EP0384268A1 - Process for the fixation of impurities in paper making - Google Patents

Abstract

The invention relates to a process for fixing foreign substances in papermaking, wherein the agents used for fixing the foreign substances are polymers, consisting of cationic groups, of 50 to 100% by weight of quaternised dimethylaminopropylacrylamide or dimethylaminopropylmethacrylamide and 0 to 50% by weight of acrylamide, acrylic acid, methacrylic acid or acrylamidomethylpropanesulphonic acid, which have an intrinsic viscosity of less than 150 ml/g. The fixing agent is added to the pulp run and/or to the circulating water in quantities of up to 1% by weight relative to the dry weight of the paper produced.

Description

The invention relates to a method for fixing contaminants in papermaking.

In the past few decades, the paper industry has managed to drastically reduce the specific fresh water consumption and the specific amount of wastewater by constricting and closing water cycles in paper production. The reasons for the narrowing of the cycle are, on the one hand, the avoidance of material losses with the wastewater, and on the other hand, the official requirements with regard to the composition and quantity of the wastewater discharged according to the Wastewater Tax Act.

A number of new problems have arisen from this narrowing of the water quantities. Due to the increased proportion of circulating water, the temperature of the pulp system sometimes increases considerably. This can result in increased mucus formation. Higher electrolyte concentrations in the process water lead to faster corrosion. Anaerobic zones in the water cycle can lead to the formation of odor problems.

However, the most serious problem in connection with the narrowing of the circulation is the accumulation of organic substances in the circulation water, the so-called contaminants. According to Auhorn, "Wochenblatt für Papierfabrikation 112, 37-48 (1984)", impurities are dissolved or colloidally dissolved anionic oligomers or polymers and nonionic hydrocolloids. They arise in the production and processing of cellulose, wood pulp and waste paper as lignans or poly- or oligosaccharides derived from hemicelluloses. Other contaminants have their origin in the anionic auxiliaries used in papermaking.

The concentration of these water-soluble substances rises sharply as the water cycles become narrower. The circulating water of the paper machine is particularly contaminated with these contaminants when wood-containing paper is produced.

The contaminants affect the production of paper in many ways. They influence the pulp grinding through less fiber swelling and delayed grinding development, lead to increased deposits in the circulation system and in the headbox of a paper machine.

A deterioration in retention, drainage, sheet formation and paper strength must also be noted. The effectiveness of practically all chemical aids is affected by the contaminants. Retention and drainage aids, wet and dry strength agents, sizing agents, defoamers, bleaching chemicals and dyes are mentioned. The concentration of contaminants can become the limiting factor for narrowing the circulation.

These problems were largely prevented by the addition of aluminum sulfate, which was common in the past. The strong adsorption capacity of the intermediate Al complexes relieves the circulation water of inorganic and organic fiber. In today's neutral driving style, the problem arises that aluminum sulfate cannot be used as a precipitating and fixing agent. This also results from the increasing use of calcium carbonate as a coating and filling pigment from economic and qualitative considerations.

Due to the increased use of calcium carbonate, the production problems with the processing of the calcium carbonate-containing coating boards and the waste paper in the acidic pH range have increased considerably. The problem therefore arose of removing the contaminants from the circulating water, while minimizing the otherwise usual aluminum sulfate, from the paper mills.

The first approaches to solving this problem are already known. According to Arheilger and von Medvey, "Wochenblatt für Papierfabrikation 114, 958-961 (1986)", coated paper with a high wood content is produced using calcium carbonate without the addition of alum. This was achieved by adding polydiallyldimethylammonium chloride (PolyDadmac) to the circulating water. However, the PolyDadmac does not seem to have all the positive properties of the alum. Among other things, there were enormous difficulties with mucus control, which were only remedied by using other means.

In addition, in contrast to alum from PolyDadmac, chromophoric substances were also fixed so well that the addition of the fixing agent caused a drop in white of approx. 1.5 white points in operational use, which caused a significant increase in bleach costs.

So there remains the problem of finding substitutes for aluminum sulfate for eliminating contaminants that do not show any negative side effects.

Another route is followed in DE-OS 36 20 065: there special drainage, retention and flocculants, namely high molecular weight, water-soluble polymers of N-vinyl amides, are used which have their effectiveness only in the presence of interfering substances that contain oligomers and / or polymers from the wood's constituents that contain phenolic groups as accompanying substances. These special N-vinylamide polymers are therefore insensitive to the contaminants that are always present in paper production in restricted or closed water cycles.

The disadvantage of this method is that there is no fixation of contaminants, but in particular that the conventional flocculants, dewatering and retention agents based on cationic polymers used in the paper industry cannot be used.

The object of the invention is therefore to fix the contaminants in a simple and effective manner without having to resort to aluminum sulfate and the known and proven auxiliaries based on cationic polymers as drainage aids, retention aids and flocculants continue without impairing their effect can be used.

This object is achieved according to the invention by the use of polymers (homo- and / or copolymers) based on quaternized dimethylaminopropyl (meth) acrylamide, which are added to the headbox and / or the circulating water, these polymers having an intrinsic viscosity of less than 150 ml / g measured in 10% by weight sodium chloride solution.

The polymers used according to the invention advantageously consist of 50 to 100% by weight of quaternized dimethylaminopropyl (meth) acrylamide and 0 to 50% by weight of acrylamide, acrylic acid, methacrylic acid, acrylamidomethylpropanesulfonic acid or from mixtures of the cationic and anionic monomers mentioned.

The dimethylaminopropyl (meth) acrylamide is quaternized with the usual known quaternizing agents, e.g. Dimethyl sulfate, dimethyl carbonate, benzyl chloride, methyl chloride or ethyl bromide.

The polymers are used in an amount of 0.05 to 1% by weight, based on the dry weight of the paper produced, in addition to the customary auxiliary in which they are added to the headbox and / or the circulation water. The polymer according to the invention used as a fixing agent is preferably used in an amount of 0.2 to 0.8, based on the dry weight of the paper produced.

The total amount of polymer added to fix impurities can advantageously be distributed over various addition points.

• a) die im Fabrikationswasser enthaltenen Störstoffe an der Papierfaser fixiert werden und
• b) der Weißegrad des so produzierten Papiers durch die Stör­stoffadsorbtion dennoch nicht beeinträchtigt wird.

Surprisingly, the polymers used according to the invention achieve that

• a) the contaminants contained in the manufacturing water are fixed on the paper fiber and
• b) the degree of whiteness of the paper produced in this way is nevertheless not impaired by the adsorption of impurities.

The polymers used as fixatives according to the invention are preferably used in a neutral manner without the addition of aluminum sulfate. However, it is also quite possible to combine these products with Alumi Use sodium sulfate according to the pseudo-neutral driving style.

The polymers used according to the invention have a particularly advantageous effect in those paper manufacturing processes in which the water cycle is closed to more than 90%.

The invention is illustrated by the following examples:

Unless otherwise defined below, parts are always parts by weight.

A) Preparation of the polymers Polymer 1:

250 parts of acrylamidopropyltrimethylammonium chloride are dissolved in 750 parts of water. A pH of 5.0 is set. The mixture is heated to 75 ° C. while introducing nitrogen gas. After addition of 0.6 part of potassium peroxodisulfate, the polymerization begins.

The final temperature of 90 ° C is reached within 5 minutes. After cooling, the product has a viscosity of 1050 mPa.s, the intrinsic viscosity is 120 ml / g.

Polymer 2:

180 parts of acrylamidopropyltrimethylammonium chloride and 180 parts of acrylamidomethylpropanesulfonic acid are dissolved in 568 parts of water in succession. A pH of 5.0 is set with 72 parts of 45% sodium hydroxide solution.

The mixture is heated to 75 ° C. while introducing nitrogen gas. After addition of 0.6 part of potassium peroxodisulfate, the polymerization begins. The final temperature of 92 ° C is reached within 10 minutes. After cooling, the product has a viscosity of 860 mPa.s, the intrinsic viscosity is 75 ml / g.

Polymer 3:

200 parts of acrylamidopropyltrimethylammonium chloride are dissolved in 709 parts of water. After adding 50 parts of acrylic acid, a pH of 5.0 is set with 41 parts of 45% sodium hydroxide solution. The mixture is heated to 75 ° C. while introducing nitrogen gas. After addition of 0.4 part of potassium peroxodisulfate, the polymerization begins. The final temperature of 94 ° C is reached within 7 minutes. After cooling, the product has a viscosity of 750 mPa.s, the intrinsic viscosity is 98 ml / g.

Polymer 4:

210 parts of methacrylamidopropyltrimethylammonium chloride are dissolved in 638 parts of water. After adding 90 parts of methacrylic acid, a pH of 5.0 is set with 62 parts of 45% sodium hydroxide solution. The mixture is heated to 75 ° C. while introducing nitrogen gas. After the addition of 0.8 part of potassium peroxodisulfate, the polymerization begins. The final temperature of 91 ° C is reached within 15 minutes. After cooling, the product has a viscosity of 890 mPa.s, the intrinsic viscosity is 105 ml / g.

Polymer 5:

210 parts of methacrylamidopropyltrimethylammonium chloride and 30 parts of acrylamidomethylpropanesulfonic acid are dissolved in 646 parts of water in succession. After adding 60 parts of acrylic acid, the pH is adjusted to 5.0 with 54 parts of 45% sodium hydroxide solution. After the addition of 0.8 part of potassium peroxodisulfate, the polymerization begins. The final temperature of 94 ° C is reached within 12 minutes. After cooling, the product has a viscosity of 740 mPa.s, the intrinsic viscosity is 88 ml / g.

A polydimethyldiallylammonium chloride with an intrinsic viscosity of 95 ml / g was used as the comparative polymer in the application tests.

B) Application tests:

• 1. Die Wirkung von kationischen Entwässerungs- und Reten­tionsmitteln wird durch die anionischen Störstoffe herabge­setzt. Nach Zugabe der Fixierstoffe wird die Entwässerungs- bzw. Retentionswirkung verbessert und quantitativ erfaßt.
• 2. Der beim Papier erreichte Weissegrad wird nach DIN 53145 gemessen. Durch die Fixierung bestimmter Störsubstanzen und Chromophore an den Papierfasern wird eine Reduzierung der Weisse des Papiers verursacht.

The following methods are customary for the detection of the immunity fixation:

• 1. The effect of cationic drainage and retention agents is reduced by the anionic contaminants. After the fixatives have been added, the drainage or retention effect is improved and quantified.
• 2. The degree of whiteness achieved with paper is measured in accordance with DIN 53145. The fixation of certain interfering substances and chromophores on the paper fibers causes a reduction in the whiteness of the paper.

The degree of whiteness is naturally greatest without fixative and is reduced significantly less by the fixative according to the invention than by the comparison substances.

1. Paper drainage, Schopper-Riegler method

The apparatus used is described in "Zellstoff Papier, 5th edition, VEB Fachbuchverlag Leipzig, pp. 387-388" and was modified in such a way that both outlet nozzles are emptied together into a common collecting vessel. This means that it is no longer the degree of grinding that is determined, but only the material drainage.

Waste paper with a solids concentration of 4% was used. 3 g of dry substance are diluted with tap water at 20 ° dH to a volume of 300 ml. The fixative is diluted to a volume of 300 ml and added to the stock suspension. The suspension is poured three times. The drainage aid is then diluted to 400 ml and added to the suspension. This system is then poured once and drained in the Schopper-Riegler apparatus.
The time for 700 ml of filtrate is determined.
With the blank value, the drainage is carried out without fixative and drainage aid, with the zero value without fixative, but with drainage aid.
A 25% cationic polyacrylamide is used as a drainage aid. Drainage tests Schopper-Riegler (Time in seconds for 700 ml of filtrate) Drainage aids (%) 0.00 0.01 0.02 0.03 Blank value: 255 Zero value: 121 83 67 Fixing agent 1: 0.3% 89 71 59 " 1: 0.6% 78 65 54 Fixing agent 2: 0.3% 96 76 63 "2: 0.6% 86 69 57 Fixing agent 3: 0.3% 93 74 62 "3: 0.6% 82 64 57 Fixing agent 4: 0.3% 92 71 61 "4: 0.6% 82 65 55 Fixing agent 5: 0.3% 94 74 63 "5: 0.6% 83 66 56 Comparison : 0.3% 115 81 65 ": 0.6% 105 76 61

2. Determination of retention (Britt Jar test)

The apparatus used for determining the retention is described in "New methods for monitoring retention", Tappi February 1976, Vol. 59, No. 2, KW. Britt and JE uncomfortable. 2.5 g of dry material (90% wood pulp and 48 ° SR, 10% chalk as 71% slurry with 60% smaller 2 µm particle size) are diluted with tap water at 20 ° dH to a volume of 400 ml. After adding the fixative, the suspension is shaken 10 times. The retention aid is then added as a 0.01% solution and the suspension is shaken three times. After dilution with water to 500 ml, the suspension is added to the Britt Jar tester and stirred at a speed of 800 rpm for 15 seconds. Then, with further stirring, the outlet valve is opened for 30 seconds and the filtrate is collected. After filtering the filtrate through a suction filter with a black belt filter, the non-retained fine material is determined by drying. The retention is stated as a percentage of the non-retained fine material in the total fine material. Britt Jar test (Retention in%) Drainage aids (%) 0.00 0.02 0.03 Blank value: 48.9 Zero value: 57.1 61.6 Fixing agent 1: 0.3% 66.5 71.3 " 1: 0.6% 69.8 75.4 Fixing agent 2: 0.3% 64.6 70.8 "2: 0.6% 68.4 75.1 Fixing agent 3: 0.3% 64.3 70.1 "3: 0.6% 68.9 74.3 Fixing agent 4: 0.3% 65.2 69.9 "4: 0.6% 69.2 74.8 Fixing agent 5: 0.3% 64.8 69.3 "5: 0.6% 68.2 73.9 Comparison : 0.3% 58.3 62.7 ": 0.6% 63.9 67.3

3. Determination of the degree of whiteness a) Leaf formation

The waste paper stock with a solids concentration of 4% is diluted in an amount of 2.5 g dry to 500 ml volume with tap water. The fixative is added in an amount of 0.4%, based on dry substance, as a 0.5% solution and stirred for 30 seconds at 500 rpm with a magnetic stirrer. Then the drainage aid, a 25% cationic polyacrylamide, is added in an amount of 0.03% as a 0.01% solution and stirred for a further 30 seconds. 4 liters of tap water are placed in the sheet former and made to bubble by blowing in air. Now the stock suspension is added and, after thorough mixing, suctioned off.

The cover card is placed over the sheet formed and the sheet is pulled off the screen. The mixture is then dried in a vacuum dryer for 10 minutes and then in a drying cabinet at 110 ° C. for 5 minutes. The zero value is obtained without fixative.

b) White measurement

Based on DIN 53145, the degree of whiteness of the sheets produced is determined. The measurements were carried out with the Elrepho device from Zeiss, using filter No. 7, with calibration against MgO. Whiteness measurement White (in%) Zero value 65.9 Fixing agent 1 62.8 Fixing agent 2 63.2 Fixing agent 3 62.7 Fixing agent 4 61.3 Fixing agent 5 61.9 comparison 57.3

Claims (8)

1. A method for fixing impurities in paper manufacture by adding fixatives, characterized in that polymers are used as fixatives, which consist of
a) 50 to 100 wt .-% quaternized dimethylaminopropylacrylamide or dimethylaminopropylmethacrylamide and
b) 0 to 50% by weight of acrylamide, acrylic acid, methacrylic acid, acrylamidomethylpropanesulfonic acid or mixtures of these monomers,
these polymers having an intrinsic viscosity of less than 150 ml / g. 2. The method according to claim 1, characterized in that the polymers are used in an amount of 0.05 to 1, preferably 0.2 to 0.8 wt .-%, based on the dry weight of the paper produced. 3. The method according to claim 1 or 2, characterized in that the quaternized dimethylaminopropyl (meth) acrylamide has been quaternized with dimethyl sulfate, methyl chloride, ethyl bromide, dimethyl carbonate or benzyl chloride. 4. The method according to claim 1, characterized in that the total amount of the polymer added is distributed over different addition points. 5. The method according to claim 1, characterized in that the polymers are used in conjunction with conventional cationic paper auxiliaries. 6. The method according to claim 1, characterized in that the polymers are used without the addition of aluminum sulfate. 7. The method according to claim 1, characterized in that the polymers are used in combination with aluminum sulfate. 8. The method according to claim 1, characterized in that the polymers are used in such paper manufacturing processes in which the water cycle is closed to more than 90%.