Method and machine for producing a multi-layer fibrous web

Abstract

The invention relates to a method for producing a multi-layer fibrous web, in particular a multi-layer paper or cardboard web, wherein at least two layers are formed from fibrous suspensions supplied by means of a multi-layer headbox to a long screen or TopFormer, in particular a TopFormer F ® of the applicant, which is provided with a breast roll shaking. In addition, a machine suited for carrying out the method is specified for producing a multi-layer fibrous web, in particular a multi-layer paper or cardboard web.

Description

[0001] The invention relates to a method and a machine for producing a multi-layer fibrous web, in particular a multi-layer paper or cardboard web.

[0002] To date, multi-layer headboxes have been used, among other things, on gap formers to produce multi-layer paper. Multi-layer wire machines or fourdrinier machines with hybrid formers, which use two-layer headboxes, are also known. This application has so far been primarily for testliner. However, the long-established multi-layer technology has also been attempted for various other paper grades.

[0003] Such known methods and machines are described in the applicant's documents DE102010029617 A1 and DE19706940 A1.

[0004] The main problem with a multi-layer headbox, however, is layer purity. As a rule, a cover weight of at least 40 g / m² is required to achieve a uniform color across the top layer. To achieve the best possible coverage at low weights, a very specific headbox and former setting is often necessary. A narrow window for headbox consistency and stock suspension jet-to-wire speed difference is particularly important, as both parameters have a strong influence on paper strength and formation. Since the headbox consistency and jet-to-wire speed difference should be higher for good coverage, a correspondingly higher tensile length ratio (RLV) must be accepted, which leads to poorer transverse strengths (SCT-CD, RCT-CD).The tear length ratio (RLV) is the ratio of the tear length in the machine direction (MD) to the tear length in the cross-machine direction (CD). The strip crush resistance (SCT) determines the crush resistance of a flat paper strip of standardized dimensions, while the ring crush resistance (RCT) indicates the crush resistance of a ring-shaped paper strip of standardized width and length.

[0005] The invention is based on the object of providing an improved method and an improved machine of the type mentioned above, which eliminate the aforementioned problems. In particular, the aim is to achieve good coverage combined with high transverse strength of the formed fibrous web on the respective fourdrinier wire or top former.

[0006] According to the invention, this object is achieved by a method and a machine for producing a multi-layer fibrous web, in particular a multi-layer paper or cardboard web, having the features of claim 1 and claim 6, respectively. Preferred embodiments of the method according to the invention and preferred embodiments of the machine according to the invention emerge from the subclaims, the present description, and the drawing.

[0007] The method according to the invention for producing a multi-layer fibrous web, in particular a multi-layer paper or board web, in which at least two layers are formed from fibrous suspensions fed by means of a multi-layer headbox to a fourdrinier wire or TopFormer provided with a breast roll shaker, in particular TopFormer F ®< from the applicant, is characterized in that a top layer and a bottom cover or protective layer are formed from the fibrous suspensions supplied by the multi-layer headbox on a first fourdrinier wire guided around a breast roll with associated breast roll shaker, and a middle layer is formed on a second fourdrinier wire from a fibrous suspension fed to it by means of a further headbox, the top layer and bottom cover or protective layer as well as the middle layer are couched together at a point of contact between the first fourdrinier wire and the second fourdrinier wire,and the layers thus couched together, in particular in the area of a couch roll around which the first wire is guided after couching the top layer and under-deck or protective layer with the middle layer, are couched with a reserve layer formed on a third wire from a fiber suspension supplied by means of a further headbox.

[0008] The breast roll, which is provided with a corresponding shaking device and around which the corresponding wire is guided in the area of the multi-layer headbox, can be shaken back and forth by the shaking device, particularly horizontally in the transverse direction.

[0009] The process according to the invention makes it possible, among other things, to produce, for example, two different fiber materials or dyed fiber materials with the same or different fiber length and / or fines and / or filler spectrum using only one forming unit, whereby the cover quality is significantly improved compared to conventional operation without screen shaking. With uniform, good formation, good layer purity is achieved. The use of screen shaking also equalizes flakes or streaks, which previously formed predominantly in the upper layer due to the required low turbulence at the beginning of sheet formation and could therefore previously have a negative impact on the cover quality.The screen shaking according to the invention thus also offers the advantage that the formation losses and surface irregularities caused by low-pulsation sheet formation are compensated for without causing mixing of the various layers or plies, as would occur, for example, through the introduction of turbulence. Furthermore, the screen shaking compensates for a larger tear length ratio (RLV) that arises from the headbox operation in the under- or over-accumulation mode, which is advantageous for covering and formation. The screen shaking according to the invention thus also avoids or at least reduces a larger tear length ratio (RLV) and the associated reduction in transverse strength, which has often had a detrimental effect, particularly in the production of packaging paper.Finally, by eliminating the need for a headbox and top former, the length of the paper machine in question can be reduced accordingly, which also results in correspondingly lower manufacturing costs.

[0010] Preferably, at least two different or differently colored fiber suspensions are fed to the respective fourdrinier wire or TopFormer by means of the multi-layer headbox.

[0011] It is particularly advantageous if at least two fiber suspensions with the same or different fiber lengths and / or the same or different filler spectrum are fed to the respective Fourdrinier wire or TopFormer by means of the multi-layer headbox.

[0012] According to a preferred practical embodiment of the method according to the invention, a vacuumed sieve table is assigned to the respective fourdrinier wire or top former for fixing a covering layer formed from a fiber suspension fed to the respective fourdrinier wire or top former by means of the multi-layer headbox.

[0013] Good layer purity requires, on the one hand, rapid fixation of the covering layer or ply and, on the other hand, as even a good formation as possible, which, like frosted glass, compensates for the unavoidable translucence of the other layer or ply, especially with low basis weights of the covering layer or high color contrast between the two layers. The preferred suction screen table enables faster fixation of the covering layer, thus essentially preventing unwanted mixing of the covering layer and the other layer, preferably with the smallest possible pulses.

[0014] Preferably, a sieve table generating as little impulse as possible is used as the suction-fed sieve table in order to at least substantially prevent undesired mixing of the covering layer with a respective further layer formed from a different fiber suspension supplied by the multi-layer headbox.

[0015] A two-layer headbox is advantageously used as a multi-layer headbox.

[0016] It is particularly advantageous if a top layer and an under-deck or protective layer are produced from the fiber suspensions supplied by the multi-layer stock line.

[0017] According to a preferred practical embodiment of the method according to the invention, a four-layer fibrous web is produced.

[0018] It is particularly advantageous if a multi-layer fibrous web is produced with a top layer, a bottom layer or protective layer, a middle layer and a back layer.

[0019] The machine according to the invention, which is particularly suitable for carrying out the method according to the invention, for producing a multi-layer fibrous web, in particular a multi-layer paper or board web, in which a multi-layer headbox is provided for forming at least two layers and the fibrous suspensions supplied by this multi-layer headbox are fed to a fourdrinier wire or TopFormer provided with a breast roll shaker, in particular TopFormer F ®< from the applicant, for forming the at least two layers, is characterized in that a top layer and a bottom cover or protective layer are formed from the fibrous suspensions supplied by the multi-layer headbox on a first fourdrinier wire guided around a breast roll with associated breast roll shaker, and a middle layer is formed on a second fourdrinier wire from a fibrous suspension fed to the first fourdrinier wire by means of a further headbox,the top layer and under-deck or protective layer as well as the middle layer are couched together at a point of contact between the first wire and the second wire, and the layers thus couched together are couched with a reserve layer formed on a third wire from a fiber suspension supplied by means of a further headbox, in particular in the area of a couch roll around which the first wire is guided after the top layer and under-deck or protective layer have been couched with the middle layer,

[0020] Preferably, at least two different and / or differently colored fiber suspensions are fed to the respective fourdrinier wire or TopFormer by means of the multi-layer headbox.

[0021] It is particularly advantageous if at least two fiber suspensions with the same or different fiber lengths and / or the same or different filler spectrum are fed to the respective Fourdrinier wire or TopFormer by means of the multi-layer headbox.

[0022] According to a preferred practical embodiment of the machine according to the invention, a vacuumed sieve table is assigned to the respective fourdrinier wire or top former for fixing a covering layer formed from a fiber suspension fed to the respective fourdrinier wire or top former by means of the multi-layer headbox.

[0023] In this case, a sieve table generating as small an impulse as possible is preferably provided as the suction-fed sieve table in order to at least substantially prevent undesired mixing of the covering layer with a respective further layer formed from a different fiber suspension supplied by the multi-layer headbox.

[0024] In certain cases it is advantageous if the multi-layer headbox is designed as a two-layer headbox.

[0025] It is also particularly advantageous if a top layer and a bottom layer or protective layer are produced from the fiber suspensions supplied by the multi-layer headbox.

[0026] A preferred practical embodiment of the machine according to the invention is characterized in that it is designed to form a four-layer fibrous web.

[0027] The machine according to the invention can be designed in particular to form a multi-layer fibrous web with a cover layer, a lower cover or protective layer, a middle layer and a cover layer.

[0028] The invention is explained below using an exemplary embodiment with reference to the drawing, in which: Fig. 1 is a schematic representation of a conventional machine for producing a four-layer cardboard web, and Fig. 2 is a schematic representation of an exemplary embodiment of a machine according to the invention for producing a four-layer cardboard web, for example.

[0029] Fig. 1 shows a schematic representation of a conventional machine 10 for producing a four-layer board web with a cover layer, a bottom cover or protective layer, a middle layer and a backing layer.

[0030] The top layer is formed from a fiber suspension applied to a first wire 14 by means of a first headbox 12, the under-deck or protective layer is formed from a fiber suspension applied to a second wire 18 by means of a second headbox 16, and the middle layer is formed from a fiber suspension applied to a third wire 22 by means of a third headbox 20. In the present case, for example, a former 24 is assigned to the third wire 22. The reserve layer is formed from a fiber suspension applied to a fourth wire 28 by means of a fourth headbox 26.

[0031] The underdeck or protective layer formed on the second wire 18 is couched with the middle layer formed on the third wire 22 at a contact point 30 between the two wires 18 and 22. The underdeck or protective and middle layers couched together in this way are then couched with the reserve layer formed on this fourth wire 28 at a contact point 32 of the second wire 18 with the fourth wire 28. The layers couched together in this way, i.e. underdeck or protective layer, middle layer and reserve layer, are finally couched with the cover layer at a contact point 34 of the fourth wire 28 with the first wire 14.

[0032] Such a conventional machine has, among other things, the disadvantages mentioned above.

[0033] Fig. 2shows a schematic representation of an exemplary embodiment of a machine 36 according to the invention for producing a multi-layer fibrous web. In this case, the machine 36 is designed, for example, for producing a four-layer cardboard web.

[0034] This machine 36, as a multi-layer headbox, comprises, for example, a two-layer headbox 38 and a first fourdrinier wire 40, on which a top layer and a bottom layer or protective layer are formed by the fiber suspensions delivered by the two-layer headbox 38. In the area of the two-layer headbox 38, the first fourdrinier wire 40 is guided around a breast roll 42, which is assigned a breast roll shaker 44, via which the breast roll 42 and thus the first fourdrinier wire 28 are shaken horizontally in the transverse direction (CD direction) of the machine.

[0035] A middle layer is formed on a second wire 46 from a fiber suspension fed to it by means of a further headbox 48. As shown, this second wire 46 can, for example, be assigned a former 50. The top layer and under-deck or protective layer as well as the middle layer are couched together at a contact point 52 of the first wire 40 and the second wire 46. Finally, the layers thus couched together, namely the top layer, the under-deck or protective layer and the middle layer, are couched at a contact point 54, in this case in the area of a couch roll 56, around which the first wire 40 is guided after the top layer and under-deck or protective layer have been couched with the middle layer, with a reserve layer formed on a third wire 58 from a fiber suspension fed by means of a further headbox 60.

[0036] By means of the two-layer headbox 38, for example, two different and / or differently colored fiber suspensions can be fed to the first fourdrinier wire 40. For example, two fiber suspensions with the same or different fiber lengths and / or the same or different filler spectrum can be fed to this first fourdrinier wire 40 by means of the two-layer headbox 38.

[0037] For faster fixation of the covering layer or top layer, a vacuum-fed sieve table can be assigned to the first fourdrinier wire 40. In particular, a sieve table generating the smallest possible impulses can be used as the vacuum-fed sieve table in order to at least substantially prevent undesired mixing of the top layer with the under-cover or protective layer formed from the other fiber suspension supplied by the two-layer headbox.

[0038] With such a machine according to the invention it is possible, among other things, to produce two different and / or differently colored fiber materials with the same or different fiber length and / or fines and / or filler spectrum using only one forming unit and to significantly improve the covering quality compared to conventional operation without screen shaking. Good layer purity requires, on the one hand, rapid fixing of the covering layer and, on the other hand, as uniform a formation as possible, which equalizes the unavoidable translucence of the other layer, particularly when the covering layer has a low basis weight or there is a high color contrast between the two layers, like frosted glass. The rapid fixing of the covering layer is ensured, for example, by the aforementioned vacuum-operated screen table, which preferably uses the smallest possible impulses to prevent undesired mixing of the two layers orthe top layer and the under-deck or protective layer is essentially prevented.

[0039] Due to the low turbulence required at the beginning of sheet formation, flakes or surface streaks can form, particularly in the covering layer, which negatively impacts the quality of the covering. These flakes or streaks are now leveled out by the inventive use of sieve shaking. This has the particular advantage of compensating for the formation losses and surface irregularities caused by the low-pulsation sheet formation without causing mixing of the covering layer and the subsequent layer, as would occur, for example, through introduction by turbulence.

[0040] In addition, the screen shaking according to the invention compensates for the increased tear length ratio (RLV) that results from the headbox operation in under- or over-accumulation, which is advantageous for covering and formation. A higher tear length ratio (RLV) and the associated reduction in transverse strength, which have often been detrimental to the production of packaging paper, are thus avoided or at least reduced by the screen shaking according to the invention. Another advantage is that the machine length is shorter and a headbox is eliminated, thus correspondingly reducing production costs. List of reference symbols

[0041] 10 Conventional machine 12 First headbox 14 First wire 16 Second headbox 18 Second wire 20 Third headbox 22 Third wire 24 Former 26 Fourth headbox 28 Fourth wire 30 Contact point 32 Contact point 34 Contact point 36 Machine according to the invention 38 Multi-layer headbox, two-layer headbox 40 First wire 42 Breast roll 44 Breast roll shaking 46 Second wire 48 Further headbox 50 Former 52 Contact point 54 Contact point 56 Couch roll 58 Third wire 60 Further headbox

Claims

1. Method for producing a multi-ply fibrous web, in particular a multi-ply paper or board web, in which at least two plies are formed from fibrous slurries supplied by means of a multi-layer headbox (38) to a Fourdrinier wire (40) or top former, in particular TopFormer F® of the Applicant, provided with a breast roll shaker (44), characterized in that a top ply and an underliner or protection ply are formed from the fibrous slurries delivered by the multi-layer headbox (38) on a first Fourdrinier wire (40) guided around a breast roll (42) with an associated breast roll shaker (44), and a middle ply is formed on a second Fourdrinier wire (46) from a fibrous slurry supplied thereto by means of a further headbox (48), the top ply and the underliner or protection ply as well as the middle ply are couched with one another at a point of contact (54) between the first Fourdrinier wire (40) and the second Fourdrinier wire (46), and the plies so couched with one another are couched, in particular in the region of a couch roll (56) around which the first Fourdrinier wire (40) is guided after couching of the top ply and the underliner or protection ply with the middle ply, with a back ply formed on a third Fourdrinier wire (58) from a fibrous slurry supplied by means of a further headbox (60).

2. Method according to Claim 1, characterized in that at least two different and / or differently coloured fibrous slurries are supplied by means of the multi-layer headbox (38) to the Fourdrinier wire (40) or top former in question.

3. Method according to Claim 2, characterized in that at least two fibrous slurries with the same or different fibre length spectra and / or the same or different filler spectra are supplied by means of the multi-layer headbox (38) to the Fourdrinier wire (40) or top former in question.

4. Method according to at least one of the preceding claims, characterized in that the Fourdrinier wire (40) or top former in question has an associated suctioned forming board for fixing of a covering layer formed from a fibrous slurry supplied by means of the multi-layer headbox (38) to the Fourdrinier wire (40) or top former in question.

5. Method according to at least one of the preceding claims, characterized in that the multi-layer headbox used is a two-layer headbox (38).

6. Machine (36) for producing a multi-ply fibrous web, in particular a multi-ply paper or board web, in particular for carrying out the method according to one of the preceding claims, wherein a multi-layer headbox (38) for forming at least two plies is provided and the fibrous slurries delivered by this multi-layer headbox (38) are supplied, in order to form the at least two plies, to a Fourdrinier wire (40) or TopFormer F®, in particular TopFormer F of the Applicant, provided with a breast roll shaker (44), characterized in that a top ply and an underliner or protection ply are formed from the fibrous slurries delivered by the multi-layer headbox (38) on a first Fourdrinier wire (40) guided around a breast roll (42) with an associated breast roll shaker (44), and a middle ply is formed on a second Fourdrinier wire (46) from a fibrous slurry supplied thereto by means of a further headbox (48), the top ply and the underliner or protection ply as well as the middle ply are couched with one another at a point of contact (54) between the first Fourdrinier wire (40) and the second Fourdrinier wire (46), and the plies so couched with one another are couched, in particular in the region of a couch roll (56) around which the first Fourdrinier wire (40) is guided after couching of the top ply and the underliner or protection ply with the middle ply, with a back ply formed on a third Fourdrinier wire (58) from a fibrous slurry supplied by means of a further headbox (60).

7. Machine according to Claim 6, characterized in that at least two different and / or differently coloured fibrous slurries are supplied by means of the multi-layer headbox (38) to the Fourdrinier wire (40) or top former in question.

8. Machine according to Claim 7, characterized in that at least two fibrous slurries with the same or different fibre length spectra and / or the same or different filler spectra are supplied by means of the multi-layer headbox (38) to the Fourdrinier wire (40) or top former in question.

9. Machine according to at least one of the preceding claims, characterized in that the Fourdrinier wire (40) or top former in question has an associated suctioned forming board for fixing of a covering layer formed from a fibrous slurry supplied by means of the multi-layer headbox (38) to the Fourdrinier wire (40) or top former in question.

10. Machine according to at least one of the preceding claims, characterized in that the multi-layer headbox (38) is designed as a two-layer headbox.

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