FI93882B - Method for making paper - Google Patents

Description

93882

The present invention relates to a process for the production of paper using a combination of substances for improving retention and dewatering. More specifically, the invention relates to the use of a combination of a cationic silica-based sol and a cationic, organic, polymeric retention aid in papermaking.

It has been previously known in papermaking to use a combination of inorganic silica sols and cationic retention aids. In this case, anionic silicon azoles have been used together with cationic retention aids, such as, for example, cationic starch and cationic polyacrylamide. Such systems are described, for example, in EP patent 41056 and EP patent application 218674. The efficiency of systems containing an anionic silica sol and a cationic component is based on the interaction of these two differently charged substances, and it is assumed that sol sol particles with strongly anionic charges provide some degree of polymeric retention agent crosslinking.

Cationic inorganic silica-based colloids are known per se, and their use in specific papermaking processes is also known. Thus, U.S. Patents 4,309,247 and 4,366,068 describe the use of cationic inorganic silica colloids in the manufacture of a cellulosic fiber-based filter media. JP patent application 85-260377 has also disclosed the use of cationic colloidal silica in an ink jet printer recording paper to improve the water resistance and light resistance of water-soluble dyes. An example of this JP application describes the preparation of ink jet recording paper from a pulp slurry containing talc, cationic starch and cationic colloidal silica.

2 93882 In accordance with the present invention, it has surprisingly been found that a combination of a cationic silica-based sol and a cationic organic polymeric retention aid can be used in papermaking, and that a combination of these two charged components provides improved retention and dewatering. The combination according to the invention provides improved retention of fine fibers and possible fillers and better infiltration, which makes the papermaking process more efficient.

Thus, the present invention relates to a process for the production of paper by web and filtration of a suspension of cellulosic fibers and possibly fillers on a wire such that the webing and filtration take place in the presence of a cationic silica-based sol and a cationic polymeric retention aid selected from cationic guar gum and cationic synthetic polymers.

Silica soles with positively charged particles are, as noted above, known per se, and their preparation is described, for example, in U.S. Patents 3007873, 3620978 and 3719607. General methods for preparing cationic silica sols begin with the silica of the silica. lyses which are reacted with a basic salt of a polyvalent metal to give sol particles with a positive surface charge, and in which the process often uses stabilizers such as boric acid, alkali metal bases, alkaline earth metal bases, ammonia, etc. The polyvalent metal salt is usually an aluminum salt, its availability and cheapness, although it is of course also possible to use basic salts of other polyvalent metals, such as chromium, zirconium, etc., to prepare cationic silica - based sols. Any basic salt which is water - soluble and provides the desired positively charged surface can be.

3 93882 uses, and generally cationic sols are prepared using metal chlorides, nitrates or acetates.

The particles of cationic sols have a small average particle size, usually less than 100 nm, and generally range in size from 2 nm to 100 nm, more generally in the range of 2 nm to 80 nm. Suitably the particle size is in the range of 3 to 20 and preferably 3.5 to 14 nm. The surface of the cationic silica particles has a positively charged polyvalent metal, preferably aluminum, and the molar ratio of aluminum to surface silica may be in the range of 1: 8 to 4: 1, suitably in the range of 1: 6 to 4: 1 and preferably in the range of 1: 4 to 4: 1. Most preferably, the ratio is in the range of 1: 2 to 4: 1. The molar ratio of aluminum to surface silica is calculated here as in U.S. Pat. No. 3,956,171, i.e. based on 8 silicon atoms / nm2 silica surface, with the proportion of total silica on the surface becoming 8x10-4xA, where A is the specific surface area of the soo particles m2 / g. The cationic silica sols used according to the invention can be prepared from any anionic silica sol by reaction with a basic salt of a polyvalent metal as described above. Thus, they can be prepared from commercial sols of colloidal silica and silica sols formed from polymeric silicic acid prepared by acidifying an alkali metal silicate, e.g. by mixing mineral acid and water glass or using acidic ion exchange resins. Cationic silica is added to the stock as an aqueous sol. The concentration of the cationic sol can be up to about 50% by weight for sols made from commercial anionic silica sols and up to about 10% by weight made from polysilicic acid. The stability of sols of the latter type is limited, and thus concentrations of about 5% or less are suitable. Stability is generally better if more aluminum is present, within the relationships outlined above. In practice, in any case, it is suitable to dilute the sols to concentrations of 0.05 to 5.0% by weight • 4 93882 cationic particles, preferably 0.1 to 2% by weight, before adding them to the stock.

Cationic retention aids used in combination with cationic silica sols are conventional organic, polymeric retention aids in papermaking which have a net cationic charge at the pH at which they are used and are either cationic guar gum or synthetic cationic polymers. Examples of suitable synthetic cationic polymers are cationic polyacrylamides, polyethyleneimines and polyamidoamines. A mixture of two or more of the foregoing cationic retention aids may also be used, and any of these may be used in combination with cationic starch. Synthetic cationic retention aids are preferred, and in particular cationic polyacrylamide.

The amounts of cationic silica and cationic retention aid used will, of course, depend on the stock used, the presence of fillers and other papermaking conditions. Generally, amounts of 0.005 to 2.0% by weight of cationic silica, dry, calculated on the dry fibers and possible fillers, give good results, and the amounts used are suitably 0.005 to 1% by weight.

.. Amounts in the range of 0.03 to 0.3% by weight are recommended. The ratio of cationic retention aid to cationic silica varies widely depending on, e.g., the papermaking conditions, the cationic polymer used, and other desired effects thereof. Generally, the weight ratio of cationic retention aid to cationic silica should be at least 0.01: 1 and suitably at least 0.2: 1. The upper limit for a lower cationic retention aid such as guar gum is not critical, and such cationic polymers can be very high, up to 100: 1, and higher, and the limit is usually determined for economic reasons. Catheters in the range of 0.2: 1 to 20: 1

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The ratios of the retention aid to cationic silica are suitable for most systems.

The two-component system of the present invention can be used for papermaking from various types of papermaking pulps, suitably pulps containing at least 50% by weight of cellulosic fibers. The components can be used, for example, as additives in non-woven pulp made from chemical pulp, such as sulphate and sulphite pulp, thermomechanical pulp, pulp or ground pulp, both hardwood and softwood. The system of the invention can advantageously also be used in connection with recycled fibers. As mentioned, the stock may also contain mineral fillers of the conventional type, such as, for example, kaolin, titanium dioxide, gypsum, lime and talc. Particularly good results have been obtained with pulps which are generally considered difficult and which contain quite large amounts of non-cellulosic substances such as lignin, i.e. different types of mechanical pulps such as groundwood. The two-component system of the invention is particularly suitable for slurries having at least 25% by weight of mechanical pulp and provides a significantly better effect on such systems than anionic silica sols and cationic retention aids. The terms paper and papermaking used herein, of course, include not only paper and its manufacture, but also other cellulosic fibrous sheet or web products such as pulp sheets, cardboard and paperboard, and their manufacture.

The cationic silica sol and the cationic polymeric retention aid may be added to the stock separately, simultaneously or premixed. They can also be added in two or more additions. It is recommended that these two components be added separately. It appears that the order of addition of the sol and the cationic retention aid has some effect on the power obtained, and that when the sols 93882 6 contain smaller particles, a better effect is obtained if the cationic retention aid is added before the cationic silica sol, when cationic silica is added first and cationic retention aid is then added. The addition of cationic silica and a cationic retention aid according to the invention considerably improves the retention of fine fibers and fillers when used, and also considerably improves dewatering compared to using a cationic retention aid alone. Thus, smaller amounts of cationic polymer can be used to achieve the desired effect, and thus significant cost savings can be achieved with expensive cationic polymers such as polyacrylamide. By using the system of the invention, the papermaking process can thus be made more efficient without adversely affecting the strength and other important properties of the papermaker's paper. Mechanisms affecting the beneficial effect of the two components with the same charge have not been fully elucidated, but it is believed that the cationic silica of the sol at least partially neutralizes the dissolved anionic wood constituents and also improves the strength of the floc with added cationic retention aid. forms a stock of dissolved and ... solid components, with the ability to penetrate flocs and neutralize them with respect to charge.

In addition to the two additives according to the invention, conventional additives can, of course, be used in the papermaking process according to the invention. Fillers have been discussed above, and examples of other additives include sizing agents, rosin-based or synthetic adhesives, cationic starch, wet strength resins, and aluminum-based compounds such as alum, aluminate, aluminum chloride, or polyaluminum compounds. The papermaking process using the combination of agents of the invention to improve retention 93882 7 and dewatering can be performed over a wide pH range, from about four to about nine. A particular advantage of the system of the invention is that it can produce papers with high wood fiber contents with high retention without detrimental effects on paper formation.

The invention will now be described in detail by the following examples, which are not intended to limit it. Parts and percentages are by weight unless otherwise indicated.

Example 1

The cationic silica sols used in Examples 1 and 2 were prepared as follows. The aluminum chlorohydrate of formula Al 2 (OH) 5 Cl 2 H 2 O was heated to 47 ° C with stirring in a flask equipped with a heating mantle. When this temperature was reached, anionic silica sols deionized to sodium ions and diluted with deionized water were added over a period of time to allow reaction with aluminum chlorohydrate. As a more specific preparation procedure, the following is typical: 408 g of a 50% Al 2 (OH) 5Cl 2 H 2 O solution was heated to 47 ° C. 657 g of anionic silica sol containing 15.21% SiO 2 was diluted with 928 g of deionized water. The particle size of this sol was about 7 nm. The sol was added over 90 minutes at 47 ° C, and the resulting cationic sol was then allowed to cool to room temperature.

In the following tests, dewatering was evaluated with a "Canadian Freeness" tester, a common method for characterizing dewatering or leaching ability according to SCAN-C 21:65.

The pulp system contained 60% bleached birch sulfate pulp and 40% bleached pine sulfate pulp, and 30% kaolin was added to the rack. Chemical additions are calculated in kg / ton of dry stock system (fibers + filler) and the amounts of sols and cationic polymers are given as dry matter. All chemical additions were performed at a stirring speed of 800 rpm in a Britt Dynamic Drainage Jar with the removal closed for 45 seconds and the stock systems were then added to the Canadian Free-ness. The sol was added in all tests before the polymer.

Various sols were used: a) Cationic aluminum-modified silica sol, molar ratio of aluminum to surface silica groups 1.30: 1 and particle size about 7.5 nm.

b) Cationic aluminum-modified silica sol, molar ratio of aluminum to surface silica groups 2.95: 1 and particle size about 7 nm.

c) Cationic aluminum-modified silica sol, molar ratio of aluminum to surface silica groups 3.25: 1 and particle size about 6 nm.

d) Cationic aluminum-modified silica sol, molar ratio of aluminum to surface silica groups 2.40: 1 and particle size about 14 nm.

The following cationic polymers were used: A) Cationic polyacrylamide, PAM 1, Medium Kati onity, sold by Allied Colloids under the name Percol 292.

B) Polyethyleneimide, PEI, sold by BASF AG under the name Polymin.

C) Cationic polyacrylamide, PAM 2, low cationicity, sold by Allied Colloids under the name Percol 140.

The following table shows the results of freeness tests in ml CSF. The table also shows comparative results from the additions of the corresponding cationic polymers alone.

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The comparison was also performed with an anionic aluminum-modified silica sol having a particle size of about 5.5 nm.

Sol / amount Cat.polym./amount Pulp pH CSF kq / tonl_kq / tonnl_ml_ a / 1.0 PAMl / 0.5 4.5 560 a / 1.0 PAMl / 1.0 4.5 620 a / 1.0 PAMI / 2.0 4.5 675 b / 1.0 PAMl / 0.5 4.5 540 b / 1.0 PAMl / 1.0 4.5 605 b / 1.0 PAMI / 2.0 4.5 640 C / 1.0 PAMl / 0.5 4.5 565 c / 1.0 PAMl / 1.0 4.5 620 C / 1.0 PAMI / 2.0 4.5 660 d / 1.0 PAMl / 0.5 4.5 530 <3 / 1.0 PAMl / 1.0 4.5 590 <3 / 1.0 PAMI / 2.0 4.5 640 PAMl / 0.5 4.5 430 PAMl / 1, 0 4.5 515 PAM1 / 2.0 4.5 570

Anionic / 1.0 PAM1 / 0.5 4, 5 305

Anionic / 1.0 PAM1 / 1.0 4.5 495

Anionic / 1.0 PAMl / 2.0 4.5 5 80 • li. a / 1.0 PEI / 0.6 7.0 430 a / 1.0 PEI / 1.0 7.0 470 a / 2.0 PEI / 2.0 7.0 485 PEI / 0.6 7.0 350 PEI / 1.0 7.0 410 PEI / 2.0 7.0 435 10 93882

Sole / amount Cat. Polymer / amount Pulp pH CSF

kq / ton_kg / ton_ml_ a / 1.0 PAM2 / 0.5 4, S 555 a / 1.0 PAM2 / 1.0 4.5 625 a / 1.0 PAM2 / 2.0 4.5 690 PAM2 / 0 .5 4.5 410 PAM2 / 110 4.5505 PAM2 / 2.0 4.5 575

Example 2 In this test, the dewatering effect of the cationic aluminum-modified silica sol and polyacrylamide Percol 292 labeled in Example 1a) was measured and compared with a system of anionic aluminum-modified silica sol, particle size about 5.5 nm, and polyacrylamide. The stock was prepared from ground pulp ground in 130 ml of CSF and the pH was adjusted to 5 with sulfuric acid. In tests with a cationic sol, this was added to the stock before the polyacrylamide except in one experiment where the order of addition was reversed. In tests with an anionic sol, this was added to the stock after the polymer. The added amounts, expressed in kg / tonne, are calculated as dry chemicals from the dry mass.

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Cationic Anionic Polyak- CSF

salt salt rylamide ml kq / ton_kg / tonl_kg / tonl_ 130 0.5 210 1.0 230 2.0 250 3.0 245 1.0 - 0.25 290 1.0 - 0.5 325 1.0 - 0.75 340 1.0 - 1.0 355 1.0 - 2, 0 360 1.0 (in reverse order) 1.0 270 3.0 - 0.25 330 3.0 - 0.5 375 3.0 - 1.0 425 3.0 - 2.0 405 1.0 0.5 190 1.0 0.75 230 1 , ° 1.0 255 1.0 2.0 280 3, ° 0.5 190 3.0 1.0 240 3.0 2.0 320 3.0 3.0 360 31 ° 4.0 350 · 12 93882

As can be seen from the table, in the cationic sol system the maximum CSF level is reached with a much lower polyacrylamide addition than in the anionic sol system.

Example 3 In this example, various cationic silica sols a), b), c) and d) were used.

Soles a) and d) were prepared as follows: 19.49 g of a 50% solution of polyaluminum chloride [Al 2 (OH) 5 Cl 2 H 2 O] x was diluted to 200 g. To this solution was added 1000 g of 1% polysilicic acid slowly over 45 minutes at room temperature. Polymeric silica was prepared as follows: Water glass (Na 2 O 3 SiO 2) was dissolved in water to a SiO 2 content of 5% by weight. The aqueous solution was deionized using Amberlite IR-120 ion exchange resin to pH 2.3. The specific surface area of the obtained polymeric silicic acid was measured by titration by the method described by Sears in Analytical Chemistry 28 (1956) 1981, and therefore 1450 m * / g was obtained.

This polymeric silicic acid, which was subsequently treated with polyaluminum chloride, contained particles on the order of about 1 nm in size, which had to some extent aggregated into chains and networks. The analysis of the obtained cationic silica sol was as follows: 0.39% Al 2 O 3 and 0.84% SiO 2, and thus the molar ratio of Al to surface silica was about 1: 2. Sol a) was prepared from freshly prepared polysilicic acid and sol c) from polysilicic acid that was one day old.

Soles b) and d) were prepared as follows: 9.75 g of a solution of polyaluminum chloride [Al 2 (OH) 5Cl 2 H 2 O] x 50% was diluted to 200 g and to this solution was added 1000 g of 1% polysilicic acid prepared as described above. . The analysis of the product obtained was as follows: 0.20%

Al 2 O 3 and 0.83% SiO 2, and thus the molar ratio of Al to surface

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• · 13 93882 hin was about 1: 4 Sole b) was made from freshly prepared polysilicic acid and sol d) from polysilicic acid that was one day old.

Soles a) to d) were used in combination with cationic polyacrylamide (PAM), sold by Allied Colloids under the name Percol 292, in a stock containing 60% birch sulphate pulp and 40% pine sulphate pulp. In addition, the stock contained 30% calcium carbonate and 1 g / l Na 2 SO 4 .10H 2 O. The pH of the stock was 8.5. Polyacrylamide was added to the stock before the cationic silica sol, unless otherwise noted. Dewatering was assessed as described above using a Canadian Free-ness instrument. The results are shown in the following table.

PAM Sol, amount of CSF

kq / tonni_kq / tonni_ml 390 0.5 - 475 b); 1,395 0.5 a); 1,595 0.5 b); 1,605 0.5 ° C); 1,590 0.5 d); 1,600 *** 0.5 b); 1 (reverse 505 order sequences)

A comparison was also made with an anionic aluminum-modified silica sol having a particle size of about 5.5 nm to give 1 kg / ton together with 0.5 kg / ton PAM CSF 520.

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Example 4

Sols a) and b) of Example 3, as well as sols e) and f), were studied in combination with cationic polyacrylamide in a pulp made of ground pulp. Step e) was prepared as follows: 27.84 g of a solution of polyaluminum chloride [Al 2 (OH) gCl 2 H 2 O] x 50% was diluted to 200 g. To the polyaluminum chloride solution was added 1000 g of 1% polysilicic acid as in Example 3, and the product obtained contained 0.56% Al 2 O 3 and 0.83% SiO 2, and thus the molar ratio of Al to surface silica was about 1: 1.5. Step f) was prepared as follows: 34.80 g of a solution of polyaluminum chloride [Al 2 (OH) gCl 2 H 2 O] x 50% was diluted to 200 g and to this solution was added 1000 g of 1% polysilicic acid. The product contained 0.70% Al 2 O 3 and 0.83% SiO 2, and thus the molar ratio of Al to surface silica was about 1: 1.2.

The ground stock contained 2 g / l Na 2 SO 4 .10H 2 O and had a pH of 7.0. The dewatering effect was studied as above. In most cases, the cationic polyacrylamide was added to the stock prior to the addition of the sol, unless the reverse order of addition (reverse) was indicated. The amount of cationic polyacrylamide added was 1.0 kg / ton, which was found to be the optimum amount for this stock when used alone. The tests showed that the water collected from the freeness device was much clearer when using combinations of sol and cationic polyacrylamide than when polyacrylamide alone was used, and this shows very good fine fiber retention.

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PAM Sol, amount of CSF

kq / tonni_kg / tonnl_ml_ 120 1.0 - 195 b); 1.0 120 1.0 a); 1.0 400 1.0 a); 1.5 445 1.0 a); 2.0 485 1.0 a); 2.5 510 1.0 a); 1.0 (reverse) 3 30 1.0 a); 1.5 (reverse) 345 1.0 a); 2.0 (reverse) 355 1.0 a); 2.5 (reverse) 3 60 1.0 b); 1.0 420 1.0 b); 1.5 480 1.0 b); 2.0 505 1.0 b); 2.5 530 1.0 e); 1.5 400 1.0 e); 2.0 440 1.0 e); 2.5 435 1.0 f); 1.5 390 1.0 f); 2.0 425 1.0 f); 2.5 435

Example 5 In this example, the retention of filler and fine fibers was evaluated by a factory test. The stock contained 30% chemical pulp, 24% ground pulp and 46% CaCO 3 filler. The stock concentration was 0.5% and the pH was 8.3. The measured filler and fine fiber content was 76.9%.

A Britt Dynamic Drainage Jar was used to assess retention. The agitator speed was set at 800 rpm and a 200 mesh wire was used.

The cationic silica sol used was sol) a) of Example 1 and was added before the cationic retention aid. The following cationic retention aids were used in various experimental runs: A) Cationic polyacrylamide Percol 292, manufactured by Allied Colloids.

B) Cationic guar gum

The test results are shown in the following table. The retention of filler and fine fibers (FP ret.) Is given as a percentage of the different doses of the corresponding cationic polymers. The dose is calculated as the dry polymer from the dry mass and the filler. Cationic silica sol was used in an amount of 1 kg / ton of dry mass and filler. Comparisons were made with the addition of cationic polymer alone.

Added cation. Addition amount Added FF ret.

polymer kg / ton salt% _kg / ton_ A 0.25 1 75 A 0.50 X 97 A 0.75 X 100 A 0.25 - 43 A 0.50 - 61 A 0.75 - 8 ° E 2 1 15 B 4 1 95 · .. B 6 1 95 B 2 - 45 B 4-83 B 6-90 li 17 93882

Example 6 In this example, the cationic silica sol of Example 1 and the cationic polyacrylamide were tested in a magazine paper mill. The stock contained 19% sulphate pulp, 73% abrasive pulp, 20% thermomechanical pulp and 24% clay, i.e. it was a pulp with a large amount of non-cellulosic substances. The pH was 4.45. Retention was measured with a Britt Dynamic Drainage Jar and a freeness Canadian Freeness.

Additions kg / tonne

Sooli_PAM_Retentio% _Freeness ml 0.25 26.4 110 0.50 44.6 140 1.0 57.6 190 2.0 0.25 41.7 150 2.0 0.50 65.0 200 2.0 1.0 85.6 305 1

Claims (9)

A process for making paper, by forming and dewatering a suspension of ce 1 lulosa-containing fibers and any fillers on a wire, with improved retention and dewatering, characterized in that the forming and dewatering takes place in the presence of a cationic silica-based sol and a cationic polymeric retention agent selected from the groups of cationic guar gum and synthetic cationic polymers. Process according to claim 1, characterized in that the cationic silica sol particles are aluminum-modified silica particles. Process according to claim 1 or 2, characterized in that the cationic silica particles have particle sizes in the range from 2 nm to 100 nm. Process according to claim 1, 2 or 3, characterized in that the cationic polymeric retention agent is a synthetic cationic polymer. Process according to claim 4, characterized in that the cationic polymeric retention agent is cationic polyacrylamide. Process according to claim 5, characterized in that the cationic polymeric retention agent is cationic polyacrylamide and that it is used in combination with cationic starch. Process according to claim 1, characterized in that the amount of cationic silica sol is in the range of 0.005 to 2.0% by weight, calculated as dry on dry fibers and any fillers. 11 93882 8. A process according to claim 1 or 7, characterized in that the weight ratio of cationic retention agent to cationic silica is at least 0.01: 1. Method according to claim 8, characterized in that the weight ratio of cationic retention agent to cationic silica is at least 0.2: 1.