Abstract:
A machine for producing a fibrous web is characterized in that a measuring arrangement for measuring the ash content is mounted inside the machine, particularly inside the wire section, the press section, the drying section or after the drying section in front of a calendar. This measuring arrangement is connected, via a signal line, to a controller that is mounted inside a device for producing the fibrous material suspension.

Description:
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 Jun. 1, 2005.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     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.  
         [0004]     2. Description of the Related Art  
         [0005]     A method for the production of a fibrous stock suspension which contains a precipitation product, namely calcium carbonate, is described in U.S. Pat. No. 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.  
         [0006]     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.  
         [0007]     A method for loading of fibers with calcium carbonate (“Fiber Loading Technology”) is known from DE 100 33 979 A1 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.  
         [0008]     DE 102 04 254 A1 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 5μ. 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.  
         [0009]     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/m 2 . 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.  
         [0010]     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.  
         [0011]     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/m 2 . The freeness value varies from 600 to 50 CSF or 20 to 80° SR, relative to the manufactured end product.  
         [0012]     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/m 2  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.  
         [0013]     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.  
         [0014]     Filter paper is being produced, having a base weight of 12 to 1200 g/m 2 . In an air filter for example said base weight is between 100 and 200 g/m 2 , in an oil or fuel filter between 50 and 80 g/m 2 , in a food stuff filter as high as 1000 g/m 2 , in a coffee filter as high as 100 g/m 2 , in a tea bag between 12 and 20 g/m 2  and in a vacuum cleaner bag between 100 and 150 g/m 2 . 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.  
         [0015]     For the production process in modern 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/m 2 , 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.  
         [0016]     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.  
         [0017]     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  
       [0018]     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.  
         [0019]     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.  
         [0020]     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.  
         [0021]     Calcium carbonate is an advantageous precipitation product which is precipitated from calcium hydroxide by way of carbon dioxide.  
         [0022]     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.  
         [0023]     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.  
         [0024]     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.  
         [0025]     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.  
         [0026]     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  
       [0027]     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:  
         [0028]      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;  
         [0029]      FIG. 2  is an illustration of the pump disperger according to  FIG. 1 , in direction of the arrows A;  
         [0030]      FIG. 3  is an illustration of a machine for producing a fiber web, shown in a simplified illustration; and  
         [0031]      FIG. 4  is a schematic of the control arrangement. 
     
    
       [0032]     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  
       [0033]     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&#39;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 .  
         [0034]     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.  
         [0035]     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 screw  18  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.  
         [0036]     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.  
         [0037]     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.  
         [0038]     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.  
         [0039]     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.  
         [0040]     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.  
         [0041]     The fibrous stock suspension is then routed from the area  46  into the pump disperger  12  where the carbon dioxide is supplied.  
         [0042]     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 A1 and DE 102 04 254 A1, wherein the German patent application “FL-high ash content” by the applicant whose reference is HPP 11846  DE also describes a possible device.  
         [0043]     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  
         [0044]     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.  
         [0045]     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 .  
         [0046]     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  
       [0000]    
       
           10  Device  
           12  Pump Fluffer  
           14  Reaction channel  
           16  Plates  
           18  Plug screw  
           20  Infeed screw  
           22  Channel or housing  
           24  Connection  
           26  Channel  
           28  Channel  
           30  Feeding screw  
           32  Connection  
           34  Drive shaft  
           36  Swirl cross  
           38  Outlet  
           40  Inlet  
           42  Pulper  
           44  Area  
           46  Area  
           48  Machine for the production of a fiber web  
           50  Fiber web  
           52  Headbox  
           54  Wire section  
           56  Press section  
           58  Dryer section  
           60  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