JP2008518112A - Sacrificial and recoverable displacer that improves paper dewaterability - Google Patents

Abstract

  A method and apparatus for reducing the amount of rewet in a press part of an industrial press, a press cloth that conveys a sheet, and a press that applies pressure to the press cloth to escape water from the sheet to the press cloth. And means for applying a reusable displacement agent to at least one side of the press fabric, the displacement agent absorbs interfacial water that has escaped the press fabric and prevents rewetting of the sheet.

Description

  The present invention relates to a papermaking technique. In particular, the invention relates to a reusable and recoverable sacrificial substitute for use in press fabrics in the press section of a paper machine.

  During the papermaking process, a fiber web made of cellulose is formed by depositing a fiber slurry, ie an aqueous suspension of cellulose fibers, on a forming fabric that moves in a forming section of a paper machine. A large amount of water is discharged from this slurry through the forming cloth, and a cellulose fiber web remains on the surface of the forming cloth.

  The newly formed cellulose fiber web proceeds from the forming section to a pressing section having a series of press nips. This cellulosic fibrous web passes through a press fabric or belt, or often a press nip supported by two such press fabrics. In the press nip, a compressive force is applied to the cellulose fiber web by squeezing water and adhering the cellulose fibers of the web together to form a paper sheet from the cellulose fiber web. This water is received by the press fabric or various fabrics and ideally does not return to the paper sheet.

  The paper sheet eventually proceeds to a drying section having at least a series of rotatable drying drums or cylinders that are heated internally with steam. The newly formed paper sheet is directed with a dry cloth to a serpentine path arranged continuously around each of the series of drums, where the paper sheet is placed close to the surface of the drum. Hold. The heated drum reduces the moisture content of the paper sheet to the desired level by evaporation.

  As should be understood, the forming cloth, press cloth and drying cloth all take the form of endless loops on the paper machine and have the function of a conveyor. It should also be understood that papermaking is a continuous process that proceeds at a significant rate. That is, the fiber slurry is continuously deposited on the forming fabric of the forming section, while the newly manufactured paper sheet is continuously wound on the roll after escaping from the drying section.

  The present invention particularly relates to a press cloth used in a press section. Press fabrics play an important role during the papermaking process. One of its functions is to support and transport the paper sheet produced through the press nip as described above.

  The press fabric is also involved in finishing the surface of the paper sheet. That is, the press fabric is designed to have a smooth surface and a uniform elastic structure so as to complement the smooth, markless surface of the paper while passing through the press nip.

  Perhaps most importantly, the press fabric receives a large amount of water extracted from the wet paper in the press nip. In order to perform this function, in order to allow water to escape, a space, commonly referred to as a void volume, is literally required inside the press fabric, which is sufficient for water for all of its service life. Need to have good permeability. Ultimately, the press fabric must be able to prevent water received from the wet paper from returning back to the paper that has escaped the press nip and rewetting.

  Modern press fabrics are manufactured in a variety of forms designed to meet the requirements of paper machines introduced for the grade of paper being manufactured. Generally, a press fabric has a woven base fabric in which a fine, non-woven fiber material is needling punched. The base fabric may be woven from monofilaments, twisted monofilaments, multifilaments, or twisted multifilament yarns, and may be in a single layer, multilayer or laminated state. These yarns are typically molded from any of a variety of synthetic polymer resins, such as polyamides and polyesters, used for this purpose by those skilled in the paper machine fabric art.

  The woven base fabric itself takes many different forms. For example, the fabric may be endlessly woven, or may be endless in the form of a plain weave and a woven seam. Alternatively, the fabric may be manufactured by a process commonly referred to as modified endless weaving, which uses machine direction (MD) yarns at the widthwise ends of the base fabric. A seam loop is provided. For this purpose, this MD yarn weaves back and forth at the ends and forms a seam loop as it goes back and forth between the widths of the fabric. The base fabric produced in this manner is placed in an endless form while being mounted on the paper machine. For this reason, it is referred to as a fabric that can be joined on a machine. In order to place such a fabric in an endless form, its two widthwise ends are taken together and the seam loops at the two ends are interdigitated with each other at the meshed seam loops. A seam pin or pintle is inserted into the formed passage.

  Furthermore, the press cloth may be formed of a plurality of layers. For example, the fabric may have a woven base layer and an intermediate layer laminated together.

  The present invention is initially aimed at improving the dewatering properties of a press fabric by using a sacrificial and reusable displacer applied to the surface of the press fabric.

  The present invention relates to a method for reducing the amount of rewet in the press section of a paper machine. The method includes the steps of providing a press cloth, depositing a fiber paper web with water on the press cloth to form a sheet, and depositing a substitute on one side of the press cloth. including. After pressing the press fabric, fiber paper web and displacement agent combination in the press nip and then exiting the press nip, the displacement agent absorbs interfacial water or at least minimizes paper web rewet. And

  Another aspect of the invention relates to an apparatus for reducing the amount of paper web rewet in a press nip. The apparatus includes at least one press cloth that conveys the sheet and a press that applies pressure to the press cloth and causes water to escape from the sheet to the press cloth. The apparatus also includes means for applying a reusable replacement agent to at least one side of the press fabric and means for recovering the replacement agent for reuse.

  The present invention will be described in detail below with frequent reference to the following drawings.

  The following detailed description, which is given by way of example and is not intended to limit the invention exclusively, is better understood in conjunction with the appended drawings. In the drawings, like reference numerals indicate like elements and parts.

  A preferred embodiment of the present invention will be described in the context of a paper machine press fabric. However, it should be noted that the present invention is applicable to those used in other industrial settings as well as the fabric used in other parts of the paper machine.

  Examples of other types of fabrics to which the present invention can be applied include paper machine forming fabrics, paper machine drying fabrics, breathable drying fabrics and pulp forming fabrics.

  One aspect of the present invention is to place an active sheet / press cloth interface at the press nip of a paper machine so that the paper sheet is successfully provided with the interfacial water absorbency that exists between the sheet and the press cloth. It relates to the use of dispersed fine particles. Typically, in the pressing process, interfacial water moves to both the press cloth and the sheet that are present in the nip. However, the return of water to the sheet results in “rewet”, which is a highly undesirable phenomenon in the papermaking process.

  The mechanism believed to be responsible for this undesirable rewet is the pore size of the sheet compared to the press nip that escapes and expands the nip. The paper sheet typically has a smaller pore size distribution than the press fabric. As believed, the pore size of the paper sheet is up to 10 times smaller than the pore size of the press fabric containing fine surface batt fibers. Arithmetically, it has a mean flow pore diameter of 0.5 to 1 μm for paper sheets compared to 10 to 20 μm for press fabrics. Very fine pores preferably allow more water to move into the paper web structure.

  Conventionally, efforts have been made to produce press fabric surface materials having a pore size approximate to that of a paper sheet. One of these efforts has been to use a membrane that is integrated with the press fabric to help promote water removal. However, this prior attempt has generally failed because these membranes are less durable compared to traditional press fabrics having a paper contact surface formed of fine vat fibers.

  One aspect of the present invention constrains the durability of prior art membranes by eliminating the requirement to continuously affix preferential pore size materials to the press fabric. Disappear. Instead, the present invention, which is used to reduce operating costs while reducing the amount of paper rewet, applies a “displacing agent” to assist dewatering in the press nip, Recovering and reshaping. A further aspect of the present invention is a particulate collection step of recovering water-competitive particulate from any of the “water sprays” present on the sheet surface, the surface of the press fabric or the nip. particulate collection process).

  In FIG. 1, one Example of the press process using a substituent is shown. The displacement agent 10 may be applied to the surface of the press fabric 12 or the lower side of the paper web or sheet as a rewet barrier and is recovered immediately by the recovery means 14 after the action of the press 16. If the particles temporarily adhere to the paper web itself, it may be recovered for reuse after multiple pressing and drying steps. The end point at which the replacement agent is recovered may depend on the individual placement of the press sections as well as the properties of the replacement agent. The application of the displacing agent may be performed on various presses.

  This concept is similar to a catalyst in a chemical reaction. In essence, the displacing agent is not consumed, but seems to need to be refreshed or reformed, for example, in a reformer 18. The displacement agent may be applied in the form of a full width shower when the displacement agent is dispersed in a liquid state. Alternatively, the displacing agent may be a solid and may be applied from a spool in the form of a film. The displacement agent may also be applied, for example from a roll, used to apply a coating or sizing agent on the paper web using conventional coating methods.

  The two main requirements for the displacement agent are to compete with the water in the boundary layer as well or better than the paper web to be dewatered, and are essential for the paper web to be dewatered for collection and reshaping. It is not attached to.

  A further embodiment of the present invention is shown in FIG. 2, which shows that the displacement agent is recovered from the surface of the paper sheet in contact with another PMC fabric or belt specifically designed to draw the displacement agent. In this regard, the displacement agent may be applied as fine particles to the lower side of the press cloth, or may be conveyed to the nip by the press cloth so as to interlock with the paper sheet in the nip.

  A substantial proportion of the displacement agent may temporarily adhere to the paper sheet exiting the nip; however, it can be easily removed. In FIG. 2, a second paper machine belt or fabric 20 may be used to draw and remove the substitute from the paper sheet 22.

  The belt 20 may have a smoother surface than, for example, a paper sheet, or a surface that utilizes the properties of a substituent that separates from the paper sheet 22 so as not to adversely affect the paper sheet 22. You may have.

  Modifications to the above will be apparent to those skilled in the art, but are not intended to modify the invention beyond the scope of the appended claims.

  In order to show the effect of the displacement agent described in the present invention, a test was conducted in comparison with either a press cloth alone or a press cloth combined with a membrane. Experiments were also conducted to show that the replacement agent can be efficiently reused and recycled. Finally, experiments were performed to identify whether there are significant advantages to using displacement agents and surface membranes. These experiments were performed using a known press nip simulator (SPNS) that can simulate the pressure, residence time and pressure pulses present in commercial press nips. The results of these experiments are shown in FIG. In FIG. 3, “SRDA” refers to the case where a sacrificial and recoverable replacement agent is used.

  As is apparent with reference to FIG. 3, the final dryness of the press cloth alone was about 34.6%, whereas the press cloth was used together with the substituent disclosed in the present invention. The final dryness increased to over 45%. This exceeds 44.6% of the dryness obtained by combining the press cloth and the surface membrane. It has been found that the desiccability of the displacement agent is not significantly reduced even when the displacement agent is reused or recycled. The final dryness for the recycled particles was 44.7%, which was slightly lower than the single pass case, but retained a value comparable to the press fabric and surface membrane combination. Finally, an experiment was conducted to determine whether a greater effect can be obtained when a combination of a substitution agent and a surface membrane is used. As a result, when used in combination, the final dryness was 46.1%, and the dryness increased somewhat.

  Thus, the use of the displacer described in the present invention showed improved drying characteristics that were comparable or better than those obtained using prior art surface membranes. Furthermore, even when these displacement agents are reused, the ability to achieve an acceptable final dryness is maintained.

1 is a side view of a press section of a paper machine according to one embodiment of the present invention. FIG. FIG. 4 is a side view of a press section of a paper machine according to a second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substituting agent 12 Press cloth 14 Collecting means 16 Press part 18 Reformer 20 Belt 22 Paper sheet

Claims (12)

A method for reducing the amount of rewet in the press section of a paper machine, comprising:
Providing a press cloth;
Depositing a paper sheet with water on the press cloth;
Depositing a displacer on at least one side of the press fabric;
Pressing the press fabric, paper sheet and displacement agent combination in a press nip;
Have
After exiting the press nip, the displacement agent absorbs interfacial water and prevents re-wetting of the sheet.   The method of claim 1, further comprising recapturing the replacement agent.   The method of claim 1, further comprising reconstituting the displacing agent.   The method of claim 1, further comprising removing the displacement agent with a cloth.   The method of claim 1, wherein the displacement agent is applied between the press cloth and the sheet.   The method of claim 1, wherein the displacer reduces the amount of rewet of the sheet after pressing the water from the sheet to the press fabric. A device that reduces the amount of rewet in the press section of a paper machine:
At least one press cloth carrying the sheet;
A press that applies pressure to the press cloth and causes water to escape from the sheet and to the press cloth;
Means for applying a reusable displacement agent to the press fabric;
A device characterized by comprising:   8. The apparatus of claim 7, further comprising means for recapturing the displacement agent.   8. The apparatus of claim 7, further comprising means for reconstructing the displacement agent.   The apparatus of claim 7, wherein the displacer is removed with a cloth.   The apparatus of claim 7, wherein the displacement agent is applied between the press cloth and the sheet.   8. The apparatus of claim 7, wherein the displacement agent reduces the amount of rewet of the sheet after pressing water from the sheet to the press fabric.

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