Backflow prevention device

A backflow prevention device for an injection molding machine, comprising:

• a screw tip defined by a longitudinal axis and having a tip end, a central body member connected to the tip end, a thrust ring positioned at a rear end of the body member, and a mounting end extending from the rear end of the body member for attachment to a plasticizing screw;
• a locking ring arranged in coaxial relationship to the longitudinal axis and having first and second sealing surfaces, said locking ring being movable in the direction of the longitudinal axis between an open position, in which the first sealing surface rests against a shoulder of the tip end, allowing passage of material, and a closed position, in which the second sealing surface rests against a shoulder of the thrust ring, prohibiting entry of material, wherein the locking ring and the body member define together an annular gap;
• and
• at least one mixing element disposed in the annular gap and constructed in the form of a circular ring in coaxial relationship to the locking ring, said mixing element having circumferential bores in spaced-apart disposition for transport of material in the direction of the longitudinal axis.