Injection device

Abstract

To provide an injection device that satisfactorily curbs leaking of molding resin in a molten state from a gap between an inner peripheral surface of a cylinder in a base end part of the cylinder and an outer peripheral surface of a plunger inserted into an interior space of the cylinder.SOLUTION: An injection device comprises: a cylinder in which an ejection port for injecting molding resin in a molten state is formed in a distal end part thereof; a plunger slidably inserted into an interior space of the cylinder from a base end part of the cylinder; and a seal ring formed of high melting point resin being resin having a melting point higher than that of the molding resin and attached to a ring groove formed in an outer peripheral surface of a distal end part of the plunger. The seal ring is formed such that breadth is smaller than breadth of the ring groove and an inner peripheral length is longer than a peripheral length of a bottom of the ring groove.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to injection devices, and more particularly to plunger type injection devices. [Background technology]

[0002] 2. Description of the Related Art There is known an injection molding machine (injection molding device) that manufactures a resin molded product of a predetermined shape by injecting a molten molding resin into a cavity of a mold and then solidifying the resin inside the cavity.

[0003] Patent Document 1 discloses a pre-plasticization type injection molding device that includes an injection cylinder having an injection port formed at its tip for injecting molten molding resin and a resin discharge path formed at its base for discharging molding resin remaining in the internal space to the outside, an injection plunger inserted into the internal space from the base end of the injection cylinder, and a seal ring made of a high-melting point resin having a higher melting point than the molding resin, fitted liquid-tightly and slidably around the injection plunger and fixed to the base end of the injection cylinder. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-39943 A Summary of the Invention [Problem to be solved by the invention]

[0005] An example of an injection device of an injection molding machine is a plunger-type injection device that advances a plunger slidably inserted into the internal space of a cylinder (barrel) relative to the cylinder to inject molten molding resin supplied into the internal space of the cylinder. In a plunger-type injection device, in order to prevent poor sliding of the plunger relative to the cylinder, it is necessary to provide a certain amount of gap between the inner peripheral surface of the cylinder at the base end of the cylinder and the outer peripheral surface of the plunger inserted into the internal space of the cylinder. Therefore, the molten molding resin may leak from the gap.

[0006] The leakage of the molten molding resin causes the following problems. The amount of molding resin injected into the mold cavity by the injection device is reduced, which may result in a decrease in material yield and the occurrence of short shots. -Leaked molding resin is discarded, resulting in waste of raw materials. - The removal of molding resin requires stopping production, which may result in reduced productivity. Since the leaked molding resin and the injection unit are hot, the work of removing the above-mentioned molding resin may involve the risk of injury or illness, such as burns or heat stroke, to workers. If leaked molding resin is left for a long period of time, it may carbonize.

[0007] In order to prevent leakage of the molding resin, it is conceivable to attach a seal ring to the sliding portion between the inner peripheral surface of the cylinder and the outer peripheral surface of the plunger. However, even if a seal ring is attached to the sliding portion, the following problems arise. The molding resin that accumulates in the gap between the inner circumferential surface of the cylinder at the base end and the outer circumferential surface of the plunger inserted into the internal space of the cylinder may remain there for a long time without being discharged to the outside and deteriorate. Therefore, if the deteriorated molding resin is unintentionally injected into the cavity after replacing the mold, etc., the deteriorated molding resin may be mixed into the resin molded product, causing product defects. In order to prevent product defects due to the deterioration of the molding resin as described above, it is essential to periodically remove the molding resin that has accumulated in this gap. Although the frequency of the molding resin removal work can be reduced by attaching a seal ring to the sliding part, it is difficult to reduce the frequency to zero.

[0008] Therefore, there is a need for technology that can more reliably prevent molten molding resin from leaking through the gap between the inner surface of the cylinder at the base end of the cylinder and the outer surface of the plunger inserted into the internal space of the cylinder.

[0009] The present disclosure has been made to solve such problems, and aims to provide an injection device that effectively prevents molten molding resin from leaking from the gap between the inner surface of the cylinder at the base end of the cylinder and the outer surface of a plunger inserted into the internal space of the cylinder. [Means for solving the problem]

[0010] An injection device in one embodiment has a cylinder having an injection port formed at its tip for injecting molten molding resin, a plunger slidably inserted into the internal space of the cylinder from its base end, and a seal ring made of a high-melting point resin having a higher melting point than the molding resin and attached to a ring groove formed on the outer peripheral surface of the tip of the plunger, the seal ring being formed so that its width is smaller than that of the ring groove and its inner circumference is longer than the peripheral length of the bottom of the ring groove. Effect of the Invention

[0011] The present disclosure makes it possible to provide an injection device that effectively prevents molten molding resin from leaking from the gap between the inner surface of the cylinder at the base end of the cylinder and the outer surface of a plunger inserted into the internal space of the cylinder. [Brief description of the drawings]

[0012] [Figure 1]1 is a cross-sectional view showing an outline of an injection device according to a first embodiment. [Diagram 2] FIG. 2 is a partially enlarged view of the injection device shown in FIG. [Diagram 3] FIG. 13 is a diagram showing verification results of an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] First embodiment Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiment. In addition, in order to clarify the description, the following description and drawings are appropriately simplified. What is shown in the drawings is only a part of the whole, and in reality, many other configurations that are not shown are included. In the following description, the same or equivalent elements are given the same reference numerals, and duplicated descriptions are omitted.

[0014] First, FIG. 1 is a cross-sectional view showing an outline of an injection device according to a first embodiment. The injection device 1 shown in FIG. 1 is combined with a clamping device (not shown) to form an injection molding machine. The injection molding machine is a device that solidifies a molten molding resin R to manufacture a resin molded product of a predetermined shape. The clamping device may be of any type, and for example, a fixed platen on which a fixed mold is attached is fixed on a bed B. In addition, a movable platen on which a movable mold is attached relative to the fixed platen is provided so as to be movable in the mold opening and closing direction on a guide provided on the bed B. The fixed mold and the movable mold are clamped to form a mold cavity.

[0015] In the following description, "molding resin" refers to the resin material supplied to the injection device 1 according to this embodiment, and is mainly a thermoplastic resin. Pellet-like molding resin R refers to the resin material in a solid state when supplied to the injection device 1. Molten molding resin R refers to the resin material that has become fluid by being maintained at or above its glass transition temperature or melting point. A "resin molded product" refers to an article molded into a predetermined shape by solidifying the molten molding resin R.

[0016] As shown in FIG. 1, the injection device 1 is placed on a bed B. The injection device 1 has a base 11, an intermediate support portion 12, and a rear support portion 13 as support portions. The injection device 1 also has a barrel 21, a plunger 22, and a screw 23 as injection portions. The injection device 1 also has a first drive means 31, a second drive means 32, a third drive means 33, and a rotation drive means 34 as drive portions. The injection device 1 will be described in detail below, with the tip side of the injection device 1 (left side in FIG. 1) defined as the front, and the base side of the injection device 1 (right side in FIG. 1) defined as the rear.

[0017] The injection device 1 supplies molten molding resin R to the internal space S1 by rotating a screw 23 rotatably arranged in an internal space S2 of a plunger 22 inserted in the internal space S1 of a barrel 21, and advances the plunger 22 and the screw 23 relative to the barrel 21 to inject the molten molding resin R supplied to the internal space S1 into a cavity of a mold. The molding resin R is, for example, polypropylene (PP). The melting point of PP is about 110°C to 170°C.

[0018] [Support part] The base 11 is provided so as to be movable in the front-rear direction relative to the bed B by a first driving means 31. An intermediate support part 12 is placed on a base end part of the base 11. The intermediate support part 12 is provided so as to be movable in the front-rear direction relative to the base 11 by a second driving means 32. The intermediate support part 12 is a member that supports a plunger 22. A rear support part 13 is placed on a base end part of the intermediate support part 12. The rear support part 13 is provided so as to be movable in the front-rear direction relative to the intermediate support part 12 by a third driving means 33. The rear support part 13 is a member that supports a rotation driving means 34. In addition, a barrel 21 is fixed to a tip end part of the base 11.

[0019] [Injection part] The barrel 21 is a specific example of a cylinder. The barrel 21 is a member having a substantially cylindrical shape extending in the front-rear direction. The barrel 21 incorporates a first heating means 21a such as a plurality of cartridge heaters extending in the circumferential direction. The first heating means 21a heats the molding resin R supplied to the internal space S1. In addition, an injection port 21c for injecting the molten molding resin R is formed in a cylinder head 21b, which is the tip of the barrel 21. The injection port 21c is formed at the tip of the cylinder head 21b. In addition, a nozzle 211 is attached to the tip of the cylinder head 21b. The nozzle 211 has an opening / closing mechanism 211a such as a shutoff valve that closes the injection port 21c. The injection port 21c communicates with the cavity of the mold via the nozzle 211. The base end of the barrel 21 is open. And, a plunger 22 is slidably arranged in the internal space S1. Since the inner diameter of the barrel 21 is slightly larger than the outer diameter of the plunger 22, a gap CL1 is formed between the inner surface 21s of the barrel 21 at the base end of the barrel 21 and the outer surface 22s of the plunger 22 inserted into the internal space S1.

[0020] The plunger 22 is a member having a substantially cylindrical shape extending in the front-rear direction. The plunger 22 is slidably inserted into the internal space S1 from the base end of the barrel 21. The plunger 22 is a member for pushing out the molten molding resin R supplied to the internal space S1 and injecting it from the injection port 21c. The plunger 22 incorporates second heating means 22a such as a plurality of cartridge heaters extending in the circumferential direction. The second heating means 22a heats the molding resin R supplied to the internal space S2. In addition, a discharge port 22c for discharging the molten molding resin R is formed in the plunger head 22b, which is the tip of the plunger 22. The discharge port 22c is formed at the tip of the plunger head 22b. The discharge port 22c has a tapered shape in which the diameter becomes smaller toward the tip.

[0021] At least one ring groove 22d is formed on the outer peripheral surface 22s of the plunger head 22b. A seal ring 40, which is a member for preventing the molten molding resin R from leaking from the gap CL1, is attached to the ring groove 22d. It is preferable that a plurality of ring grooves 22d are provided on the outer peripheral surface 22s of the plunger head 22b so as to be spaced apart from each other in the front-rear direction. By attaching the seal ring 40 to each of the plurality of ring grooves 22d, it is possible to further suppress the molten molding resin R from leaking from the gap CL1 when the injection device 1 performs an injection operation. The ring groove 22d may be provided on the sliding portion of the outer peripheral surface 22s of the plunger 22 that slides against the inner peripheral surface 21s, and the position in the front-rear direction is not particularly limited as long as the sealing force of the seal ring 40 is not impaired. In the injection device 1 shown in FIG. 1, three ring grooves 22d are provided on the outer peripheral surface 22s of the tip portion of the plunger head 22b so as to be spaced apart from each other in the front-rear direction. A seal ring 40 is attached to each ring groove 22d.

[0022] The seal ring 40 is a ring-shaped member. The seal ring 40 is made of a high-melting-point resin, which is a resin having a higher melting point than the molding resin R. By keeping the temperature of the molten molding resin R filled in the internal space S1 at a temperature higher than the melting point of the molding resin R and lower than the melting point of the high-melting-point resin (more preferably, lower than the continuous use temperature of the high-melting-point resin), the seal ring 40 will not melt even if the molten molding resin R comes into contact with the seal ring 40. The high-melting-point resin is, for example, polyetheretherketone (PEEK). The melting point of PEEK is 334°C (typical value), and the continuous use temperature is 250°C (according to UL796B).

[0023] A hopper 231 is attached to the base end of the plunger 22. The hopper 231 is a funnel-shaped member for supplying pelletized molding resin R to the plunger 22. An inlet 231a for injecting the pelletized molding resin R is formed on the upper surface of the hopper 231. A material supply path 231b is formed at the lower end of the hopper 231. The material supply path 231b communicates with the internal space S2. The base end of the plunger 22 is open. A screw 23 is rotatably disposed in the internal space S2.

[0024] The screw 23 is a member having a spiral blade 23a formed on its outer circumferential surface. The screw 23 is inserted into the internal space S1 from the base end of the plunger 22. The screw 23 is a member for melting the pellet-shaped molding resin R supplied to the internal space S2 and discharging the molten molding resin R from the discharge port 22c to supply the molten molding resin R to the internal space S1. The screw 23 has a backflow prevention mechanism 23b such as a check ring at its tip. The base end of the screw 23 is rotatably supported by the rear support part 13 via the output shaft 34d.

[0025] [Drive unit] The first driving means 31 moves the base 11 in the front-rear direction. The first driving means 31 has an electric motor 31a and a ball screw 31b including a ball screw shaft and a ball screw nut. The ball screw shaft of the ball screw 31b is rotatably supported on the bed B by bearings 61 and 62. The ball screw nut of the ball screw 31b is fixed to the base 11 so as not to rotate. When the electric motor 31a rotates forward or backward, the ball screw shaft of the ball screw 31b rotates forward or backward. As a result, the base 11 reciprocates in the front-rear direction together with the ball screw nut of the ball screw 31b screwed to the ball screw shaft. As the base 11 moves, the intermediate support unit 12, the rear support unit 13, the injection unit, the second driving means 32, the third driving means 33, and the rotation driving means 34 move in the front-rear direction. If it is not necessary to move the base 11, the first driving means 31 can be omitted.

[0026] The second driving means 32 moves the plunger 22 together with the screw 23 in the front-rear direction. The second driving means 32 has an electric motor 32a and a ball screw 32b including a ball screw shaft and a ball screw nut. The ball screw shaft of the ball screw 32b is rotatably supported on the base 11 by bearings 63 and 64. The ball screw nut of the ball screw 32b is fixed to the intermediate support part 12 so as not to rotate. When the electric motor 32a rotates forward or backward, the ball screw shaft of the ball screw 32b rotates forward or backward. As a result, the intermediate support part 12 reciprocates in the front-rear direction together with the ball screw nut of the ball screw 32b screwed to the ball screw shaft. As the intermediate support part 12 moves, the rear support part 13, the plunger 22, the screw 23, the third driving means 33, and the rotation driving means 34 move in the front-rear direction.

[0027] The third driving means 33 moves the screw 23 in the front-rear direction. The third driving means 33 has an electric motor 33a and a ball screw 33b including a ball screw shaft and a ball screw nut. The ball screw shaft of the ball screw 33b is rotatably supported on the intermediate support part 12 by bearings 65, 66. The ball screw nut of the ball screw 33b is fixed to the rear support part 13 so as not to rotate. When the electric motor 33a rotates forward or backward, the ball screw shaft of the ball screw 33b rotates forward or backward. As a result, the rear support part 13 reciprocates in the front-rear direction together with the ball screw nut of the ball screw 33b screwed to the ball screw shaft. The screw 23 and the rotation driving means 34 move in the front-rear direction in accordance with the movement of the rear support part 13.

[0028] The rotation drive means 34 rotates the screw 23. The rotation drive means 34 has an electric motor 34a, an output pulley 34c fixed to an output shaft 34b of the electric motor 34a, an input pulley 34e fixed to an output shaft 34d connected to a base end of the screw 23, and a transmission belt (not shown) wound around the output pulley 34c and the input pulley 34e. The screw 23 rotates when the rotation drive force of the electric motor is transmitted to the output shaft via a drive force transmission mechanism including the output pulley 34c, the input pulley 34e, and the transmission belt. Note that the drive force transmission mechanism may include a reducer or the like instead of the output pulley 34c, the input pulley 34e, and the transmission belt.

[0029] In the above-mentioned injection device 1, when the molding resin R in pellet form is supplied from the input port 231a to the internal space S3 of the hopper 231, the molding resin R slides down through the material supply path 231b and moves to the internal space S2 of the plunger 22. When the screw 23 is rotated by the rotation drive means 34, the molding resin R that has moved to the internal space S2 moves along the spiral groove of the screw 23 toward the discharge port 22c, while mechanical energy (friction between the molding resins R, shear by the inner circumferential surface of the plunger 22 and the screw 23) is imparted to the molding resin R. As a result, the temperature of the molding resin R increases and it melts. The injection device 1 supplies the molding resin R in a molten state to the internal space S1 by the rotation of the screw 23, and advances the plunger 22 and the screw 23 relative to the barrel 21 to inject the molding resin R in a molten state supplied to the internal space S1 from the injection port 21c.

[0030] Next, Fig. 2 is a partially enlarged view of the injection device 1 shown in Fig. 1. Fig. 2 is an enlarged cross-sectional view of the periphery of one seal ring 40 (the seal ring 40 arranged at the most forward side) in the injection device 1. One of the features of the injection device 1 according to this embodiment is the seal structure that seals the gap CL1 with the seal ring 40. Therefore, the seal structure of the injection device 1 will be described in detail with reference to Fig. 2.

[0031] The seal ring 40 is attached to the ring groove 22d such that the outer peripheral surface 40a abuts against the inner peripheral surface 21s and at least a part of the rear end surface 40b abuts against the rear wall surface 22f of the ring groove 22d. Furthermore, the seal ring 40 is formed so that the width W1 is smaller than the width W2 of the ring groove 22d and the inner peripheral length (the circumferential length of the inner peripheral surface 40c of the seal ring 40) is longer than the circumferential length of the bottom 22e of the ring groove 22d (the circumferential length of the bottom 22e). As a result, when the injection device 1 performs the injection operation, the molten molding resin R supplied to the internal space S1 is guided to the gap CL2 between the seal ring 40 and the ring groove 22d. When the molten molding resin R is filled into the gap CL2 in this manner, the pressure P of the molten molding resin R from the seal ring 40 toward the wall surface 22f and the pressure P of the molten molding resin R from the seal ring 40 toward the inner peripheral surface 21s are applied to the seal ring 40. The pressure P of the molten molding resin R from the seal ring 40 toward the wall surface 22f increases the adhesion of the seal ring 40 to the barrel 21, and the pressure P of the molten molding resin R from the seal ring 40 toward the inner peripheral surface 21s increases the adhesion of the seal ring 40 to the plunger 22. Therefore, the width W1 of the seal ring 40 is smaller than the width W2 of the ring groove 22d, and the inner peripheral length of the seal ring 40 is formed longer than the peripheral length of the bottom portion 22e, thereby improving the sealing force of the seal ring 40. As a result, the leakage of the molten molding resin R from the gap CL1 is suppressed.

[0032] Here, if the width W1 is too small, the contact area between the inner peripheral surface 21s and the outer peripheral surface 40a becomes small, so that the sealing force of the seal ring 40 may be insufficient. On the other hand, if the width W1 is too large, the contact area between the inner peripheral surface 21s and the outer peripheral surface 40a becomes large, so that the sliding resistance of the plunger 22 may increase. Also, if the gap CL2 is too small, the seal ring 40 is less likely to receive the pressure P, so that the sealing force of the seal ring 40 may be insufficient. On the other hand, if the gap CL2 is too large, the seal ring 40 behaves within the ring groove 22d, so that the sealing force of the seal ring 40 may be insufficient or may not be able to seal. Also, the adhesion force of the seal ring 40 to each of the barrel 21 and the plunger 22 increases as the pressure P increases due to the reaction force of the pressure P. Therefore, the sealing force of the seal ring 40 changes depending on the pressure P.

[0033] (Example) The injection device 1 will be described in more detail below with reference to examples. However, the examples do not limit the present disclosure. In the examples, the nozzle 211 having the opening and closing mechanism 211a was replaced with a throttle nozzle, and the injection device 1 was operated under the following injection conditions. In the examples, PP was used as the molding resin R, and PEEK was used as the high melting point resin.

[0034] [Equipment conditions] Barrel 21 Inner Diameter: 105.0mm Outer diameter of plunger 22: 104.9mm Quantity of Seal Ring 40: 3 Width W1 of seal ring 40 for gap CL2 distance of 1.0 mm: 4.0 mm, 6.0 mm, 6.5 mm, 6.8 mm, 7.0 mm Distance of gap CL2 for width W1 of 6.0 mm: 1.0 mm, 0.4 mm, 0.2 mm, 0.08 mm [Injection conditions] ·Temperature of inner space S1 (all zones): 220℃ - Advance start position of plunger 22: 430 mm -Plunger 22 forward stop position: 30mm Injection pressure (pressure in internal space S1): 160Mpa

[0035] Then, the following leak test was performed to verify the relationship between the width W1 and the amount of leakage of the molding resin R, and the relationship between the distance of the gap CL2 and the amount of leakage of the molding resin R. The leakage amount of the molding resin R is the amount of the molding resin R that leaks from the gap CL1 to the outside when the injection device 1 performs an injection operation. The distance of the gap CL2 is the distance between the front end face 40d of the seal ring 40 attached to the ring groove 22d and the rear wall face 22g of the ring groove 22d, and is the difference between the width W1 and the width W2.

[0036] [Leak test method] 1. The injection operation of the injection device 1 was started under the hydrostatic pressure generated by setting the throttle amount of the throttle nozzle to the "fully closed" state, and then the injection operation was stopped. The device conditions and injection conditions of the injection device 1 in step 1 were as described above. 2. The amount of change in the position of the plunger 22 was measured based on the forward movement start position of the plunger 22 when the injection operation started and the forward movement stop position of the plunger 22 when the injection operation stopped. 3. The forward speed (mm / s) of the plunger 22 was calculated from the amount of change in the position of the plunger 22 measured in step 2. 4. Using the specific gravity of the molding resin R, the forward movement speed of the plunger 22 calculated in step 3 was converted into a leakage amount (g / s).

[0037] [Verification results] FIG. 3 is a diagram showing the verification results. Graph G1 shown in the upper part of FIG. 3 shows the relationship between the width W1 of the seal ring 40 and the amount of leakage of the molding resin R when the distance of the gap CL2 is 1.0 mm. As shown in the graph G1, when the width W1 is 4.0 to 6.5 mm, the amount of leakage decreases as the width W1 increases, and when the width W1 is 6.5 to 7.0 mm, the amount of leakage is zero. Graph G2 shown in the lower part of FIG. 3 shows the relationship between the distance of the gap CL2 and the amount of leakage of the molding resin R when the width W1 of the seal ring 40 is 6.0 mm. As shown in the graph G2, when the distance of the gap CL2 is 1.0 to 0.2 mm, the amount of leakage decreases as the distance of the gap CL2 becomes smaller, but when the distance of the gap CL2 is 0.08 mm, the amount of leakage increases compared to when the distance of the gap CL2 is 0.2 mm.

[0038] From the verification results shown in FIG. 3, when the distance of the gap CL2 is 1.0 mm, it is particularly preferable that the width W1 is 6.5 to 7.0 mm. Also, from the above verification results, when the width W1 is 6.0 mm, it is particularly preferable that the distance of the gap CL2 is 0.2 mm. In this way, in the injection device 1, the amount of leakage can be significantly reduced by adjusting at least one of the width W1 relative to the width W2 and the gap CL2 relative to the width W2. Therefore, according to the injection device 1 of this embodiment, it is possible to suitably suppress leakage of the molten molding resin R from the gap CL1.

[0039] Here, for example, if the pressure P is larger than necessary, the seal ring 40 receiving the pressure P is excessively pressed against the barrel 21, which may result in wear of the seal ring 40, galling occurring between the inner peripheral surface 21s and the outer peripheral surface 22s, and an increase in the sliding resistance of the plunger 22. In contrast, in the injection device 1 according to the present embodiment, a suitable pressure P is obtained by adjusting at least one of the width W1 relative to the width W2 and the gap CL2 relative to the width W2, so that it is possible to prevent the seal ring 40 receiving the pressure P from being excessively pressed against the barrel 21. As a result, wear of the seal ring 40, galling occurring between the inner peripheral surface 21s and the outer peripheral surface 22s, and an increase in the sliding resistance of the plunger 22 are suppressed.

[0040] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0041] 1 Injection device 1 11 Base 12 Intermediate support section 13 Rear support section 21 barrel 21a first heating means 21b cylinder head 21c injection port 21s inner peripheral surface 22 plunger 22a second heating means 22b plunger head 22c discharge port 22s outer circumferential surface 22d ring groove 22e bottom 22f, 22g wall 23 Screw 23a Blade 23b Backflow prevention mechanism 31 First driving means 31a Electric motor 31b Ball screw 32 second driving means 32a electric motor 32b ball screw 33 third driving means 33a electric motor 33b ball screw 34 Rotation drive means 34a Electric motor 34b, 34d Output shaft 34c Output pulley 34e Input pulley 40 Seal ring 40a Outer surface 40b, 40d End surface 40c Inner surface 61~66 Bearings 211 Nozzle 211a Opening and closing mechanism 231 hopper 231a inlet 231b material supply path B Bed CL1, CL2 Gap G1, G2 Graph P Pressure R Molding resin S1, S2, S3 Internal space W1, W2 Width

Claims

[Claim 1] a cylinder having an injection port formed at its tip for injecting molten molding resin; a plunger slidably inserted into an internal space of the cylinder from a base end of the cylinder; a seal ring formed of a high melting point resin having a melting point higher than that of the molding resin and attached to a ring groove formed on an outer circumferential surface of the tip portion of the plunger; The seal ring has a width smaller than that of the ring groove and an inner circumferential length longer than a circumferential length of a bottom portion of the ring groove.

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