WO1999011859A1

WO1999011859A1 - An apparatus for increasing internal bond strength of a web

Info

Publication number: WO1999011859A1
Application number: PCT/US1997/015557
Authority: WO
Inventors: David Hope
Original assignee: Beloit Technologies, Inc.
Priority date: 1997-09-04
Filing date: 1997-09-04
Publication date: 1999-03-11
Also published as: AU4249797A

Abstract

An apparatus is disclosed for increasing the internal bond strength of a web. The apparatus includes a headbox (10) which is connected to a source of stock (15), the headbox having an upstream and a downstream end. The headbox includes a tube bank (18) for the flow therethrough of the stock. A slice chamber (30) is disposed downstream relative to the tube bank (18), the slice chamber having an upstream portion for receiving the stock flowing through the tube bank at a downstream slice opening (34) for the ejection therethrough of the stock. A plurality of trailing elements (64) are disposed within the chamber, each element being pivotally secured adjacent to the upstream portion. A twin wire former (11) is disposed downstream relative to the slice opening for receiving the stock from the headbox. The headbox (10) also includes a consistency profiling device (36, 40) for adjusting the consistency profile of the web in a cross-machine direction and for adding materials into a region disposed in the middle of the thickness of the web, such materials enhancing the bonding of the fibers within the stock particularly located within the region.

Description

PATENT APPLICATION

TITLE: AN APPARATUS FOR INCREASING INTERNAL BOND STRENGTH OF A WEB

BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates to an apparatus for increasing the internal bond strength of a web.

More specifically, the present invention relates to an apparatus for forming a web of paper formed by a twin wire former, the arrangement being such that the internal bond strength of the resultant web is increased.

INFORMATION DISCLOSURE STATEMENT In the prior art, twin wire formers such as the BelLiner and the BelBaie have been used to form a web from stock.

Typically, a headbox supplied with stock is disposed adjacent to an upstream end of a forming section defined between a first and a second forming wire.

However, with twin wire formers, there is a tendency for fines within the stock to migrate through the web and through the respective forming wires. Such fines appear to enhance the fiber bonding of the web so the loss of such fines from the web has a detrimental effect on the bond strength of the resultant web.

The present invention provides a way of improving the bond strength of a web formed by a twin wire former by putting fines or fibers back into the middle of the sheet, that is, in the middle of the sheet in a thickness or Z direction.

More specifically, the present invention introduces the fines into a region in the middle of the thickness of the sheet and inhibits the homogeneous spread of such fines outwardly throughout the sheet.

Consistency profiling was introduced with the Concept IV headbox. The Concept IV headbox included a plurality of rows of flow tubes each row extending in a cross-machine direction with the rows being either aligned vertically relative to each other or staggered relative to each other.

Profiling tubes were arranged in a cross-machine direction at the upstream end of the flow tubes so that either Whitewater or additives could be added to the main flow of stock for selectively adjusting the consistency of the resultant flow in a cross-machine direction thereby permitting adjustment of the basis weight of the resulting web in a cross-machine direction. U.S. Patent No. 5,560,807 assigned to Beloit Technologies, Inc. describes the general concept of cross-machine directional profiling using an additive injection system.

Also, U.S. Patent No. 5, 1 97,091 to Hergert teaches cross-machine directional profiling including the addition of Whitewater for dilution and cross-machine directional profiling.

The present invention improves the internal bond strength of a web formed by a twin wire former.

Therefore, the primary objective of the present invention is the provision of an apparatus for increasing the internal bond strength of a web formed in a twin wire former by adding materials into a region disposed in the middle of the thickness of the web.

Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.

SUMMARY OF THE INVENTION The present relates to an apparatus for increasing the internal bond strength of a web. The apparatus includes a headbox which is connected to a source of stock, the headbox having an upstream and a downstream end.

The headbox includes a tube bank for the flow therethrough of the stock. A slice chamber is disposed downstream relative to the tube bank with the slice chamber having an upstream portion for receiving the stock flowing through the tube bank and a downstream slice opening for the ejection therethrough of the stock. A plurality of trailing elements are disposed within the chamber with each element of the plurality of trailing elements being pivotally secured adjacent to the upstream portion.

A twin wire former is disposed downstream relative to the slice opening for receiving the stock from the headbox.

The headbox also includes consistency profiling means for adjusting the consistency profile of the web in a cross-machine direction and for adding materials into a region disposed in the middle of the thickness of the web, such materials enhancing the bonding of the fibers within the stock particularly located within the region. Many modifications and variations of the present invention will be readily apparent to those skilled in the art by consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the apparatus of the present invention.

FIG. 2 is an enlarged isometric view, partly cut away, of the headbox shown in FIG. 1 .

FIG. 3 is a cross-sectional view of the apparatus of FIG. 1 taken along the section line 3-3.

FIG. 4 is an enlarged isometric view of one of the tubes of the apparatus of FIG. 1 .

FIG. 5 is a diagrammatic representation of the tapered tubes taken along section line 5-5 of FIG. 6.

FIG. 6 is a cross-sectional view of the apparatus of FIG. 1 taken along section line 6-6.

Similar reference characters refer to similar parts shown in the various views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to FIGS. 1 -6, wherein like numbers refer to similar parts, a headbox apparatus 10 is shown in FIG. 1 together with a twin wire former generally designated 1 1. The twin wire former 11 includes an upstream and downstream end 110 and 112, respectively. The former 1 1 also includes a first and second wire 1 14 and 1 16, respectively which define therebetween a forming section 1 18. As shown in FIG. 2, the headbox 10 has a housing 14 which is connected to a pressurized source 15 of stock. The housing 14 defines a tapered inlet of the stock supply manifold 16 through which stock is introduced to a tube bank 18. The tube bank 18 comprises an array of tubes 24 which are stacked alongside and one above the other. A means for introducing the materials or emollients at selected levels within the formed paper web is provided by an arrangement of supply conduits described more fully below.

Each tube 24 extends from the supply manifold 16 to the slice chamber 30. The tube bank thus has an upstream end 20 at the manifold 16, and a downstream end 22 at the slice chamber 30. The upstream end 20 of the tube bank 18 joins the interior of the headbox manifold 16 at a stock supply wall or surface 21 , shown in FIG. 2. Thus, the individual tubes 24 penetrate the stock supply wall 21 and, thus, communicate with the interior 23 of the headbox manifold 16 and are, thus, supplied with stock.

The tube bank 18 has an array of tubes 24. The array has a plurality of super-positioned rows 50 of tubes 24, generally five to seven rows, or the exemplary six rows shown in FIGS. 1 , 2, and 3. Each row 50 has up to several hundred tubes 24 and extends substantially the entire length of the housing 14. The length of the housing 14 is approximately equal to the width of the paper web formed by the stock flowing through the headbox 10.

The downstream end 22 of the tube bank 18 is connected to the inlet or upstream end 32 of the slice chamber 30. The stock supplied to the slice chamber 30 passes through the slice chamber 30 and is ejected from the downstream end or lip or slice opening 34 of the slice chamber 30 onto a forming wire 12, shown in FIG. 1 . The rows 50 of the tube bank 18 define the width of the paper web formed on the wire 12 and each of the rows defines a portion of the through thickness or z-direction of the web. As shown in FIG. 2, trailing elements 64, long, thin hinged members disposed between rows 50 of the tube bank 18, keep the flow from the individual rows 50 separated from one another. The trailing elements 64 terminate adjacent to the lip 34 of the slice 30. The flow from each row 50 of tubes thus deposits fibers which form super-positioned, partially intermingled, strata in the z-direction of a paper web formed on the wire 12.

As shown in FIG. 3, individual rows 50 of tubes 24 provide a nearly continuous sheet of stock to the slice 30. The rows 50 of tubes 24 are super-positioned with the uppermost row 51 corresponding to the uppermost layer of fibers in the paper web formed. The lowermost row 53 corresponds to the paper fibers at the bottom of the sheet in the z-direction which are formed against the moving wire 12.

As shown in FIG. 5, six rows of individual tubes 24 are vertically arrayed and extend from the supply wall 21. The tubes 24, thus, are positioned to receive stock from the stock manifold 16. Each tube 24 in a vertical array is from a different super-positioned row 50 of the tube bank 18. A plurality of supply conduits or tubes 36 discharge emollients or materials into the manifold 16. A single supply conduit 36 injects emollients such as fibers or starch into the manifold 16 through the stock supply wall 21.

Although conduits may be positioned at different levels within the manifold, an exemplary supply conduit 36 is shown in FIG. 5 injecting stock between two rows 50 of tubes 24. As shown in FIG. 3, a plurality of supply conduits 36 connect a source of materials 38 to a multiplicity of emollient injection points or openings 39 between individual tubes 24 in a row of tubes 50.

The illustrated emollient injection points 39 are positioned to add emollients to the center of the paper web. Emollients which may be added to the center of the paper web would include starch, stock having a higher consistency than the main source of stock. Also, the materials or emollients added could include fines made by highly refining softwood kraft to a very low f reeness level of less than 100 Canadian Standard Freeness.

Such materials have been introduced to the stock in the headbox at a consistency of 1 % via the consistency profile tubes. The total flow rate through the consistency profiling tubes is about 5% of the total headbox flow rate and the addition rate of the "fines" material is between 5 to 10% of the total fiber depending on the headbox consistency used which is lower than the consistency of the materials. Typical consistency of the headbox stock is .7%. Trials have indicated that the internal bond strength values increased by up to 100% when the "fines" material was added using the consistency profile tubes.

In the present invention, use of consistency profiling tubes to add chemicals, fiber or other materials to the middle in the Z direction plane of the sheet for the purpose of increasing test properties in the case of fiber, or increased retention in the case of chemicals is achieved.

Furthermore, the bond strength is enhanced by adding "fines" material to the middle of the sheet and for adjusting the consistency profile by opening values in the supply tubes for supplying materials that would be higher than the headbox consistency thereby increasing the basis weight in localized areas where the basis weight is found to be low. The materials may include highly refined stock and various procedures may be employed for obtaining fines at the correct consistency. Also, because of the increase in consistency, cleanliness of the consistency profiling tubes and valves associated therewith must be provided in order to achieve the desired objective.

When base weight paper or liner board is formed between a twin wire former, the center of the sheet can be subject to delamination. The center of the sheet can be strengthened by the selective addition of a binding agent such as starch to the central portion of the fiber web.

The headbox 10 is designed to produce a uniform orientation and consistency of fibers laid down in the cross-machine direction on the wire 12. This uniformity starts with an attenuator (not shown) disposed upstream relative to the headbox for damping pressure pulses caused by the stock pumping equipment. The stock then flows into the manifold 16. The manifold is tapered in a cross-machine direction, either linearly or parabolically so that the pressure within the manifold remains constant in the cross-machine direction.

The job of each tube 24, an example of which is best shown in FIG. 4, is to change the direction of the stock flow from the cross-machine direction to the machine direction. Each tube has an upstream section 54 which is generally cylindrical and which receives stock from the manifold 16. The upstream section 54 is joined at an expansion joint 61 to a flattened downstream section 60 which discharges stock onto the wire 12. The length of the upstream section 54 of the tube 24 is selected so the flow becomes completely symmetrical and aligned in the machine direction. The flow then undergoes a sudden expansion at the juncture 61 with the downstream section 60. The sudden expansion creates shear for improved fiber dispersion, and also creates head loss for cross-machine uniformity. Because flow through a pipe 24 is dependent on the entire pressure drop, a large pressure drop caused at the expansion joint 61 reduces the effect of upstream pressure variations so increasing uniformity of the flow through all of the tubes 24 in the tube bank 18.

The transition between the circular first section 54 and the circular second section 60 produces uniform and stable profiles within a short distance downstream of the expansion joint 61. The flow then smoothly transitions to a generally rectangular shaped outlet 62. The perimeter of the tube is kept constant, allowing the cross-sectional area to be decreased. The result is a tube section in which the flow accelerates, enhancing both flow stability and uniformity.

The critical parameter is the length of the downstream section 60 after the expansion joint 61. Proper length prevents a water rich, low consistency layer from building up near the tube walls.

Consistency measurements obtained by direct sampling of flow as it exits tubes of different lengths, shows that the longer the tube, the greater the consistency profile non-uniformity. The pressure drop in the tubes 24 combined with the uniform pressure profile within the manifold 16 means that the injection points 39 of the supply conduit 36 have minimal or no effect on the volumetric flows through the individual tubes 24. Further, because the injection points will preferably be evenly spaced in the cross- machine direction, any dilution effects caused by the emollient will be uniform in the cross-machine direction. Flow stability is enhanced in the slice chamber 30 by utilizing trailing elements 64 which have thicker base dimensions which limit the expansion of the flow as it enters the nozzle formed by the slice 30. For grades that are sensitive to paper orientation, it is desirable to align the flow path so that it is in line from the manifold 16 through the tube bank 18 and the slice 30.

As shown in FIG. 3, valves 88 may control the addition of emollients in the cross-machine direction from the emollient source 38. However, the valves will in general be adjusted to achieve a uniform injection of emollients in the cross-machine direction. Although the valves could be adjusted for downstream measurements of the effect produced by the emollients, they will in general remain relatively constantly actuated over time, and in many instances, valves 88 will not be required.

As shown in FIG. 2, a control means 40 may be installed between a source of emollient 38 and the supply conduits 36. One typical control means may be a metering pump which can supply a precisely controlled quantity at a controlled flow rate of emollient to the supply conduits 38 which inject through the injection points 39 into the manifold 16.

It should be understood that the high turbulent expansion joints 61 may facilitate the uniform mixing of the emollients with the stock flowing through the tubes 24.

Since the additives are injected directly into the headbox, the amount of fluid shear applied to the additives is minimized. This ensures minimum breakdown of high molecular weight polymers, and the maximum effectiveness of the chemicals used. Also, using several small injection tubes ensures better distribution of the emollients, and the localized mixing is improved as the region over which the additives diffuse is greatly reduced. It should further be understood that the flow of the injection tubes can be supplied by a commonly controlled source to provide equal emollient addition at multiple injection locations. Alternatively, the additional flow rate to the various injection tubes can be regulated separately, providing the added flexibility to vary the additive addition rate in the cross-machine and z- or thickness direction for most effective emollient use. Further, it should be understood that this new method of injecting emollients which is controlled in both the z-direction and the cross-machine direction may advantageously be employed in the development of new chemical and chemical systems which cannot be utilized today because of the requirement of mixing the emollient or additive throughout the stock supply. Further, it should be understood that a parabolically tapered manifold, in one example where the manifold is nine meters long, would vary from the linear profile by approximately thirty millimeters at the point of maximum difference between the linear and the parabolic curve of the manifold.

The problem identified with twin wire formers is that the two way dewatering can cause an area of weakness in the center of the sheet. Such is thought to be due to the migration of the fines into the outer layers of the sheet. A consequence of such migration can be a significant reduction in the internal bond strength.

According to the present invention, the aforementioned problem is overcome and counteracted by the injection of additional fines within the fines deficient area. The addition of such fines is achieved by utilizing the consistency profiling tubes.

Trials have been run to evaluate the arrangement of the present invention. One grade and speed were used during the trials. The grade was 100 grams per square meter at 400 meters per minute. In separate trials, quantities of starch and highly refined bleach softwood kraft "fines" were added to the sheet utilizing the consistency profiling tubes positioned in the center row of a five row headbox.

The results indicated that introducing highly refined material by way of the consistency profiling system was effective in improving internal bond strength.

It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces such modified forms thereof as come within the scope of the following claims.

Claims

WHAT IS CLAIM IS:

1 . An apparatus for increasing internal bond strength of a web, said apparatus comprising: a headbox connected to a source of stock, said headbox having an upstream and a downstream end; said headbox including: a tube bank for the flow therethrough of the stock; a slice chamber disposed downstream relative to said tube bank, said slice chamber having an upstream portion for receiving the stock flowing through said tube bank and a downstream slice opening for the ejection therethrough of the stock; a plurality of trailing elements disposed within said chamber, each element of said plurality of trailing elements being pivotally secured adjacent to said upstream portion; a twin wire former disposed downstream relative to said slice opening for receiving the stock from said headbox; and said headbox further including; consistency profiling means for adjusting the consistency profile of the web in a cross-machine direction and for adding materials into a region disposed in the middle of the thickness of the web, such materials enhancing the bonding of fibers within the stock particularly located within said region.

2. An apparatus as set forth in claim 1 wherein the web is a multi-ply web.

3. An apparatus as set forth in claim 1 wherein the source of stock has a consistency within the range .5 to .9%.

4. An apparatus as set forth in claim 1 wherein the consistency of the stock is within the range .6 to .8%.

5. An apparatus as set forth in claim 1 wherein: said tube bank includes a plurality of rows of tubes, each row extending in a cross-machine direction, said plurality of rows being disposed vertically relative to each other.

6. An apparatus as set forth in claim 5 wherein each tube of one row is vertically aligned relative to an adjacent tube of an adjacent row.

7. An apparatus as set forth in claim 1 wherein said slice chamber is disposed immediately downstream relative to said tube bank.

8. An apparatus as set forth in claim 1 wherein: each trailing element of said plurality of said trailing elements is a flexible sheet.

9. An apparatus as set forth in claim 8 wherein said flexible sheet is a LEXAN sheet, said sheet having an upstream extremity and a downstream extremity, said upstream extremity being pivotally secured adjacent to said upstream portion, said downstream extremity freely floating within said slice chamber.

10. An apparatus as set forth in claim 1 wherein said twin wire former includes: a first and a second forming wire, said wires cooperating together to form therebetween a forming section having an upstream and a downstream end, said upstream end being disposed immediately adjacent to said slice opening so that stock ejected from said slice chamber is received between said wires, the arrangement being such that during movement of the stock through said forming section, said bonding of the fibers within the .stock particularly located within said region is enhanced thereby increasing the internal bond strength of the web.

1 1 . An apparatus as set forth in claim 1 wherein said consistency profiling means includes: a plurality of supply tubes, said supply tubes extending in a cross- machine direction and being disposed within said tube bank such that the materials are added to said flow of stock for enhancing the bonding of fibers in the middle of the thickness of the resultant web.

1 2. An apparatus as set forth in claim 1 wherein said materials include: fibers manufactured by highly refining softwood kraft to a freeness level less than 100 csf (Canadian Standard Freeness).

1 3. An apparatus as set forth in claim 1 wherein said materials include fibers having a consistency within the range .98 to 1 .2%.

14. An apparatus as set forth in claim 1 wherein the total flow of the materials into said headbox is within the range 3 - 7% of the flow of the stock and the materials added thereto.

1 5. An apparatus as set forth in claim 1 wherein said materials constitute between 5 and 10% of the total fiber contained within the resultant web.

1 6. An apparatus as set forth in claim 1 wherein said materials include: a secondary flow of stock having highly refined fibers therein and a consistency which is higher than the consistency of said source of stock, the arrangement being such that profiling of the web is achieved by increasing the basis weight selectively in a cross-machine direction in order to achieve a uniform basis weight in a cross-machine direction across the width of the resultant web.