WO2006097180A1

WO2006097180A1 - Method and device for charging fibers contained in a fibrous suspension with a filler

Info

Publication number: WO2006097180A1
Application number: PCT/EP2006/001587
Authority: WO
Inventors: Klaus Doelle; Stefan Hartmann
Original assignee: Voith Patent Gmbh
Priority date: 2005-03-17
Filing date: 2006-02-22
Publication date: 2006-09-21
Also published as: DE102005012168A1

Abstract

A method for charging fibers contained in a fibrous suspension with calcium carbonate comprises the following steps: introducing calcium hydroxide in a liquid or dried form or calcium oxide into the fibrous suspension; dewatering the fibrous suspension until a fibrous suspension is obtained that is no longer liquid but still moist, the fibrous suspension being at least partially thickened in a screw (1); introducing gaseous carbon dioxide into the moist fibrous suspension; and precipitating the calcium carbonate by means of the carbon dioxide. The inventive method is characterized in that the fibrous suspension is heated by steam in the area of the screw (1).

Description

Method and device for loading fibers contained in a pulp suspension with filler

The invention relates to a method for charging a pulp suspension with

Cellulose fibers with calcium carbonate with the following procedural steps: introduction of calcium hydroxide in liquid or dry form or from

Calcium oxide in the pulp suspension,

Dehydrate the pulp suspension until a no longer liquid but still moist

Pulp suspension is formed, wherein the pulp suspension is at least partially compressed in a screw, introducing gaseous carbon dioxide into the moist pulp suspension,

Precipitation of calcium carbonate by the carbon dioxide.

Several processes for loading pulp fibers with calcium carbonate are already known. US 5,223,090 discloses a process employing fibrous material having elongated fibers with a cell wall surrounding a cavity, the fibers having a humidity sufficient to form a dewatered pulp slurry. The fibers have a moisture content corresponding to a proportion of 40 to 50% of the weight of the fibers. The water is essentially present inside the fibers and inside the fiber walls. Subsequently, alternatively calcium oxide or calcium hydroxide is added to the pulp so that at least part of the incorporated calcium oxide or calcium hydroxide is associated with the water present in the pulp. Subsequently, the fibrous cellulosic material is contacted with carbon dioxide while simultaneously subjected to a shear mixing process to produce a fibrous material having a substantial amount of calcium carbonate in the hollow interior and within the fibrous walls of the cellulosic fibers.

Further methods and arrangements for loading fibers contained in a pulp suspension with a filler or auxiliary substance are known from DE 101 07 448 A1 and DE 101 13 998 A1.

DE 197 12 653 A1 discloses a method and a device for dispersing paper pulp. In this case, the paper pulp is converted into fine Faserstoffkrümel so that it can be heated relatively quickly to the temperature required for dispersing. The heating and dispersing of the pulp takes place according to the invention in the same apparatus, in particular in a disperser.

It is the object of the invention to provide another method for loading a pulp suspension.

According to the invention, this object is achieved in that the pulp suspension is heated by steam in the region of the screw.

The inventive method is suitable for all types of paper and board, but especially for tissue paper whose production requires a large amount of water. Tissue paper is produced at a very low basis weight, depending on the final product to be produced, for example, cellulosic filling material (8 to 30 g / m ² ), cosmetic or tissue paper for the sanitary sector (14 to 25 g / m ² ), sanitary paper (8 to 30 g / m ² ), napkin paper (20 to 30 g / m ² ) and tissue paper (20 to 40 g / m ² ) is between 8 and 40 g / m ² . Another factor is the low degree of grinding of the tissue papers, which is required for a high suction and drying capacity of the end products. As is known, the freeness is an important parameter for determining the mechanical properties of each paper product.

The invention describes a method for producing a loaded one

Pulp suspension and the resulting papers, for which essentially a sulphate or sulphate bleached pulp suspension is used under

Circumstances in a mixture with another pulp suspension, the subsequently processed on a machine with a cylinder or a Fourdrinier Yankee machine, or on another paper machine, regardless of whether the product comprises a filler material obtained by a precipitation process, such as in a refining process, in another manufacturing process. The material that is currently used in a conventional process is currently either a precipitated material or an artificial material, such as plastic. As calcium carbonate, talc, silicate, etc. The conventional materials can be replaced by the fiber-loading process. The products concerned are: sanitary papers, tissue paper, wax tissue paper, wrapping papers, for example, for fruits and vegetables, various toilet, sanitary or cosmetic papers, tissue papers, napkin or diaper papers, wipes, wax papers, wrapping papers, all for sanitary, but also for non-sanitary use, as well as various other tissue products.

The invention is also suitable for the production of graphic papers, cardboard. and packaging papers of all kinds, sack paper of all kinds, filter paper, etc. Likewise, the invention can be used in the production of cigarette paper. The following applies to this: Cigarette paper is a paper with a basis weight of 16 to 26 g / m ² . It should be very thin, smoldering and tasteless. In addition, it should have good optical values with respect to the whiteness. The glowing power is usually achieved through impregnation to leave a good-looking white ash. Cigarette paper is mostly made from linen or hemp fibers, cotton, sulphate pulp, papermaking pulp and other fiber sources. The filler content of cigarette paper is between 5 and 40%, with 30% being the standard value.

Packaging papers and cardboard can be divided into three main classes:

Crate board for packaging applications, crate board for consumer packaging applications and specialty papers such as wallpaper,

Spine, etc .. Packaging papers are usually called multilayer - A -

Product produced with basis weights above 150 g / m ² . The freeness varies from 600 to 50 CSF or 20 to 80 ⁰ SR, based on the final product produced.

Sack papers require high porosity and high mechanical strength to meet the high demands of rough handling during filling and during use, such as cement bags. The paper must be strong enough to absorb shock, and accordingly have a high rate of energy absorption. The sack paper must also be porous and sufficiently air permeable to ensure easy filling. Sack papers are commonly produced as a product having basis weights between 70 and 80 g / m ² from a long fiber kraft pulp and with a freeness between 600 to 425 CSF or 20 to 30 ^° SR. In addition, a medium freeness, as described above, is sought, which is usually achieved by high consistency milling, while conventional grades of paper, such as graphic papers, use low consistency milling. The result of the high consistency milling are good connections between the fibers and a high porosity. The sack kraft paper is predominantly made from bleached and unbleached fibers, with a filler content of 5 to 15% in the sack paper produced.

Filter paper requires a high controlled porosity and pore distribution. It must have a sufficiently high mechanical strength to counteract the flow of the medium to be filtered.

Filter paper is produced with a basis weight of 12 to 1200 g / m ² . For example, for an air filter it is between 100 and 200 g / m ² , for an oil and fuel filter between 50 and 80 g / m ² , for a food filter up to 1000 g / m ² , for a coffee filter up to 100 g / m ² , with a teabag between 12 and 20 g / m ² and with a vacuum cleaner bag between 100 and 150 g / m ² . All filters are bleached and bleached from a variety of fibers, such as pulp fibers unbleached fibers, Kraft pulp, DIP (deinked) paper, recycled fiber, TMP (thermo-mechanical) paper, etc. For all these papers, the invention is suitable, but especially for the production of tissue papers for various applications.

According to the invention, a new process for producing a fibrous web, in particular a tissue web and new tissue products, is created, in which the process of fiber loading (loading of the fibrous suspension with calcium carbonate) is integrated. This process allows the production of individual calcium carbonate particles which are equally spaced and which adhere well to and coat the fibers uniformly. This is achieved through an online manufacturing process in which the calcium carbonate is generated simultaneously with the processing of the pulp suspension. Thus, filler particles are introduced into the pulp suspension according to the following variables or constraints: a wet pulp suspension, calcium or calcium hydroxide in liquid or dry form, carbon dioxide, a gas feed area, a stator co-operating with a stator, producing the crystals in a gas atmosphere without the use of mixing energy.

After being mixed with calcium hydroxide, the pulp suspension is introduced into a disperser, fluffer or refiner, the pulp suspension having a solids content of between 5 and 60%, in particular between 15 and 35%. Insofar as the term "disperser" is used in the context of this patent application, this always alternatively means a fluffer, refiner or crystallizer.

The pulp suspension is contacted with carbon dioxide. The carbon dioxide can be added at temperatures between -15 ° C and 120 ° C, especially in a temperature range between 20 ° C and 90 ° C. The pulp suspension enters a gas zone in which each individual fiber is exposed to a gas atmosphere, so that directly the reaction of the Calcium hydroxide to calcium carbonate occurs. This forms different crystal types, for example rhombohedral or scalenohedral crystals. The crystal size depends on the selected temperature range, the carbon dioxide and the Calciumhydroxdid content in the pulp suspension. After this pulp suspension has passed through a zone for the introduction of carbon dioxide and the precipitated calcium carbonate crystals have formed in the lumen on the fibers and embedded between the fibers, they are passed between a stator and a rotor, whereby the final position of the crystals in the pulp suspension induced becomes; Here, only a low shear energy is used.

As the pulp suspension passes the rotor, a distribution of the crystal sizes is caused due to the shear, which is in the range between 0.05 and 0.5 μm, preferably between 0.3 and 2.5 μm. The shape of the filler particles is substantially rhombohedral with a spatial size in the range between 0.05 and 2.0 microns or scalenohedrisch with a length between 0.05 and 2.0 microns and a diameter between 0.01 and 0.5 microns in Dependence on the paper quality used.

The farther the pulp suspension moves outwardly on the rotor disk, the less shear energy acts on the pulp suspension due to the water supplied from the outside for dilution. The concentration of the pulp suspension flowing past the rotor disk is between 0.1 and 50%, preferably between 5 and 35%. The pressure used in the carbon dioxide feed line is between 0.1 and 6 bar, preferably between 0.5 and 3 bar, to ensure uniform delivery of the carbon dioxide and to maintain the chemical reaction. Since the carbon dioxide is a compressible gas, the feed can be increased slightly with increasing pressure to ensure complete reaction with the calcium hydroxide. The supply of carbon dioxide and thus the precipitation reaction to calcium carbonate is controlled by the pH. This should be between 6.0 and 10.0, preferably between 7.0 and 8.5. The energy used in this process is between 0.3 kWh / t and 8 kWh / t, preferably between 0.5 kWh / t and 4 kWh / t. In addition, dilution water is added and mixed with the pulp suspension to achieve a final dilution of the filler-laden pulp suspension ranging between 0.1 and 16% solids, preferably between 2 and 6% solids. Subsequently, the pulp suspension is introduced at normal pressure in a subsequent machine or chest or in a paper machine.

The rotational speed of the rotor is at its outer diameter between 20 and 100 m / s, preferably between 40 and 60 m / s. The gap between the rotor and the stator has a width between 0.5 and 100 mm, preferably between 25 and 75 mm. The diameter of the rotor and the stator is between 0.5 m and 2 m. The reaction time is preferably between 0.01 and 60 seconds, preferably between 0.1 and 10 seconds. With these constraints, a pulp suspension can be made with evenly spaced particles adhering to the fibers.

A pulp suspension treated by the fiber loading process has a higher freeness degree (freeness) or lower SR values. These values range between 5 and 100 ml of CSF (CSF = Canadian Standard

Freeness) or in the range between 0.2 and 15 ° R depending on the

Freeness or freeness. Additionally have loaded with calcium carbonate particles

Fibrous fibers have a lower water retention level of between 2 and 25%, depending on the pulp used. This will be a more economical

Production of paper allows, because the water faster out of the

Pulp suspension can be removed, and the sheet dries faster. For

For applications of tissue paper where there is no need for filler, the free precipitated calcium carbonate, i. H. the calcium carbonate not bound in or on the fibers to be removed by a washing process before the

Pulp suspension is forwarded to a paper machine, or even more before the grinding process. Also in this case, calcium carbonate-covered fibers remain, giving the advantage of good drainability and good drying as well as less rewetting of the finished tissue product. The fiber loading process can be implemented as needed for the final product before or after a milling process. Since the loading of the pulp gives higher freeness values, a higher freeness can be achieved, which leads to better mechanical properties of the final product. The better water retention and better drying also have a positive effect if the product is to be printed later.

Advantageous embodiments of the invention will become apparent from the dependent claims, the description and the drawings.

Particularly advantageous is a method in which the vapor is introduced from openings in a shaft of the screw in the pulp suspension. The openings are in the lateral surface and / or additionally on a side facing a downstream transfer cylinder end face.

A further advantage results if the pulp suspension is subsequently converted and dispersed in a pulp crumb in a comminution step.

Another advantage is a method in which the pulp suspension is mixed in an arrangement with relatively rotating plates, in particular with a stator and a rotor, with low shear energy.

It is advantageous if the pulp suspension is comminuted and loosened between the stator and the rotor.

The invention also relates to an arrangement for carrying out one of the methods listed above. The arrangement is characterized in that it has a

Screw for thickening the pulp suspension and heating the Fiber suspension by means of steam, one of the screw in the transport direction of the pulp suspension downstream transfer cylinder and a disperser comprises.

An advantage is an arrangement in which the screw is designed as a screw press. Preferably, the screw comprises a shaft formed as a hollow shaft through which heating steam can be passed, which can be introduced from openings in the shaft in the pulp suspension.

Likewise, an embodiment of the arrangement is advantageous in which the transfer cylinder comprises rotation crushers for receiving a component of movement of the pulp suspension in the direction of rotation.

Likewise, it is advantageously provided that the disperser comprises a distribution cross.

Preferably, the crystalliser has a disc set of triangular finishes whose teeth are e.g. seen in the circumferential direction have a triangular contour.

An advantageous arrangement is also characterized in that supply lines for introducing reactants, in particular chemicals, are connected to the transfer cylinder and / or the disperser.

A further advantageous arrangement is that at the Disperger a circular surrounding supply line for water is connected.

The invention will be described in detail in an embodiment with reference to the single figure. This represents a sectional view of a screw press, one of these downstream transfer cylinder and a Dispergers or crystallizer. ,

- 10 -

A pulp suspension provided in a manner known per se, for example from DE 101 07 448 A1, with filler (calcium oxide or calcium hydroxide), fibers, aggregates and water, is introduced into a screw press 1 (FIG. 1), in which the pulp suspension is compressed, whereby water is pressed out of the pulp suspension through openings in the jacket wall 2 of the screw press 1.

The screw press 1 comprises a motor-driven hollow shaft 3, through which heating steam is introduced in the direction of an arrow A _1, which also denotes the direction of movement of the pulp suspension or pulp. This flows out of openings 4 of the hollow shaft 3 out to heat the pulp suspension. Around the hollow shaft 3 around a coil 5 extends, which presses the pulp suspension so that the water escapes from the holes in the casing wall 2.

It can also be provided that additional steam escapes from the front end 6 of the hollow shaft 3. By means of flaps 7, which are actuated by a motor, in particular hydraulically, the area of the screw press 1 can be separated from a subsequently arranged transfer cylinder 8, when at the beginning of operation within the screw press 1 only a certain minimum solids content of the pulp suspension is to be achieved.

The transfer cylinder 8 is provided with rotation crushers 9, d. H. with projections on the inside of its shell wall, which receive the rotational component in the movement of the pulp suspension. Subsequently, this is forwarded to a distribution cross 10 of a disperser or crystallizer 11.

From the distribution cross 10, the pulp suspension passes through a gap of a crystallizer pulley set 12 comprising a stator 13 and a rotor 14. The rotor 14 preferably moves together with the distribution cross 10. The stator 13 and the rotor 14 each have projections with a triangular cross-section to comminute the pulp. A shaft 15, on the rotor 14 is mounted, can be moved in the direction of a double arrow B to change the gap width of the gap between the stator 13 and the rotor 14. It is understood that alternatively and / or additionally, the stator can be arranged to be movable in the direction of arrow B.

In the area in which adjoins the transfer cylinder 8 of the crystallizer 11, a supply line 16 is provided for supplying carbon dioxide. It can also be provided several, distributed over the circumference leads. Or it is an annular ring over the circumference of the transfer cylinder 8 extending, supplied by one or more leads with carbon dioxide feed ring available to achieve the most uniform distribution of carbon dioxide in the pulp suspension. Likewise, at least one supply line 17 for reaction chemicals is provided in the connection region of the transfer cylinder 8 to the crystallizer 11.

Around the crystallizer 11 extends a ring 18 which serves to supply dilution water. This is pressed under pressure into the crystallizer 11 in order to compensate for the pressure with which the carbon dioxide is introduced into the pulp suspension. At one point on the crystallizer 11, a drain line 19 for the pulp suspension, d. H. the Accept, provided, which is forwarded from there to further processing units, for example, to a refiner, or directly to a machine for producing a fibrous web.

Characterized in that according to the invention, the pulp suspension is already heated in the screw press 1 and not only in the crystallizer 11, the temperature and pressure of the heating steam can be adjusted independently of the required conditions in the crystallizer 11 boundary conditions.

Claims

claims

1. A method of charging a pulp suspension with cellulose fibers with calcium carbonate, comprising the following steps:

Introduction of calcium hydroxide in liquid or dry form or of calcium oxide into the pulp suspension, dewatering of the pulp suspension until a no longer liquid, but still moist pulp suspension is formed, wherein the pulp suspension is at least partially compressed in a screw (1),

Introduction of gaseous carbon dioxide into the moist pulp suspension,

Precipitation of calcium carbonate by the carbon dioxide, characterized in that the pulp suspension in the region of the screw (1) is heated by steam.

2. The method according to claim 1, characterized in that the vapor from openings (4) in a shaft (3) of the screw (1) is introduced into the pulp suspension.

3. The method according to claim 1 or 2, characterized in that the pulp suspension is then converted and dispersed in a comminution step in fine pulp crumbs.

4. The method according to claim 3, characterized in that the pulp suspension in an arrangement (11) with relatively rotating plates, in particular with a stator (13) and a rotor (14) is mixed with low shear energy.

5. The method according to claim 4, characterized in that the pulp suspension between the stator (13) and the rotor (14) is crushed and loosened.

6. Arrangement for carrying out a method according to aφ. of claims 1 to 5, characterized in that it comprises a screw (1) for thickening the pulp suspension and the

Heating the pulp suspension by means of steam, one of the screw (1) in the transport direction of the pulp suspension downstream transfer cylinder (8) and a disperser or crystallizer (11).

7. Arrangement according to claim 6, characterized in that the screw is designed as a screw press (1).

8. Arrangement according to claim 6 or 7, characterized in that the screw comprises a shaft formed as a hollow shaft (3) through which heating steam can be passed, which can be introduced from openings (4) in the shaft (3) in the pulp suspension.

9. Arrangement according to one of claims 6 to 8, characterized in that the transfer cylinder (8) comprises rotation crushers (9) for receiving a component of movement of the pulp suspension in the direction of rotation.

10. Arrangement according to one of claims 6 to 9, characterized in that the disperser or crystallizer (11) comprises a distribution cross (10).

Having 11. Arrangement according to claim 10, characterized in that the disperser or crystallizer (11) has a designed as Dreiecksrefinergärnitur disc set (12).

12. Arrangement according to one of claims 6 to 11, characterized in that the transfer cylinder (8) and / or the disperser (11) supply lines (16,

17) for introducing reactants, in particular chemicals, are connected.

13. Arrangement according to one of claims 6 to 12, characterized in that on the Disperger (11) a circular surrounding this supply line (18) is connected for water.