FI20215936A1

FI20215936A1 - Process of producing a fiber web

Info

Publication number: FI20215936A1
Application number: FI20215936A
Authority: FI
Inventors: Henri Vaittinen; Tapio Pitkäniemi
Original assignee: Valmet Technologies Oy
Priority date: 2021-09-06
Filing date: 2021-09-06
Publication date: 2022-06-20

Abstract

The invention relates to a process of producing a fiber web, which process comprises a sizing stage and a drying stage, in which process the fiber web is sized with a sizing agent in the sizing stage by a sizing system comprising a sizing nip (N) and in which process the fiber web (W) is dried in a drying stage by drying equipment after the sizing stage. Nip pressure in the sizing nip (N) is at least 10 MPa. The process in configured to increase the SCT CD index of the fiber web (W) at least + 5 Nm/g.

Description

Process of producing a fiber web Technical field In general, present invention relates to producing of fiber webs in a fiber web production line. More especially the present invention relates to a process according to preamble part of the independent process claim.

In this description and the following claims by fiber webs are meant for example a paper and board webs. Background The fiber webs are produced in a fiber web producing process. As known from the prior art in fiber web producing processes typically comprise an assembly formed by a number of apparatus arranged consecutively in the process line. A typical production and treatment line comprises a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and/or sections for finishing the fiber web, for example, a pre-calender, a sizer, a final-calender, a coating section. The production and treatment line also typically comprise at least one slitter- winder for forming customer rolls as well as a roll packaging apparatus.

In production of fiber webs, for example in production of paper or board webs, N sizing is used to alter the properties of a fiber web by adding sizing agents, for N example starch. Sizing can be divided to internal sizing and surface sizing. In 2 internal sizing the sizing agent is added to pulp in the wet end of the fiber web © 30 machine before forming. In surface sizing the sizing agent is added onto the I surface of the fiber web typically at the dry end of the fiber web machine, typically = passing the fiber web through a sizing nip formed between two sizing rolls. & Surface sizing is used in production of many fiber web grades, for example in = production of uncoated fine papers and of several board grades. Sizing is used in S 35 order to improve paper web properties, in particular water resistance, water absorption properties, strength, internal strength, surface strength and bending stiffness, as well as to improve adherence of a coating substance to the surface of the fiber web. In addition, runnability as well as dusting tendency can be affected favorably. Different technologies are used to apply sizing agents onto the surface of the fiber web, for example curtain sizing and spray sizing. In curtain application of sizing agents typically two main types of application devices are used, namely application devices with slot-fed and application devices with slide-fed. In the slide fed application devices, sizing agent is fed by means of a nozzle assembly onto an inclined plane and the sizing agent flows down towards an edge of the plane constituting a nozzle lip and the curtain is formed as the sizing agent falls off the nozzle lip onto the web. In the slot-fed application devices sizing agent is pumped through a distribution chamber into a narrow vertical slot and the curtain is formed at its lip and falls onto the web. Sizing agent can be applied in one or more layers on one or both surface/-s of the fiber web. The sizing can be direct sizing, in which the sizing agent directly falls onto the surface of the fiber web before the sizing nip, or indirect sizing in which the sizing agent first falls onto a surface of a roll or like moving surface, via which the sizing agent is transferred onto the surface of the fiber web in the sizing nip. It is known from prior art to enhance sizing by increasing pressure in the sizing nip by using hard sizing rolls to form the sizing nip. Typically, as the hard roll is used a roll produced of hard material or provided with a hard coating or cover, for example as the hard roll is used a ceramic or metallic roll or advantageously, a roll with a hard-polymeric roll cover — (rubber, polyurethane or composite) having surface hardness 60 — 100 shoreD. Summary A particular object of the invention is to create a process for sizing the fiber web to improve quality of the sizing result of sizing. N A particular object is to create a process of producing a fiber web, in which N disadvantages and problems of processes known from prior art are eliminated or 2 at least minimized. © 30 I To achieve the objects mentioned above and later the process according to the = invention is mainly characterized by the features of the characterizing part of the & independent process claim.

LO S 35 Advantageous features and embodiments of the invention are defined in the dependent claims. According to the invention the process of producing a fiber web comprises a sizing stage and a drying stage, in which process the fiber web is sized with a sizing agent in the sizing stage by a sizing system comprising a sizing nip and in which process the fiber web is dried in a drying stage by drying equipment after the sizing stage, wherein nip pressure in the sizing nip is at least 10 MPa, and the process in configured to increase the SCT CD index of the fiber web at least + 5 Nm/g. According to an advantageous feature the sizing system of the sizing stage comprises sizing rolls and one or both of the sizing rolls is/are a metal roll/-s having hardness of at least 300 HV and/or one or both of the sizing rolls is/are a — roll/-s having a composite cover with reinforcements and hardness of at least 80 Shore D. According to an advantageous feature the sizing system of the sizing stage comprises sizing rolls and at least one of the sizing rolls is a deflection compensated roll configured to adjust linear nip load in cross-direction of the fiber web in the sizing stage. According to an advantageous feature linear load in the sizing nip is at least 200 kN/m.

According to an advantageous feature linear nip load in the sizing nip is at least 250 kN/m, advantageously at least 300 kN/m. According to an advantageous feature the application device/-s is/are spray sizing — or curtain sizing or pond sizing or blade sizing or soft rod sizing or soft surface element sizing application device/-s.

N N According to an advantageous feature in the drying stage the drying is configured 2 to be conducted by drying eguipment comprise cylinder drying eguipment and/or © 30 air impingement drying equipment and/or infrared drying equipment. = = According to an advantageous feature the sizing agent is starch. 3 = According to an advantageous feature the process is configured to increase the S 35 SCT CD index of the fiber web + 6 Nm/g, advantageously + 7 Nm/g. According to an advantageous feature the process is configured to increase the density of the fiber web + 30 kg/m”3, advantageously + 40 kg/mf3, more advantageously +50 kg/m”3.

According to an advantageous feature the nip pressure in the sizing nip is 20 MPa - 60 MPa.

In the process according to the invention the density of the fiber web increases and it smoothens as the effect of the hard nip corresponds in this respect the effect of calendering. In the process the high pressure of the sizing nip more sizing agent is provided in fiber junction points as in the fiber web the fiber distance is relatively small and the porous volume is small, the large pressure increases the liquid diffusion. According to an advantageous aspect in the process the sizing nip is formed between two hard sizing rolls. Advantageously, one or both of the sizing rolls is/are a metal roll/-s having hardness of at least 300 HV and/or one or both of the sizing rolls is/are a roll/-s having a composite cover with reinforcements and hardness of at least 80 Shore D, advantageously at least 90 Shore D. Advantageously the composite cover is epoxy reinforced with glass fiber and/or carbon fiber and/or aramid fiber. One or both of the sizing rolls may also be a ceramic roll/-s having a hardness of at least 300 HV. Also as one or both sizing rolls a roll/-s with a hard- polymeric roll cover (rubber, or polyurethane) having of at least 80 Shore D, advantageously at least 90 Shore D, can be used. According to an advantageous aspect at least one of the sizing rolls is deflection compensated rolls by which the pressure in the sizing nip can be adjusted in N cross-direction of the fiber web. Advantageously, the deflection compensated roll N is of the type marketed by the applicant under tradenames SymZ or SymCD 2 and/or of the type disclosed in FI patent applications 875443 and/or 941107. © 30 I According to an advantageous aspect the linear load in the sizing nip is at least = 200 kN/m, advantageously at least 250 kN/m, more advantageously at least 300 > KN/m.

D O 35 According to an advantageous aspect the sizing technology used for applying the sizing agent is spray sizing or curtain sizing or pond sizing or blade sizing or soft rod sizing or soft surface element sizing.

According to an advantageous aspect after the sizing the fiber web is dried by cylinder drying and/or air impingement drying and/or infrared drying.

According to an advantageous aspect the amount of the sizing agent is in the 5 range of 4-40 g/m”2. Advantageously, the sizing agent is starch. Instead of starch also other chemicals can be applied, for example carboxy methyl cellulose (CMC), polyvinyl alcohol (PVOH), polyvinyl acetate (PVA), lignin based chemicals or other synthetic or bio-based polymer latexes, with mineral pigments (for example just GCC, kaolin, titanium oxide, talc) and/or fillers, micro-fibrillated cellulose (MFC), — nano-fibrillated cellulose (NFC), or mixtures of those. The sizing substance may comprise other chemicals as well and it can be a mixture of the above.

According to an advantageous aspect the SCT (short-span compression test (SCT) indicating the compressive strength of paper, ISO 9895 EN 54518 or TAPPIT 826) index in CD-direction, SCT CD index, of the fiber web is improved in the process at least + 5 Nm/g, advantageously + 6 Nm/g, more advantageously + 7 Nm/g. Typically the SCT CD index of the base fiber web before sizing is in the range of 10-45 Nm/g, typically in the range of 10-30Nm/g.

According to an advantageous aspect the density of the fiber web is increased in the sizing and the drying + 30 kg/m”3, advantageously + 40 kg/Mm/3, more advantageously +50 kg/m”3. (Standard SFS-EN ISO 534 ”Paper and Board. Determination of Thickness, Density and Specific Volume”) According to an advantageous aspect the Burst index increase of the fiber web after the sixing and the drying is at least 50%. (Standard ISO 2758)

N N According to an advantageous aspect of the invention in the process of producing 2 the fiber web, in the sizing stage the fiber web is sized with a sizing agent on one © 30 or both sides in a sizing system comprising two sizing rolls, between of which a I sizing nip is formed, and at least one application device, by which the sizing agent = is applied directly onto the fiber web before its passing through the sizing nip or & indirectly via surface/-s of the sizing rolls onto the fiber web passing through the = sizing nip, and in which process the fiber web is dried by drying equipment after S 35 application of the sizing agent in the drying stage,

By the invention and its advantageous aspects and features many advantages are achieved, especially the strength of the fiber web is improved, savings in raw materials for example in pulp stock and in sizing agent are achieved and also production costs are decreased due to savings in raw materials, as well as due to energy savings in drying. The exemplifying embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" and its derivatives are used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features described hereinafter are mutually freely combinable unless explicitly stated otherwise. Brief description of the drawings In the following the invention is further explained in detail with reference to the accompanying drawing in which: In figure 1 is schematically shown an advantageous example of the process according to the invention, in which as application technology spray sizing is used. In figure 2 is schematically shown an advantageous example of the process according to the invention, in which as application technology curtain sizing is used.

In figure 3 is schematically shown test results of a test example. N Detailed description & 2 In the following description same reference signs designate for respective © 30 components etc. unless otherwise mentioned and it should be understood that the I examples are susceptible of modification in order to adapt to different usages and - conditions. 3 = In the example of figure 1 is schematically shown an example of a sizing system S 35 10 for the process comprising a sizing stage and a drying stage (not shown), in which as application technology spray sizing is used. In this advantageous example the fiber web W is running in direction S slightly inclined but substantially downwards and is sized in a spray sizer 10 comprising a sizing nip N formed between two sizing rolls 11, 12. Advantageously, one or both of the sizing rolls is/are a metal roll/-s having hardness of at least 300 HV and/or one or both of the sizing rolls is/are a roll/-s having a composite cover with reinforcements and hardness of at least 80 Shore D, advantageously at least 90 Shore D.

Advantageously the composite cover is epoxy reinforced with glass fiber and/or carbon fiber and/or aramid fiber. The amount of the sizing agent is in the range of 4-40 g/m”2. Advantageously at least one of the sizing rolls is a deflection compensated roll, by which linear nip load NP in the sizing nip N can be adjusted in cross-direction of the fiber web. Advantageously, the deflection compensated roll is of the type marketed by the applicant under tradenames SymZ or SymCD and/or of the type disclosed in FI patent applications 875443 and/or 941107. Thus, between the hard sizing rolls a hard sizing nip N is formed. The linear load NP in the sizing nip N is at least 200 kN/m, advantageously at least 250 kN/m, more advantageously at least 300 kN/m and high nip pressure in the sizing nip N is — provided, advantageously at least 10 MPa, more advantageously 20 MPa - 60 MPa. An application device 14S, 15S is located in connection for each sizing roll 11, 12 for applying sizing agent T onto the surface of the sizing roll 11,12 and the fiber web W is sized by indirect sizing as the sizing agent T is transferred on the surface of the rotating sizing roll 11, 12 to the sizing nip N and there onto the therethrough passing fiber web W. The rotation direction of the sizing rolls 11, 12 are indicated by arrows R11, R12. The application device in this example is a spray sizing application device 14S, 15S. The sizing agent T is then via the surface of the sizing roll 11, 12 guided onto the surfaces of the fiber web W such that in the sizing nip N the sizing agent is pressed to the fiber web surfaces.

Advantageously, the sizing agent is starch. Instead of starch also other chemicals can be applied, for example carboxy methyl cellulose (CMC), polyvinyl alcohol N (PVOH), polyvinyl acetate (PVA), lignin based chemicals or other synthetic or bio- N based polymer latexes, with mineral pigments (for example just GCC, kaolin, 2 titanium oxide, talc) and/or fillers, micro-fibrillated cellulose (MFC), nano-fibrillated © 30 cellulose (NFC), or mixtures of those. The sizing agent may comprise other I chemicals as well and it can be a mixture of the above. After the sizing the fiber = web is dried by cylinder drying and/or air impingement drying and/or infrared E drying.

O 35 — In figure 2 is shown an example of a sizing system 10 for the process comprising a sizing stage and a drying stage (not shown), in which as application technology curtain sizing is used. In this advantageous example the fiber web W is running in direction S slightly inclined but substantially upwards and is sized in a curtain sizer

10 comprising a sizing nip N formed between two sizing rolls 11, 12. Advantageously, one or both of the sizing rolls is/are a metal roll/-s having hardness of at least 300 HV and/or one or both of the sizing rolls is/are a roll/-s having a composite cover with reinforcements and hardness of at least 80 Shore D, advantageously at least 90 Shore D.

Advantageously the composite cover is epoxy reinforced with glass fiber and/or carbon fiber and/or aramid fiber.

The amount of the sizing agent is in the range of 4-40 g/mf2. According to an advantageous aspect in the process the sizing nip N is formed between two hard sizing rolls.

Advantageously, one or both of the sizing rolls is/are a metal roll/-s having hardness of at least 300 HV and/or one or both of the sizing rolls is/are a roll/-s having a composite cover with reinforcements and hardness of at least 80 Shore D, advantageously at least 90 Shore D.

Advantageously at least one of the sizing rolls is a deflection compensated roll, by — which linear nip load NP in the sizing nip N can be adjusted in cross-direction of the fiber web.

Advantageously, the deflection compensated roll is of the type marketed by the applicant under tradenames SymZ or SymCD and/or of the type disclosed in FI patent applications 875443 and/or 941107. Thus, between the hard sizing rolls a hard sizing nip N is formed.

The linear nip load NP in the sizing nip N is at least 200 kN/m, advantageously at least 250 kN/m, more advantageously at least 300 kN/m and high nip pressure in the sizing nip N is provided, advantageously at least 10 MPa, more advantageously 20 MPa - 60 MPa.

An application device 14C, 15C is located in connection for each sizing roll 11, 12 for applying sizing agent T onto the surface of the sizing roll 11,12 and the fiber web Wis sized by indirect sizing as the sizing agent T is transferred on the surface of the rotating sizing roll 11, 12 to the sizing nip N and there onto the therethrough N passing fiber web W.

The rotation direction of the sizing rolls 11, 12 are indicated N by arrows R11, R12. The application device in this example is a curtain sizing 2 application device 14C, 15C.

The sizing agent T is then via the surface of the © 30 sizing roll 11, 12 guided onto the surfaces of the fiber web W such that in the I sizing nip N the sizing agent is pressed to the fiber web surfaces.

Advantageously, = the sizing agent is starch.

Instead of starch also other chemicals can be applied, & for example carboxy methyl cellulose (CMC), polyvinyl alcohol (PVOH), polyvinyl = acetate (PVA), lignin based chemicals or other synthetic or bio-based polymer S 35 latexes, with mineral pigments (for example just GCC, kaolin, titanium oxide, talc) and/or fillers, micro-fibrillated cellulose (MFC), nano-fibrillated cellulose (NFC), or mixtures of those.

The sizing agent may comprise other chemicals as well and it can be a mixture of the above. After the sizing the fiber web is dried by cylinder drying and/or air impingement drying and/or infrared drying. The SCT CD index of the fiber web W is improved in the process at least + 5 Nm/g, advantageously + 6 Nm/g, more advantageously + 7 Nm/g. Typically the SCT CD index of the base fiber web before sizing is in the range of 10-45 Nm/g, typically in the range of 10-30 Nm/g. The density of the fiber web is increased in the sizing and the drying + 30 kg/m”3, advantageously + 40 kg/m”3, more advantageously +50 kg/m”3.

Test example The test was conducted in a pilot sizer, by using spray sizing application and a hard sizing nip. The diameters of the sizing rolls were 1400 mm and 1400 mm. One of the sizing rolls used was a fusion welded steel based roll cover, with hardness of 450 HV10 and another of the sizing rolls used was a roll with composite roll cover, with hardness of 90 ShD. The sizing agent used was wheat starch having solids content of 15% and viscosity of about 43 mPas. In the test applied starch amount was about 7 g/m”2. In the figure 3 shown reference value was of an example with film sizing with rubber cover sizing rolls having hardness of 20 P&J and diameters of 1425 mm and 1425 mm. In the test fiber web grade of testliner 120 g/m/2 was used. After the sizing the fiber web W was dried. As can be seen from figure 3 in film sizing reference with nip load of 21 kN/m, the SCT CD index increase was 37%. In hard nip sizing with nip load of 100 kN/m, the SCT CD index increase was 43%. In hard nip sizing with nip load of 200 kN/m, the SCT CD index increase was 53%. In hard nip sizing with nip load of 300 kN/m, N the SCT CD index increase was 56%. The burst index (Standard ISO 2758) N increase in film sizing reference with nip load of 21 kN/m was 46%. The burst 2 index increase in hard nip sizing with nip load of 100 kN/m was 53%. The burst © 30 index increase in hard nip sizing with nip load of 200 kN/m was 54%. The burst I index increase in hard nip sizing with nip load of 300 kN/m was 54%. In the test as = the fiber web grade the testliner 120 g/m/2 was used and it should be noted that in & light fiber web grades, as the testliner 120 g/m”2, the burst index increases to a certain value due to saturation.

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In the description in the foregoing, although some functions and elements have been described with reference to certain features, those functions and elements may be performable by other features whether described or not. Although features have been described with reference to certain embodiments or examples, those features may also be present in other embodiments or examples whether described or not. Above the invention has been described by referring to some advantageous examples only, to which the invention is not to be narrowly limited. Many — modifications and alterations are possible within the inventive idea.

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Claims

1. Process of producing a fiber web, which process comprises a sizing stage and a drying stage, in which process the fiber web is sized with a sizing agent in the sizing stage by a sizing system comprising a sizing nip (N) and in which process the fiber web (W) is dried in a drying stage by drying equipment after the sizing stage, characterized in that nip pressure in the sizing nip (N) is at least 10 MPa, and that the process in configured to increase the SCT CD index of the fiber web (W) at least + 5 Nm/g.

2. Process according to claim 1, characterized in that the sizing system of the sizing stage comprises sizing rolls (11, 12) and one or both of the sizing rolls is/are a metal roll/-s having hardness of at least 300 HV and/or one or both of the sizing rolls is/are a roll/-s having a composite cover with reinforcements and hardness of at least 80 Shore D.

3. Process according to claim 1 or 2, characterized in that the sizing system of the sizing stage comprises sizing rolls (11, 12) and at least one of the sizing rolls is a deflection compensated roll configured to adjust linear nip load (NP) in cross-direction of the fiber web in the sizing stage.

4. Process according to any of the previous claims, characterized in that linear load (NP) in the sizing nip (N) is at least 200 kN/m.

5. Process according to any of the previous claims, characterized in that linear nip load (NP) in the sizing nip (N) is at least 250 kN/m, N advantageously at least 300 kN/m.

O 3 25 6. Process according to any of the previous claims, characterized in that the © application device/-s (14S, 15S; 14C, 15C) is/are spray sizing or curtain 7 sizing or pond sizing or blade sizing or soft rod sizing or soft surface = element sizing application device/-s.

E 7. Process according to any of the previous claims, characterized in that in N 30 the drying stage the drying is configured to be conducted by drying N eguipment comprise cylinder drying eguipment and/or air impingement drying equipment and/or infrared drying equipment.

8. Process according to any of the previous claims, characterized in that the sizing agent is starch.

9. Process according to any of the previous claims, characterized in that the process is configured to increase the SCT CD index of the fiber web (W) + 6 Nm/g, advantageously + 7 Nm/g.

10.Process according to any of the previous claims, characterized in that the process is configured to increase the density of the fiber web (W) + 30 kg/m”3, advantageously + 40 kg/m”3, more advantageously +50 kg/m”3.

11. Process according to any of the previous claims, characterized in that the nip pressure in the sizing nip (N) is 20 MPa - 60 MPa.

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