Apparatus for purification of plastic material intended for food contact

A plastic extrusion plant for extrusion of plastic material intended for food contact, the plastic extrusion plant comprising an apparatus for purification of the plastic material from contaminants, and an extruder for extruding the plastic material,

• the apparatus for purification of the plastic material comprising at least one reactor for receiving the plastic material to be purified, the at least one reactor comprising:
• a closed housing having an opening for the plastic material to be loaded into the housing and an opening for the plastic material to be unloaded therefrom;
• a vent relief;
• respective valve means associated with the openings for loading and unloading the plastic material and closing and opening of the openings;
• a vacuum pump connected in fluid communication with the vent relief with an interposition of further valve means;
• stirring means located in the housing for ensuring that the plastic material is stirred in the reactor during the process, and
• heating means associated with the reactor, the heating means comprise radiant heating means for supplying energy to the plastic material contained in the reactor, and comprise heating means associated with walls of the at least one reactor, and comprise electrical resistors and/or a cavity with heated liquids flowing therein,
• the extruder for extruding the plastic material is located downstream from the apparatus for purification of the plastic material from contaminants, wherein the extruder comprises a chassis, containing a twin-screw extruder, the extruder having an inlet for the plastic material to be extruded and comprises a plurality of venting zones with vent ports, a sealing zone and a conveying and metering zone actuated by the screws, wherein:
• the two screws of the extruder are co-rotating so as to have a same direction of rotation,
• a first venting zone is provided for venting to atmosphere, and the first venting zone for venting to the atmosphere is equipped with an extraction hood,
• a second venting zone is provided, which comprises a first vent with a vacuum pump and a second vent with a vacuum pump in tandem,
• a sealing zone is provided between the first and second venting zones, which is made up of a series of cams located on the screws, which are loaded with a quasi-molten material under light pressure to prevent deterioration of the material being processed.

A plastic extrusion plant for extrusion of plastic material intended for food contact the plastic extrusion plant comprising a heater, an apparatus for purification of the plastic material from contaminants, and an extruder for extruding the plastic material,

• the heater comprises:
• a housing comprising feeding means with a shaft having a horizontal axis of rotation with blades for feeding the plastic material between an inlet and an outlet;
• ventilation means for blowing a flow of heated air (A) in the housing of the heater, countercurrent to a direction of feed of the plastic material in the heater, and radiant heating means supplying energy to the plastic material contained in the heater,
• the radiant heating means of the heater comprising at least one microwave radiant heating device for promoting excitation of polar molecules the apparatus for purification of the plastic material comprising at least one reactor for receiving the plastic material to be purified, the at least one reactor comprising:
• a closed housing having an opening for the plastic material to be loaded into the housing and an opening for the plastic material to be unloaded therefrom;
• a vent relief;
• respective valve means associated with the openings for loading and unloading the plastic material and closing and opening of the openings;
• a vacuum pump connected in fluid communication with the vent relief with an interposition of further valve means;
• stirring means located in the housing for ensuring that the plastic material is stirred in the reactor during the process, and
• heating means associated with the reactor, wherein the heating means comprise radiant heating means for supplying energy to the plastic material contained in the reactor,
• the at least one reactor is fed with the plastic material to be purified from the heater located upstream from the reactor,
• the extruder is located downstream from the apparatus for purification of the plastic material from contaminants, wherein the extruder comprises a chassis, containing a twin-screw extruder, the extruder having an inlet for the plastic material to be extruded and comprises a plurality of venting zones with vent ports, a sealing zone and a conveying and metering zone actuated by the screws, wherein:
• the two screws of the extruder are co-rotating so as to have a same direction of rotation,
• a first venting zone is provided for venting to atmosphere, and the first venting zone for venting to the atmosphere is equipped with an extraction hood,
• a second venting zone is provided, which comprises a first vent with a vacuum pump and a second vent with a vacuum pump in tandem,
• a sealing zone is provided between the first and second venting zones, which is made up of a series of cams located on the screws, which are loaded with a quasi-molten material under light pressure to prevent deterioration of the material being processed.