CS264703B1 - Method of producing modified paper - Google Patents

Abstract

The essence of the solution lies in the fact that the paper pulp is treated with a water-insoluble cross-linked urea-formaldehyde condensate in the form of powder, paste or suspension, with a nitrogen content of 36 to 41% by weight and a content of surface-bound methylol groups of 0.1 to 6% by weight based on the dry weight of the paper pulp. The solution is applicable in the paper industry.

Description

The invention relates to the production of modified paper with improved properties, whereby the conditions are chosen so as to reduce the basis weight of the paper, improve its mechanical and optical properties while maintaining its utility properties.

The paper industry uses a large number of inorganic fillers and pigments such as kaolin, talc, asbestos (agalite), bentonite, barite (natural), satin (Byzantine) white, barite white (blanc-fix), diatomaceous earth (infusoria clay), gypsum, carbonate fillers (calcium carbonate, barium carbonate, magnesium carbonate) and fillers based on TiC^. Of the fibrous fillers, finely dispersed and hydrated calcium silicates deserve attention. The so-called white pigments, which are used to fill and whiten paper at the same time, are important. These include very white kaolin, all types of whites (blanc-fixes), titanium preparations, zinc oxides, white talc, chalk, etc. (Hnetkovský and colleagues: Papírenská průhovka, SNTL,

Prague 1983).

The above inorganic pigments are partially replaced by fillers, or rather pigments based on urea and/or melamine-formaldehyde condensates. Efforts in this direction are represented by US Pat. No. 3,869,311, 3,909,348, 3,912,532, 3,928,122, 3,953,421, 3,981,845, 3,988,522, etc., which pay attention to the physical properties of the applied filler, especially the size and specific surface area of the particles.

Although the above-mentioned processes meet the requirements of the paper industry in terms of filler quality, this invention ensures further improvement of paper properties.

According to the invention, the method of producing modified paper with improved properties, such as strength, homogeneity, opacity and printability, by the action of a modifier based on urea-formaldehyde condensates is carried out in such a way that the paper stock at a temperature of 0 to 103 °C is treated with a water-insoluble cross-linked urea-formaldehyde condensate in the form of a powder, paste or suspension, with a nitrogen content of 36 to 41 wt. %, preferably 37.5 to 38.8 wt. % and a content of surface-bound methylol groups of 0.1 to 6 wt. %, preferably 0.7 to 3 wt. % in an amount of 0.1 to 10 wt. %, preferably 1 to 5 wt. %, based on the dry weight of the paper stock and the resulting paper stock is processed into paper in a known manner.

Among the advantages of the process according to the invention, it is possible to include in particular the fact that by appropriate selection of the chemical properties of the filler surface, the retention capacity is increased and the mechanical properties of the paper are improved. Another advantage is approximately 10 times lower formaldehyde emission in the paper production process, or from the finished product compared to the known state of the art.

A healthy paper with a reduced basis weight is obtained while maintaining its useful properties, i.e. in particular whiteness, opacity, smoothness, softness, etc., thus saving raw materials and energy.

The term water-insoluble cross-linked urea-formaldehyde condensate means a chemical composition consisting of 4 to 100% condensate with 0.1 to 6% by weight of surface-bound methylol groups.

The production of modified paper is illustrated by examples of designs, but is not limited to them in any way.

Example 1

In a Dutcher, 25 l of 3% bleached sulphate pulp is ground at 40°SR. Then 2% of a reinforced sizing agent (calculated on a.s. weight of pulp) and 2% of aluminium sulphate (also calculated on a.s. weight of pulp) are added to this pulp. The suspension is further mixed thoroughly with a light pull of the Dutcher and 15% and 20% of fillers are added according to the following designation (all calculated on a.s. pulp):

Table 1

sample no. % kaolin % MF condensate ^x 1 20 - 2 15 5 3 10 5 4 -

^x urea-formaldehyde condensate containing 2.7% by weight of surface-bound methylol groups.

From the paper stock prepared in this way, paper with a basis weight of 40, 60 and 80 g/m2 is produced on a paper machine. The properties of these papers are then listed in Table 2, which shows a higher effect in the achieved indicators.

Example 2

475 kg of bleached sulphite pulp (KRPA Hostinné) ground at 50°SR is mixed in a Dutcher with Nymfllla Green ground at 45°SR at a concentration of 4.92% and Sálej 4 kg of starch, kg of reinforced resin glue T 35, 17 kg of aluminium sulphate, 1.8 kg of OZP Rylux and Sálej the following fillers (calculated per a.s. pulp loading):

Table 3 sample no. % kaolin % MF-condensate ^x

10

10

10

10 ^x urea-formaldehyde condensate containing 5.6% by weight of surface-bound methyl groups.

From the paper stock prepared in this way, writing papers with different basis weights are prepared. The influence of a filler with a defined surface activity can be seen from the following table 4.

Table 4

Sample No. Weight per unit area g/m ² Tearing length m Pressure strength kPa Tear strength mN Gurley (ČSN 500 321) s Whiteness (ČSN 500 241) % Opacity % K+N test 40 5880 133 240 117 87 54 37 1 60 6380 221 394 285 85 66 41 80 6240 291 566 605 84 75 46 40 5510 126 225 81 87 57 44 2 60 6260 226 421 194 85 71 49 80 6170 249 546 357 85 79 48 40 5990 125 220 55 84 61 45 3 60 5940 186 395 151 82 74 48 80 5960 268 550 209 85 79 47 40 5200 117 220 49 87 59 49 4 60 5900 188 405 119 85 74 56 80 5760 281 600 190 86 81 53

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Claims (1)

SUMMARY OF THE INVENTION A method for producing a modified paper with improved properties, such as strength! , homogeneity, opacity and suppressability, by the action of a urea-formaldehyde condensate modifier, characterized in that the pulp at 0 to 103 ° C is treated with water-soluble crosslinked urea-formaldehyde condensate in the form of powder, paste or suspension, with a nitrogen content of 36 to 41% %, preferably 37.5 to 38.8 wt. and containing surface-bound methylol groups of from 0.1 to 6% by weight, preferably from 0.7 to 3% by weight, in an amount of from 0.1 to 10% by weight, preferably from 1 to 5% by weight, on the dry matter of the pulp and the resulting paper. is processed into paper.