Patent Application
20090056888
1. Field of the Invention
The present invention relates to a process for loading a fibrous slurry with a filler.
2. Description of the Related Art
A number of processes from fiber loading technology for loading pulp fibers with calcium carbonate are already known. In U.S. Pat. No. 5,223,090 a process is described in which fibrous material with elongated fibers having a cell wall surrounding a cavity is used, the fibers having a moisture content which is sufficient to form a dewatered suspension of a pulp. In this case, the fibers have a moisture content which corresponds to a proportion of 40 to 50% of the weight of the fibers. The water is present substantially in the interior of the fibers and within the fiber walls. Alternatively, calcium oxide or calcium hydroxide is then added to the pulp, so that at least some of the calcium oxide or calcium hydroxide introduced will associate with the water present in the pulp. The fibrous material is then brought into connection with carbon dioxide, and simultaneously subjected to a shear mixing process, in order to produce a fiber material having a considerable quantity of calcium carbonate in the hollow interiors and within the fiber walls of the pulp fibers as a result of precipitation.
DE 102 04 254 A1 discloses a further process for loading a fibrous slurry. The process comprises the following steps: introduction of calcium hydroxide in liquid or dry form or of calcium oxide into the fibrous slurry, introduction of gaseous carbon dioxide into the fibrous slurry, and precipitation of calcium carbonate by the carbon dioxide.
What is needed in the art is a process for loading a fibrous slurry in which the advantages of the loading process are increased, and possibly a considerably higher loading effect can also be achieved.
The present invention provides a process, for producing fibrous material loaded with calcium carbonate (FLPCC or fiber loaded precipitated calcium carbonate), in particular for pulp production or for the use of pulp in papermaking. The raw fibrous material to be loaded is produced, for example, from recycled paper, from DIP (deinked paper), from secondary fibrous material, bleached or unbleached chemical pulp, groundwood of any type, any paper raw chemical pulp, bleached or unbleached sulphate pulp, finished material broke, linen, cotton and/or hemp fibers (predominantly used for cigarette paper) and/or any other raw paper material which is used in a paper machine. The process can be employed irrespective of the raw fibrous material to be loaded.
The area of application of the present invention extends to the production of paper and pulp and the process technology including the filler produced, and comprises areas of application in all grades of paper including packaging paper grades and the broke accumulating during production, which has a filler content of between 1% and 60% and/or has a white top layer with a filler content of between 1% and 60%. The filler content can preferably lie between 5% and 50%.
If a fibrous slurry is treated with fiber loading technology during the paper production, this results in a completely novel product, which has new and improved properties as compared to products known on the market. Such a process makes it possible to precipitate filler (calcium carbonate) directly during stock preparation in a paper mill, the filler being distributed uniformly and deposited exclusively on and in the fibrous material, in particular the paper fibers.
In the process according to the present invention, the fractionation can beneficially be carried out with hydrocyclones, which produce a high centrifugal field which, for example, corresponds to 200 times the effect of the earth's force of gravity.
Another possibility lies in the application of pressure screens, in particular if they are designed as fiber fractionators, that is to say are provided with fine screen openings. Of course, multi-stage separation systems and/or combinations of various separation principles are also conceivable.
The process according to the present invention is carried out advantageously such that the different effect of the loading of the fibrous material suspension is either utilized or, by means of appropriate measures, is partly or completely compensated again. In the loading process on which this invention is based, for example, a fibrous material suspension composed of various types of fibers is formed. On the basis of the different properties, it is possible that the loading is not the same in all the participating fibers. In addition, a statistical influence is conceivable such that, on the basis of parameter fluctuations during the precipitation process, be they temporal or local, the precipitation is not uniform. The different level of loading, that is to say the quantity of precipitated crystals adhering to the fibers, permits fractionation following the loading process, in which at least two fractions with a different level of loading are formed. Since it is to be assumed that more highly loaded fibers are heavier than less highly loaded ones, the designations heavy fraction for fibers with a higher level of loading and light fraction for fibers with a lower level of loading are chosen here.
Depending on the requirements on the process, two possibilities are conceivable in order to treat the different fractions further.
One embodiment of the present invention is to carry out the loading process again by way of recirculation of the light function in a part of the plant which is located before the loading, which is advantageous in particular, for example, when these fibers carried in the light fraction are able to achieve a significantly higher level of loading as a result of being loaded once more. The reason may be that, on account of the fiber properties, a longer period for loading or a higher concentration of the chemicals would be more beneficial. In such cases, it is more economical not to tune the process to the “heaviest fibers” but to optimize it economically as a whole.
Another embodiment of the present invention is to use the specific fractions formed differently during the paper or board production. As is known, during the production of paper for the individual grades and, possibly, also layers on the paper machine, different quality requirements are set. It is therefore possible to improve the entire process of paper production by means of the fractionation.
As compared with conventional processes for the production of a fibrous slurry, the loading makes it possible to achieve a higher level of refining with energetic benefits; for example, up to 50% of the refining energy can be saved. This has an effect in particular on all paper grades which pass through a refining process during the production and, above all, in those which have a high or very high level of refining, such as FL (FL fiber loaded) cigarette papers, FL printing and writing paper, FL sack kraft papers and FL filter papers. In these papers, which do not need fillers, free filler which is not deposited in or on the fibers can be removed after the refining process or before the introduction of the fibrous slurry into the machine chest or before the supply to the paper machine. The fibers themselves are, however, provided with filler on the outside and/or inside and outside, so that the positive effects of the fiber loading technology are maintained.
The loading has a positive effect on the production of all paper grades since, as a result of process-induced mechanical loadings in the various sections of the paper machine, such as in the press section, in the drying section or in the region in which the paper web is reeled up, the intermediate product produced and the end product to be produced is highly loaded mechanically by the use of reeling, winding, rewinding and converting machines.
A further advantage in using the technology according to the present invention in the paper grades listed above is that these can also be processed further in a calendar. The fact that, when the fiber loading technology is used, fiber loading particles are deposited in, around and on the fibers means that blackening, i.e. calendar blackening, is avoided.
In one embodiment of the present invention, the starting material used is aqueous fibrous material, in particular aqueous paper stock, from 0.1 to 20% consistency, preferably between 2 and 8%. Calcium hydroxide in aqueous or in dry form or calcium oxide is mixed into the aqueous paper stock in a range between 0.01 and 60% of the proportion of solids present. For the mixing operation, a static mixer, a mixing chest or a pulper system is used; in this case, a pH in the range between 7 and 12, preferably between 9 and 12, is used. The reactivity of the calcium hydroxide is between 0.01 and 10 minutes, preferably between 1 second and 3 minutes. Dilution water is mixed in accordance with predefined reaction parameters.
Carbon dioxide is mixed in accordance with the reaction parameters in a wet paper stock dimension. In the process, calcium carbonate is precipitated in the carbon dioxide atmosphere.
The process temperature preferably lies between −15° C. and 120° C., in particular between 20° and 90° C. Rhombohedric, scalenohedric and spherical crystals are preferably produced, the crystals having dimensions between 0.05 and 5 μm, in particular between 0.3 and 2.5 μm.
In order to produce a fibrous slurry loaded with calcium carbonate, static and/or movable, in particular rotating, mixing elements are used.
The process is preferably carried out in a pressure range between 0 and 15 bar, in particular between 0 and 6 bar. Likewise, the process is advantageously carried out at a pH between 6 and 10, in particular between 6.5 and 9.5. In this case, the reaction time is between 0.03 seconds and 1 minute, in particular between 0.05 and 10 seconds.
It is possible, for example, for precipitation product particles of rhombohedral form with a respective grain size in a range from about 0.05 to about 2 μm to be produced. In specific cases, it is also an advantage to produce precipitation product particles of a scalenohedric form with a respective length in a range from about 0.05 to about 2 μm and a respective diameter in a range from about 0.01 to about 0.05 μm.
According to a preferred refinement of the process according to the invention, the solids concentration of the fibrous slurry provided for precipitation is chosen to lie in a range from about 0.1 to about 60% and preferably in a range from about 15 to 35%.
According to an loading process, expedient practical refinement the carbon dioxide is added of the to the fibrous slurry at a temperature in a range from about 15 to about 120° C. and preferably in a range from about 20 to about 90° C.
The above-mentioned and other features and advantages of the present 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:
Corresponding reference characters indicate corresponding parts throughout the views. The exemplification set out herein illustrates an embodiment of the invention and is not to be construed as limiting in scope of the invention in any manner.
Referring now to the drawings and more particularly to
Then, directly or after intermediate treatment, such as refining, there follows fractionation of the loaded fibrous slurry S′. To this end, by way of example and advantageously, a cleaner plant with highly effective hydrocyclones 13 is used here. These form heavy fraction 2 and light fraction 1. Fibers which are more highly loaded with adhering fillers are specifically heavier than less highly loaded fibers. They can also be stiffer. The fractionation carried out in accordance with the invention, in particular, when sedimentation or centrifugal forces are used, makes use of these differences. It is therefore possible to assume that heavy fraction 2 contains fibers more highly loaded with fillers than light fraction 1.
Here, light fraction 1 is recirculated into the loading process, that is to say led into the feed of screw press 16. Heavy fraction 2 is made available as fibrous slurry 28, for example, to a paper machine, not shown.
The part of the plant shown in
As already mentioned, the fractionation of the loaded fibrous material can also be used to produce different stock qualities or to provide different qualities during paper production. For this procedure,
Headbox 32 in this example forms three layers. Light fraction 1 is advantageously led into the inner layer and heavy fraction 2 into the outer layers, in particular, when the higher strength and/or the better retention of the more highly loaded fibers are to be used. A plurality of layers can also be formed with the aid of a plurality of headboxes.
The stock approach system of the paper machine is not shown here.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 029 642.7 | Jun 2006 | DE | national |
This is a continuation of PCT application No. PCT/EP2007/002535, entitled “METHOD OF LOADING A PULP SUSPENSION WITH FILLER”, filed Mar. 22, 2007, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2007/002535 | Mar 2007 | US |
| Child | 12254857 | US |
