FI90448C - Method in papermaking - Google Patents

Abstract

A method for the production of paper by forming and dewatering a suspension of cellulose containing fibres on a wire. The forming and dewatering takes place in the presence of an anionic, inorganic colloid, an aluminate and a cationic synthetic polymer. The process gives improved dewatering and improved retention of fines and optional fillers.

Description

90448

Method in papermaking -satt vid framstailning av papper

This invention relates to an improved retention and dewatering system for use in papermaking. More particularly, the invention relates to the use of a combination of a cationic synthetic polymer, an anionic inorganic colloid and aluminate as a retention and dewatering system in papermaking.

It is previously known to use combinations of cationic retention aids and inorganic colloids as retention and dewatering agents in papermaking. European Patent Application 0218674 discloses the use of polyacrylamide in combination with anionic silica salts as a binder and retention aid. It is assumed that the colloidal particles in the sols with their strong charge provide a bridging bond in the polymeric retention aids and that a very good retention and dewatering effect is achieved thanks to t3m3. It is also previously known from GB 2015614 to use polymeric cationic retention aids in combination with polyaluminum compounds. Furthermore, it is known from U.S. Pat. No. 4,643,801 to use as a binder in papermaking a combination of cationic starch, anionic silica sol and an anionic high molecular weight polymer, especially anionic polyacrylamide. The ternary system of U.S. Pat. No. 4,847,607 may further comprise aluminum compounds, alum, sodium aluminate or polyhydroxyaluminum chloride.

According to this invention, it has been shown that the retention and dewatering effect in papermaking is enhanced when aluminate is used in combination with a cationic synthetic polymer and an anionic inorganic colloid. As the dewatering effect increases, the speed of the paper machine can be increased and, in addition, less water must be dried in the drying section of the paper machine.

The present invention thus relates to a process for papermaking by forming a suspension of cellulose-containing fibers and possible fillers and dewatering it with a wire, the formation and dewatering taking place in the presence of an anionic inorganic colloid, aluminate and a cationic synthetic polymer.

The three components of N3m3 can be added to their fiber mass in an arbitrary order. The best effect is obtained if the aluminate is first added to the pulp, after which the cationic synthetic polymer and after that the anionic inorganic colloid are added. A considerable improvement over the prior art is achieved myds if the anionic inorganic colloid is added to its pulp first, followed by the cationic polymer and aluminate in arbitrary order. The separate addition of the three components of the N3 is considered to be the most suitable, although there is the possibility of premixing the two components before the addition.

Suitable cationic synthetic polymers according to the invention are those cationic, organic nitrogen-containing polymers which are normally used in papermaking as retention aids and / or as resilience enhancers. Particularly suitable are cationic polyacrylamides, polyethyleneimines, polyamine and polyamidoamine resins, etc. Polyamine resins and polyamidoamine resins are preferably used in the epichlorohydrin-modified form. Other cationic synthetic polymers used include cationic melamine formaldehyde and urea formaldehyde brand strength resins. The weight of the cationic synthetic polymer should be 0.01 to 3% by weight, preferably 0.03 to 2% by weight, based on the dry fibers and any filler.

3,90448 The anionic inorganic colloids used have been known to be used in the past in papermaking. Examples of such compounds are montmorillonite, bentonite, titanyl sulphate sols, silica sols, aluminum-modified silica sols or aluminum silicate sols. The terms colloid and colloidal refer to very small particles. Particles of anionic substances

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the female surface should be greater than about 50 m-Vg, more preferably greater than 100 m 2 / g, and most preferably 50 to 1000 m 2 / g. Silica-based colloids are considered to be the most suitable anionic ep3organic colloid.

Particularly suitable silica-based colloids are those silica sols having colloidal particles disclosed in European Patent Publication No. 41056, which is incorporated herein by reference, and those aluminum-containing silica sols disclosed in European Patent Publication No. 0218674, which is also incorporated herein by reference. The colloidal silica specific surface area of the N3 sols should preferably be 50-1000 m2 / g, and more preferably about 100-1000 m2 / g, with the best results being obtained when the specific surface area has been about 300-700 m2 / g. It has been found that colloidal silica particles must have a mean particle size of less than 20 nm and preferably from about 10 nm up to about 1 nm (a colloidal silica particle with a specific surface area of about 550 m 2 / g corresponds to a mean particle size of about 5 nm). Good results are obtained using said silica sols in the form of an alkali-stabilized sol containing about 2 to 60% by weight of SiO 2, preferably about 4 to 30% by weight of SiO 2. The silica sol can be stabilized with alkali in a molar ratio of SiO 2: M 2 O of 10: 1 to 300: 1, preferably 15: 1 to 100: 1 (M is an ion from Na, K, Li and NH 4). As stated above, very good results are obtained when using colloidal particles in which at least the surface layer is aluminum silicate or Aluminum-modified silica sol, so that the surface groups of the particles 4 90448 contain silicon and aluminum atoms in a ratio of 9.5: 0.5 to 7.5: 2 , 5 and the reported surfaces and particle sizes apply to MySs these silica sols. Silica sols that meet the aforementioned specifications are commercially available, for example, through Eka Nobel AB.

The amount of anionic colloid to be added to the pulp must be 0.005 and 2% by weight, preferably 0.01 and 0.4% by weight, based on the dry cellulosic fibers and possible filler. The concentration of colloid, preferably colloidal silica, in the sol added to the pulp is not critical. From the point of view of use, it is suitable that the concentration of sols when added to the fibrous mass is 0.05 and 5.0% by weight of wool.

By aluminate is meant an alkali metal aluminate which is well known in the art of papermaking, especially in hydrophobitating with mantle resin. Sodium aluminate (Na 2 Al 2 O 4) is most preferably used, but it is of course possible to use potassium aluminate, although at a lower cost. The amount of aluminate can vary within wide limits. The aluminate is preferably added to the pulp in the form of aqueous solutions, the concentration of which is not critical but is adapted according to practical criteria. According to the invention, it has been found that even a very small amount of aluminate, compared to the amount of anionic inorganic colloid, achieves a considerable improvement in the dewatering effect. The improvement is achieved with a weight ratio of aluminate to inorganic colloid calculated as Al 2 O 3 of 0.01: 1. The Yia limit is not critical. However, no significant improvement is achieved when the silent ratio of aluminate to inorganic colloid is greater than 3: 1. The ratio is preferably 0.02: 1 to 1.5: 1 vile, most preferably 0.05: 1 to 0.7: 1 vile. All ratios shown relate to the weight ratio of aluminate to inorganic colloid calculated as Al 2 O 3.

5,90448

The improved retention and dewatering effect of the system according to the invention is achieved with a wide pH of the pulp. The pH may range from about 4 to about 10. The pH is preferably above 5 and more preferably from 6 to 9. If the desired pH is not reached with additional aluminate solution, which is itself alkaline, additional pH, for example sodium hydroxide, can be obtained at the pH of the pulp. When an alkaline buffering filler such as chalk is used, the desired pH is normally reached without yield. Of course, it is possible to use fillers other than chalk, but care must then be taken to ensure that the pH of the pulp remains within the limits set out above.

The papermaking according to the invention may contain mineral fillers of the usual type, for example kaolin, titanium oxide, gypsum, chalk and talc. The term "mineral filler" in this context includes, in addition to these fillers, myfis wollastonite and glass fibers and myfis low density mineral fillers such as expanded perlite. The mineral filler is usually added in the form of an aqueous slurry at the concentrations of nile used for such fillers. Optionally, the filler may be treated with the components of the dewatering and retention system of the invention, for example cationic synthetic polymer and aluminate, or an inorganic anionic colloid, the fraction of which is added to the pulp.

The three-component system according to the invention can be used in the production of paper from different types of cellulosic fibers. The pulps must contain at least 50% by weight of fibers containing cellulose. The three-component system can be used, for example, for chemical pulps such as sulphate and sulphite pulps, hot mills, refined pulps or both pulps formed from hardwood pulpwood fibers. It can, of course, also be used for pulps formed from recycled fibers. In this context, the terms paper and papermaking used do not, of course, include only paper and its manufacture, but also other cellulosic fibrous sheets or web-shaped products such as cellulose sheets, cardboard and paperboard and their manufacture.

The method according to the invention can be applied in a manner known per se and other known additives, such as hydrophobing agents, etc., can be added to the fiber mass.

The invention is more particularly illustrated in the following structural example, in which parts and percentages are by weight unless otherwise indicated.

Example 1

In the following experiments, the dewatering effect has been investigated using the "Canadian Freeness Tester", which is a conventional method for characterizing the dewatering ability according to SCAN-C 21:65.

The pulp was based on bleached birch / mantysulfate pulp (60:40) and contained 30% by weight chalk. The pulp had a pH of 8.5 and a CSF of 300 ml.

The chemical additive levels given in the table refer to tonnes of dry pulp (fibers + fillers). The anionic colloid was an alkali-stabilized silica sol with a surface area of 500 m 2 / g. The cationic synthetic polymer was a medium cationic polyacrylamide with a medium cationicity sold by Allied Colloids under the name Percol 292. Sodium aluminate was added in the form of 0.025% aqueous solution 7,90448 and the reported aluminate masses are expressed in kilos of Al 2 O 3.

Chemical additions were made to 1 liter of diluted pulp (about 0.3%) every 15 seconds with agitation of aluminate, cationic polymer, inorganic colloid. The flocculated pulp was transferred to a "free-ness" device and measurements were made for 15 seconds on the last lisseys jaike. Accumulated water is a measure of dewatering ability and is expressed in ml Canadian Standard Freeness (CSF) · The water obtained in the experiments using the three components was very clear and showed that a good retention effect on the fine fiber adhering to the flocs is achieved at the same time.

Koe Al203 Cat. polymer An. colloid CSF

no._kq / t_kq / t_kq / t_ml 1 - - 300 2 - 0.3 - 370 3 0.6 - 385 4 0.9 - 390 5 0.15 - - 290 6 0.15 0.3 - 350 7 - 1.0 295 8 0.15 - 1.0 290 9 - 0.3 0.5 420 10 - 0.3 1.0 430 11 - 0.3 1.5 440 12 0.075 0.3 0.5 495 13 0.15 0.3 1.0 520 14 0.225 0.3 1.5 515 15 - 0.6 0.5 425 16 - 0.6 1.0 490 17 - 0.6 1.5 510 18 0.075 0, 6 0.5 495 19 0.15 0.6 1.0 570 20 0.225 0.6 1.5 585 8 90448

As can be seen from the table, the use of even very small aluminate series results in a substantially improved dewatering capacity for the cationic polymer and anionic colloid system. A similar effect of aluminate does not occur if it is used exclusively in combination with a cationic polymer or an anionic colloid.

Example 2 This example corresponded exactly to Example 1 Silia with the only difference that other cationic synthetic polymers were used. N3m3 were A) epichlorohydrin-modified polyamidoamine resin sold by Hercules Inc. under the name Kymene 557 H and B) modified polyamine resin sold by Hercules Inc. under the name Delfloc-50.

Koe AI2O3 Cat. polymer An. colloid CSF

no._kq / t_tyyppi; kq / t_kq / t_ml 1 - - 300 2 - A; 0.6 - 305 3 - A; 1.2 - 315 4 - A; 2.4 - 315 5 - A; 1.2 0.5 325 6 - A; 1.2 1.0 330 7 - A; 1.2 1.5 310 8 0.075 A; 1.2 0.5 360 9 0.15 A; 1.2 1.0 390 10 0.225 A; 1.2 1.5 410 11 0.30 A; 1.2 2.0 395 12 - B; 1.2 - 290 13 - B; 1.2 1.5 280 14 0.225 B; 1.2 1.5 335 9 90448

Example 3 In this experiment, a ground fiber pulp was used which did not contain fillers. 0.5 g / l Na 2 SO 4 .10H 2 O had been added to the pulp to bring the ionic strength to a level • similar to that in use. The cationic polymer was the same polyacrylamide as in Example 1. The anionic colloid was an aluminum-modified, 15% alkali-stabilized silica sol in which the surface of the colloidal particles was modified with 9% of Al atoms and the surface area of the particles was 500 m 2 / g. An additional sequence was sodium aluminate, a cationic polymer followed by an anionic colloid. The experiments were performed at both pH 6 and pH 7.5 of the pulp, which had been obtained with dilute H 2 SO 4 or dilute NaOH.

Koe Al203 Cat. polymer An. colloid CSF

no._kg / t_kg / t_kg / t_ml ph 6.0 1 - - 120 2 - 0.3 - 190 3 - 0.6 - 220 4 - 0.9 - 245 5 - 1.2 - 250 6 - 0.6 0.5 275 7 - 0.6 1.0 305 8 - 0.6 1.5 300 9 0.075 0.6 0.5 325 10 0.15 0.6 1.0 345 11 0.225 0.6 1.5 350 pH 7,5 12 - 0,6 - 220 13 - 0,6 0,5 245 14 - 0,6 1,0 270 ίο 90 448 15 - 0,6 1,5 275 16 0,075 0,6 0,5 295 17 0.15 0.6 1.0 325 18 0.225 0.6 1.5 340 19 - 0.9 1.5 310 20 0.225 0.9 1.5 370

As in Example 3, ground fiber pulp supplemented with 0.5 g / l Na 2 SO 4 .10 H 2 O was used. The pH of the fibrous pulp was 6.5 and the chemicals added were sodium aluminate, a cationic polyethylene mine sold by BASF harden-13 Polymin SK, and an anionic colloid consisting of benthic rivet colloid having a specific surface area in water of about 400-800 m 2 / g.

Koe Al203 Cat. polymer An. colloid CSF

no._kq / t_kq / t_kq / t_ml 1 - - 120 2 0.3 - 175 3 0.6 - 230 4 - 0.9 - 300 5 1.2 - 310 6 - 0.6 0.5 260 7 - 0 .6 1.0 280 8 - 0.9 1.0 340 9 0.075 0.6 0.5 295 10 0.15 0.6 1.0 335 11 0.15 0.9 1.0 390

Claims (10)

A method of making paper by forming a suspension of a cellulose-containing fiber and by dewatering it on a wire, characterized in that the forming and dewatering takes place in the presence of an anionic inorganic colloid with the exception of anionic inorganic colloid made of polymeric silicic acid having a specific surface area of at least 1050 m 2 / g, an aluminate and a cationic synthetic polymer. Process according to claim 1, characterized in that the anionic colloid is made of a silica-based colloid. Process according to Claim 1 or 2, characterized in that the colloid is a silica sol, a silica sol with particles having at least one aluminum silicate surface layer or an aluminum modified silica sol. 4. A process according to claim 1, 2 or 3, characterized in that the colloid particles have a specific surface within the range of 50 - 1000m2 / g. 5. A method according to claim 3, characterized in that the particle size of the colloid is at most 20 nm. 6. A process according to claim 1, characterized in that the cationic synthetic polymer is constituted by a cationic polyacrylamide, polyethyleneimine, polyamine or polyamidoamine. Process according to any one of the preceding claims, characterized in that the aluminate was added to the fiber suspension for the anionic inorganic colloid and the cationic synthetic polymer. 14 90448 A process according to any one of claims 1, 2, 3, 4 or 5, characterized in that the amount of anionic inorganic colloid is in the range 0.005 and 2% by weight, shaved on dry fiber and any fillers. A process according to any one of claims 1 or 6, characterized in that the amount of cationic synthetic polymer is in the range of 0.01 to 3% by weight, based on dry fiber and any fillers. 10. A process according to claim 1, characterized in that the weight ratio of aluminate, calculated as Al2 O3, to anionic inorganic colloid is in the range of 0.01: 1 to 3: 1.