CS210668B2 - Manugacturing process of filler for paper industry - Google Patents

Abstract

Fillers for use in the paper industry are made by forming a is not >75 wt.% suspension of CaCO3 (opt. contg. impurities) in water and adjusting the pH of the suspension to 5-12 with organic and/or inorganic acid(s). The pH may be adjusted in two or more stages with different acids, or in several stages with a single acid. Process is esp. useful for treating the causticising sludge obtd. as a by-prod. in the regeneration of sulphate cellulose, and consisting mainly of CaCO3 contaminated with K,Na,Mg,OH,S and silicate ions, to give a material which can be used as a filler in papermaking. The slurry of causticising sludge may be mixed with a calcium hypochlorite slurry, using is not >25 pts. wt. Ca in the hypochlorite per 100 pts. wt. Ca in the causticising sludge. Up to 10 wt.% water glass may be added to the suspension before adding the acid.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of a filler for the paper industry, wherein at most 75% of an aqueous suspension is produced from calcium carbonate, optionally containing impurities.

As used herein, fillers include fillers added to the papermaking stock.

In the manufacture of paper, it has long been known that expensive and relatively difficult to obtain fibrous materials are replaced by fillers of mineral origin. The filler content varies between 10 and 30% in various paper grades. A further advantage of using fillers in paper making is that the finely divided fillers fill the spaces between the fibers, thereby producing paper with a flatter and smoother surface and reducing the transparency of the paper, which is one of the basic requirements for the types of paper for printing and writing. On the other hand, the drawback in this case is that increasing the amount of filler reduces the sizing of the paper or more resins to achieve the same sizing, further reducing the tear length of the paper.

Fillers are classified on the basis of their chemical composition into silicates, sulphates, carbonates and oxides. In the paper industry, kaolin belonging to the silicate group is most used. The main reason for the expansion of kaolin is its relatively favorable price and 60 to 70% retention. The retention value indicates how much filler mixed into the paper stock remains in the finished product.

The use of chalk belonging to the carbonate group is limited, despite its favorable technological properties, by a retention value which is about 50 to 55% compared to kaolin. Chalk used as a filler is produced from the remains of microscopically fine algae, which are often found in nature, by floatation or precipitation from a solution of calcium chloride by sodium or from a solution of calcium hydroxide by carbon dioxide. The latter calcium carbonate is the so-called precipitated or precipitated.

In addition to very poor retention, natural or precipitated calcium carbonate has another disadvantage of being very sensitive to the aluminum sulfate used to precipitate glue.

During the chemical regeneration carried out in kraft cellulose plants, a large amount of so-called causticized calcium sludge is formed, contaminated inter alia by calcium, sodium, magnesium, hydroxyl ions, sulfide and silicate ions and containing predominantly calcium carbonate. This sludge is blue-green, has an unrecoverable odor and a basic reaction. Possibilities of utilization or regeneration of causticized lime sludge are small. Highly contaminated causticized lime sludge with a high water content is therefore exported to the heap in most cellulose plants.

However, the removal heaps require a very large area and, on the other hand, result in considerable environmental pollution.

Another polluting by-product of cellulosic pulp production is also the calcium hypochlorite residue or deposit used in the bleaching of cellulose, the amount of which, as well as the loss of chlorine produced during its manufacture, can not be reduced or even difficult.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process in which the by-products of the paper industry are used as fillers.

In the process according to the invention, this object is solved by burning off the waste liquor produced in the production of straw cellulose and caustifying, producing a 75% aqueous suspension from the resulting lime slurry, and adjusting the pH of the suspension stepwise with organic and / or inorganic acids. pH 5 and 12.

The pH is conveniently adjusted in two stages with two different acids. However, the pH of the suspension can also be adjusted in several stages with the same acid.

Optionally, the calcium hypochlorite slurry is admixed with the slurry, preferably by adding up to 25 parts by weight of calcium contained in the calcium hypochlorite slurry to the causticized lime sludge slurry, which is 100 parts by weight.

In another preferred embodiment of the process according to the invention, at most 10% water glass is added before the acid is added to the suspension.

The process according to the invention is explained in more detail in the following examples of a specific embodiment.

Example 1

A suspension with a dry matter content of 50 g / l is prepared from caustic lime sludge. The pH of the suspension is adjusted first to 10 with hydrochloric acid and then to 5 with hydrofluoric acid.

With the suspension, 20% of treated lime sludge, based on the fibrous mass, is fed to the mass of wood-machine-printed printing paper.

The paper mass is flattened and sheets of paper are formed on the laboratory equipment. The following values shall be obtained for paper obtained, respectively compared:

Working length 3200 m

Whiteness 63%

Fillers content 13.0%

For a reference sample obtained from the same paper mass with 20% kaolin under the same conditions, the corresponding paper shall have the following values:

Market length 2920 m

Whiteness 62;%

Fillers content 10.4%

Example 2

A suspension having a dry matter content of 50 g / l is prepared from caustic lime sludge. The suspension is adjusted to 10 in the first stage with sulfamic acid and 9 in the second stage with sulfuric acid.

20% of the treated lime sludge, based on the fiber mass, is fed to the mass of wood-machine-printed printing paper.

The paper mass is flattened and sheets of paper are prepared on a laboratory apparatus. The following values are obtained for the correspondingly obtained paper:

Market length 3150 m

Whiteness 63%

Filler content 10.6%

For a reference sample prepared from the same paper mass with 20% kaolin under the same conditions, the corresponding paper shall have the following values:

Market length 2900 m

Whiteness 62%

Filler content 10.6%

Example 3

From the causticized lime slurry, a slurry having a dry matter content of 200 g / l is prepared, and so much hypochlorite sludge is added that 10 parts by weight of calcium added as causticized lime slurry to the slurry is 1 part by weight of calcium added with hypochlorite sludge. The pH of the suspension is adjusted to 9.5 after stirring for 15 minutes in the first stage with acetic acid and in the second stage with phosphoric acid to 8.

20% of lime sludge, based on the fiber mass, is fed to the mass of the semi-wood office paper with the suspension.

The paper mass is flattened and sheets of paper are made on a laboratory apparatus. The following values shall be obtained for paper obtained, respectively compared:

Average market wound 3710 m

Whiteness 72%

Fillers content 11.9%

For a reference sample prepared from the same paper mass with 20% kaolin under the same conditions, the corresponding paper shall have the following values:

Average market length 3440 m

73% whiteness

^Filler content 10.7 ^Ό / ο

Example 4

A suspension with a dry matter content of 350 - g / l is prepared from caustic lime. Then, so much hypochlorite sludge is added that, per 100 parts by weight of calcium added with causticized lime sludge to the suspension, there are 25 parts by weight of calcium added with hypochlorite. sludge. After stirring for 30 minutes, the pH of the suspension is adjusted to 12.5 in the first step with sulfuric acid and then to 12 in the second step with phosphoric acid.

With the slurry, 25% of the treated lime sludge, based on the fibrous mass, is fed into the mass of the non-wood machine glazed book printing paper. The paper stock is leveled and on a paper machine 420 cm wide at 320 m / min. produces sheets.

The following values are obtained for the appropriately aligned paper produced:

Average market length 3210- m

Whiteness degree 82 ’%

Fillers content 17.8%

For a comparative sample prepared from the same paper mass with 25% kaolin under the same conditions, the correspondingly matched paper has the following values:

Average market length 2960- m

Whiteness degree 82%

Fillers content 15.6%

Example 5

A suspension with a dry matter content of 350 - g / l is prepared from caustic lime sludge. Then, so much hypochlorite sludge is added that, per 100 parts by weight of the calcium added with the causticized lime sludge, 10 parts by weight of the calcium added with the hypochlorite sludge were added. After stirring for 25 minutes, the pH of the suspension is adjusted to 8.5 in the first step with sulfuric acid and then to 7 in the second step with phosphoric acid.

25% of the treated calcium, based on the fibrous mass, is fed to the woodfree banknote mass with the suspension. - The paper mass is straightened and on a paper machine with a working width -with at -speed - 320 m / min. produces sheets of paper.

Average market length 2950 m

Whiteness 81-%

Fillers content 19.6 ° / o

For a reference sample prepared from the same paper stock under the same conditions, the corresponding paper shall have the following values:

Average market length 2700 m

Whiteness 80%

Fillers content 15.6%

Example 6

From the precipitated calcium carbonate, a suspension having a dry matter content of 50 g / l is prepared, and 1.5% sulfuric acid and 0.5% phosphoric acid based on calcium carbonate are added thereto. 250 parts by weight of the suspension are admixed with 1000 parts by weight of bleached kraft cellulose.

The paper mass is leveled and sheets of paper are made on a Rapid-Kothen machine.

The paper obtained, respectively compared, has the following values:

Working length 6000- m

Fillers content 14%

Example 7

5% water glass, based on the amount of calcium carbonate, is added to the suspension obtained according to Example 6 before the acid is added. The procedure of Example 6 is again followed and the correspondingly obtained paper obtained has the following values:

Working length 5600 m

Fillers content 16,6%

Example 8

For comparison, the paper types prepared according to Examples 6 and 7 are prepared from a precipitated calcium carbonate slurry having a dry matter content of 50 g / l and of which 250 parts by weight are added to 1000 parts by weight of bleached kraft cellulose.

The paper stock is leveled and sheets of paper are made on a Rapid-Kothen machine. The paper obtained, respectively compared, has the following values:

Working length 4660- m

Fillers content 12.0%

Example 9 ______________

For comparison, the same amount of kaolin was added to the types of paper produced according to Examples 6 and 7 instead of precipitated calcium carbonate. Paper was produced according to Example 8, having the following values:

The following values shall be obtained for paper produced, respectively compared:

The market length is 4860 'm

Fillers content 13.2 ° / o

It is clear from the examples that the sensitivity of the caustified lime sludge or calcium carbonate treated according to the invention to aluminum sulphate is surprisingly less than untreated or precipitated calcium carbonate. Looking towards this, its retention value reaches the value of kaolin retention and even exceeds it.

Another significant advantage of the process according to the invention is that with increasing filler amounts, the degree of comparison (germination) and the market length of the finished product are not reduced or only slightly.

Equally surprising is the fact that the process according to the invention yields a white product from causticized lime sludge which is initially colored and impure according to the conditions of origin, which can only be obtained by using high-quality kaolin corresponding to the standard of pollution .

From the environmental point of view, the subject matter of the invention is particularly important, since all causticized lime sludge can be utilized in paper production.

Claims (6)

CLAIMS 1. A filler process for the papermaking industry, characterized in that the waste liquor resulting from the production of cellulose from straw is incinerated and caustified, the resulting lime sludge is prepared with a 75% aqueous suspension, and the pH of the suspension is adjusted stepwise with organic and and / or inorganic acids to a value between 5 and 12. 2. The process according to claim 1, wherein the pH of the suspension is adjusted in two steps with two different acids. 3. The process according to claim 1, wherein the pH of the suspension is adjusted in several steps with the same acid. OF THE INVENTION 4. The process of claim 1, wherein calcium slurry is added to the slurry. 5. The process of claims 1 and 4, wherein the amount of calcium added to the slurry with causticized lime sludge of 100 parts by weight is supplemented with at most 25 parts by weight of calcium contained in the calcium hypochlorite sludge. 6. The process of claim 1, wherein up to 10% waterglass is added to the slurry prior to the addition of the acid.