Self-cleaning filter removes contaminants from plastic scrap

Melt filter. The U.S. Patent and Trademark Office has awarded a patent to Nordson Corp., Westlake, Ohio, for a self-cleaning filter that removes dirt, metal and other contaminants from plastic scrap before it is extruded into pellets or new products. The system’s cleaning unit is designed to automatically compensate for variations in melt pressure in the filter chamber and for wear of the cleaning scraper, resulting in consistent and reliable performance.

The device consists of a housing with a filter chamber for holding the melted plastic, a dirt outlet for discharging contamination, a filter element and a cleaning unit with a servomechanism coupled to at least one scraper member. Further, the servomechanism has a bellows cylinder with a foot section, a head section, a deformable bellows element and a variable-volume pressure chamber.

The bellows cylinder makes it possible “to control in a targeted manner the amount of pressing force with which the scraper member is pressed onto the filter element,” the patent states. “This ensures that the scraper members exert a uniform pressing force against the surface of the filter element, regardless of the service life of the scraper member and its concomitant degree of wear.”

In a preferred development of the invention, a mechanism guides the head section of the bellows cylinder, ensuring that force is exerted in a targeted manner on the scraper.

Patent 10,974,177; issued April 13

Expandable plastic foam recycling. Winterthur, Switzerland-based Sulzer Management AG has received a patent for its system and process for recycling expandable plastic foams, such as polystyrene (PS) and polypropylene (PP).

The system includes an extruder, a mixer/heat exchanger unit and a melt pump. The expandable plastic is melted in the extruder and cooled in the mixer/heat exchanger unit prior to being extruded or injection molded. The plastic’s expansion agent is not degassed during the process, so the agent stays in the plastic. According to the patent, the invention makes recycling expandable plastics more efficient and also results in no significant loss of the expansion agent.

“In particular, the process of the invention has only very little loss of expansion agent, and therefore in many embodiments little or no dosing of additional expansion agent is required,” the patent states. “In addition, not only may the expansion agent be recycled … but also any additives contained in the expandable plastic material to be recycled.”

Furthermore, because little or no expansion agent must be dosed, an overall lower processing temperature profile and melt temperature can be used. This allows temperature-sensitive additives, such as flame retardants, to be dosed directly in the extruder, according to the patent.

Patent 11,000,979; issued May 11

Separation. Berry Plastics Corp., Evansville, Indiana, has patented a process to sort recovered plastics of different densities.

Various types of plastic flakes are agitated in a tank that contains a fluid consisting of vegetable oil and an additive. The fluid has a density greater than all but one of the types of plastics.

According to the patent, plastic flakes “are placed in a higher density fluid separator that allows flakes made of a first plastics material to sink in the higher density fluid and thus be separated from flakes that are made from a second and third plastics material [that] float in the higher density fluid.”

PS, polyvinyl chloride and polyethylene terephthalate are among the plastics that sink in the higher density fluid, while PP and high-density polyethylene (HDPE) float. Those lower density plastics then can be processed in a separator with lower density fluid, allowing the HDPE to sink and the PP to float.

Patent 11,020,751; issued June 1