KR20070067120A - Method and appratus for reducing the amount of rewet in a press section of an papermaking machine - Google Patents

Abstract

A method and apparatus for reducing the amount of rewet of in a press section of an industrial press including a press fabric for carrying a sheet, a press for applying pressure to the press fabric and for forcing water out of the sheet and into the press fabric, and means for applying a reusable displacing agent at least one side of press fabric, the displacing agent absorbing interfacial water upon exiting the press and preventing rewet of the sheet.

Description

METHOD AND APPRATUS FOR REDUCING THE AMOUNT OF REWET IN A PRESS SECTION OF AN PAPERMAKING MACHINE}

The present invention relates to paper machines, and more particularly to reusable and recoverable sacrificial substituents for use in press fabrics in press portions of paper machines.

During the papermaking process, a fibrous web is formed by depositing an aqueous dispersion of fibrous slurry, ie, cellulose fibers, on a moving forming fabric in the forming section of the paper machine. . In this process a large amount of water is discharged from the slurry through the forming fabric, leaving behind a cellulose fiber web on the surface of the forming fabric.

The newly formed cellulose fiber web proceeds from the forming section to the press section comprising a series of press nips. The cellulosic fibrous web passes through a press nip supported by one press fabric or, as is often the case, between two press fabrics. In the press nip, the cellulose fiber web is subjected to a compressive force, which squeezes water from the web and adheres the fibers in the web to each other to convert the cellulose fiber web into a paper sheet. This water is received by the press fabric and ideally does not return to paper.

The paper sheet finally goes to the drying section, which comprises at least one series of rotatable drying drums or cylinders which are internally heated by steam. The newly formed paper proceeds along a winding path continuously around the series of drums by a dry fabric which adheres the paper against the surface of the drum. The heated drum reduces the moisture content of the paper to the desired level through evaporation.

It should be appreciated that forming fabrics, press fabrics and dryer fabrics all take the form of endless loops in the paper machine and function like a conveyor. It should also be appreciated that the papermaking process is a continuous process that proceeds at a significant speed. That is, even while the newly produced paper is continuously wound onto a roll after exiting the drying section, the fiber slurry is continuously deposited onto the forming fabric in the forming section.

The present invention relates in particular to press fabrics used in the press section. Press fabrics play a crucial role in the papermaking process. One of the functions of the press fabric is to support and transport the paper product produced through the press nip as implied above.

Press fabrics also participate in the finishing of paper surfaces. That is, the press fabric is designed to have a smooth surface and a uniform resilient structure so that a smooth, unmarked surface is imparted to the paper during passage through the press nip.

Perhaps most important is that the press fabric contains a large amount of water extracted from the wet paper in the press nip. In order to satisfy this function, the press fabric must have a space, commonly referred to as void volume, to allow water to pass through the press fabric, and must have adequate permeability to water for the entire useful life. Finally, the press fabric should be able to prevent the water received from the wet paper from rewetting the paper as it returns to the paper and exits the press nip.

Current press fabrics are made in a variety of styles to meet the requirements of the paper machine on which they are mounted, depending on the grade of paper being manufactured. Generally, press fabrics include woven base fabrics in which a batt of delicate nonwoven fibrous material is needled therein. The base fabric may be woven from monofilament yarns, plied monofilament yarns, multifilament yarns, or fused multifilament yarns, and may be single or multi-layered or laminated. The yarns are typically made by extruding any synthetic polymeric resin used for this purpose by those skilled in the art of papermaking fabrics, such as polyamides, polyester resins.

The woven base fabrics take many different forms. For example, they may be woven into an endless phase or flat woven and then circulated by a woven seam. Alternatively, they can be produced by a process commonly referred to as modified endless weaving, wherein the widthwise edge portions of the base fabric are seaming loops using their own MD yarns. ). In this process, the MD yarns are woven successively back and forth between the widthwise edges of the fabric, back at each edge to form one seaming loop. Press fabrics produced in this way become circulatory when mounted on a paper machine, and for this reason are referred to as on-machine-seamable fabrics. In order to circulate this fabric, after joining the two widthwise edge portions together, the seaming loops of the two edge portions are interdigitated with each other, and then the seaming pins are passed through the passages created by the interposed seaming loops. Insert a seaming pin or seaming pintle.

In addition, the press fabric can be made of multiple layers. For example, the fabric may comprise a woven base and an interlayer made of thin plates together.

The present invention is directed primarily to the improvement of dewatering characteristics of press fabrics through sacrificial and reusable water substituents applied to the surface of the press fabrics.

The present invention relates to a method for reducing the rewet amount in the press section of the paper machine. The method includes providing a press fabric, depositing a fibrous paper web comprising water on the press fabric for making the sheet, and depositing a substituent on one side of the press fabric. After pressurizing the combination of the press fabric, the fibrous paper web and the substituent, the substituent absorbs water between the interfaces as it exits the press nip to prevent or at least minimize rewetting of the sheet.

Another aspect of the invention relates to an apparatus for reducing the rewetting amount of a paper web in a press nip. The apparatus includes at least one press fabric carrying a sheet and a press to pressurize the press fabric to pressurize water drawn out of the paper sheet into the press fabric. The apparatus also includes means for applying a reusable substituent to at least one side of the press fabric and restoring the substituent for reuse.

Hereinafter, the present invention will be described in more detail with reference to the drawings described below.

The following detailed description is given by way of example and should not be intended to limit the invention to the present invention, but best understood by the accompanying drawings, in which like reference numerals refer to like elements and parts. .

1 is a view from the side of the press of the paper machine according to an embodiment of the present invention, and

2 is a side view of the press portion of the paper machine according to another embodiment of the present invention.

Preferred embodiments of the present invention will be described with respect to paper press fabrics. However, it should be noted that the present invention may find other applications with the fabrics used in other sections of the paper machine as well as those used in other industrial environments.

Some examples of other fabric types to which the present invention is applicable include paper machined fabrics, dry fabrics, through-air-drying fabrics, and pulp molded fabrics.

One aspect of the present invention relates to the use of particulate dispersion disposed in a sheet / press fabric interface that is active in a paper machine's press nip to successfully participate in a paper sheet and absorb water between interfaces between the sheet and the press fabric. . Typically, the water between the interfaces in the press process migrates to the press fabric and sheet from the nip. However, the movement of water to the sheet results in "rewet", which is very undesirable for paper machines.

The mechanism believed to be responsible for this undesirable rewet is the pore size of the sheet compared to the press fabric when it comes out of the nip and expands. The paper sheet usually has a smaller size distribution than the press fabric. It is known that the pore size of the paper sheet is 10 times smaller than the pore size of the press fabric contained in the fine surface batt. The average pore diameter of a sheet of paper is about 0.1 to 1 micron, compared to a 10-20 micron press fabric. Due to the very fine pores, optionally more water is forced back into the paper web structure.

Previously, efforts have been made to produce press fabric surfactants that have a tighter pore size than paper sheets. Part of this effort has been the use of membranes incorporated into press fabrics to facilitate moisture removal. However, these previous attempts generally failed. This is because these membranes have poor durability when compared to typical press fabrics that contact paper with a surface formed of fine bat fibers.

One aspect of the invention removes the durability limitations of conventional membranes by eliminating the need for competitive pore sized materials to adhere to the press fabric for long. Instead, the present invention is used to reduce the cost of reducing the amount of rewetting of paper, and relates to the application, recovery and reformulation of substituents that aid in dehydration in the press nip. Another aspect of the invention relates to a process for collecting particulates that recovers from any of the sheet surface, press fabric surface and “water spray” from the nip to competitive particulates of water.

1 illustrates an embodiment of a press process using a substituent. The substituent 10 may be applied to the surface of the press fabric 12 or to the bottom surface of the paper web or sheet as a barrier against rewetting, and to the recovery means 14 after the action of the press section 16. By recovery immediately after several presses or drying steps and then reclaimed for reuse if the particles themselves are temporarily attached to the paper web. Determining when the substituents will be recovered depends on the nature of the substituents as well as the placement of each press. The application of the substituents can be performed on any press.

This concept is similar to what the catalyst does in chemical reactions. In essence the substituents are not consumed and probably need to be regenerated or reformed, for example, in the reformer 18. The substituents may be used as showrs of full width when dispersed into a fluid. In addition, the substituents may be solid and may be used from a spool in the form of a film. The substituents may also be applied using existing coating applications in a roll, for example when applied as a coating or sizing agent to a paper web.

The two main requirements for the substituents are that the substituents should be better than paper webs competing or dehydrating with the water in the boundary layer, not inherently attached to the dewatering paper webs, and then collection and reformation should occur. .

Another aspect of the invention is that, as shown in Figure 2, the substituent is recovered from the surface of the paper sheet by contacting with another PMC fabric or belt specifically designed to attract the substituents. In this regard the substituents can be applied in particulate form on the underside of the press fabric and carried to the nip by the press fabric in contact with the paper sheet of the nip.

A large proportion of substituents may be temporarily attached to the surface of the paper sheet from the nip. But this can be easily removed. In FIG. 2, a second paper machine belt or fabric 20 can be used to pull and remove the substituent from the paper sheet 22.

The belt 20 may have, for example, a smooth surface than the paper sheet or a surface utilizing the features of a substituent that can be separated from the paper sheet 22 without adversely affecting the paper sheet 22.

Experimental Example

Tests conducted to illustrate the effect of the substituents can be made as described above when compared to press fabrics alone or to press fabrics with a membrane bonded thereto. Moreover, the experiments showed that the substituents could be effectively reused and recycled. In the end, the experiment showed that there were significant advantages of the use of a substituent and surface membrane. Such experiments were performed on a device known as a press nip simulator ("SPNS"), which was able to test pressure, residence time and pressure pulses present in commercially available press nips. This experimental result is shown in FIG. Reference numeral “SRDA” of FIG. 3 is a case where a sacrificial recoverable displacing agent is used.

As can be seen with reference to FIG. 3, the press fabric only had a final drying of only 34.6% while the final drying increased to 45% or more when the press fabric was used with a substituent. This exceeds the drying rate of 44.6% achieved by the press fabric and the surface membrane. It can be seen that the drying capacity of the substituents was not significantly reduced when the substituents were reused and recycled. The final drying of recycled particles, which was less than in the first pass but favorably compared to press fabrics and surface membranes, was 44.7%. Finally, experiments have shown that the use of a combination of a substituent and a surface membrane can achieve a much better effect. The results show a further increased 46.1% final drying when used in combination.

Thus, the present experiments can achieve improved drying characteristics comparable to or exceeding those achieved by the use of surface membranes as previously known using the substituents described herein. Moreover, when such substituents are reused, they have the ability to achieve satisfactory final drying.

Such modifications will be apparent to those skilled in the art, but the invention should not be altered beyond the scope of the appended claims.

Claims (12)

Providing a press fabric; Depositing a paper sheet comprising water on the press fabric; Depositing a substituent onto at least one side of the press fabric; And Pressurizing the combination of press fabric, paper sheet, and substituent in a press nip; And a rewetting amount reduction method in the press part of the paper machine which absorbs water between the interfaces when the substituent exits the press nip to prevent rewetting of the sheet. The method according to claim 1, Recapturing method of reducing the rewet in the press section of the paper machine, characterized in that it further comprises the step of recapturing the substituent for reuse. The method according to claim 1, Re-wetting amount reduction method in the press section of the paper machine further comprising the step of reconstituting the substituent for reuse. The method according to claim 1, Re-wetting amount reduction method in the press portion of the paper machine further comprising the step of removing the substituent by the fabric (removing). The method according to claim 1, The method of reducing wettability in the press portion of the paper machine, characterized in that the substituent is applied between the press fabric and the paper sheet. The method according to claim 1, And the substitution agent reduces the rewet amount in the press section of the paper machine, characterized in that it reduces the amount of sheet rewetting that impedes the flow of water from the next paper sheet to the press fabric. At least one press fabric carrying the sheet; Press to pressurize the press fabric to pressurize water drawn from the paper sheet into the press fabric; Means for applying a reusable substituent to the press fabric; Re-wetting amount reduction device in the press portion of the paper machine comprising a. The method according to claim 7, Re-wetting amount reduction device in the press section of the paper machine further comprising means for bringing back the substituent. The method according to claim 7, Re-wetting amount reduction device in the press section of the paper machine comprising a means for restoring the substituent. The method according to claim 7, Re-wetting amount reduction device in the press portion of the paper machine, characterized in that the substituent is removed by the fabric. The method according to claim 7, And said substituent is applied between the press fabric and the paper sheet. The method according to claim 7, And said substituent reduces sheet rewet amount that impedes the flow of water from the next paper sheet to the press fabric.

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