JPH0346595B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides an improved method for making multilayer paperboard webs. In producing multilayer paperboard, layers of different properties are used. The core, which provides strength and stiffness to the paperboard, is often made from pulp made from waste paper, when at least one of its surface layers is made from bleached pulp, which is a better material. When using a multilayer paperboard making machine where several pulp layers are combined by wet pressing, a strong rigid packaging board with good printing properties and a grammage of 200-600 g/ ^m2 is used as a low raw material. It can be made at a cost. According to the oldest method of making multilayer boards, the layers are made by circular mesh. The driving speed of the circular mesh is relatively slow;
It was not possible to use a material with a high raw material concentration, which would mean a large amount of dewatering. In addition, multiple meshes must be used to make the planks. Fourdrinier paper machines can be driven at higher speeds than cylinders and also provide better control over sheet formation. Multiwire fourdrinier paper machines are ideal for producing thin sheet materials. However, these machines require high investment and working capital, which limits their use. The main object of the invention is to provide a method for producing high grammage (500-700 g/m ^<2> ) multilayer paperboard by simple means. This is achieved by the method of the invention, whose main features are:
Two overlapping pulp layers are formed by headboxes placed sequentially on the same fourdrinier paper wire, but since the raw material concentration in at least two headboxes is extremely high, the formed pulp layers When the fibers reach the slice groove of the headbox or after the raw material is discharged from the slice of the headbox, the degree of entanglement is such that the fibers cannot move significantly relative to each other on the wire and dewatering takes place within both pulp layers through the wire. . The present invention will be explained below based on the illustrated embodiments. The web forming section of the paperboard machine shown in the first figure is a twin wire former, comprising a first wire 1 and a second wire 4, the first wire 1 running mainly horizontally from the breast roll 2 to the forming roll 3. , the second wire 4 forms a gap 5 with the first wire 1, which gap tapers toward the forming roll. After the forming roll, both wires run diagonally downward and the second wire separates from the first wire. A known wire-supported dehydrator is arranged below the horizontal portion of the first wire. For example, this dehydrator dehydrates water in a downward direction via a wire using a Mako Gix and a foil. The raw material forming the first surface layer of the multilayer board is fed onto the first wire 2 by a headbox 6 located at the breast roll 2 and operated in the usual concentration range of 0.1-1.2%. The layers forming the core of the multilayer paperboard are produced by feeding the raw material onto the wire on top of the web layer already formed by the two thick head boxes 7,8. These two headboxes 7, 8 are placed at a certain distance from each other and the concentration of the raw material therein is much higher (for example 3%) than the concentration in a normal headbox. A headbox of this type is shown, for example, in Finnish Patent Publication No. 56221. When the slicing jet reaches the wire at this concentration, the pulp does not drain as it would at a normal headbox concentration, and the fibers form a continuous network through the entire thickness of the web in or immediately after the slicing grooves of the headbox. ) the web is formed in such a way that it forms a The web structure is intertwined and there are relatively strong Z-oriented fibers within the web. During web formation, intertwined structures are more open than those of layered structures. Therefore, such a web can be more easily dehydrated than a web formed at a normal concentration, so the web is dehydrated again in a downward direction from the pulp layer formed by head box 8 through the pulp layer formed by head box 7. becomes possible. Since the amount of water to be dewatered from the pulp layer in this method is much smaller than that from a pulp layer formed at normal consistency, both layers can be thick and a thick core can be made with two head boxes. . Due to the fiber orientation, a core with greater bulk than a core formed with normal concentrations can be obtained. The web formation of multilayer paperboard can be improved by smoothing the web by means of a die-day roll 9 placed between head boxes 7 and 8. A second thin surface layer is supplied from a headbox 10 located in front of the gap formed between the first and second wires, which is operated in a normal concentration range. The web layer on the forming roll 3 is squeezed between the first wire 1 and the second wire 4, and the water is dewatered upward through the wire 4 by centrifugal force, after which the formed 4-layer web is conducted in a known manner to the pressing and drying section of the paperboard machine for further processing. The raw material concentration in the high concentration head is between 1.5 and 6% or higher, preferably between 2 and 4%. The grammage of the intermediate layer formed at high concentration is 100 to 300
g/m ² or higher, preferably 150-250
g/ ^m2 . This results in a 4-layer paperboard with approximately 600
g/m ² can be produced with relatively short twin wire formers. The web-forming section of the multilayer paperboard machine shown in the second figure includes a combination of a twin wire former 11 and an underlying fourdrinier wire section 12. The second surface layer is formed by the headbox 6 which is operated at normal concentration, and the intermediate layer is obtained at high concentration by the headboxes 7, 8 in the twin wire former. In the horizontal part of the wire 1 the water is dewatered downward through the wire, and on the forming roller 3 the water is dewatered upward through the second wire 4. The second surface layer is formed by transferring the raw material to the fourdrinier wire 13 by means of a head box 14 operated at a normal concentration.
It is formed by supplying it to the top. The web layer is transferred to the layer formed on the wire 13 by a transfer roller 15.
bonded by squeezing the layers formed in the twin wireformer by. The web forming portion of the multilayer paperboard manufacturing apparatus shown in FIG. 3 includes a twin wire former 16, a fourdrinier wire former 17, and a fourdrinier wire section 18 disposed below them. The thin underliner is operated in the normal density range of double wireformer headbox 1.
9, on which an intermediate layer of two high concentration head boxes 20 and 21 is formed. The surface layer is formed by Fourdrinier paper former,
The backing paper layer is formed of fourdrinier wire. The web is bonded on the wire 22 of the fourdrinier wire section. example

[Table] The present invention is not limited to the embodiments described above, and various modifications and applications can be made within the scope of the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a web forming portion of a paperboard manufacturing machine to which the present invention is applied. FIG. 2 shows another embodiment, and FIG. 3 shows still another embodiment. [Explanation of symbols of main parts], 1...first wire,
2... Breast roll, 3... Forming roll, 4... Second wire, 5... Gap, 7, 8...
...High density headbox, 10...Normal density headbox, [Main drawings], Figure 1.

Claims (1)

[Scope of Claims] 1. Pulp formed by extremely high raw material concentration in at least two head boxes when superimposed pulp layers are formed by head boxes sequentially arranged on the same Fourdrinier papermaking wire. When the layer reaches the slice groove of the headbox or after the raw material is discharged from the slice of the headbox, the degree of entanglement is such that the fibers cannot move much relative to each other on the wire and the dewatering is carried out through the wire into both pulp layers. 1. A method for producing a multilayer paperboard web, characterized in that the method is carried out by: 2. The manufacturing method according to item 1, wherein the raw material concentration is greater than 1.5%. 3. The manufacturing method according to item 2, wherein the raw material concentration is 2 to 4%. 4. The manufacturing method according to any one of items 1 to 3, wherein the pulp layer has a grammage of 150 to 300 g/ ^m2 . 5. The manufacturing method according to any one of items 1 to 4, wherein the formed pulp layer is smoothed by a dandy roll before the next layer is formed on the pulp layer. 6. The manufacturing method according to any one of items 1 to 5, wherein the pulp layer forms a core of a multilayer paperboard. 7. Process according to claim 6, characterized in that the core is formed on a thinner pulp layer formed on the same wire and supplied at a lower concentration. 8. The manufacturing method according to item 6 or 7, wherein the thin pulp layer is formed on a core of raw material supplied at a low concentration.