FI75383C - Process for making multi-layer board. - Google Patents

Abstract

A method of manufacturing a thick multilayer board. Intermediate layers are formed by two consecutive head boxes disposed on a fourdrinier wire, in which layers the pulp suspension consistency is so high that the forming pulp layer reaches in a head box slice or immediately after it such a fibrage degree that fibres cannot significantly move themselves as regards to one another. Dewatering of both pulp layers takes place though a fourdrinier wire.

Description

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Method for making multi-ply board - Förfarande för framställning av flerskiktskartong

The present invention relates to an improved method of making multilayer paperboard webs.

Layers with different properties are used in the manufacture of multilayer board. The body part, which gives the board strength and rigidity, is often made of pulps made of recovered paper, while the surface layers, at least one of them, are usually of better quality, bleached pulp.

With multi-ply board machines, in which several layers of pulp are joined together by wet pressing, it is thus possible to obtain a strong, rigid packaging board with a good printing properties and a basis weight of 200-600 g / m2 with low raw material costs.

The oldest method of making multilayer board is to make layers with wire cylinders. However, the running speed of the wire cylinders is relatively low and high pulp slurry densities cannot be used, so the amounts of water to be treated are large. In addition, several wire cylinders are required if the board thickness is large.

Flat wire machines can be run at higher speeds than wire cylinders and sheet formation is more controllable. Multi-wire machines are best suited for use in the manufacture of thin grades of paperboard. However, high acquisition and operating costs limit their use.

Finnish patent application 841895 discloses a method of manufacturing three-ply paperboard in which a pulp suspension forming a second surface layer is fed to a first, inner wire, an intermediate layer pulp suspension fed to a web layer 2 is guided over a curved surface, after which the first wire and both web layers are guided against a third wire on which the pulp suspension forming the second surface layer is fed and in which the pulp suspension forming the intermediate layer is fed at a much higher consistency than the pulp suspensions forming the surface layers.

The main object of the invention is to enable the production of multilayer board with a high basis weight (500-700 g / m) with simple devices. This is achieved by the method according to the invention, which is mainly characterized in that at least two of its overlapping pulp layers are successively formed on headboxes arranged on the same flat wire, where the consistency of the pulp the fibers are no longer able to move significantly relative to each other on the wire and that water is removed from both pulp layers through the flat wire.

In the following, the invention will be described in detail with reference to the application examples of the invention shown in the figures of the accompanying drawings.

Figure 1 shows a schematic side view of a web-forming part of a board machine for applying the method according to the invention.

Figure 2 shows a schematic side view of another web-forming part of a board machine for applying the method according to the invention.

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Figure 3 shows a schematic side view of another web-forming part of a board machine for applying the method according to the invention.

The web-forming section of the board machine shown in Fig. 1 is a double wire former comprising a first wire 1 running substantially horizontally from the chest roll 2 to the forming roll 3 and a second wire 4 forming a taper 5 tapering towards the forming roll with the first wire after the forming roll. 4 separates from the first wire. Below the horizontal part of the first wire, dewatering devices known per se (not shown) supporting the wire are arranged, such as, for example, foils and suction cups, by means of which water is removed downwards through the wire.

The pulp slurry forming a thin second surface layer of paperboard is fed to the first wire 2 by a headbox 6 arranged at the breast roll 2, which operates in the normal consistency range of 0.1-1.2%.

The layers forming the body of the multilayer board are obtained by feeding the pulp slurry onto the web layer already formed by means of two spaced-apart thick pulp boxes 7 and 8 in which the consistency of the pulp is substantially higher than a normal headbox consistency, e.g. 3%. Such a headbox is described, for example, in Finnish patent publication 56221. When a lip jet enters the wire at this consistency, the pulp does not seep in the same way as a normal headbox consistency, but the web is formed so that the fibers form a uniform network through or immediately after the headbox lip channel. The structure of the web then becomes felted and the web has a relatively strong z-orientation of the fibers. Correspondingly, the structure of the web formed at normal consistency is deposited. The felt structure remains more open in the web formation than the layered structure, so that the formed dough is more easily drained from the web formed at normal consistency, which allows the pulp layer formed by the headbox 8 to be dewatered downwards through the headbox 7. Since the amount of water to be removed from the pulp layers is considerably smaller than that to be removed from the pulp layers formed at normal consistency, both layers can be thick, so that two headboxes can provide a thick body part. Due to the fiber orientation, the body part also has a larger bulk than the body part formed at normal consistency.

By treating the formed web with a wire roll or eguturizer 9 arranged between the headboxes 7 and 8, the bottom of the plywood can be improved.

The second thin surface layer is fed in front of the groove formed by the first and second wires by a headbox 10 arranged in a normal consistency range. With the forming roll 3, the web layers are pressed between the wires 1 and 4 and water is removed upwards through the wire 4 by the effect of centrifugal force. The formed four-layer web is then fed to the press and drying section of the board machine in a manner known per se for further processing.

The consistency of the pulp slurry in the thick pulp box may be 1.5-6% or greater, preferably 2-4%. The basis weight of the interlayers formed thick can be 100-300 g / m or 2 higher, preferably 150-250 g / m. In this way, a four-ply board with a basis weight of about 600 g / m can be produced with a relatively short double-wire former.

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The web forming section of the multilayer board machine shown in Fig. 2 comprises a double wire former 11 connected to a flat wire section 12 below it.

The second surface layer is formed by a headbox 6 operating in the normal consistency range and the intermediate layers by thickening headboxes 7 and 8 in a double wire former. With the horizontal portion of the wire 1, water is removed downwards through the wire and with the forming roller 3 upwards through the second wire 4.

The second surface layer is formed by feeding the pulp slurry through a headbox 14 operating in the normal consistency range to the flat wire 13. The web layers are joined together by pressing the layers formed in the double wire former against the layer formed by the wire 13 by means of a transfer roll 15.

The web forming section of the board machine shown in Fig. 3 comprises a double wire former 16, a flat wire former 17 and a flat wire section 18 below them.

The headbox 19 operating in the normal consistency range of the double wire former is provided with a thin protective layer, on top of which intermediate layers are formed by the thick pulp headboxes 20 and 21.

The surface layer is formed with a flat wire former and the backing layer with a flat wire. The webs are joined together by the wire 22 of the flat wire section.

Example: 2

Headbox - basis weight g / m consistency%

Surface layer 0.4 50

Protective layer 0.8 100

First interlayer 3.0 250

Second interlayer 3.0 250

Background layer 0.4 50 6 75383

The invention is not limited to the embodiments shown by way of example, but can also be applied, for example, to other similar solutions in which one part has a dewatering part formed by two or more thick pulp boxes.

Claims (7)

1. A method for producing multilayer carton web by joining several layers of web layers formed on a flat wire, characterized in that at least two layers of its adjacent layers are formed by one another in the same flat wire arranged inlets, where the concentration of the mass is so great that the pulp layer, which is then formed in the inlet lip of the inlet or immediately after the maid has flowed out of the inlet lip, the lip opening achieves such a degree of filtration that the fibers cannot move substantially relative to each other on the wire and that water is removed from the pulp as water is removed from water web layers. Process according to claim 1, characterized in that the stock concentration is higher than 1.5%. Method according to claim 2, characterized in that the stock concentration Sr 2 - 4%. Method according to claims 1, 2, or 3, characterized in that the surface weight of the pulp layer is 150-300 g / m 2. 5. A method according to claims 1, 2, 3 or 4, characterized in that the pulp layer formed is leveled by means of an ego extractor before the next layer is formed thereon. Method according to any of claims 1 to 5, characterized in that the pulp layers form the body of the multilayer carton. 7. A method according to claim 7, characterized in that the body is formed on one side. sanuna planvira formed pulp layer, which is thinner and more diluted.