FI115234B - A process for making a laminated paper or board web - Google Patents

Description

115234

FIELD OF THE INVENTION The present invention relates to a process for the production of a laminated paper or board web comprising the step of diluting the second pulp fraction containing on average finer material than the second pulp fraction is applied to the top layer or layers of paper or board web and the second pulp fraction containing average coarser material than the first pulp fraction to the central layer or layers of paper or board web.

U.S. Patent No. 5,746,889 discloses a multi-layered headbox mass feeding system wherein different mass compositions are produced from the same fresh mass to be fed to different layers of a multi-layered headbox. The pulp feeding system comprises at least one screen for transferring long fibers from the pulp which forms the surface layer of the paper to the pulp which forms the inner layer of the paper. The system may also include a second screen for transferring the • »; '20 Coat the fibers from the pulp for the inner layer of paper to the pulp for the surface of the paper.

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The WO application publications 0 129 311 A1 and 0 222 947 A1 describe vortex purification fractionation methods, in which the first vortex purification process. The accept of # 25 is led to the surface layers of the web to be formed, and the accept of the vortex purification * ·, ···, second or lower steps of the plant is conducted to the middle layers of the web to be formed. Fractionation of the pulp yields a lower <· fines content and a greater average fiber length to the middle layers of the web than to the surface layers of the web. Rai- * · '!' nanoparticles, on the other hand, have a higher content of fines and fillers than the central>> · •.: 30 layers, which, among other things, improves the printing properties of the paper.

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The fibers of the accept that are distinguished by mass fractionation are, on average, shorter, thinner and more flexible, and the accept contains more fine and filler material than reject. For the sake of simplicity, the fraction obtained by fractionation will be referred to as the fine pulp fraction below, and the rejection generated by the fractionation will be referred to as the next 5 coarse pulp fraction.

It is typical for fractionation that the acceptance consistency decreases and the rejection consistency increases compared to the feed consistency. Because of this, the reject often has to be diluted before it can be led to the headbox of a paper machine. In WO 0 222 947, the rejects of the fractionation steps are diluted with tap water taken from the wire well before being passed to the next step. In WO 0 129 311 the same tap water is used to dilute both the accept and the rejection before being fed to the different layers of the multilayer headbox. Diluting the coarse pulp fraction for the middle layers of the web with "dirty", i.e., high-content and high-filler tap water, loses at least part of the benefits of fractionation. Under the influence of tap water, the drainage capacity of the reject may be reduced to near accept level and its filler content may increase close to the acceptor filler content.

The object of the invention is to provide an improved method of making a web from a single mass by layering its various fractions. In particular, the aim is to preserve the different fractions produced by fractionation, so that the layers of the pulp layered. The objectives set for the Commission are even easier to achieve.

• * * ... 25 To achieve these and later objects, according to the invention! this method is characterized by what is set forth in the characterizing part of claim 1 # ·.

• t · t i t ’; By using water containing less ...: * 30 solids from ordinary pulp to dilute the coarse pulp, the pulps used for the various layers of paper or board can be better considered to have different properties, which improves the coating performance of the paper or paperboard. in the manufacture of paperboard.

By tap water is meant a filtrate removed from the forming web by a wire section, collected in a wire well or the like, containing fine and filler material derived from the pulp. A significant portion of this solids contained in the primary tap water is returned to the process by using tap water to dilute the thick pulp in a short cycle of the papermaking machine.

The water suitable for diluting the coarse pulp fraction is characterized in that the consistency of the water is substantially lower than that of the tap water used to dilute the thick pulp before fractionation. Preferably, the consistency of the dilution water is less than 60% of that of the primary tap water.

Possible water fractions for reject dilution include, for example, cloudy or clear filtrate from fiber recovery, water from level winding boxes, separately collected paper machine jets, water from the press section, and tap water fractionated by clarification or other means. One alternative is to dilute the tap water with one of its substantially purer water fractions such that; “The consistency of the water used to dilute the 20 coarse fractions is substantially '·] lower than the original consistency of tap water.

M 1 • «• 2 The invention will now be described with reference to the following examples, which are not to be construed as limiting.

25, · 1 · t Figure 1 illustrates schematically the production of layered paper in a pulp fraction; _ using thionisation and multilayer headbox.

I · '! Figure 2 illustrates the production of a multilayer web by pulverization and two

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·: Using 30 separate web forming units.

115234 4

As shown in Figure 1, the thick pulp M is introduced into the paper machine through a wire well 10 where it is diluted with tap water from the wire section. The diluted mass Mi is led by pump Pi to the first vortex purification stage 11 of the vortex purification plant, where the mass is fractionated into two mass fractions A5 and B. Fractionation is performed such that the first mass fraction A contains on average thinner, shorter therefore the mass fractions are referred to as fine mass fraction A coarse mass fraction B below.

The fine pulp fraction A from the fractionation is conducted in two sub-streams A1 and A2, through the pumps PA1 and PA2 and through machine screens 13A1 and 132 into two layers 14A1 and 14A2 of the multilayer headbox 15 used to form the top and bottom layers of the paper or board web being manufactured.

Dilute the coarse fraction fraction B from the fractionation and dilute the mass flow rate

Bi is fed through pump P2 to another vortex purification plant 12 of the vortex purification plant, where impurities are removed from the pulp. The accept B2 of the vortex cleaning step 12 is passed through the pump Pb and the machine screen 13b to the layer 14b of the multilayer headboard ** used to form the middle layer 20 of the paper or board web.

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Since fractionation increases the consistency of coarse pulp fraction B, pulp B must be dissipated; prior to its introduction into headbox 15. Conventionally, dilution has been carried out using a salt water Di from a wire well 10, which is rich in fiber, ... 25 fines and filler. In the solution according to the invention, a water flow D of a consistency less than the consistency Di of the tap water taken from the wire well 10 is introduced into the dilution of the coarse pulp 'B'. Such water may be derived, for example, from a fiber recovery filter, jet water recovery, or plane simulators. Water from the well 10 can also be used as dilution water provided that: first, sufficient solids have been removed in a separate process step (not shown).

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Dilution water substantially cleaner than tap water is also obtained by diluting the water from the well 10 with a cleaner water fraction.

Figure 2 shows another solution according to the invention. Therein, the diluted mass 5 Mi is fractionated in the first vortex purification sport 11 of the vortex purification plant into two mass fractions A and B. The fine mass fraction A obtained from the fractionation is fed to a headbox 16 which feeds the pulp to the flat wire 18 to form the first web Wi. The coarse pulp fraction B from the fractionation is diluted with a water flow Do of less consistency than the water 10 Di from the wire 10 taken from the wire well 10 and fed to the second vortex purification stage 12 of the vortex purification plant. 19 to form a second web W2. The second web W2 is guided over the first web Wi on the wire 18 guided by the wire 19 and the webs Wi and W2 are joined together to form a double-layered cardboard web W.

Of course, in the manufacture of a multilayer web, there may be more than two separate forming units, and the forming units may comprise, in addition to a suitable composite, a gritformer.

'1,!' 20 • ** Instead of the vortex cleaning apparatus described above, the fractionation may also be carried out by pressure sieves in a manner known per se. Fractionation Techniques and Fractionation • I> »'. ; By varying the reject ratio, different types of properties can be achieved for different layers of the web. Of course, there may be more than one fractionation step.

; *. The claims which follow, within the scope of the inventive idea defined, may vary and deviate from those set forth by way of example only.

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Claims (10)

A process for manufacturing a layered paper or board web, in which a thick mass (M) fed to a paper machine is diluted with the wirewater and the diluted mass (MO fractionated to produce two different mass fractions (A, B), of which the first pulp fraction (A), which on average contains finer material than the second pulp fraction (B), is led to one or more surface layers of the paper or cardboard web and the second pulp fraction (B) which on average contains coarser material other than the first pulp fraction (A), is passed to one or more middle layers of the paper or cardboard web, characterized in that the coarse pulp fraction (B) obtained at the fractionation is diluted prior to feeding to an inlet carriage (15; 17) with water, the thickness of which is substantially less than the thickness of the wire water added in the thick mass (M) prior to fractionation. Process according to claim 1, characterized in that the coarse mass fraction (B) obtained during the fractionation is diluted with water, the thickness of which is not more than 60% of the thickness of the wirewater used for dilution of the mass prior to fractionation. 20 3. A process according to any of the preceding claims, characterized in that for the dilution of the coarse mass fraction (B) obtained during the fractionation, water derived from the collection of fiber, from the flat seam and / or the press portion and used is used. / or separately collected tissue assist water and / or purified wire water. » 4. A process according to any of the preceding claims, characterized in that for the dilution of the coarse mass fraction (B) obtained in the fractionation, viral water which has been diluted with any water fraction which is substantially cleaner than the viral water is used. ! 115234 9 Process according to any of the preceding claims, characterized in that the coarse mass fraction (B) obtained during the fractionation is led to the inlet carriage (15; 17) via a purification device (12) and that the mass fraction (B) in question is diluted. before being measured in said purification device (12). 5 Process according to any of the preceding claims, characterized in that the fractionation is carried out with swirl cleaner (11). Process according to any of the preceding claims, characterized in that the fractionation is carried out with screens. Process according to any of the preceding claims, characterized in that the fractionation is carried out in two or more steps. 15 9. A method according to any of the preceding claims, characterized in that the fine mass fraction (A) obtained during the fractionation leads to a layer (14ai, 14a2) in a multilayer inlet tray (15), which layer is used to form a surface layer of the paper or cardboard web, and the coarse pulp fraction (B) obtained during fractionation leads to at least another layer (14b) 20. the same multilayer inlet (15), which layer is used to form a center * look of the paper or cardboard web. A method according to any of claims 1-8, characterized in that the fine mass fraction (A) obtained during the fractionation is fed to at least one inlet carriage (16) used to form a surface layers of a multilayer web, and; the coarse mass fraction (B) obtained in the fractionation is led to at least a second inlet carriage (17) which is used to form a middle layer of the multilayer web.