Deinking

Deinking is the industrial process of removing printing ink from paperfibers of recycled paper to make deinked pulp. Deinking is the industrial process of removing printing ink from paperfibers of recycled paper to make deinked pulp. The key in the deinking process is the ability to detach ink from the fibers. This is achieved by a combination of mechanical action and chemical means. In Europe the most common process is froth flotation deinking. Paper is one of the main targets for recycling. A concern about recycling wood pulp paper is that the fibers are degraded with each cycle and after being recycled 4–6 times the fibers become too short and weak to be useful in making paper. Before the invention of the paper machine in 1799 the most common fibre source was recycled fibres from used textiles, hence the name rag paper. The rags were from hemp, linen and cotton. It was not until the introduction of wood pulp in 1843 that paper production was independent of recycled materials. Recycling of used paper before the industrialisation of paper production, rag paper was recycled to make low-grade board. A process for removing printing inks from recycled paper was invented by German jurist Justus Claproth in 1774. He practiced together with German paper producer Johann Engelhard Schmid. Today this method is called deinking. First in the 1950s and 1960s the use of recycled fibres from paper made of wood pulp begun to increase, and was mainly used in packaging paper and paperboard. In the 1950s the froth flotation technique was adapted for deinking recycled paper. Use of recovered paper increased in the 1970s mainly in graphic and hygienic papers, and accelerated in the 1980s. The annual growth in use of recovered paper increased by 6% between 1980 and 1996. The use of virgin fibres only increased 2% in the same period. In 1997 recovered paper production was 42% of the total paper production. Waste paper may contain a mixture of different paper types made of mixtures of different paperfibers. These must be sorted before processed. Broke (paper waste from paper production) is normally used directly in the papermachine. Recycled paper can be used to make paper of the same or lower quality than it was originally. The sorted paper is baled and shipped to a papermill. The pulpmill uses waste paper grade according to the paper quality they want to make. The bales are opened and large foreign objects are sorted out on the conveyor belt to the pulper. Many extraneous materials are readily removed. Twine, strapping, etc. are removed from the hydropulper by a 'ragger'. Metal straps and staples can be screened out or removed by a magnet. Film-backed pressure-sensitive tape stays intact: the PSA adhesive and the backing are both removed together.