Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/01—Waste products, e.g. sludge

Definitions

• the present invention relates to a process for recycling cleaner rejects from the preparation of paper, paperboard and cardboard and to their use for the preparation of paper in the paper stock or as a coating slurry for the paper industry.
• the raw material i.e., wood pulp, wood, fine straw pulp or rag pulp
• repulped half-stock 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.
• 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.
• primary pigments or recycled coating pigments which may be derived from coating residuals or from coated rejects.
• 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.
• cleaner rejects obtained therein also referred to as coated rejects
• coated rejects mainly consist of minerals and fibers and may comprise from 1 to 4% of the total volume of the paper produced.
• they are disposed of in dumps.
• the total amount of the cleaner rejects obtained and passed to disposal is not reduced.
• the object of the invention is to provide a process for the recycling of cleaner rejects while energy costs and costs of raw materials, shipping costs as well as costs for dumping are saved.
• cleaner rejects especially from centrifugal cleaners, from the preparation of paper, paperboard and cardboard, characterized in that cleaner rejects, which contain fibers, coating pigments and/or fillers, are milled to the desired grain size distribution, optionally with the addition of water, coating pigment, fresh filler and/or filler slurry, and employed as a raw material for the paper stock and/or coating slurry.
• the cleaner rejects which are usually solid, contain valuable raw materials which can be recovered by means of the present invention and, after milling, recycled to various processes of papermaking.
• the cleaner rejects from paper mills which prepare coated paper or cardboard grades contain large quantities of coating pigment flakes. The thicker the coating layer, the more difficult is the recovery of the flakes by the prior art technologies. Double-coated grades or coated cardboard grades may be mentioned here as particular examples.
• Another group of paper industries are the SC-paper producing plants, which lose large amounts of fillers through cleaner rejects.
• the cleaner rejects are milled and optionally admixed with water, coating pigment, filler and/or filler slurry.
• the cleaner reject slurry or the milled powder is then recycled to the papermaking process for the paper stock and/or as a coating slurry.
• the distribution of the particle sizes of the cleaner rejects is essentially the same as the original distribution in the coating pigments, fillers or filler/pigment slurries.
• more than 95% of the total cleaner rejects, or even the full amount thereof, can be recovered and recycled to production.
• the cleaner rejects processed according to the invention serves, for example, as a filler, whereby the consumption of fresh filler or pigment can be reduced consistently.
• the milling of the cleaner rejects is preferably installed in a centrifugal cleaner system downstream from the last of usually several stages of a centrifugal cleaner.
• the accepted stock from the additional cleaner system is recycled to the previous stage, and the residual amount of the cleaner rejects forms the final reject.
• the simplest application area is intended to comprise installing the milling after the last but one cleaner stage and employing the last cleaner process as a final stage.
• fillers and coating pigments either as powders or in the form of concentrated slurries with a solids content of preferably from 30 to 85% by weight for the paper stock or for the preparation of coating slurries.
• the fresh fillers and pigments are usually supplied by the manufacturers with the desired whiteness and grain size distribution as a slurry or powder.
• cleaner rejects In the processing of cleaner rejects, it is of course required to separate and discard the coarse dirt contents consisting of splinters, sand grains and other impurities.
• multistage centrifugal cleaners are usually employed.
• the screenings thus obtained consist of fibers, fillers, pigments, fine sand, black particles and agglomerates of fillers and pigments, or pigments, fibers and fillers.
• “Filler” usually means the fine particles employed in the paper stock; “pigment” means the fine particles employed in the coat.
• the milling into powders or slurries can be performed continuously or discontinuously in usual dry mills or wet mills, especially agitator ball mills, for example, having a content of from 700 to 5000 l or more.
• Milling media preferably milling balls, especially having a diameter of from 1 to 4 mm, are used.
• Screens preferably sieve bends, for separating impurities (ball crushings, separating materials, rust etc.) are usually used for processing.
• Laser measuring instruments serve to determine and control the milling fineness during the milling process and for the computer-based control of the agitator ball mill system.
• the ratio of fillers and/or pigments to fibers can vary widely. It is particularly preferred according to the invention to employ cleaner rejects having an optionally enriched concentration of fillers and/or coating pigments within a range of from 5 to 90% by weight, especially from 30 to 70% by weight, based on the solids content.
• the fiber content, on the one hand, or the content of filler and/or coating pigment may vary, for example, from 1 to 99% by weight, or from 99 to 1% by weight. “Enrichment” within the meaning of the present invention especially comprises the addition of fresh filler and/or fresh pigment.
• china clay natural or precipitated calcium carbonates, artificial or natural aluminum silicates and oxide hydrates, titanium dioxide, satin white, dolomite, mica, metal flakes, especially aluminum flakes, bentonite, rutile, magnesium hydroxide, gypsum, sheet silicates, talcum, calcium silicate and other rocks and earths are preferably used as the fresh pigment and/or fresh filler before, after and/or during the milling.
• the fresh pigment or fresh filler is preferably employed as a powder, aqueous fresh-pigment containing and/or fresh-filler containing slurries in the presence of the cleaner rejects and optionally usual milling aids and/or dispersing aids to give a slurry with a solids content of, for example, from 30 to 85% by weight, especially from 40 to 75% by weight.
• the added amount of fibers, coating pigments and/or fillers is from 1 to 100% by weight, based on the cleaner rejects.
• the addition of water in order to employ the cleaner rejects milled according to the invention in a diluted slurry for the stock flow.
• the milling is performed in the presence of water in an amount of from 1 to 1000% by weight, especially from 100 to 1000% by weight, based on the solids content.
• the cleaner rejects are preferably milled to a slurry or powder having a grain size distribution of from 10 to 99% by weight of particles ⁇ 1 ⁇ m, especially from 10 to 95% by weight of particles ⁇ 1 ⁇ m, respectively based on the equivalent diameter.
• cleaner rejects Even though per se known wetting agents, stabilizers, milling aids and dispersing aids may be employed according to the invention during the mixing and milling of the cleaner rejects, as known, for example, from EP 0 625 611 A1, the quantity thereof required is clearly reduced according to the invention as compared to the prior art.
• the cleaner rejects already contain some amount of the mentioned agents which are recycled to the papermaking process according to the invention.
• the powders or slurries obtainable according to the present invention may be employed to particular advantage in the paper industry, especially for the preparation of a coat for paper coating or in the paper stock.
• the cleaner rejects milled according to the invention is preferably employed in the coating slurry, and when the fiber content is high, it is preferably employed in the paper stock. According to the invention, a good retention on the screen is obtained. Particularly preferred is the use of the cleaner rejects milled according to the invention for the preparation of offset paper.
• the slurries according to the invention are also suitable for the preparation of a coating slurry for light-weight coated papers, especially with high coating speeds, and for the preparation of rotary offset papers, especially for the preparation of light-weight coated rotary offset papers, the coating of cardboard and special papers, such as labels, wallpapers, silicone base paper, self-copying paper, and for admixture with intaglio printing paper.
• the coating pigment slurries obtainable according to the invention may be employed, in particular, in sheet-fed offset papers, especially for sheet-fed offset single coating, sheet-fed offset double coating: sheet-fed offset precoating and sheet-fed offset top coating; in rotary offset papers, especially for LWC rotary offset single coating, rotary offset double coating: rotary offset precoating and rotary offset top coating; in intaglio printing, especially for LWC intaglio single coating, intaglio double coating: intaglio precoating and intaglio top coating; in cardboard, especially for cardboard double coating: cardboard precoating and cardboard top coating; and for special papers, especially for labels and flexible packings.
• the process offers the opportunity to employ the pigment slurries prepared according to the invention without a loss in quality in the base papers, coatings and especially final qualities prepared therewith.
• CMC carboxymethylcellulose
• Cleaner rejects from the process of a commercially available papermaking machine of the prior art were milled in a 15% by weight suspension to a slurry having a grain size of ⁇ 10 ⁇ m and added to the stock flow of the paper stock.

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• Paper (AREA)
• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
• Processing Of Solid Wastes (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)

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• 2001
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• 2003
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