Pressure holding device, injection device, and resin material injection method

Abstract

The dwelling device is equipped with a stopper member that regulates the amount of retraction of a dwelling plunger. When filling a dwelling path with a resin material, a second engaging member of the stopper member regulates the amount of retraction of the dwelling plunger at a first position that engages with a first engaging member fixed to the dwelling plunger. When depressurizing the mold after dwelling, the second engaging member moves from the first position to a receded second position to release regulation of the amount of retraction of the dwelling plunger.

Description

[Technical Field]

[0001] The present invention relates to a pressure-holding device, an injection device, and a method for injecting a resin material. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in an injection device for injection molding a resin material, a resin material measuring step, a resin material injection filling step into a mold, and a pressure holding step are carried out continuously in this order. Also known are injection machines equipped with a pressure-holding device that has a plunger that moves forward and backward independently of the injection screw (see, for example, Patent Documents 1 to 4). In this type of injection machine, the plunger of the pressure-holding device is advanced to hold the pressure of the injection-molded product while the injection screw performs the metering process, thereby shortening the molding cycle of the injection-molded product. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5535595 [Patent Document 2] Patent No. 2928750 [Patent Document 3] Patent No. 3352917 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-240114 Summary of the Invention [Problem to be solved by the invention]

[0004] Once the above-mentioned dwelling process is complete, the dwelling device stops pressurizing the resin and retracts the plunger to release the resin pressure (depressurize / decompress).If the resin is not sufficiently released, problems such as nozzle clogging in the hot runner or stringiness at the gate of the molded product (the area corresponding to the gate hole in the injection cavity mold where the resin from the hot runner flows in) (molding defects caused by the gate not being solidified sufficiently) can occur.

[0005] The amount of retraction of the plunger of the pressure holding unit during pressure release varies greatly depending on the internal volume of the hot runner's resin passage. The internal volume of the hot runner's resin passage varies depending on differences in gate structure (valve gate type, open gate type, etc.) and the resin passage specifications based on the production volume of injection molded products. When releasing pressure from a hot runner with a large internal volume of the resin passage, possible measures to increase the internal volume of the pressure holding passage include using a larger plunger or lengthening the pressure holding passage on the pressure holding unit side.

[0006] However, if the internal volume of the pressure holding passage is increased as described above in a pressure holding device that fills the pressure holding passage by retracting the plunger in a free state during injection, the amount of resin injected and filled in the pressure holding passage will increase unnecessarily, which may reduce the effectiveness of shortening the molding cycle.Furthermore, if the internal volume of the pressure holding passage is increased, the pressure holding device will also become larger, which may lead to an increase in the cost of the device.

[0007] Furthermore, if the amount of resin filled into the pressure holding passage for pressure holding is inaccurate, the molding conditions set for the injection device may not function properly, and the quality of the manufactured injection-molded product may deteriorate.

[0008] Therefore, the present invention has been made in consideration of these problems, and aims to provide a pressure holding device that can properly perform pressure release after holding pressure for a variety of molds while shortening the molding cycle and maintaining the quality of injection molded products. [Means for solving the problem]

[0009] One aspect of the present invention is a pressure holding device that is attached to a pressure holding path branching from a resin path of an injection device and that holds pressure in the resin path and the pressure holding path after injecting a resin material into a mold. The pressure holding device includes a pressure holding plunger having a first engagement member fixed to its outer periphery and that moves back and forth through the pressure holding path, a pressure holding piston that drives the pressure holding plunger, and a stopper member that regulates the amount of retraction of the pressure holding plunger. The stopper member has a second engagement member that engages with the first engagement member and a drive member that moves the second engagement member back and forth in a direction intersecting the direction of movement of the pressure holding plunger. When filling the pressure holding path with resin material, the second engagement member regulates the amount of retraction of the pressure holding plunger at a first position where it engages with the first engagement member. When depressurizing the mold after holding, the second engagement member moves from the first position to a second position, retracted, to release the regulation of the amount of retraction of the pressure holding plunger. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide a pressure-holding device that can properly perform pressure release after holding pressure on a variety of molds while shortening the molding cycle and maintaining the quality of injection-molded products. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram illustrating a state at the start of injection in the injection device of the present embodiment. [Figure 2] FIG. 2 is a diagram illustrating a state before the start of pressure holding in the injection device of the present embodiment. [Figure 3] FIG. 10 is a diagram showing a state in which pressure is released in the injection device of the present embodiment. [Figure 4] 10A and 10B are diagrams illustrating a resin discharge state of a pressure holding path in the injection device of the present embodiment. [Figure 5] FIG. 10 is a diagram showing a retracted state of a stopper member in the pressure maintaining device. [Figure 6] 10A and 10B are diagrams illustrating a protruding state of a stopper member in the pressure maintaining device. [Figure 7] 10A and 10B are diagrams illustrating an example of the configuration of a stopper member. [Figure 8] 1 is a diagram showing a molding flow in an injection molding apparatus including the injection apparatus of the present embodiment. [Figure 9] FIG. 10 is a diagram showing a reinforcing mechanism of the pressure holding device. [Figure 10] FIG. 1 is a diagram showing an example of a molding apparatus equipped with a pressure holding device. [Figure 11] FIG. 1 is a diagram showing an example of a molding apparatus equipped with a pressure holding device. [Figure 12] FIG. 1 is a diagram showing an example of a molding apparatus equipped with a pressure holding device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiments, in order to make the explanation easier to understand, the structures and elements other than the main parts of the present invention will be explained in a simplified or omitted manner. Furthermore, the same elements will be given the same reference numerals in the drawings. Note that the shapes, dimensions, etc. of the elements shown in the drawings are shown schematically and do not represent the actual shapes, dimensions, etc.

[0013] 1 to 4 show an example of an injection apparatus 1 having a pressure maintaining device 3 of this embodiment. FIGS. 5 to 7 show an example of the pressure maintaining device 3 of this embodiment.

[0014] The injection device 1 of this embodiment is applied, for example, to supply a resin material to a mold of an injection molding device that produces a bottomed, cylindrical resin preform. The preform is applied, for example, to blow molding of a resin container. Although not particularly limited, the injection device 1 may be mounted in a blow molding device of a hot parison system (also called a one-stage system) that blow-moldes a resin container by utilizing the heat retained during injection molding (internal heat) without cooling the preform to room temperature.

[0015] A hot runner is preferably provided between the injection device 1 and the mold. Furthermore, the injection device 1 is preferably configured such that an injection nozzle (described later) abuts against a sprue (resin inlet) 51 of the hot runner 50, and molten resin material is introduced into a cavity (molding space) of a mold (injection mold) 60 via a resin path within the hot runner 50. Note that although the hot runner 50 and mold 60 are omitted in Figures 2 to 6 and 9, the hot runner 50 and mold 60 are also provided in these figures in the same arrangement as in Figure 1.

[0016] As shown in Figures 1 to 4, the injection device 1 has an injection cylinder 11, an injection screw 12, an injection nozzle 13, a drive cylinder (drive actuator) 14, a rotation mechanism (not shown), a shutoff device 2, and a pressure holding device 3. Although not shown, a hopper for supplying resin material, a drive device for rotating the injection screw 12, and the like are provided on the rear side of the injection device 1 (opposite the injection nozzle). Although not particularly limited, Figures 1 to 4 are bird's-eye views (top views) of the injection device 1 mounted on the machine base of various molding machines.

[0017] If the pressure dwelling unit 3 is placed above the injection cylinder 11, the pressure dwelling unit 3 will be positioned directly in front of the mold, which will make molding and other operations less efficient. Therefore, it is preferable to place the pressure dwelling unit 3 approximately horizontally on the side (side surface) of the injection cylinder 11. Similarly, it is preferable to place the cutoff unit 2 approximately horizontally on the side of the injection cylinder 11.

[0018] An injection screw 12 is rotatably supported (held) inside the injection cylinder 11. The injection screw 12 can move forward and backward relative to the injection cylinder 11 by the operation of a drive cylinder 14. A hopper (not shown) that supplies resin material is connected to the injection cylinder 11, and the resin material is supplied from the hopper to the inside of the injection cylinder 11. The injection cylinder 11 is set to a high temperature equal to or higher than the melting point of the resin material in order to melt the solid resin material accommodated between the inner wall of the injection cylinder 11 and the groove of the injection screw 12.

[0019] A screw head 12a is provided at the tip of the injection screw 12. The injection screw 12 heats the solid resin material inside the injection cylinder 11 as it rotates, turning it into a molten state (plasticizing the resin material). In the metering step of the injection molding process, the injection screw 12 moves backward while charging the molten resin material in front of the screw head 12a. After charging the resin material is complete, the injection screw 12 moves forward in a non-rotating state by the drive cylinder 14 in the injection step of the injection molding process, thereby injecting the molten resin material.

[0020] An injection cylinder head 15 is provided at the tip of the injection cylinder 11 (the side facing the hot runner 50). A resin passage 4 is formed inside the injection cylinder head 15, and an injection nozzle 13 is connected to the tip of the injection cylinder head 15. The injection nozzle 13 is connected to a sprue 51 of the hot runner 50. The resin passage 4 communicates with a cavity (molding space) of a mold 60 used for injection molding via a resin passage (runner) inside the hot runner 50.

[0021] A shutoff device 2 is disposed between the injection screw 12 and the injection nozzle 13 of the injection cylinder head 15. A pressure holding path 5, which communicates with the resin path 4, branches off and is formed between the shutoff device 2 of the injection cylinder head 15 and the injection nozzle 13. The pressure holding path 5 is formed at an angle diagonally rearward (to the right in the figure) relative to the resin path 4 (or the front of the hot runner 50), and its end opposite the resin path 4 is connected to the pressure holding device 3. The resin filled into the cavity of the mold 60 can be held at pressure by driving the pressure holding device 3 via the resin in the resin path of the hot runner 50, the pressure holding path 5, and the resin in the resin path 4.

[0022] The cutoff device 2 has a cutoff plunger 21 that moves forward and backward in a direction perpendicular to the resin path 4 (the up and down direction in the drawing) to cut off the resin path 4, and a cutoff cylinder (cutoff actuator) 22 that drives the cutoff plunger 21 to move forward and backward relative to the resin path 4. The cutoff cylinder 22 is connected to the injection cylinder 11 (specifically, the injection cylinder head 15), and a piston rod 22a connected to the cutoff plunger 21 is supported inside a cylinder barrel (cylinder tube) 22b via a piston 22c so as to be able to move forward and backward.

[0023] As pressure oil is supplied to the cylinder barrel 22b of the shutoff cylinder 22 and pressure oil is discharged from the cylinder barrel 22b of the shutoff cylinder 22, the piston rod 22a is driven to move forward and backward inside the shutoff cylinder 22. As a result, the shutoff plunger 21 connected to the piston rod 22a moves forward and backward relative to the resin path 4. When the shutoff device 2 is in the closed state, the shutoff plunger 21 moves forward toward the resin path 4, closing the resin path 4 on the front side of the screw head 12a (the hot runner 50 side), and cutting off the connection with the injection nozzle 13. On the other hand, when the shutoff device 2 is in the open state, the shutoff plunger 21 moves backward from the resin path 4, and the resin path 4 on the front side of the screw head 12a is connected to the injection nozzle 13.

[0024] The tip of the pressure maintaining device 3 is connected between the injection nozzle 13 of the injection cylinder head 15 and the blocking device 2. As shown in Figures 1 to 6, the pressure maintaining device 3 has a pressure maintaining device tip member (pressure maintaining path forming member) 31 connected to the injection cylinder 11 (specifically, the injection cylinder head 15), a pressure maintaining plunger (pressure maintaining plunger) 32, and a pressure maintaining cylinder (pressure maintaining actuator, pressure maintaining cylinder) 33. The tip 32a of the pressure maintaining plunger 32 advances and retreats in the axial direction (left and right directions in Figures 5 and 6) along the cylindrical pressure maintaining device tip portion 31 and the pressure maintaining path 5 of the cylinder head 15.

[0025] The pressure maintaining cylinder 33 is fixed to a first holding member 39a, and the pressure maintaining device tip member 31 is fixed to a second holding member 39b. The first holding member 39a and the second holding member 39b are connected via a plurality of supports 34. The pressure maintaining device tip member 31 and the second holding member 39b may be integrated.

[0026] The pressure maintaining cylinder 33 is connected to the tip end 31 of the pressure maintaining device via a plurality of support columns 34 extending in the axial direction. Inside the pressure maintaining cylinder 33, a piston rod 33a connected (coupled) to the distal end side of the pressure maintaining plunger 32 is supported so as to be movable back and forth in the axial direction via a piston 33c. Pressurized oil is supplied to the cylinder barrel 33b of the pressure maintaining cylinder 33, thereby applying a pressing force to the piston rod 33a of the pressure maintaining plunger 32, and the pressing force of the pressure maintaining cylinder 33 on the pressure maintaining plunger 32 is released (released) by opening a discharge path for the pressurized oil to the cylinder barrel 33b of the pressure maintaining piston 33.

[0027] When the pressure maintaining cylinder 33 applies a pressing force until the pressure maintaining plunger 32 moves to the forward end of the pressure maintaining path 5, the tip 32a of the pressure maintaining plunger 32 protrudes into the resin path 4. When the pressing force of the pressure maintaining cylinder 33 is released, the resin material from the resin path 4 presses the tip 32a of the pressure maintaining plunger 32, causing the pressure maintaining plunger 32 to retract. As a result, the resin material is introduced from the resin path 4 into the pressure maintaining path 5, and the resin material is filled (charged) into the pressure maintaining path 5.

[0028] Furthermore, the portion of the pressure maintaining device 3 where the support 34 is arranged constitutes a plunger exposed portion 3a where the pressure maintaining plunger 32 is exposed to the outside. A potentiometer (linear potentiometer, linear sensor, position detection device for the pressure maintaining plunger 32) 35, a stopper member 40, and a convex member (flange-shaped member) 47 are provided on the plunger exposed portion 3a of the pressure maintaining device 3.

[0029] The potentiometer 35 has a shaft 35a, a sensor body 35b, and a position detection plate 35c, and detects the axial position of the pressure holding plunger 32. The shaft 35a of the potentiometer 35 is attached parallel to the pressure holding plunger 32 and the support 34. The position detection plate 35c is fixed to the pressure holding plunger 32, and the shaft 35a is inserted through it. The position detection plate 35c moves along the shaft 35a in response to the movement of the pressure holding plunger 32. The sensor body 35b detects the position of the position detection plate 35c on the shaft 35a, and outputs a signal indicating the axial position of the pressure holding plunger 32.

[0030] The stopper member 40 is attached to a predetermined position of the plunger exposed portion 3a via a base 37 fixed to the pressure-maintaining cylinder 33 (specifically, the first holding member 39a). The stopper member 40 has an air cylinder 41, a connecting member 42, a pair of rod members 43, and a stopper body 44.

[0031] The air cylinder 41 is disposed between a first mounting plate 45 and a second mounting plate 46, which are fixed to the base 37. A rod 41a of the air cylinder 41 passes through the second mounting plate 46 and extends in a direction away from the pressure holding plunger 32. The tip of the rod 41a of the air cylinder 41 and one end of each rod member 43 are connected by a connecting member 42 that extends parallel to the second mounting plate 46.

[0032] Each rod member 43 penetrates the first mounting plate 45 and the second mounting plate 46, and extends in a direction intersecting (or perpendicular to) the extension direction of the pressure holding plunger 32. A stopper body 44 extending parallel to the first mounting plate 45 is attached to the other end of each rod member 43 so as to face the pressure holding plunger 32. The stopper body 44 is an example of a second engagement member, and can be switched between a first position in which it protrudes toward the pressure holding plunger 32 and a second position in which it is retracted from the pressure holding plunger 32 by extension and contraction of the rod 41a of the air cylinder 41.

[0033] The convex member 47 is an example of a first engagement member, and is provided on the pressure maintaining plunger 32 or the piston rod 33a. Preferably, the convex member 47 is provided at a connection position between the pressure maintaining plunger 32 and the piston rod 33a (a position approximately on the distal end side of the pressure maintaining plunger 32).

[0034] The cross-sectional area of ​​the convex member 47 is larger than the cross-sectional areas of the pressure maintaining plunger 32 and the piston rod 33a. Therefore, the convex member 47 can interfere with the stopper body 44 that has moved (protruded) toward the pressure maintaining plunger 32. It is preferable that the position detection plate 35c is connected to the convex member 47 at a location where the stopper body 44 does not interfere (for example, at a location opposite the location where the stopper member 40 is provided).

[0035] When the rod 41a of the air cylinder 41 extends, the connecting member 42 moves in a direction away from the second mounting plate 46 (downward in the figure). As a result, the stopper body 44, which is integrated with the connecting member 42 via the rod member 43, also moves in a direction away from the pressure maintaining plunger 32, and the stopper body 44 moves to a second position retracted from the pressure maintaining plunger 32. As shown in Figures 5 and 7, the stopper body 44 in the second position is located farther from the pressure maintaining plunger 32 than the end of the convex member 47, and allows the pressure maintaining plunger 32 or the convex member 47, which is fixed to the piston rod 33a, to move in the axial direction.

[0036] On the other hand, when the rod 41a of the air cylinder 41 is retracted, the connecting member 42 moves in a direction approaching the second mounting plate 46 (upward in the figure). This causes the stopper body 44, which is integrated with the connecting member 42 via the rod member 43, to move in a direction approaching the pressure maintaining plunger 32, and the stopper body 44 moves to a first position protruding toward the pressure maintaining plunger 32. As shown in FIG. 6, the stopper body 44 in the first position is positioned to interfere with the convex member 47. As a result, the stopper body 44 in the first position engages with the convex member 47 when the pressure maintaining plunger 32 retracts from the forward end, thereby restricting the amount of retraction of the pressure maintaining plunger 32. The position of the stopper member 40 in the axial direction of the pressure maintaining plunger 32 is determined depending on the amount of resin material filled in the pressure maintaining passage 5.

[0037] Next, the operation of the injection device 1 will be described with reference to FIGS. FIG. 1 shows the state of the injection unit 1 at the start of injection. The shutoff device 2 in FIG. 1 is in an open state with the shutoff plunger 21 retracted from the resin path 4. Also, in the pressure holding unit 3 in FIG. 1, the pressing force of the pressure holding piston 33 is released, and the pressure holding plunger 32 is in a state in which it can move freely in the axial direction. Therefore, the tip 32a of the pressure holding plunger 32 can retract from the forward end position. Also, the position detection plate 35c of the pressure holding plunger 32 is located closer to the pressure holding path 5 than the position of the stopper member 40, and the stopper member 40 of the pressure holding unit 3 is in a first position in which the stopper body 44 protrudes relative to the pressure holding plunger 32. Also, in the example of FIG. 1, the necessary molten resin material is secured (metering process, charging) in one injection operation.

[0038] 1, the drive cylinder 14 moves the injection screw 12 forward in a non-rotating state, and the molten resin material is injected from the injection nozzle 13 through the hot runner 50 into the mold 60 (injection process). At this time, the resin in the resin path 4 flows into the pressure holding path 5, pushing the pressure holding plunger 32 back (i.e., toward the pressure holding cylinder 33), and the pressure holding path 5 is filled with the resin material for pressure holding. The amount (volume, weight) of the resin material for pressure holding measured (filled) above corresponds at least to the amount of the resin material (thermoplastic resin) introduced into the mold 60 that is cooled and contracted upon contact with the mold 60 during the secondary pressure holding process (described below).

[0039] Because the pressure holding plunger 32 is in a free state, the pressing force of the resin flowing in from the resin path 4 causes the pressure holding plunger 32 to move back within the pressure holding path 5, but as shown in Figure 2, the convex member 47 engages with the stopper body 44 in the first position, stopping the pressure holding plunger 32 and preventing it from moving back any further. This allows the pressure holding device 3 to fill the pressure holding path 5 with the appropriate amount of resin material for pressure holding.

[0040] After the resin is filled inside the mold 60, the drive cylinder 14 is maintained in the driven position (pressurized state) for a predetermined time. By applying pressure to the injection screw 12, the resin material in the resin passage 4 is introduced into the cavity of the mold 60, and the resin material in the cavity is held under pressure (primary holding pressure process).

[0041] 2, the shutoff plunger 21 of the shutoff device 2 moves forward toward the resin path 4, and the shutoff device 2 enters a closed state. In the pressure dwelling device 3, the pressure dwelling plunger 32 is pressurized by driving the pressure dwelling cylinder 33. Then, the resin material in the pressure dwelling path 5 flows toward the resin path 4, and an appropriate amount of resin for dwelling is additionally introduced into the cavity, and the resin material in the cavity is dwelled (secondary pressure dwelling process). Meanwhile, in the space on the injection screw 12 side, which has been cut off from the resin path 4 by the shutoff device 2, the drive cylinder 14 is depressurized and the injection screw 12 moves backward while rotating, and the metering process of the resin material for the next injection begins.

[0042] When the second dwelling by the pressure-holding device 3 is completed, as shown in FIG. 3, the pressure of the pressure-holding cylinder 33 is reduced from that during dwelling, and the pressure-holding plunger 32 of the pressure-holding device 3 is retracted. This releases the internal pressure of the hot runner 50 (and further the resin path 4 and the pressure-holding path 5) (decompressing the resin material in each resin path). In FIG. 3, the stopper member 40 of the pressure-holding device 3 is in the second position, with the stopper body 44 retracted relative to the pressure-holding plunger 32. This allows the pressure-holding plunger 32 to retract beyond the position of the stopper member 40. In other words, the internal volume of the pressure-holding path (the total volume of the resin path inside the hot runner 50, the pressure-holding path 5, and the resin path 4 on the front side (hot runner 50 side) separated by the shutoff plunger 21) when filling the resin material for pressure-holding (specifically, for the second dwelling) is larger during pressure release, allowing the resin to be sufficiently depressurized.

[0043] During the dwelling process, high pressure is applied to the molten resin material, so the resin material is introduced into the cavity of the mold 60 in a slightly compressed state (slightly reduced in volume) compared to during the injection process. Therefore, the volume of the resin material increases during depressurization. Furthermore, the longer the resin path inside the hot runner 50 and the larger the total volume of the resin path, the larger the volume of the resin material during depressurization, and the greater the amount of retraction of the dwelling plunger 32. In the dwelling device 3 and dwelling method of this embodiment, the volume of the resin path (internal volume of the dwelling path) can be changed using the convex member 47 and the stopper member 40. In this embodiment, the total volume of the resin path can be increased during depressurization compared to during the injection process, and the amount of movement of the dwelling plunger 32 can be increased. This allows sufficient depressurization of the resin material after dwelling without increasing the size of the dwelling device 3.

[0044] Thereafter, as shown in FIG. 4, the shutoff plunger 21 of the shutoff device 2 retracts from the resin path 4, and the space on the injection screw 12 side is reconnected to the resin path 4. Then, the pressure holding cylinder 33 applies a pressing force to the pressure holding plunger 32 again, and the pressure holding plunger 32 is advanced until the tip 32a protrudes into the resin path 4. This causes the resin material in the pressure holding path 5 to be discharged into the resin path 4. In addition, the stopper member 40 of the pressure holding device 3 switches to a first position in which the stopper body 44 protrudes relative to the pressure holding plunger 32. This completes one cycle of operation of the injection device 1.

[0045] <Injection molding flow including pressure holding process of this embodiment> FIG. 8 is a diagram showing a molding flow in an injection molding apparatus including the injection apparatus of this embodiment.

[0046] First, in the injection molding device, the mold 60 is closed (S1). At this stage, the injection device 1 is in the state at the start of injection shown in Fig. 1, and the injection device 1 has completed securing (metering process, charging) the necessary molten resin material in one injection operation.

[0047] In the injection step (S2), in the injection device 1, the injection screw 12 is moved forward in a non-rotating state by the drive cylinder 14, and the molten resin material is injected from the injection nozzle 13 through the hot runner 50 into the mold 60.

[0048] In the injection process of the injection device 1, the resin in the resin path 4 flows into the pressure holding path 5, pushing back the pressure holding plunger 32, and the pressure holding resin material is filled into the pressure holding path 5. At this time, the convex member 47 engages with the stopper body 44 at the first position, stopping the pressure holding plunger 32, and the appropriate amount of pressure holding resin material is filled into the pressure holding path 5.

[0049] In the primary dwell step (S3), after the interior of the mold 60 has been filled with resin, the pressurized state of the drive cylinder 14 in the injection device 1 is maintained for a predetermined time, and the resin material is introduced into the cavity of the mold 60 in an amount equal to the volume that has shrunk due to cooling. As a result, the resin material in the cavity of the mold 60 is dwelled through the resin path of the hot runner 50, the resin path 4, and the pressure dwell path 5.

[0050] In the second dwell step (S4), in the injection unit 1, the shutoff plunger 21 of the shutoff device 2 advances toward the resin path 4, and the shutoff device 2 is closed. In the pressure dwell device 3, the pressure dwell plunger 32 is pressurized by driving the pressure dwell cylinder 33, and the resin material is introduced into the cavity of the mold 60, and the resin material in the cavity of the mold 60 is held under pressure through the resin path of the hot runner 50, the resin path 4, and the pressure dwell path 5. At this time, in the space on the injection screw 12 side of the injection unit 1, the drive cylinder 14 is depressurized and the injection screw 12 moves backward while rotating, and the resin material metering process for the next injection begins.

[0051] After the second dwelling is completed, the internal pressure release process is performed (S5). In the internal pressure release process, the injection device 1 reduces the pressing force of the pressure-holding cylinder 33 to a level lower than that during dwelling, and moves the pressure-holding plunger 32 of the pressure-holding device 3 back. At this time, the stopper member 40 of the pressure-holding device 3 is in a second position where the stopper body 44 is retracted relative to the pressure-holding plunger 32, and the pressure-holding plunger 32 can move back beyond the position of the stopper member 40. This releases pressure from the resin path of the hot runner 50, the resin path 4, and the resin material in the pressure-holding path 5.

[0052] 4, in the injection device 1, the shutoff plunger 21 of the shutoff device 2 retracts from the resin path 4, and the space on the injection screw 12 side is reconnected to the resin path 4. Then, the pressure holding cylinder 33 applies a pressing force to the pressure holding plunger 32 again, and the pressure holding plunger 32 is moved forward until the tip 32a protrudes into the resin path 4. In addition, the stopper member 40 of the pressure holding device 3 switches to a first position in which the stopper body 44 protrudes relative to the pressure holding plunger 32.

[0053] After the pressure release step is completed, the mold 60 is opened and the injection molded product (preform) is carried out.

[0054] By repeating the above steps S1 to S5, the injection molding device can manufacture molded products in a continuous cycle.

[0055] <Reinforcement mechanism of pressure holding device 3> The pressure dwelling device 3 is supported in a cantilevered manner with its pressure dwelling device tip member 31 (fixed end) fixed (screwed) to the injection cylinder head 15. The pressure dwelling device 3 weighs several tens of kilograms or more, and in the case of a large pressure dwelling device 3 that can utilize a large amount of resin for pressure dwelling, the weight may exceed 100 kilograms. Therefore, if the pressure dwelling device 3 is only fixed as in the configuration shown in Figure 1, etc., it may bend under its own weight, causing the free end side (the cylinder barrel 33b side) to sag.

[0056] Furthermore, vibrations from the molding machine and injection cylinder 11 are also transmitted to the pressure holding device 3, which can cause the free end of the pressure holding device 3 to swing significantly or become prone to sagging. If the free end of the pressure holding device 3 sags, the pressure holding device 3 will no longer be able to operate accurately and may be damaged. To prevent this, a reinforcing member (sagging prevention member) 38 as shown in FIG. 9 may be provided in the pressure holding device 3 (or injection device 1).

[0057] The reinforcing member 38 includes at least a first plate-shaped member 38a fixed to a first holding member 39a, a second plate-shaped member 38b fixed to a first holding member 39b, a third plate-shaped member 38c fixed to the injection cylinder head 15 of the injection device 1, a first rod-shaped member 38d connecting the first plate-shaped member 38a and the second plate-shaped member 38b, and a second rod member 38e connecting the second plate-shaped member 38b and the third plate-shaped member 38c. A cover member 38f may be provided between the first plate-shaped member 38a and the second plate-shaped member 38b. The above-described components constituting the reinforcing member 38 are provided above the pressure maintaining device 3 and the injection cylinder head 15 (in a direction opposite to the direction in which the free ends hang down, in a direction opposite to gravity).

[0058] The reinforcing member 38 extending from the injection nozzle head 15 supports the free end of the pressure maintaining device 3 in the anti-gravity direction, preventing sagging or bending of the pressure maintaining device 3. In order to reduce the horizontal space (width) occupied by the pressure maintaining device 3 and improve workability, it is preferable to arrange the potentiometer 35 and reinforcing member 38 above the pressure maintaining device 3 and the stopper member 40 below.

[0059] <Molding device equipped with pressure holding device 3> The pressure holding device 3 of the above embodiment can be mounted on, for example, the molding devices shown in the following Figures 10 to 12. Note that the molding devices described below are merely examples, and the pressure holding device 3 of the above embodiment may be mounted on molding devices other than those shown in Figures 10 to 12.

[0060] Figure 10 shows an example of the configuration of a one-stage blow molding machine. A one-stage blow molding machine blows a container by utilizing the heat retained during injection molding (internal heat) without cooling the preform to room temperature.

[0061] 10 includes, for example, four molding stations, specifically, an injection molding section 110 that injection-moldes preforms, a temperature adjustment section 120 that adjusts the temperature of the preforms, a blow molding section 130 that flow-moldes the temperature-adjusted preforms, and an ejection section 140 that ejects blow-molded containers. The four molding stations are arranged at positions rotated by a predetermined angle (for example, 90 degrees) around a conveying mechanism 150.

[0062] The transport mechanism 150 includes a transfer plate (not shown) that rotates around an axis perpendicular to the plane of the paper in Fig. 10. The transport mechanism 150 transports the preforms or containers held by the neck molds between the molding stations by moving the transfer plate through the injection molding section 110, the temperature adjustment section 120, the blow molding section 130, and the removal section 140 in that order.

[0063] In the blow molding apparatus of Figure 10, the injection molding section 110 has a cavity mold, a core mold, a neck mold (collectively referred to as an injection mold), and a hot runner mold. Also connected to the injection molding section 110 is an injection unit 1 having a pressure holding unit 3 of this embodiment. The pressure holding unit 3 supplies a resin material (e.g., PET) to the cavity (molding space) of the injection mold via the hot runner mold to hold the pressure. In the injection molding section 110, the resin material is introduced from the injection unit 1 into the mold in a closed state, and a preform is injection molded.

[0064] The preforms produced in the injection molding section 110 are transported to the temperature adjustment section 120, where they are temperature-adjusted to a temperature suitable for the final blow. The temperature-adjusted preforms, still retaining the heat from injection molding, are then transported to the blow molding section 130, where they are shaped into containers by blow molding using a blow mold. The blow-molded containers are transported to the removal section 140, where they are removed from the apparatus.

[0065] Figure 11 shows an example of the configuration of a 1.5-stage blow molding device that combines the advantages of both the hot parison and cold parison methods. In the 1.5-stage blow molding method, containers are manufactured by blow molding preforms that retain heat during injection molding, similar to the hot parison method (1-stage method). However, the blow molding cycle in the 1.5-stage method is set shorter than the preform injection molding cycle. Then, multiple preforms molded in one injection molding cycle are blow molded in multiple blow molding cycles (for example, three times).

[0066] 11, the blow molding apparatus 200 includes an injection molding section 210 that injection molds preforms, a cooling section 220 that cools the preforms, a heating section 230 that heats the cooled preforms, and a blow molding section 240 that blows the heated preforms. The blow molding apparatus 200 also includes a continuous conveying section 250 that conveys the preforms discharged from the cooling section 220 to the blow molding section 240 via the heating section 230.

[0067] In the blow molding apparatus of Figure 11, the injection molding section 210 has a cavity mold, a core mold, a neck mold (collectively referred to as an injection mold), and a hot runner mold. Also, an injection unit 1 having a pressure holding device 3 of this embodiment is connected to the injection molding section 210. The pressure holding device 3 supplies a resin material (e.g., PET) to the cavity (molding space) of the injection mold via the hot runner mold to hold the pressure. In the injection molding section 210, the resin material is introduced from the injection unit 1 into the mold in a closed state, and injection molding of a preform is performed.

[0068] The preforms injection molded in the injection molding section 210 are supplied from the injection molding section 210 to the cooling section 220. The cooling section 220 forcibly cools the preforms molded in the injection molding section 210. The preforms are carried out from the cooling section 220 in a state where they have been cooled to a predetermined temperature, and are continuously conveyed along the conveying line of the continuous conveying section 250. In addition, the preforms conveyed in the continuous conveying section 250 pass through the heating section 230, where they are heated to a temperature suitable for stretching.

[0069] The preforms heated in the heating section 230 are transferred from the continuous conveying section 250 to the intermittent conveying section 260 and conveyed at predetermined intervals to the blow molding section 240. The blow molding section 240 stretch blow molds a predetermined number of preforms to manufacture containers. The containers manufactured in the blow molding section 240 are conveyed by the intermittent conveying section 260 to a removal position P outside the blow molding section 240 and removed from the apparatus.

[0070] FIG. 12 shows an example of the configuration of a two-stage injection molding apparatus 300 that does not have a blow molding section. The injection molding apparatus 300 includes an injection molding section 310, an ejection section 320, a cooling section 330, and a transport mechanism. The cooling section 330 includes a cooling pot (not shown) that accommodates a preform and cools the body of the preform from the outside, and a cooling rod (not shown) that is inserted into the hollow portion of the body of the preform and cools the body from the inside. The transport mechanism includes a first holding member 341 that transports the preform from the injection molding section 310 to the cooling section 330, and a second holding member 342 that transports the preform from the cooling section 320 to the ejection section 24. The injection molding section 310 is provided with a cavity mold, a core mold, a neck mold (collectively referred to as an injection mold), and a hot runner mold. An injection device 1 having a pressure-holding device 3 according to this embodiment is connected to the injection molding section 310. The pressure-holding device 3 supplies a resin material (for example, PET) to a cavity (molding space) of an injection mold via a hot runner mold, and holds the pressure.

[0071] In injection molding apparatus 300, a resin material (e.g., PET) is introduced from injection device 1 into a mold in a closed state in injection molding section 310, and a preform is injection molded. Thereafter, the preform is released from the mold in a high-temperature state (e.g., a state in which the outer surface of the body is 100 to 130°C) and transported to cooling section 330. In cooling section 330, the preform is cooled to a temperature at which shrinkage deformation such as sink marks will not occur even if left at room temperature (e.g., a state in which the outer surface of the body is 50 to 60°C or less). Next, the sufficiently cooled preform is transported to removal section 320 and removed from the apparatus.

[0072] The effects of this embodiment will be described below. The injection device 1 of this embodiment is equipped with a stopper member 40 in the pressure holding device 3 that regulates the amount of retraction of the pressure holding plunger 32. When filling the pressure holding passage 5 with resin material, the stopper body 44 (second engaging member) of the stopper member 40 regulates the amount of retraction of the pressure holding plunger 32 at the first position where it engages with the convex member 47 (first engaging member). This allows the appropriate amount of resin material for pressure holding to be filled into the pressure holding passage 5. Furthermore, because the stopper member 40 suppresses variations in the filling amount of resin for pressure holding, the injection molding conditions set for the operation of the injection screw 12 (such as the VP switching position (switching position between speed control and pressure control) of the injected molten resin) function well, preventing overpacking and variations in the filling amount, making it easier to maintain consistent quality of injection-molded products.

[0073] On the other hand, when depressurizing the mold after dwelling, the stopper body 44 moves from the first position to a retracted second position, thereby releasing the restriction on the amount of retraction of the dwell plunger 32. This increases the internal volume of the dwelling channel during depressurization compared to the internal volume of the dwelling channel when filling the dwelling resin material. Therefore, even for hot runners 50 with large internal volumes of resin channels, such as molds with open-gate gate structures or molds with three resin channels, it is possible to sufficiently depressurize the mold after dwelling. This separates the resin material constituting the gate portion at the bottom of the preform from the resin material in the nozzle portion of the hot runner 50, allowing the resin material in the gate portion to solidify sufficiently, allowing the preform to be properly released from the mold.

[0074] If the resin in the resin passage in the hot runner 50 cannot be sufficiently depressurized after the dwelling step, the resin material is prevented from solidifying at the gate hole (first narrowed portion) of the cavity mold that communicates with the hot runner 50. This can result in stringiness at the gate portion at the bottom of the preform, resulting in molding defects. Furthermore, if the gate portion of the preform does not solidify properly, the resin material will remain in an improperly solidified state at the nozzle portion (second narrowed portion) of the hot runner 50 that communicates with the gate hole of the cavity mold 60, causing the nozzle portion of the hot runner 50 to become clogged.

[0075] Furthermore, in this embodiment, the internal volume of the pressure holding channel can be increased when releasing pressure without increasing the internal volume of the pressure holding channel when filling with resin material for pressure holding, so there is no reduction in the effect of shortening the molding cycle.

[0076] In this embodiment, the first engaging member and the stopper member 40 are provided on the plunger exposed portion 3a of the pressure maintaining device 3 where the pressure maintaining plunger 32 is exposed to the outside. Therefore, it is easy to add the first engaging member and the stopper member 40 to a conventional pressure maintaining device later. In addition, in this embodiment, the amount of retraction of the pressure maintaining plunger 32 is restricted by engaging the stopper body 44 with the pressure maintaining plunger 32 or the convex member 47. Therefore, compared to the configuration of the conventional pressure maintaining device 3, it is not necessary to attach additional parts to the pressure maintaining plunger 32, which helps to suppress increases in device costs. Furthermore, it is not necessary to increase the size of the pressure maintaining device 3 (pressure maintaining cylinder 33 and pressure maintaining plunger 32) just to ensure the internal volume of the pressure maintaining path when depressurizing, which also helps to suppress increases in device costs.

[0077] The present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention. For example, injection molded articles manufactured using the injection device of the present invention are not limited to preforms, and the injection device may be applied to the manufacture of other molded articles.

[0078] Furthermore, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0079] 1...injection unit, 2...shutoff device, 3...pressure holding device, 3a...plunger exposed portion, 4...resin path, 5...pressure holding path, 11...injection cylinder, 13...injection nozzle, 31...pressure holding cylinder, 32...pressure holding plunger, 33...pressure holding cylinder (pressure holding actuator), 34...support, 35...potentiometer, 35a...shaft, 35b...sensor body, 35c...position detection plate, 40...stopper member, 41...air cylinder, 41a...rod, 42...connecting member, 43...rod member, 44...stopper body, 45...first mounting plate, 46...second mounting plate, 47...convex member, 50...hot runner, 51...sprue, 60...mold

Claims

1. a pressure holding device attached to a pressure holding path branching from a resin path of an injection device, for holding pressure in the resin path and the pressure holding path after injecting a resin material into a mold, a pressure maintaining plunger having a first engagement member fixed to its outer periphery and moving back and forth along the pressure maintaining path; a pressure maintaining actuator that drives the pressure maintaining plunger; a stopper member that limits the amount of retraction of the pressure-retaining plunger, The stopper member is a second engaging member that engages with the first engaging member; a drive member that moves the second engagement member back and forth in a direction intersecting with the movement direction of the pressure-retaining plunger, When the resin material is filled into the pressure holding passage, the second engaging member is at a first position where it engages with the first engaging member, thereby restricting a retreat amount of the pressure holding plunger; When depressurizing the mold after dwelling, the second engaging member moves from the first position to a retracted second position to release the restriction on the retraction amount of the dwelling plunger. Pressure holding device.

2. The first engaging member and the stopper member are provided at a plunger exposure portion of the pressure maintaining device where the pressure maintaining plunger is exposed to the outside. The pressure maintaining device according to claim 1 .

3. a potentiometer for detecting the position of the pressure-holding plunger; The first engagement member is a member of the potentiometer fixed to the pressure-holding plunger. The pressure maintaining device according to claim 1 or 2.

4. an injection cylinder having a resin passage for injecting a resin material into a mold and a pressure holding passage branching from the resin passage; An injection apparatus comprising: the pressure maintaining device according to claim 1 attached to the pressure maintaining path.

5. A method for injecting a resin material using the injection device according to claim 4, a first step of injecting a resin material into the mold through the resin passage and filling the pressure holding passage with the resin material; a second step of maintaining pressure in the resin path and the pressure maintaining path by the pressure maintaining device after the first step; a third step of reducing the pressing force of the pressure holding device to a value lower than that during pressure holding, thereby depressurizing the mold, after the second step; In the first step, the second engaging member is disposed at a first position where the second engaging member engages with the first engaging member to restrict a retreat amount of the pressure-retaining plunger; In the third step, the second engaging member is disposed at a second position retracted from the first position, thereby releasing the restriction on the retraction amount of the pressure-holding plunger. A method for injecting resin materials.

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