Deinking

Deinking is the English word for ink removal (of English = ink " ink ", " ink " ) and refers to the key process in paper recycling to remove the ink from printed wastepaper. The paper is thereby bleached mechanical and chemical methods. In Germany, waste paper is de-inked in order to produce newsprint, office paper ( copy paper ) and tissue paper. This is determined primarily by the optical properties of the utility value. Dark recovered paper (packaging, cardboard ) can not be de-inked, so they must be sorted out before. Such varieties are used again for the production of cardboard or corrugated cardboard.

History

The origin of the deinking process is due to the discovery of Justus Claproth in 1774, in which the printing ink from printed paper was washed out in order to restore writable paper. To 1843 fibers were used in old clothes for recycling paper, then held the wood pulp as raw material feed. With the use of flotation for the deinking of paper in the 1950s, paper fibers could be used as raw material in paper production. Previously, the paper was suitable only for the production of cardboard. The now attainable whiteness allowed henceforth the production of newsprint and sanitary papers.

Deinking process

Before the mid-1970s the deinking systems consisted of disintegration (addition of deinking chemicals in the pulping drum ) sorting and flotation to remove the ink. There were thickening ( separation of the material conditioning water circuit from the paper machine water loop ) hot dispersion of fine fragmentation of the remaining contaminants and fine- sort using very fine slots. This ( stickies ) can be removed in addition to the ink so-called stickies. The present deinking process often includes a second flotation and thickening and cleaning of the circulating water (DAF = Dissolved Air Flotation ) to achieve a higher quality level. [Picture from book page 89 ] In addition to the usual in Europe flotation deinking there is also the washing deinking (more common in North America). The flotation gives higher yields and requires significantly less water than washing. The laundry is used in the production of sanitary papers where targeted especially the long fibers without fines and fillers are filtered out.

The flotation removes the ink from the paper used, thus increasing the degree of whiteness. It uses the hydrophilic ( water-attracting ) property of the fibers. These are wetted by water, while the hydrophobic ( water-repellent ) ink remains largely unwetted. From this process, the requirements to conduct appropriate paper from the deinking. This deinking is defined in a paper - species list.

From made ​​in flexo printing newspapers, which are common in England and Italy, the ink can not be removed in the flotation. This poses considerable problems for recycling. Even small amounts of Flexozeitungen in the waste paper mixture lead to poor whiteness. The binder of the flexographic ink dissolves in weakly alkaline medium and releases the Promärpigmente of color, these particles are very small and not hydrophobic, therefore, does not work for them the flotation process. Similar problems in the flotation prepare pigmented inkjet inks, digital printing process with polyethylene liquid toner and UV coating. Newly developed polyester based liquid toners are like classic dry toner, however excellent deinkable.

Deinkability is now accepted as a criterion for the recyclability of a paper product. First, the Nordic Swan (Nordic Eco-label ) and the Austrian Ecolabel for printed products deinkability took on as a criterion. The 2012 adopted European Eco-label for printed products (EU Ecolabel for printed paper ) also contains deinkability as an important prerequisite.

Recycled paper from waste paper is de-inked, with so-called environmental paper is waived. In the treatment of the waste paper to recycled paper no chemicals are added to inks are not removed from the recycled pulp and a bleaching is omitted. The recycling process can not be repeated, because the paper loses not only by remaining ink particles in brightness, but the quality demands of today's print and no longer sufficient amplification method with an intensified recycling. One consequence is that these very dark paper are fewer buyers and end up back faster in the trash.

Recycled fibers are theoretically 4 - to 6- times recyclable because they are weakened and shortened at each recycling cycle. Small fragments are, however, washed out, and fresh fibers about from magazines compensate for the losses. Thus, in the present composition of the waste paper from ever recycled paper (eg newspapers) and virgin fiber (eg from magazines ) not to worry about " recycling collapse".

Other deinking variants that are sometimes used in addition, are the enzymatic deinking or " DAF " (dissolved air flotation ).

Deinking chemicals

Much like washing clothes is for deinking a detergent needed. Prerequisite for the removal of the ink from the waste paper material is the replacement of the ink particles from the fibers. For this purpose, the necessary chemicals are usually added already in the pulping of waste paper in the pulper or in the drum. Deinking formulations contain sodium hydroxide, sodium silicate, hydrogen peroxide and a surfactant ( soap). These chemicals help the dissolution of the waste paper and bring together with the mechanical stress that the ink separates from the fibers. In order to fully exploit the effects of the chemicals specified reaction times must be adhered to. Therefore, the paper solute outsourced to the fraying usually some time in large vats before it is cleaned and de-inked. Straight wood-containing paper yellowed slightly under the action of caustic soda, so already peroxide is added here. This bleach counteracts yellowing of the fibers, support the replacement of inks and can also cause a bleaching effect (destruction pale sensitive dyes). Peroxide is readily decomposed by heavy metal ions, and therefore a peroxide stabilizer is often added just before the pulper. The purpose of water glass ( sodium silicate), still the best peroxide stabilizer; Complexing agents are virtually no longer used in waste paper processing. Water glass also supports both the ink- detachment and the removal of printing inks in the flotation. If the ink is released from the fiber, a collector must bind the ink particles in and provide in flotation for attachment to the bubbles. This is the task of washing active substances, in most soaps (anionic surfactants), with which the best results are obtained according to experience in the conventional deinking. Surfactants improve the release of the ink. Therefore, they are usually added in the pulper, usually 0.5-1.0 %. In contrast to the laundry washing deinking surfactants need hard water, at least 1.8 mmol / l ( 10 ° dH). With soft water, calcium ions are added or used synthetic surfactants. In the course of the predominant part of the deinking chemical is destroyed (e.g., peroxide). The surfactants are removed by flotation.

Deinking residues

The deinking residues, so-called Deinkingschlämme consist of fillers (calcium carbonate, kaolin, silicates), fiber, extractives (fats, soluble inks and line binder components ) and fines (insoluble inks and coating color components, adhesive components ). With the exploitation of these materials, the thermal treatment ( incineration ) plays a central role. Almost all residues fall in the paper industry with relatively low solids contents, but bring because of the high content of organic components usually have such a high calorific value that they burn without fire support, so energy is obtained. Therefore more than 55% of deinking residues are burned as a substitute fuel in its own power plants of paper mills or externally, so as to generate energy. The non-combustible components remain as (possibly actionable ) ash as slag and as a filter dust. Approximately 42% of deinking residues are recycled. For example, they are used because of the high fiber content in the perforated brick manufacture. Here they are a welcome Porosierungshilfsmittel - when burning the bricks, the fibers leave tiny cavities which improve the thermal insulation effect of the bricks. Deinking residues are also responsible for production of cement, due to the high aluminum content (from the kaolin, which is among other things used in the paper coating ), are suitable. Depending on the tone used, the addition of residues improve the quality of the cement. Organic substances such as paper fibers or residues from printing inks burn while burning the cement.

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