FI70617B - VID PAPPERSINDUSTRIN ANVAENDBAR OORGANISK FYLLMEDELSBLANDNING MED HOEG RETENTION - Google Patents

Description

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INORGANIC FILLER MIXTURE FOR THE PAPER INDUSTRY WITH GOOD RETENTION

The invention relates to an inorganic filler mixture for the paper industry known from patent application 823 128, which has a good retention. The mixture according to the invention contains from 65 to 95% by weight of an inorganic filler for the paper industry and from 5 to 35% by weight of an additive comprising an aluminum salt and optionally sodium aluminate.

The invention relates to a mixture by means of which the filler loss of the paper industry can be considerably reduced. Improving the retention of filler and fine fibers brings significant economic benefits.

The following inorganic minerals are used as fillers in the paper industry: - silicates (such as kaolin, talc, etc.), - sulphates (such as BaSO 4, CaSO 4, etc.), - carbonates (such as MgCO 2, CaCO 2, etc.), - oxides (such as T1O2, ZnO, etc.), sulphides (such as ZnS, etc.).

Of the above-mentioned fillers, kaolin and talc are the most widely used for industrial applications, and barium sulfate and titanium dioxide are used for special purposes.

When these substances are used in the paper industry, an aqueous suspension is first prepared and this suspension is added to the cellulosic fiber suspension. A significant amount of filler is lost during papermaking. The amount of loss depends on the type and amount of filler added and the technical conditions used in papermaking.

Significant filler losses are mainly due to the fact that inorganic mineral filler prepared by conventional methods and industrial cellulose 7061 7 2 fiber types both have a negative surface charge (zeta potential) in aqueous suspensions. The zeta potentials of cellulose and some typical fillers are listed below:

Cellulose fiber -13 to -27 mV

Hungarian kaolin (mined in Szeg) -28 to -32 mV

Austrian kaolin (Aspenger A-2) -16 to -20 mV

Czechoslovak kaolin -15 to -25 mV

Titanium dioxide -40 to -50 mV

Austrian talc -30 to -40 mV

"Zeolex 113" (a synthetic silicate type filler manufactured by Zeofinn Oy,

Finland) -35 to -40 mV

because cellulose fibers and filler particles have a strong negative surface charge, they repel each other in an aqueous suspension, and therefore a significant amount of filler particles are leached with process water through the papermaking screen along with short cellulose fibers (broken fibers and finely divided sludge).

It has now surprisingly been found that when the mixture according to the invention is used, the filler adheres to the cellulosic fibers and thus the loss is kept to a minimum.

When the mixture of the present invention is suspended in water, a suspension is obtained in which the internal particles have a positive surface charge (zeta potential).

The filler mixture according to the invention is prepared by adding one or more air-dry compounds which release aluminum ions, preferably alurine sulphate or sodium aluminate or both, to the filler in the last step of a conventional filler bleaching process, i. during comminution of the dried filler.

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When this air-dry mixture of a certain composition is suspended under the conditions used in the paper industry, the filler particles have a positive charge (i.e., they have a positive zeta potential). Thus, when a suspension of filler particles is added to a suspension of surface-negative cellulosic fibers, the filler particles adhere to the surface of the cellulosic fibers due to electrostatic attraction and at the same time increase the hetero- or homocoagulation of broken and finely divided fibers. These effects greatly improve the retention of filler and fine fibers in the paper structure.

The zeta potentials of some typical filler compositions of this invention, measured in aqueous suspensions, are shown in Table I.

TABLE I

Filler- Percentage of filler and Additive- Zeta polotype Additive potential

weight ratio composition mV

A12 (SO4) 5 Na aluminate

Hungarian kaolin 10: 2 80 20 +13 - +16

Austrian kaolin 10: 2 80 20 + 14- + 16

Czechoslovak kaolin 10: 3 80 20 +15 - +17

Titanium dioxide 10: 3 80 20 +15 - +17

Austrian talc 10: 2 80 20 +10 - +14 "Zeolex 113” 10: 2 80 20 + 9- + 11

A filler suspension with a positive surface charge can also be obtained when the ratio of ingredients 4 7061 7 is not in the optimal range. The positive surface charge occurring during the preparation of the suspension does not depend on the degree of dilution of the suspension. By varying the ratio of alurine sulfate to sodium aluminate, it is possible to prepare fillers suspensions with a positive charge on the surface, the pH of which varies over a wide range (pH 2.0 to 10.0). In this way, the pH of the suspension can always be adjusted to the desired value, which is advantageous for paper impregnation.

As is known, aqueous suspensions of fillers used in conventional methods in the paper industry contain particles with a negative surface charge which repel each other, as well as cellulosic fibers which also have a negative surface charge. Therefore, the retention of the filler and fine fibers is poor.

In contrast, when the mixture of this invention is suspended in water, the filler particles have a positive surface charge (zeta potential), resulting in optimal retention of the filler. The retention achieved according to the present invention is very much better than the retention of fillers and finely divided fibers which have hitherto been achieved under conventional conditions. In addition, the compositions of this invention have the advantage that they do not require conventional retention aids (these retention aids are expensive, should be added separately and are less effective than the compositions of this invention), and by adjusting the pH of the filler suspension to the required value any desired gluing method.

According to the invention, a cationic polyelectrolyte (e.g. polyacrylamide or polyamide-amine, etc.) is preferably added to the mixture, whereby the retention is further increased and the strength of the paper is increased.

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The polyelectrolyte is added to the filler mixture in finely divided form during the preparation of the filler mixture. (The amount of cationic polyelectrolyte in the whole filler mixture is 0.1 to 6 #, preferably 0.25 to 2.5 # and most preferably 0.1 to 1.5 *.)

The invention is illustrated by the following examples, which are not intended to limit the invention.

The following filler compositions are prepared: Example 1

Kaolin 950 kg

Crystalline aluminum sulphate 50 kg

A total of 1,000 kg

Example 2

Kaolin 950 kg

Potassium aluminum sulphate 25 kg

Sodium aluminate 25 kg

A total of 1,000 kg

Example 3

Kaoli ini 91 0 kg

Mixture of crystalline aluminum sulphate and potassium aluminum sulphate 1: 1 70 kg

Sodium aluminate 20 kg

Total 1,000 kg 6 7061 7

Example 4

Titanium dioxide 835 kg

Crystalline aluminum sulphate 135 kg

Sodium aluminate · 30 kg

A total of 1,000 kg

Example 5

Talc 650 kg

Potassium aluminum sulphate 175 kg

Sodium aluminate 175 kg

A total of 1,000 kg

Example 6

Titanium dioxide 650 kg

Mixture of crystalline allurine sulphate and potassium aluminum sulphate 1: 1 350 kg

A total of 1,000 kg

Example 7

Kaolin 940 kg

Crystalline aluminum sulphate 40 kg

Sodium aluminate 10 kg

Cationic polyacrylamide (polyelectrolyte) 10 kg 1,000 kg

The retention of the kaolin filler used in the paper industry under conventional conditions without a retention aid is 50 to 60 depending on the type and amount of kaolin added. In contrast, the retention of the kaolin-containing mixtures of this invention is 80-85 # under the same conditions (compare Examples 1-3).

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The retention of titanium dioxide filler used in the paper industry under conventional conditions without a retention aid is 30 to 40 $ 6 depending on the amount of titanium dioxide added. However, the retention of the titanium dioxide-based alloys of this invention is 50-60% under the same conditions (Examples 4 and 6), and in addition, these alloys are much less expensive than a conventional titanium dioxide filler (Example 4).

In the paper industry, the retention of the talc filler used under conventional conditions without a retention aid is 60 to 70%, depending on the amount. On the other hand, the retention of the talc-based mixture of the present invention is 80-90% under the same conditions, and in addition, the seoe is cheaper than a conventional talc filler.

(When polyelectrolyte (Example 7) is used, the retention of small fibers and cellulose fibers is even better than when the mixtures according to Examples 1 to 3 are used, and in addition, the strength of the paper is improved without loss of filler.)

Claims (5)

8 70617 Inorganic filler mixture for the paper industry with good retention, characterized in that the mixture contains 65 to 98% by weight of inorganic filler for the paper industry and 2 to 35% by weight of an additive, comprising an aluminum salt and optionally aluminate, and that the mixture contains 0.1 to 6 % of cationic polyelectrolyte. Mixture according to Claim 1, characterized in that the proportion of aluminum salts contained in the additive is from 50 to 100%. Alloy according to Claim 1, characterized in that it contains aluminum sulphate, potassium aluminum sulphate or aluminum chloride as the aluminum salt. Mixture according to Claim 1, characterized in that it contains sodium aluminate as aluminate. Mixture according to Claim 1, characterized in that it contains a cationic polyacrylamide as the cationic polyelectrolyte.