SU971968A1 - Method of producing paper - Google Patents

Description

(54) METHOD OF MANUFACTURING PAPER

The invention relates to the pulp and paper industry, more specifically to methods for producing paper that is durable in a dry and wet state. A known method for producing wet-strength paper by introducing aluminum sulfate in the amount of 10-15% by weight of absolutely dry fibers at a pH of 4.3 to cellulose fibers based on cellulose fibers 1. The paper obtained by this method has low characteristics of moisture resistance and mechanical strength. A known method of making paper by grinding cellulose, introducing into the paper mass an aluminum salt, for example sodium aluminate or aluminum chloride, in an amount of 2, to a mass of absolutely dry fibers at a pH of 8-9.5 for 5-10 minutes before casting, followed by heat treatment 120-150 ° C for 1-15 minutes The known method allows to obtain paper with relatively high moisture resistance and mechanical strength under conditions of alkaline media 2. However, the use of alkaline media at low tide leads to the need to neutralize a large amount of wastewater, which reduces the efficiency of the method. Upon receipt of paper in a neutral environment, additive salts of aluminum increase the strength of the paper slightly. A disadvantage of the known method is the high cost of aluminum salts. The purpose of the invention is to increase the moisture resistance, mechanical strength and reduce the cost of paper. This goal is achieved in that according to the method of making paper by grinding cellulose, introducing Inorganic binder into the paper mass, casting the sheet, drying and heat treating it, amorphous iron hydroxide gel is used in the amount of 0.05-2% by weight as inorganic binder. completely dry pulp. It is known that the amorphous form of aluminum hydroxide, which initially formed during the outflow from the hydrolysis of aluminum salts, quickly loses its bound water. The aging process of aluminum hydroxide proceeding in this way leads to the destruction of the structure of hydroxide

aluminum, to a sharp decrease in the number of hydroxyl groups capable of forming hydrogen bonds with cellulose. As a result, the possibility of forming three-dimensional structures such as cellulose fiber - aluminum hydroxide - cellulose fiber is reduced. As a result, of all the introduced additive, only a small part of it is involved in crosslinking. In order to create the required amount of cross-links, the total content of the aluminum salt additive in the paper pulp is high (2.5-5% for sodium aluminate and aluminum chloride in an alkaline medium and 10-15% aluminum sulfate in an acidic medium, where the possibility of cross-linking is Zey even lower). The rate of dehydration of alumina depends on very many factors (temperature, time, concentration, acidity of the medium), which makes the paper production process difficult to control under production conditions and can lead to unsatisfactory reproducibility of the mechanical characteristics of the paper produced.

The use of amorphous iron hydroxide gel instead of aluminum salts eliminates these drawbacks.

Amorphous iron (Fe) hydroxide gel, also called ferrogel, exists in a medium with a pH of more than 3.5 as a polymeric compound of the structural formula

IT ONON

I I

O-Fe-0-Fe -...- O-Fe-OH

 NgO

Polymer form ferrogel contains a large amount of water, which is divided into three types according to the nature of the bond; weakly bound sorption water, imparting iron hydroxide properties inherent in the gel, coordination bound water and chemically bound water. Sorption water is removed to 80 ° C, coordination water is from 80 to 200 ° C, chemical water is from 200 to 300 ° C. The removal of the latter two types of water during the drying process in the presence of cellulose results in the renegotiation of the liberated hydroxide and water bonds on the bond of the hydroxide and hydroxyl groups of cellulose.

The iron atom, in contrast to the aluminum atom, has an empty Ze-orbital, which, during the formation of the hydroxide, holds an additional one water molecule.

During the drying process, this coordinated water is removed, and the 3d-db of the iron atom is switched to the retention of nearby hydroxyl bonds of cellulose. As a result, in addition to the hydroxyl groups of iron hydroxide (similar to the hydroxyl groups of aluminum hydroxide)

in the formation of bonds with cellulose, the 3d-dp bond also takes part in the case of the iron hydroxide gel. This property of iron hydroxide gel increases the efficiency of use as a binder when

production of various types of paper and cardboard, and to achieve high mechanical characteristics, it is possible to limit the introduction of small (0.05-2%) amounts of amorphous iron hydroxide gel. The use of smaller amounts of binder (0.05%) does not lead to a significant increase in strength, the use of additives more than 2% worsens the retention of iron hydroxide.

Thus, the amorphous hydroxide form - ferrogel contains coordination-bound water and a large number of hydroxyl groups capable of forming hydrogen bonds with hydroxyl groups of cellulose. At the same time, three-dimensional structures of the cellulose-iron hydroxide-cellulose type appear, providing high strength of the paper in the wet state at any pH above 3.5. The best conditions for the existence of active with respect to cellulose iron hydroxide are in a neutral medium at pH 5.5-7. In such a medium, iron hydroxide gel is stable for a long time during normal temperature; The dehydration of the gel and the deterioration of the properties of iron hydroxide as a binder do not occur for several days, which allows the additive to be added to the pulp at any point in the process prior to casting.

The iron hydroxide gel retention during casting is 96-OO / o, which makes it possible to use recycled water without difficulty.

During storage or artificial aging, the properties of papers containing hydroxide iron are changed slightly.

The implementation of the method.

Unbleached sulphite pulp of grade Zh-4 (GOST 6501-73) is milled to 60 ° ShR and iron hydroxide gel obtained in a known manner at a rate of 0.5-2% based on Ge2Oz by weight of absolutely dry fibers is introduced into the resulting pulp. After the introduction of ferrogel, the pH of the mass is in the range of 5.5-7.0. Introduction of amorphous iron hydroxide gel can

be carried out at any point in the process before the paper is poured. The pouring of the paper, the piece and its heat treatment are carried out in a known manner.

At the same time, paper was obtained in a known manner with the addition of 2.5% sodium aluminate on cellulose of the same brand (G-4).

The table shows the test results.

As can be seen from the table, the introduction of the iron hydroxide gel as a binder increases the mechanical characteristics of the papers by 1.3 times in the dry state and 2 times in moisture resistance in comparison with the prototype.

The proposed method allows paper to be produced at a lower cost. With a sodium aluminate price of 437 r. for the formula of the invention

A method of making paper by grinding cellulose into a paper mass of an inorganic binder, casting the paper, drying it and heat treating it, characterized in that gel is used as an inorganic binder to increase moisture resistance, mechanical strength and reduce the cost of paper.

Well, and the consumption of aluminate per ton of paper is 50 kg. The prototype costs are 21.85 r. With the price of iron hydroxide gel 314 p. per ton and consumption of iron hydroxide 20 kg Per ton of pulp costs are 6.28 p. The cost difference per ton of paper is 15.57 p. With an average daily productivity of 200 tons of paper, saving per year is 700 thousand rubles.

amorphous iron hydroxide in the amount of 0.05-2% by weight of absolutely dry cellulose.

Sources of information taken into account in the examination

1. The patent of Germany No. 1141876, cl. 55 f 11/01, 1962.

2. USSR author's certificate

No. 679690, cl. D 21 H 3/66, 1977 (prototype).

Claims (1)

Claim A method of manufacturing paper by grinding pulp, introducing an inorganic binder into the pulp, casting the web, drying and heat treating it, characterized in that, in order to increase the moisture resistance, mechanical strength and reduce the cost of the paper, amorphous iron hydroxide gel is used as an inorganic binder in an amount 0.05–2% of the mass of absolutely dry cellulose35 vines.