Recycled PET from post-consumer bottle flake is highly sought-after in the industry as a raw material for thermoforming packaging, fibres or packaging tapes. However, a key issue impacting the usability of this material is purity, which means that the efficiency of the melt filtration process is far more critical than usual on the recycled material production line.
To address this problem, Ettlinger’s latest laser-drilled microperforation ECO melt filters feature a filtration fineness of 60 µm, allowing contaminants like paints, silicones, barrier materials, cross-linked fractions and gels to be removed from the melt. Germany-based Ettlinger, a member of the Maag Group, claims the new filters will enable cost-efficient conversion of post-consumer PET bottle flake and fines, which generally occur in large amounts, into recycled material with excellent usage properties.
The drawbacks of traditional woven steel mesh screens are mainly that the square mesh - the simplest and most common type applied - can, in practice, allow particles larger than the nominal mesh size to pass, owing to the diagonal. Furthermore, the individual wires are only linked together loosely. As the filter cake grows and the pressure rises, some meshes may be enlarged, again allowing larger-sized particles to slip through. Also, contaminants contained in the PET bottle flake such as aluminium or paper as well as “black specks” – black, degraded plastic particles that occur during the process –regularly find their way into the recycled material
With laser-drilled screens, the separation efficiency of the self-cleaning ECO filter systems is improved to the extent that the occurrence of black specks and other particles is very considerably reduced. The filter is a rotating, cylindrical steel screen with millions of conical holes. When melt flows through this screen from the outside to the inside, any contaminants are retained on the surface and continuously removed by a scraper. The filtration surface remains absolutely clean. Contaminants such as small elastic particles, which could otherwise ultimately be forced through the screen, are unable to collect on the surface.
The new melt screens open up new possibilities for materials that have traditionally been considered too heavily contaminated or that contain extremely problematic contaminants, such as PET fines from recycled bottles. These fines - up to 20 tons per month, even at small PET bottle recycling plants – are generated during the sorting, grinding and washing processes and tend to be contaminated with large amounts of paper and aluminium. Until now, these were simply sold.