Cartaspers SCH Liquid

Cartaspers® SCH liquid is a water-based polymer emulsion with a high glass transition temperature (Tg). It has no affinity for hydrophilic material, for example, cellulose fibres, but associates with hydrophobic contaminants such as resinous substances, recycled adhesive and latex particles. Stickie agglomerates containing the Cartaspers® particles become less tacky and soften at a higher temperature. The tendency for stickies to ‘pick’ from a sheet, which is in contact with a hot surface, is reduced.

The unique physical properties of the product, with its very low particle size, provide over 1,000 trillion polymer spheres per dry gram, creating a high surface area and excellent covering power. The product is not able to form a film; it merely dries to a dust. When stickies are coated with the high Tg polymer, the surface tackiness is significantly reduced, even at higher temperatures. This passivation technique has proven successful in the prevention of contaminant deposition on machinery.

The slightly anionic nature of Cartaspers® SCH liquid ensures rapid distribution of the emulsion particles through the papermaking stock. This dilution effect initiates the process of destabilization. The emulsifier in the product, protecting and stabilizing the tiny emulsion particles, is not stable in hard water when heavily diluted in the pulp. Unstabilized polymer spheres ‘seek’ other hydrophobic particles to form agglomerates with a higher Tg. This principle of stickies passivation is similar to that achieved through the use of talc. However, there is a significant difference in particle size of the products (<100 nm for Cartaspers® SCH liquid and typically 1-2 μm for talc) and the surface area per kilogram of Cartaspers® SCH liquid particles is 20 times larger than that of talc which means the organic particle is much more efficient.

Stickies passivation and control

The concept of stickies control was studied in the laboratory using a unique test method, developed specifically for the assessment of Cartaspers® SCH liquid. Debris from doctor blades in the drying section of a paper machine is pulped with bleached fibre and the slurry is added to glass beakers, which have been fitted with a strip of 150 μm polyester film. There is a strong tendency for small stickie particles to adhere to the film and after 15 minutes stirring time, the strips of film are removed from the beakers and carefully washed with deionized water. The strips are allowed to air dry and the particles of stickie material can then be counted. If each particle is touched with a permanent marker pen, at the time of counting the visual effect is more pronounced. Various chemical additives may be evaluated using this method, simply by adding the product to the pulp in one of the tests. Adding Cartaspers® SCH liquid to the fibre blend significantly reduces the number of adhesive particles on the hydrophobic film.

Destabilization of the Cartaspers® SCH liquid emulsion with cations intensifies the adsorption of the product on the surface of the stickies and lowers the forces of adhesion between the contaminants and the strip of film (illustrated). Cations may be in the form of an organic or inorganic cationic fixative/coagulant, or calcium ions in the form of water hardness.