Method of preparing pigment for manufacturing paper and cardboard

FIELD: paper-and-pulp industry.

SUBSTANCE: invention relates to pigment, which can be used in manufacture of paper with filler, coated paper, and cardboard. Calcium hydroxide and calcium carbonate powders taken in proportion between 1.0:2.2 and 1.0:23.5 are added to vigorously stirred water, after which temperature of mixture is raised to 80-85°C and resulting reaction mixture is kept being stirred for 90-180 min to form dispersion of pigment containing 20-35% solids.

EFFECT: improved quality of pigment at lower cost and extended application area.

3 tbl

 

The invention relates to the production of pigments, as well as to the technology of making paper with filler, coated paper and cardboard.

At the present time in the manufacture of paper and paperboard much attention is paid to the development of pigments to improve the optical and mechanical characteristics of the paper filler and coating on the coated paper and cardboard. Developed technology that provides the ability to centrally receive pigments in powder form, followed by its use in various enterprises.

A method of obtaining white pigment by treating the aqueous suspension of calcium hydroxide aluminium sulphate in their stoichiometric ratio with getting silicates of calcium - sativas (U.S. Pat. U.S. No. 3615768, CL 106/306, publ. 1971).

However, this method can be obtained paste pigment concentration of solids to 25%, and due to the high viscosity of the dispersions of sativas it can be used in coating compositions only as a Supplement to other major pigments. In addition, the pigment obtained by this method, dried and ground into powder, loses its beneficial properties.

The closest analogue of the proposed method is a method of obtaining a pigment for making paper and paperboard, which can the be used in the manufacture of coating compositions. This method consists in the preparation of an aqueous suspension of calcium silicates by treatment with calcium hydroxide aluminium sulphate, mixed with a suspension of natural inorganic component kaolin, removal of water by drying, preferably by spraying, with the formation of the pigment powder is a mechanical mixture of the silicates of calcium and kaolin content of silicates of calcium 10-30% by weight of the mixture. The powder then redispersion in water and use in coating compositions (see US, 3876443 And NCL 106-306, IPC 09 With 1/02, publ. 08.04.1975).

In a known way to get the pigment powder is only possible when the content of sativas in its mixture with kaolin no more than 30%. In addition, it is not envisaged the possibility of obtaining a pigment, the modified binder is starch or polyvinyl alcohol (PVA).

A positive result from the use of the present invention is to reduce the cost of the pigment due to the replacement of scarce kaolin cheap calcium carbonate (chalk) and, accordingly, the value of the products obtained with the use of a pigment as filler or component in coating compositions, as well as giving the pigment of a new quality by modifying its binder. When the method is achieved by raising the white pigment due to the high grinding the decayed material and increases the uniformity of the particle size distribution of the pigment powder.

The modification of the pigment binder extends the field of application of such a pigment - with the introduction of pigment not only in coverage, but in the pulp.

The positive effect is achieved by the fact that in the proposed method of obtaining a pigment for making paper and paperboard, comprising a mixture of calcium hydroxide, aluminum sulfate and natural inorganic component in the dispersion in water, according to the invention as a natural inorganic component used calcium carbonate, whereby it is prepared by stirring a mixture of calcium hydroxide with calcium carbonate at a ratio of these components respectively from 1.0:2.2 to 1.0 to:23.5cm, after which the resulting dispersion gradually add aluminum sulfate at a ratio of the latter to the total mass of calcium hydroxide and calcium carbonate from 1.0:0.9 to 1.0 to:5,8, then the temperature of the mixture was raised to 80-85°and the reaction mixture is maintained under stirring for 90-180 min with formation of a dispersion of pigment-containing 20-35% of dry substance.

In the dispersion of calcium hydroxide and calcium carbonate can enter the junction from the group consisting of starch and polyvinyl alcohol, in kolichesvto 1.0 to 4.0% by weight of solids of pigment.

Upon receipt of the pigment in the form of a powder mixture of calcium hydroxide and calcium carbonate cooking is at a ratio respectively from 1.0:3.8 to 1.0 to:23,5 with subsequent drying of the dispersion of the pigment and getting it powder.

The method is as follows: in the static mixer is equipped with high-speed agitator and a steam jacket, serves a specified amount of water, which under vigorous stirring in a predetermined amount is gradually fed powders of calcium hydroxide and calcium carbonate, the dispersion is stirred for 5-10 minutes and then there was added a solution of aluminum sulfate containing a given quantity of aluminum sulfate in the form of Al2(SO4)3·N2O. After the filing of a solution of aluminum sulfate, the temperature of the mixture in the reactor was raised to 80-85°and the mixture at this temperature and vigorous stirring withstand 90-180 minutes

The result is a pigment dispersion with a solids content of 20-35%, which can be used directly, for example, in the manufacture of paper filled with or in obtaining coating compositions. In other cases, the dispersion is subjected to drying the layer at a temperature of up to 85°and then crushed into powder or spray drying.

Upon receipt of pigments modified binder is starch or PVA, calcium hydroxide and calcium carbonate is dispersed in water containing a specified amount of the binder is determined by the mass of solids of the final product is a pigment.

Because depending on the destination poluchaemoj the product of its paste is diluted, for example, with the introduction of pigment into pulp as a filler, or mixed in the form of paste or powder with the other components (agents, dispersing agents, pigments, resins, latexes and the like) during the formation of coating compositions with different total concentration of dry substances and, consequently, with different physical parameters (e.g., viscous properties), as the characteristics of the final product is a pigment in the form of paste or powder choose the stability of the paste with a solids content of 20% or more, the ease of grinding pigment, dried layer at 75°With, the presence or absence of cemented Agamirov in the crushed powder, the ability to redispersion powder without loss of properties of the pigment, optical white pigment powder.

As the characteristics of the pigments, modified binders, use the degree of retention of the pigment binder which is defined as follows.

A certain amount of the obtained dispersion of the modified binder of the pigment is mixed by a high-speed stirrer with a certain amount of water. Diluted several times the variance of stand alone before the separation. The bottom layer is a free-floating sediment, and the top layer is transparent, not containing solid phase of water. In this layer determine the content swazoo is it. Then recalculation on weight of solids of pigment taken on the dilution of the sample variance to determine the number of binding, as related by the pigment and the aqueous phase pigment. The degree of retention of binding is expressed as percent of the binder is submitted to the system during the manufacturing process of the modified pigment.

Physico-chemical processes upon receipt of the pigment can be represented as follows.

Under vigorous stirring in an aqueous environment all components of calcium hydroxide, calcium carbonate, aluminum sulfate is in the system there are two reactions: the reaction of interaction of aluminum sulfate with calcium hydroxide, passing with very high speed and at normal temperature (15-20° (C), as well as the slow reaction of interaction of aluminum sulfate with calcium carbonate, the speed of which increases significantly with increasing temperature. Accordingly, the calcium hydroxide in the proposed method, at the beginning of the process completely reacts with aluminium sulphate with the formation of an appropriate number of silicates of calcium - sativas.

In the reaction of aluminum sulfate with calcium carbonate, the excess of the latter in the reaction mixture, aluminum sulfate ultimately consumed completely. As a result of this reaction is a white pigment, n is which properties similar to sativas. For example, he has a high whiteness, high stability in systems with acidic pH values, has a particle size in the dispersion is not more than 2 μm, has the ability to be modified binder. These characteristics improve with increasing degree of conversion of calcium carbonate in the reaction with aluminum sulfate.

In addition, the product of the reaction of calcium carbonate with aluminium sulphate, dried, for example, in the layer very easily crushed into a powder with particle sizes less than 1 micron and again redispersible in water to obtain a low viscosity dispersion with a pigment concentration to 45%.

When the joint receipt of sativas and converted to calcium carbonate pigment is also quite easily crushed with a share of sativas in the composition of the pigment to 45%. Powder well redispersible preserving characteristics of the pigment.

The process of obtaining a pigment according to our proposal is preferably carried out when the temperature of the reaction mixture 80-85°C. To obtain a pigment with a higher degree of conversion of calcium carbonate required is a longer process.

The ability of the pigment particles to retain their hydration shells substances such as starch, PVA, due, apparently, a strong polar interaction of the pigment with the water molecules and the corresponding significant structuring what about the volume of the aqueous layer in hydration shells around the particles of the pigment in the moment of their formation. Even after repeated dilution of the system and vigorous stirring of the water shell structured particles containing a binder, not diffuse.

Conditions of carrying out the method according to the examples and characteristics of products are shown in the tables. In table 1 we give the conditions run the examples in the proposed method, table 2 - characteristics of the samples in these examples.

To compare some characteristics determine the control samples, prepared according to the prototype (table 3, examples 9-12), i.e. mechanical mixing paste silicates of calcium kaolin, as well as samples with calcium carbonate in the mixture instead of kaolin while maintaining the aspect ratio (table 3, examples 13-16).

White used raw materials: kaolin - 89.5 per cent, of calcium carbonate is 84.5%.

The pigment is dried at 75°in the layer, grinding the pieces is carried out in a porcelain mortar. Ease of grinding judged by the presence or absence of powder particles larger than 10 microns. Difficulty in grinding the samples in examples 9 and 13 of table 3 were associated with the presence in the dried pigments cemented, resistant to crushing and abrasion of the agglomerates.

As can be seen from the tables, the proposed method provides superior quality pigment for white, the ability to grinding the dried Mat is the Rial, allows redispersible powder pigment while maintaining its properties. The method also gives the opportunity to expand the scope of use of the pigment due to its modification of the binder.

Table 1
Conditions of carrying out the process according to the invention.
no examplesCalcium hydroxide CA(Oh)2Calcium carbonate, caso3Sulfate Al2(SO4)3·18H2OMass. ratioMass. RatioProcess temperature, °The process duration, min
113,6429,2849,771:2,21:0,8685180
210,2329,2544,631:3,861:0,8885160
310,2358,6426,181:5,71:2,638590
48,5354,7832,061:to 6.431:1,9780 120
58,5336,5649,371:4,31:0,9085150
66,839,049,261:5,71:0,9380150
73,480,314,361:23,51:5,88590
83,443,9148,991:12,871:0,9680100

Table 2
Characteristics of samples of the pigment obtained according to the invention
no examplesShare sativas in mixture, %The concentration of solids in the dispersion, %The stability of the dispersion within 48 hoursThe degree of conversion of calcium carbonateEasy grinding into powderAgglomerates in the powderWhite powder, %The possibility of redispersible powderBinderThe amount of binder % by weight of solidsThe degree of retention of the binder, %
1 4220Stable95Grinding is difficultNo88,63MayStarch4,099,8
23625-"-95Without difficulty-"-88,23-"-PVA2,099,8
32630-"-30-"--"-86,88-"----
42835-"-50-"--"-87,13-"-Starch1,099,4
52730-"-95-"--"-88,11-"-PVA1,099,6
62335-"-95-"--"-87,11-"----
71035-"-20 -"-86,75-"----
81235-"-95-"--"-87,03-"----

Table 3
Characteristics of samples of the pigments obtained according to the prototype of a mixture of sativas with kaolin (examples 9-12) and sativas with calcium carbonate (examples 13-16)
no examplesShare sativas in mixture, %The concentration of solids in the dispersion, %Easy grinding into powderAgglomerates in the powderThe suitability of the powder to redispersionWhite powder, %
94020Grinding is difficultAvailableNot suitable89,6
103030Without difficultyNoSuitable89,57
112030-"--"--"-89,35
1235-"--"-"-89,0
134020Grinding is difficultAvailableNot suitable87,40
143030Without difficultyNoSuitable86,95
152030-"--"--"-86,30
161035-"--"--"-85,6

1. A method of obtaining a pigment for making paper and paperboard, comprising a mixture of calcium hydroxide, aluminum sulfate and natural inorganic component in the dispersion in water, characterized in that as a natural inorganic component used calcium carbonate, whereby it is prepared by stirring a mixture of calcium hydroxide with calcium carbonate at a ratio of these components respectively from 1.0:2.2 to 1.0 to:23.5cm, after which the resulting dispersion mixture gradually add aluminum sulfate at a ratio of the latter to the total mass of calcium hydroxide and calcium carbonate from 1.0:0.9 to 1.0 to:5,8, then the temperature of the mixture increased to 8-85° C and the reaction mixture is maintained under stirring for 90-180 min with the formation of the pigment dispersion with a content of dry substances of 20-35%.

2. The method according to claim 1, characterized in that the dispersion of calcium hydroxide and calcium carbonate impose a binder from the group consisting of starch and polyvinyl alcohol in the amount of 1.0 to 4.0% by weight of solids of pigment.

3. The method according to claim 1, characterized in that the mixture of calcium hydroxide and calcium carbonate is prepared at a ratio respectively of from 1.0:3.8 to 1.0 to:23,5 with subsequent drying of the dispersion of the pigment and getting it powder.



 

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