EP0282415A1 - Process for producing paper - Google Patents

Abstract

Process characterised in that one (or more) cationic starch(es) and one (or more) anionic starch(es) other than a starch phosphate are introduced, separately from each other, at two or more points (8, 12, 13, 14), especially at the wet end, into the fibre composition forming the raw material. <IMAGE>

Description

The subject of the invention is a process for manufacturing paper, the term "paper" designating in the following any flat structure or sheet not only based on cellulose fibers - the raw material most frequently used in the paper industry and cardboard-- but also based
- synthetic fibers such as polyamide, polyester and polyacrylic resin fibers,
- mineral fibers such as asbestos, ceramic and glass fibers,
- all combinations of cellulosic, synthetic and mineral fibers.

The well-known use of cationic starches which are introduced into the mass of fibers before the sheet is formed has made it possible to increase the retention of fibers and fillers, to improve drainage and to increase the characteristics paper physical; in fact, the preferential fixation of these starches on the anionic reaction sites of the fibers and of the fillers, made possible by their cationic or cationic nature, makes it possible to increase the number of bonds between fibers as well as between fibers and fillers, whence greater resistance of the paper: and thanks to this greater resistance of the paper, it became possible to reduce the concentration of the mass of fibers or to resort to fibers of lower quality.

It turns out that the advantages obtained by the use of cationic starches have not always, for several years, made it possible to compensate for the increasing disadvantages created by the increasing degradation of the quality of the raw materials.

Indeed, to face increasingly strict concerns about economic profitability, not only the semi-chemical pulp traditionally used for example for the manufacture of paper for corrugated cardboard saw its share reduced in favor of pulp from cellulose recovery fibers, commonly called FCR, but moreover the very quality of these FCR is more and more poor due to the increasing number of recycling "old paper".

Added to this is the fact that at the level of paper machines, the trend is more and more towards the systematic closing of circuits, hence an enrichment of production waters with organic and mineral materials.

These factors contribute to the decrease in the strength of the paper; the proportion of cationic starches that can be fixed on the fibers decreases, resulting in less resistance of the sheet.

Various solutions have been proposed to remedy these drawbacks.

Thus, we have developed starches characterized by an increasingly high cationicity, but obviously limited by the maximum cationicity that can achieve conventional methods of obtaining cationic starches. And, in any case, whatever the degree of cationicity, the closing of the circuits and the degradation of the quality of the fibers results in an inevitable drop in the resistance of the papers.

Knowing that the effectiveness of a cationic starch is all the greater the greater its probability of fixation on the fiber, use has been made (see US Pat. No. 4,066,495) to increase this probability of fixation to combinations of "cationic starch - polyacrylamide" or "cationic starch - alumina sulfate or poly aluminum chloride".

This use of two or more compounds of the same ionicity in fact has the sole objective of increasing the retention of the charges and the fibers without, however, modifying the composition of the paper.

In the same vein, we appealed (see patent FR 1,499,781) to starches containing both cationic groups and anionic phosphate groups.

These starches, although consequently comprising groups of different ionicity, nevertheless have an essentially cationic character, consequently implying their own limits of use.

The successive application of a starch phosphate and a cationic starch only improves the resistance of the paper obtained and this in an insufficient proportion. In addition, these phosphate starches contribute to increasing the pollutant load by the presence of nitrogen compounds from their manufacturing process.

In the so-called "dual" techniques, it was not starches comprising both cationic groups and phosphate groups or the use of starch phosphates and cationic starches that were used, but to associations of cationic starches and compounds of different ionicity.

Thus (see EP 41.056), cationic starches were used in association with colloidal silicic acid; moreover, patent EP 60,291 describes the preparation of a gel based on cationic starch and carboxymethylcellulose or on a uronic acid polymer, this gel being partially dehydrated by the action of a colloidal solution of acid. polysilicon or an oxypolyaluminum compound.

Dual techniques lead to an improvement in retention, thus making it possible to manufacture paper with a higher content of fillers. They allow a substantial saving of cellulose, but are not applicable in all cases. In addition, the amount of starch attached to the cellulose at the time of the formation of the sheet remains still limited, the physical characteristics of the paper thus obtained are not always improved sufficiently.

To obtain a paper having increased mechanical characteristics, it is therefore necessary to subject the paper produced according to one of the preceding techniques, to a surface treatment carried out in particular in a machine of the "size-press" type; such a treatment makes it possible to increase the proportion of starch entering into the constitution of this paper, thus giving it better resistance.

However, such a solution is not satisfactory from an economic point of view, any additional operation being costly; switching to "size-press" also results in a significant reduction, of the order of 15 to 20%, in the speed of the machines and therefore in the production of paper.

It follows from the above that none of the existing methods leads, with a satisfactory cost price, to obtaining paper having the desired characteristics.

The object of the invention is therefore, above all, to provide a process for the production of paper which responds better than those which already exist to the various wishes of the practice.

However, the Applicant Company has found, after in-depth research, that it becomes possible, in particular under conditions deemed to be difficult, to increase significantly, that is to say by at least 30%, or even 50% or even more than 100%, the limit threshold for fixing the starch in the fibrous composition when a starch is introduced into the mass of fibers, in particular in the wet part, separately from each other cationic and an anionic starch other than starch phosphate.

The expression “limit threshold for fixing starch in the fibrous composition” denotes the amount of starch fixed per unit weight of dry fibrous composition, the latter comprising all of the insoluble constituents used to form the sheet paper.

It follows that the process for manufacturing paper according to the invention is characterized in that one introduces into the fibrous composition constituting the raw material, at two or more points, in particular in the wet part, separately one on the other, one (or more) cationic starch (s) and one (or more) anionic starch (s) other than starch phosphate.

According to an advantageous embodiment of the above process, the anionic starch other than a starch phosphate is chosen from the group comprising starch phosphonates, carboxyalkyl starches and, preferably, starch sulphates, starches sulfoalkylated and sulfocarboxyalkylated. In what follows, the expression “anionic starch” designates all products of this type with the exception of starch phosphates.

According to another advantageous embodiment of the above process, is added to the fibrous composition constituting the raw material intended for papermaking, an amount of 0.2% to 5% of cationic starch and an amount of 0.2 to 5% anionic starch.

Preferably, the amounts of cationic and anionic starch are between 0.4% and 3%, more preferably between 0.7% and 2.5%, the percentages being expressed as dry starch relative to the dry fibrous composition.

The cationic and anionic starches are advantageously introduced into the fibrous composition in the form of a dilute aqueous glue with a concentration of less than 5%, preferably less than 3% and, more preferably, less than 1%, the lower limit being 0.01%. .

The preparation of adhesives (if the starch used is not directly soluble in cold water, in which case a simple dispersion in water is sufficient) is carried out in a manner known per se, by discontinuous or continuous cooking, for example in a continuous pressure cooker capable of ensuring the dosing, cooking and dilution operations.

according to an advantageous embodiment of the invention, it may be proposed for the sake of simplification of the process in question to use anionic or cationic starches directly soluble in cold water and to introduce them, in powder form , directly in the fibrous suspension.

According to another advantageous embodiment of the process according to the invention, the proportion of cationic starch relative to the anionic starch must be between 10/1 and 1/10, preferably between 5/1 and 1/3 and, more preferably still, between 3/1 and 1/2, these ratios being expressed in dry weight of starch.

The point of introduction of the cationic and anionic starches is defined according to the physicochemical characteristics of the system, this choice resulting in different values of the contact time with the fibrous composition.

The optimum concentrations of cationic starch and anionic starch used in accordance with the invention, that is to say those allowing the best performance to be obtained, are determined within the limits indicated, depending in particular on the mass of fibers used, and the aqueous medium used (ionic environment) or the characteristics specific to each paper machine.

Within these limits, the performances inherent in the invention, as measured for example using the starch retention test, are higher than those which could be expected by simple addition of the relative individual performances. with the use respectively of cationic starch or anionic starch, consequently translating a synergistic effect.

The cationic starches used in accordance with the invention are selected from those having an acceptor electronic state, obtained using substituent groups of an electropositive nature, called cationic.

The most commonly used substituents are those containing a tertiary or quaternary nitrogen atom, although phosphonium and sulfonium groups can also be used.

dans lesquelles
    - A représente les groupements :

    - X représentant dans les susdites formules un atome d'halogène, tel que par exemple le chlore,
    - R₁ et R₂ représentent chacun, indépendamment l'un de l'autre, un radical alkyle à chaîne droite ou ramifiée en C₁-C₄ ou bien sont réunis en une structure cyclique,
    - R₃ représente un radical alkyle à chaîne droite ou ramifiée en C₁-C₄ et n représente un nombre entier de 1 à 3.As cationic reagents for starch, halohydrins or epoxides corresponding to the following formulas can be used:

in which
- A represents the groups:

- X representing in the above formulas a halogen atom, such as for example chlorine,
- R₁ and R₂ each represent, independently of one another, a straight-chain or branched C₁-C alk alkyl radical or else are combined in a cyclic structure,
- R₃ represents a straight-chain or branched C₁-C₄ alkyl radical and n represents an integer from 1 to 3.

The cationization reagents used are preferably:
- diethylamino chloroethane,
- epoxypropyl trimethylammonium chloride,
- trimethylammonium chloride chloro-1-hydroxy-2-propane.

The electrophilic power of these starches is quantified by measuring the degree of substitution (DS), that is to say the number of hydroxyl functions which have been substituted by elementary glucoside unit. As a general rule, the DS is at most equal to 0.3; it is preferably between 0.02 and 0.20 and, more preferably, between 0.04 and 0.15.

For the preparation of the anionic starches used in accordance with the invention, the anionic substituents are introduced into the starch molecule using functional reagents, preferably:
- in the case of starch phosphonates, diethylphosphonic acid aminochlorethane.
- in the case of starch sulfates, sulfamic acid, sulfamates or even electron donating SO encore complexes such as SO₃-TMA (trimethylamine), SO₃-pyridine,
- in the case of starch sulfoalkyls, 2-chloroethane sulfonates and 3-chloro-2-hydroxypropanesulfonate,
- in the case of starch carboxyalkyls, the salts of halo-1-carboxylic acids such as sodium monochloroacetate or sodium chloropropionate, lactones such as propiono- or butyrolactone, acrylonitrile (reaction followed by saponification), acid anhydrides such as maleic, succinic, phthalic and other anhydrides,
- in the case of starch sulfocarboxyls, chloro-3-sulfo-2-propionic acid.

Although the strength of the nucleophilic power of starches containing anionic groups should, in theory, be specified by the value of pKA, we measure in practice the DS.

The maximum value that the DS can reach is equal to 3. However, as a general rule, we will retain, for the anionic products targeted by the invention, a DS at most equal to 1.5 and, preferably, at most equal to 0.5.

The attachment to starch of a reagent carrying a cationic or anionic group is well known [see:
- "Starch: Chemistry and Technology", edited by Whistler et al, vol. II (Industrial aspects), 1967, Academic Press;
- "Starch Production Technology", edited by JA Radley, 1976, Applied Science Publishers Ltd. London;
- "Starch: Chemistry and Technology", edited by Whistler et al, 2nd edition (1984), Academic Press, Inc., pages 354-385].
In the current state of the art, the reaction can take place in the wet phase, that is to say on a starch suspension, in aqueous medium or in solvent medium, but also in the dry phase, in the presence of an alkaline catalyst. The solvent phase or the dry phase will preferably be chosen in the case where the solubility in water becomes important when the DS increases. The fixing can also be carried out during the solubilization of the starch under the conditions described above.

The binding reactions on the starch of these cationic or anionic groups were carried out and described with starches from all sources such as those of corn, rice, wheat, potato, cassava and others. They can, according to an advantageous embodiment of the invention, be carried out on starches having previously undergone a more or less extensive crosslinking treatment. This treatment gives the anionic or cationic starches thus obtained particular properties resulting in greater freedom as to the choice of their point of introduction during their implementation in the context of the invention.

In a preferred embodiment of the invention, the Applicant Company was able to observe, at the level of the anionic starches and the cationic starches used, differences in behavior more or less visible, depending in particular on the cellulose pulps and aqueous media. used.

It is generally the cationic potato starch which is recognized as providing the best performance. Particular preference is given to anionic starches belonging to the group of sulfocarboxyalkyl derivatives.

The remarkable colloidal properties of the starches used in accordance with the invention have important repercussions on the manufacture of paper, making it possible for example to improve the retention of cellulose fines and of fillers during the preparation of the sheet and the speed of dripping water through the sheet.

In the context of the process according to the invention, use may also be made of other additives such as, for example, flocculating agents traditionally used in stationery such as, for example, alumina sulfate, polychoride of Al , polyethyleneimine, polyacrylamide and others.

Finally, the invention can be better understood using the following examples which are either comparative or relating to advantageous embodiments.

To evaluate the results obtained by implementing the method according to the invention, use is made of an installation suitable for reproducing at least certain stages of the production of paper from cellulosic fibers and shown diagrammatically in the single figure.

The installation in question comprises a vat 1 inside which is prepared the composition comprising a mass of fibers which is suspended and homogenized using an agitator 2. Agitation is maintained. throughout the duration of the test so as to ensure perfect regularity of supply to the circuit. It is however low enough not to modify over time the state of refining of the fibrous composition studied and not to degrade the flocs.

Once prepared, the fibrous composition is conveyed by a pipe 3 equipped with a P₁ pump in a transit vat 4 provided with an agitator 5 and in which it can be maintained for a predetermined time to allow contact with one or more adjuvants used at this stage; it is also possible not to plan any stay in the vat room 4; in this case, the fibrous composition simply crosses the vat and is brought by a pipe 6 directly to a pump P₂ located at the outlet of the vat 4.

In all cases, the fibrous composition will be drawn from the vat 1 with a rigorously constant flow.

Downstream of the pump P₁, the pipe 3 is equipped with an enclosure 7 inside which it is possible to adjust the pH of the fiber suspension by adding alkali or acid; and downstream of the enclosure 7, the pipe 3 comprises an element schematically shown at 8 and suitable for allowing the introduction of one or more adjuvants into the fibrous composition.

The pump P₂ conveys the suspension of fibers by a line 9 to two mixers in series respectively M₁ and M₂ equipped with agitators respectively 10 and 11; the adjustment of the rotational speeds and the shape of the blades of the agitators 10 and 11 are chosen so that the conditions prevailing inside the mixers are as close as possible to the shear conditions existing in the wet part of an industrial circuit paper making.

Three elements schematically shown in 12, 13 and 14 and adapted to allow the introduction of adjuvants in the fibrous composition are arranged on the line 9 at the outlet of the pump P₂ for the first and respectively before the inlet of the mixers M₁ and M₂ for the other two; these elements make it possible to choose the order of introduction, the shearing conditions before or after addition and the contact times between the adjuvants and the fibrous composition.

The second mixer M₂ is connected by a pipe 15 to a measuring device 16 called "Britt-Jar" in the art, described in the following publications:
TAPPI, October 1973, Volume 56, ^No. 10, p. 46 - 50
TAPPI, February 1976, Volume 59, ^No. 02, p. 67 - 70
TAPPI, July 1977, Volume 60, ^No. 07, p. 110 - 112
TAPPI, November 1978, Volume 61, ^No. 11, p. 108 - 110
(TAPPI = Technical Association of the Pulp and Paper Industry) and suitable for simulating the drainage of paper pulp on the canvas of a paper machine.

At the exit of the "Britt-Jar", one collects in an enclosure 17 draining water which can be assimilated to what is called "water under canvas" in the technique of papermaking, expression retained in this following.

The canvas water recovered in enclosure 17 is
- for a part, rejected in the sewer by a line 18,
- for another part, recycled by a pipe 19 fitted with a pump P₃ to the pipe 9 at a point 20 located between the elements 12 and 13.

The enclosure 17 is connected, moreover, to a secondary circuit making it possible to bring a third part of the water under canvas contained in the said enclosure to a tubidimeter 22 at the outlet of which the water under canvas which have passed through it are brought back to enclosure 17 by a pipe 23.

Perfect homogenization of the canvas water is ensured in this secondary circuit.

The turbidimeter 22 makes it possible to assess the content of water under canvas in mineral and organic materials (fibers, fillers and others); it turns out that the measurements carried out continuously using this device are in direct relation to the retention and more or less proportional to the amount of soluble and insoluble matter present in the water under canvas.

We also use a photometer which can be that known under the brand NANOCOLOR 50D (manufactured by the Company Macherey-Nagel, 5160-Duren, RFA, and marketed by the Company Techmation, 20 Quai de la Marne, 75019 Paris), and which allows measurements to be made reflecting the overall level of starch fixation; the principle of these measurements is based on the expression of the difference between the measurement carried out on a supernatant stripped of a few minutes of rest of the cellulose fibers and of the fillers, and colored with iodine, and that carried out on the same non-colored supernatant .

EXAMPLE 1

For a first series of tests, a pulp of the so-called "acid medium" type was prepared from cellulosic fibers using the following main constituents:
- 35% soda ash - long fibers,
- 35% soda ash - short fibers,
- 15% of "coated broken" (that is to say recycled pasta) loaded with calcium carbonate,
- 15% of "coated broken" loaded with kaolin.

After refining the resulting mixture into potable water at 48 ° SR (Schopper-Riegler degree, AFNOR standard NF Q 50-003), the following were introduced:
- 35% kaolin (grade G),
- 4% of alumina sulfate.

The fibrous composition or paste thus prepared had the following characteristics:
- concentration of the paste before introduction of the fillers (kaolin and alumina sulfate): 8 g / kg,
- concentration of loaded dough: 10.6 g / kg
- pH 4.7 (in vats)
- resistivity: 623 Ω-cm
- acidity: 140 mg / l (counted as sulfuric acid).

The acidity was measured by simple assay from an N / 10 sodium solution with phenolphthalein as a colored indicator.

Several experiments were carried out by treating this paste with a cationic starch and then with an anionic starch.

By way of cationic starch, a cationic potato starch was used having a nitrogen content fixed on dry comprised between 0.55 and 0.60% (which corresponds to a DS comprised between 0.063 and 0.069); in this case, it is that marketed by the Applicant Company under the brand HI-CAT® 180.

For its implementation, this cationic starch was dissolved on a continuous cooking appliance, under the following conditions:
- milk with 10% commercial matter
- temperature: 120 ° C, under sufficient pressure for cooking to take place in the liquid phase,
- holding time: 30 seconds,
- online dilution with cold water to bring the refractometric reading to less than 0.5%.

As anionic starches, those identified below were used:
- a starch sulfosuccinate having a DS of 0.05 (in this case that marketed by the Applicant Company under the brand VECTOR® A 180),
- a sulphated starch with a DS of 0.087, referenced AS,
- a phosphate starch with a DS of about 0.04 (in the one marketed by AVEBE under the RETABOND AP brand).

The anionic starches studied were prepared by steaming in an open tank under the following conditions:
- milk with 4% commercial matter
- hold for 5 minutes at 95-98 ° C
- online dilution with cold water to bring the refractometric reading to 2%.

The installation described above has been used in connection with the single figure.

The operating parameters of the installation have been defined as follows:
the rotational speeds of the mixers M₁ and M₂ were respectively 1000 and 2000 revolutions per minute,
- the flow rates of pumps P₁, P₂ and P₃ (return of water under canvas) were 400 milliliters per minute),
- turbidimeter setting: variable amplifier × 5.

The respective points of introduction of the cationic starch and of the anionic starches studied were arbitrarily chosen.

HI-CAT® 180 cationic starch is introduced through element 8, hence a contact time of 5 minutes before switching to "Britt-Jar".

The anionic starches are introduced by the element 12, from where a contact time of 30 seconds before the passage on "Britt-Jar".

The amount of cationic starch used is 1% on a dry basis relative to the dry fibrous composition.

For anionic derivatives, the quantity fixed is that allowing the lowest turbidimetric reading.

The number of experiments carried out is five, namely:
TEST 1: Control (without starch)
TEST 2: HI-CAT® 180 alone (1%)
TEST 3: HI-CAT® 180 (1%); VECTOR® A 180 (1.5%)
TEST 4: HI-CAT® 180 (1%); AS (1.6%)
TEST 5: HI-CAT® 180 (1%); RETABOND AP (0.65%).

The measurements are as follows:
- measurement of the turbidity of the water under canvas,
- evaluation of the overall proportion of starch fixed using the photometer,
- measurement of the quantity of fibers and fillers retained, commonly known as "canvas retention",
- measurement of charge retention.

We express "canvas retention" by the ratio

We express the retention of charges by the ratio

The results of these measurements are collated in Table I.

The results presented in Table I show that the sequential introduction of anionic starch of the sulfated type and more particularly of the sulfosuccinate type and cationic starch significantly increases the retention of fibers and fillers while ensuring perfect fixation of the starchy materials used.

This fixing of the starches is all the more remarkable since the concentration of starches used in tests 3 and 4 is at least twice that introduced in test 2.

On the other hand, it is noted that the results obtained in the presence of phosphate starches are clearly less satisfactory in particular from the point of view of the fixing of the starch (cf. photometric reading) and of the retention of the charges.

EXAMPLE 2

For this second series of tests, a thick paste of the so-called "acid medium" type, based on waste paper, was removed from an industrial machine, which, diluted with clarified water from the same factory, provided an introduced paste. in the vat room and whose characteristics were as follows:
- total concentration: 12.25 g / l,
- soluble matter concentration: 3.7 g / l,
- pH: 6.10,
- resistivity: 438 Ω-cm,
- hardness: 174 ° TH,
- starch in the filtrate: less than 0.1 g / l,
- soluble calcium: 575 mg / l,
- soluble aluminum: 2 mg / l,
- ash at 900 ° C: 2.2 mg / l.

In this series of tests, the cationic starch used is that of Example 1, prepared under the same conditions.

The anionic starch used is the sulphate starch of Example 1. It is prepared by steaming in an open tank under the following conditions:
- milk with 5% commercial matter,
- hold for 5 minutes at 95-98 ° C,
- online dilution with cold water to bring the refractometric reading to 2%.

The installation is that of the single figure.

The operating parameters of the installation have been defined as follows:
- mixer M₁: stirring at 1000 revolutions / minute,
- mixer M₂: stirring at 2000 revolutions / minute,
- the flow rates of the pumps P₁ and P₂ are 500 milliliters per minute,
the flow rate of the pump P₃ is 400 milliliters per minute, the excess being discharged through line 18,
- the pH was maintained at 5.7 with dilute sulfuric acid, introduced into the canvas water supplied for dilution.

The respective introduction points of the cationic starch and the anionic starch were chosen as follows:
- the cationic starch was introduced by element 8 (contact time of 10 minutes) and an additional quantity was, in certain tests, was introduced by element 14,
- the anionic starch was introduced by element 12.

The amounts of cationic starch and anionic starch and the point of introduction are indicated in Table II.

The amounts of cationic and anionic starch are expressed on a dry basis relative to the dry fibrous composition contained in the vat 1.

The measurements carried out are those of the turbidity of the water under canvas, the web retention and the amount of starch (in mg / l) found in the water under canvas determined by enzymatic assay.

The results are collated in Table III.

The pH of the canvas water is 5.7 to 5.8.

In light of these results, it can be seen that
- the correct fixation limit for the cationic starch used, introduced at two points as specified above, is around 2% (see test 8),
- When cationic and anionic starches are used successively, it is possible to achieve, for equivalent results, starch levels of the order of 3.5%; the retention gain can then be 3 points, which is important in the system used.

As an additional experiment, the fibrous composition was taken after the second mixer, instead of carrying out the measurements on "Britt-Jar" and "formettes" (sheets of paper) of a grammage were prepared. approximately 150 g / m² using this paste using the RAPID-KOETHEN type material marketed for example by the company Enrico Toniolo SpA (Milan, Italy) and well known to those skilled in the art.

Since the pulp studied is essentially intended for fluting paper, the CMT 60, that is to say the Concora index (see standard TAPPI T 809 su 66), was measured, the results being collated in Table IV.

It will be seen from reading these results that the gain in CMT is roughly proportional to the amount of transformed starch attached. The use of 2% cationic starch makes it possible to increase the CMT by 45 N (test 8). The overall use of 3.5% transformed starch (test 11) allows an overall gain of 71 N, which constitutes a decisive advantage of the process according to the invention.

EXAMPLE 3

In this example, the cationicity of the starch is varied.

A thick pulp obtained from old paper was removed on an industrial machine, then diluted with canvas water from the same machine to form the fibrous composition intended to supply the installation according to the single figure.

Analysis of said composition leads to the following values:
- total concentration: 16.5 g / l
- soluble matter concentration: 4.8 g / l
- pH: 5.7
- acidity: 253 mg / l counted as sulfuric acid
- resistivity: 338 Ω-cm
- soluble aluminum: 3 mg / l
- soluble sodium: 310 mg / l
- soluble calcium: 650 mg / l
- soluble magnesium: 24 mg / l
- starch: 0.39 g / l
- reducing sugars: 0.12 g / l
- ash at 900 ° C: 2.8 g / l.

A first cationic starch was used, namely that of Example 1, which was prepared by cooking in a continuous cooker.

A second cationic starch, namely a cationic starch having an average DS of 0.12 (1% of fixed nitrogen) referenced AMIDON 608, was also used.

The anionic starch used is one of those used in Example 1, namely the starch sulfosuccinate VECTOR® A 180.

STARCH 608 and VECTOR® A 180 were cooked in an open vat with live steam (5 minutes at 95-98%) from milk with 4% commercial dry matter. The adhesives thus obtained were then diluted to 2% with cold water.

The installation used is that shown in the single figure.

The operating parameters of this installation have been defined as follows:
- mixer M₁: agitation of 1000 revolutions / minute,
- mixer M₂: agitation of 2000 revolutions / minute,
- the flow rates of pumps P₁ and P₂: 500 milliliters per minute; the flow rate of the pump P₃: 400 milliliters per minute; the excess is eliminated.

The cationic starches were introduced by element 8, which gives a contact time of 5 minutes.

The anionic starch was introduced by element 12, which gives a contact time of 30 seconds.

As already indicated above, the quantities of anionic starch used are those for which the turbidimetric reading is the lowest.

Five tests were carried out (12 to 16), the amounts of starch introduced being:
TEST 12: none (control test)
TEST 13: 1.5% of AMIDON 608
TEST 14: 1.5% of HI-CAT® 180
TEST 15: 2% of AMIDON 608
TEST 16: 2% of AMIDON 608 + 0.96% of VECTOR® A 180.

The measurements of the turbidity and the measurements of the web retention were carried out and the overall proportion of starch fixed in the water under canvas was evaluated using the photometer.

The results are collated in Table V.

The pH of the water under canvas is from 6.2 to 6.4.

Tests 13, 14 and 15 (cationic starch alone) clearly demonstrate that, under the conditions adopted for this example, the use of a cationic starch with a higher DS makes it possible to increase the retention while bringing about a clarification of the waters under canvas.

Test 16 shows that the successive use of a cationic starch of the AMIDON 608 type and an anionic starch leads to very clear water under canvas despite high doses of starchy foods (approximately 3%) and to excellent retention. In addition, the amount of starch attached is remarkable.

EXAMPLE 4

In the context of this example, a different type of fibrous composition was used than those envisaged so far; it is a paste called "acid medium" but charged, in this case with kaolin.

The composition was taken from an industrial machine, then diluted with water under canvas from the same machine.

Analysis of the preparation thus obtained gave the following elements:
- total concentration: 11 g / l
- soluble matter concentration: 0.86 g / l
- pH: 5.6
- acidity in H₂SO₄: 20 mg / l
- resistivity: 1917 Ω-cm
- reducing sugars: 0 g / l
- soluble starch: 0.31 g / l
- soluble aluminum: 1 mg / l
- ash at 900 ° C: 1.6 g / l.

As a cationic starch, a cationic starch having a fixed nitrogen content of between 0.35 and 0.40 (ie a DS between 0.04 and 0.046) was used, in occurrence that marketed by the Applicant Company under the HI-CAT® 142 brand.

The method of preparation proper for its implementation is that described for the cationic starch HI-CAT® 180.

In addition, anionic starch VECTOR® A 180, already described in Example 1, was used as anionic starch.

We always use the installation shown in the single figure.

The operating parameters of the installation are defined as follows:
- mixer M₁: agitation of 1000 revolutions / minute,
- mixer M₂: agitation of 2000 revolutions / minute,
- flow rates of pumps P₁, P₂ and P₃: 400 ml / minute.

The cationic starch is introduced through element 8, which gives a contact time of 5 minutes.

The anionic starch is introduced through the element 12, which gives a contact time of 30 seconds.

Three tests are carried out (17 to 19), the amounts of cationic and anionic starch introduced being:
TEST 17: Witness (none)
TEST 18: 1.2% HI-CAT® 142
TEST 19: 1.2% of HI-CAT® 142 - 0.66% of VECTOR® A 180.

The turbidity, the web retention, the load retention were measured and the proportion of starch fixed by photometry was evaluated.

The results are collated in Table VI.

It follows from this table that the sequential use of anionic starch and cationic starch makes it possible, from the point of view of retention, to obtain remarkable results while considerably depleting the water under canvas.

The fixing of starches on the fibers is likewise improved.

EXAMPLE 5

Another series of tests was carried out using an unfilled paper pulp, worked in a neutral medium.

The basic composition is here:
- 40% bleached Kraft
- 15% bleached mechanical pulp - long fibers
- 45% bleached mechanical pulp - short fibers.

By diluting the thick industrial paste with the water under canvas from a machine, the preparation is obtained with the help of which the system is fed according to the single figure.

The analysis of this preparation gives the following values:
- total concentration: 12.5 g / l
- soluble matter concentration: 1 g / l
- pH: 5.8
- acidity in H₂SO₄: 21 mg / l
- resistivity: 1542 Ω-cm
- reducing sugars: 0.17 g / l
- soluble starch: 0.38 g / l
- soluble aluminum: 0.6 mg / l
- ash at 900 ° C: 3.3 g / l.

Was used, using the installation according to the single figure, as cationic starch, that known under the brand HI-CAT® 142 and, as anionic starch, that known under the brand VECTOR® A 180.

The operating parameters of the installation are as follows:
- mixer M₁: agitation of 1000 revolutions / minute,
- mixer M₂: agitation of 2000 revolutions / minute,
- flow rates of pumps P₁, P₂ and P₃: 400 ml / minute.

The pH is adjusted to a value of 7-7.2 by introduction of dilute sodium hydroxide at the junction 20 of the lines 19 and 9.

Furthermore, the cationic starch is introduced through element 8, which gives a contact time of 5 minutes.

The anionic starch is introduced through the element 12, which gives a contact time of 30 seconds.

Three tests were carried out (20 to 22), the nature and the quantities of starch introduced being:
TEST 20: Witness (none)
TEST 21: 1.2% of HI-CAT® 142 and
TEST 22: 1.2% of HI-CAT® 142 and 0.54% of VECTOR® A 180.

The amount of anionic starch was chosen so that the lowest turbidimetric reading was obtained.

The physical tests carried out on the papers obtained from tests 20 to 22, namely the determination:
- grammage (in g / m²)
- Scott-Bond (in Joules / m², TAPPI T 506 su 68 standard)
- ash (in%)
led to the results collated in Table VII.

The values collected in Table VII show that the results obtained are remarkable.

Following what and whatever the embodiment adopted, there is thus a paper manufacturing process whose characteristics result from the above and which has the advantage of leading to results clearly superior to those obtained by implementation of the methods according to the prior art.

Claims (9)

1. A method of manufacturing paper, characterized in that one (or more) starch is introduced into the fibrous composition constituting the raw material at two or more points, in particular in the wet part, separately from one another (s) cationic (s) and one (or more) anionic starch (s) other than starch phosphate. 2. A method of manufacturing paper according to claim 1, characterized in that the cationic starches are selected from those having an electronic acceptor state, obtained using substituent groups of electropositive nature, the most commonly used substituents being those containing a tertiary or quaternary nitrogen atom, the phosphonium and sulfonium groups can also be used. 3. Method according to claim 2, characterized in that the degree of substitution of the cationic starch used is at most equal to 0.3, preferably between 0.02 and 0.20 and, more preferably, between 0.04 and 0.15. 4. A method of manufacturing paper according to one of claims 1 to 3, characterized in that the anionic starch is chosen from the group comprising starch phosphonates, carboxyalkyl starches and, preferably, sulfates of starch, sulfoalkylated and sulfocarboxyalkylated starches. 5. Method according to claim 4, characterized in that the degree of substitution of the anionic starch used is at most equal to 1.5, preferably at most equal to 0.5. 6. A method of manufacturing paper according to one of claims 1 to 5, characterized in that one adds to the fibrous composition constituting the raw material, an amount of 0.2% to 5% of cationic starch and 0.2 to 5% anionic starch, the percentage tages being expressed as dry starch relative to the dry fibrous composition. 7. A method of manufacturing paper according to one of claims 1 to 6, characterized in that the amounts of cationic and anionic starch used are between 0.4% and 3%, more preferably between 0.7 % and 2.5%, the percentages being expressed as dry starch relative to the dry fibrous composition. 8. A method of manufacturing paper according to one of claims 1 to 7, characterized in that the cationic and anionic starches are introduced into the fibrous composition in the form of dilute aqueous glue with a concentration of less than 5%, preferably less than 3% and, more preferably, less than 1%, the lower limit being 0.01%. 9. A method of manufacturing paper according to one of claims 1 to 8, characterized in that the proportion of cationic starch relative to the anionic starch is between 10/1 and 1/10, preferably between 5 / 1 and 1/3 and, more preferably still, between 3/1 and 1/2, these ratios being expressed in dry weight of starch.

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