Label paper Drying: Equipment Selection

There is one hard constraint in selecting for label paper: it cannot be rubbed. Flakes in a rotary dryer are lifted and dropped repeatedly, and every contact can leave a tear or a crease, while label stock is used by the sheet and by the label, so a damaged sheet is a wasted sheet. A flash airflow line carries the material in the hot air the whole way, with a contact time measured in seconds and almost no mechanical action, which is why it suits paper. The inlet temperature follows the coating's heat limit, and the air volume is adjusted separately: hold the temperature first, then raise the air volume slowly, because curl caused by drying too fast is harder to recover than a moisture figure that is out of spec.

Flakes cannot be rubbed, and that is the first hard constraint in selecting the machine. A label paper has three layers: the base paper, the coating and the adhesive, and the coating fails first — pushed past its limit it forms a hard skin, the surface turns brittle and curling follows. Our approach is a flash airflow line: the sheets are carried by the hot air and heat transfer is completed within seconds, with almost no mechanical action. The inlet temperature is set by the coating's heat limit, typically somewhere between 120 and 150°C depending on the grade, and the air volume is adjusted separately: hold the temperature first, then raise the air volume slowly so the sheets do not curl as they dry fast. At 500 kg/h dry basis taking moisture from 30 percent down to 2 percent, an airflow line needs parallel units or a larger air volume, so calculate the evaporation rate before selecting rather than sizing on dry tonnes.

Should label paper go on a flash airflow dryer or a rotary dryer?
A flash airflow dryer. Label paper is a flake material, and the flights of a rotary drum lift and drop it repeatedly, so sheets rub against each other and can crease, which a thin coating does not survive. A flash airflow line carries the sheet in the hot air with almost no mechanical contact and completes heat transfer in seconds, which is the more suitable route for paper.

What temperature does label paper need?
Set it by the coating's heat limit rather than by a general figure. Common coatings tolerate somewhere between 120 and 150°C, depending on the grade, and the limit has to be confirmed against the paper and the coating formulation. Ask for the heat limit of the stock being sent, and do not copy the temperature from an earlier order.

Why does dried label paper curl?
In most cases because it dried too fast: the surface lost water before the inside did, and while the core is still wet the outer layer contracts, so the sheet goes out of balance and curls. The remedy is to separate temperature from air volume: take the surface moisture off at low air volume first, then raise the volume gradually instead of opening it fully at once.