JPS6350595A - Method for reducing shring quantity during drying of paper web - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing the amount of Z-direction or thickness shrinkage during drying of a paper web formed from waste paper stock. More particularly, the present invention relates to a method of reducing the amount of shrinkage during drying of a paper web through the use of surfactants that are added to the wastepaper stock prior to drying of the pressed web.

In the manufacture of various grades of paper and cardboard, it is necessary that those grades meet specified thickness standards. Moreover, those grades must also meet certain specific gravity standards. -For example, on high-quality paper,
Controlling a paper product within a narrow range of thickness so that it progresses smoothly through a machine designed for a particular thickness of paper, such as a copier or a forming machine for making envelopes or the like. must be done.

In order to maintain the desired hardness of the product, various materials such as cardboard and paperboard are formed into bulky or dense workpieces. For example, the side walls of a milk carton must be stiff enough to retain the contents within the carton without undue expansion of the carton. Since hardness varies approximately as the cube of thickness, control of the thickness and density of each grade of paper and cardboard is very important in the manufacture of paper products.

Stretch clamp presses have been used commercially in recent years in the manufacture of paperboard to remove more water in the press than was possible with conventional press arrangements. The stretch clamp press not only provided energy savings, especially in the drying section, by removing a greater portion of the water from the formed web, but also provided increased productivity.

The additional water removal accomplished in the draw-nip press results from the significant compression of the web while passing through the nip sections of the draw-nip press. This produces successively thinner yet denser paper or cardboard. Such higher density results in more fiber-to-fiber adhesion and stronger paper.

- As an example, if a web with a caliper or thickness of 0.089 ca+ is desired, it was found that after conventional pressing the wet thickness of the cardboard may be 0.14 ca+. Importantly, however, while drying, the cardboard shrinks to a target of 0.089 cm in the thickness or Z direction. Such contraction occurs as a result of Campbell forces. (Campbell force is the force between the fibers due to the surface tension of water.) As the water evaporates, the surface tension pulls the fibers closer together, creating hydrogen bonds. This force becomes stronger as less water is present. in this way,
In conventional methods of pressing formed webs, it has been found that it is not uncommon for the thickness or caliper of the cardboard or paper web to shrink by as much as 40% during the evaporative drying process. . In addition, such Z-direction contraction is also caused by fiber crushing.

However, through the use of the stretch clamp press technique, the dryness of the resulting paper or cardboard is improved by 7-14% in terms of dryness after the press section. This corresponds to a reduction of between 25 and 50% of the water to be evaporated.

Although such a reduction in the water that must be evaporated during passage through the drying section is highly desirable from a thermal energy conservation standpoint, it is important to note that the web being pulled out of the stretch clamp press after being pressed is zero.
There is a problem in that it is further hardened from 14 cm to 0.10 cm. From these numbers, it can be seen that the web pulled out of the stretch clamp press will have a 15 to 30
% also has an extra reduced caliper or thickness. A small portion of this thickness reduction will be carried through the drying process, and it is not uncommon for the web thickness to be reduced by an additional 40% as it passes through the drying section. For example, 0,10CII
If a web with a thickness of l enters the drying section, the dried web will result in a thickness of 0.06 cI11. Thus, the cardboard produced after being pressed and dried to the desired degree will have a thickness that is less than the target or desired thickness. Although the strength properties of the web, such as tensile strength, are enhanced as a result of the high density, such enhanced strength is not always needed or required in practice.

Therefore, a method has been found which makes it possible to enhance the water removal in the press section as desired, but without resulting in the thickness of the dried web being below the desired or target value. There were challenges.

Certain hardwood fibers, or thermomechanical valves, provide thickness recovery after the pressing process to achieve higher thicknesses than stock made from softer materials. Although this is true, there does not appear to be any way to achieve more water removal by pressing in the press section without also reducing the wet thickness of the paper or cardboard. Obviously, the enhanced drying is a direct result of the enhanced compaction.

The present invention does not seek to reduce the compaction that occurs during the pressing process, but rather seeks to overcome the aforementioned problems by reducing the shrinkage that occurs during the evaporative drying of the sheet. Since the thickness loss that occurs during drying is greater than the loss due to the enhanced wet pressing process, attempts to restore thickness by acting on the thickness of the web passing through the drying section are most effective. It was discovered that this would be the case. The present invention provides a method for addressing the largest source of thickness loss, surface tension or Campbell forces, which pull the fibers together tightly enough to allow hydrogen bonding during evaporative drying.

TAPPI Vol. 35, No. 1, pp. 13-15 (1952)
J, A, Van den Akke published in
The paper by R. R. reports on the effect of sublimation on the paper drying process such that surface tension is minimized. Although no thickness or specific gravity values are given, the results indicate that the tensile strength is significantly reduced, the opacity is increased, and the degree of hydrogen bonding is reduced.

TAPPI Vol. 38 No. 7 pp. 412-415 (1955
Broughton and Wang found that the strength of paper produced and dried in the low surface tension of non-polar liquids instead of water was reduced, as published in 2010.

TAPPI's 1974 Englnecring
Conf'erencc proceedings
(Seattle, WA), pp. 327-332, J., W., Swanso.
n reported on the effect of surfactants on fibers. It has been found that anionic surfactants reduce surface tension and have a clear correlation in reducing sheet-to-sheet adhesion. It has been found that cationic surfactants provide a significant reduction in sheet properties determined by adhesion.

The present invention overcomes the prior art in the manufacture of cardboard and paper by providing a method of manufacturing cardboard or paper that produces products of desired thickness and specific gravity without the use of stretch clamp presses. attempts to overcome the aforementioned imperfections of the method. Another object of the present invention is to provide a method for reducing the amount of shrinkage during drying of a paper web formed from wastepaper stock. This method involves the addition of a surfactant to the waste paper stock.

Another object of the present invention is to improve the quality of paper webs by adding cationic surfactants to the waste paper stock to reduce both surface tension and adhesion between adjacent fibers in the formed and pressed web. The object of the present invention is to provide a method for reducing the amount of shrinkage during drying.

Although the present invention is primarily directed to reducing the amount of shrinkage in the Z direction of webs exiting a stretch clamp press, the present invention further reduces such shrinkage of webs produced by conventional high-load presses. It is also intended to reduce the amount of shrinkage.

Moreover, although the invention is described below with particular reference to the addition of surfactants to feedstocks, the invention is not limited to such applications of surfactants. The present invention, as defined by the appended claims, also includes the addition of surfactants by spraying or similar methods onto the formed web prior to its drying. The surfactant may alternatively be introduced at the wet end, ie at the press section. Moreover, surfactants may even be introduced in the drying section. In the production of multilayer papers, surfactants may be incorporated on a single layer or on more than one layer.

Other objects and benefits of the invention will be readily apparent to those skilled in the art from consideration of the detailed description and appended claims.

The present invention relates to a method for reducing the amount of shrinkage during drying of a paper web formed from wastepaper stock. The method includes the step of adding a surfactant to the wastepaper stock prior to its formation into a paper web from the stock. The surfactant is dispersed throughout the raw material such that the surfactant and the raw material are essentially mixed. The mixture of surfactant and feedstock is fed to a headbox of the paper forming section, and the mixture of feedstock and surfactant is jetted from the headbox onto the forming wire of the forming section. A first portion of water is drained from the stock so that a paper web is formed on the forming wire.

The formed web is directed from the forming section to a stretcher press, and the formed web is passed through the stretcher press such that a second portion of the drainage water is removed from the web. A third portion of water is removed from the formed and pressed web such that the surfactant prevents adhesion between adjacent fibers in the pressed web so that the amount of shrinkage during drying of the pressed web is reduced. The pressed web is directed from the stretch-nip press to a drying section to remove the .

In a more specific embodiment of the invention, the surfactant is
It is a cationic surfactant that is effective in reducing both surface tension and adhesion between adjacent fibers within the formed and pressed web.

Although the present invention specifically directs the use of surfactants added to the wastepaper stock, other chemicals can be added to the stock to prevent adhesion between adjacent fibers during the drying process. It will be apparent to those skilled in the art that the use of such chemicals does not depart from the spirit and scope of the invention as defined by the appended claims.

In addition, although the present invention primarily directs the way to reducing the amount of shrinkage in webs produced by stretch clamp presses, the present invention does not require the addition of such surfactants to webs produced by conventional high-load presses. It also includes the application of agents.

Additionally, the present invention includes the addition of surfactants to the web at the wet end or press section or even in the dry section, and additionally, when producing multilayer papers. also includes the addition of such surfactants to a single or multiple layers.

Although surfactants are commonly used in the paper industry for a variety of applications, Applicant has developed an interfacial agent in the waste paper stock to overcome the problem of reduced thickness when using a stretch clamp press. I am not aware of any precedent using activators. Applicants are aware that surfactants have been used by tissue paper manufacturers to prevent adhesion in order to produce products that are softer to the touch.

Fluffy bulbs are made using agents that prevent adhesion, and such bulbs are then more easily redispersed in water or in air for airborne products such as disposable diapers.

However, the present invention is directed to a method of controlling the final thickness of the paper or cardboard emerging from the drying section. Laboratory experiments have shown that the final thickness can be effectively controlled by the use of surfactants in the wastepaper stock, as shown by the experimental results illustrated in Figure 2 of the drawings. It is shown that. These results, which can be read from Figure 2, indicate that the thickness of the resulting dry web can be controlled by controlling the concentration of surfactant added to the aqueous slurry of raw materials, i.e. fibers. ing.

As shown in FIG. 3, the use of surfactants or other non-adhesive agents can reduce the amount of shrinkage that occurs during drying to meet targets. It is clear from FIG. 3 that by adding a surfactant to the raw material prior to pressing, the thickness of the web that comes out of the drying section is greater than when no surfactant is used.

By the aforementioned method, such a controlled addition of surfactant, especially when the surfactant is a cationic surfactant, significantly increases the amount of water removed during passage through the stretch clamp press, while At the same time, the thickness of the final sheet or cardboard is controlled to meet the characteristic properties. Therefore, the process according to the invention allows for significant savings in the amount of steam used in the drying section, producing more than offsetting the cost of such surfactants added to the valve slurry at low concentrations. It brings about improvement in sex.

- Layers Referring in detail to the drawings, FIG. 1 shows in a comparative manner the variation in the thickness of the cardboard during pressing and during drying. - Layers Specifically, the thickness in tenth inch (0,0254a+m) increments is indicated by the vertical axis 10. The resulting pressed web thickness using a conventional press is indicated by 12. Moreover, the thickness of the web emerging from the stretch-nip press is designated by 14. This comparison shows that by using a stretch clamp press that provides a significantly reduced water content and increased specific gravity to the pressed web, a non-negligible thickness reduction results. There is. The number 16 is
The target or desired web thickness is shown after the web has passed through the drying section. This reduction in thickness due to shrinkage of the web after passing through the drying section from a conventional press represents an amount of reduction of approximately 40%.

If a stretch clamp press is used and drying is performed conventionally without the use of a surfactant according to the present invention, the resulting dried web will, as can be seen, be of the desired thickness. It will have a thickness indicated by 18 that is less than the target. However, when using a conventional press, the web shrinks from the thickness indicated by 12 to the desired thickness indicated at 20.

FIG. 2 is a graph showing the effect of using different surfactants at various concentration levels in the feedstock or slurry. The vertical axis shows the percentage increase in web thickness or caliper as it exits the drying section, while the horizontal axis shows the percentage increase in caliper per unit amount of surfactant added prior to feeding into the headbox. Shows percentage. Graph 22
shows the increase in thickness resulting from the use of Arquad 2HT-75, while graph 24
The use of aerosols of C-61 shows an increase associated with the use of particularly low concentrations of surfactants.

Both graphs 22 and 24 can be applied when using paperboard pulp. Arquad is a registered trademark and Arquad 2
HT-75 is Armour & CoIlpan
Armak Corporation, a subsidiary of Y.
Powered by on.

Similarly, graphs 26 and 28 respectively show softwood kraft paper bleached using various concentrations of surfactants (
Figure 2 shows the corresponding thickness increase when producing cardboard or paper webs from B, S, W, ).

FIG. 3 is a comparative diagram in which the thickness of the paper or cardboard after being pressed or dried is represented on the vertical axis. Reference numeral 30 indicates the thickness after pressing in the conventional manner, and 32 indicates the thickness after drying when both the conventional pressing and drying are used.

34 indicates the thickness after being pressed using a reinforced press technique obtained by utilizing a stretch clamp press, and 36 indicates the thickness after being further dried using a conventional drying system. It shows. 36 indicates a web thickness that is significantly less than the target thickness indicated by horizontal dash line 38.

40 designates the thickness of the web as it comes out of the drawing clamp press, and 42, indicated by a dotted line, designates the thickness resulting from the addition of surfactant to the raw material according to the invention. There is.

When such a surfactant-loaded web is passed through a conventional drying system, the thickness of the web is
While passing through the drying system, it is reduced to the target thickness 38, shown as the dried thickness 44.

According to the present invention, a method is provided for reducing the amount of shrinkage during drying of a paper web formed from waste paper stock. The method includes the step of adding a surfactant, preferably a cationic surfactant, to the wastepaper stock before the stock is formed into paper or cardboard. As shown in Figure 2, the surfactant is preferably added to the feedstock in only a small amount. The raw material may be paperboard or bleached softwood kraft paper as shown in FIG. However, because
The present invention is equally applicable to the use of surfactants added to any type of raw material; moreover, the surfactant may be an anionic surfactant in nature; It may also be a type of surface active agent. Before the raw material is fed into the headbox of the paper forming section,
The surfactant is dispersed throughout the feedstock so that the surfactant is essentially mixed with the feedstock. A surfactant and feedstock are supplied to the headbox and the feedstock is ejected onto the forming wire in the forming section. Water is discharged from the forming wire or forming roller so that a web of paper or cardboard is formed. At this forming station, a first portion of the water is drained from the feedstock, and the web is then passed through a stretch clamp press that removes a second portion of the water from the formed web.

This second portion of water forced out of the web is greater than the amount of water removed in a conventional press. Therefore, the resulting web thickness or caliper is less than the caliper of the web emerging from a conventional press. Moreover, the density of this web emerging from the punch is relatively greater than the density of the web produced by conventional pressing. The pressed web is then directed to a conventional drying system. However, because more water is removed in the stretch clamp press, such conventional drying systems require fewer drying drums, or if the same number of drying drums are used. Then less thermal energy would be required in the drying section. The addition of surfactants into the feedstock improves the internal strength of the web because the surfactants help prevent hydrogen bonding that would result in the web having a thickness less than the target thickness if the surfactants were not used. Adhesion between adjacent fibers is prevented.

Furthermore, according to the invention, such shrinkage in the Z direction can be reduced by the introduction of surfactants in the wet end or press section or even in the dry section. Moreover, when multilayer papers are produced, such surfactants can be added to a single layer or to more than one layer.

The present invention has the advantage of resulting in a pressed and dried web having the desired thickness and density, while more than offsetting the expense of adding low concentrations of surfactant to the valve slurry. Provides significant savings in the cost of supplying drying steam.

[Brief explanation of the drawing]

FIG. 1 is a comparison diagram showing typical values of the thickness of cardboard after pressing and drying for sheets pressed in a conventional press section and sheets pressed in a stretch clamp press. It is. FIG. 2 is a graph showing the effect of several surface-active agents on sheet thickness. FIG. 3 shows the resulting thickness when using a conventional press and a stretch clamp press, and also shows the effect achieved in terms of thickness by applying the method of the invention. It is a comparison diagram. 10... Vertical axis, 12... Thickness of web pressed by conventional press, 14... Stretching clamp press (
Thickness of the web pressed by ENP (enhanced press), 16...Target value of the thickness of the web after drying. 18...Thickness of the web pressed by an stretch-nip press (ENP, reinforced press) and dried in the conventional manner, 20
... Thickness of the web pressed and dried by a conventional press, 22 ... Thickness increase due to use of Arkato 2HT-75 when waste paperboard is used as raw material, 24
...Increase in thickness by using C-61 aerosol when waste paperboard is used as raw material, 26...Bleached softwood kraft paper (B, S. W, Ni, ) as raw material Case Arkato 2HT-7
Increase in thickness due to the use of 5, 28... C when bleached softwood kraft paper (B, S, W, etc.) is used as raw material
- Increase in thickness due to the use of 61 aerosols, 30...
・Thickness of the web after being pressed in the conventional manner, 3
2... Thickness of the web after conventional pressing and drying, 34.40... Thickness of the web after strengthening press using ENP. 36...Thickness of the web after being strengthened and further dried, 38...Target value of thickness, 42...Thickness of the web after the raw material to which a surfactant has been added is strengthened and pressed. 44...Thickness of the web after the raw material to which a surfactant has been added is pressed for strength and further dried Patent applicant Beloit Corporation Agent Ben
Physician Masaru Akashi FIG, 1 FIG, 3

Claims (2)

[Claims] (1) A method for reducing the amount of shrinkage during drying of a paper web formed from a wastepaper raw material, comprising: adding a surfactant to the wastepaper raw material prior to forming the raw material into the paper web; Dispersion of the surfactant throughout the feedstock such that the surfactant is essentially mixed with the feedstock and the surfactant mixed with the feedstock into the headbox of the paper forming section. ejecting a mixture of the raw material and the surfactant from the head box onto the forming wire of the forming section; and discharging the raw material from the raw material such that the paper web is formed on the forming wire. evacuation of a first portion of water, guiding the web from the forming section to a stretch clamp press, and passing through the stretch clamp press such that a second portion of water is removed from the formed web. The amount of shrinkage during the passage of the web and drying of the pressed web is reduced and adhesion of adjacent fibers within the pressed web is achieved to reduce the amount of shrinkage and to obtain a dried web of the desired thickness. and directing the pressed web from the stretch clamp press to a drying section for removing a third portion of water from the formed and pressed web that the surfactant prevents. A method for reducing the amount of shrinkage during drying of a paper web. (2) A method for reducing the amount of shrinkage during drying of a paper web formed from a waste paper raw material, which includes supplying the raw material to a head box of a paper forming section and forming wires from the head box to the forming section. ejecting said raw material upwards and draining a first portion of water from said raw material such that said paper web is formed on said forming wire; and guiding said web from said forming station to a high-load press. , passing the web through the press such that a second portion of water is removed from the web, and a third portion of water from the formed and pressed web from the press to a dryer section. guiding of the pressed web to remove the and the cationic surfactant, which is effective in reducing both adhesion and surface tension between adjacent fibers within the pressed web, prevents adhesion between adjacent fibers within the pressed web. and adding a cationic surfactant to the raw material at any of the aforementioned steps as described above.