WO2003072875A2

WO2003072875A2 - Method for producing a fibrous web

Info

Publication number: WO2003072875A2
Application number: PCT/EP2003/050032
Authority: WO
Inventors: Klaus Doelle; Ralf Sieberth
Original assignee: Voith Paper Patent Gmbh
Priority date: 2002-02-28
Filing date: 2003-02-25
Publication date: 2003-09-04
Also published as: AU2003219139A8; AU2003219139A1; EP1481129A2; WO2003072875A3; DE10208983A1

Abstract

The invention relates to a method for producing a fibrous web, especially a web of paper or carton. According to the inventive method, the fibers are charged with a precipitation product, thereby producing crystalline precipitation product particles, supplying the fibers so treated in the form of a pumpable fiber suspension to a sheet forming process and controlling and/or regulating during said sheet forming process the filler distribution resulting across the web cross-section via a corresponding impingement with a vacuum.

Description

Process for producing a fibrous web

The invention relates to a method for producing a fibrous web, in particular paper or cardboard web.

It is known to use precipitated calcium carbonate (PCC = precipitated calcium carbonate) as a filler in papermaking. However, it is currently not technically possible to distribute the filler particles as evenly as possible through the sheet formed in order to achieve a constant ash content or level and to have the best possible printability.

Loading with an additive, e.g. Filler, for example by a chemical precipitation reaction, i.e. in particular by means of a so-called "fiber loading" process, as described, inter alia, in US Pat. No. 5,223,090. In such a "fiber loading" process, at least one additive, in particular filler, is embedded on the wetted fiber surfaces of the fiber material. The fibers can be loaded with calcium carbonate, for example. For this purpose, calcium oxide and / or calcium hydroxide is added to the moist, disintegrated fiber material in such a way that at least a part thereof is associated with the water present in the fiber material. The fiber material treated in this way is then subjected to carbon dioxide.

The aim of the invention is to provide an improved method of the type mentioned in the introduction. In particular, a more uniform distribution of the filler particles and better printability should be achieved.

This object is achieved according to the invention by a method for producing a fibrous web, in particular paper or cardboard web, in which the fibers are loaded with a precipitation product and thereby crystalline precipitate product particles are produced, the fibers treated in this way in the form of a pumpable fiber Material suspension are fed to a sheet formation process and during this sheet formation process the filler distribution resulting over the web cross section is adjusted or controlled and / or regulated by means of a corresponding vacuum application.

According to a preferred practical embodiment of the method according to the invention, crystalline precipitation product particles are of a size in a range from approximately 0.05 to approximately 0.5 μm, in particular in a range from 0.1 to approximately 2.5 μm and preferably in a range generated from about 0.3 to about 0.8 microns.

Advantageously, crystalline precipitate product particles can be produced in a size in a range from approximately 0.05 to approximately 0.1 μm and preferably in a range from approximately 0.3 to approximately 0.8 μm.

According to a preferred embodiment of the method according to the invention, the precipitation product is calcium carbonate.

It is also particularly advantageous if calcium oxide and / or calcium hydroxide is added to the fiber suspension to load the fibers with calcium carbonate and the precipitation is triggered by exposure to the fiber suspension with carbon dioxide.

For example, when loading the fibers with filler, calcium carbonate (CaCO ₃ ) can be embedded on the wetted fiber surfaces by adding calcium oxide (CaO) and / or calcium hydroxide (Ca (OH) ₂ ) to the moist fiber material, at least some of which of which can associate with the water of the amount of fiber. The fiber material treated in this way can then be exposed to carbon dioxide (CO ₂ ).

The term "wetted fiber surfaces" can encompass all wetted surfaces of the individual fibers. The case is also included, in particular where the fibers are loaded with calcium carbonate or any other precipitation product both on their outer surface and inside (lumen).

For example, the fibers may e.g. are loaded with the filler calcium carbonate, the attachment to the wetted fiber surfaces being carried out by a so-called "fiber loading" process as described as such in US Pat. No. 5,223,090. In this "fiber loading" process e.g. the carbon dioxide with the calcium hydroxide to water and calcium carbonate.

The specified method is particularly advantageous, for example, for the production of newspaper printing, in particular with an ash content of 5 to 20%, of SCA paper, of paper coated with LWC, of ULWC paper, of wood-free uncoated paper, of wood-free coated paper, of white liner and / or bleached cardboard can be used.

The specified process enables the production of a completely new type of paper with even filler distribution over the entire cross-section of the paper and on the surface. The paper manufacturer can thus produce a sheet of paper which results in a more even distribution of the filler content, which leads to savings in the raw material, mainly wood or secondary fibers, as well as improvements on the paper machine side, where fewer chemicals are required for the paper production process. It is now possible to make the same type of paper on a much lighter basis by achieving the same gloss after fillers are more evenly distributed, resulting in overall filler and fiber savings. On the paper product side, improvements in the physical and optical paper properties and thereby an improvement in the paper quality are achieved. Improvements in printing result from the fact that an even distribution of ink particles is made possible especially on the printable surface, since the paper surface has a lower roughness and a higher uniformity. With the specified method, better printability properties result. The process relates to both fabric and paper manufacturing. In the manufacture of fabrics, for example, secondary fibers or primary fibers obtained from waste paper pulp are disintegrated, stripped and cleaned. The filler material in the form of precipitated calcium carbonate (PCC = precipitated calcium carbonate) is added in this part of the fiber preparation relating to the fabric production in such a way that all fibers have a more uniformly distributed PCC layer. This is done by exposing the wood fibers or cellulose fibers to Ca (OH) ₂ and mixing the whole. The mixture is then exposed to CO ₂ in a reactor in which the CaCO ₃ (PCC) crystals are formed. The size of the crystals can be in a range from approximately 0.05 to approximately 0.5 μm, in particular in a range from approximately 0.1 to approximately 2.5 μm and preferably in a range from approximately 0.3 to approximately 0 , 8 μm. The crystals can be attached to the inside and outside of the fibers and can be provided as free PCC particles, ie as a solid in the water of the pulp. The fiber pulp treated in this way can then be fed to the sheet formation or paper formation process as a pumpable fiber suspension. Various steps such as dewatering, pressing, calendering are required to form a fibrous web or paper sheet.

By manufacturing the fabric in the manner indicated above, a new paper product can be created by modifying the manufacturing process on the paper machine side.

The following machines or devices are generally used to produce a paper web: Fourdrinier machine, hybrid former (DuoFormer ™ D), gap former (DuoFormer ™ CFD). The filler distribution that results over the cross section also results from the drawing purely by way of example. The use of some type of forming device results in a more or less low ash content on the paper surface side, which can negatively influence the printability of the paper. Even if a surface coating of light weight is subsequently used on the paper, there is preferably no filler distribution on the top surface itself. The coating surface penetrates the openings or gaps but does not cover the paper surface, which makes it difficult to print on the paper. The printing ink must cover the color of the fibers. Since white light consists of the sum of all complementary rainbow colors, white light radiation as such does not exist. This means that a certain pigment size is only good for one color. Other colors are reflected differently. Transferred to paper, this means that a high filler content is required to produce a higher whiteness if the particles are not evenly distributed. The coating surface adds more white pigments to the paper, making the white surface thicker, so the light beam's runtime is longer, which results in a white color. For example, if you paint a room of brown or black color, four or five layers of white paint are required to cover the base color. The same is true for paper, where more white pigments are required to mask black color to produce high opacity paper. The whiter the paper, the less ink is needed to get the same result. In other words, if the filler particles are evenly spaced, less printing ink is required and the ink also has to penetrate less into the base paper sheet in the z direction. A better filler distribution can be achieved by adjusting the vacuum on the formers (cf. in particular also the blue or dashed curve in FIG. 1 of the drawing). With the use of pulp to produce a precipitate loaded into the fibers, in conjunction with any of the various formers combined with a low degree (generally minus 1.5m to 4m) or high degree vacuum (generally minus) vacuum 4 m to 7.5 m) and preferably of medium degree (generally minus 2 m to 6 m) and a device for a coating of (very) light weight, a much better filler distribution and a better topographic surface of the paper can be found in the paper sheet, ie a more uniform paper surface can be achieved. This means in particular in particular, also lower filler fluctuation, better running properties (runnability) of the paper machine and a lower need for retention aids and opacity-increasing agents.

As for SC papers, where the fibers are plasticized by pressure and heat even during the calendering process, i.e. the paper surface is smoothed, a much lower calendering effort is required to achieve a certain quality of the calendered paper.

With a better filler distribution in the paper sheet, less coating and, consequently, less drying is required, since the fibers are better covered with filler and the relevant covering or colored layer (coating).

The printability of the paper can also be improved, for example, by using a multi-layer headbox with which the filler distribution (PCC) in the paper can be influenced in the direction of the cross profile (X-section). However, this is only possible for paper types that have basis weights that allow the use of multi-layer headboxes (> 80 g / m ² ).

Multi-layer headboxes cannot be used for extremely lightweight grades such as Newsprint (40-50 g / m ² ) and phone book paper (28-40 g / m ² ). However, it is conceivable to use multi-layer headboxes for basis weights above 50 g / m ² .

The so-called "linting" is prevented by the "FL" technology, ie the so-called "fiber loading" technology, whether with a modified (multilayer) or conventional (single-layer) headbox. "Linting" is the extraction of the fillers during dewatering, ie a so-called "first pass retention" of the fillers. Improvements in the range from 5 to 50%, preferably in the range from 10 to 25%, are possible. "FL" fabric, ie fabric treated according to the "FL" technique, has about 25 to 200 times higher "freeness" than conventionally manufactured fabric, based on the refining process.

The base paper produced in this way has a higher drainage, which can be influenced with a modified drainage (DuoFormer, Fourdrinier, Gap-Former).

The higher dewatering results in a higher dry content after the press section. This means, for example, that the paper enters the press with a higher or the same dry content, but leaves the press with a higher dry content (1% higher dry content saves about four drying cylinders). The improved drying range could be, for example, in a range from approximately 0.1 to approximately 5% and preferably from approximately 0.5 to approximately 2%.

An application of the "FL" technique described above is particularly suitable for papers that require good printability with the highest possible degree of filler with the lowest possible fiber content in the paper.

The advantage is that the filler particles are located on the fiber and not, as with conventional fillers, between the fiber cavities. This improves printability because the printing ink is applied to the filler particles and does not have to cover the fiber first. As a result, the printing ink penetrates less into the fibers.

The uniform filler distribution in a given paper sheet is thus achieved by using the so-called "fiber loading" process, by which the filler particles known as precipitated calcium carbonate (PCC) are deposited on, in and between the fibers. The "fiber loading" process is used in the fabric manufacturing facility known as stock preparation. The treated fabric can be refined before or after to prepare it for the paper machine process.

Once the material treated by a "fiber loading" process has been applied to a respective sheet forming screen, a paper sheet with an even filler distribution is produced. The filler content can be, for example, about 50% based on the solid mass weight. Since up to 25% of the total ash content is deposited in and on the fibers, the result is that the sheet already has an ash content in the transverse direction of 25% of the desired total ash content. The filler retention in the paper machines is in a range of about 30 - 60% based on the total filler content. This means that the base ash content in the transverse direction of a "FL" treated sheet is in a range from about 50% to about 85%, compared to which a conventional process reaches values between 30% and 60%. During the subsequent pressing and dewatering process in the paper machine, the filler content in the transverse direction can be improved. While the goal in the conventional paper sheet forming process is up to 30 to 70% uniformly distributed filler content in the transverse direction, depending on the paper production process, when using "FL" -treated substance in the paper machine, the filler content evenly distributed in the transverse direction paper sheet produced is around 55% or even 95% based on the paper manufacturing process.

A uniform filler distribution leads to better gloss values. Better gloss values mean a higher whiteness of the sheet. Since white light is formed by the sum of all complementary rainbow colors, white light radiation as such does not exist. This means that a pigment size is only good for one color. Other colors are reflected differently. On paper, this means that a high filler content is required to produce a higher whiteness if the particles or particles are not evenly distributed. A uniform distribution of the filler particles can achieve a higher whiteness with a lower filler content, since the Filler particles are evenly spaced across the cross-section of the paper and are evenly distributed on the fibers. The optimal crystal size is in a range from about 0.05 to about 0.1 μm and preferably in a range from about 0.3 to about 0.8 μm.

By using the optimal crystal size, less filler is required because the filler pigments are evenly distributed over the fibers to achieve optimal optical properties. Another advantage is that more filler is retained by the paper forming process because smaller particles allow better penetration within the sheet. This means that the sheet itself is filled with filler from the inside to the outside, i. H. better filler retention is achieved through the sheet formation process, which results in an even distribution in the paper, which results in higher paper production by treating the fabric in the following manner:

The fiber suspension previously mixed with Ca (OH) ₂ is in a crystallization unit, for example a fluffer, refiner, diperger or the like, at a consistency or solids concentration in a range from about 5 to about 60%, preferably in a range from about 15 to about 35%. The Ca (OH) ₂ can be added in liquid or dry form. The pulp or dry pulp is exposed to CO ₂ . The CO ₂ can e.g. B. at temperatures in a range between about -15 ° C and about 120 ° C and preferably at temperatures in a range between about 20 ° C and about 90 ° C.

The fiber suspension enters the gas zone, where each individual fiber is exposed to a gas atmosphere, followed by the precipitation reaction, which immediately results in the CaCO ₃ . The shape of the CaCO ₃ crystals can be, for example, rhombohedral, scalenohedral or spherical, the amount of crystal in particular being dependent on the temperature range chosen for the fiber suspension and on the CO ₂ and Ca (OH) ₂ content in the fiber suspension. To- After the pulp suspension with the crystals formed has passed the gas zone, the PCC or the pulp suspension with the crystals in the lumen, on the fiber and between the fibers is passed through a rotor and a stator, where the distribution of the crystals in the pulp suspension with mixing is completed with low shear.

As the fiber / crystal suspension passes the rotor, a shear distribution occurs which brings about a size distribution of the crystals of approximately 0.05 to approximately 0.5 μm and preferably approximately 0.3 to approximately 1.0 μm.

The shape of the filler particles used is, for example, rhombohedral with a respective cube size in a range from approximately 0.05 to approximately 1 μm or scalenohedral with a respective length in a range from approximately 0.05 to approximately 1 μm and a respective diameter in one Range from about 0.01 to about 0.5 μm, depending on the type of paper to be made.

The further the fiber suspension is found on the rotor disk, the lower the shear, depending on the H ₂ O added for dilution. The concentration of the fiber suspension passing the rotor disk is about 0.1% to about 50% and preferably about 35% to about 50%.

The pressure acting on the CO ₂ supply line is in particular in a range from approximately 0.1 to approximately 6 bar, and preferably in a range from approximately 0.5 to approximately 3 bar, in order to provide a constant CO ₂ supply to the gas ring for it - to ensure the desired chemical reaction. The CO ₂ supply and thus the precipitation reaction which produces the CaCO ₃ can be controlled and / or regulated via the pH value.

For example, pH values in a range from 6.0 to approximately 10.0 pH, preferably in a range from approximately 7.0 to approximately 8.5 pH, can be envisaged for the final reaction of the CaCO ₃ crystals. The energy used for this process can be in a range between approximately 0.3 kWh / t and about 8 kWh / t and preferably in a range between about 0.5 kWh / t and about 2.5 kWh / t. Dilution water can be added and mixed with the pulp suspension to obtain a final dilution in which the pulp suspension produced with filler has a consistency or solid concentration in a range from, for example, about 0.1% to about 16%, preferably in a range from about 2 % to about 6%. The pulp suspension is then exposed to the atmosphere in a machine, a container or the next process machine.

The rotational speed of the rotor disk can be on the outside diameter, in particular in a range from approximately 20 to 100 m / s and preferably in a range from approximately 40 to approximately 60 m / s.

The speed through the rotor and the stator is in a range of, for example, about 0.02 m / s to about 0.55 m / s and preferably in a range of about 0.05 m / s and about 0.2 m / s , depending on the filler content and the crystal size.

According to current knowledge, the crystal filler content, the crystal size and the speed are linearly linked.

The gap between the rotor and the stator is, for example, approximately 0.5 to approximately 100 mm and preferably approximately 25 to approximately 75 mm.

The diameter of the rotor and the stator can in particular be in a range from approximately 5 m to approximately 2 m.

The reaction time is, for example, in a range from about 0.01 min to 1 min, preferably in a range from about 0.1 sec to about 10 sec. The method described above enables the production of individual particles that are equally spaced from one another and attached to the fibers, covering the fibers in the required manner.

In Figures 1 to 10 of the accompanying drawing, purely as an example, different filler or ash distributions for different mold sections are shown schematically.

FIG. 10 of the drawing shows the influence of certain factors on the filler distribution in the z direction purely by way of example and schematically.

FIG. 11 of the drawing shows, purely by way of example and schematically, a comparison of a total ash distribution in a conventional paper with a possible total ash distribution in a "FL" paper product.

Claims

Process for producing a fibrous web

claims

Process for the production of a fibrous web, in particular paper or cardboard web, in which the fibers are loaded with a precipitate and thereby crystalline filler product particles are produced, the fibers treated in this way in the form of a pumpable fibrous suspension

Sheet formation process are supplied and during this sheet formation process the filler distribution resulting over the web cross-section is adjusted or controlled and / or regulated via a corresponding vacuum application.

A method according to claim 1, characterized in that crystalline falling product particles of a size in a range from about 0.05 to about 0.5 microns, in particular in a range from about 0.1 to about 2.5 microns and preferably in a range of about 0.3 to 0.8 μm can be generated.

A method according to claim 1 or 2, characterized in that crystalline precipitation product particles of a size in a range from about 0.05 to about 0.1 microns and preferably in a range from 0.05 to about 0.1 microns are generated.

Method according to one of the preceding claims, characterized in that the precipitation product is calcium carbonate. Method according to one of the preceding claims, characterized in that calcium oxide and / or calcium hydroxide are added to load the fibers with calcium carbonate and the precipitation is triggered by exposure to the fiber suspension with carbon dioxide.

Method according to one of the preceding claims, characterized in that the calcium hydroxide is added to the fiber suspension in liquid form.

Method according to one of the preceding claims, characterized in that the calcium hydroxide is added to the fiber suspension in dry form.

Application of the method according to one of the preceding claims for the production of newspaper printing.

Application of the method according to one of the preceding claims for the production of SCA paper.

Application of the method according to one of the preceding claims for the production of paper coated with LWC.

Application of the method according to one of the preceding claims for the production of ULWC paper.

Application of the method according to one of the preceding claims for the production of wood-free uncoated paper. Application of the method according to one of the preceding claims for the production of wood-free coated paper.

Application of the method according to one of the preceding claims for the production of white-covered liner.

Application of the method according to one of the preceding claims for the production of bleached cardboard types.