Paper making and fiber liberation – Processes and products – Reclamation – salvage or reuse of materials
Reexamination Certificate
1999-01-08
2001-04-10
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes and products
Reclamation, salvage or reuse of materials
C162SDIG009, C162S190000, C210S928000
Reexamination Certificate
active
06214166
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for recycling fillers and coating pigments from the preparation of paper, paper-board and cardboard found in the residual water sludges from coating plant waste waters, deinking plants, internal water treatment plants or separators, and to the use of thus obtained pigment slurries as fillers for the preparation of paper or as a pigment slurry for the preparation of a coating compound for the paper industry.
In the preparation of paper, the raw material, i.e. wood pulp, wood, fine straw pulp or rag pulp, is admixed with paper pulp, fillers and pigments in order to achieve a closed surface and thus to improve the properties of the paper, especially the whiteness, opacity and printability.
Almost all papers are admixed with fillers which confer a uniform look-through, improved softness, whiteness and touch especially to printing and writing papers. These fillers, mostly called “ashes” since they remain as ashes in the combustion analysis, are either added to the fiber suspension or applied in the coating step.
Uncoated papers contain up to 35% by weight of fillers, coated papers contain from 25 to 50% by weight thereof. The amount of fillers employed is highly dependent on the intended use of the paper. Highly filled papers have a lower strength and poorer sizing properties.
The filler content in the paper stock is usually between 5 and 35% by weight and consists of primary pigments or recycled coating pigments which may be derived from coating residuals or from coated rejects. In addition to the whiteness of the filler which is important for whitened papers, the grain size plays an important role since it has a strong influence on the filler efficiency and the physical properties of the paper, in particular porosity. The proportion of filler remaining in the paper is between 20 and 80% of the amount added to the fiber suspension. The efficiency depends on the nature of the filler and on the composition of material, the degree of beating, the fixing of the filler particles by resin and aluminum sulfate, the basis weight, the paper machine speed, the method of water removal and the mesh of the wire.
As judged by their consumption, the following products have rather great importance today as fillers and coating pigments: china clay, calcium carbonate, artificial aluminum silicates and oxide hydrates (alumina trihydrate), titanium dioxide, satin white, talcum and calcium silicate.
In the recycling of waste paper, the fillers and pigments are obtained as a waste product, especially in deinking plants. Such a waste product consists of, for example, 50% by weight of cellulose, 25% by weight of china clay, and 20% by weight of calcium carbonate; however, further small contents of calcium sulfate, titanium dioxide, talcum or other solids may also be present, and those mixtures may have a varying fiber content.
In EP 0 492 121 B1, the processing of waste paper as performed to date is described as involving the separation of these waste products from the process as a mixture of waste water and solids to yield a pure waste product which contains about 50% of solids and is disposed of in dumps. It is proposed to intimately mix the sludge-like mass of water and solids, and then to comminute this mixture of water and solids coarsely, finely or extremely finely, and only then to use it further with the addition of corresponding aggregates. The use of this material as a starting material for dyes, adhesives, fillers and hydraulic binders is suggested.
DE 40 34 054 C1 proposes a process for the recovery of raw materials from the mechanical residual water sludge of the paper industry. In this process, after the coarse junk has been separated off, the residual waste water sludge is first freed of its black particle content by centrifuging, and thereafter separated into fibers, fillers, pigments and agglomerates by fractional screening. The agglomerates are subjected to shearing and discarded while the fibers, fillers and pigments are selectively directed to reuse, optionally after further treatment.
From EP 0 576 177 A1, a process is known for the recycling and reuse of raw materials from the residual water sludges of the paper industry, characterized in that in a first process step, the sludge suspension is subjected to a first screening/purification process while it is relatively low-viscous, then concentrated, heated and passed through a dispersing apparatus, after which the resulting sludge is reused in paper production.
EP 0 554 285 B1 reports that all recovery processes are directed to the separation of materials from cycles which are per se less contaminated since the recycling of the so-called stuff or slush pulp, which consists of fibers and fillers, to the papermaking process is out of the question because of its higher dirt content. Accordingly, a process is described for recovering the usable fibers and fillers contained in the residual waste water sludge from the mechanical water treatment plant.
SUMMARY OF THE INVENTION
This process is characterized by adjusting a defined solids content, separating the coarse junk contents, separating the black particle contents, fractional fine-screening of the usable contents, and recycling the fiber contents and the filler and pigment contents to the raw material processing of the paper factory.
In the residual water sludges from coating plant waste waters, deinking plants, internal water treatment plants or separators, the fillers and coating pigments are often present in an agglomerated form and with low whiteness which limits the possibility of direct reuse in raw material processing, especially in the coat.
It has been the object of the invention to provide a process for recycling raw materials for papermaking, especially the fillers and coating pigments, while energy costs and cost of raw materials as well as shipping costs are saved.
According to the invention, the above object is achieved by a process for recycling fillers and coating pigments from the preparation of paper, paperboard and cardboard found in the residual water sludges from coating plant waste waters, deinking plants, internal water treatment plants or separators, characterized in that the residual water sludges containing the fillers and coating pigments are subjected to mixing and then milling together with fresh pigments or fresh fillers in the form of powders, fresh-pigment containing slurries and/or fresh-filler containing slurries to yield a pigment slurry.
By means of the above described process according to the present invention, a defined concentrated pigment slurry or filler slurry is obtained which can be employed in the preparation of paper, paperboard and cardboard.
In papermaking, it is usual to employ the fillers and coating pigments either as powders or in the form of concentrated slurries with a solids content of from 50 to 80% by weight. Those fillers and pigments are usually supplied by the manufacturers with the desired whiteness and grain size distribution. Now, the core of the present invention resides in supplying the pigment in a kind of “basic grade”, preferably as a solid or as a highly concentrated slurry, with a solids content of, for example, from 70% by weight to 85% by weight or more, and an average grain diameter of, for example, 50% less than 2 &mgr;m to 10 &mgr;m, especially 2 &mgr;m to 5 &mgr;m, and milling in an aqueous phase in situ in a satellite milling plant to obtain the desired whiteness and grain size. Thus, the above mentioned residual water sludges are not added to the ready-supplied or ready-prepared raw materials, but they are first given the desired whiteness and fineness by mixing and then milling together with fresh pigments or fresh fillers in the form of powders, fresh-pigment containing slurries and/or fresh-filler containing slurries, and then used as a filler or coating pigment. The mineral fillers and pigments mentioned are usually milled to give the desired grain size in a wet or dry milling method. In wet milling, a large amount of water is inherently required.
Alpha Calcitt Fullstoff GmbH
Brobeck Phleger & Harrison LLP
Nguyen Dean T.
LandOfFree
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