CH617478A5 - Method of controlling the acidity and water hardness in paper production - Google Patents

Description

The invention relates to a method for controlling the acidity and the water hardness of fibrous stock suspensions in the manufacture of paper, in particular in plants which work with a totally closed circuit and / or which are wet-strengthened with urea-formaldehyde and / or melamine-formaldehyde condensation products Process waste paper.

Due to the chemical composition, type of valences, spatial arrangement of the atoms in the molecule, etc., alkali fluorosilicates have very special features and effects that can be used with many advantages in the manufacture of paper.

CS-PS No. 133 084 describes the use of sodium fluorosilicate and the corresponding compounds of the divalent elements in fiber processing, while increasing retention on the sieve and improving sewage treatment.

DE-PS No. 2 143 251 describes the use of mixtures of alkali metal fluorosilicates with magnesium compounds in fiber preparation for increasing retention on the screen, increasing the strength of the paper and improving the waste water treatment. DE-OS No. 2 143 251 describes the use of alkali fluorosilicates in mixtures and / or combinations with alkali polyphosphates in the fight against slime in the paper industry.

DE-PS No. 2 142 012 describes paper auxiliaries based on alkali silicate glasses which have been modified in the melt by borates, phosphates and fluorides and which are mainly used as a fluorine source in their production, all of which are described in DE-PS No. 2 142 012 DE-OS No. 2 425 242 is discussed in detail, and new silicate-containing auxiliaries for the paper industry are proposed in the paper industry, which are obtained by modifying the properties of the alkali silicates with alkali fluorosilicates and alkali salts with a strongly polar anion. These tools have a particularly wide range of applications in the paper industry and can in many cases significantly influence paper production.

Finally, DE-OS No. 2 433 325 proposes a process for the production of solid paper and cardboard based on waste paper in plants with a closed circuit, tools according to DE-OS No. 2 425 242 being used, namely tools with a high level stoichiometric excess of alkali fluorosilicate over the alkali silicate. In particular, the aids proposed in the last two DE-OS and the method proposed therein are widely applicable in paper technology practice and bring many advantages.

On the other hand, only auxiliaries and / or methods have so far been described in which the alkali metal fluorosilicates are used in mixtures with or in addition to other compounds, depending on the nature of the compounds in use, depending on the mixing ratio etc., achieving specific effects desired for specific purposes will.

It has now been found that in special cases of paper production, e.g. when working in a totally closed circuit, or when dissolving hard-to-dissolve waste paper that has been wet-strengthened with urea-formaldehyde and / or melamine-formaldehyde condensation products, it is much more advantageous to use the alkali metal fluorosilicates and / or the corresponding acid, d. H. the hexafluorosilicic acid without using admixtures and / or any modification.

The process according to the invention is thus characterized in that the hardness of the circulating water and the pH of the substance suspensions are set and kept constant by adding hexafluorosilicic acid and / or its alkali metal salts.

You can e.g. Use technical quality hexafluorosilicic acid, sodium fluorosilicate and / or potassium fluorosilicate. Preferably, the hexafluorosilicic acid and / or at least one alkali salt thereof, preferably the sodium salt and / or the potassium salt, is added at the start of production on the whipping device or before the grinding or de-stripper section.

When working in a totally closed circuit, the process according to DE-OS No. 2 433 325 does an excellent job, but even in this case certain amounts of alkali salts are added to the circuit, the higher the amount of alkali silicate, the higher the amount and the amounts of other admixtures to the alkali fluorosilicate are present in the mixture. As a result, there is always a certain salting of the circuit with alkali salts, predominantly with alkali sulfate.

The use of alkali fluorosilicates, on the other hand, leads to minimal salting of the circuit with its maximum softening.

In addition to these technical advantages, the direct use of alkali fluorosilicates also has other advantages.

It has been shown that salting of the totally closed circuit can be achieved even less if the alkali metal fluorosilicates are partially or completely replaced by hexafluorosilicic acid.

It has been shown that the concentration of soluble salts in the circuit, the activities of the individual ions etc. have an enormous influence on the size of the water molecule accumulations (clusters) and thus on the entire paper production.

It has further been shown that hexafluorosilicic acid and / or its alkali metal salts (alkali metal fluorosilicates) are expediently not used at will in paper production, but preferably in amounts which soften the circulating water to 2 to 30 ° dH and at the same time adjust the pH in Set the range from 3.5 to 6.8. These values can be seen s

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achieve according to the respective production conditions by adding 0.01 to 2.50% of the hexafluorosilicic acid and / or its alkali salts; the additives relate to atro fabric.

It has also been shown that hexafluorosilicic acid and / or its alkali metal salts can be used with many advantages when dissolving difficult-to-dissolve waste paper that has been wet-strengthened with urea-formaldehyde and / or melamine-formaldehyde condensation products. 10th

As is well known, these waste papers have to be digested in the acidic pH range, using previously acidic auxiliaries which are used in amounts of 0.5-5.0%, based on dry substance, in order to reduce the pH of the fibrous stock suspension . is

These tools, especially when working in a closed circuit, lead to enormous salting of the circuit water and in many cases to serious corrosion of the paper technology systems.

Even in cases in which auxiliaries containing phosphoric acid or polyphosphate are used to dissolve wet-strength waste paper, which lead to the formation of corrosion-reducing protective layers on the metal surface, this technology leadership is not without problems, because the enrichment of the circulating water with phosphates causes intensive slime formation 2s the result, which must also be eliminated by adding anti-mucus agents. This complicates production, increases production costs and also leads to further salting of the circulating water.

It has now been found that the above-mentioned wet-solid papers can be quickly dissolved by using the hexafluorosilicic acid and / or

or acidify their alkali salts to a pH of about pH 3.5-4.5, the specific pH being somewhat dependent on the degree of wet solidification. 3s

At the pH mentioned, the wet-strength papers

617478

very quickly unlocked, which is accelerated by the extensive water softening and by the more intensive swelling of the fibers in the softened water.

As already mentioned above, the salting-up of the circulating water is minimal when using hexafluorosilicic acid and / or its alkali salts. It should also be mentioned in particular that the silicic acid formed in the circulating water by the hydrolysis of the hexafluorosilicic acid and / or its alkali metal salts flocculates and largely remains in the paper, i. H. this also leads to minimal pollution of the circulating water by soluble substances.

However, the silica can also deposit somewhat on the metal surfaces and form thin, compact and firmly adhering protective layers on them, which protect the metal surface from corrosion.

Because hexafluorosilicic acid and its alkali salts are excellent biocides and fungicides, there is no need to add an anti-mucus agent.

The following examples are intended to illustrate the invention:

example 1

In the production of packaging paper based on waste paper in a plant with a totally closed circuit, 0.15 ± 0.05% K2SÌF6, based on dry substance, was added. For the entry into the pulper, the circulating water was softened to 20 ± 5 ° dH and kept at this degree of hardness, the pH value being regulated within the limits of pH 6.5 ± 0.3. The changes in the dosing quantity of potassium fluorosilicate compensated for the fluctuations in the waste paper quality in the entry over long operating times and kept the water hardness and the pH value within the above-mentioned control ranges. The evaluation of the results for the production of corrugated material 128 g / m2, in which 3% starch was used in addition to the tested aids in two comparable cases, gave the following picture:

previous technology new technology

Tools

Degree of hardness of the circulating water pH

Mucus deposits and problems

Odor nuisance

Bitumen problems

CMT value

2 slime control agents, total 0.3%

90-110 ° dH 6.0-7.2

present in irregular

Intensely irregular intervals exist 18 ± 1 kp

Potassium fluorosilicate

0.15 ± 0.05%

20 ± 5 ° dH

6.5 ± 0.3

none none none 20 ± 1 kp

Example 2 so 3-4% aluminum sulfate det with 0.5% sodium fluorosili-

Replaced when dissolving wet-strength, highly glued label paper and 0.4% hexafluorosilicic acid. The comparison of pier waste in the pulper at 60-70 ° C was the usual use of both methods brought the following results:

previous technology new technology

Tools

Aluminum sulfate. 18 hydrate

Na2SiF6 + H2SÌF6

Dosage

3-4%

0.5% + 0.4%

pH in the pulper

3.5-4.0

3.5-3.8

Duration of serving in the pulper

30-60 min

25-35 min

Quality of the fabric after the deflickers:

individual specks up to 3 mm in size without specks

Corrosion phenomena:

serious corrosion, especially minor signs of corrosion

for pumps on some sharp edges in the pump

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Claims (4)

617478 1. A process for regulating the acidity and the water hardness of fibrous stock suspensions in the manufacture of paper, in particular in plants which work with a totally closed circuit and / or which use urea-formaldehyde and / or melamine-formaldehyde condensation products. Process products with wet-strengthened waste paper, characterized in that by adding hexafluorosilicic acid and / or its alkali salts, the hardness of the circulating water and the pH of the stock suspensions are set and kept constant. 2. The method according to claim 1, characterized in that by adding 0.01 to 2.5%, based on dry substance, of hexafluorosilicic acid and / or at least one alkali salt thereof, the circulating water is kept constant in the range from 2 to 30 ° dH , while the pH of the stock suspensions is kept in a range from 3.5 to 6.8. 2nd PATENT CLAIMS 3. The method according to claim 1 or 2, characterized in that one uses hexafluorosilicic acid, sodium fluorosilicate and / or potassium fluorosilicate of technical quality. 4. The method according to any one of claims 1 to 3, characterized in that the hexafluorosilicic acid and / or at least one alkali salt thereof, preferably the sodium salt and / or the potassium salt, at the start of production at the whipping device or before the grinding or de-stipper - adds distance.