US Patent 7399178 Injection device having a reciprocal plunger

In an injection device 10 having a plunger 11 reciprocably inserted into a heating cylinder 16, in which a molten material M is injected by the plunger 11 via a nozzle 21, a sealing portion 13 set so that the molten material M is prevented from easily entering a gap A between the plunger 11 and an inner wall 32 of the heating cylinder 16 is provided on the portion of the plunger 11, on the side of the nozzle 21, and the portion of the sealing portion 13, on the side of the nozzle 21 is a core keeping portion 14 provided so that an annular portion 20 which is formed on a front portion of the plunger 11 and is connected to a storage portion 19 of the molten material M is formed between the core keeping portion 14 and the inner wall 32 of the heating cylinder 16.