form. 200 grams / ton (0.2 per thousand) of the amphoteric terpolymer previously prepared at A are then added. Thirty seconds are stirred.

Then added 1400 grams / ton (0.14%) of bentonite, of the type sold by the Applicant under the name CP-B1, having a density of 900 kilos / cubic meter, a bulking power of 40 ml / 2g, a cation exchange capacity of 85 meq / 100 g dry, and an average size less than 75 microns. Stirred again for thirty seconds, then drain by vacuum.

The turbidity in white waters is then measured by weighing the dry matter as well as the weight of the dried formed sheet. The mass balance makes it possible to establish the retention figure according to the formula: $$\frac{\text{Sheet weight}}{\text{Leaf weight + dry weight in white waters}}\text{x 100}$$

82% retention is thus obtained.

In the same way as above, retention tests are repeated at variable doses of the amphoteric terpolymer above (A) predominantly weakly cationic previously prepared according to the method described above (A). The results are collated in Table 1. Table 1 % terpolymer A % retention 0.05 71 0.2 82 0.3 85 0.5 89 0.75 91.1

There is an improvement in retention directly linked to the terpolymer assay. Excess terpolymers do not have opposite effects.

Example 2 :

Example 1 is repeated, replacing the amphoteric terpolyacrylamide with a linear cationic polyacrylamide marketed by the Applicant under the name FO 3190, with a UL 2.8 cps viscosity and having 10 mole percent cationicity (MAPTAC) and in common use for the retention in stationery. The following results are obtained: % FO 3190 % retention 0.2 69 0.5 77.5 0.75 74

It is observed that the retention obtained by means of the product (example 1) is 15 to 20% higher than that obtained with its counterpart (example 2).

In addition, with an excess of linear cationic polymer, an opposite effect is quickly observed.

B - Manufacture of an amphoteric terpolymer

• 11950,5 kilogrammes d'acrylamide 30 % dans l'eau ;
• 2622 kilogrammes de chlorure de méthacrylamidopropyltriméthylammonium (MAPTAC) à 50 % en solution dans l'eau ;
• 427,5 kilogrammes d'acide acrylique.

In a reactor, the following are mixed at ambient temperature:

• 11950.5 kilograms of 30% acrylamide in water;
• 2622 kilograms of methacrylamidopropyltrimethylammonium chloride (MAPTAC) at 50% in solution in water;
• 427.5 kilograms of acrylic acid.

A solution is obtained whose pH is 3.6. Cool to 0 ° C, add (1000) thousand ppm of catalyst: isobutyronitrile (AZDN) (or 15 kilograms) and degas by bubbling nitrogen for thirty minutes. A transfer agent (sodium formate) is then added at the rate of three thousand (3000) ppm relative to the load, ie (45 kilograms).

Then added 13.3 ppm of ammonium persulfate (20 grams) and 3.2 ppm of iron in the form of Mohr salt (22 ppm of Mohr salt, or 33.45 grams). The exothermic reaction is allowed to continue for approximately one hour, until the temperature of 90 ° C. is reached.

A gel is then obtained which is left to age for two hours, then which is ground, dried with hot air and re-embossed again, until a particle size of less than one millimeter is obtained.

A perfectly soluble white powder is then obtained up to 40 grams per liter at room temperature, having an insoluble content of less than 0.02 percent (0.02%). This amphoteric terpolyacrylamide B powder has a Brookfield viscosity close to 2.2 cps (0.1% UL in a 1M Nacl solution at 25 ° C at sixty revolutions per minute (60 rpm).

• acrylamide :   85 %
• acide acrylique :   5 %
• MAPTAC :   10%

The polymer obtained has the following molar composition:

• acrylamide: 85%
• acrylic acid: 5%
• MAPTAC: 10%

Example 3

We study the retention of Kaolin in a slightly acid medium. The fibrous composition is 40% refined bleached kraft and 60% bleached hardwood. 20% load is introduced relative to the fibers. Bonding and carried out with rosin reinforced at the rate of 1.3 percent dry; the pH is adjusted to 5 with alumina sulfate.

On this suspension, retention tests are carried out comparatively with the amphoteric terpolymer according to the invention prepared in Example B and with the linear powder copolymer sold by the Applicant under the name "FO 3190" in Example 2.

The following results are obtained: Polymers used % ° dry polymer compared to dry paper total retention FO 3190 0.2 76.5 0.5 85 Terpolymer B 0.2 89 0.5 94.5

C - Manufacture of a moderately cationic terpolymer

• 6861 kilogrammes d'acrylamide 30 % dans l'eau ;
• 4760 kilogrammes de chlorure de triméthylaminoéthylacrylate (ADAM CH₃Cl) à 75 % en solution dans l'eau ;
• 379,5 kilogrammes d'acide acrylique et 2579,5 kilogrammes d'eau ;
• 2 % par rapport à la matière active, d'acide adipique (soit 12 kilogrammes).

In a reactor, the following are mixed at ambient temperature:

• 6861 kg of acrylamide 30% in water;
• 4760 kilograms of trimethylaminoethylacrylate chloride (ADAM CH₃Cl) at 75% in solution in water;
• 379.5 kilograms of acrylic acid and 2,579.5 kilograms of water;
• 2% compared to the active ingredient, adipic acid (12 kilograms).

A solution is obtained whose pH is 3.6. Cool to 0 ° C, add (1000) thousand ppm of catalyst: isobutyronitrile (AZDN) (or 15 kilograms) and degas by bubbling nitrogen. A transfer agent (sodium formate) is then added at the rate of two thousand (2000) ppm relative to the load, ie (15 kilograms).

Then 4.2 ppm of ammonium persulfate (63 grams) and 0.86 ppm of iron in the form of Mohr salt (6 ppm of Mohr salt, ie 90 grams) are added. The exothermic reaction is allowed to continue for approximately one hour, until the temperature of 90 ° C. is reached.

A gel is then obtained which is left to age for two hours, then which is ground, dried with hot air and re-embossed again, until a particle size of less than one millimeter is obtained.

A perfectly soluble white powder is then obtained up to 40 grams per liter at room temperature, having an insoluble content of less than 0.02 percent (0.02%). This terpolyacrylamide powder has a Brookfield viscosity close to 3.0 cps (0.1% UL in a 1M Nacl solution at 25 ° C at sixty revolutions per minute (60 rpm).

• acrylamide :   55 %
• acide acrylique :   10 %
• ADAM CH₃Cl :   35 %.

The molar composition of the polymer obtained is as follows:

• acrylamide: 55%
• acrylic acid: 10%
• ADAM CH₃Cl: 35%.

Example 4 :

In known manner, a paper pulp is prepared comprising thirty percent (30%) of recovered paper, thirty percent (30%) of bleached kraft, twenty percent (20%) of calcium carbonate, ten percent (10%) of broken -bed and ten percent (10%) of bleached hardwood.

This fibrous suspension is dissolved in water at the rate of 2.5 grams / liter. The pH of this suspension is 7.6.

The retention tests are carried out in the same manner as in Example 1 with the product obtained from Example C, then compared to a linear copolyacrylamide of the same cationicity, with a viscosity UL of 3.0, marketed by the Applicant under the name FO 4440.

The results are reported in Table 2 below. Table 2 Dosage% polymer FO 4440% retention Terpolymer C% retention 0.03 58 72 0.05 64 81 0.2 75 87 0.3 77 90 0.5 76.5 90.5 0.7 74.5 92.5

There is a clear advantage of the moderately cationic amphoteric polymer according to the invention compared to a cationic copolymer with the same charge. The amphoteric product sees its effect start much faster and allows access to very high retention figures.

The method according to the invention, which consists, among the polyacrylamides, of having chosen an amphoteric ternary polyacrylamide in powder form in combination with bentonite, not only makes it possible to improve the retention rate unexpectedly compared to the other polyacrylamides , therefore the effectiveness of the treatment, but also makes it possible to improve the clarity of the water under canvas and this without opposite effect. In addition, it makes it possible to successfully process loaded pasta.

Compared to the combination of bentonite and linear polyacrylamide powder, as described in US Pat. Nos. 3,052,595 and 4,305,781 cited in the preamble, an improvement in the retention rate of about ten to twenty percent (10 to 20%), which results in a consequent reduction in pollution and allows better recirculation of fines and charges in the machine circuit, and better control of these machines. In addition, there are fewer bacterial deposits in the circuit, therefore fewer faults, fewer breaks, fewer holes in the paper.

Compared to mixtures of bentonite and polyacrylamide emulsions, there is less rejection of oil or surfactants, which as already mentioned, affect the properties of the finished paper.

Compared to other powdered polyacrylamides, the use of amphoteric polyacrylamides allows high dissolution rates, avoids over-flocculation, therefore the absence of flocking on the paper, and as already said, the absence of reverse effect in the event of overdose.

Claims (4)

1 / Process for the manufacture of paper or cardboard with improved retention, in which a polyacrylamide and bentonite are added to the fibrous suspension, characterized in that the polyacrylamide is a linear amphoteric terpolymer, and is introduced into the fibrous suspension in powder form dissolved, at a rate of 0.03 to 1.0 per thousand (0.03 to 1.0 ‰) by weight, of the dry weight of the fibrous suspension. 2 / A method according to claim 1, characterized in that the amphoteric terpolyacrylamide is a high molecular weight polyelectrolyte formed of acrylamide and at least two other monomers, respectively an anionic and the other cationic, but of cationic nature predominant. 3 / Method according to claim 2, characterized: - in that the anionic monomer is chosen from the group consisting of acrylic acid and acrylamidomethylpropylsulfonic acid (AMPS); - And in that the cationic monomer is chosen from the group consisting of acrylamide propyl methyl ammonium chloride (APTAC), methacrylamidopropyltrimethylammonium chloride (MAPTAC), dimethylaminoethyl acrylate (ADAME), dimethylaminoethyl methacrylate quaternized or salified (MADAME ), trimethylaminoethylacrylate chloride, trimethylaminoethylacrylate methyl sulfate, trimethylaminoethyl methacrylate chloride, trimethylaminoethyl methacrylate methyl sulfate. 4 / A method according to claim 3, characterized: - in that the amphoteric terpolymer is a terpolymer with a cationic preponderance comprising by molar weight: . at least 40 mole percent acrylamide; . from 5 to 15 mole percent of anionic monomer; . from 10 to 50 mole percent of cationic monomer; - And in that the anionic charge is at most equal to the cationic charge.