Sticky contaminants may significantly disturb the manufacturing process and influence negatively the quality of the paper.
The source of the stickies may vary: they originate essentially from resins of wood, additives used during manufacturing, binders of coating, glues used in converting, printing-ink binders, or other products used in converting.
Primary and derivate (or secondary) stickies are distinguished.
Primary stickies are those sticky contaminants which are not dispersed due to their high resistance. They have compact forms and can easily be screened.
Secondary stickies originate from sticky contaminants of the waste paper whose particle size may vary during the process, due to thermal, chemical, and mechanical influences.
During the preparation of the recycled fibres this may cause disintegration of contaminants which at the beginning have had a relatively big size, which at the end of the process may form small particles of different sizes. Their size may vary between molecular dispersed and roughly dispersed.
These particles may then re-agglomerate to secondary stickies on the paper machine through thermal, mechanical or chemical action.
Mainly those secondary stickies cause problems during finishing and converting, as well as on the paper machine. They are transported by the sheet through the paper machine and cause undesired deposits on press felts, dryer felts, dryer cans and calendar rolls.
Additionally, they are found in the finished paper, deteriorating its quality.