CA2569884A1 - Method and machine for producing a fibrous web - Google Patents

Abstract

A machine for producing a fibrous web (50) is characterized in that a measuring arrangement (68) for measuring the ash content is mounted inside the machine (48), particularly inside the wire section (54), the press section (56), the drying section (58) or after the drying section in front of a calender (62, 64). This measuring arrangement is connected, via a signal line (70), to a controller (72) that is mounted inside a device (10) for producing the fibrous material suspension.

Description

METHOD AND MACHINE FOR PRODUCING A FIBROUS WEB
Cross Reference To Related Applications [0001] This is a continuation of PCT application No. PCT/EP2005/005862, entitled "METHOD AND MACHINE FOR PRODUCING A FIBROUS WEB", filed June 1, 2005.
BACKGROUND OF THE INVENTION

1. Field of the Invention [0002] The current invention relates to a method for the production of a fibrous web in a machine including a headbox, a wire section, a press section and a dryer section wherein a first, fiber-containing fibrous stock suspension is used in which the fibers are loaded, at least partially, in a precipitation process in a reactor with a precipitation product representing a portion of the ash contained in the fibrous web.

2. Description of the Related Art [0003] A method for the production of a fibrous stock suspension which contains a precipitation product, namely calcium carbonate, is described in US 5,223,090, wherein a fibrous material with elongated fibers is used in which a cellulose wall surrounds a hollow interior, and wherein the fibers possess a moisture content sufficient to form a dewatered slurry of a pulp.

The fibers have a moisture content which corresponds to 40 to 50% of the fiber weight. The water is present essentially in the interior of the fibers and inside of the fiber walls. Calcium oxide or alternatively calcium hydroxide is subsequently added to the pulp so that at least a portion of the added calcium oxide or calcium hydroxide is combined with the water that is contained in the pulp. The fibrous cellulose material is then brought into contact with carbon dioxide wherein it is subjected to a shear-mixing process at the same time, in order to produce a fibrous material having a substantial amount of calcium carbonate inside the hollow interior and within the fiber walls of the cellulose fibers.

' CA 02569884 2006-12-08 [0004] A method is known from JP-A-60-297 382 for adding calcium hydroxide into a one-percent suspension of a beaten or unbeaten pulp. Subsequently carbon dioxide is added into the fibrous stock suspension and calcium hydroxide mixture in order to convert the calcium hydroxide into calcium carbonate.

[0005] A method for loading of fibers with calcium carbonate ("Fiber Loading Technology") is known from DE 100 33 979 Al wherein a calcium oxide and/or calcium hydroxide containing medium is added to the fibrous stock suspension and wherein the herewith treated fibrous stock suspension is processed with additional pure carbon dioxide or a carbon dioxide containing medium in at least one reactor. During the course of the chemical reaction, the essentially complete conversion of the starting substances calcium oxide or calcium hydroxide and carbon dioxide into the reaction product calcium carbonate and water is ensured by regulating the pH
value in the fibrous stock suspension accordingly.

[0006] DE 102 04 254 Al relates to a method for the processing of fibers contained in a fibrous stock suspension wherein the fibers which are loaded with the precipitation product are refined in order to produce precipitation product particles having optimum dimensions in a range of approximately 0.05 and approximately 5 . This produces crystalline precipitation product particles. The production of the crystalline precipitation product particles occurs in an on-line process, directly in the stock preparation line.

[0007] Papers containing fillers or ash are utilized in a multitude of applications, for example in the production of cigarette paper which has a base weight of between 16 to 26 g/m2. It is frequently enhanced with a water mark and it should be very thin, capable of glowing combustion and tasteless. In addition it should possess good optical values with regard to the brightness. The glowing combustion capability is usually achieved by impregnation in order to leave behind a visually attractive white ash. Cigarette paper is usually produced from linen or hemp fibers, cotton, sulfate pulp, paper machine broke as well as from other sources of fiber.
The filler content in cigarette paper is between 5 and 40%, wherein 30% is considered a standard value.

[0008] The freeness value of cigarette paper varies between 100 and 25 CSF
(CSF = Canadian Standard Freeness), or between 68 and 90 SR relative to the manufactured end product.

[0009] The fibrous stock loaded with calcium carbonate can also be utilized in the production of packaging papers and cardboards. Here, a distinction can be made between three main categories: container board for packaging applications, container board for applications in the field of consumer packaging and specialty papers such as wall papers, book spines, etc.
Packaging papers are usually produced as multi-ply products having base weights higher than 150 g/m2. The freeness value varies from 600 to 50 CSF or 20 to 80 SR, relative to the manufactured end product.

[0010] Sack papers require a high porosity and a high mechanical strength in order to meet the high requirements which occur due to the rough handling during the filling process and throughout the duration of their use, as is the case for example with cement bags. The paper must be strong enough to absorb impacts and must therefore possess an accordingly high energy absorption rate. The sack paper must also be porous and sufficiently air permeable in order to ensure an effortless filling process. Sack papers are normally manufactured from a long-fiber kraft pulp as a product having a base weight of between 70 and 80 g/mz and having a freeness value of between 600 to 425 CSF or 20 to 30 SR. Moreover a medium freeness value as described above is strived for which is usually achieved through high consistency refining while low consistency refining is utilized for conventional paper grades, for example graphic papers.
The result of high consistency refining is good adhesion of the fibers with each other as well as high porosity. The sack kraft paper is produced predominantly from bleached and unbleached fibers, wherein a filler content of 5 to 15% may be present in the manufactured sack paper.

[0011] Filter paper requires a high controlled porosity and pore distribution.
It must possess a sufficiently high mechanical strength in order to counteract the flow of the medium which is to be filtered.

[0012] Filter paper is being produced, having a base weight of 12 to 1200 g/m2. In an air filter for example said base weight is between 100 and 200 g/m2, in an oil or fuel filter between 50 and 80 g/m2, in a food stuff filter as high as 1000 g/m2, in a coffee filter as high as 100 g/mz, in a tea bag between 12 and 20 g/m2 and in a vacuum cleaner bag between 100 and 150 g/m2. All filters are produced from a plurality of fibers, such as chemical pulp fibers, bleached and unbleached fibers, kraft pulp, DIP (deinked) paper, recycled fibers, TMP ( thermo-mechanical) paper, etc., wherein a freeness value of 600 to 350 CSF or 20 to 35 SR is strived for.

[0013] For the production process in modem paper machines for both the manufacture of the aforementioned types of paper as well as the manufacture of graphic papers having a base weight of 25 to 150 g/mz, it is necessary to maintain the ash content in the paper as constant as possible and to minimize process fluctuations. In current machinery for the production of fiber webs the ash content is kept constant by adding fresh ash in addition to the ash that is carried along with the fibers. The volume of fresh ash is controlled by way of measuring the ash content in that area of the paper in which the web is being wound to a roll.

[0014] The retention of the fiber web in the wire section is controlled in that the amount of retention agent is added according to the stock consistency measured in the wire water and the headbox. It has been demonstrated that a retention control results in an improved constancy of the fiber web characteristics, for example the stock consistency or the sheet characteristics. It also has an advantageous effect upon the runnability of the paper machine - or in other words its efficiency - and upon the paper quality.

100151 What is needed in the art is to optimize the process of producing a fiber web from a loaded fibrous stock suspension.

SUMMARY OF THE INVENTION

[0016] The present invention provides a method wherein the ash content in the fiber web which is being produced from the fibrous stock suspension is measured during the production of said fiber web and wherein the addition of the precipitation product into the fibrous stock suspension entering the headbox is controlled, based on the measured ash content in the fiber web.

[0017] According to an embodiment of the present invention, the ash content in a first fiber-containing fibrous stock suspension which is being supplied to the machine is controlled by mixing, according to a measured value from the first fiber-containing fibrous stock suspension, the first fiber-containing fibrous stock suspension and a second fiber-containing fibrous stock suspension including a second plurality of fibers which at least essentially does not include the precipitation product, subsequently supplying to the headbox a mixture of the first fiber-containing fibrous stock suspension and the second fiber-containing fibrous stock suspension.
[0018] It is also especially advantageous if the ash content in the fibrous stock suspension being supplied to the machine is controlled in the first fibrous stock suspension through metering of a first substance which is to be precipitated and a second substance which causes the precipitation reaction, thereby creating the precipitation product in the first fibrous stock suspension.

[0019] Calcium carbonate is an advantageous precipitation product which is precipitated from calcium hydroxide by way of carbon dioxide.

[0020] It is also advantageous if the ph-value of the first fibrous stock suspension is controlled during the precipitation in the reactor while producing the precipitation product.

[0021] Here it is advantageous if each pH value is compared with a corresponding desired value and the deviation is reduced or removed through at least one of the following process regulated conditions: dwell time of the fibrous stock reaction in the reactor, infeed speed of the fibrous stock suspension, pressure of the carbon dioxide, temperature of the fibrous stock suspension and/or the calcium hydroxide, pressure in the reactor, temperature and/or pressure of the carbon dioxide, concentration of the carbon dioxide in the liquid phase, concentration of the calcium hydroxide and the fibers, by way of a specific fiber surface.

[0022] A machine according to the present invention is characterized in that a measuring arrangement to measure the ash content is located in the machine, especially in the wire section, the press section, the dryer section or after the dryer section before a calender, wherein said measuring arrangement is connected via a signal line with a controller which is located in a device for the production of a fibrous stock suspension. The machine therefore includes a controller or regulator to adjust or control the ash content in the fiber web which is being produced from the fibrous stock suspension, which is located in the area of the paper machine after the headbox.

[00231 The present invention ensures constant processes for the production of a fiber web, leading to an increase in quality and efficiency. A metered addition of fresh ash is no longer necessary. Retention agents are being saved and the ash content which was brought into the fibrous stock suspension by way of the fiber loading process can be maximized by regulating said content through direct adjustment or control. This simplifies the overall process and again clearly reduces that component of ash which is not adhered to the fibers.

[0024] The regulating variable in the fiber loading process for controlling of the ash content in the paper is the metered addition of the calcium hydroxide component. Also, in order to control the degree of conversion of the Fiber Loading Reaction by way of regulating the pH value and through the metered addition of the carbon dioxide the conversion of the milk of lime into calcium carbonate must also be verified. This, in combination with a retention control leads to a high stability of the processes, in other words a high stability in the fiber loading process and the paper manufacturing process. The ash content in the fibrous stock which is loaded with calcium carbonate amounts to between 0.05 and 60%, preferably between 1 and 40%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0026] Fig. 1 is a schematic drawing illustrating a device for loading fibers which are contained in a fibrous stock suspension with a filler by way of a chemical precipitation reaction, with a pump disperger;

[0027] Fig. 2 is an illustration of the pump disperger according to Fig. 1, in direction of the arrows A;

[0028] Fig. 3 is an illustration of a machine for producing a fiber web, shown in a simplified illustration; and [0029] Fig. 4 is a schematic of the control arrangement.

[0030] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Referring now to the drawings, and more particularly to Fig. 1, there is shown a fiber stock suspension being supplied in a device 10 (Fig. 1), to a pump disperger, that is a pump fluffer 12, where it is treated by shear forces in order to break down the fiber material into individual fibers, exposing the fiber surfaces and increasing the contact surfaces accordingly.
The pump disperger 12 is simultaneously utilized as a reactor for the chemical precipitation reaction. It can specifically be designed so that a reduction of the fibrous suspension's flow speed occurs in a reduction channel 14. In the present example it is designed so that the fibrous stock suspension is generally transported in radial direction toward the outside, originating from a central, radial inner area. A static mixer may be utilized in place of and/or in conjunction with the pump disperger 12.

[0032] The reaction channel 14 of the pump disperger 12 is restricted at least partially by structured surfaces which can be formed for example by bar or knife sets. The reaction channel 14 is formed between two plates 16 which are located opposite each other and which have structured surfaces between which the fibrous stock suspension is transported in radial direction towards the outside.

[0033] A plug screw 18 is located prior to the pump disperger 12, in order to compress the fibrous suspension by forming a plug. The plug screwl8 is preceded by an infeed screw 20 which is located in an at least essentially cylindrical channel or housing 22.
The channel 22 is equipped with a connection 24 for admitting a mixture which consists for example of at least the fibrous stock suspension, water and calcium oxide and/or calcium hydroxide.

[0034] The plug screw 18 is located rotating in a cone-shaped channel 26 whose cross section tapers in the direction of the stock flow S, in order to compress the fibrous suspension by way of forming a plug in a channel 28 that links up with the plug screw 18, immediately before the pump disperger 12. This channel 28 which is located immediately before the pump disperger 12 is equipped with a feed screw 30 and is equipped with a connection 32 for the immediate supply of carbon dioxide into the fibrous stock suspension which is no longer liquid, but which is still moist. The screws 18, 20, 30 either share a common drive shaft 34, or they can be driven separately, at least partially. A swirl cross 36 which is located in the center of the plug screw 18 serves to loosen the plug and the surfaces of the fiber material will be accordingly enlarged. The structured surfaces of the plates 16 that are located opposite each other produce shear forces in the fiber stock, causing enlargement of the contact surfaces of the carbon dioxide which is reacting with the calcium hydroxide that is attached on the fibers, thereby ensuring a speedy and efficient reaction.

[0035] The pump disperger 12 is equipped with an outlet 38 for the thickened loaded fibrous suspension which is located at least essentially tangential to the plates 16.
A carbon dioxide supply line may also be provided as an option in this area for the purpose of adjusting the desired pH value.

[0036] In addition, the pump disperger 12 may be equipped with an inlet 40 that is located at least essentially tangential to the plates 16 for the purpose of diluting the loaded stock with water and/or calcium hydroxide - especially stock from an upstream stock thickening unit - to less than 6%, preferably 3% to 6%. Appropriate thinning will render the stock again pumpable.

[0037] The fibrous suspension is produced, for example, by dissolving pulp or waste paper with additives in a pulper 42, or is supplied to the loading process as non-dried fiber stock.
[0038] Subsequently calcium oxide or calcium hydroxide are added - the latter in dry or liquid form - in an area 44 and are mixed thoroughly into the fibrous stock suspension. The fibrous stock suspension is then thickened by way of dewatering in an area 46 to such an extent as to create a pulp that is still moist. This creates a fibrous stock suspension which is no longer liquid, but still moist.

[0039] The fibrous stock suspension is then routed from the area 46 into the pump disperger 12 where the carbon dioxide is supplied.

' CA 02569884 2006-12-08 [0040] The device depicted in Figs. 1 and 2 for loading fibers which are contained in a fibrous stock suspension with a filler depict merely one possible arrangement from a plurality of possible devices. Additional devices with exemplary characteristics are known, for example, from the already mentioned German disclosure documents DE 100 33 979 Al and DE 102 04 254 Al, wherein the German patent application "FL-high ash content" by the applicant whose reference is HPP11846 DE also describes a possible device.

[0041] Inside a machine 48 (Fig. 3) for the production of a fiber web 50, which is located adjacent to the area for the stock preparation illustrated in Figs. 1 and 2 and which includes a headbox 52, a wire section 54, a press section 56, a dryer section 58, an applicator unit 60 for the application of adhesive, as well as calenders 62, 64 and a winder 66, a measuring arrangement 68 is provided for on-line measuring of the ash content in the fiber web 50. Said measuring arrangement is located either in the wire section 54, in the press section 56 or in the dryer section 58 or following said dryer section, for example before the calender 64.
Installation of the measuring arrangement 68 in the dryer section 58 is particularly advantageous.
The measuring arrangement 68 is connected via a signal line 70 to a controller 72 (Fig. 4) which is mounted inside device 10 or following said device in order to regulate the composition of the fibrous stock suspension [0042] The measuring arrangement measures- for example optically - the ash content of the fiber web 50 as a controlled variable and from this creates a signal value that it supplied to the controller 72. Said controller for its part produces signal values for the addition of calcium oxide or calcium hydroxide 74, for the associated stoichiometric carbon dioxide addition 76, for the addition of dilution water 78 and for the addition of additional chemicals 80, for example a retention agent in an area 82 which is located either inside the reactor for the production of the fibrous stock suspension containing loaded fibers, or located following the reactor.

[0043] The controller 72 also controls - if present - the addition of a fibrous stock suspension supplied from another apparatus via a line 84 through a valve 86 whose fibers are not loaded with calcium carbonate in order to reduce or increase the content of fibrous stock suspension containing loaded fibers which is supplied via a line 88 to the headbox 52.

[0044] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Component Identification Device 12 Pump Fluffer 14 Reaction channel 16 Plates 18 Plug screw Infeed screw 22 Channel or housing 24 Connection 26 Channel 28 Channel Feeding screw 32 Connection 34 Drive shaft 36 Swirl cross 38 Outlet Inlet 42 Pulper 44 Area 46 Area 48 Machine for the production of a fiber web Fiber web 52 Headbox 54 Wire section 56 Press section 58 Dryer section Applicator unit 62 Calender 64 Calender 66 Winder 68 Measuring arrangement 70 Signal line 72 Controller 74 Addition of calcium oxide or calcium hydroxide 76 Carbon dioxide addition 78 Addition of dilution water 80 Addition of additional chemicals 82 Area 84 Line 86 Valve 88 Line

Claims (7)

1. A method for the production of a fibrous web in a machine including a headbox, a wire section, a press section, and a dryer section, said method comprising the steps of:
loading a first plurality of fibers of a first fiber-containing fibrous stock suspension at least partially in a precipitation process in a reactor with a precipitation product representing a portion of an ash included in the fibrous web;

during a production of the fiber web, measuring an ash content in the fiber web which is being produced from said first fiber-containing fibrous stock suspension; and controlling an addition of said precipitation product into said first fiber-containing fibrous stock suspension entering the headbox based on a measured said ash content in the fiber web.

2. The method in accordance with claim 1, wherein said ash content in said first fiber-containing fibrous stock suspension which is being supplied to the machine is controlled by mixing, according to a measured value from said first fiber-containing fibrous stock suspension, said first fiber-containing fibrous stock suspension and a second fiber-containing fibrous stock suspension including a second plurality of fibers which at least essentially does not include said precipitation product, subsequently supplying to the headbox a mixture of said first fiber-containing fibrous stock suspension and said second fiber-containing fibrous stock suspension.

3. The method in accordance with claim 1, wherein said ash content in said first fiber-containing fibrous stock suspension being supplied to the machine is controlled in said first fiber-containing fibrous stock suspension by metering of a first substance which is to be precipitated and a second substance which causes a precipitation reaction, said precipitation product created in said first fiber-containing fibrous stock suspension.

4. The method in accordance with claim 1, wherein said precipitation product is calcium carbonate which is precipitated from calcium hydroxide by carbon dioxide.

5. The method in accordance with claim 4, further comprising controlling a ph-value of said first fiber-containing fibrous stock suspension during a precipitation in said reactor while producing said precipitation product.

6. The method in accordance with claim 5, wherein each said pH value is compared with a corresponding desired value and a deviation is one of reduced and removed through at least one of a plurality of process regulated conditions including a dwell time of a fibrous stock reaction in said reactor, an infeed speed of said first fiber-containing fibrous stock suspension, a pressure of said carbon dioxide, a temperature of at least one of said first fiber-containing fibrous stock suspension and said calcium hydroxide, a pressure in said reactor, at least one of a temperature and a pressure of said carbon dioxide, a concentration of said carbon dioxide in a liquid phase, a concentration of said calcium hydroxide and a plurality of fibers by a specific fiber surface.

7. A system for producing a fibrous web, said system comprising:
a stock preparation device for producing a fibrous stock suspension;
a paper machine comprising:

at least one of a wire section, a press section, a dryer section, and an area after a dryer section before a calendar; and a measuring arrangement for measuring an ash content, said measuring arrangement located in said machine in one of said wire section, said press section, said dryer section, and said area after said dryer section before said calender;

a controller coupled with said measuring arrangement, said controller configured for:
loading a plurality of fibers of said fibrous stock suspension at least partially in a precipitation process in a reactor with a precipitation product representing a portion of an ash included in the fibrous web;

during a production of the fiber web, measuring said ash content in the fiber web (50) which is being produced from said fibrous stock suspension; and controlling an addition of said precipitation product into said fibrous stock suspension entering a headbox based on a measured said ash content in the fiber web.