SU606913A1 - Method of manufacturing double-layer board - Google Patents

Description

The invention relates to a method for producing two-layer cardboard from fibrous semi-finished products with a yield of 55-85% and is intended for use in the pulp and paper industry. A known method of manufacturing double-layer cardboards (cardboard with a top fibrous layer) consists in grinding the mass for each layer separately according to the individual process conditions 1. By grinding in a separate stream, the necessary properties determined by the degree of grinding are given to a separate fiber mass, fiber length, etc. However, the known method of manufacturing two-layer cardboard has serious drawbacks. The need to impart specific properties to each layer requires the creation of separate development flows, which significantly complicates the technological process and also requires considerable investment in construction and equipment acquisition. There is also known a method of making multilayer materials, which involves the fractionation of pulp and the manufacture of a base layer from a long fiber fraction, and a coating layer from a short fiber fraction 2. This method is the prototype of the proposed invention. This method is characterized by insufficient mechanical strength of the obtained cardboard. The aim of the invention is to increase the mechanical strength of two-layer cardboard from high yield semi-finished products and products thereof. The goal is achieved by the fact that according to the proposed method, the casting of the base layer is carried out from a fraction with an average fiber length of 2.3-3.0 mm, and the covering layer from a fraction with an average fiber length of 0.6-1.2 mm. The method of making double-layer cardboard is carried out as follows. The welded fibrous semi-finished product with a yield of 55-85% is subjected to grinding, sorting, washing and then divided into two fractions: short fiber in an amount of 5-30% (by weight abs. Dry fiber) with an average fiber length of 0.6-1.2 mm and long fiber, making up respectively 70-795% of the total mass with an average fiber length of 2.3-3.0 mm. In this case, the grinding of cellulose is carried out up to 14-30 ° SH and is pumped to the fractionator. The fractionation modes used ensure continuous selection of skin

fibrous and long fibrous fractions.

After the fractionator, the individual fibrous fractions by gravity flow into the individual mixing basins, the fibrous mass is diluted with water to the required concentration, and pumps are fed into the discharge devices of a papermaking machine equipped with two discharge boxes. For the new fiber fraction is fed to the first pressure box and the main cardboard layer is formed from it on the paper net, the short fiber fraction is fed to the second pressure box, it flows under the pressure on the base layer and forms a covering layer.

Next, double-layer cardboard is subjected to compression and cyiHKe by a known method. The physicomechanical parameters of the resulting cardboard are given in Table. 1. For comparison, table. I shows the performance of cardboard made using a short fiber fraction with an average fiber length of 1.5-1.7 mm and a long fiber fraction with an average fiber length of 2.0-2.2 mm.

From the above results it follows that the proposed method; due to the more optimal fiber length of the coating and base layer, it allows to obtain cardboard and finished products with higher mechanical strength indices, on average in all indicators by 15-20%.

It should be noted a higher, by 50%, surface smoothness of the cardboard obtained by the proposed method, which provides the best printing properties of the surface of the finished product - boxes, boxes, etc.

Production of double-layer cardboard according to the proposed method was carried out using various types of high-yield semi-finished products.

Example 1. Coniferous bisulfite hemicellulose with a yield of 62% is milled to 25 ° SR and then the short-fibrous fraction in the amount of 20-25% (by weight of abs. Dry xy fiber) is separated from it. The short-fiber fraction isolated in such an amount is used for the coating layer of double-injected castings. A long fiber fraction of 75-80% by weight of abs. dry fiber, used for the base layer. The total mass of two-layer castings is 250 g / m.

The degree of grinding of the short-fiber fraction is 27 ° SHR, the average fiber length is 0.65 mm. The milling degree of the long fiber fraction is 22 ° SHR, the average fiber length is 2.7 mm. . For comparison, the bisulfite hemicellulose without pre-fractionation for each layer is milled separately, respectively, for the base layer to 22 ° SR and for the covering layer to 27 ° SR, and two-layer castings are also made.

Physico-mechanical parameters are given in table. 2

From Table 2, it follows that the proposed method allows to obtain a cardboard with high mechanical indicators.

strength, and such an indicator as the resistance of the izlo.mu much higher than that of cardboard, obtained by a known method, i.e. by separate grinding of the fibrous semi-finished product for each layer.

Example 2. Sulfate softwood pulp with a yield of 62% is ground to 25 ° ShR and a pump at a concentration of 2.9-3.1%, is fed to an experimental-industrial fractionator (capacity up to 10 tons / day). The selected fractionation mode provides a continuous release of a short-fiber fraction in an amount of 25% (by weight of abs. Dry fiber) with a grinding degree of 40 ° SR and an average fiber length of 0.8 mm. The long-fiber fraction is 75% of the mass of the total abs. the dry fiber entering the fractionation has a grinding degree of 18 ° 111P and an average fiber length of 2.8 mm.

After the fractionator, the individual fibrous fractions by gravity flow into the individual mixing basins, are brought to the required concentration with water, and are pumped into the inlets of the papermaking machine. The paper cutting machine with a width of 500 mm is equipped with two pressure boxes. The long fiber fraction is fed to the first tray box and the main layer of cardboard is formed from it on the paper machine's grid, the short fiber strip is fed to the second pressure box, it follows Q. the pressure on the main layer and forms a coating layer. Next, a two-layer cardboard is pressed and the essence by a known method. The coating weight is 25% by weight of the entire board. For comparison, two-layer cardboard is made according to known technology. Sulfate coniferous cellulose is used for the main si with a yield of 52%, sulphate coniferous cellulose is used for a covering pulp with a yield of 48%, then fed to the first and second discharge boxes and then by a known method ° The weight of the coating layer is also 25% of masses of all cardboard. Physico-mechanical properties of the resulting cardboard are given in table. 3..

5 From the above results, it follows that the proposed method allows to obtain cardboard with higher mechanical strength indices. Thus, the tensile load, withstand cardboard, made on the offer-. This method is 34% higher, its extensibility

0 ggry breaking higher by 31%, resistance to fracture by 20%, resistance to bursting more by 30%, stiffness on the destruction of the ring in the transverse direction is higher by 15% compared with cardboard, manufactured by a known method. The last indicator characterizes the operational properties of products made from containerboard.

According to preliminary calculations, the specific energy consumption during the emission of a two-layer cardboard according to the proposed method is reduced by 15-20% due to the reduction of unproductive electricity consumption at idle, and the irretrievable losses (rinsing) of fine fiber are reduced by 25 ° -OUT.

The proposed method for producing two-ply cardboard has been tested in laboratory and semi-industrial conditions.

140

0.24 37.2 22.4 29,

1.5

Offered 137 0.22 43.4 28.4 35.9 2.0 2.6 2.3

Izvesta3, 6

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Prev3, 6

01 haemy 21.2 26.8 1.4 2.1 1.75

28.4 35.9 2, C 2.6 2.3

137 0.22

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Table 1

812 109О 951

2.3 1.9

289,261,275 3.5 37.2

sixteen

954 1390 1172 283 265 274 4.4 41.7

25

table 2

337

6.2

2.24

2.31

733

6.3

Table 3

36.5

3.4

41.7

4.4

265,274

Claims (2)

954 1390 1172 283 786 117О 978 286 263 275 7 Claim. A method of manufacturing two-layer cardboard, including grinding the fibrous semi-finished product with a yield of 55 ---- 85%, fractioning the fibrous mass, the base layer of the long fiber fraction and the covering layer are made of a short fiber , or if it is due to the fact that, in order to increase the mechanical strength of 8 cardboard, the main layer is drained from the fraction with an average fiber length of 2.3-3.0 mm, and the covering one from the fraction with an average fiber length of 0.6 -1.2 mm. Sources of information taken into account in the examination: 1. Lapinsky «Board-making machines, M., 1966, p. 217. 2. US Patent No. 3791917, cl. 162-55, 1974.