Stickies (papermaking)

Stickies are tacky substances contained in the paper pulp and process water systems of paper machines. Stickies have a large tendency to make deposits on the processing equipment in certain stages of the papermaking process. Contaminations of paper that that are classified as tacky are also called stickes. The main sources for stickies are recycled paper,^[1] waxes, and soft adhesives.^[2]

Composition

Stickies are an indefinite mixture of organic compounds, with the main part being different esters. The components might stem from:

• Printing inks
• Coating binders (synthetic latex)
• Waxes
• Hot melt adhesive and unsupported pressure sensitive adhesives
• Plastics
• Wet strength resins
• Pitch
• Papermaking additives

Properties

Stickies that passes through a slotted plate screen of 0.10 - 0.15 mm are called micro stickes. Micro stickies can be finely dispersed (100 µm - 100 nm), colloidal (100 - 10 nm) or molecular dissolved ( < 10 nm). Macro stickies are those who retain as a screening residue. The reason for this classification is that macro stickes are easy to remove from the deinked pulp in the deinking process with filtration. Micro stickies follows the pulp to the paper machine and might agglomerate and cause problematic deposits.

Stickies have often thermoplastic properties.

Chemical-physical alterations like pH, temperature and charge changes might cause colloidal destabilization and agglomeration of micro stickies.

Stickies control

Several methods are used to control them are used:

• Alteration of the physical properties, like using recycling friendly paper coatings,
• Avoidance of troublesome components that causes stickies,
• Removal by more effective deinking process, like improved screening, cleaning, washing and flotation,
• Passivation with process additives like fixation agents,
• Prevention by washing wires or protecting equipment parts with chemicals.

References