CONTINUOUS PAPERMAKING MACHINES AND METHODS FOR CONTINUOUS PAPERMAKING

Abstract

A continuous papermaking machine including a headbox for discharging a suspension of cellulose fibers in water, a forming wire moving in a process direction, the forming wire receiving the suspension from the headbox such that a web is formed on the forming wire, a top former above the forming wire for upwardly removing water from the web, the top former comprising a lead out roll, a dewatering device below the forming wire and downstream from the top former, and an applicator positioned above the forming wire and downstream from the lead out roll of the top former, the applicator discharging onto the web a mixture that includes microfibrillated cellulose and a carrier.

Description

FIELD

The present application relates to the fields of continuous papermaking machines and methods for continuous papermaking.

BACKGROUND

In the related art, dewatering devices, such as gravity boxes or vacuum boxes, have been used to downwardly remove water from a pulp suspension in a forming section of a continuous papermaking machine. However, dewatering effectiveness of known dewatering devices is limited. For example, with vacuum boxes particularly, there is a tendency for the vacuum pressures to form pinholes in the pulp suspension.

Accordingly, those skilled in the art continue with research and development in the field of continuous papermaking machines and methods for continuous papermaking.

SUMMARY

Disclosed are continuous papermaking machines.

In one example, the disclosed continuous papermaking machine includes a headbox discharging a suspension of cellulose fibers in water, a forming wire moving in a process direction, the forming wire receiving the suspension from the headbox such that a web is formed on the forming wire, a top former above the forming wire for upwardly removing water from the web, the top former comprising a lead out roll, a dewatering device below the forming wire and downstream from the top former, and an applicator positioned above the forming wire and downstream from the lead out roll of the top former, the applicator discharging onto the web a mixture that includes microfibrillated cellulose and a carrier.

In another example, the disclosed continuous papermaking machine includes a headbox discharging a suspension of cellulose fibers in water, a forming wire moving in a process direction, the forming wire receiving the suspension from the headbox such that a web is formed on the forming wire, a dewatering device positioned below the forming wire, and an applicator positioned upstream from the dewatering device, the applicator discharging onto the web a mixture that includes microfibrillated cellulose and a carrier.

Also disclosed are methods for continuous papermaking.

In one example, the disclosed method for continuous papermaking includes discharging a suspension of cellulose fibers in water onto a moving forming wire to yield a web on forming wire, draining water from the web through the forming wire, upwardly removing water from the web, applying a mixture that includes microfibrillated cellulose and a carrier on top of the web after the step of upwardly removing water from the web, and passing the web having the mixture thereon over one or more dewatering devices to downwardly remove water from the web.

In another example, the disclosed method for continuous papermaking includes discharging a suspension of cellulose fibers in water onto a moving forming wire to yield a web on the forming wire, draining water from the web through the forming wire, passing the web over a dewatering device to downwardly remove water from the web, and, prior to passing the web over the dewatering device, applying on top of the web a mixture that includes microfibrillated cellulose and a carrier.

Other examples of the disclosed continuous papermaking machines and methods for continuous papermaking will become apparent from the following detailed description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a two-dimensional representation of an exemplary continuous papermaking machine according to an aspect of the present description.

FIG. 2 is a two-dimensional representation of a portion of the exemplary continuous papermaking machine of FIG. 1.

FIG. 3 is a two-dimensional representation of a portion of the exemplary continuous papermaking machine of FIG. 2, including an applicator.

FIG. 4 is a two-dimensional representation of the applicator of FIG. 3.

FIG. 5 is a three-dimensional representation of a cross section of the applicator of FIG. 4.

DETAILED DESCRIPTION

FIGS. 1-3 are two-dimensional representations of an exemplary continuous papermaking machine according to an aspect of the present description. FIGS. 4 and 5 are two-dimensional and three-dimensional representations of a non-limiting example of a suitable applicator according to an aspect of the present description.

The exemplary continuous papermaking machine 10 is illustrated and described in detail. However, the invention of the present description is not limited to use with continuous papermaking machine 10 as illustrated and described in the drawings.

Referring to FIGS. 1-3, in one example, the disclosed continuous papermaking machine 10 includes a forming section 100, a pressing section 200, and a drying section 300 arranged along a process direction 11. The exemplary continuous papermaking machine 10 may further include other sections, such as a dryer section, finishing section, and after drying section, in which the finishing section may perform functions such as chemical applications (e.g., starch), coating, calendering, and reeling.

The forming section 100 of the exemplary continuous papermaking machine 10 of the present description includes a headbox 110, which functions to discharge a dilute suspension of separate cellulose fibers suspended in water onto a forming wire 120 through which water is drained from the suspension, leaving behind a web 122 of fibers. The forming wire 120 may be, for example, a fabric. In the forming section 100, water may be drained from the web 122 by way of gravity and/or vacuum.

Referring to FIG. 1, the forming section 100 of the exemplary continuous papermaking machine 10 of the present description includes a top former 130. The top former 130 functions to remove water upwardly from the web 122. The presence of the top former 130 in the forming section 100 may improve efficiency of the water removal process and/or may improve a uniformity of the properties of the resulting web of cellulose fibers being formed. The top former 130 may include, for example, a top wire 132, various rolls, and vacuum devices. As illustrated in FIG. 1, the top former 130 includes at least a lead out roll 131, which is the final roll of the top former 130. Upon exiting from the top former 130, the web 122 may define a top layer in which water content is reduced.

Referring to FIGS. 1-3, the forming section 100 of the exemplary continuous papermaking machine 10 of the present description includes an applicator 140 positioned downstream of the lead out roll 131 of the top former 130.

In the illustrated embodiment, the applicator 140 may apply a curtain C (e.g., a continuous curtain) of a mixture that includes microfibrillated cellulose (MFC) and a carrier, such as water, on top of the web 122 exiting the top former 130. Optionally, the mixture of microfibrillated cellulose and carrier may further include additional additives/components, such as, for example, flow modifying agents and/or agents that improve drainage. The curtain C may flow under the force of gravity (i.e., not pressurized). Other types of discharges from the applicator 140 (e.g., non-curtain discharges) are also contemplated.

In an alternative embodiment, the applicator 140 may be pressurized, and may discharge a jet (e.g., a continuous jet) or a spray (e.g., a continuous spray) of a mixture that includes microfibrillated cellulose and a carrier, such as water, on top of the web 122 exiting the top former 130. Internal fluid pressure can be controlled to adjust jet/spray velocity of the mixture, thereby minimizing film disruption. Optionally, the mixture of microfibrillated cellulose and carrier may further include additional additives/components, such as, for example, flow modifying agents. Therefore, at this point, those skilled in the art will appreciate that the mixture of microfibrillated cellulose, carrier, and optional additives applied to the moving web 122 may be applied in a pressurized or non-pressurized manner.

As previously mentioned, the web 122 exiting the top former 130 may have a top layer in which water content is reduced. This may facilitate retention of the mixture of microfibrillated cellulose, carrier, and optional additives on the web 122. As a result, the mixture of microfibrillated cellulose, carrier, and optional additives may function as a sealing layer, which may improve the effectiveness of the dewatering process, particularly at the dewatering devices 150 downstream of the applicator 140.

The mixture of microfibrillated cellulose, carrier, and optional additives applied by the applicator 140 can be a relatively dilute mixture. In one implementation, the content of microfibrillated cellulose in the dilute mixture may be about 0.01 percent by weight to about 10 percent by weight of microfibrillated cellulose. In another implementation, the content of microfibrillated cellulose in the dilute mixture may be about 0.1 percent by weight to about 5 percent by weight of microfibrillated cellulose. In yet another implementation, the content of microfibrillated cellulose in the dilute mixture may be about 0.5 percent by weight to about 1.5 percent by weight of microfibrillated cellulose.

Referring to FIG. 1, the forming section 100 of the exemplary continuous papermaking machine 10 of the present description includes one or more dewatering devices 150 (e.g., gravity boxes and/or vacuum boxes) positioned downstream of the lead out roll 131 of the top former 130. The one or more dewatering devices 150 are positioned underneath the web 122 to remove water downwardly from the web 122. The one or more dewatering devices 150 include at least one dewatering device 150 positioned downstream of the applicator 140. By positioning at least one dewatering device 150 of the one or more dewatering devices 150 downstream of the applicator 140, the dewatering effectiveness of the dewatering devices may be increased by the mixture of microfibrillated cellulose, carrier, and optional additives, which may form a continuous (or at least substantially continuous) film on the surface of the web 122, which may act as a sealing layer that reduces (if not eliminates) the formation of pinholes during the dewatering process.

It is believed that the application of the mixture of microfibrillated cellulose, carrier, and optional additives to the surface of the web 122 can result in improved surface properties, particularly after web calendering, either with a heated thermo-roll or not. Such improved surface properties include smoothness, porosity, print-ability, and coefficient of friction, among others. It is also believed that the application of the mixture of microfibrillated cellulose, carrier, and optional additives to the surface of the web 122 can also improve further surface finishing, such as water base pigment coating, starch application, and barrier coatings. Surface properties, such as smoothness and barrier (oil and grease; water), are some of the properties improved by such application. Coat weight and surface applications can be reduced to provide similar or improved performance. It is also believed that the application of the mixture of microfibrillated cellulose, carrier, and optional additives to the surface of the web 122 can result in improved strength properties of the paperboard, such as short span compression (SCT), tensile, and minimizing differences between machine-direction and cross-direction properties.

Referring to FIG. 1, the forming section 100 of the exemplary continuous papermaking machine 10 of the present description may include, for example, trim squirts 160. The trim squirts 160 may be positioned at sides of the web 122 to trim the web 122 using, for example, a high velocity water stream to cut side edges of the web 122. The forming section 100 of the exemplary continuous papermaking machine 10 of the present description may further include additional devices, such as steam box 170 and a lump-breaker (not shown).

After the forming section 100, the web passes to the pressing section 200. The pressing section 200 mechanically squeezes water from the web. As shown in FIG. 1, the web is passed into a nip between rolls 201 to remove water that was not be removed in the forming section 100. The water is squeezed from the web in between the rolls 201. Press felts may be positioned in between the nips of the rolls 201.

After the pressing section 200, the web passing into the drying section 300 for water removal by heating. Referring to FIG. 1, the drying section 300 may include, for example, heated rolls 301 for heating of the web.

Thus, the applicator 140 of the present disclosure may function to apply a mixture of microfibrillated cellulose, carrier, and optional additives on top of a moving web 122, particularly at a location that is downstream of the top former 130 and/or upstream of one or more dewatering devices 150.

As best shown in FIGS. 3-5, in one particular realization, the applicator 140 of the present disclosure functions to apply a continuous curtain C of the mixture of microfibrillated cellulose, carrier, and optional additives on top of the moving web 122 exiting the top former 130. The continuous curtain C is shown in FIGS. 3-5 being applied under the force of gravity and forces being generated by a pump (not shown).

Constructional details of an exemplary, non-limiting embodiment of an applicator 140 are referenced in FIGS. 3-5. It should be understood that the constructional details of the applicator may vary within the scope of the present description.

As shown in FIGS. 3-5, the applicator 140 according to the exemplary embodiment may include, for example, a basin defined by one or more basin walls 141 for holding a mixture of microfibrillated cellulose, carrier, and optional additives. The applicator 140 may further include a first flow control barrier 142 and a second flow control barrier 143 for limiting a flow of the mixture of microfibrillated cellulose, carrier, and optional additives from the basin defined by the one or more basin walls 141.

The applicator 140 shown in FIGS. 3-5 may further include a flow-down surface 144 for flowing the mixture of microfibrillated cellulose, carrier, and optional additives from the first and second flow control barriers 142, 143 to a first flow control slope 145, at which the mixture of microfibrillated cellulose, carrier, and optional additives may form a curtain (e.g., a continuous curtain) of the mixture of the microfibrillated cellulose, carrier, and optional additives. The first flow control slope 145 may lead to a second flow control slope 148, at which the mixture of microfibrillated cellulose, carrier, and optional additives forms a curtain of the mixture of the microfibrillated cellulose, carrier, and optional additives prior to applying the curtain of the mixture to a top surface of the web 122. The flow control slopes 145, 148 may have a minimum slope angle of 1 degree, and up to 20 degrees.

The applicator 140 shown in FIGS. 3-5 may further include a separating wall 146 for separating the interior of the continuous applicator 140 from the top former 130.

The applicator 140 may further include a flow direction change surface 147 for reversing a flow of the mixture of microfibrillated cellulose, carrier, and optional additives. The flow direction change surface 147 may include a curved surface leading to the second flow control slope 148 to facilitate maintaining or forming the curtain of the mixture of microfibrillated cellulose, carrier, and optional additives upon descent of the mixture down the second flow control slope 148 to the top surface of the web 122.

As will be understood, the applicator 140 as illustrated in FIG. 4 is merely a two-dimensional representation of a applicator 140 suitable for use as the applicator 140 of the present disclosure. The applicator 140 may include various constructional details for maintaining relative positions of the functional components of the applicator 140. For example, the applicator 140 may include an opening 149 to connect the applicator chambers in the longitudinal direction. While not shown, the applicator 140 may also include a by-pass line, a recirculation system, and/or a mixing system.

FIG. 5 shows a three-dimensional representation of a portion of the applicator 140 shown in FIGS. 3 and 4. Constructional details for maintaining relative positions of the functional components of the applicator 140 are not shown but would be understood by persons skilled in the art.

As shown in FIGS. 3-5, applicator 140 may have an overall shape of a wedge to facilitate applying the curtain C of the mixture of microfibrillated cellulose, carrier, and optional additives directly after leaving the lead out roll 131 of the top former 130.

Further, the disclosure comprises examples according to the following clauses:

Clause 1. A continuous papermaking machine, comprising: a headbox discharging a suspension of cellulose fibers in water; a forming wire moving in a process direction, the forming wire receiving the suspension from the headbox such that a web is formed on the forming wire; a top former above the forming wire for upwardly removing water from the web, the top former comprising a lead out roll; a dewatering device below the forming wire and downstream from the top former; and an applicator positioned above the forming wire and downstream from the lead out roll of the top former, the applicator discharging onto the web a mixture comprising microfibrillated cellulose and a carrier.

Clause 2. The continuous papermaking machine of Clause 1, wherein the applicator is positioned upstream from the dewatering device.

Clause 3. The continuous papermaking machine of Clause 1 or Clause 2, wherein the dewatering device comprises a vacuum box.

Clause 4. The continuous papermaking machine of Clause 1 or Clause 2, wherein the dewatering device comprises a gravity box.

Clause 5. The continuous papermaking machine of any preceding clause, further comprising a pressing section downstream from the dewatering device for mechanically squeezing water from the web.

Clause 6. The continuous papermaking machine of Clause 5, wherein the pressing section comprises a plurality of rolls for squeezing the web.

Clause 7. The continuous papermaking machine of Clause 5 or Clause 6, further comprising a drying section downstream from the pressing section for removing water by heating the web.

Clause 8. The continuous papermaking machine of Clause 7, wherein the drying section comprises a plurality of heated rolls for heating the web.

Clause 9. The continuous papermaking machine of any preceding clause, wherein the applicator comprises a basin defined by one or more basin walls for holding the mixture.

Clause 10. The continuous papermaking machine of Clause 9, wherein the applicator comprises a first flow control barrier for limiting a flow of the mixture.

Clause 11. The continuous papermaking machine of Clause 10, wherein the applicator further comprises a second flow control barrier for limiting a flow of the mixture from the first flow control barrier.

Clause 12. The continuous papermaking machine of Clause 10 or Clause 11, wherein the applicator further comprises a flow-down surface for flowing the mixture from the first flow control barrier.

Clause 13. The continuous papermaking machine of any preceding clause, wherein the applicator comprises a first flow control slope for flowing the mixture.

Clause 14. The continuous papermaking machine of Clause 13, wherein the applicator further comprises a second flow control slope for flowing the mixture from the first flow control slope.

Clause 15. The continuous papermaking machine of Clause 14, wherein the applicator further comprises a flow direction change surface for reversing a flow of the mixture from the first flow control slope to the second flow control slope.

Clause 16. The continuous papermaking machine of any preceding clause, wherein the mixture comprises about 0.01 percent by weight to about 10 percent by weight microfibrillated cellulose.

Clause 17. The continuous papermaking machine of any preceding clause, wherein the mixture further comprises a flow modifying agent.

Clause 18. A continuous papermaking machine, comprising: a headbox discharging a suspension of cellulose fibers in water; a forming wire moving in a process direction, the forming wire receiving the suspension from the headbox such that a web is formed on the forming wire; a dewatering device positioned below the forming wire; and an applicator positioned upstream from the dewatering device, the applicator discharging onto the web a mixture comprising microfibrillated cellulose and a carrier.

Clause 19. The continuous papermaking machine of Clause 18, wherein the dewatering device comprises a vacuum box.

Clause 20. The continuous papermaking machine of Clause 18 or Clause 19, wherein the applicator discharges the mixture under a force of gravity.

Clause 21. The continuous papermaking machine of Clause 18 or Clause 19, wherein the applicator discharges the mixture under pressure.

Clause 22. A method for continuous papermaking, comprising: discharging a suspension of cellulose fibers in water onto a moving forming wire to yield a web on the forming wire; draining water from the web through the forming wire; upwardly removing water from the web; applying a mixture comprising microfibrillated cellulose and a carrier on top of the web after the step of upwardly removing water from the web; and passing the web having the mixture thereon over one or more dewatering devices to downwardly remove water from the web.

Clause 23. The method of Clause 22, further comprising mechanically squeezing water from the web.

Clause 24. The method of Clause 23, further comprising removing water from the web by heating.

Clause 25. The method of any one of Clauses 22-24, wherein the mixture comprises about 0.01 percent by weight to about 10 percent by weight microfibrillated cellulose.

Clause 26. The method of any one of Clauses 22-24, wherein the mixture comprises about 0.1 percent by weight to about 5 percent by weight microfibrillated cellulose.

Clause 27. The method of any one of Clauses 22-24, wherein the mixture comprises about 0.5 percent by weight to about 1.5 percent by weight microfibrillated cellulose.

Clause 28. The method of any one of Clauses 22-27, wherein the carrier comprises water.

Clause 29. A method for continuous papermaking, comprising: discharging a suspension of cellulose fibers in water onto a moving forming wire to yield a web on the forming wire; draining water from the web through the forming wire; passing the web over a dewatering device to downwardly remove water from the web; and prior to passing the web over the dewatering device, applying on top of the web a mixture comprising microfibrillated cellulose and a carrier.

Although various embodiments of the disclosed continuous papermaking machines and methods for continuous papermaking have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.

Claims

1. A continuous papermaking machine, comprising: a headbox discharging a suspension of cellulose fibers in water;a forming wire moving in a process direction, the forming wire receiving the suspension from the headbox such that a web is formed on the forming wire;a top former above the forming wire for upwardly removing water from the web, the top former comprising a lead out roll;a dewatering device below the forming wire and downstream from the top former; andan applicator positioned above the forming wire and downstream from the lead out roll of the top former, the applicator discharging onto the web a mixture comprising microfibrillated cellulose and a carrier.

2. The continuous papermaking machine of claim 1, wherein the applicator is positioned upstream from the dewatering device.

3. The continuous papermaking machine of claim 1, wherein the dewatering device comprises a vacuum box.

4. The continuous papermaking machine of claim 1, wherein the dewatering device comprises a gravity box.

5. The continuous papermaking machine of claim 1, further comprising a pressing section downstream from the dewatering device for mechanically squeezing water from the web.

6. The continuous papermaking machine of claim 5, wherein the pressing section comprises a plurality of rolls for squeezing the web.

7. The continuous papermaking machine of claim 5, further comprising a drying section downstream from the pressing section for removing water by heating the web.

8. The continuous papermaking machine of claim 7, wherein the drying section comprises a plurality of heated rolls for heating the web.

9. The continuous papermaking machine of claim 1, wherein the applicator comprises a basin defined by one or more basin walls for holding the mixture.

10. The continuous papermaking machine of claim 9, wherein the applicator comprises a first flow control barrier for limiting a flow of the mixture.

11. The continuous papermaking machine of claim 10, wherein the applicator further comprises a second flow control barrier for limiting a flow of the mixture from the first flow control barrier.

12. The continuous papermaking machine of claim 10, wherein the applicator further comprises a flow-down surface for flowing the mixture from the first flow control barrier.

13. The continuous papermaking machine of claim 1, wherein the applicator comprises a first flow control slope for flowing the mixture.

14. The continuous papermaking machine of claim 13, wherein the applicator further comprises a second flow control slope for flowing the mixture from the first flow control slope.

15. The continuous papermaking machine of claim 14, wherein the applicator further comprises a flow direction change surface for reversing a flow of the mixture from the first flow control slope to the second flow control slope.

16. The continuous papermaking machine of claim 1, wherein the mixture comprises about 0.01 percent by weight to about 10 percent by weight microfibrillated cellulose.

17. The continuous papermaking machine of claim 1, wherein the mixture further comprises a flow modifying agent.

18. A continuous papermaking machine, comprising: a headbox discharging a suspension of cellulose fibers in water;a forming wire moving in a process direction, the forming wire receiving the suspension from the headbox such that a web is formed on the forming wire;a dewatering device positioned below the forming wire; andan applicator positioned upstream from the dewatering device, the applicator discharging onto the web a mixture comprising microfibrillated cellulose and a carrier.

19. A method for continuous papermaking, comprising: discharging a suspension of cellulose fibers in water onto a moving forming wire to yield a web on the forming wire;draining water from the web through the forming wire;upwardly removing water from the web;applying a mixture comprising microfibrillated cellulose and a carrier on top of the web after the step of upwardly removing water from the web; andpassing the web having the mixture thereon over one or more dewatering devices to downwardly remove water from the web.

20. A method for continuous papermaking, comprising: discharging a suspension of cellulose fibers in water onto a moving forming wire to yield a web on the forming wire;draining water from the web through the forming wire;passing the web over a dewatering device to downwardly remove water from the web; andprior to passing the web over the dewatering device. applying on top of the web a mixture comprising microfibrillated cellulose and a carrier.