FI71379C - METHOD VID PAPPERSFRAMSTAELLNING - Google Patents

Description

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Papermaking Process

The invention relates to a papermaking process in which a polysaccharide type additive is used together with a synthetic retention aid to improve the dry strength properties or to degrade the paper.

The main raw material for the manufacture of paper and board is wood pulp made by either chemical or mechanical methods. According to the manufacturing method, we speak of either chemical or mechanical pulp. Fillers (kaolin, talc, CaCO 3, etc.) and various additives are used as other raw material components. Fillers are used on the one hand to reduce raw material costs and on the other hand to improve the printing properties of the product. The purpose of the additives is to give the product certain special properties, to improve the retention of the filler or to increase the strength of the product.

It is required to have a certain strength in all applications of paper and board. The required level of strength affects the choice of raw material components. In general, it can be said that the better the strength of a particular mass component, the more expensive it is. If the mass selection does not achieve sufficient strength, it can be increased by using the so-called Additional strength of the materials. These include, for example, starch, mucilages and polyacrylamide. Current known strength additives are generally not able to substantially reduce raw material costs, as the additional cost of strength additives is approximately the same as the resulting reduction in raw material costs. However, in order to meet the strength requirements, these additives have to be commonly used.

The application rates of strength additives are generally 0.5-2% by weight for dry adhesives of the polysaccharide type, 0.2-1% by weight for dry mucilages and polyacrylamides.

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In previous years, filler retention has been achieved with alum. As the speed of paper machines increased, alum power was no longer sufficient and synthetic polymers, mainly polyacrylamides, were introduced. Recently, on the one hand for cost reasons and on the other hand, in order to achieve a better printing result, it has been used to use ever larger amounts of filler. In this case, some mills have encountered difficulties with the strengths of the paper and, as a result, a strength additive has been added to the pulp. This known joint has not led to any surprising increase in strength. The probable reason has been that the filler has adsorbed the added retention aid more strongly than other pulp components.

The concomitant use of cationic starch and an anionic polyacrylamide-type retention aid is also known in the production of so-called superfilled paper grades. Namely, it is proposed to produce such grades of paper with two or three times higher than usual filler contents by means of said additive combination (STFI contact no. 3, 1982, pp. 3-4). For example, 5% cationic starch and 0.3% anionic polyacrylamide can be used in the production of paper containing 50% kaolin. Such use of cationic starch in combination with an anionic polymer is based, according to the publication, on the fact that the cationic and anionic components are dosed in the same proportion in charge, causing the starch to precipitate and remain on the paper in amounts greater than the adsorption capacity of the pulp. The improvement obtained with an filler content of 0% is surprisingly small. A similar result should be obtained by dosing about 2% of the starch alone.

Cationic starch and anionic polyacrylamide in a laboratory study (TAPPI 5j) (1976); 6, 120-122) was also found to function as a two-component retention agent combination. The effect of strength has not been studied in the experiments. Aggregate, 5-10% T1O2, was also used in these experiments, additive dosing was based on charge optimization.

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Acrylamide, which has an optimal molecular weight of between 100,000 and 500,000, can be used in paper as a dry adhesive. Combinations of such an anionic acrylamide and cationic starch or mucilage have been tried as a dry adhesive without any significant positive result (J.P. Casey: Pulp and Paper Chemistry and Chemical Technology, 3rd ed., Vol. Ill., Wiley &

Sons 1981, p. 1456). The reason for the poor result is probably that the conditions could not be chosen correctly.

Thus, it has now surprisingly been found that the use of a polysaccharide-type additive and a synthetic polymeric retention aid can be arranged so as to achieve an unexpectedly large improvement in the dry strength properties of paper or board with even smaller addition rates.

The main features of the invention appear from the appended claims.

By polysaccharide-type additive is meant herein those polysaccharides intended for addition to pulp and their derivatives or mixtures, which are mainly known as dry casting additives and which are described in more detail in the aforementioned work (J.P. Casey pp. 1475-1514). In addition to the dry strength, these substances can influence the separation of water from the web on a paper machine, the optimal formation of the paper web, and especially in the case of derivatives, also the retention and wet strength. Said substances have the ability to form hydrogen bonds with cellulose and thus increase the strength in the paper. Due to price factors, the most commonly used of these polysaccharide type additives are starches and their derivatives. Due to their good retention properties, cationic starch grades are preferably used. Other polysaccharide-type additives according to the invention include mucilages (e.g. guar gum with its derivatives), alginate and cellulose derivatives such as carboxymethylcellulose, methylcellulose and hydroxyethylcellulose.

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The synthetic retention aids according to the invention are high molecular weight, long-chain polymers, such as polyethylene oxide or polyacrylamides, the latter either as such or partially or completely hydrolysed or substituted or copolymerized. The polyethylene oxide is nonionic and preferably has a molecular weight of more than 1,000,000. The latter can be anionic, cationic or nonionic and have molecular weights of more than 200,000, preferably more than 1,000,000. It is also possible to use the substances as a combination or mixture.

Substantially filler-free grades of paper or board means those in which no or only small amounts of fillers have been used, up to 10% and generally less than 5%.

The retention of cationic starch at the application rates according to the invention is 90-100% (Casey, pp. 1492, 1495). The increase in strength obtained according to the invention cannot thus be based on the fact that the retention aid provides a complete substantial improvement in the retention of the polysaccharide additive (as opposed to known methods in which strength is increased by precipitating

On the other hand, the retention aid according to the invention alone does not have a significant effect of increasing strength when the amount of use remains at the level according to the invention, i.e. in its order of magnitude corresponding to normal use of retention aid. Thus, the surprising effect according to the invention must be based on the strong synergistic effect of the substances used.

In the method according to the invention, the retention agent is selected on a case-by-case basis using known methods, such as laboratory-scale retention tests, so as to obtain an optimal retention result. Whether the best result is obtained with an anionic, 5 71379 cationic or nonionic retention aid depends on the conditions (effect of mass, water, gluing, etc.). Thus, one deviates from the known method in that the charges of the polysaccharide-type additive and the retention aid do not have to cancel each other out, nor even have opposite signs.

The process according to the invention can be advantageously used in the production of grades of paper and board free or almost free of mineral fillers, such as kraft paper, newsprint and paperboard. However, the use of the invention is not limited to their preparation. However, in the preparation of filler-containing grades, the tendency of the retention aids to be generally adsorbed primarily on the surfaces of the filler particles should be taken into account. When the dosage of the retention aid is increased beyond the amount adsorbed by the fillers so that the retention aid can function as required by the invention and adhere to the fibers, uneconomically large addition amounts have to be readily used. Therefore, it is advantageous to carry out the filler-containing paper according to the invention by treating the filler separately with a retention aid found to be suitable for it (which may be the same as the retention aid according to the invention) and then adding the filler to the pulp treated according to the invention. Another way is to pre-treat the filler in a manner known per se (e.g. by the method described in the aforementioned STFI contact publication: cationic starch is obtained on the filler surface after the filler has first been dispersed anionically). In this way, the nature of the filler surface is completely changed, so that it can possibly be mixed into the mass even before the retention aid, without losing the strength advantage obtained by the polymer system according to the invention. The pretreatment of the filler can, of course, also be arranged in the presence of the pulp.

Some embodiments of the invention are illustrated in the following examples.

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Example 1

The pulp mixture was 50% chemical pulp, 50% mechanical pulp. The pulp was taken from a headbox and 0.7% of cationic starch "Posamyl B" (Avebe, The Netherlands) and 0.125% of resin glue "T-glue" (Hercules, USA) and 0.4% of alum were added to the machine box to achieve the desired degree of gluing. Different amounts of the anionic polyacrylamide best found to be used with the pulp were added to the pulp, followed in the second set of experiments first by 0.4% cationic starch and then by different amounts of polymer. 60 g / m sheets were made from the pulp and tested. The results were as follows:

Polyacrylic Pulp (contains 0.7% cat. Pulp (contains 0.7% amide starch) cat. Starch) + 0.4% cationic _starch_% Column strength. Tensile strength Palst.luj. Tensile strength J / irr kN / m J / rrr kN / m 0 (known) 185 2.55 190 2.80 0.01 185 2.80 265 3.05 0.02 230 3.0 300 3.05 0.03 240 3.0 360 3.3 0.04 250 3.0 530 3.32

It can be seen from the results that with the addition of up to 0.01% polyacrylamide, the strength of the sheets was improved. According to the state of the art, such small additions of polyacrylamide should not significantly affect the strength of the pulp.

Example 2

As in Example 1, except the pulp was taken before the machine type, i.e. it did not contain any additives. The sizing agents were added to the pulp first, then polyacrylamide and last 0.4% cationic starch. The results were: 7,71379

Polyacrylamide,% O 0.01 0.02 0.03 o

Peel strength, J / m 110 125 125 135

The peel strength was lower than in Example 1 because there was 0.7% less cationic starch. However, the results show that the addition of polyacrylamide has a strength-improving effect.

Example 3

As in Example 2, but the starch was added before the polyacrylamide and its amount was also varied. The results were as follows:

Cationic starch,%

Polyacrylic— _Q / 4_ _0.6_ __0 / 8_ liamide, Palst.luj. Tensile strength. Palst.luj. Tensile strength. Palst.luj. Tensile strength.

% J / m2 kN / m J / m2 kN / m J / m2 kN / m 0 105 1.48 105 1.70 115 1.65 0.01 120 1.70 120 1.82. 120 1.85 0.02 135 1.98 135 2.10 140 2.20 0.03 155 2.30 220 2.35 (experiment completed)

A number of studies in the paper industry have shown that the promising results obtained on a laboratory scale have not been valid after switching to a production machine. Therefore, the chemical system according to the invention was tested on a board machine. The machine is the so-called. Invertorm-type. The surface and backing layer are made of pure chemical pulp and about 50% mechanical pulp is used for the middle layer. The additional use of mechanical pulp is limited by the peel strength of the finished board 2. It is normally 85-90 J / m, in which case 0.8% of cationic starch is added to the mass of the middle layer.

Higher amounts, up to 2%, have also been tried, but to no avail.

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Example 4

A factory test run was performed. The cationic starch was continuously metered into the machine pan. Its amount ranged from 0.6 to 1.2%.

2 At this time, the peel strength was about 90 J / m: Polyacrylamide was added after the sieves and its dosage was gradually increased. As the dosage increased by 0.042%, the peel strength increased to 120 J / m.

Example 5

A second factory test run was performed. In this experiment, 1.2% of cationic starch was fed to the machine vat at all times. The amount and location of polyacrylamide application was varied, and in addition, at a few test points, an additional amount of starch was administered after the polyacrylamide. In each case, the best results and the amounts of polyacrylamide required were as follows:

Additive dosing Peel strength J / m2 85-90 0.045% polyacrylamide after sieves 125 0.025% polyacrylamide before 170 sieves + 0.6% cationic starch after sieves 0.025% polyacrylamide before 150 mixing pumps +0.6% cationic starch after sieves

Example 6

The effect of various polyacrylamide-type retention aids on the dry strength of paper was investigated by performing experiments on a laboratory sheet mold. The pulp contained 45% pulp and 55% groundwood. The pulp was taken from an equalization box and contained 1.2% 2 cationic starch. 60 g / m 3 sheets were made from the pulp in a circulating water sheet mold and 0.02% polyacrylamide was added to the pulp just before the pulp was poured into the sheet mold. The results were: 9,71379

Polyacrylamide type Paling strength, ionicity of retention aid J / iti (without retention aid) 332 cationic 389 nonionic 357 anionic 388

It is found that the best result is obtained by using either a cationic or anionic retention aid, i.e. both cationic and anionic polyacrylamide, giving good strength together with cationic starch.

Example 7

The experiment of Example 6 was repeated except that a pulp containing 23% waste cellulose and 77% groundwood was used, the amount of cationic starch was 0.7% and the polyacrylamide dosage was 0.03% and the sheets were made at 100 J / m without circulating water. The results were:

Polyacrylamide-type Peeling Tensile Index Retention Agent Ionicity Strength Nm / g J / m (without Retention Agent) 102 17.5 Cationic 133 18.5 Slightly Anionic 124 18.7 Strongly Anionic 137 18.0

Again, it is found that the beneficial interaction with cationic starch is achieved with both anionic and cationic polyacrylamide.

Example 8

60 J / m circulating water sheets were made from a pulp containing 25% groundwood and 75% 2 folding boxboard wrecks with a laboratory sheet mold. Either native guar gum mucus or amphoteric guar gum mucus was added to the pulp well in advance (min. 0.5 h) prior to sheet preparation. The amount of both was 1.2%.

Just before the pulp was poured, 0.03% of various polyacrylamide-type retention aids were added to the sheet mold. The results were:

Peeling ^ - strength, J / m zero test (= no mucilage or retention aid) 177

Guar-gum, native 270

Guar gum, amphoteric 248

It is found that a beneficial interaction similar to that obtained with the cationic starch-retention agent combinations is also available with the vegetable mucus retention agent combinations.

Claims (5)

11 71379 A method of making paper or paperboard by adding a polysaccharide type additive and a synthetic retention aid and optionally a filler to the pulp suspension to improve the dry strength of the paper or paperboard, characterized in that 0.2-3% by weight of the pulp wherein: A) the addition is performed to a pulp suspension that is substantially free of filler, B) at least a portion of the retention aid is added to the pulp suspension prior to the addition of filler, or C) the pretreated filler is added to the pulp. 2. A method according to claim 1, which comprises a mixture of fiber mass suspensions, 0.8 to 1.5% by weight of polysaccharide type. Process according to Claim 1, characterized in that 0.8 to 1.5% of a polysaccharide-type additive, based on the dry weight of the pulp, is added to the pulp suspension. 3. A patented composition according to claims 1 or 2, which comprises a polysaccharide type of starch or a derivative, which forms a cationic starch. Process according to Claim 1 or 2, characterized in that starch or a derivative thereof, preferably cationized starch, is used as the polysaccharide-type additive. 4. A preferred form of an encapsulated retention solution having a mass retention ratio of 0.02 to 0.05% of the synthetic retention medium. Process according to one of the preceding claims, characterized in that 0.02 to 0.05% of a synthetic retention aid, based on the dry weight of the pulp, is added to the fibrous pulp suspension. Process according to one of the preceding claims, characterized in that polyacrylamide or a derivative or copolymer thereof, polyethylene oxide or a combination thereof is used as the synthetic retention agent. Method according to one of the preceding claims, characterized in that at least part of the polysaccharide-type additive is added to the pulp suspension before the synthetic retention aid. 12 71 379 1 .0 Fertilizers for the manufacture of paperboard or paperboard for the manufacture of paperboard or paperboard for the manufacture of solid pulps with the aid of polysaccharide types and synthetic retention media, preferably Raksnat av massans torrsubstansvikt, 0,2-3% tillsatsmedel av polysackaridtvp och 0,005-0,1% svntetiskt retentionsmedel, varvid: före fyllmedelstillsatsen, eller C) till fibermassan tillsättes förbehandlat fyllmedel. 5. A preferred embodiment of the present invention is to provide a synthetic retention medium comprising a polyacrylamide or a derivative or a copolymer or a polyethylene oxide or a mordant.