Self-sealing injection device for thermoplastic material

An apparatus comprising:

• an injector device for injecting a thermoplastic material into a mold cavity (2), the material being in the fluid state when raised to a temperature that is not less than a determined limit temperature higher than the temperature of ambient air, said injector device including:
• a dispenser (8) suitable for being maintained at an injection temperature higher than said determined limit temperature and defining a thermoplastic material dispensing passage (11) having at least one outlet (25) for delivering thermoplastic material in a determined longitudinal direction (130) to one side of the dispenser;
• an injection nozzle (7) which is suitable for being maintained at an injection temperature higher than said determined limit temperature and situated on said side of the dispenser (8), being secured thereto, and defining at least one longitudinal transit passage (12) for the thermoplastic material, said passage being placed in fluid-flow connection with the outlet (25) from the dispenser (8) in the direction (131) that is opposite to said direction (130) and opening out in said direction (130) in a front face (13) suitable for being integrated in the mold cavity (2);
• at least one longitudinal closure needle (21) mounted to slide longitudinally inside the transit passage (12) between a position in which it closes it and a position in which it opens it, and presenting a longitudinal extender (24) extending in the direction (131) opposite to said direction (130), passing through the dispenser (8) into ambient air on the side of the dispenser (8) that is longitudinally opposite from said side thereof, via means (38) for guiding longitudinal sliding and presented securely by the dispenser (8) for this purpose, going longitudinally away from said outlet (25), the guide means (36) and the extender (24) of the needle (21) presenting respective inner and outer cylindrical longitudinal peripheral faces (41, 42) in mutual guiding contact for relative longitudinal sliding, with one of said peripheral faces (41) presenting an annular transverse groove for receiving a sealing gasket relative to the other one of said peripheral faces (42) in the closed and open positions of the closure needle (21), and also in all longitudinal positions between them;
• and
• controlled means (30) for causing the closure needle (21) to slide longitudinally between said closed and open positions, said controlled means being disposed in ambient air on the side of the dispenser (8) that is longitudinally opposite from said side thereof, and being functionally connected to the extender (24) of the closure needle (21) the device being characterized in that said groove (43) is offset longitudinally relative to the dispensing passage (11) in the direction (131) opposite to said direction (130) by a distance (d) that is determined in such a manner that under the effect of ambient air thermal conduction causes it to be placed at a temperature which is lower than the injection temperature but higher than said determined limit temperature when the dispenser (8) and the injection nozzle (7) are maintained at the injection temperature, and the thermoplastic material leaking in the fluid state between said inner and outer peripheral faces (41, 42) reaches said groove (42), fills said groove, and presents viscosity therein such as to remain stopped therein and itself constitute the sealing gasket.