Apparatus for manufacturing white kraft linerboard and use of the apparatus for manufacturing white kraft linerboard

Abstract

The invention relates to an apparatus (100) for manufacturing white kraft linerboard (102), the apparatus having a screen section (104), a press section (106) and a drying section (108). According to the invention, the forming units (120, 130) of the screen section (104) are arranged in such a way that the lighter cover layer (112) of the white kraft linerboard (102) points downwards when leaving the screen section (104). Furthermore, the press section (106) comprises at least three press nips (164, 172, 176), wherein the first press nip (164) is formed by a shoe press roll (166) and a suction counter roll (168), the second press nip (172) is formed by the suction counter roll (168) and a smooth central roll (174), the third press nip (176) is formed by the smooth central roll (174) and a further shoe press roll (176), and wherein the white kraft linerboard (102) comes into contact with the smooth surface of the smooth central roll (174) with its lighter cover layer (112) not only in the second press nip (172) but also in the third press nip (176).

Description

TECHNICAL FIELD

[0001] According to a first aspect, the invention relates to an apparatus for manufacturing a white top kraftliner paperboard, in particular for manufacturing a white top kraftliner paperboard having a grammage of at least 125 g / m 2 BACKGROUND

[0002] In contrast to the Testliner paper type which is made mainly, if not exclusively, from recycled fibers, the Kraftliner paper type is made mainly, if not exclusively, from fresh fibers. However, fresh fibers are more difficult to dewater at least in the press section than recycled fibers.

[0003] White Top Kraftliner has a lighter colored top ply made from bleached and mainly short fiber kraft pulp, which is the reason for the name component of "White Top", and a darker colored back ply made from unbleached and mainly long fiber kraft pulp. When the White Top Kraftliner manufacturing is finished, the lighter colored top ply should be as white and smooth as possible to ensure good printability, while the darker colored back ply gives the paper web the required stability or strength. SUMMARY

[0004] It is the task of the invention to provide an apparatus for manufacturing a White Top Kraftliner paperboard, in particular at particularly low cost, while it is able to achieve a higher quality White Top Kraftliner paperboard.

[0005] ​The task according to the application is solved by a device for manufacturing a white kraft linerboard, that is to say for manufacturing a multi-layered fibrous web having at least one darker backside layer and a lighter cover layer, which device comprises a screen section for forming the white kraft linerboard, a press section for further dewatering the white kraft linerboard and a drying section for drying the white kraft linerboard, wherein the screen section comprises at least one first forming unit for forming the darker backside layer of the white kraft linerboard and at least one second forming unit for forming the lighter cover layer and a nip area, wherein the first forming unit and the second forming unit are arranged and configured to transfer the darker backside layer onto the lighter cover layer within the nip area for forming the white kraft linerboard, such that the lighter cover layer is pointing downwards upon leaving the screen section, wherein the press section comprises at least three press nip areas, wherein the first press nip area is formed by a shoe press roll and a suction counter roll, the second press nip area is formed by a suction counter roll and a smooth central roll and the third press nip area is formed by the smooth central roll and a further shoe press roll, and wherein the white kraft linerboard is guided through the three press nip areas such that the white kraft linerboard is in contact with the smooth surface of the smooth central roll not only in the second press nip area but also in the third press nip area with its lighter cover layer.

[0006] According to the application, the white kraft linerboard is manufactured in a so-called "top on bottom" layout, that is to say, upon leaving the screen section, the lighter cover layer is pointing downwards. This is actually disadvantageous, because after the pressing, the dewatering of the darker backside layer is effected by the lighter cover layer, whereby the danger of a greying of the lighter cover layer occurs. However, the inventors have found that this drawback is acceptable, because in this way a machine design can be realized in which the lighter cover layer is in contact with the smooth surface of the central roll in a simple manner and this even within two press nip areas, such that the lighter cover layer is effectively smoothed.

[0007] According to the application, the white kraft linerboard can also be effectively dewatered in the press section, because the first press nip area and the third press nip area are configured as extended press nip areas by applying shoe press rolls. Furthermore, the white kraft linerboard is dewatered in the first press nip area towards the darker backside layer based on the action of the suction roll.

[0008] In a refinement of the application, the dewatering effect in the first press nip can be constituted more symmetrically by arranging a press felt on the side of the white linerboard which is remote from the suction roll. This in turn results in that the asymmetric dewatering in the second and third press nip has little effect on the symmetric influence of the paper in the press section. A certain dewatering by the lighter cover layer is even desirable in the press section, since in this way more filler is left in the lighter cover layer, which in turn results in a greater compaction of the cover layer, which is advantageous. A stronger compaction of the cover layer means that the fibres and filler are fixed more firmly and defects such as so-called fuzzing or dusting are less likely to occur, for example in a subsequent printing process.

[0009] In the screen section, however, a certain dewatering can also be achieved by the darker back layer, for example, by the screen of the first forming unit and the screen of the second forming unit extending parallel to each other for a predetermined distance directly after the nip, and at least one dewatering unit, for example at least one suction box, being arranged on the side of the darker back layer within this predetermined distance. Additionally or alternatively, it is also conceivable to turn the white linerboard downwards after the nip around a turn roll. Due to the turning downwards, a centrifugal force acts on the water contained in the white linerboard, which expels the water from the white linerboard through the darker back layer. If desired, a shoe press roll can also be arranged at the turning position in order to enhance the effect.

[0010] In the second press nip and / or in the third press nip, further dewatering of the white linerboard can be achieved when the white linerboard is supported here from the darker back layer by means of a press felt.

[0011] It should also be added that the risk of an excessive linear load of the white linerboard and thus of damaging the white linerboard can be reliably ruled out on the basis of the application of two elongated press nips. Thus, in particular, a relatively high force, in particular a linear force, can be present in the first press nip, which is exerted on the fibrous web in order to enhance the dewatering, without the risk of hydrodynamic damage, so-called "crashing", having to be taken into account here.

[0012] According to a further aspect, the application also relates to the use of the aforementioned device for the manufacture of white linerboard. With regard to the advantages which can be achieved by this use, reference is made to the above description of the device according to the application. BRIEF DESCRIPTION OF DRAWINGS

[0013] The application is explained below in one embodiment and in further detail with reference to the drawings. In which:

[0014] Figure 1 A schematic representation of a device for the manufacture of white linerboard according to the application is shown. DETAILED DESCRIPTION

[0015] Figure 1 The device according to the application is generally designated with 100. The device 100 is used for manufacturing a multi-layered fibrous web 102 of a white kraft linerboard. The device 100 comprises a wire section 104 for forming the fibrous web 102, a press section 106 for further dewatering the fibrous web 102 and a drying section 108 of a first drying group 108a for drying the fibrous web 102. It is to be noted here that, Figure 1 In the overview only the first part of the drying section 108 is shown.

[0016] The white kraft linerboard has at least two layers. A first layer 110 forms a darker back or back layer of the white kraft linerboard and a second layer 112 forms a lighter cover or cover layer. The grammage of the white kraft linerboard may, for example, be at least 125 g / m 2 .

[0017] For forming the first layer 110 of the white kraft linerboard, the wire section 104 comprises a first forming unit 120 having a first flow box 122 via which a fibrous suspension, for example containing unbleached long fiber kraft pulp, is fed. Furthermore, for forming the second layer 112 of the white kraft linerboard, the wire section 104 further comprises a second forming unit 130 having a second flow box 132 through which a fibrous suspension, for example containing bleached short fiber kraft pulp, is fed. For dewatering the back layer 110 and the cover layer 112, fixed dewatering elements 126 or 136 are arranged within the loop of the wire 124 of the first forming unit 120 and within the loop of the wire 134 of the second forming unit 130.

[0018] Finally, the forming units 120, 130 are arranged and configured relative to each other so as to construct the white kraft linerboard such that the darker back layer 110 formed within the first forming unit 120 is transferred within the press nip 140, that is to say at the couch roll 142, onto the lighter cover layer 112 of the white kraft linerboard formed within the second forming unit 130. The lighter cover layer 112 is thus directed downwardly upon leaving the wire section 104.

[0019] In other words, the white liner paper board is arranged "bottom side up" when leaving the screen section 104. This is actually disadvantageous, since after the calendering, the dewatering of the darker back side layer 110 takes place through the lighter cover side layer 112, thereby creating the danger of a blushing of the lighter cover side layer 112. In order to suppress this effect, the two screens 124, 134 can also be guided parallel to each other for a predetermined distance behind the couch roll 142, wherein the two screens accommodate the calendered layers 110 and 112 therebetween. What this enables is that additional dewatering elements 128 or 138 are provided not only under the screen 134, but also above the screen 124, which enable the dewatering of the white liner paper board not only through the lighter cover side layer 112, but also through the darker back side layer 110.

[0020] It is noted here that the stationary dewatering elements 126, 128, 136, 138 can be formed by at least one doctor blade and / or at least one foil, which can be arranged in at least one suction box, if desired.

[0021] The white liner paper board formed in the screen section 104 is removed from the screen 134 through the water-uptaking upper dewatering belt 160 and introduced into the press section 106.

[0022] The dewatering belt 160 then guides the fibrous web 102 through a first press nip 164 of the press section 106 in common with a water-uptaking dewatering belt 162 extending below the fibrous web 102.

[0023] The first press nip 164 is configured in an elongated manner and for this is formed by a lower shoe press roll 166 and an upper suction press roll 168. The shoe press roll usually has an elastic roll cover, the pressure shoe of which is used to press a concave press surface of the elongated press nip against a cylindrical counter roll. Due to the elongated residence time of the fibrous web 102 in the press nip, the fibrous web can achieve an intensified and still protected dewatering.

[0024] Since the fibrous web 102 has a relatively high moisture content in the first press nip 164, it is sufficient to protect the volume of the fibrous web 102 if the shoe length of the respective shoe press roll 166 is less than 270 mm, preferably less than 220 mm, in particular less than 140 mm. Here, the linear load in the first press nip 164 should be greater than 100 kN / m, preferably greater than 150 kN / m, in particular greater than 175 kN / m.

[0025] In order to be able to influence the dewatering better over the width of the fibrous web 102, it is also advantageous if the shoe press roll 166 of the first press nip 164 has a plurality of, preferably three, pressure zones arranged side by side transversely to the web running direction L and controllable individually.

[0026] The suction press roll 168 has a perforated roll cover, like the suction guide rolls 170 (of which only one is provided with reference numeral 170 for overview reasons) around which the through-air dewatering belts 160 and 162 are wrapped, the interior space of which is at least partially connected to a source of negative pressure. Furthermore, it is advantageous if at least one of the suction guide rolls 170 is coupled to a drive.

[0027] Due to the increased load in the first press nip 164, it is advantageous for the cylindrical suction press roll 168 of the first elongated press nip 164 to have a cover thickness of at least 40 mm. The suction press roll 168 can be coupled to a drive in an advantageous manner.

[0028] The negative pressure present in the suction press roll 168 not only supports the discharge of water pressed out of the fibrous web 102, but also supports the adhesion of the fibrous web 102 to the upper through-air dewatering belt 160, so that the lower through-air dewatering belt 162 can be guided away from the fibrous web 102 after passing through the first press nip 164.

[0029] After passing through the first press nip 164, the fibrous web 102, together with the upper through-air dewatering belt 160, passes through a second press nip 172 of the press section 106, which is formed by the suction press roll 168 and a further cylindrical press roll 174 having a smooth cover surface.

[0030] Subsequently, the fibrous web 102 is guided alone over the smooth cover surface of the press roll 174 towards a third press nip 176, which is likewise configured as an elongated press nip. The third press nip 176 is formed by the further cylindrical press roll 174 and a further shoe press roll 180 arranged above the fibrous web 102 and wrapped by a through-air dewatering belt 178 which is subjected to suction.

[0031] Since the water content in the first press nip 164 is significantly greater than the water content in the third press nip 176, both being elongated press nips, it is sufficient to protect the fibrous web volume if the first press nip 164 is at most as long as the third press nip 176 and / or the linear load in the first press nip 164 is at most as great as the linear load in the third press nip 176. For example, in the first press nip, a linear load of between 100 kN / m and 300 kN / m, for example approximately 200 kN / m, can be exerted on the fibrous web, in contrast to which, in the third press nip, a linear load of more than 900 kN / m, preferably more than 1000 kN / m, is exerted on the fibrous web. The shoe used to form the third press nip is preferably longer than the shoe used to form the first press nip.

[0032] In order to intensify the dewatering, the fibrous web 102 can be supplied with hot steam within the press section 106 via one or more (not shown separately) steam blow boxes. Particularly suitable for this purpose are Figure 1The area marked 182 between the first pressing zone 164 and the second pressing zone 172, and between the second pressing zone 172 and the third pressing zone 176.

[0033] In addition, the web guidance within the extended pressing zones 164 and 176 can be improved by ensuring that the fiber web 102 is wound around the corresponding cylindrical pressing rollers 168 and 174 before and after each extended pressing zone for a travel distance of at least 20 mm.

[0034] The dewatering belts 160, 162, and 178 that absorb water can be advantageously constructed as press felts.

[0035] exist Figure 1 In this embodiment, the upper dewatering belt 178 leaves the fiber web 102 after passing through the third pressing zone 176, and the fiber web 102 continues to be guided alone on the sleeve surface of the smooth cylindrical press roller 174 until it transitions to the drying screen 190 of the subsequent drying section 108 for drying the fiber web 102.

[0036] However, an alternative that can be conceived in principle is that the cylindrical pressure roller 174 is continuously wound around a smooth, semi-permeable or impermeable conveyor belt, which passes below and together with the fiber web 102 through the second press zone 172 and the third press zone 176. After passing through the third press zone 176 and being rewound by the smooth central roller 174, the fiber web 102 can transition from the conveyor belt to the drying screen 190 of the subsequent drying section 108 without free pulling.

[0037] according to Figure 1 The cylindrical pressure roller 174 and the aforementioned conveyor belt are so smooth that the fiber web 102 can adhere sufficiently to the pressure roller 174, or the conveyor belt, and the dewatering belt 178 can be guided away from the fiber web 102 after passing through the third pressing zone 176. This adhesion can also be strengthened by briefly rewinding the dewatering belt 178 onto the lower pressure roller 174.

[0038] To support the transition of the fiber web 102 to the breathable drying screen 190, the fiber web is wound around the suction guide roller 192 during the pipe-feeding process; however, when removed from the pressure roller 174, the vacuum level of the suction guide roller is no greater than 20 kPa.

[0039] Within the drying section 108, the fiber web 102 is supported by a drying screen 190 and meanders alternately, guiding the heated drying cylinder 194 and suction guide rollers 196. The axes of the drying cylinder 194 and the suction guide rollers 196 are vertically offset from each other. Furthermore, these axes are horizontally spaced from each other, a distance greater than 80%, preferably greater than 90%, and particularly greater than 95%, of the sum of the radii of the drying cylinder 194 and the suction guide rollers 196.

[0040] List of reference signs

[0041] 100 Apparatus for manufacturing a paper form for "white kraft liner" paperboard

[0042] 102 Fibrous web

[0043] 104 Screen section

[0044] 106 Press section

[0045] 108 Drying section

[0046] 110 Darker back layer

[0047] 112 Lighter cover layer

[0048] 120 First forming unit

[0049] 122 Headbox

[0050] 124 Screen

[0051] 126 De-watering element

[0052] 128 Further de-watering element

[0053] 130 Second forming unit

[0054] 132 Headbox

[0055] 134 Screen

[0056] 136 De-watering element

[0057] 138 Further de-watering element

[0058] 140 Press nip

[0059] 142 Couch roll

[0060] 160 De-watering belt

[0061] 162 De-watering belt

[0062] 164 First press nip

[0063] 166 Shoe press roll

[0064] 168 Suction press roll

[0065] 170 Suction guide roll

[0066] 172 Second press nip

[0067] 174 Smooth central roll

[0068] 176 third press nip

[0069] 178 dewatering belt

[0070] 180 shoe press roll

[0071] 190 drying screen

[0072] 192 suction pilot roll

[0073] 194 drying cylinder

[0074] 196 suction pilot roll

Claims

1. An apparatus (100) for manufacturing white kraft paperboard, said white kraft paperboard being a multi-layered fiber web (102) having at least one darker backing layer (110) and a lighter-colored top layer (112), said apparatus comprising: • Screen segment (104), said screen segment being used to form the white kraft paperboard, • Press section (106), the press section being used for further dehydration of the white kraft paperboard, and • Drying section (108), the drying section being used to dry the white kraft paperboard. The screen segment (104) includes at least one first forming unit (120) for forming the darker back layer (110) of the white kraft paperboard, at least one second forming unit (130) for forming the lighter top layer (112) of the white kraft paperboard, and a pressing area (140). The first forming unit (120) and the second forming unit (130) are arranged and configured to transfer the darker back layer (110) within the pressing area (140) onto the lighter top layer (112) to form the white kraft paperboard, such that the lighter top layer (112) points downwards when leaving the screen segment (104). The pressing section (106) includes at least three pressing zones (164, 172, 176). The first pressing zone (164) is formed by a shoe-type pressure roller (166) and a suction roller pair (168); the second pressing zone (172) is formed by the suction roller pair (168) and a smooth central roller (174); and the third pressing zone (176) is formed by the smooth central roller (174) and another shoe-type pressure roller (180). The white kraft paperboard is guided through three pressing zones (164, 172, 176), so that the white kraft paperboard comes into contact with the smooth surface of the smooth central roller (174) not only in the second pressing zone (172) but also in the third pressing zone (176) with its lighter-colored cover layer (112). The screens (124) of the first forming unit (120) and the screens (134) of the second forming unit (130) extend parallel to each other for a predetermined distance immediately following the pressing area (140), and within the predetermined distance, at least one dehydration unit (128) is arranged not only on the darker back layer (110) side, but also on the lighter cover layer (112) side.

2. The device according to claim 1, Its features are, A dewatering belt (162) is also arranged on the side of the white kraft paperboard away from the suction roller (168).

3. The device according to claim 1 or 2, Its features are, At least one suction box is arranged as a dehydration unit (128) on the side of the darker back layer (110) within the predetermined distance.

4. The device according to claim 1, Its features are, After the white kraft paperboard is pressed (140), it is turned downward around the turning roller.

5. The device according to claim 1, Its features are, The white kraft paperboard is supported from the darker back layer (110) by means of dewatering belts (160, 178) within the second press zone (172) and / or the third press zone (176).

6. The use of the apparatus (100) according to any one of claims 1 to 5 for manufacturing white kraft paperboard.

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