Systems for Graphic Paper Grades

The product from a secondary fiber preparation plant for white grades is usually called DIP (Deinked Pulp) as there is at least one process step for ink removal integrated in the system. In most of the cases this deinking step is done by selective flotation. Washers may be used for deinking in special cases when very finely dispersed printing inks (like water-based flexo inks) are present in the recovered paper or when not only the ink, but also the major share of the ash content needs to be removed, as is true e. g. for tissue grades. 

The main parameters characterizing the quality of a DIP are brightness, stickies content, dirt specks and ash content. Depending on the application, namely the recovered paper grades used and the paper grades produced, different requirements are imposed on the DIP quaHty and thus on the system layout and efficiency. 

A fiber preparation system for white paper grades generally consists of the process steps shown in Fig. 4.57. 

The multistage fine screening system operates with slot widths of 0.15 mm. If the fine screening stage is the only slot screening stage in the system, a cleaner plant ahead of it for sand removal is recommended for protection against wear. 

Quality parameters Process stage Brightness Dirt specks content Stickles content Ash content Debris content Fiber design 

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